weak tidal correlation of nw bohemia vogtland earthquake swarms we analyze the possible effect of solid earth tidal stresses upon a vertical strike slip fault in nw bohemia vogtland central europe typical by occurrence of swarm earthquakes the horizontal components of solid earth tidal stresses were found strongly to prevail and to reach the level of 2 kpa we examined tidal triggering as influence of tidal stresses to launching the swarm activity in relative absence of other stress disturbances the onset times of 46 swarms of mostly ml 3 earthquakes that occurred in the period 1991 2005 displayed an increased occurrence near the fortnightly maximum of tidal extensive normal stress the statistical test however did not prove a statistically significant correlation indicating a triggering effect of fault extension due to tidal loading we also examined tidal effects to the already running seismic activity of the prominent 2000 swarm by comparing the tidal stress distribution in the investigated period with the distribution of tidal stresses in the occurrence times of each earthquake the results show that these distributions are almost similar which indicates that individual earthquakes occur independent of tidal stresses the unclear tidal correlation of the swarm seismicity may be interpreted by small amplitudes and rates of tidal stress changes compared to the amplitudes and rates of coseismic stress perturbations and of pressure bursts of deep generated fluids

subcrustal lithosphere around the saxothuringian moldanubian suture zone a model derived from anisotropy of seismic wave velocities abstract we have modelled the thickness and large scale fabric of the subcrustal lithosphere from the variations of p wave delay times and the shear wave splitting observed at seismological observatories and four mobile stations in central europe the saxothuringian s lithosphere is characterized by a total thickness of 90 120 km and by a coherent fabric in its mantle part with olivine a c foliation planes dipping to the north northwest the moldanubian m lithosphere is generally thicker 120 140 km on the average and characterized by a c foliations dipping to the south the divergently dipping anisotropic structures may represent remnants of successive paleosubductions of the ancient oceanic lithosphere frozen in the subcrustal lithosphere of both units a long time before their variscan collision the deep s m contact is marked by a lithosphere thinning to about 80 90 km beneath the s m surface boundary within the subcrustal lithosphere a complex structure of the transition of both units extends to about 150 km toward the south as indicated by the anisotropic characteristics of body waves

heat flux through sea ice in the western weddell sea convective and conductive transfer processes the heat flux through the snow and sea ice cover and at the ice ocean interface were calculated at five sites in the western weddell sea during autumn and early winter 1992 the ocean heat flux averaged 7 2 w m2 from late february to early june and average ice air heat flux in the second year floes depended on the depth of the snow cover and ranged from 9 to 17 0 8 w m2 in late february three of the five sites had an ice surface which was depressed below sea level resulting at two of the sites in a partially flooded snow cover and a slush layer at the snow ice interface as this slush layer froze to form snow ice the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower salinity nutrient rich seawater from the ocean upper layer we estimate that about half of the second year ice in the region was covered with this slush layer early in the winter as the slush layer froze over a 2 to 3 week period the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover on an area wide basis approximately 10 cm of snow ice growth occurred within second year pack ice primarily during a 2 to 3 week period in february and march this ice growth near the surface of the ice provides a salt flux to the upper ocean equivalent to 5 cm of ice growth despite the thick about 1 m ice cover in addition to the ice growth in the small area less than 5 open water regions

river stage tomography a new approach for characterizing groundwater basins received 19 june 2008 revised 16 february 2009 accepted 12 march 2009 published 9 may 2009 1 data from tomographic surveys make an inverse problem better posed in comparison to the data from a single excitation source a tomographic survey provides different coverages and perspectives of subsurface heterogeneity nonfully redundant information of the subsurface fusion of these pieces of information expands and enhances the capability of a conventional survey provides cross validation of inverse solutions and constrains inherently ill posed field scale inverse problems basin scale tomography requires energy sources of great strengths spatially and temporally varying natural stimuli are ideal energy sources for this purpose in this study we explore the possibility of using river stage variations for basin scale subsurface tomographic surveys specifically we use numerical models to simulate groundwater level changes in response to temporal and spatial variations of the river stage in a hypothetical groundwater basin we then exploit the relation between temporal and spatial variations of well hydrographs and river stage to image subsurface heterogeneity of the basin results of the numerical exercises are encouraging and provide insights into the proposed river stage tomography using naturally recurrent stimuli such as river stage variations for characterizing groundwater basins could be the future of geohydrology however it calls for implementation of sensor networks that provide long term and spatially distributed monitoring of excitation as well as response signals on the land surface and in the subsurface

alpha recoil track dating of quaternary volcanics like fission track dating alpha recoil track art dating is based on the accumulation of nuclear particles that are released by natural radioactivity and produce etchable tracks in solids arts are formed during the alpha decay of uranium and thorium as well as of their daughter nuclei when emitting an alpha particle the heavy remaining nucleus recoils 30 40 nm leaving behind a trail of radiation damage through etching the art tracks become visible with interference phase contrast microscopy under the presupposition that all tracks are preserved since the formation of a sample their total number is a measure for the sample s age the technique has already been proposed more than three decades ago huang w h walker r m 1967 fossil alpha particle recoil tracks a new method of age determination science 155 1103 1106 but due to inherent difficulties it was hardly applied or made any substantial progress since then the present paper describes a methodology by which reliable art ages of dark mica can be obtained the technique is applicable to tiny 0 5 mm single mica flakes in the 102 to 106 years age range it is tested on quaternary volcanics from the eifel region germany alpha recoil dating has a great potential for quaternary chronometry and tephrochronology

lower jurassic magnetostratigraphy at the breggia gorge ticino switzerland and alpe turati como italy summary the breggia gorge ticino switzerland provides a continuous outcrop of mesozoic limestones covering the time between the lower jurassic and upper cretaceous the jurassic section from the lower pliensbachian to aalenian is well dated by ammonites the limestones of these stages are a good quality recorder of the polarity of the geomagnetic field during this time interval more than 500 cores have been drilled along a 120m thick section with a median distance between cores of about 20cm detailed thermal and af demagnetization and further rock magnetic studies were used to determine the characteristic nrm direction for each sample initial nrm intensities and low field susceptibilities reflect variations in oxidation potential and sedimentation rate during carbonate deposition the breggia section covers an estimated 12 myr of lower to middle jurassic time during which more than 60 distinct reversals of the geomagnetic field are recorded this corresponds to a comparatively high mean reversal frequency of about 5 reversals myr the breggia polarity zonation can be correlated with the nearby section at alpe turati como italy and comparable polarity patterns are recognized in other biostratigraphically well dated magnetostratigraphic profiles from hungary and umbria italy

tidal parameters for an inelastic earth abstract the gravimetric factors for an elliptical uniformly rotating earth are computed according to a new definition with respect to wahr s results and considering the mantle inelasticity the love numbers h and k are defined in the elliptical earth case to correspond to the love spherical definition they become latitude dependent the tidal parameters discussed in this paper are computed for an inelastic earth s mantle the numerical results show an increase of 0 4 of the gravimetric factors with respect to the wahr s values the love numbers h and k increase by 1 4 to 3 with respect to the elastic case

fluid flow triggered migration of events in the 1989 dobi earthquake sequence of central afar during the august 1989 sequence of earthquakes beneath the dobi graben in central afar principal events including 10 shocks with ml 5 5 propagated 50 km north westwards in 50 h the sequence is analyzed in terms of triggering by propagation of a critical pore pressure wave in a compressible fluid through a fractured medium the macroscopic fluid diffusion tensor d in the crust beneath the graben is estimated its principal eigenvector strikes n115 e nearly parallel to the graben axis with a value it is about 10 times larger than the other two consistent with fissure anisotropy in the graben the order of magnitude of the permeability 10 8 m is compatible with characteristic fissure widths ranging from 1 mm to 3 cm estimating such parameters in other extensional regions might help to understand better the temporal evolution of seismic swarms

a dual porosity model for water level response to atmospheric loading in wells tapping fractured rock aquifers a fractured rock aquifer may be viewed as a permeable fracture network embedded within a less permeable porous matrix this permeability contrast gives rise to distinct pressure fields in the pore space and fractures and therefore to a response to atmospheric loading different from that of nonfractured porous media assuming that fracture sizes and orientations are uncorrelated and sufficiently random to ensure homogeneous and isotropic elastic behavior of the rock mass at the continuum scale an effective stress model proposed by tuncay and corapcioglu 1995 is used to develop a linear elastic stress strain relationship for dual porosity media elastic constants of the fractured rock mass required by the model are estimated using theoretical relations derived by budiansky and o connell 1976 the stress strain relationship and the coupled continuity equations for flow in deformable fractured media are combined to derive expressions for the undrained static confined barometric efficiency of a dual porosity medium two limiting cases are considered the initial instantaneous pressure response in the pore space and fractures due to a change of confining stress and the later stage of pressure equilibrium between the two phases the dual porosity response model developed here may be used to characterize hydraulic properties in fractured aquifers including low porosity and low permeability media the model is evaluated on water level hydrograph data from a borehole tapping fractured volcanic rocks water level and barometric data are supplemented by independent measurements of matrix porosities fracture spacing and rock elastic properties allowing an assessment of total porosity and specific storage at the site for the observed static confined barometric efficiency of 0 78 the instantaneous pressure response model yields plausible values for both parameters

spectrum response of lj well to various stresses during non seismic and seismic periods the well water level in a deep well has significant frequency dependence on various crustal stresses which can provide an effective pathway for determining the well aquifer properties and investigating the response mechanism of groundwater however due to the limitations and complexity of the field conditions there is a lack of on site stress strain data for rocks therefore it is difficult to directly and quantitatively interpret the transfer response between the strain stress and the well water level the observation item data for the lj well in china are relatively complete including rainfall barometric pressure volumetric strain and deep water level data by calculating the spectral period spectral density coherence function and transfer function of various physical variables the spectrum response characteristics of the well aquifer system to various stresses can be effectively obtained when the crust is in a relatively stable state the semidiurnal and diurnal waves are dominant moreover the transfer functions of the well water level s response to the theoretical semidiurnal and diurnal earth tides and the barometric pressure are basically consistent with the correlation analysis results in addition when earthquakes occur the signals of the volumetric strain and the well water level can more effectively highlight the relatively intermediate and high frequency information the transfer function between the well water level and the volumetric strain is nearly an order of magnitude smaller than that in the stable state indicating that the hydrogeological conditions of the lj well aquifer change instantaneously when subjected to seismic waves all the above conclusions show that the correlation and transfer function based on spectral analysis is a feasible and advantageous method of determining the correlation of various physical variables these results provide a foundation for further research on the hydrogeological characteristics of aquifers

palynological evidence for astronomical forcing in early miocene lacustrine deposits from rubielos de mora basin ne spain pollen and paleomagnetic analysis of the rubielos de mora 1 core rubielos de mora basin ne spain has been carried out with the aim of reconstructing floral vegetational and climatic changes within an accurate time framework based on biostratigraphic information the magnetostratigraphy atnts04 resulting in an age of early miocene for the cored sedimentary sequence the high percentages of thermophilous taxa and the diverse subarid flora in the pollen spectra points to a very dry subtropical climate with a marked seasonality reflecting the onset of the miocene climatic optimum on the other hand taxa with high water requirements riparian are also abundant alternation in pollen taxa thermophilous vs mesothermic riparian coincide with sedimentological changes which are related to lake level fluctuations and vegetation changes in turn the vegetational pattern indicates cyclic changes in temperature and precipitation which is controlled by astronomically forced obliquity cycles

hydrologic effects on water level changes associated with episodic fault creep near parkfield california as part of the parkfield california earthquake prediction experiment water level is monitored in a well 460 m from the main trace of the san andreas fault on middle mountain in the preparation zone of the anticipated parkfield earthquake the well configuration allows water level to be monitored in two fluid reservoirs at depths of 85 and 250 m below land surface during 1987 water level changes were recorded during 12 of the 18 episodes of accelerated fault creep detected by a creep meter spanning the fault trace 750 m northwest of the well the creep related water level changes in the shallow reservoir have durations of less than 1 day whereas in the deeper reservoir the changes persist for as long as 2 months these data suggest that the transient nature of the water level changes in the shallow interval is due to vertical flow to the water table and is not evidence that creep events propagate past the well phase leads of earth tidal constituents in the water level data from the shallow interval relative to the same constituents in the local volume strain tide support the interpretation of significant flow to the water table at periods of 1 day or less the form of the water level changes in the deep interval is affected by horizontal flow to the well bore this effect can be removed from the water level records using a theoretical response curve constrained by the phases of earth tidal constituents in the deep interval relative to the local volume strain tide for the events where the signal in the shallow interval has been large enough to measure the sizes of the simultaneous water level changes in the two reservoirs are consistent with the same amounts of volume strain occurring at both depths

static stress transfer and earthquake triggering no lower threshold in sight the main objective of this study is to see if a lower threshold for earthquake triggering exists resolving this issue is important for the understanding of earthquake mechanics and for the purpose of hazard analysis we compute the cumulative static stress changes imposed on 63 m 4 5 earthquakes in central california between 1969 and 1998 by adding the stress changes imposed by all previous m 4 5 earthquakes as a function of time prior to the events we find that 85 of the cumulative stress changes at the time of rupture are positive for stress change magnitudes of 10 kpa 0 1 bar and 70 are positive for stress changes of 10 kpa 0 1 bar as well as 1 kpa 0 01 bar a comparison between these results and those obtained for synthetic catalogs in which the timing or focal mechanisms of the earthquakes were randomized shows that this degree of triggering is very unlikely to be found in a random catalog thus we conclude that no lower threshold for earthquake triggering in central california has been found we show that the temporal distribution of stress changes that discourage failure is consistent with the theoretical prediction that the time delay increases with the magnitude of the stress change

absence of earthquake correlation with earth tides an indication of high preseismic fault stress rate because the rate of stress change from the earth tides exceeds that from tectonic stress accumulation tidal triggering of earthquakes would be expected if the final hours of loading of the fault were at the tectonic rate and if rupture began soon after the achievement of a critical stress level we analyze the tidal stresses and stress rates on the fault planes and at the times of 13 042 earthquakes which are so close to the san andreas and calaveras faults in california that we may take the fault plane to be known we find that the stresses and stress rates from earth tides at the times of earthquakes are distributed in the same way as tidal stresses and stress rates at random times while the rate of earthquakes when the tidal stress promotes failure is 2 higher than when the stress does not this difference in rate is not statistically significant this lack of tidal triggering implies that preseismic stress rates in the nucleation zones of earthquakes are at least 0 15 bar h just preceding seismic failure much above the long term tectonic stress rate of 10 4 bar h

borehole water level response to barometric pressure as an indicator of aquifer vulnerability the response of borehole water levels to barometric pressure is a function of the confining layer and aquifer properties this study aims to use this response as an aid towards quantitative assessment of groundwater vulnerability applying the techniques to the confined semi confined part of the chalk aquifer in east yorkshire uk time series analysis techniques are applied to data collected from twelve monitoring boreholes to characterize and remove components contributing to the borehole water level signal other than barometric pressure such as recharge and earth tides barometric response functions are estimated using the cross spectral deconvolutionaveraging technique performed with up to five overlapping frequency bands a theoretical model was then fitted to the observed barometric response functions in order to obtain estimates of aquifer and confining layer properties derived ranges for pneumatic and hydraulic diffusivities of the confining layer vary over four orders of magnitudes 0 9 to 128 0 m2 day and 10 0 to 5 0 104 m2 day respectively indicating that the aquifer is nowhere purely confined discrepancies between estimates of aquifer transmissivity derived from the barometric response function and pumping tests have been explored using slug tests and results suggest that aquifer model transmissivity are highly sensitive to borehole construction a simple flow model constructed to test the potential impact of confining layer heterogeneity on the barometric response function shows that while high frequencies reflect the immediate vicinity of the borehole low frequencies detect confining layer properties up to some 500 meters distant from the borehole a characteristic time scale is introduced as a function of derived properties of the confining layer and is used as a quantitative measure of the degree of aquifer confinement it is concluded that barometric response functions are sensitive to confining layer properties and thus can provide a useful tool for the assessment of aquifer vulnerability

modeling and detecting interactions between earth tides and earthquakes with application to an aftershock sequence in the pyrenees abstract assuming that earthquakes are governed by solid friction and that the fault plane solutions are known a simplified model of correlation between the seismicity and a specified component of the tidal stress is proposed in the case of an earthquake sequence with a uniform time distribution and with a prevailing focal mechanism a test of statistical significance is derived from a binomial probability distribution this interaction model is checked over the aftershock sequence of a magnitude 5 earthquake which occurred within a seismic array in the pyrenees on 29 february 1980 the tidal stress field including the ocean tide effect is computed for this area the global time decrease of the seismicity is taken into account by a time transformation in order to deal with the time and space complexity of the stress field a moving window analysis is used it is shown that during one 7 day period out of a total of 30 days a positive correlation appears between earth tides and seismicity in agreement with the proposed model

early miocene repetitive vegetation and climatic changes in the lacustrine deposits of the rubielos de mora basin teruel ne spain pollen analysis of a lower miocene succession from the rubielos de mora basin ne spain has been carried out with the aim of reconstructing the flora vegetation and climatic changes previous paleobotanical studies on these sedimentary rocks and adjacent areas interpreted very diverse climates for the early miocene from humid temperate to dry subtropical in this study a rich thermophilous pollen spectrum and a diverse subarid flora including nitraria caesalpiniaceae ephedra and acacia indicative of a dry subtropical climate are identified on the other hand mesothermic taxa with high water requirements are also abundant therefore the pollen assemblages evidence the juxtaposition of very contrasted environments the presence of subdesertic taxa typical of plants growing in the lowlands and conditioned by a long warm dry season together with others with very high water requirements needing constant water this can be explained by the presence of the rubielos de mora lake providing local conditions for developing riparian forests the vegetation was clearly controlled by the water availability under a subtropical and dry seasonal climate pollen changes along the succession which coincide with sedimentological changes are related to climatic variations alternation in pollen taxa thermophilous dry vs mesothermic riparian reflects the influence of the cyclicity of temperature and precipitation on the lake level and vegetation

determination of aquifer transmissivity from earth tide analysis the water level in an open well tapping an artesian aquifer responds to pressure head disturbance caused by earth tide dilatation of the aquifer because a finite amount of time is needed for water to flow into and out of the well there exists a phase shift or time lag between the tidal dilatation of the aquifer and the water level response in the well we derive an analytical solution that expresses the phase shift as a function of the aquifer transmissivity storage coefficient well radius and the period of the harmonic disturbance this solution is rather insensitive to the storage coefficient thus if the phase shift is known for a harmonic disturbance the transmissivity can be calculated given a rough estimate of the storage coefficient theoretical analysis shows that a significant phase shift may be present even if the disturbance is slowly varying as in the case of earth tides this opens the possibility of estimating aquifer transmissivity from water level records that show earth tide fluctuations a case study using data from a site near parkfield california is presented to illustrate application of the theory phase shifts of the o1 25 82 hour period and m2 12 42 hour period tidal constituents are chosen for analysis because they are free of systematic contamination by fluctuations in barometric pressure a brief error analysis suggests that the computed o1 phase shift is subject to large uncertainty while the computed m2 phase shift is substantially more accurate based on an assumed storage coefficient range of 10 4 to 10 6 the estimated transmissivity range is 8 10 6 to 2 10 5 m2 s while hydraulic tests have not been performed to validate these estimates the range is consistent with the transmissivity value determined by other investigators from analysis of the water level response to an earthquake

considering barometric pressure in groundwater flow investigations 1 water level elevation measurements in wells are commonly used as a basis to delineate groundwater flow patterns i e flow direction and hydraulic gradient barometric pressure fluctuations however can have a discernible impact on well water levels these barometric effects may lead to erroneous indications of hydraulic head within the aquifer total hydraulic head within the aquifer not well water level elevation is the hydrologic parameter for determining groundwater flow direction and hydraulic gradient conditions for low gradient unconfined aquifer sites exhibiting variable vadose zone characteristics e g thickness pneumatic diffusivity barometric pressure fluctuations can cause temporal changes in lateral flow direction and flow velocity discrete water level measurements used to determine the average or long term groundwater flow conditions therefore may provide nonrepresentative results calculation of the barometric response characteristics for individual wells provides the basis to account for the temporal effects of barometric pressure fluctuations from monitor well measurements so that average long term groundwater flow pattern behavior can be determined

some aspects of magnetic viscosity in subaerial and submarine volcanic rocks summary the magnetic viscosity of 334 upper tertiary and pre bruhnes quaternary volcanic rocks from the massif central france and the steens mountain oregon and of 40 basaltic cores from dsdp leg 37 has been investigated thellier s viscosity index follows a log normal distribution with mean values equal to 6 and 3 5 per cent for subaerial and submarine rocks respectively for subaerial rocks the average intensity of the viscous remanent magnetization vrm acquired in the earth s field since the beginning of the bruhnes polarity epoch t 0 7 myr is estimated to be equal to one quarter of the average intensity of the primary remanence alternating field demagnetization of vrms acquired in low fields for acquisition times t ranging from 2 day to 32 month indicates the resistance to alternating fields is quite different from sample to sample and increases linearly with log t neel s diagnostic parameter of domain structure of the grains involved in magnetic viscosity shows that hard vrm is carried by single domain grains and soft vrm carried by multidomain particles single domain particles carrying hard vrm in subaerial volcanic rocks are almost equant magnetite intergrowths with size near the superparamagnetism threshold resulting from high temperature oxidation of titanomagnetite soft vrm is carried by low curie point homogeneous titanomagnetite unlike his single domain theory neel s multidomain theory of magnetic viscosity does not account quantitatively for the resistance of vrm to alternating fields

structural characterization of an island aquifer via tidal methods 1 a set of water level time series collected along a transect through a sedimentary island aquifer was used to test the utility of various simple models of ocean tidal propagation in bounded one dimensional aquifers fourier spectra were calculated for the ocean tidal modes and compared with spectra measured in wells along the island transect other sources of fluctuation could be neglected an observed spatial bias in the well responses attenuations and lags could not be modeled by a homogeneous aquifer theory a theory involving composite heterogeneity accounted well for the spatial bias yielding estimates of aquifer transmissivities and storage coefficients indicating a fivefold difference in hydraulic diffusivity along the transect a lack of well locations toward one end of the transect reduced the statistical significance of this result with correlations between regression parameters evident at the same time a second bias was seen involving the ratio of signal amplitude and lag with penetration distance into the aquifer as observed in prior tidal studies a brief set of numerical experiments showed that horizontal layering in aquifer properties was the most probable cause of this propagation bias application of these results to the island data set supported a conceptual stratigraphic model of a highly conductive sloping stratum underlying a less conductive superficial sand layer this model is inconsistent with well logs along the island transect but is supported by additional off transect well logs it was concluded that one dimensional tidal propagation models may be useful in inverse characterization of aquifers with macroscale hydrogeological structures and that the analysis of measured propagation bias has the potential to yield extra information on aquifer properties in the vertical direction

temperature variations in lake ice in central alaska usa abstract in winter 2002 03 and 2003 04 thermistors were installed in the ice on two shallow pondsin central alaska in order to obtain data on ice temperatures and their response to increasing anddecreasing air temperatures and flooding and snow ice formation snow depth and density and icethickness were also measured in order to understand how they affected and were affected by icetemperature variability the lowest ice temperature 15 5 8 c and steepest temperature gradient 39 8 8 cm 1 occurred during a 9week period in autumn when there was no snow on the ice withsnow on the ice temperature gradients were more typically in the range 20 to 5 8 cm 1 average icetemperatures were lower during the warmer first winter and higher during the cooler second winterbecause of differences in the depth and duration of the snow cover isothermal ice near the freezingpoint resulted from flooding and snow ice formation and brief episodes of warm weather with freezingrain under these circumstances congelation ice growth at the bottom of the ice cover was interrupted even reversed it is suggested that the patterns in temperatures brought about by the snow ice formationand rain events may become more prevalent due to the increase in frequency of these events in centralalaska if temperature and precipitation change as predicted by arctic climate models

palaeomagnetism of the permian volcanic rocks of moissey french jura implications for the palaeofield and tectonic evolution rocks from the massif de la serre in the french jura latitude 47 3 n longitude 5 6 e belonging to an ignimbritic assemblage dominated by vitrophyric rhyolites and whose age of formation is probably permian autunian to saxonian have been studied by applying thermal and alternating field demagnetization the characteristic magnetization has a mean direction derived from 89 samples of d 170 i 16 k 26 2 95 3 and a corresponding north palaeopole at 41 n 172 e a95 5 the pole which is very close to the permian european poles can thus be considered as a new contribution some samples are found to carry a unique normal polarity magnetization others carry both normal and reverse polarities it therefore seems that similar to permian series in the ussr these west european rocks have registered a normal event in the kiaman interval from a structural point of view we may conclude that during the alpine tectonic phases the massif de la serre has not been subjected to substantial rotation

revisiting the tidal activation of seismicity with a damage mechanics and friction point of view the load unload response ratio theory lurr puts forward the idea that the ratio of seismicity during times of increased tidal loading to times of decreased tidal loading takes on anomalously large values as the preparatory region of the earthquake approaches a critical state we repeated the calculations of lurr for several earthquakes in california for which results had been published using estimates of the parameters which could be determined from the published work we were unable to confirm any lurr ratio predictive significance we test an alternative method of evaluating the influence of tidal stresses on earthquakes based on damage mechanics as in rock mechanics experiments it may be that anomalous activation of seismicity prior to large earthquakes occurs only during those time intervals when the applied stress exceeds values previously attained we applied this approach to analyze the same data set used to test the lurr hypothesis and it also failed to reveal any significant precursory indications it may be that time dependent failure processes such as self driven nucleation occur on a time scale longer than the diurnal tide thus destroying the expected synchronization

structural implications of paleomagnetic data from pelvoux belledonne area french alps abstract paleomagnetic studies were carried out in triassic lias lavas from five new sites of the external zone of the french alps pelvoux belledonne area and compared with previous data in two sites magnetization seems to have been disturbed during alpine deformation but the paleomagnetic directions obtained in the other sites allow one to define the eastern boundary of the anticlockwise rotated taillefer block and the importance of local rotation along the aspres les corps faults the major anticlockwise rotation of taillefer is probably of ante nummulitic age but other rotations in the pelvoux belledonne area could have occurred during this same period or be of more recent age

the late carboniferous to early triassic geodynamic evolution of variscan europe in the light of magnetic overprints in early permian rhyolites from the northern vosges france and central black forest germany summary this paper demonstrates how magnetic overprints of a geological series can provide information over a long time period which can be interpreted in terms of geotectonic evolution according to these new results the late carboniferousearly permian rhyolites from the northern vosges have recorded the magnetic field over a major part of the permian recent radiometric dating assigns a late carboniferous early permian age 298 ma to the previously middle permian rhyolitic volcanism of the northern vosges a palaeomagnetic study was undertaken on rhyolites of the nideck donon massif and on neighbouring permian basins villc saint die in order to obtain a new pole for the early permian and to detect overprints standard palaeomagnetic and rock magnetic experiments demonstrate that over 90 per cent of the characteristic directions of magnetizations are of secondary origin the high temperature magnetizations carried by secondary haematite and haematized titano magnetite fail the fold test and display directions consistent with the saxonian thuringian directions from variscan europe nideckdonon 186 17 k 167 for 26 sites vgp 50 n 178 e saint dic basin 184 20 5 for two sites vgp 53 n 180 e villc basin 191 5 25 for two sites vgp 53 n 168 e vosges dikes 197 5 26 5 for two sites vgp 53 n 158 e part of the magnetizations with intermediate unblocking temperatures of magnetite consists also of post tectonic overprints two consistent mean directions with lower inclinations obtained in the nideck donon rhyolites 182 7 k 459 for 13 sites vgp 45 n 1840 e and pyroclastic deposits from the villc basin 178 9 k 519 for three sites vgp 46 n 190 e were probably acquired during late autunianearly saxonian times in rhyolites the pre and post tectonic characteristic mag netizations are carried by magnetite while in the ash fall deposits the carrier is allogenic haematite a few older magnetizations 191 3 two sites vgp 42 n 173 e consistent with magnetizations carried by magnetite from rhyolites of the central black forest and results from coeval volcanics as well as from autunian sediments have been observed in tuffs from the villi basin 188 1 5 two sites vgp 40 n 177 e the oldest magnetizations 207 10 k 329 vgp 32 n 155 e presumably of stephanian age were identified in two rhyolitic stocks within the granitic basement from the central vosges and central black forest the distribution of the palaeomagnetic directions suggests that from the late autunian to the late thuringian overprinting due to low temperature alteration of titano magnetite and crystallization of secondary haematite was more or less continuous the apparent polar wander path apwp computed with the new results and the published poles shows a hairpin which implies a drastic change of the european plate motion during the permian the clockwise rotation of europe initiated in the late visean namurian stopped in the late autunian early saxonian this event corresponds to the end of the variscan convergence and of the appalachian

anisotropy of magnetic susceptibility data bearing on the transport direction of mid tertiary regional ignimbrites candelaria hills area west central nevada in west central nevada the oligocene candelaria pyroclastic sequence reaches a local thickness of up to 1 3 km in what has been referred to as the candelaria trough but more generally the accumulation of ash flow tuffs and related volcanic rocks is less than 300 m thick complete to near complete outcrops are scattered over about 3200 km2 in the candelaria hills and surrounding ranges of the southern walker lane structural zone three regionally extensive compound cooling units within the overall sequence 25 8 ma metallic city 24 1 ma belleville and 23 7 ma candelaria junction tuffs have distinguishing characteristics and are the focus of study at 106 sites anisotropy of magnetic susceptibility ams data provide an estimate of transport direction of each tuff inferred transport directions based on the ams data are corrected for a modest clockwise yet variable magnitude vertical axis rotation that affected these rocks in late miocene to pliocene time as revealed by paleomagnetic studies the ams data show a somewhat orderly pattern of magnetic fabrics that we interpret to define unique transport directions for the metallic city and candelaria junction tuffs the low susceptibility and degree of anisotropy of the belleville tuff limits our interpretation from this pyroclastic deposit the metallic city and candelaria junction tuffs typically show gentle south southeast and southeast dipping magnetic fabric imbrication respectively and very gently plunging magnetic lineations these ams fabric elements indicate the tuffs were transported to the north northwest and northwest respectively the ams fabric data from the metallic city and candelaria junction tuffs suggest relatively unrestricted flow during emplacement evidence across the 3 200 km2 area to support more regionally controlled channelized flow into and or flow along the east northeast west southwest axis of the candelaria trough is lacking the ignimbrites clearly filled a topographic depression inferred to have formed concurrent with early localized basin and range extension during pyroclastic emplacement but based on the uniformity of ams fabric data we infer that the depression quickly filled and did not hinder flow across the region unrecognized eruptive centers for the three ignimbrites may lie buried beneath neogene basin fill sediments south southeast of the candelaria hills or concealed below younger deposits farther southeast into the palmetto mountains

tidal triggering of earthquakes analysis of the tidal stress tensor at the time of moderate to large earthquakes strongly suggests that shallow 30 km larger magnitude oblique slip and dip slip earthquakes are triggered by tidal stresses no corresponding triggering effect is seen for shallow strike slip earthquakes or for any type of intermediate or deep focus earthquakes which have been studied tidal triggering is also discussed from the viewpoint of the dilatancy diffusion model specifically the model as usually stated excludes the possibility of small earthquakes being tidally triggered

model simulation of the effects of climate variability and change on lake ice in central alaska usa the canadian lake ice model climo is used to simulate the effects of climate variability and change on lake ice phenology freeze up fu break up bu ice cover duration and total thickness and composition snow ice congelation ice in central alaska usa the model results suggest that due to the pacific decadal oscillation shift that occurred in 1976 the ice cover duration is shorter 4 days due to earlier bu in spring and thinner 0 05 m due to a reduction in the formation of snow ice sensitivity tests indicate that air temperature changes cause the duration change and snow depth changes cause the total ice thickness and composition change the role of annual and monthly air temperature and snow depth changes is examined further in a series of experiments designed to elucidate the possible effects of future climate change air temperature is varied in 18c increments between 4 and 48c and snow depth is varied in 25 increments between 100 and 100 of the long term averages for 1952 75 and 1977 2000 the fu and bu dates ice duration are most affected by annual air temperature change total ice thickness and composition are most affected by annual and monthly snow depth change a key finding is that snow depth increases cause total ice thickness to increase as a consequence of increased snow ice formation on top of the ice cover at the expense of congelation ice formation at the bottom of the ice cover

determination of flow directions by combining ams and thin section analyses implications for oligocene volcanism in the kerguelen archipelago southern indian ocean we report an anisotropy of magnetic susceptibility ams study carried out on seven oligocene volcanic sections widely distributed on the surface of the kerguelen archipelago the statistical results at flow scale and at section scale were checked with ams density diagrams and thin section analysis because of the axis permutations frequently observed for lava flows two possible flow directions were nicely defined for the majority of the sections we then used two alternative approaches imbrication of the minimum axis and symmetry of the ams distribution to infer a flow direction for each section these two methods and thin section analysis not being decisive for choosing between the two solutions geological and geomorphological observations were finally used to obtain confident interpretations the results of this study enable the supposed eruptive centres of the kerguelen archipelago to be located more precisely

strong neotectonic block rotations related to the africa eurasia convergence in northern algeria paleomagnetic evidence from the mitidja basin

lacustrine oil shale basins in tertiary grabens from ne spain western european rift system abstract in the ne iberian plate the convergent motion and collision of the european iberian and african plates resulted in the development of paleogene compressional features strike slip systems thrust fold belts and late oligocene to mainly neogene extensional structures which are superimposed on the former these extensional structures are represented by horsts half grabens and tilted blocks often developed in connection with preexisting inherited faults from the late oligocene and during the neogene both strike slip and extensional regimes alternated and coexisted giving rise to a number of fault bounded basins the deposition of organic rich facies and in particular oil shales took place in the lacustrine complexes developed in some of these basins campins basin late oligocene ribesalbes and rubielos de mora basins early middle miocene libros basin late miocene and cerdanya basin late miocene deep lacustrine sequences ranging from 100 up to 250 m thick were deposited in all the above mentioned basins the organic rich sequences are characterized by thin lamination absence of bioturbation rare benthonic fauna if present it is supplied from other parts of the basin and excellent preservation of exotic fossils plant leaves insects amphibians the suitable depth conditions needed for permanent stratification in the water bodies and anoxia in the deeper parts of the lakes were due essentially to increasing subsidence outstripping deposition intense tectonic activity is recorded by the occurrence of olisthostromes and slumps affecting the lacustrine deposits as well as by the syntectonic structures recorded in the basin fill successions the late oligocene late miocene paleoclimatic regimes ranging from warm tropical to subtropical conditions were favourable for the development of permanently stratified lakes moreover chemical ectogenic meromixis may have contributed in some cases to the establishment of permanent stratification the eastern iberian rift system makes up the southernmost part of the larger western european rift system the occurrence of lacustrine sediments ranging from the late eocene to late miocene is frequent in the fault bounded basins of this complex rift system and lacustrine oil shale deposits have been recorded in several of these basins thus the western european rift system presents an interesting model of intracontinental rifting in a foreland platform setting where favourable conditions for organic rich deposits often took place the high potential of this kind of tectonic settings for lacustrine oil shale exploration must be stressed

indications for a successively triggered rupture growth underlying the 2000 earthquake swarm in vogtland nw bohemia 1 the characteristics of earthquake swarms can neither be described by simple laws nor are the underlying mechanisms presently understood swarm activity is often assumed to be caused by an intrusion of fluids into the seismogenic zone we have studied the earthquake catalog of the large earthquake swarm that occurred in the year 2000 in vogtland se germany and nw bohemia an area well known for its episodic swarm generation we observe a significant decrease of the gutenberg richter b value during the swarm evolution as well as a fractal temporal clustering of the earthquakes the spatial spreading of the swarm s activity which is approximately confined to one plane cannot simply be explained by a process of fluid diffusion instead we observe a simple relationship between the spatial spreading and the seismic moment release which is in good agreement with empirical relationships derived for tectonically driven earthquakes and theoretical crack growth models this observation points to a progressively growing main fracture underlying the swarm activity in addition we find that the swarm earthquakes themselves trigger aftershocks near the border of their rupture area the stick slip behavior of the rupture propagation can be explained by stress transfers and induced fluid flows due to earthquakes in a fluid permeated critically loaded fault zone however during the first phase the temporal behavior is found to be different pointing to intrusion of fluids initiating the swarm activity

slip generated patterns of swarm microearthquakes from west bohemia vogtland central europe evidence of their triggering mechanism 1 we investigated space time relations between consecutive events of west bohemian 2000 swarm and their association with the coulomb stress changes induced on a fault plane by prior swarm events a few thousand m 3 3 strike slip swarm earthquakes clustered along a fault plane at depths 6 5 10 5 km and showed common rake angle of 30 in order to disclose earthquake interaction we investigated the space time relations between consecutive earthquakes we determined relative position vectors for each consecutive event pair the prior event and the immediate aftershock ia and we measured time lags between them the resulting cluster of relative position vectors shows a high density of aftershocks near the origin which decays with distance it points out a triggering effect of the prior event upon subsequent aftershocks the spatial distribution of the relative positions disclosed dominance of aftershocks in the slip parallel directions which is manifested by pronounced elongation of the cluster of the relative positions and of the angular dependence of the rate of ias the temporal distribution of the relative positions indicates that some aftershocks prove high interevent velocities and occur systematically at greater distances suggesting the existence of two distinct triggering mechanisms acting at large and small timescales we evaluated the complete coulomb stress change upon the fault plane due to the prior event and showed that the observed space time distribution of the relative positions can be explained by a common effect of both static and dynamic stress changes which act on different distance and timescale

a new approach to earthquake prediction the load unload response ratio lurr theory the response to loading is different from that to unloading when the focal media is approaching instability the ratio of the response rate during loading to that during unloading called load unload response ratio y lurr could be a measure of the closeness degree to instability and is used in a new approach to earthquake prediction retrospective examination of some one hundred earthquake cases from m 4 to m 8 6 indicates that for more than 80 of the examined ones the value of y is much higher than 1 for a period before the main shock but the y value always fluctuates slightly about 1 during two decades for seven stable regions so that the parameter y could indicate a dangerous degree of an impending earthquake several earthquakes occurring on the chinese mainland in recent years as well as the northridge california u s a earthquake jan 17 1994 m w 6 7 have been predicted beforehand with this method

temperature fluctuations underneath the ice in diamond lake hennepin county minnesota 1 diamond lake in minnesota is covered every winter with ice and snow providing a modified thermal insulation between water and air autonomous temperature sensors data loggers were placed in this lake so that hourly measurements could be obtained from the snow covered ice and water the sensors that became frozen measured damped and delayed thermal response from the air temperature fluctuation those sensors that were deeper within the snow covered ice measured continuous almost constant temperature values near freezing several of them were within the liquid water and responded with a fluctuation of 24 h periods of amplitudes up to 0 2 c our analysis of the vertical temperature profiles suggested that the source of periodic water heating comes from the lake bottom because of the absence of daily temperature variations of the snow covered ice the influence of the air temperature fluctuation can be ruled out we attribute the heating process to the periodic inflow of groundwater to the lake and the cooling to the heat diffusion to the overlying ice cover the periodic groundwater inflow is interpreted due to solid earth tides which cause periodic fluctuations of the groundwater pressure head

great salt lake and precursors utah the last 30 000 years sediment cores up to 6 5 m in length from the south arm of great salt lake utah have been correlated radiocarbon ages and volcanic tephra layers indicate a record of greater than 30 000 years a variety of approaches have been employed to collect data used in stratigraphic correlation and lake elevation interpretation these include acoustic stratigraphy sedimentologic analyses mineralogy geochemistry major element c o and s isotopes and organics paleontology and pollen the results indicate that prior to 32 000 year b p an ephemeral saline lake playa system was present in the basin the perennial lake which has occupied the basin since this time rose in a series of three major steps the freshest water conditions and presumably highest altitude was reached at about 17 000 year b p the lake remained fresh for a brief period followed by a rapid increase in salinity and sharp lowering in elevation to levels below that of the present great salt lake the lake remained at low elevations and divided at times into a north and south basin until about 8 000 year b p since that time with the exception of two short rises to about 1290 m the lake level has remained near the present elevation of 1280 m

evidence for tidal triggering of earthquakes as revealed from statistical analysis of global data 1 we observe tidal triggering of earthquakes by measuring the correlation between the earth tide and earthquake occurrence we used the times locations and focal mechanisms of the 9350 globally distributed earthquakes with magnitude 5 5 or larger from the harvard centroid moment tensor catalog the tidal stress was theoretically computed by using the preliminary reference earth model and a recent ocean tide model nao 99b we considered the shear stress on the fault plane and the trace of stress tensor j1 defining the tidal phase angle at the occurrence time for each earthquake we statistically tested the phase selectivity using the schuster s method for all the earthquakes no significant correlation is found between the earth tide and earthquake occurrence both for the shear stress and for j1 by classifying the data set according to fault types however we find a high correlation with the shear stress for reverse fault type the correlation is particularly clear for shallow and smaller earthquakes of this type significant correlation with j1 also appears for larger earthquakes of reverse fault type and for shallow and larger ones of normal fault type we find no correlation for strike slip type for all the cases of high correlation earthquakes tend to occur when the tidal stress accelerates the fault slip indicating that high correlation is not coincidental but is physically justified this result strongly suggests that a small stress change due to the earth tide encourages earthquake occurrence when the stress in the future focal area is near a critical condition

oil shales evaporites and ore deposits abstract the relationships between oil shales evaporites and sedimentary ore deposits can be classified in terms of stratigraphic and geochemical coherence oil shale and black shale deposition commonly follows continental red beds and is in turn followed by evaporite deposition this transgressive regressive sequence represents an orderly succession of depositional environments in space and time and results in stratigraphic coherence the amount of organic carbon of a sediment depends on productivity and preservation both of which are enhanced by saline environments work on great salt lake utah allows us to estimate that only 5 of toc originally deposited is preserved inorganic carbonate production is similar to toc production but preservation is much higher oil shales and black shales commonly are enriched in heavy metals through scavenging by biogenic particles and complexation by organic matter ore deposits are formed from such rocks through secondary enrichment processes establishing a geochemical coherence between oil shales and ore deposits the permian kupferschiefer of n europe is used as an example to define a kupferschiefer type kst deposit here oxygenated brines in contact with red beds become acidified through mineral precipitation and acquire metals by dissolving oxide coatings oxidation of the black shale leads to further acid production and metal acquisition and eventually to sulfide deposition along a reducing front in order to form ore bodies the stratigraphic coherence of the red bed black shale evaporite succession must be joined by the geochemical coherence of the ore body evaporite black shale association the cretaceous cu zn deposits of angola the zambian copperbelt as well as the creta oklahoma deposits are other kst examples in the zambian copperbelt evaporites are indicated by the carbonate lenticles thought to be pseudomorphs after gypsum anhydrite nodules mvt deposits are also deposited by acid brines but at more elevated temperatures and with carbonates as principal host rocks the pine point deposits are cited for their close association with evaporites alkaline metal rich brines are postulated for the hyc deposit of mcarthur river australia such brines are known from the green river formation and deposits formed from such brines constitute the grt class they can be recognized by the presence of magadi type cherts and zeolite analcime k spar tuffs the cu co ore bodies of outokumpu finland might also belong to this type a new classification of sedimentary ore deposits is proposed based on their geochemical environment kst and mvt are formed from acid ore fluids while grt and ct creede type are derived from basic ore fluids ph of the fluids is best evaluated not from the ores themselves but from their effect on the host rocks

response of the water level in a well to earth tides and atmospheric loading under unconfined conditions the response of the water level in a well to earth tides and atmospheric loading under unconfined conditions can be explained if the water level is controlled by the aquifer response averaged over the saturated depth of the well because vertical averaging tends to diminish the influence of the water table the response is qualitatively similar to the response of a well under partially confined conditions when the influence of well bore storage can be ignored the response to earth tides is strongly governed by a dimensionless aquifer frequency q u the response to atmospheric loading is strongly governed by two dimensionless vertical fluid flow parameters a dimensionless unsaturated zone frequency r and a dimensionless aquifer frequency qu the differences between q u and qu are generally small for aquifers which are highly sensitive to earth tides when q u and qu are large the response of the well to earth tides and atmospheric loading approaches the static response of the aquifer under confined conditions at small values of q u and qu well response to earth tides and atmospheric loading is strongly influenced by water table drainage when r is large relative to qu the response to atmospheric loading is strongly influenced by attenuation and phase shift of the pneumatic pressure signal in the unsaturated zone the presence of partial penetration retards phase advance in well response to earth tides and atmospheric loading when the theoretical response of a phreatic well to earth tides and atmospheric loading is fit to the well response inferred from cross spectral estimation it is possible to obtain estimates of the pneumatic diffusivity of the unsaturated zone and the vertical hydraulic conductivity of the aquifer

the thermal conductivity of seasonal snow twenty seven studies on the thermal conductivity of snow k eff have been published since 1886 combined they comprise 354 values of k eff and have been used to derive over 13 regression equation and predicting k eff vs density due to large and largely undocumented differences in measurement methods and accuracy sample temperature and snow type it is not possible to know what part of the variability in this data set is the result of snow microstructure we present a new data set containing 488 measurements for which the temperature type and measurement accuracy are known a quadratic equation where is in g cm 3 and k eff is in w m 1 k 1 can be fit to the new data r 2 0 79 a logarithmic expression can also be used the first regression is better when estimating values beyond the limits of the data the second when estimating values for low density snow within the data set snow types resulting from kinetic growth show density independent behavior rounded grain and wind blown snow show strong density dependence the new data set has a higher mean value of density but a lower mean value of thermal conductivity than the old set this shift is attributed to differences in snow types and sample temperatures in the sets using both data sets we show that there are well defined limits to the geometric configurations that natural seasonal snow can take

determination of fluid flow properties from the response of water levels in wells to atmospheric loading the water level in a well that taps a partially confined aquifer is often sensitive to atmospheric loading the magnitude and character of this response is partly governed by the well radius the lateral hydraulic diffusivity of the aquifer the thickness and vertical pneumatic diffusivity of the unsaturated zone and the thickness and vertical hydraulic diffusivity of the saturated zone overlying the aquifer these key elements can be combined into five dimensionless parameters that partly govern the phase and attenuation of the response in many cases the response of a well to atmospheric loading can be broken up into a high intermediate and low frequency response the high frequency response is governed largely by the well radius and lateral diffusivity of the aquifer the intermediate frequency response is governed by the loading efficiency of the aquifer the low frequency response is governed by the vertical pneumatic diffusivity and thickness of the unsaturated zone and the vertical hydraulic diffusivity and thickness of the saturated material above the aquifer cross spectral estimation is used to fit the response to atmospheric loading of three water wells to the theoretical curves in order to yield estimates of three of the key dimensionless parameters these estimates then are used to make estimates or place bounds on the vertical pneumatic diffusivity of the unsaturated zone the lateral permeability of the aquifer and the composite vertical hydraulic diffusivity of the overlying saturated materials

tertiary lacustrine sediments from sentinel butte north dakota and the sedimentary record of ectogenic meromixis abstract about 10 meters of probable oligocene or miocene lacustrine sediments which crop out on top of sentinel butte in western north dakota consist mostly of greenish gray zeolitic mudstone interbedded with relatively thin layers of dolomite limestone and chalcedony the dolomite layers are several centimeters thick and are mostly dolomicrite with laminae or lenses of arkosic sand and pellets they probably formed by deposition of protodolomite in shallow closed saline lakes the limestone layers are up to 30 centimeters thick their basal portions contain varve couplets of micrite and organic matter graded bedding in micrite laminae and concentration of aeolian silt in organic laminae suggest that deposition of carbonate took place during a relatively brief portion of each year pres rvation of varves fossil fish and coprolites in the limestone imply deposition in a meromictic lake in contrast poor preservation of fish and bioturbation in the upper parts of two limestone beds record transition to holomictic conditions some variations in varve thickness appear rhythmic and possibly related to the sunspot cycle several asymmetric cycles of contrasting carbonate facies ideally consisting of massive dolomite overlying clay and underlying laminated limestone imply that the ancient lake in which the sequence was deposited underwent several episodes of shrinkage and closure during which its salinity increased followed by expansion accompanied by abrupt development of ectogenic meromixis changes in authigenic mineralogy and upward increase in thickness of limestone beds relative to dolomite beds record a long term trend toward freshening of basinal hydrology models involving ectogenic meromixis can explain intimate associations of evaporitic facies with varved sediments in other sedimentary sequences and may be applicable to some precambrian iron formations

tidal coulomb failure stresses in the northern andean intermediate depth seismic clusters implications for a possible correlation between tides and seismicity abstract a recent statistical analysis of the relationship between tides and seismic activity in colombia has suggested the existence of correlation anomalies for the case of intermediate depth events in the bucaramanga nest and the cauca cluster moncayo et al 2019 in this work we explore in detail the hypothesis that tides may be triggering seismic activity in these regions and extend the analysis to two other seismic clusters in northern central south america specifically in the areas of el puyo ecuador and pucallpa peru for this purpose we use the available focal mechanism information for seismic events at these locations and calculate for each event the tidal coulomb failure stress tcfs as obtained from estimations of the tidal strain tensor tidal strains are computed considering the earth body tides and the effect of the ocean tidal loading since our purpose is to elucidate the role of tides in earthquake nucleation calculations of the tcfs are conducted not only for the time of earthquake but also for the time of the closest maximum strain within a window of a few hours before the events our results tend to support the hypothesis that tidal stresses are contributing to earthquake generation in all the studied areas this trend is especially stronger when tcfs are calculated at pre earthquake times the physical explanation for the positive contribution of tides to earthquake triggering in intermediate depth clusters may lie in the fact that a wide diversity of fault plane orientations is possible within a relatively small volume of subducted lithosphere so making the tides more likely to help loosening up the blocks at the fault plane to promote slip

from qualitative to quantitative magnetic anisotropy analysis the prospect of finite strain calibration abstract a method of separating low field susceptibility anisotropies due to ferrimagnetics and the matrix proposed hitherto in cases where the principal axis of these two components are merged is generalized in cases where the axes are distinct the method consists of analysing in specimens close in the same sample anisotropies the differences of which are due to the variation of respective percentages of the two components although the strain rate remains constant one thus uses the cause which itself renders global anisotropy unusable a first application is presented where a control using the anisotropy of isothermal remanent magnetization allows the validity of the method to be tested a discussion of the choice of the best ellipsoid relative either to the matrix or to the ferrimagnetics to give the best indication of relative finite strain rate is opened

the fortnightly tide and the tidal triggering of earthquakes in this paper we test the southern california network earthquake catalog and the world wide earthquake catalog for a fortnightly tidal periodicity and find none in studies that test the hypothesis of tidal triggering of earthquakes it is usually necessary to resolve the tidal shear stress onto the plane of the fault and in the direction of the slip vector to determine if the stress is compatible with the fault motion heaton 1975 1982 this analysis requires accurate focal mechanisms and knowledge of the focal plane on which slip occurred for as many earthquakes as possible to improve the statistical sampling of the data set however if we consider the fortnightly tide which is a simple amplitude modulation focal mechanism information is not required our analysis assumes that we have a large data base of earthquakes with varying mechanisms the alignment of the slip vector with the tidal shear stress will vary from earthquake to earthquake however if tidal triggering of earthquakes does occur more earthquakes should be triggered out of the total population when the tidal stress is large than when it is small if the largest semi diurnal tide is normalized to an amplitude of 1 0 the fortnightly tide would have an amplitude of 0 17 on this scale and a period of about 2 weeks munk and macdonald 1960 therefore the effect on the occurrence of earthquakes by the tidal shear stress will be modulated with a 2 week period considering the fortnightly tide allows us to utilize entire catalogs of data to test the tidal triggering hypothesis without knowledge of the focal mechanisms

sedimentological and palaeohydrological responses to tectonics and climate in a small closed lacustrine system oligocene as pontes basin spain a small closed lacustrine system developed during the restraining overstep stages of the oligocene as pontes strike slip basin spain the increase in basin accommodation and the headward spread of the drainage which increased the water input triggered a change from shallow holomictic to deeper meromictic conditions the lower shallow lacustrine assemblage consists of mudstone carbonate cycles recording lacustrine palustrine ramp deposition in a saline lake high sr content in some early diagenetic calcites suggests that aragonite and calcite made up the primary carbonate muds early dolomitization took place together with widespread pedogenic activity the upper deep freshwater lacustrine assemblage includes bundles of carbonate clay rhythmites and fine grained turbidite beds primary calcite and diagenetic siderite make up the carbonate laminae the mg content of the primary carbonates records variations in mg ca ratios in lacustrine waters d 18 o and d 13 c covariance trends in calcite reinforce closed drainage conditions d 18 o data indicate that the lake system changed rapidly from short lived isotopically light periods i e from seasonal to pluriannual to longer steadystate periods of heavier d 18 o i e from pluriannual to millennial the small d 13 c changes in the covariant trends were caused by dilute inflow changing the contributions of dissolved organic carbon in the system and or internal variations in lacustrine organic productivity and recycling in both shallow and deep carbonate facies sulphate reduction and methanogenesis may account respectively for the larger negative and positive d 13 c shifts recorded in the early diagenetic carbonates calcite dolomite and siderite the lacustrine system was very susceptible to high frequency climatically forced water balance variations these climatic oscillations interfered with the lowfrequency tectonic and morphological changes in the basin catchment this resulted in the superposition of high order depositional mineralogical and geochemical cycles and rhythms on the lower order lacustrine infill sequence

magnetic properties of marine limestones numerous paleomagnetic investigations have been carried out on limestones but their rock magnetic properties have often been neglected in this review geological and rock magnetic factors which determine whether marine limestones are suitable for paleomagnetic study are summarized and laboratory techniques for the identification of the magnetic mineralogy are evaluated the conditions under which pelagic limestones form are especially favorable for the acquisition of a stable primary natural remanence nrm probably by a postdepositional alignment process the effectiveness and timing of acquisition of this remanence are influenced by the thoroughness of bioturbation other remanence components can be acquired during diagenesis in the soft sediment right after deposition or much later even in the indurated limestone the magnetic mineralogy of a limestone is difficult to describe optically because of the small grain size and low concentration magnetic techniques are more convenient direct analysis of extracted magnetic minerals is handicapped by the difficulty of obtaining a representative extract a particularly useful technique involves combined observations of isothermal remanent magnetization irm acquisition in strong fields up to at least 4 t and the subsequent destruction of this irm during stepwise or continuous thermal demagnetization the magnetic minerals most commonly identified by these techniques are magnetite goethite hematite and maghemite these magnetic minerals occur in different combinations in the marine limestones of central europe and the mediterranean realm pyrite is common in certain limestones where it can be the precursor of an unwelcome late goethite pyrrhotite may be responsible for unstable magnetization in the swiss helvetic limestones but otherwise is rare thermal demagnetization of some limestones causes changes of susceptibility and coercivity at quite low temperatures 300 400 c due to the breakdown of a metastable mineral such as maghemite goethite or pyrrhotite at high temperatures above 500 c pronounced changes of magnetic mineralogy occur in all limestones because of the growth of new magnetite this necessitates great care in interpretation of thermal demagnetization of high blocking temperature components and often results in observational difficulties due to viscous remanent vrm behavior of the newly formed magnetite vrm is a widespread component of nrm in many limestones but it can usually be removed effectively by standard magnetic cleaning techniques the susceptibility serves as a simple control of mineralogical change during heating and can serve as an indicator of lithologic variation of magnetic mineral concentration and type in magnetostratigraphic profiles the susceptibility is anisotropic and shows a classical depositional pattern of the distribution of principal axes however the probable postdepositional mechanism of nrm acquisition especially in bioturbated sediments implies that the anisotropy pattern results from postdepositional compaction of the sediment

strainmeters and tiltmeters despite steady effort over the last century continuously recording tiltmeters and strainmeters have not yet been successful except for earth tide measurements this article reviews the techniques and instrument designs that have been developed in this field the continuous measurement of true tectonic motions which have rates of 10 14 s 1 requires extremely high instrument stability but more rapid motions tides and seismic waves apart are even smaller and not much more easily detectable much past effort has been spent improving the transducers used in these instruments which usually measure small displacements the commonest choices are optical the most accurate capacitive the most sensitive and inductive the most rugged nowadays building a transducer is the easiest part a much harder task equally important to a good design is attaching the instrument to the ground so that it can detect the signal wanted this part of the design includes choosing a location a large underground opening is thermally stable but distorting a surface installation is easy to build but noisy because of soil weathering and a borehole is inaccessible to weather but also to the operator all such installations and indeed the whole field of strain and tilt measurement of course rely on the assumption that the deformations of interest can be measured over baselengths of a few hundred meters or less this is true for tides and seismic waves but unproven for tectonic motions appropriate attachment techniques differ for each location and many mundane details such as cementing techniques for borehole instruments remain to be worked out the goal of measuring tectonic and tidal tilt has created many tiltmeter designs most are relatively small instruments that use some form of pendulum or bubble level a few use a liquid surface to measure tilts over a long baseline repeated experience has shown the latter type when well built to be superior to the former proving end monument motions to be a dominant source of noise the same appears to hold true for strainmeters the best results coming from long base laser instruments though strainmeters using rigid or flexible material length standards are useful for special purposes and borehole instruments show promise because achieving a good design has been so difficult it is important to select the goals an instrument must meet and be prepared to compromise on others the difficulty of validating results from this type of instrument makes comparison tests essential such tests as have been made so far show that good results cannot be gotten at low cost or without careful attention to details