geomagnetic paleointensity derived from single plagioclase crystals we suggest a new approach for the determination of absolute geomagnetic paleointensity that uses single plagioclase crystals to avoid problems caused by alteration during thellier thellier analyses transmission electron microscope imaging and rock magnetic data indicate that plagioclase crystals from a recent basalt flow in hawaii 1955 kilauea eruption contain pseudo single to single domain titanomagnetite inclusions these feldspars yield paleointensity values that agree within error with magnetic observatory data and paleointensity values reported from whole rock samples these results suggest that single plagioclase crystals from older igneous rocks may provide a viable source of paleointensity data

development of magnitude bound relations for paleoliquefaction analyses new zealand case study abstract magnitude bound relations are often used to estimate paleoearthquake magnitudes from paleoliquefaction data this study proposes new zealand based magnitude bound curves that are developed using a liquefaction field observations and b a newly proposed back calculation approach that combines the simplified liquefaction evaluation procedure with a regionally appropriate ground motion prediction equation for b both deterministic and probabilistic frameworks are proposed the magnitude bound curves back calculated using either the deterministic or probabilistic frameworks are advantageous in that they can be used to predict the spatial distribution of liquefaction in regions where historical liquefaction field observations are limited or poorly documented and because soil and site specific conditions can be incorporated into magnitude bound analyses moreover curves developed using the probabilistic framework allow for the range of possible causative earthquake magnitudes to be better understood and quantified to demonstrate the use of the proposed relations paleoliquefaction features discovered in eastern christchurch nz are analyzed the 1869 mw4 8 christchurch earthquake and or 1717 mw8 1 alpine fault earthquake are found to be the most likely candidates amongst known historical and paleoearthquakes for triggering liquefaction over the permissible time range ca 1660 to 1905 a d this study demonstrates the potential of the proposed magnitude bound curves to provide insight in to past present and future hazards proving their utility even in cases of limited evidence the approach of developing and applying magnitude bound curves proposed herein is not limited to parts of new zealand but rather can be applied worldwide

surface rupture during the 2010 mw 7 1 darfield canterbury earthquake implications for fault rupture dynamics and seismic hazard analysis the september 2010 m w 7 1 darfield canterbury earthquake in new zealand is one of the best recorded earthquakes of this magnitude the earthquake occurred on a previously unidentified fault system and generated a 29 5 0 5 km long surface rupture across a low relief agricultural landscape high accuracy measurements of coseismic displacements were obtained at over 100 localities along the greendale fault maximum net displacement d max 5 3 0 5 m and average net displacement d avg 2 5 0 1 m are anomalously large for an earthquake of this m w d max surface rupture length srl and d avg srl ratios are among the largest ever recorded for a continental strike slip earthquake geologically derived estimates of moment magnitude m w g are less than the seismologically derived m w derived using widely employed srl m w scaling regressions m w g is greater than m w using d max and d avg m w regressions the geologically derived static stress drop of 13 9 3 7 mpa provides a context with which to compare this earthquake rupture to interplate and intraplate ruptures of similar m w this data set provides fundamental information on fault rupture processes relevant to seismic hazard modeling in this region and analogous settings globally

thermoremanence anhysteretic remanence and susceptibility of submicron magnetites nonlinear field dependence and variation with grain size we have measured initial susceptibility 0 and the dependence of anhysteretic remanent magnetization arm and thermoremanent magnetization trm on applied field for seven samples of magnetite with mean grain sizes from 40 to 540 nm trm acquisition is nonlinear in geomagnetically relevant weak fields contrary to the usual assumption made in paleointensity determination over the 40 540 nm range 0 varies with particle shape but only weakly with particle size d and can be used to correct for varying magnetite concentrations in sediment cores arm is strongly size dependent over the same range and is the best parameter for monitoring grain size variations in natural samples arm and trm have similar variations as d 1 for d 1 m suggesting a common source for this pseudo single domain psd dependence on grain size however trm is 10 20 times more intense than arm in grains around 0 2 m in size the trm microstate seems to be a two domain structure whereas the arm microstate may be a vortex structure which has never before been convincingly demonstrated by magnetic measurements independent evidence comes from theoretical fits to trm and arm field dependence data in moderate and strong fields trm in 215 540 nm magnetites is explained by two domain theory but arm is not in smaller grains d 0 1 m a psd theory predicts that trm is carried by single domain sd moments of entire grains but arm resides in moments 1 per grain 20 40 times weaker these remanence levels match those of metastable sd and vortex states respectively we therefore propose that magnetite grains in the 0 1 0 5 m size range can remain in metastable sd or two domain states following acquisition of trm but revert to a vortex ground state when field cycled for example in arm acquisition or alternating field demagnetization

mechanisms for precipitation variability of the eastern brazil sacz convective margin the present study examines the mechanisms for the connection between the precipitation variability in eastern brazil and the south atlantic convergence zone sacz convective margin eastern brazil sacz convective margin and the variability of low level inflow on interannual time scales during austral summer theauthors methodologyisbasedontheanalysisofobservationaldatasetsandsimulationsby theuniversity of california los angeles ucla atmospheric general circulation model agcm coupled to the simplified simple biosphere model it is demonstrated that the inflow variability is associated with the leading mode of wind variability over subtropicalsouth america andtheconnection isestablishedthroughthemechanismofananalyticprototype for convective margin shifts proposed in previous studies over the eastern brazil sacz convective margin the weaker stronger convection tends to occur together with stronger weaker low level inflows in reference to the mean easterly trades by changing the ventilation effect stronger weaker inflows with low moist static energy from the atlantic ocean suppress promote convection the causal relationship is verified by agcm mechanism testing experiments performed in perpetual february mode in which low level nondivergent wind perturbations are imposed in a region overlapping eastern brazil and the western atlantic ocean with solely the imposed wind perturbations acting on the moisture advection in the model equation the agcm can reproduce the precipitation variability in the eastern brazil sacz convective margin the capability of the agcm in capturing such precipitation sensitivity to the low level inflow variability also suggests that the mechanism can be applied to other regions of convective margins or to other time scales

the shaw method of palaeointensity determinations and its application to recent volcanic rocks summary our new version together with previous versions of the shaw method has been compared by applying them to recent volcanic samples for which we have well determined palaeointensity values although the earlier modifications to the shaw method give a linear portion to the nrm trm diagram of all the specimens about half of the calculated palaeointensities deviate by more than 20 per cent from the expected values this may be caused by alteration of the magnetic minerals during the laboratory heating or by chemical alteration prior to the laboratory experiments the new modification uses a double heating of samples above the curie temperature in the laboratory after heating the specimen twice in the same field the measured intensity from the second heating is compared with the laboratory field intensity if the difference is larger than the experimental error then we assume that the anhysteretic remanent magnetization arm correction is not applicable and the sample is therefore rejected this technique provides a powerful criterion with which to select samples using this selection technique palaeointensities are generally within 10 per cent difference of the expected values with a success rate of about 40 per cent

new advances for paleomagnetic studies of sediment cores using u channels accurate and detailed paleomagnetic data can be obtained from continuous measurements of u channels extracted from sedimentary cores using a small diameter pass through magnetometer and high resolution signal response pick up coils the spatial resolution is not significantly lower than that obtained by measuring standard paleomagnetic samples and features on the order of 3 5 cm can be confidently resolved we propose a method to analyze the demagnetization data based on the angular dispersion of the directions between successive demagnetization steps and the downcore changes in the rate of intensity decrease this technique allows us to distinguish very rapidly between intervals with well identified characteristic magnetic components and zones characterized by a more complex behavior during demagnetization it is also possible to directly measure the magnetic susceptibility and to induce and measure most rock magnetic properties along the u channels thus all parameters necessary for a complete paleomagnetic study of sediment cores can be confidently obtained directly from u channels without extracting individual samples finally this equipment makes possible the measurement and complete demagnetization of up to 10 single samples at a time in less than one hour by using techniques similar to those developed for the u channels

paleointensity experiments using alternating field demagnetization abstract experiments for absolute paleointensity involve a large number of heatings and thus increase the probability of mineralogical changes which considerably reduce the success rate magnetic granulometry also plays an important role in the presence of multidomain grains thermal demagnetization of natural remanent magnetization nrm is not linearly related to acquisition of thermal remanence trm in the laboratory so that the nrm trm diagrams are characterized by two slopes neither of them providing a correct field determination after briefly reviewing most current techniques for paleointensity and various attempts to improve the results the present paper investigates approaches relying on alternating field a f demagnetization measurements have been performed on at least eight samples from seven contemporary flows from hawaii classical thermal experiments were also conducted with poor success in contrast 30 of the nrm trm curves obtained after a f demagnetization were perfectly linear over the entire spectrum of coercivities and thus appropriate to determine a paleointensity this difference was caused by the possibility of measuring a much larger number of samples the mean field is less than 10 higher than the present field and in better agreement for a subset of samples with nrm and trm heated at 300 c prior to a f demagnetization these values are acceptable within the uncertainties inherent in any study of absolute paleointensity thus a f techniques can be used with confidence provided that the whole spectrum of coercivities is involved in the field determination and exempt from any correction this condition is necessary and sufficient to demonstrate the absence of alteration after heating because of the rapidity of such experiments an approach combining a f and thermal experiments is certainly the best way to increase considerably the number of field determinations per lava flow and hence the overall quality of paleointensity studies

palaeointensity study of the oshima 1986 lava in japan implications for the reliability of the thellier and ltd dht shaw methods abstract we have performed a palaeointensity study of the oshima 1986 lava in order to examine the reliability of the thellier and ltd dht shaw methods with special reference to high temperature oxidation states of magnetic grains coe s version of the thellier method was applied to fifteen specimens from five block samples the palaeointensities determined by this thellier method ranged from 44 8 to 59 0 t with an average of 51 0 4 1 t n 15 they are systematically higher than the expected intensity 45 5 t from the dgrf 1985 since the in situ magnetic survey at the sampling site indicates no strong local magnetic anomaly these high palaeointensities are overestimation probably due to some rock magnetic property and or some thermal alteration during the experiments microscopic observations show that the samples where some titanomagnetites surrounding vesicles were classified with intermediate oxidation indices of iii v gave 10 30 higher palaeointensity values therefore the erroneously high thellier palaeointensities have a relation to the high temperature oxidation state for eight of the fifteen specimens used in the thellier experiments the applied dc field was perpendicular to the primary nrm component for quantitative evaluation of laboratory induced chemical remanent magnetisation crm directional changes of nrm thermally demagnetised during the thellier experiments indicate that most of the samples more or less acquired crm due to laboratory heating suggesting that some magnetic phase with high blocking temperatures was produced for the specimens of intermediate oxidation level the crm appears to have been gradually acquired at relatively low temperatures 400 c it would appear to be difficult to detect this gradual thermal alteration with the standard ptrm check weak field susceptibility measurements and hysteresis parameter changes we also applied the double heating technique of the shaw method combined with low temperature demagnetisation ltd dht shaw method to seven specimens from the same block samples the palaeointensities determined by the ltd dht shaw method yielded an average of 46 4 4 7 t n 6 which agrees with the expected intensity indicating no dependence on the high temperature oxidation states

the intensity of the geomagnetic field from 2 4 ga old indian dykes precambrian paleomagnetic records from dyke swarms provide a unique source of information regarding the archean geomagnetic field and more specifically the average field strength produced by the early dynamo we sampled 16 paleomagnetic sites from the dharwar giant dyke swarm in southern india which was emplaced between 2 365 and 2 368 ga despite taking great care in selecting locations exempt of any geological disturbance only two of these sites provided primary directions with very steep inclinations and therefore were emplaced in close to a magnetic pole paleointensity experiments were conducted on a subset of samples from the dyke margins the characteristic magnetization is carried by single domain magnetite grains with a very narrow range of unblocking temperatures inferred from the sharp decrease by at least 75 of their remanence above 520 c the paleointensity results indicate an average low field of 9 2 7 t consistent with reported values from canadian dyke swarms for the same period these results combined with the thellier thellier determinations obtained so far for the precambrian suggest that a low field period prevailed from circa 2 3 to 1 8 ga while the preceding and following time intervals are characterized by significantly stronger paleointensities although this suite of episodes is not fully incompatible with previous models for the long term evolution of the geodynamo it is tempting to make the link with the recent suggestion of an early dynamo sustained within a conductive magma layer at the base of the mantle from 3 5 to 2 5 ga which progressively declined until convection became sufficiently efficient to reactivate a strong dynamo process within the earth s liquid core

the climate of the altiplano observed current conditions and mechanisms of past changes abstract the large scale controls on the climate of the south american altiplano are investigated using local observations reanalysis data and general circulation model experiments the objective is to gain understanding of causes of climate variability and climate change by relating mechanisms that operate on timescales ranging from the intraseasonal to the glacial interglacial our results suggest that on all timescales the climatic conditions on the altiplano are closely related to the upper air circulation with an easterly zonal flow aloft favoring wet conditions and westerly flow causing dry conditions different factors influence the upper air circulation on the different timescales intraseasonal variability is a reflection of the position and intensity of the bolivian high which is modulated by rossby waves emanating from the midlatitude south pacific the annual cycle of dry winter and wet summer conditions is caused by the seasonal expansion of the equatorial easterlies in the upper troposphere rather than direct insolation forcing over the altiplano or moisture changes in the source area interannual variability is primarily related to changes in the mean zonal flow over the altiplano reflecting changes in meridional baroclinicity between tropical and subtropical latitudes which in turn is a response to sea surface temperature changes in the tropical pacific orbitally forced changes in the land sea contrast drive continental scale circulation changes which significantly alter the zonal flow over the altiplano on glacial interglacial timescales the contrast in heating between northern and southern hemispheres during the glacial leads to upper air easterly anomalies throughout the tropics on modern timescales the marked submonthly seasonal and interannual changes of moisture over the altiplano cannot be accounted for by moisture changes in the humid tropical lowlands however the model experiments suggest that cooler conditions during a glacial reduce moisture availability from the tropical lowlands which counteracts the effect of the upper level circulation resulting in little overall change in precipitation this observational and modeling analysis provides a physical framework for relating the mechanisms of both internal and forced climate change on the altiplano on a wide range of timescales

time variations in geomagnetic intensity 1 after many years spent by paleomagnetists studying the directional behavior of the earth s magnetic field at all possible timescales detailed measurements of field intensity are now needed to document the variations of the entire vector and to analyze the time evolution of the field components a significant step has been achieved by combining intensity records derived from archeological materials and from lava flows in order to extract the global field changes over the past 12 kyr a second significant step was due to the emergence of coherent records of relative paleointensity using the remanent magnetization of sediments to retrace the evolution of the dipole field a third step was the juxtaposition of these signals with those derived from cosmogenic isotopes contemporaneous with the acquisition of records new techniques have been developed to constrain the geomagnetic origin of the signals much activity has also been devoted to improving the quality of determinations of absolute paleointensity from volcanic rocks with new materials proper selection of samples and investigations of complex changes in magnetization during laboratory experiments altogether these developments brought us from a situation where the field changes were restricted to the past 40 kyr to the emergence of a coherent picture of the changes in the geomagnetic dipole moment for at least the past 1 myr on longer timescales the field variability and its average behavior is relatively well documented for the past 400 myr section 3 gives a summary of most methods and techniques that are presently used to track the field intensity changes in the past in each case current limits and potential promises are discussed the section 4 describes the field variations measured so far over various timescales covered by the archeomagnetic and the paleomagnetic records preference has always been given to composite records and databases in order to extract and discuss major and global geomagnetic features special attention has been devoted to discussing the degree of confidence to be put in the data by considering the integration of multiple data sets involving different techniques and or materials

lake sediments record high intensity shaking that provides insight into the location and rupture length of large earthquakes on the alpine fault new zealand abstract understanding the seismic hazard posed by large earthquakes requires paleoseismic investigation because most faults have not ruptured repeatedly during the period of historic records however determining the location and length of fault ruptures using paleoseismic data remains challenging our study demonstrates that lake sediments record the high intensity shaking that occurs proximal to fault rupture allowing the location and length of ruptures to be reconstructed in two lakes adjacent to the alpine fault new zealand seismic shaking is recorded as subaqueous mass wasting derived turbidites formed by coseismic subaqueous slope failures which are overlain by sets of hyperpycnites representing elevated fluvial sediment fluxes from earthquake induced landslides precise radiocarbon age models show that shaking events are synchronous between the two lake sites and correlate with the timing of known alpine fault earthquakes modelled shaking intensities for the last two alpine fault earthquakes show that subaqueous mass wasting occurs when shaking intensities exceed modified mercalli scale mm vi vii and that fluvial sediment fluxes from earthquake induced landslides occur when shaking intensities exceed mm ix the data demonstrate that lake records distinguish between strong mm vi and violent mm ix shaking at a lake site the ability to map the spatial extent of mm ix shaking provides new insights into the timing and extent of rupture for the last five earthquakes on the alpine fault the study demonstrates that lake deposits constrain the spatial extent of rupture during large earthquakes and may yield long records of the spatial and temporal patterns of fault rupture

deflection of paleomagnetic directions due to magnetization of the underlying terrain in the summers of 1989 and 1991 we made 344 near ground level measurements of the ambient geomagnetic field above recent basalts on the island of hawaii using a three component fluxgate magnetometer we studied 12 surface features including a lava pond lava channels long tilted blocks smooth sloping surfaces two fissures and a deep u shaped road cut we observed substantial differences up to 20 between the observed and expected international geomagnetic reference field igrf magnetic field directions over these features except those composed of shelly pahoehoe and a flat horizontally thin lava pond we also observed inclinations that were systematically shallower than the igrf field by up to 5 we show that these shallower inclinations can be explained by the magnetization of the regionally sloping surface of the southern side of the island we found that all of the observed inclination deflections can be explained by simple two dimensional models which assume uniform induced and remanent magnetization parameters in the local terrain our observations imply that the inclination deflections cannot be corrected without a complete knowledge of the preexisting terrain and the remanence in the underlying flows upon which the lavas cooled since this information is rarely available it is difficult or impossible to discriminate between dispersion of paleomagnetic directions caused by the magnetic terrain effect and dispersion due to other factors such as paleosecular variation psv we therefore conclude that psv dispersion parameters cannot be accurately determined from paleomagnetic measurements on highly magnetic volcanic flows we also suggest that some of the geomagnetic excursions inferred from measurements on volcanic rocks may be at least in part due to the magnetic terrain effect it is unnecessary to invoke ad hoc mechanisms such as clastic block or crustal rotations distortion of the top crust or flow deformation to explain the large between site dispersions or inclination anomalies observed in many of the paleomagnetic data from volcanic rocks our observations also bring into question the general reliability of paleomagnetic pole positions inferred from volcanic rocks as a systematic inclination deflection due to local and regional slopes and irregular terrain such as those we observed would lead to a corresponding error in the inferred paleolatitude the magnetic terrain effects also offer alternative explanations for anomalous paleomagnetically inferred plate motions

the constitution and structure of the lunar interior the current state of understanding of the lunar interior is the sum of nearly four decades of work and a range of exploration programs spanning that same time period missions of the 1960s including the rangers surveyors and lunar orbiters as well as earth based telescopic studies laid the groundwork for the apollo program and provided a basic understanding of the surface its stratigraphy and chronology through a combination of remote sensing surface exploration and sample return the apollo missions provided a general picture of the lunar interior and spawned the concept of the lunar magma ocean in particular the discovery of anorthite clasts in the returned samples led to the view that a large portion of the moon was initially molten and that crystallization of this magma ocean gave rise to mafic cumulates that make up the mantle and plagioclase flotation cumulates that make up the crust smith et al 1970 wood et al 1970 this model is now generally accepted and is the framework that unifies our knowledge of the structure and composition of the moon the intention of this chapter is to review the major advances that have been made over the past decade regarding the constitution of the moon s interior much of this new knowledge is a direct result of data acquired from the successful clementine and lunar prospector missions as well as the analysis of new lunar meteorites as will be seen results from these studies have led to many fundamental amendments to the magma ocean model much of what we know from sample analyses has been previously summarized elsewhere and only their most important aspects will be discussed in this chapter the reader is referred to the relevant chapters in the books basaltic volcanism on the terrestrial planets basaltic volcanism study project 1981 the

an absolute palaeointensity record from soh1 lava core hawaii using the microwave technique absolute palaeointensity results were obtained from 392 samples 166 of 241 flows from the upper 779 m of the scientific observation hole 1 soh1 basalt core kilauea volcano hawaii using the microwave palaeointensity technique based on k ar dates and a previously published age model this covers the last 45 ka thus giving a high resolution record of geomagnetic intensity in hawaii comparisons with other hawaiian absolute palaeointensity data show similar trend of higher intensity than present day for the last 3 ka and then a general decrease in intensity over the last 45 ka though this study reports consistently lower palaeointensity values direct comparison with previous thellier data from the soh1 core shows some discrepancies between the two methods with the thellier data yielding generally higher palaeointensity estimates than the microwave data in view of these discrepancies between the two methods the introduction of raw palaeointensity data into the public domain is suggested

toward an optimal geomagnetic field intensity determination technique 1 paleointensity determinations based on double heating techniques in field zero field cooling zero field in field cooling and two in field steps with opposite laboratory fields are generally considered to be functionally interchangeable producing equally reliable paleointensity estimates to investigate this premise we have developed a simple mathematical model we find that both the zero field first and in field first methods have a strong angular dependence on the laboratory field parallel orthogonal and anti parallel while the two in field steps method is independent of the direction of the laboratory produced field contrary to common practice each method yields quite different outcomes if the condition of reciprocity of blocking and unblocking temperatures is not met even with marginal 10 tails of partial thermoremanence our calculations suggest that the zero field first method with the laboratory produced field anti parallel to the natural remanence nrm is the most robust paleointensity determination technique when the intensity of the lab induced field is smaller than ancient field however the zero field first method with the laboratory field parallel to the nrm is the optimum approach when the intensity of the lab induced field is larger than the ancient field by far the best approach however is to alternatethe infield zerofield iz steps with zerofield infield zi steps

cold air incursions over subtropical south america mean structure and dynamics abstract synoptic scale incursions of midlatitude air moving into subtropical south america to the east of the andes cordillera are observed to occur year round with a periodicity of about 1 2 weeks during wintertime they have a profound impact upon the low level temperature field and extreme episodes produce freezing conditions from central argentina to southern brazil and bolivia warm season episodes produce less dramatic variations of temperature but they organize deep convection in the form of synoptic scale bands of convective cloudiness along the leading edge of the cool air on the basis of 17 yr of ncep ncar reanalysis and outgoing longwave radiation fields the mean synoptic scale structure and evolution of these incursions is documented using a simple compositing technique the underlying physical mechanisms responsible for the occurrence of these incursions are also investigated by diagnosing the leading dynamic and thermodynamic forcing of their development

major earthquakes occur regularly on an isolated plate boundary fault the scarcity of long geological records of major earthquakes on different types of faults makes testing hypotheses of regular versus random or clustered earthquake recurrence behavior difficult we provide a fault proximal major earthquake record spanning 8000 years on the strike slip alpine fault in new zealand cyclic stratigraphy at hokuri creek suggests that the fault ruptured to the surface 24 times and event ages yield a 0 33 coefficient of variation in recurrence interval we associate this near regular earthquake recurrence with a geometrically simple strike slip fault with high slip rate accommodating a high proportion of plate boundary motion that works in isolation from other faults we propose that it is valid to apply time dependent earthquake recurrence models for seismic hazard estimation to similar faults worldwide

paleointensity determination from sao miguel azores archipelago over the last 3 ka elsevier editorial system tm for physics of the earth and planetary interiors manuscript draft manuscript number pepi d 14 00015 title paleointensity determination from sao miguel azores archipelago over the last 3 ka article type research paper keywords paleomagnetism paleointensity azores atlantic ocean global spike corresponding author dr anita di chiara corresponding author s institution usp first author anita di chiara order of authors anita di chiara lisa tauxe prof fabio speranza dr abstract paleointensity data from the atlantic ocean are rare we present new paleointensity data from sao miguel azores islands portugal based on 20 paleomagnetic sites from 13 lava flows emplaced over the last 3 000 years ten lava flows are radiocarbon dated moore 1990 1991 moore and rubin 1991 whereas three flows were archeomagnetically dated by di chiara et al 2012 and one site was dated using stratigraphic relations all the samples previously investigated to recover paleodirections di chiara et al 2012 were subjected to izzi experiments importantly the new data are internally consistent agree with moroccan and european datasets and offer new constraints for cals style models e g korte and constable 2011 the inferred virtual axial dipole moments vadms range from 68 2 zam2 and 163 5 zam2 a peak in field strength with an estimated age of around 600 bce is well supported by two sites from the same flow furna and is comparable to the spike of intensity found in portugal of the same age nachasova et al 2009 and at about 1000 bce in the levant ben yosef et al 2009 shaar et al 2011 a gradient in vadm values with latitude observed by mitra et al 2013 between 100 to 1000 ad is confirmed as well as its absence from between 0 to 100 ad

three dimensional kinematic and microphysical evolution of florida cumulonimbus part ii frequency distributions of vertical velocity reflectivity and differential reflectivity abstract high resolution radar data collected in florida during the convection and precipitation electrification experiment are used to elucidate the microphysical and kinematic processes occurring during the transition of a multicellular storm from convective to stratiform stages a statistical technique is employed to examine the evolving properties of the ensemble small scale variability of radar reflectivity vertical velocity and differential reflectivity over the entire storm differential radar reflectivity data indicate that the precipitation at upper levels was nearly glaciated early in the storm s lifetime dual doppler radar data show that throughout the storm s lifetime both updrafts and down drafts were present at all altitudes and that most of the volume of the radar echo contained vertical velocities incapable of supporting precipitation size particles thus the ensemble microphysical properties of the storm were increasingly dominated by particles falling in an environment of weak vertic

an improved methodology for thellier type paleointensity determination in igneous rocks and its usefulness for verifying primary thermoremanence we propose a new methodology for thellier type paleointensity experiments in standard paleointensity experiments the blocking temperatures of most stable remanences are often not reached before thermal alteration of magnetic mineralogy begins and subsequent data have to be discarded we emphasize that when alteration begins at low temperature and continues throughout the experiment which then fails in standard analyses the resulting unblocking temperature tub spectrum of the alteration product does not necessarily overlap with the whole tub spectrum of natural remanent magnetization nrm because tub depends on physical characteristics of the new grains not the temperatures at which they were formed nrm may survive in an uncontaminated higher tub window if alteration remanence only has low tub then partial thermoremanent magnetization ptrm checks at temperature step tj 1 can be used to correct for alteration that has occurred at tj and furthermore thermal demagnetization of a full trm acquired in the laboratory at the end of the progressive thellier thellier experiment should reveal the true uncontaminated tub spectrum of the nrm in higher temperature intervals we propose a new experimental sequence which allows monitoring and correction of alteration and provides two semi independent estimates of palaeointensity in the circumstances described above we illustrate the issues involved through new experimental work on igneous rocks from a paleozoic charnockitic syenite where we unravel trm from multidomain isothermal remanence despite massive alteration during laboratory heating finally we point out the value of these experiments for verifying primary trm in igneous rocks indicating properties that distinguish trm from other remanence

modeling tropical convergence based on the moist static energy budget abstract the vertically integrated moist static energy equation provides a convenient starting point for the construction of simple models of the time mean low level convergence in the tropics a vertically integrated measure of the moist static stability the gross moist stability proves to be of central importance minima in this quantity mark the positions of the tropical convergence zones we argue that the positions of these minima are determined by the time mean moisture field which is in turn closely tied to the time mean surface temperature

absolute paleointensity and magnetomineralogical changes determinations of absolute paleointensity are often hampered by magnetomineralogical changes produced within samples of lava flows during successive heatings such changes which directly affect the capacity for a sample to acquire a partial thermoremanent magnetization ptrm are reflected by negative ptrm checks a deviation between the original ptrm and a repeated measurement after heating at a higher temperature because the deviations indicated by the ptrm checks can provide a direct estimate of the effects to the ptrms we suggest that they can be used to correct ptrms the correction method we present requires additional measurements in particular ptrm checks performed after each ptrm and specific diagrams to detect acquisition of chemical remanence performing multiple successive ptrm checks can also provide information on the blocking temperatures of the alteration product these experiments conducted on lava flows from different localities show that the magnetomineralogical changes mainly involved grains with blocking temperatures lower than the last heating step the corrections have been tested on recent and historic lava flows from several localities we have also compared results on samples from the same lava flows that were heated in air and in vacuum the mean paleointensity values were found to lie within less than 10 from the expected field intensity at each site the corrections resulted in the recovery of reliable paleointensity determinations for about twice as many specimens heated in vacuum and 65 additional data for specimens heated in air successive heatings at the same temperature in air are often accompanied by a time dependent oxidation of the natural remanent magnetization which is responsible for paleointensity values lower than the expected field a problem that is not related to the corrections we conclude that corrections can be used with fairly high confidence to the ptrms performed in vacuum and in air

absolute paleointensity from hawaiian lavas younger than 35 ka abstract paleointensity studies have been conducted in air and in argon atmosphere on nine lava flows with radiocarbon ages distributed between 3 3 and 28 2 ka from the mauna loa volcano in the big island of hawaii determinations of paleointensity obtained at eight sites depict the same overall pattern as the previous results for the same period in hawaii although the overall average field intensity appears to be lower since the present results were determined at higher temperatures than in the previous studies this discrepancy raises questions regarding the selection of low versus high temperature segments that are usually made for absolute paleointensity the virtual dipole moments are similar to those displayed by the worldwide data set obtained from dated lava flows when averaged within finite time intervals the worldwide values match nicely the variations of the sint 200 synthetic record of relative paleointensity and confirm the overall decrease of the dipole field intensity during most of this period the convergence between the existing records at hawaii and the rest of the world does not favour the presence of persistent strong non dipole components beneath hawaii for this period

partial anhysteretic remanent magnetization in magnetite 1 additivity 1 we have tested the additivity of partial anhysteretic remanent magnetization parm for suites of eight synthetic magnetites with mean grain sizes from 65 nm to 18 m and 18 natural samples including lake sediments oceanic and continental volcanic rocks gabbros and granites in both synthetic and natural sample suites domain states inferred from hysteresis and other magnetic properties vary from single domain sd through pseudosingle domain psd to multidomain md for each sample total arm intensity was compared with sums of partial arms of three different types four conjugate pairs of parallel parms four pairs of perpendicular parms and one set of five neighboring parallel parms in each case the intervals of alternating field af over which a steady field h was applied to produce the partial arms are nonoverlapping and cover the entire af range 0 100 mt used to produce the total arm additivity of partial arms was verified to better than 3 for all the samples whatever the domain state sd psd and md or composition ranging from pure magnetite to x 0 6 titanomagnetite the universality of parm additivity is unexpected because its analog partial thermoremanent magnetization ptrm deviates from ideal behavior as the grain size increases and the domain structure becomes md the different behaviors probably result from the fact that parm is produced at ordinary temperatures over short times whereas the most intense ptrm is produced at temperatures approaching the curie point with significant dwell times promoting such processes as isothermal remanence acquisition domain nucleation and domain wall reequilibration verification of the law of additivity of parms is an encouraging first step toward validating pseudo thellier and other methods of paleointensity determination that use arm in place of or in addition to trm

magnetic anomalies of lava fields in the canary islands possible consequences for paleomagnetic records abstract measurements of the total magnetic field have been performed above the surface of 12 lava flows in the canary islands of la palma and tenerife directions can differ by up to 15 and intensity changes reach 20 the mean flow directions do not coincide and the mean flow virtual dipole moments vdms differ by more than 10 the deviations are linked to topographic features at the surface of the flows and should persist during emplacement of the next overlying flow such effects can thus limit the resolution of paleomagnetic records of detailed geomagnetic features and the field intensity variations above the flows and between the mean flow values could explain a significant part of the scatter inherent to many paleointensity studies historical field variations have been recorded from the same flows and are in agreement with the european curve for the same period however there is also some correlation with the present field which suggest that the underlying magnetized bodies could have affected the paleomagnetic records biases induced by the crustal field would increase considerably during periods of reduced field intensity like during reversals and induce erroneous records samplings performed over large distances within each lava flow would provide the best way to average out the contribution of the anomalies in any case such effects should not be neglected in paleomagnetic studies

geomagnetic field strength during late miocene first paleointensity results from baja california 1 thellier paleointensity experiments were carried out on 73 selected samples from the late miocene baja california volcanic flows for the first time the selected samples showed a stable remanent magnetization observed upon thermal treatment and reasonably reversible continuous susceptibility curves compatible with ti poor titanomagnetites judging from the ratios of hysteresis parameters it seems that the samples fall in the small pseudosingle domain grain size region thirty three samples from 10 individual flows yielded acceptable paleointensity estimates the natural remanent magnetization nrm fractions used for paleointensity determination range from 37 to 81 and the quality factor varies between 4 5 and 24 5 being normally 5 the mean paleointensity values per flow obtained in this study range from 18 1 3 1 to 45 6 4 3 t and the corresponding virtual dipole moments vdms range from 3 8 0 6 to 8 8 0 8 1022 a m2 these values correspond to mean value of 6 6 1 7 1022 a m2 which is 85 of the present geomagnetic axial dipole the average vdm value for late miocene according to all available selected data is 6 1 1 5 1022 a m2 which is higher than average paleofield for the period 5 160 ma 4 2 2 3 1022 a m2 after juarez and tauxe 2000 given the large dispersion and the very poor distribution of reliable absolute intensity data it is hard to draw any firm conclusions regarding the time evolution of the geomagnetic field more high quality determinations are strongly needed

linear response of a stratified tropical atmosphere to convective forcing abstract the three dimensional response of the tropical atmosphere to an isolated heat source is investigated using a primitive equation model linearized about a resting basic state on an equatorial plane the model equations are solved by applying vertical and horizontal normal mode transforms the thermal forcing was chosen to simulate the convection which occurs over tropical south america during the southern hemisphere summer the vertical dependence of the forcing is such that the heating is zero at the top and bottom boundaries with a variable level of maximum beating the model results with steady forcing are compared with the average circulation over tropical south america for a 19 day period in the southern hemisphere summer of 1979 and it is shown that the model reproduces many aspects of the observed circulation the partition of the energy of the steady state response between the vertical modes is calculated and it is shown that the internal mode with an equivalent depth of 208 m is domina

late holocene rupture history of the alpine fault in south westland new zealand abstract strata and fault relationships revealed in five trenches excavated across the recent trace of the alpine fault at the haast okuru and turnbull rivers south westland new zealand record the three most recent surface faulting events using back stripping techniques to remove the three faulting events and the sedimentary units associated with the faulting restores the cross sections to gravel bed floodplains at the haast and okuru rivers at about a d 750 horizontal and vertical offsets of stream channels and terrace risers reveal characteristic displacements of about 8 9 m dextral and up to 1 m vertical per event cumulative dextral displacement is 25 3 m in the past three events the most recent surface rupture event was probably in a d 1717 and the next prior events were about a d 1230 50 and about a d 750 50 the timing of these events is consistent with past large great earthquakes on the southern section of the alpine fault inferred from off fault data but there are fewer events identified in trenches our three event dataset indicates the average surface rupture recurrence interval for the south westland section of the fault is about 480 years much longer than the current elapsed time of 295 years therefore the alpine fault in south westland may not be close to rupture as is often speculated

the shaw paleointensity method can the arm simulate the trm alteration abstract the effectiveness of the arm correction in shaw s paleointensity method was investigated for four kinds of volcanic samples with different remanence characteristics from single domain to multidomain samples were heated in air and vacuum for successively longer times of 10 20 50 100 200 and 500 min and changes in the af demagnetization curves of the arm and trm were observed drastic changes of the arm and trm were observed in three cases from two samples in which changes of the remanence magnitude were coherent between the arm and trm for a wide range of the af demagnetization however the coherent change of the arm and trm due to alteration was not completely proportional giving a moderate to large error in the arm correction this suggests that the double heating methodology should be practiced for the shaw method to ascertain the effectiveness of the arm correction in two cases of andesite lava with a multidomain nature the arm corrected shaw plots with marginally linear data points were obtained from a heavily altered sample indicating the insensibility of the coercivity spectra to changes in the blocking temperature this fact suggests that strict linearity of the nrm to the corrected trm should be posed in the analysis of shaw plots

on the dynamics of droughts in northeast brazil observations theory and numerical experiments with a general circulation model abstract it is proposed that a possible mechanism for the occurrence of severe droughts over northeast brazil is the establishment of a thermally direct local circulation which has its ascending branch at about 10 n and its descending branch over northeast brazil and the adjoining oceanic region the driving for this anomalous circulation is provided by warming due to enhanced moist convection associated with warmer sea surface temperature anomalies over the northern tropical atlantic and cooling associated with colder sea surface temperature anomalies in the southern tropical atlantic the combined effects of thermally forced subsidence and reduced evaporation and moisture flux convergence produces severe drought conditions over northeast brazil we have examined the monthly mean sea surface temperature anomalies over the tropical atlantic and rainfall anomalies over two selected stations fortaleza 3 46 s 38 31 w and quixeramobim 5 12 s 39 18 w for 25 years 1948 72 it is found that the most sever

paleoseismology of the 2010 mw 7 1 darfield canterbury earthquake source greendale fault new zealand abstract the previously unknown greendale fault ruptured in the september 2010 moment magnitude mw 7 1 darfield earthquake surface rupture fracture patterns and displacements along the fault were measured with high precision using real time kinematic rtk gps tape and compass airborne light detection and ranging lidar and aerial photos no geomorphic evidence of a penultimate surface rupture was revealed from pre 2010 imagery the fault zone is up to 300 m wide and comprises both distributed folding and discrete faulting deformation dominated by right lateral displacement surface fracturing accommodates 30 of the total right lateral displacement in the central fault zone the remainder is accommodated by distributed deformation ground penetrating radar and trenching investigations conducted across the central greendale fault reveal that most surface fractures are undetectable at depths exceeding 1 m however large discrete riedel shears continue to depths exceeding 3 m and displace interbedded gravels and sand filled paleochannels at one trench site a riedel shear displaces surface agricultural markers e g fences and plow lines and a subsurface 0 6 m deep paleo channel by 60 cm right laterally and 10 cm vertically indicating the paleochannel has been displaced only in the darfield earthquake optically stimulated luminescence osl dating of the displaced paleochannel yields an age of 21 6 1 5 ka two additional paleochannels at 2 5 m depth with osl ages of 28 4 2 4 ka and 33 2 ka have been displaced 120 cm right laterally and 20 cm vertically the doubling of displacement at depth is interpreted to indicate that in the central section of the greendale fault the penultimate surface rupturing event occurred between ca 20 and 30 ka the greendale fault remained undetected prior to the darfield earthquake because the penultimate fault scarp was eroded and buried during late pleistocene alluvial activity similar active faults with low slip rates i e lower than sedimentation erosion rates are likely to be concealed in alluvial settings globally

paleointensity estimates from historic and modern hawaiian lava flows using glassy basalt as a primary source material abstract published paleointensity estimates derived from lavas extruded in known fields are highly variable and rarely recover the expected field strength within an accuracy of better than 10 inconsistent results on modern volcanic rocks lend even greater uncertainty to intensity experiments performed on lava flows emplaced during periods of unknown geomagnetic field strength the majority of published paleointensity data are collected from the slowly cooled massive centers of lava flows where the magnetic grains are more likely to be multi domain and produce non ideal experimental results glassy volcanic material found on subaerial lava flow tops and in sub aqueous and subglacial environments however is rapidly cooled and therefore most likely of all volcanic materials to behave as single domain particles demanded by neel theory we present a new paleointensity study of historic and modern hawaiian lavas and test the viability of subaerially emplaced glassy basaltic material as an accurate recorder of magnetic field intensity six of eight lava flows sampled on the big island of hawaii 1843 1859 1935 1950 1960 1990 c e produce well behaved arai plots and recover an average intensity to within 2 7 t of the expected field strength or better than 8 accuracy we apply very strict selection criteria including a minimum of three specimens per site to prevent extraneous field estimates from affecting the final results individual volcanic glass results from the 1960 c e lava flow have a much lower variance than published data from the same volcanic unit glassy materials should therefore be collected wherever possible as they allow recovery of geomagnetic field strength with unprecedented accuracy

experimental reassessment of the shaw paleointensity method using laboratory induced thermal remanent magnetization 1 artificial thermoremanent magnetization imposed on natural basalt samples was used to check the reliability of shaw s palaeointensity method shaw 1974 kono 1978 rolph and shaw 1985 and to give an indication of the accuracy of paleointensity determinations first thermal remanence was induced in all samples 50 in total in a known field 50 0 1 t this remanence was regarded as the original natural remanent magnetization nrm the samples were divided in to three subsets a b and c and intensity experiments were performed each subset of samples used different thermal remanent magnetization trm acquisition parameters rock magnetic properties on 14 representative subsamples were also measured both before and after the trm acquisition steps to monitor possible magnetochemical alteration it has been demonstrated that intensity estimates by the shaw method give values close to the expected value 50 5 t in all three sets of basalt samples the modified method with rolph and shaw 1985 correction i e using ratios of anhysteretic remanent magnetization given before the trm step arm1 and after arm2 is proved to be a powerful approach to correct the trm capacity changes that result from magnetochemical alteration this is especially so for sample set c where the samples were heated up to 700 c and then were held at this temperature for 40 min during trm acquisition after correction 45 of set c samples gave acceptable results however some samples with strong magnetochemical alteration sometimes invalidated the arm1 arm2 ratio correction and gave wrong intensity estimates monitoring rock magnetic properties is therefore very important when applying the shaw method

inter profile correlation of the chinese loess paleosol sequences during marine oxygen isotope stage 5 and indications of pedogenesis abstract low field magnetic susceptibility has been widely used to determine the pedostratigraphy of the chinese loess paleosol sequences however uncertainties remain in correlating between the loess magnetic susceptibility and the marine oxygen isotope records because susceptibility variations are affected by both global and local paleoclimatic changes to provide a more sound paleoclimatic interpretation of magnetic susceptibility variations age models across marine oxygen isotope stage mis 5 for the jiuzhoutai jzt and yuanbao yb sections western chinese loess plateau were constructed through an integrated approach by linking the major pedostratigraphic boundaries of the loess profiles to the specmap oxygen isotope curve and by correlating relative magnetic paleointensity records with both the sint800 global paleointensity stack from marine sediments and 36cl records from the grip ice core results indicate good correlation of sirm60 mt a residual remanence of saturation isothermal remanent magnetization after a 60 mt alternating field demagnetization variations between these two sites which agree well with fluctuations in subtropical atlantic sea surface temperatures all cooling events recorded by ice core and atlantic marine sediments within mis5 have counterparts in sirm60 mt sirm60 mt is partially controlled by the degree of low temperature oxidation which is strongly temperature dependent however strong pedogenesis can decrease sirm60 mt due to further oxidation of partially oxidized magnetites above some critical points therefore we propose that sirm60 mt is best suited to record paleotemperature changes in loess profiles from the western chinese loess plateau where pedogenesis is the weakest furthermore by inter profile correlation between the yb and jzt sections we note that the seemingly uniform sub paleosol unit with a broad susceptibility peak previously assigned to mis5c between 34 4 and 37 4 m in the yb profile actually consists of two independent units lower part of s1l1 mis5b and s1s2 mis5c this indicates that susceptibility values can be strongly affected by local factors e g mainly precipitation therefore beside the simplistic traditional paleoclimatic interpretation of variations in loess susceptibility involving only cold dry and warm humid scenarios cold humid and warm dry scenarios should also be considered

simulations of the summer circulation over the south american region with an eta coordinate model abstract a multilevel limited area primitive equations model in eta coordinate is used to simulate the effects of the amazonian latent heat source and the andean topography on the summer december january february circulation over the south american region the observed circulation features such as the bolivian high and the trough near the coast of northeast brazil in the upper troposphere the elongated south atlantic convergence zone sacz oriented northwest to southeast from the southern amazon region into the atlantic ocean and the subtropical anticyclones in the south pacific and south atlantic oceans in the lower levels are well simulated although heating alone produces the sacz the mountain and the basic flow put it in the observed position it is found that regular daily pulses of heating are necessary for the maintenance of the sacz the position and intensity of the sacz change rather substantially from the no mountain case to the mountain case thus showing the importance of the effect

isolating the role of surface evapotranspiration on moist convection along the eastern flanks of the tropical andes using a quasi idealized approach abstractthe contribution of surface evapotranspiration et to moist convection cloudiness and precipitation along the eastern flanks of the tropical andes eads was investigated using the weather research and forecasting wrf model with nested simulations of selected weather conditions down to 1 2 km grid spacing to isolate the role of surface et numerical experiments were conducted using a quasi idealized approach whereby at every time step the surface sensible heat effects are exactly the same as in the reference simulations whereas the surface latent heat fluxes are prevented from entering the atmosphere energy balance analysis indicates that surface et influences moist convection primarily through its impact on conditional instability because it acts as an important source of moist entropy in this region the energy available for convection decreases by up to approximately 60 when the et contribution is withdrawn in contrast when convective motion is not thermally driven or under condit

relationship between amazon and high andes rainfall 1 a regional climate model is used to study the connections between amazon and high andes rainfall the modeling effort focuses on understanding the rainfall response during the last glacial maximum lgm 21 000 years ago as paleoproxy evidence generally suggests that the high andes were wet during this period while conditions over the amazon were drier although there is more uncertainty about the latter analysis of the yearlong present day and full lgm integrations reveals that the delayed onset of amazon convection in the lgm during austral spring is associated with an enhancement of rainfall over the high andes in the absence of convection over the amazon in the austral spring zonal geopotential height gradients over the amazon strengthen resulting in anomalous easterly flow between the amazon and the high andes instead of the low level flow paralleling the andes e g northwesterly the flow impinges more directly onto the eastern slopes of the andes during the lgm where it rises and transports moisture from the amazon up into the mountains enhancing convection over the andes this circulation mechanism explains how the moisture and rainfall over the high andes of peru and bolivia can increase such as the case for the lgm despite large scale drying over south america present day observations are then explored for 1984 2002 and 2003 to identify whether mechanisms identified in the paleoclimate modeling are observable in the present day climate comparison of these particular springs reveals a response analogous to the lgm model response suggesting that this mechanism that connects tropical atlantic sea surface temperatures amazon convection and high andes rainfall is operating in the present climate

testing determinations of absolute paleointensity from the 1955 and 1960 hawaiian flows abstract a new exhaustive study of the flows erupted in 1955 and 1960 from the kilauea volcano big island of hawaii has been conducted in order to constrain the dispersion inherent to the data of absolute paleointensity reported so far and ultimately to determine what are the most critical parameters to obtain suitable determinations the mean directions derived from both flows agree with the expected field within less than 2 paleointensity experiments have been performed using a double heating thellier procedure completed by systematic ptrm checks almost all samples display a linear nrm trm straight line but only 20 of the samples have provided suitable results less than 10 away from the expected field in the other cases the deviation from the expected paleointensity is related to the quality of the ptrm checks which thus provides a threshold value for acceptance of ptrm checks all successful determinations less than 10 away from the expected value have a maximum drat selkin and tauxe 2000 that never exceeds 5 while the mean value of all deviations is lower than 3 5 another interesting feature is the existence of a link between the unblocking temperature spectra and the accuracy of the paleofield which points out the origin of difficulties in the presence of a wide distribution of grain sizes and or the existence of several magnetic phases the results also indicate that magnetite with a narrow range of high unblocking temperatures and little variability in grain size is a favorable situation to obtain suitable determinations with a high success rate these observations may well explain the dispersion inherent to the previous studies of the hawaiian flows

recurrent liquefaction in christchurch new zealand during the canterbury earthquake sequence continuous observational monitoring of a study site in eastern christchurch new zealand following the 2010 m w 7 1 darfi eld earthquake has recorded ten distinct liquefaction episodes in the mainshock aftershock sequence three nearby accelerometers allow calibration between the geological expressions of liquefaction and the intensity of earthquake induced surface ground motion at the site sand blow formation was generated by m w 5 2 7 1 earthquakes with m w 7 5 normalized peak ground accelerations pga 7 5 of 0 057 g acceleration due to gravity silt drapes between successive sand blow deposits provide markers for delineating distinct liquefaction inducing earthquakes in the geologic record however erosion quickly modifi es the surface of sand blows into alluvial and aeolian forms that complicate geologic diagnosis the two feeder dike generations identifi ed in subsurface investigations signifi cantly underrepresent the number of liquefaction inducing earthquakes due to extensive dike reactivation new constitutive equations enable pga 7 5 variations to be estimated from the thickness and areal extent of sand blows

timing of late holocene paleoearthquakes on the hurunui segment of the hope fault implications for plate boundary strain release through south island new zealand the hurunui segment of the dextral slip hope fault extends for 42 km between the hope and hurunui river catchments and westward to harper pass at the main divide of south island we conducted paleoseismic soil and landscape dating studies in the upper hurunui valley to determine the timing of past earthquake ruptures along this geometric fault segment on a late holocene alluvial surface at matagouri flat a young channel system is displaced dextrally by 4 5 0 6 m which is attributed to the most recent faulting event a trench and soil pits excavated nearby yield evidence for the timing of the last two surface faulting events these events dated from a combination of radiocarbon dates relative soil tree and historical constraints modified within an oxcal analysis occurred at ca a d 1655 1835 and 1425 1625 the occurrence of two rupture events during the last 600 yr is consistent with previous estimates stating a short recurrence interval for the hurunui segment the most recent faulting event in our trenches predates the historic 1888 north canterbury amuri earthquake which ruptured the hope river segment to the east a comparison of the record from the hurunui segment with paleoseismic records from other segments along the hope fault zone indicates evidence for two or three rupture events within the last 700 900 yr within the age resolution of the current dates the data suggest that along strike rupture occurred along the majority of the hope fault zone between 120 and 360 yr ago i e a d 1650 1888 and may all postdate the most recent rupture of the alpine fault in ca a d 1717 in addition the timings of penultimate faulting events along the hurunui hope river and conway segments and the hanmer fault all fall in the range 400 700 yr ago these preliminary observations indicate that rupture of segments of the hope fault and indeed the alpine fault could occur as clusters that are years to decades apart rupture of the major plate boundary faults in the northern south island may therefore occur in sequences that are enhanced or even retarded by stress triggering and fault interactions

strong proximal earthquakes revealed by cosmogenic 3he dating of prehistoric rockfalls christchurch new zealand the 2011 rupture of previously undetected blind faults beneath christchurch new zealand in moment magnitude m w 6 2 and 6 0 earthquakes triggered major rockfalls that caused fatalities and infrastructure damage here we use field geospatial seismologic numerical modeling and cosmogenic 3 he data to provide first evidence for prehistoric rockfall ca 8 6 ka and a possible preceding event ca 14 13 ka at a site where extensive rockfall occurred in the christchurch earthquakes the long 7 1 k y time intervals between successive rockfall events and the high peak ground velocity thresholds required for rockfall initiation at this site 20 30 cm s preclude earthquakes from major identified seismic sources including the plate boundary alpine fault as likely rockfall triggering sources rockfalls were probably triggered by strong paleoearthquakes sourced from active faults proximal i e 10 20 km to christchurch including the sources of the 2011 christchurch earthquakes and or other currently unidentified faults given the inherent incompleteness of seismic source catalogues and challenges in obtaining earthquake chronologies for blind faults high scientific priority should be given to the search for and analysis of geologic records of strong earthquake shaking near populated areas

liquefaction features produced by the 2010 2011 canterbury earthquake sequence in southwest christchurch new zealand and preliminary assessment of paleoliquefaction features liquefaction features and the geologic environment in which they formed were carefully studied at two sites near lincoln in southwest christchurch we undertook geomorphic mapping excavated trenches and obtained hand cores in areas with surficial evidence for liquefaction and areas where no surficial evidence for liquefaction was present at two sites hardwick and marchand the liquefaction features identified include 1 sand blows singular and aligned along linear fissures 2 blisters or injections of subhorizontal dikes into the topsoil 3 dikes related to the blows and blisters and 4 a collapse structure the spatial distribution of these surface liquefaction features correlates strongly with the ridges of scroll bars in meander settings in addition we discovered paleoliquefaction features including several dikes and a sand blow in excavations at the sites of modern liquefaction the paleoliquefaction event at the hardwick site is dated at a d 908 1336 and the one at the marchand site is dated at a d 1017 1840 95 confidence intervals of probability density functions obtained by bayesian analysis if both events are the same given proximity of the sites the time of the event is a d 1019 1337 if they are not the one at the marchand site could have been much younger taking into account a preliminary liquefaction triggering threshold of equivalent peak ground acceleration for an m w 7 5 event pga7 5 of 0 07 g existing magnitude bounded relations for paleoliquefaction and the timing of the paleoearthquakes and the potential pga7 5 estimated for regional faults we propose that the porters pass fault alpine fault or the subduction zone faults are the most likely sources that could have triggered liquefaction at the study sites there are other nearby regional faults that may have been the source but there is no paleoseismic data with which to make the temporal link online material figures showing areas of liquefaction trench logs information on dike and sand blow parameters dike azimuths core logs radiocarbon samples and oxcal analysis and tables detailing units exposed in the trenches and stereonets

high resolution simulation of tropical storm ivan 2004 in the southern appalachians role of planetary boundary layer schemes and cumulus parametrization the weather research and forecasting wrf model was used to simulate the evolution of tropical storm ivan 2004 in the southeast united states using both the yonsei university ysu and mellor yamada janjic myj boundary layer parametrizations in contrast to tropical cyclone tc simulations over the ocean the effect of the surface layer becomes secondary for a dissipating hurricane along its terrestrial track although these two schemes can reproduce ivan reasonably well our results suggest that the mixing properties for damped mechanical turbulent conditions weakly stable are strongly underestimated by both parametrizations this underestimation impacts the thermodynamic properties of the storm leading to significant differences in the storm areal extent and the simulated precipitation fields suggestions for further improvements are provided an evaluation of the impact of using or not using a convective parametrization specifically the kain fritsch kf scheme at 3 km grid spacing shows marginal impact on storm coverage intensity and precipitation except for the presence of widespread light rainfall in the piedmont east of the mountains when the kf is employed analysis of the thermal structure of the simulated storm indicates that in the inner storm region the kf is either not activated or primarily produces parametrized shallow convection as a result the net heating tendency associated with adiabatic and diabatic processes is almost unaltered inside the storm together with a nearly equivalent surface momentum sink leading to similar storm areal extent and intensity light rainfall to the east of the mountains can be due to the trigger mechanism of kf which depends on boundary layer convergence forcing parametrized deep convection near the coast where surface roughness changes enhance convergence

the parametrization of surface fluxes in large scale models under free convection this paper investigates the idea of formulating free convection in large scale models as a special case of forced convection in free convection the wind speed in the surface transfer law is related to the velocity of the large eddies in the mixed layer and is proportional to the convection velocity scale the empirical coefficient is estimated with the help of large eddy simulation data by sykes et al 1993 and the resulting formulation is compared with field data by stull 1994 this concept is shown to be applicable to smooth ocean surfaces as well as rough land surfaces it is argued that within this framework free convection is a natural extension of forced convection and only needs a minor modification of traditional transfer laws

the earthquake potential of the new madrid seismic zone the fault system responsible for new madrid seismicity has generated temporally clustered very large earthquakes in a d 900 100 years and a d 1450 150 years as well as in 1811 1812 given the uncertainties in dating liquefaction features the time between the past three new madrid events may be as short as 200 years and as long as 800 years with an average of 500 years this advance in understanding the late holocene history of the new madrid seismic zone and thus the contemporary tectonic behavior of the associated fault system was made through studies of hundreds of earthquake induced liquefaction features at more than 250 sites across the new madrid region we have found evidence that prehistoric sand blows like those that formed during the 1811 1812 earthquakes are probably com pound structures resulting from multiple earthquakes closely clustered in time or earthquake sequences from the spatial distribution and size of sand blows and their sedimentary units we infer the source zones and estimate the magnitudes of earth quakes within each sequence and thereby characterize the detailed behavior of the fault system it appears that fault rupture was complex and that the central branch of the seismic zone produced very large earthquakes during the a d 900 and a d 1450 events as well as in 1811 1812 on the basis of a minimum recurrence rate of 200 years we are now entering the period during which the next 1811 1812 type event could occur

geomagnetic palaeointensities during the cretaceous normal superchron measured using submarine basaltic glass high quality palaeointensity data have been obtained from thellier thellier experiments on recent and cretaceous submarine basaltic glasses whereas the recent samples faithfully yield today s geomagnetic intensity at the site the palaeointensities for the beginning and end of the cretaceous normal superchron are only 45 and 25 respectively of today s value the data thus extend the mesozoic dipole low into the cretaceous superchron and confirm that submarine basaltic glass is an excellent material for palaeointensity studies

a new zealand specific pseudospectral acceleration ground motion prediction equation for active shallow crustal earthquakes based on foreign models abstract the applicability of foreign ground motion prediction equations gmpes for predicting geometric mean pseudospectral acceleration amplitudes from active shallow crustal earthquakes in new zealand nz is examined four different foreign gmpes were considered as well as the nz based mcverry et al 2006 mcv06 model it was found that the mcv06 model exhibited the lowest applicability with a database of 2437 recorded ground motions and that the chiou et al 2010 c10 modification of the chiou and youngs 2008b cy08 model was the most applicable discrepancies between the c10 model and the nz database which were empirically identified and theoretically justified were used to modify the c10 model for 1 small magnitude scaling 2 scaling of short period ground motion from normal faulting events in volcanic crust 3 scaling of ground motions on very hard rock sites 4 anelastic attenuation in the nz crust and 5 consideration of the increased anelastic attenuation in the taupo volcanic zone the developed nz specific model therefore contains features as evident from recorded ground motions in nz and consistent scaling for parameters not well constrained by nz data comparisons with ground motions from the 4 september 2010 darfield and 22 february 2011 christchurch earthquakes which occurred following completion of the nz specific model illustrate that it provides an empirical prediction with sufficient accuracy and precision

paleomagnetic and paleointensity study of oligocene volcanic rocks from chihuahua northern mexico abstract a detailed rock magnetic paleomagnetic and paleointensity study was carried out on oligocene volcanic formations from chihuahua northern mexico in order to obtain some decisive constraints for the tectonic evolution of the southern cordilleran orogenic belt of north america and for the geomagnetic field strength during oligocene time age of the volcanic units lies between 33 and 25 ma according to available radiometric data rock magnetic experiments reveal that remanence is carried in most cases by ti poor titanomagnetite resulting of oxy exsolution of original titanomagnetite during the initial flow cooling unblocking temperature spectra and relatively high coercivities point to small pseudo single domain magnetic grains for these titano magnetites single component linear demagnetization plots were observed in most cases nine sites yield reverse polarity magnetization three are normally magnetized and one unit shows intermediate polarity magnetization an evidence of strong lightning produced magnetization overprint was detected for one site combining all paleomagnetic data currently available for northern mexico we obtained a well defined eocene oligocene mean paleomagnetic direction with i 48 5 d 337 1 k 20 95 6 8 n 24 which deviates counterclockwise from the expected direction estimated from the north american apparent polar wander path this suggests a vertical axis tectonic counterclockwise rotation of about 16 relative to stable north america transition from laramide compression to basin and range extension occurred during oligocene around 32 30 ma tectonic rotation may then reflect east northeast extension in the mid to late cenozoic twenty three samples were pre selected for thellier palaeointensity experiments because of their low viscosity index stable remanent magnetization and reasonably reversible continuous thermomagnetic curves only 12 samples coming from three individual basaltic lava flows yielded reliable paleointensity estimates with the flow mean virtual dipole moments vdm ranging from 3 96 to 4 65 1022 am2 combination of mexican data with the available comparable quality oligocene paleointensity results yield a mean vdm of 4 1022 am2 which is comparable or slightly higher than the mean vdms calculated for the mesozoic low field period but significantly lower than present day value this low intensity may correlate with the relatively high paleosecular variation rate invoked around 30 ma by several authors

impact of amazonian evapotranspiration on moisture transport and convection along the eastern flanks of the tropical andes the weather research and forecasting wrf model was used to investigate the impact of amazonian evapotranspiration et on moisture transport and convection along the eastern flanks of the andes eads to isolate the role of surface et quasi idealized simulations down to 1 2 km grid spacing were conducted where over the amazon lowlands amzl and at every time step the surface sensible heat effects are identical to the realistic reference runs while surface latent heat fluxes are prevented from entering the atmosphere the results show that without surface et daily precipitation within the amzl decreases by as much as 75 but nearly doubles over the surrounding mountainous regions this dramatic influence is attributed to a dipole structure of convergence divergence anomalies over the amzl primarily due to the considerable cooling of the troposphere associated with suppressed convection further examination of moist static energy evolution indicates that the net decrease in convective available potential energy over the amzl is due to the removal of surface et that is only partially compensated by related regional circulation changes because of the concave shape of the andean mountain range enhanced low level divergence promotes air mass accumulation to the east of the central eads this perturbation becomes sufficiently strong around nightfall and produces significant eastward low level pressure gradient force rendering stronger winds away from the andes moisture convergence and convection over the eads vary accordingly strengthened in the day but attenuated at night nocturnal convective motion is however more widespread analytical solutions of simplified diagnostic equations of convective fraction suggest that reduction of lower troposphere evaporation is the driving mechanism additional exploratory experiments with varied surface et magnitude demonstrate that the connection between the amzl et and eads precipitation is robust

on the origin of the bolivian high and related circulation features of the south american climate abstract the climatological structure in the upper tropospheric summertime circulation over south america is diagnosed using a gcm with and without south american topography a linear model and observational data emphasis is placed on understanding the origin of observed features such as the bolivian high and the accompanying nordeste low to the east results from the linear model indicate that these two features are generated in response to precipitation over the amazon basin central andes and south atlantic convergence zone with african precipitation also playing a crucial role in the formation of the nordeste low the direct mechanical and sensible heating effects of the andes are minimal acting only to induce a weak lee trough in midlatitudes and a shallow monsoonal circulation over the central andes in the gcm the effects of the andes include a strengthening of the bolivian high and northward shift of the nordeste low primarily through changes in the precipitation field the position of

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

paleoliquefaction in christchurch new zealand liquefaction during the 2010 moment magnitude mw 7 1 darfield earthquake and large aftershocks known as the canterbury earthquake sequence caused severe damage to land and infrastructure in christchurch new zealand liquefaction occurred at mw weighted peak ground accelerations pga7 5 as low as 0 06 g at highly susceptible sites trenching investigations conducted at two sites in eastern christchurch enabled documentation of the geologic expressions of recurrent liquefaction and determination of whether evidence of pre canterbury earthquake sequence liquefaction is present excavation to water table depths 1 2 m below surface across sand blow vents and fissures revealed multiple generations of canterbury earthquake sequence liquefaction feeder dikes that crosscut holocene to recent fluvial and anthropogenic stratigraphy canterbury earthquake sequence dikes crosscut and intrude oxidized and weathered dikes and sills at both sites that are interpreted as evidence of pre canterbury earthquake sequence liquefaction crosscutting relationships combined with 14c dating constrain the timing of the pre canterbury earthquake sequence liquefaction to post a d 1660 to pre ca a d 1905 at one site and post a d 1415 to pre ca a d 1910 at another site the pga7 5 of five well documented historical earthquakes that caused regional damage between 1869 and 1922 are approximated for the study sites using a new zealand specific ground motion prediction equation only the june 1869 mw 4 8 christchurch earthquake produces a median modeled pga7 5 that exceeds the pga7 5 0 06 g threshold for liquefaction prehistoric earthquakes sourced from regional faults including the 1717 alpine fault mw 7 9 0 3 and ca 500 600 yr b p mw 7 1 porters pass fault earthquakes provide additional potential paleoseismic sources for pre canterbury earthquake sequence liquefaction the recognition of pre canterbury earthquake sequence liquefaction in late holocene sediments is consistent with hazard model based predicted return times of pgas exceeding the liquefaction triggering threshold in christchurch residential development in eastern christchurch from ca 1860 to 2005 occurred in areas where geologic evidence for pre canterbury earthquake sequence liquefaction was present highlighting the potential of paleoliquefaction studies to predict locations of future liquefaction and to contribute to seismic hazard assessments and land use planning

balancing the plate motion budget in the south island new zealand using gps geological and seismological data summary the landmass of new zealand exists as a consequence of transpressional collision between the australian and pacific plates providing an excellent opportunity to quantify the kinematics of deformation at this type of tectonic boundary we interpret gps geological and seismological data describing the active deformation in the south island new zealand by using an elastic rotating block approach that automatically balances the pacific australia relative plate motion budget the data in new zealand are fit to within uncertainty when inverted simultaneously for angular velocities of rotating tectonic blocks and the degree of coupling on faults bounding the blocks we find that most of the plate motion budget has been accounted for in previous geological studies although we suggest that the porter s pass amberley fault zone in north canterbury and a zone of faults in the foothills of the southern alps may have slip rates about twice that of the geological estimates up to 5 mm yr 1 of active deformation on faults distributed within the southern alps 100 km to the east of the alpine fault is possible the role of tectonic block rotations in partitioning plate boundary deformation is less pronounced in the south island compared to the north island vertical axis rotation rates of tectonic blocks in the south island are similar to that of the pacific plate suggesting that edge forces dominate the block kinematics there the southward migrating chatham rise exerts a major influence on the evolution of the new zealand plate boundary we discuss a model for the development of the marlborough fault system and hikurangi subduction zone in the context of this migration

paleointensity across the reunion event in ethiopia abstract paleointensity experiments have been conducted on a volcanic series of 33 flows which recorded the geomagnetic reunion event successive determinations of absolute paleointensity from 20 flows indicate that the reunion event would actually be characterized by two successive periods of low field intensity with a total duration not in excess of 30 kyr the first period has a mean paleointensity of 12 t and shows significant deviations from initial reverse polarity but no signs of fully normal polarity it is followed by field recovery then a decrease prior to the second directional episode the second period has a mean paleointensity of 17 t and is associated with full normal directions and thus likely a dominantly dipolar configuration these results are compatible with a simple earthlike magnetic field model with a large decrease in dipole field strength which yields local emergence of relatively stronger non dipole components field characteristics from this configuration would be different at different locations and could explain the variability of the paleomagnetic records collected around the world we propose that the absence of field recovery following the event is responsible for not leading to a durable polarity interval

isolating climatic and paleomagnetic imbricated signals in two marine cores using principal component analysis high resolution measurements of climatic and magnetic parameters have been performed on two cores from the eastern china sea and the western caroline basin on both cores magnetic parameters show a strong imprint of climatic changes but the absence of relationship between the inclination and the bulk density indicates that the directional changes do not depend on lithology a weak 100 ka cycle is present in the china sea inclination variations but this period is not in phase with the orbital eccentricity and thus not relevant all normalization parameters yielded similar estimates of relative paleointensity rpi but we have noticed the persistence of climatic components in the signal principal component analysis pca applied to different parameters related to climate lithology and paleointensity has allowed to extract a clean magnetic signal that we refer as principal component of paleointensity pcp which is in better agreement with the sint 2000 composite curve and provides a reliable record of relative paleointensity the presence of climatic frequencies in rpis most likely reflects the influence of lithology on the response of magnetization to field intensity we suggest that pca analysis can be very useful to approach these problems not only can the calculation separate overlapping climatic and magnetic signals but it indicates what confidence should be given to the data incidentally the present results emphasize the importance of carrying out detailed paleoclimatic analyses along with paleointensity studies

national seismic hazard model for new zealand 2010 update a team of earthquake geologists seismologists and engineering seis mologists has collectively produced an update of the national probabilistic seismic hazard psh model for new zealand national seismic hazard model or nshm the new nshm supersedes the earlier nshm published in 2002 and used as the hazard basis for the new zealand loadings standard and numerous other end user applica tions the new nshm incorporates a fault source model that has been updated with over 200 new onshore and offshore fault sources and utilizes new new zealand based and international scaling relationships for the parameterization of the faults the dis tributed seismicity model has also been updated to include post 1997 seismicity data a new seismicity regionalization and improved methodology for calculation of the seismicity parameters probabilistic seismic hazard maps produced from the new nshm show a similar pattern of hazard to the earlier model at the national scale but there are some significant reductions and increases in hazard at the regional scale the national scale differences between the new and earlier nshm appear less than those seen between much earlier national models indicating that some degree of consis tency has been achieved in the national scale pattern of hazard estimates at least for return periods of 475 years and greater online material table of fault source parameters for the 2010 national seismic hazard model

multiscale analysis of the summertime precipitation over the central andes precipitation over the central andes in south america exhibits a marked annual march with most of the rainfall concentrated during the austral summer season december february when the atmospheric circulation favors the uplifting of moist air from the lowlands to the east of the mountain range within its rainy season the central andes experiences week long rainy and dry episodes the large scale and local conditions during these episodes are investigated using satellite imagery reanalyzed atmospheric fields and in situ data despite the deep layer of conditional instability prevalent during most summertime afternoons deep convection can occur only on those days in which the mixing ratio within the local boundary layer exceeds some threshold 7gk g 21 yielding saturation of near surface air parcels rising more than 600 m above ground convective cloudiness anomalies over the central andes extend southeastward and tend to be concurrent with anomalies of opposite sign over the eastern part of the continent rainy dry episodes are also associated with anticyclonic cyclonic anomalies centered over subtropical south america that extend through the depth of the troposphere accompanied by easterly westerly wind anomalies over the central andes these anomalies are presumably forced by planetary waves originating in the southern hemisphere extratropics to gain insight into the regional processes linking the large scale and local conditions the pennsylvania state university national center for atmospheric research mesoscale model version 5 2 was used to simulate contrasting rainy and dry episodes the most marked and relevant differences are the strength and extent of diurnally varying flow over the eastern slope of the andes during the rainy simulation strong easterly winds reach the upper part of the slope by midmorning initiating an intrusion of warm and moist air high ue air originating in the eastern lowlands into the central andes in the dry case the moisture transport from the east is restricted to the eastern slope of the andes and the central andes is flooded by low ue air from the western foothills that cannot support deep convection even in the presence of localized updrafts the momentum balance based on the model output indicates that turbulent momentum mixing from aloft determined by the large scale anomalies of the upper level flow into the convective boundary layer is the leading term causing the differences in the daytime upslope flow and hence moisture transport over the upper part of the eastern side of the andes between rainy and dry simulations

palaeointensity study of the hawaiian 1960 lava implications for possible causes of erroneously high intensities summary it is known that the hawaiian 1960 lava sometimes yields higher palaeointensities than the igrf 36 2 t in order to clarify the causes we have performed a comprehensive investigation of palaeointensity measurements on 19 cores from the lava according to various rock magnetic analyses they are classified into three groups with degrees of the deuteric oxidation in coe s version of the thellier method a significantly larger mean palaeointensity of 49 0 9 6 t n 17 was observed similar to previous studies these palaeointensities showed a dependence on the oxidation indices which can be explained by thermochemical remanent magnetization tcrm acquisition during the natural cooling stage of the lava although it is generally difficult to distinguish the tcrm from thermoremanent magnetization trm a lowtemperature demagnetization ltd treatment on nrm and trm in the thellier experiment seems to allow us to detect the influence of the tcrm on nrm another possible tool for tcrm detection is the double heating technique dht of the shaw method combined with ltd ltd dht shaw method it gave a better average of 39 4 7 9 t n 9 though the success rate was much lower most of the inappropriate results were screened by a combination of the double heating test the arm correction and the ltd treatment if two outliers are further excluded the average is improved to be 35 7 3 3 t n 7 which agrees well with the expected intensity the results of both methods emphasize the importance of taking and measuring samples from the parts of various oxidation degrees in a lava flow

precipitation over concave terrain abstract many topographic barriers are comprised of a series of concave or convex ridges that modulate the intensity and distribution of precipitation over mountainous areas in this model based idealized study stratiform precipitation associated with stratified moist airflow past idealized concave ridges is investigated with a focus on windward blocking flow confluence and the associated precipitation enhancement it is found that flow confluence and precipitation enhancement by a concave ridge are controlled by the nondimensional ridge height m m nmhm u where nm is the moist buoyancy frequency hm is the maximum ridge height and u is the wind speed based on which three dynamical regimes can be defined in the linear regime m 0 4 a flow confluence zone is present over the upwind slope of the ridge vertex where precipitation is significantly enhanced the precipitation enhancement is due to the additional updraft driven by the horizontal flow convergence with a considerable contribution fr

holocene paleointensities thellier experiments on submarine basaltic glass from the east pacific rise a complete description of the geomagnetic field requires both paleodirectional and paleointensity data although the paleointensity data base has grown steadily over the last three decades it remains limited in time and space the majority of data are of holocene age and come from europe furthermore it has been difficult to assess the reliability of the paleointensity determinations here we present paleointensity determinations on precisely dated holocene 0 to 3500 years old submarine basaltic glass from the east pacific rise 15 s to 22 s although hysteresis measurements and low temperature isothermal remanent magnetization irm acquisition experiments document a significant contribution of superparamagnetic grains high blocking temperatures above 400 c and curie temperatures between 490 c and 550 c indicate a single domain low ti magnetite as the carrier of the remanent magnetization this notion is further supported by the fact that saturation of remanence is achieved in moderate fields of about 200 300 mt submarine basaltic glass proves to be nearly ideal for paleointensity determinations in that it produces a high success rate for thellier experiments twenty six out of 30 samples resulted in acceptable paleointenisty determinations multiple experiments on splits from the same sample show good reproducibility the paleointensities for zero age glasses correspond precisely with the present field intensity at the site of recovery the results of the remaining samples range from 16 7 to 53 9 t with corresponding virtual axial dipole moments vadm of 3 61 1022 to 11 9 1022 a m2 the intensities vary rapidly with time excluding a westward drifting nondipole component as the source for these fluctuations basaltic glass is frequently recovered in both dredged and drilled material from the ocean floor the availability of submarine basaltic glass throughout the world oceans therefore holds great potential for a better distribution of paleointensity data through time and space