analyzing earthquake clustering features by using stochastic reconstruction 1 on the basis of the epidemic type aftershock sequence etas model and the thinning procedure this paper gives the method about how to classify the earthquakes in a given catalogue into different clusters stochastically the key points of this method are the probabilities of one event being triggered by another previous event and being a background event making use of these probabilities we can reconstruct the functions associated with the characteristics of earthquake clusters to test a number of important hypotheses about the earthquake clustering phenomena we applied this reconstruction method to the shallow seismic data in japan and also to a simulated catalogue the results show the following assertions 1 the functions for each component in the formulation of the space time etas model are good enough as a first order approximation for describing earthquake clusters 2 a background event triggers less offspring in expectation than a triggered event of the same magnitude 3 the magnitude distribution of the triggered event depends on the magnitude of its direct ancestor 4 the diffusion of the aftershock sequence is mainly caused by cascades of individual triggering processes while no evidence shows that each individual triggering process is diffusive and 5 the scale of the triggering region is still an exponential law as formulated in the model but not the same one for the expected number of offspring

low altitude magnetic field measurements by messenger reveal mercury s ancient crustal field magnetized rocks can record the history of the magnetic field of a planet a key constraint for understanding its evolution from orbital vector magnetic field measurements of mercury taken by the mercury surface space environment geochemistry and ranging messenger spacecraft at altitudes below 150 kilometers we have detected remanent magnetization in mercury s crust we infer a lower bound on the average age of magnetization of 3 7 to 3 9 billion years our findings indicate that a global magnetic field driven by dynamo processes in the fluid outer core operated early in mercury s history ancient field strengths that range from those similar to mercury s present dipole field to earth like values are consistent with the magnetic field observations and with the low iron content of mercury s crust inferred from messenger elemental composition data

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

magnetic remanence in the murchison meteorite the murchison meteorite is a carbonaceous chondrite containing a small amount of chondrules various inclusions and matrix with occasional porphyroblasts of olivine and or pyroxene it also contains amino acids that may have served as the necessary components for the origin of life magnetic analyses of murchison identify an ultrasoft magnetic component due to superparamagnetism as a significant part of the magnetic remanence the rest of the remanence may be due to electric discharge in the form of lightning bolts that may have formed the amino acids the level of magnetic remanence does not support this possibility and points to a minimum ambient field of the remanence acquisition we support our observation by showing that normalized mineral magnetic acquisition properties establish a calibration curve suitable for rough paleofield determination when using this approach 1 2 of the natural remanence left in terrestrial rocks with trm and or crm determines the geomagnetic field intensity irrespective of grain size or type of magnetic mineral with the exception of hematite the same method is applied to the murchison meteorite where the measured meteorite remanence determines the paleofield minimum intensity of 200 2000 nt during and or after the formation of the parent body

new silurian and devonian palaeomagnetic results from the hexi corridor terrane northwest china and their tectonic implications summary a total of 239 orientated drill core samples from 23 sites were collected for palaeomagnetic study from silurian and devonian red beds marlaceous sandstone and limestone rocks in the eastern part of the hexi corridor southwest ningxia north china the characteristic high temperature component resides in both haematite and magnetite it clusters around a northwesterly and shallow to moderate downward direction and its antipode after tilt correction the primary origin of this characteristic remanent magnetization chrm is ascertained by positive fold and reversal tests at the 95 per cent confidence level the corresponding palaeopoles at 339 0 e 60 1 n with a 95 11 2 silurian and 336 0 e 56 0 n with a 95 9 2 devonian imply that the north china block ncb had a low palaeolatitude of around 15 n in the northern hemisphere during the silurian devonian period comparison with the early middle ordovician palaeopole of the ncb suggests that the ncb moved rapidly northwards by 30 8 10 9 to cross the palaeo equator during the early middle ordovician to silurian in combination with the palaeobiogeographical data from ningxia our palaeomagnetic results suggest that the ncb was located close to australia during the late devonian

earthquake patterns in diverse tectonic zones of the globe we extend existing branching models for earthquake occurrences by incorporating potentially important estimates of tectonic deformation and by allowing the parameters in the models to vary across different tectonic regimes we partition the earth s surface into five regimes trenches including subduction zones and oceanic convergent boundaries and earthquakes in outer rise or overriding plate fast spreading ridges and oceanic transforms slow spreading ridges and transforms active continental zones and plate interiors everything not included in the previous categories our purpose is to specialize the models to give them the greatest possible predictive power for use in earthquake forecasts we expected the parameters of the branching models to be significantly different in the various tectonic regimes because earlier studies bird and kagan in bull seismol soc am 94 6 2380 2399 2004 found that the magnitude limits and other parameters differed between similar categories we compiled subsets of the cmt and pde earthquake catalogs corresponding to each tectonic regime and optimized the parameters for each and for the whole earth using a maximum likelihood procedure we also analyzed branching models for california and nevada using regional catalogs our estimates of parameters that can be compared to those of other models were consistent with published results examples include the proportion of triggered earthquakes and the exponent describing the temporal decay of triggered earthquakes we also estimated epicentral location uncertainty and rupture zone size and our results are consistent with independent estimates contrary to our expectation we found no dramatic differences in the branching parameters for the various tectonic regimes we did find some modest differences between regimes that were robust under changes in earthquake catalog and lower magnitude threshold subduction zones have the highest earthquake rates the largest upper magnitude limit and the highest proportion of triggered events fast spreading ridges have the smallest upper magnitude limit and the lowest proportion of triggered events the statistical significance of these variations cannot be assessed until methods are developed for estimating confidence limits reliably some results apparently depend on arbitrary decisions adopted in the analysis for example the proportion of triggered events decreases as the lower magnitude limit is increased possibly because our procedure for assigning independence probability favors larger earthquakes in some tests we censored earthquakes occurring near and just after a previous event to account for the fact that most such earthquakes will be missing from the catalog fortunately the branching model parameters were hardly affected suggesting that the inability to measure immediate aftershocks does not cause a serious estimation bias we compare our branching model with the etas model and discuss the differences in the models parametrization and the results of earthquake catalogs analysis

does the permo triassic geomagnetic dipole low exist studies of absolute paleointensity have been conducted on specimens from permo triassic sills from the eastern areas of the kimberlite pipes sytikanskaya yubileinaya and aikhal and northwestern extrusions near noril sk city parts of the siberian platform a total of 341 specimens have been subjected to a modified thellier thellier technique which included partial thermoremanent magnetization checks and multidomain tail checks the paleomagnetic directions derived from the present set of experiments d 107 5 i 75 5 k 82 8 a95 5 3 n 10 sills for the eastern localities and d 95 1 i 71 8 k 35 2 a95 15 7 n 4 outcrops for the northwestern locality agree with the directions from previous studies the specimens from the northwestern sites noril sk did not provide any suitable result of absolute paleointensity the mean virtual dipole moment obtained from only the eastern localities has a value close to 6 01 1 45 10 22 am 2 which is over 50 higher than the results obtained by heunemann et al 2004 and shcherbakova et al 2005 on northwestern specimens the discrepancy could possibly be explained by the presence of multidomain grains in northwestern specimens where previous studies were undertaken which would reduce the paleointensity estimates at high temperatures however the present results lead us to conclude that 1 the geomagnetic field intensity at the permo triassic boundary was very close to the observed present day values and as a consequence a dipole low is not characteristic during this period of time 2 the mesozoic dipole low did not extend to the permo triassic boundary contrary to previous studies

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

lodestone natures only permanent magnet what it is and how it gets charged magnetite and titanomagnetite exhibit magnetic properties which are attributable to the micro structures developed during oxidation and exsolution all magnetite iron ores which are lodestones contain maghemite these lodestones have hc between 10 and 30 mt sirm between 8 and 18 am kg and ri between 0 10 and 0 26 magnetite titanomagnetite and metals have rem values ratio of nrm to sirm 0 05 samples called fulgarites obtained from the smithsonian institution have rem values ranging from 0 45 to 0 92 the rem value serves as a witness parameter to the magnetic fields associated with the lightning bolt if a high rem value say 0 1 can be verified as not to be due to contamination by man and does not contain md hematite then the rock has lrm lightning remanent magnetization the magnetic field associated with lightning can be revealed from an isothermal remanent acquisition ra curve

space time etas models and an improved extension for sensitive detection of anomalous seismicity such as quiescence and activation in a given region we need a suitable statistical reference model that represents a normal seismic activity in the region the regional occurrence rate of the earthquakes is modeled as a function of previous activity the specific form of which is based on empirical laws in time and space such as the modified omori formula and the utsu seki scaling law of aftershock area against magnitude respectively this manuscript summarizes the development of the epidemic type aftershock sequence etas model and proposes an extended version of the best fitted space time model that was suggested in ogata ogata y 1998 space time point process models for earthquake occurrences ann inst statist math 50 379 402 this model indicates significantly better fit to seismicity in various regions in and around japan d 2005 elsevier b v all rights reserved

gravel transport and morphological change in braided sunwapta river alberta canada the relation between morphological change and patterns of variation in bedload transport rate in braided streams was observed by repeated daily topographic surveys over a 25 day study period in a 60 m reach of the proglacial sunwapta river alberta canada there are two major periods of morphological change each lasting several days and each involving the complete destruction and reconstruction of bar complexes bar complex destruction was caused by redirection of the flow and by downstream extension of the confluence scour zone upstream reconstruction involved accretion of unit bars on bar head flank and tail and in one case was initiated by disection of a large lobate unit bar high rates of sediment movement measured from net scour and fill of the cross sections coincided with these morphological changes sediment was supplied from both bed and bank erosion and patterns and distances of transfer were highly variable rates of transport estimated by matching upstream erosional volumes with downstream deposition were much greater than those estimated from either a step length approach or a sediment budget measurements of scour and fill and observations of morphological change indicate that step lengths virtual transport distances were typically 40 100m during a diurnal discharge cycle shorter step lengths occurred when transfer was confined to a single anabranch and longer steps involved channel changes at the scale of the entire reach sediment budgeting was used to describe the spatial patterns of sediment transport associated with the morphological changes and to estimate minimum daily reach averaged transport rates mean bedload transport rates correlate with discharge but with considerable scatter the largest deviations from the mean relation can be tied to phases of channel incision bank erosion scour hole migration bar deposition and channel filling apparently controlled by changes and fluctuations in sediment supply from upstream independent of discharge these are interpreted as field evidence of autopulses or macropulses in bedload transport previously observed only in laboratory models of braided streams

a quantitative three dimensional depositional model of gravelly braided rivers a quantitative three dimensional depositional model of gravelly braided rivers has been developed based largely on the deposits of the sagavanirktok river in northern alaska these deposits were described using cores wireline logs trenches and ground penetrating radar profiles the origin of the deposits was inferred from observations of 1 channel and bar formation and migration and channel filling interpreted from aerial photographs 2 water flow during floods and 3 the topography and texture of the river bed at low flow stage this depositional model quantitatively represents the geometry of the different scales of strataset the spatial relationships among them and their sediment texture distribution porosity and permeability in the model are related to sediment texture the geometry of a particular type and scale of strataset is related to the geometry and migration of the bedform type e g ripples dunes bedload sheets bars associated with deposition of the strataset in particular the length to thickness ratio of stratasets is similar to the wavelength to height ratio of associated bedforms furthermore the wavelength and height of bedforms such as dunes and bars are related to channel depth and width therefore the thickness of a particular scale of strataset i e medium scale cross sets and large scale sets of inclined strata will vary with river dimensions these relationships between the dimensions of stratasets bedforms and channels mean that this depositional model can be applied to other gravelly fluvial deposits the depositional model can be used to interpret the origin of ancient gravelly fluvial deposits and to aid in the characterization of gravelly fluvial aquifers and hydrocarbon reservoirs

paleointensity determination on the late precambrian tudor gabbro ontario paleointensity determination by the coe modified thellier method was carried out on the 1100 ma tudor gabbro of southern ontario the tudor has a bivectorial natural remanent magnetization nrm the c nrm is a grenvillian uplift thermoviscous remagnetization which overprints the a nrm the surviving primary thermoremanent magnetization trm of the tudor intrusion a sharp junction at 530 c between the a and c vectors in laboratory thermal demagnetization matches the peak metamorphic reheating temperature of 480 500 c in nature when the difference in time scales is taken into account the unblocking temperature distributions of the a nrm and of laboratory trm also match a is carried by single domain or small pseudo single domain grains probably magnetite rods exsolved in plagioclase or pyroxene at temperatures above 580 c arai plots of nrm versus partial trm are linear from 520 c or 530 c to 580 c for 45 specimens of 19 samples from 9 sites the 45 reliable paleointensity values from these specimens give a virtual axial dipole moment vadm of 4 6 0 8 1022 a m2 around 1100 ma this is about one half of the modern field intensity but is similar to the mean cretaceous cenozoic intensity and to most archean and proterozoic vadms keweenawan rocks whose ages are within 20 myr of the tudor gabbro have a vadm of 11 4 1022 a m2 the difference between the tudor and keweenawan vadms is similar to differences recorded over similar time intervals in the cretaceous and seems to represent normal variation in geomagnetic field strength throughout earth s history

multivectorial paleointensity determination from the cordova gabbro southern ontario abstract we report geomagnetic field intensities for the a 1000 ma and b 850 ma natural remanent magnetizations of the cordova gabbro of southern ontario we interpret a and b to be secondary thermal overprints produced during regional uplift and cooling following the grenvillian orogeny multivectorial a b paleointensity data were analyzed using pairs of arai diagrams for the separated a and b vectors from 18 reliable a results and 15 reliable b results we find paleofield values of 18 1 2 1 t and 7 1 1 5 t respectively the corresponding virtual axial dipole moments vadms are 3 12 0 36 and 1 82 0 38 10 22 a m 2 about 70 and 40 of the average phanerozoic dipole moment based on data from 0 3 300 ma the cordova data and other precambrian paleointensities are generally within a range of approximately 0 5 1 5 times the phanerozoic mean vadm three sets of paleofield values as a function of paleolatitude including the cordova data support a dipole configuration for the earth s field in 25 150 ma time windows around 2700 ma 1100 ma and 850 ma

on the efficiency of shock magnetization processes abstract the acquisition of remanent magnetization caused by hypervelocity impacts may be a major contribution to the remanent magnetization of planetary surfaces and meteorites in this paper we investigate the properties of shock remanent magnetization srm and in particular the relative efficiency of this phenomenon with respect to thermoremanent magnetization trm a parameter of interest for the understanding of the magnetic signatures of impact basins on extraterrestrial bodies we imparted shock remanent magnetization on basalt and microdiorite samples using laser shock in controlled magnetic field shock modeling indicates a pressure range of 0 6 1 5 gpa for our experiments the results confirm that the srm is parallel to the ambient magnetic field srm increases linearly with the ambient field in the 1 2500 t range the intensity of srm is independent of the angle between the shock direction and the direction of the ambient field the coercivity spectrum of srm is shifted towards lower values compared to the coercivity spectra of trm and isothermal remanent magnetization for the two studied lithologies the efficiency of srm versus trm acquisition is 17 for the basalt and is 36 for the microdiorite this efficiency depends on the magnetic mineralogy and increases with decreasing coercivity the rather high efficiency values that we obtained show that a significant remanent magnetization can be acquired by the crust during an hypervelocity impact on a planetary surface in the presence of an ambient field

trm arm and isr of two natural magnetites of md and psd grain size summary trm arm and isr stabilities with respect to alternating fields and high and low temperature treatment are compared for a set of artificial rock specimens the specimens contain grain size fractions of a homogeneous natural magnetite and a natural magnetite showing exsolution lamellae the grain size fractions are in the psd md range and vary between 5 and 250 m for large md grains the coercivity spectra of arm are similar to those of isr but differ from those of trm particularly in the lower part of the spectrum for small 5 m grains the coercivity spectrum of arm is similar to that of trm and both spectra are different from the coercivity spectrum of isr the use of arm instead of trm to determine palaeo intensities is discussed in relation to the results obtained during high and low temperature treatment arm behaves similarly to isr but unlike trm for all grain sizes studied the results of this study are discussed in terms of a remanence composed of psd surface moments and md and psd bulk moments

magnetic properties of a freshly fallen ll ordinary chondrite the bensour meteorite abstract a comprehensive rock magnetic magnetic anisotropy and paleomagnetic study has been undertaken in the brecciated ll6 bensour ordinary chondrite a few months only after its fall on earth microscopic observations and electronic microprobe analyses indicate the presence of ni rich taenite tetrataenite and rare co rich kamacite tetrataenite is the main carrier of remanence magnetization and anisotropy measurements were performed on mutually oriented 125 mm 3 sub samples a very strong coherent susceptibility and remanence anisotropy is evidenced and interpreted as due to the large impact responsible for the post metamorphic compaction of this brecciated material and disruption of the parent body we show that the acquisition of remanent magnetization postdates metamorphism on the parent body and predates the entering of the meteorite in earth s atmosphere three components of magnetization could be isolated a soft coherent component is closely related to the anisotropy of the meteorite and is interpreted as a shock remanent magnetization acquired during the same large impact on the parent body two harder components show random directions at a few mm scale this randomness is attributed either to the formation mechanism of tetrataenite or to post metamorphic brecciation all components are likely acquired in very low t to null ambient magnetic field as demonstrated by comparison with demagnetization behavior of isothermal remanent magnetization two other ll6 meteorites kilabo and st mesmin have also been studied for comparison with bensour

magnetic fidelity of lunar samples and implications for an ancient core dynamo abstract some lunar rocks have stable magnetizations that provide compelling evidence for an ancient lunar core dynamo however a longstanding problem has been interpreting the unstable alternating field af demagnetization behavior observed in the remaining majority of the apollo lunar sample suite similar unstable behavior has also been observed for many meteorites it is unclear whether the behavior of these samples indicates that they formed in the absence of an ancient magnetizing field or whether they simply have poor magnetic recording properties it is necessary to distinguish between these two possibilities in order to determine whether paleomagnetic fields were present on a sample s parent body to address this issue we analyzed five samples whose rock magnetic properties span the full suite of observed demagnetization behaviors mare basalts 15556 15016 12017 10020 and troctolite 76535 we demonstrate that the effects of spurious anhysteretic remanent magnetization arm during af demagnetization in combination with multidomain magnetic carriers and magnetic remanence anisotropy are likely responsible for the apparently poor magnetic behavior of many lunar samples therefore the unstable af demagnetization behavior observed for many lunar samples is not alone sufficient for ruling out the presence of an ancient lunar core dynamo nevertheless spurious arm may explain the observation of surprisingly high 1 t apollo era paleointensity measurements for samples thought to have formed after the cessation of a lunar core dynamo

toward a robust normalized magnetic paleointensity method applied to meteorites abstract we propose a new paleointensity method based on normalization by isothermal remanent magnetization derivative vs alternating field rem method it provides an estimate of the absolute paleointensity with an uncertainty of about a factor two contrary to methods using normalization by total isothermal remanent magnetization or anhysteretic magnetization it is applicable to multicomponent magnetizations artificial or natural isothermal remanent magnetizations can be recognized and relaxation of natural remanent magnetization can be taken into account it is applicable for magnetizations carried by magnetite feni alloys and pyrrhotite the rem method is of particular interest to estimate paleointensities in meteorites as these materials are often characterized by complex multicomponent magnetization of various origins impact magnetization thermoremanence isothermal remanent magnetization and metastable magnetic minerals not suitable for thellier experiments however like other paleointensity methods the rem method underestimates the true paleointensity for meteorite samples with magnetizations that are heterogeneous on spatial scales below the sampling scale for l ordinary chondrites an upper limit of 1 t is proposed for the paleofield tentative paleofield estimates in the 0 05 0 5 t range are proposed for ll ordinary chondrites which is much lower than previous results the first paleofield estimates for rumuruti chondrites indicate the presence of magnetic fields around 6 t during the last major impact on their parent body aubrites and hed achondrites paleofields of at least 10 t may suggest the existence of a dynamo field during the cooling of their parent body results from martian meteorites are scattered between 1 and 24 t and may represent the crustal magnetic field of the planet after dynamo shutdown carbonaceous chondrites provide contrasting results with possible evidence of strong field mt processes that clearly require additional studies

on the relationship between lower magnitude thresholds and bias in epidemic type aftershock sequence parameter estimates 1 modern earthquake catalogs are often described using spatial temporal point process models such as the epidemic type aftershock sequence etas models of ogata 1998 earthquake catalogs often have issues of incompleteness and other inaccuracies for earthquakes of magnitude below a certain threshold and such earthquakes are typically removed prior to fitting a point process model this paper investigates the bias in the parameters in etas models introduced by the removal of the smallest events it is shown that in the case of most of the etas parameters the bias increases approximately exponentially as a function of the lower magnitude cutoff

the effect of remanence anisotropy on paleointensity estimates a case study from the archean stillwater complex paleomagnetism of archean rocks potentially provides information about the early development of the earth and of the geodynamo precambrian layered intrusive rocks are good candidates for paleomagnetic studies such complexes are commonly relatively unaltered and may contain some single domain magnetite armored by silicate mineral grains however layered intrusives often have a strong petrofabric that may result in a strong remanence anisotropy magnetic anisotropy can have particularly disastrous consequences for paleointensity experiments if the anisotropy is unrecognized and if its effects remain uncorrected here we examine the magnetic anisotropy of an anorthosite sample with a well developed magmatic foliation the effect of the sample s remanence fabric on paleointensity determinations is significant paleointensities estimated by the method of thellier and thellier range from 17 to 55 t for specimens magnetized in a field of 25 t we describe a technique based on the remanence anisotropy tensor to correct paleointensity estimates for the effects of magnetic fabric and use it to estimate a paleointensity for the stillwater complex mt usa of 32 t adjusted for the effects of slow cooling

paleointensity determination using anhysteretic remanence and saturation isothermal remanence 1 determining the strength of ancient planetary magnetic field is pivotal to understanding the evolution of planets and asteroids in the solar system while the thellier type double heating technique provides the most faithful field strength information for rocks carrying a thermoremanent magnetization trm many extraterrestrial rock samples respond unfavorably to heat treatment the present study systematically examined the two well known normalization techniques that avoid any heating by comparing the ratios of trm anhysteretic remanent magnetization arm and trm saturation isothermal remanent magnetization sirm both the ratios of trm arm and trm sirm are dependent on the grain size as well as the volume concentration of magnetite the remanence ratios also were found to increase as the alternating field increased during demagnetization for fine grained magnetite a new calibration relation of 2 60 1 32 for the trm arm and of 3 62 1 28 10 2 for the trm sirm was defined for an external field of 50 t the trm sirm is superior to trm arm because the former showed less dispersion in the grain size dependence the volume concentration dependence and the stability against af demagnetization in addition the standard error of the mean for the trm sirm ratio was smaller than that for the trm arm ratio thus whenever heating is inapplicable the sirm method seems to be a better choice than the arm method however it should be emphasized that the uncertainty of trm arm and trm sirm is still nearly an order of magnitude larger than that of the high fidelity thellier estimation and thus must be limited in use only when samples are irreversibly altered during heating in practice the best approach is to carry out both arm and sirm methods and check whether the two estimations agree within the uncertainties

accuracy of modern global earthquake catalogs we compare several modem 1977 present worldwide earthquake catalogs to infer their completeness earthquake origin time and hypocenter location accuracy magnitude scalar seismic moment errors and difference between individual focal mechanism moment tensor solutions the harvard centroid moment tensor cmt us geological survey usgs mt usgs first motion fm focal mechanism pde and isc catalogs have been analyzed and compared the catalogs completeness and accuracy vary in time and depend on earthquake depth and tectonic environment we propose a new statistical method for evaluating catalog completeness and show the results for the cmt dataset a difference in frequency range of seismic waves used in earthquake processing leads to varying degrees of catalog completeness for foreshocks and aftershocks close in time earthquake origin time versus centroid time as well as hypocenter location versus centroid location can be explained well by earthquake scaling relations comparing moment magnitudes and regular earthquake magnitudes yields estimated magnitude uncertainties and shows that latter magnitudes poorly estimate earthquake size for large events moment errors reported in the cmt solutions are well correlated with the cmt gs mt magnitude difference and hence indicate magnitude uncertainty well a normalized seismic moment tensor has 4 d f and its accuracy can be represented as the non double couple non dc component value the 3 d angle phi of dc source rotation and a position of the rotation pole our results suggest that a routinely determined non dc component is in most cases only an artifact the distribution of the phi value varies over catalog time earthquake depth focal mechanism and magnitude the seismic moment errors and the value of the non dc component are indicative of the phi value for the best solutions the 3 d angle in the cmt catalog is on the order of 5 7degrees the cmt catalog is obviously the best dataset in completeness and accuracy of its detailed solutions our results specifying uncertainties and completeness of global earthquake catalogs can be used in studies of geodynamic processes tectonic deformation associated with earthquakes earthquake stress analysis and in many other applications of earthquake catalog data seismogram interpretation techniques can be reviewed and possibly revised in light of these results c 2002 elsevier science b v all rights reserved

stratigraphy and infill history of the glacially eroded matane river valley eastern quebec canada terraces in the lower matane river valley eastern quebec canada were studied to describe the stratigraphic architecture of a glacially eroded valley fill the matane river valley hosted a glacial tongue connected with a regional ice cap during the early opening of a calving bay in the modern st lawrence estuary and was subsequently flooded by the goldthwait sea as the laurentide ice sheet margin retreated stratigraphic sedimentological light detection and ranging lidar and geochemical analyses as well as radiocarbon measurements allowed the identification of four stratigraphic units deposited during and following deglaciation glacial outwash unit i delta bottomsets unit ii delta foresets unit iii and fluvial deposits unit iv stable isotope 13c and c n ratio values reveal the relative influence of the two end members algae and terrestrial plants on organic matter sources between the stratigraphic units climate major relative sea level fluctuations and sediment yield are recogn

magnetic studies on shergotty and other snc meteorites abstract hysteresis measurements on three shergottite and two nakhlite meteorites indicate single domain grain size behavior for the highly shocked shergotty zagami and eeta 79001 meteorites with more multidomain like behavior for the unshocked nakhla and governador valadares meteorites high viscosity and initial susceptibility for antarctic shergottite alha 77005 indicate the presence of superparamagnetic grains in this specimen thermomagnetic curves likewise reveal a range of oxidation states for the high ulvospinel titanomagnetite grains which dominate the magnetic properties of these first five meteorites thermomagnetic analysis indicate shergotty and zagami as the least initially oxidized while eeta 79001 appears to be the most oxidized cooling of the meteorite samples from high temperature in air results in a substantial increase in magnetization due to the production of magnetite through oxidation exsolution of titanomagnetite however vacuum heating substantially suppresses this process and in the case of eeta 79001 and nakhla results in a rehomogenization of the titanomagnetite grains remanence measurements on several subsamples of shergotty and zagami meteorites reveal a large variation in intensity that does not seem related to the abundance of remanence carriers the other meteorites carry only weak remanence suggesting weak magnetizing fields as the source of their magnetic signal a paleointensity experiment on a weakly magnetized subsample of shergotty reveals a low temperature component of magnetization acquired in a field of 2 000 gammas also present was a high temperature component reflecting a paleo field strength of between 250 and 1 000 gammas depending on the nature and degree of alteration that the sample may have undergone with heating this is consistent with an earlier paleointensity estimate of 1 000 gammas for alha 77005 the weak field environment that these meteorites seem to reflect is consistent with either a martian or asteroidal body origin but inconsistent with a terrestrial origin

multi scale seismicity model for seismic risk for a general use of the frequency magnitude fm relation in seismic risk assessment we formulate a multi scale approach that relies on the hypothesis that only the ensemble of events that are geometrically small compared with the elements of the seismotectonic regionalization can be described by a log linear fm relation it follows that the seismic zonation must be performed at several scales depending upon the self similarity conditions of the seismic events and the linearity of the log fm relation in the magnitude range of interest the analysis of worldwide seismicity using the harvard catalog where the seismic moment is recorded as the earthquake size corroborates the idea that a single fm relation is not universally applicable the multi scale model of the fm relation is tested in the italian region

seismicity and geodetic anomalies in a wide area preceding the niigata ken chuetsu earthquake of 23 october 2004 central japan 1 the ordinary short term occurrence rate of earthquakes in a region is predicted using the epidemic type aftershock sequence etas model of triggering seismicity any anomalous seismic activity such as quiescence and activation can be quantified by identifying significant deviation from the predicted rate such anomalies are revealed to have occurred during the three year period leading up to the 2004 chuetsu earthquake of m6 8 mw6 6 central japan the quiescence and activation which took place in the zone of negative and positive increments of the coulomb failure stress respectively were possibly caused by aseismic slip on or near the focal fault plane such slip is further supported by transient crustal movement around the rupture source time series records of the baseline distances between permanent gps stations deviated from the predicted trends with the deviations mostly consistent with the coseismic horizontal displacements of the stations due to the chuetsu earthquake the cumulated preceding slip is estimated to be roughly equivalent to mw6

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

constraints on the size of the smallest triggering earthquake from the epidemic type aftershock sequence model bath s law and observed aftershock sequences 1 the physics of earthquake triggering together with simple assumptions of self similarity imply the existence of a minimum magnitude m0 below which earthquakes do not trigger other earthquakes noting that the magnitude md of completeness of a seismic catalog is not in general the same as the magnitude m0 of the smallest triggering earthquake we compare observed aftershock sequence parameters with the predictions made by the epidemic type aftershock sequence model to constrain the value of m0 in particular we use quantitative fits to observed aftershock sequences from three previous studies as well as bath s law to obtain four estimates of m0 we show that the branching ratio n average number of triggered earthquakes per earthquake also equal to the fraction of aftershocks in a seismic catalog is the key parameter controlling the estimate of the minimum triggering magnitude m0 conversely physical upper bounds for m0 estimated from rate and state friction indicate that at the very least 55 of all earthquakes are aftershocks

comparison of etas parameter estimates across different global tectonic zones abstract branching point process models such as the epidemic type aftershock sequence etas models introduced by ogata 1988 1998 are often used in the description characterization simulation and declustering of modern earthquake catalogs the present work investigates how the parameters in these models vary across different tectonic zones after considering divisions of the surface of the earth into several zones based on the plate boundary model of bird 2003 etas models are fit to the occurrence times and locations of shallow earthquakes within each zone computationally the expectation maximization em type algorithm of veen and schoenberg 2008 is employed for the purpose of model fitting the fits and variations in parameter estimates for distinct zones are compared and seismological implications are discussed in particular we find that estimated background seismicity rates range by a factor of nearly 500 for interplate and trench events respectively the estimated productivity parameter governing the relationship between the magnitude of an earthquake and its expected number of direct aftershocks ranges by a factor of more than five from events in the slow moving zone to events in active continental areas suggesting a much higher rate of swarming in the ridges than in the trenches and active continental zones despite the pronounced differences between the seismicity patterns and parameter estimates in the different zones the etas model with few parameters and with the same functional form seems to fit reasonably well to the seismicity in each zone

aspects of the validation of magnetic remanence in meteorites meteorite magnetic records constitute physical evidence of processes acting during early solar system evolution consequently the validation of these records is important in meteorite research the first step in the validation process should be the rem value the rem value is the ratio of natural remanence nrm to saturation remanent magnetization imparted by a 1 t magnetic field sirm the rem values range over 3 to 4 orders of magnitude for stony meteorites and for chondrules from allende c3v s1 bjurbole l4 s1 and chainpur ll3 s1 meteorites the rem values computed from published nrm and sirm data identify many orders of magnitude range in the rem values including rem values 100 10 3 these data suggest a dependence for the nrm intensity on the curatorial location from which the sample was obtained any earth rock acquiring thermoremanent magnetization trm in the geomagnetic field has a restricted range in rem mostly between 5 and 50 10 3 the exception being the mineral hematite in the multidomain size range the only terrestrial samples with rem much greater than 100 10 3 are those struck by lightning the rem value provides a physical basis for recognition between valid records and those that might be contaminated the isothermal remanence acquisition ra curve is presented as a contamination curve that allows an indication of the level of magnetic field contamination required to give the computed rem rm sirm value in the case of the bjurbole and chainpur chondrules with rem values 100 10 3 the ra curve indicates that unrealistically large contamination magnetic fields would be required to give rem values greater than 100 10 3 this would suggest contamination other than by a hand magnet that is normally available to an experimenter this would require an explanation that would involve large magnetic fields during chondrule formation or some extraordinary remanence acquisition mechanism that remains to be described magnetic contamination experiments using 80 and 40 mt magnets demonstrate that the rem values and extent of modification of the magnetic vector record are mineralogy dependent and this is mostly related to the amount and characteristics of the mineral tetrataenite the complexity of the meteorite records suggest validation of the record as a first step the rem value is the first physical statement that can be made in this validation

433 eros problems with the meteorite magnetism record in attempting an asteroid match the magnetometer experiment mag onboard the near shoemaker spacecraft detected no global scale magnetization and established a maximum magnetization of 2 1x10 6 am 2 kg 1 for asteroid 433 eros this is in sharp contrast with the estimated magnetization of other s class asteroids gaspra 2 4 x 10 2 am 2 kg 1 braille 2 8 x 10 2 am 2 kg 1 and is below published values for all types of ordinary chondrites this includes the l ll types considered to most closely match 433 eros based on preliminary interpretations of near remote geochemical experiments the ordinary chondrite meteorite magnetization intensity data was reviewed in order to assess the reasonableness of an asteroid meteorite match based on magnetic property measurements nrm natural remanent magnetization intensities for the ordinary chondrite meteorites show at least a 2 order of magnitude range within each of the h l ll groups all well above the 2 1 x10 6 am 2 kg 1 level for 433 eros the rem values ratio of the nrm to the sirm saturation remanent magnetization range over 3 orders of magnitude for all chondrite groups indicating no clear relationship between nrm and the amount of magnetic material levels of magnetic noise in chondrite meteorites can be as much as 70 or more of the nrm consequently published values of the nrm should be considered suspect unless careful evaluation of the noise sources is done goddard studies of per unit mass intensities in large 10 000gm and small down to 1 gm samples from the same meteorite demonstrate magnetic intensity decreases as size increases this would appear to be explained by demagnetization due to magnetic vector randomness at unknown scale sizes in the larger samples this would then argue for some level of demagnetization of large objects such as an asteroid the possibility that 433 eros is an ll chondrite cannot be discounted

explanation of temporal clustering of tsunami sources using the epidemic type aftershock sequence model temporal clustering of tsunami sources is examined in terms of a branching process model it previously was observed that there are more short interevent times between consecutive tsunami sources than expected from a stationary poisson process the epidemic type aftershock sequence etas branching process model is fitted to tsunami catalog events using the earthquake magnitude of the causative event from the centennial and global centroid moment tensor cmt catalogs and tsunami sizes above a completeness level as a mark to indicate that a tsunami was generated the etas parameters are estimated using the maximum likelihood method the interevent distribution associated with the etas model provides a better fit to the data than the poisson model or other temporal clustering models when tsunamigenic conditions magnitude threshold submarine location dip slip mechanism are applied to the global cmt catalog etas parameters are obtained that are consistent with those estimated from the tsunami catalog in particular the dip slip condition appears to result in a near zero magnitude effect for triggered tsunami sources the overall consistency between results from the tsunami catalog and that from the earthquake catalog under tsunamigenic conditions indicates that etas models based on seismicity can provide the structure for understanding patterns of tsunami source occurrence the fractional rate of triggered tsunami sources on a global basis is approximately 14 online material figures of residual analysis for tsunami and earthquake catalogs

deltaic infill of a deglaciated arctic fjord east greenland sedimentary facies and sequence stratigraphy abstract the deltaic fill of a deglaciated side entry fjord in western jameson land east greenland shows the record of an interplay between regional and local controls including climate and relative sea level change onshore and offshore topography and sediment yield a four phase model is suggested for the delta development and fjord filling at the deglaciation stage phase 1 the newly flooded fjord floor primarily accumulated sediment from reworked glacial material these deposits were relatively thin and draped the uneven sea floor topography the subsequent onset of paraglacial delta sedimentation phase 2 was characterized by a high meltwater runoff and extreme sediment yield and corresponded to the highstand and gradual fall of relative sea level a gilbert type delta with a short distributary plain formed at the head of the tributary fjord which received a very high amount of fine grained sediment the stage of enhanced delta progradation phase 3 was characterized by decreased sediment yield and runoff and a rapid fall of relative sea level delta progradation was fast because of rapidly decreasing accommodation space and a solitary river channel deeply incised the delta the equilibrium stage phase 4 spanned most of holocene time and involved a lowered rate of relative sea level fall seasonal runoff supplied limited amounts of sediment to the river mouth and the delta front became increasingly reworked by wave action and longshore drift the side entry fjord a small deglaciated valley invaded by the sea was filled chiefly by highstand and regressive systems tracts whereas relatively little sea floor aggradation was associated with the transgressive systems tract the stratigraphic pattern documented in this paper contrasts with the pattern usually reported from nonglaciated incised valley systems which are filled mainly by the transgressive systems tract typically involving a retreating estuarine system the pattern also differs from some large gradually deglaciated fjord valleys containing thick transgressive glaciomarine deposits accumulated during glacier retreat the study demonstrates the large variability of valley fills and illustrates the importance of topography sediment supply and climate as well as the style of deglaciation on the sediment filling of a fjord valley

missing links in earthquake clustering models 1 many clustering models imply two kinds of earthquakes spontaneous ones and those triggered by previous earthquakes the pair wise links from earlier to later earthquakes control the estimates of the clustering parameters however earthquake catalogs are limited in time space and magnitude so that triggers of some cataloged earthquakes may be unknown thus some links are unrecognized and some triggered events appear spontaneous here we present a method for identifying such earthquakes and reducing the bias from missing links we treat earthquakes probably affected by missing links as potential triggers but we exclude them in evaluating modeled effects we use an epidemic type aftershock sequence etas model to examine specifics the most affected parameter is the proportion of spontaneous earthquakes the most important missing links apparently follow earthquakes below the magnitude threshold before the start and outside the spatial boundaries of the catalog in that order

nrm irm s demagnetization plots an aid to the interpretation of natural remanent magnetization af demagnetization of thermoremanent magnetization trm and saturation isothermal remanent magnetization irm s are used to establish diagnostic criteria for primary trm and for secondary magnetization in igneous rocks in applying the approach to the interpretation of natural remanent magnetization nrm the demagnetization of irm s documents the nature of the magnetic phases in the rock while the demagnetization of the nrm gives information about the process of magnetization the ratio of nrm irm s measures the efficiency of the magnetization process

magnetic zones of mars deformation controlled origin of magnetic anomalies intense magnetic anomalies over martian surface suggest preservation of large volumes of very old crust 3 gyr that formed in the presence of a global magnetic field the global distribution of the magnetic intensities observed above the martian crust suggests a division into three zones zone 1 is where the magnetic signature is negligible or of relatively low intensity at mars global surveyor mgs satellite mapping altitude 400 km zone 2 is the region of intermediate crustal magnetic amplitudes and zone 3 is where the highest magnetic intensities are measured crater demagnetization near zone 3 reveals the presence of rocks with both high magnetic intensity and coercivity magnetic analyses of terrestrial rocks show that compositional banding in orogenic zones significantly enhances both magnetic coercivity and thermal remanent magnetization trm efficiency such enhancement offers a novel explanation for the anomalously large intensities inferred of magnetic sources on mars we propose that both large magnetic coercivity and intensity near the south pole is indicative of the presence of a large degree of deformation associated compositional zoning creates conditions for large scale magnetic anisotropy allowing magnetic minerals to acquire magnetization more efficiently thereby causing the distinct magnetic signatures in zone 3 expressed by intense magnetic anomalies we use a simple model to verify the magnetic enhancement we hypothesize that magnetically enhanced zone would reside over the down welling plume at the time of magnetization acquisition

fundamental relations of mineral specific magnetic carriers for paleointensity determination abstract a fundamental linear relationship exists between the efficiency of thermoremanent magnetization measured at room temperature and the magnitude of the ambient field at the time of acquisition the magnetic efficiency the ratio of thermoremanent magnetization to saturation remanent magnetization multiplied by the saturation magnetization is proportional to the magnetizing field where the proportionality constant is independent of magnetic mineralogy and domain state the empirical constant for this equation was determined using existing experimental data of single domain through pseudosingle domain to multidomain states of iron meteoritic iron magnetite maghemite pyrrhotite and hematite we show that the acquired magnetic efficiency is closely related to two types of demagnetizing fields that act as barriers against domain wall pinning during magnetic acquisition the first relates to the saturation magnetization that is derived from the distribution of bohr magnetons within the crystal lattice and the second originates from grain shape theoretical considerations imply a factor of two difference in the magnetic efficiency acquired during laboratory and geologic timescales this equation reveals that troilite may be a potentially important magnetic carrier for extraterrestrial magnetism using magnetic scanning techniques our relationship allows for estimating the paleointensity from samples that contain more than one magnetic species

a long lived lunar core dynamo paleomagnetic measurements indicate that a core dynamo probably existed on the moon 4 2 billion years ago however the subsequent history of the lunar core dynamo is unknown here we report paleomagnetic petrologic and 40ar 39ar thermochronometry measurements on the 3 7 billion year old mare basalt sample 10020 this sample contains a high coercivity magnetization acquired in a stable field of at least 12 microteslas these data extend the known lifetime of the lunar dynamo by 500 million years such a long lived lunar dynamo probably required a power source other than thermochemical convection from secular cooling of the lunar interior the inferred strong intensity of the lunar paleofield presents a challenge to current dynamo theory

how accurately can nrm sirm determine the ancient planetary magnetic field intensity abstract the present study tested grain size dependence of thermoremanent magnetization trm saturation isothermal remanent magnetization sirm as well as its stability against demagnetization the trm sirm ratio is dependent on the grain size of magnetite suggesting that a strong constraint on grain size characterization is necessary to be used as a paleointensity proxy in planetary magnetism in addition the trm sirm ratio increases as the alternating field increases for fine grained magnetite accuracy of trm sirm was investigated using historic showa lava erupted in 1946 it was observed that the natural remanent magnetization nrm sirm ratio of 0 032 is comparable to the field intensity of 46 80 t however the uncertainty of nrm sirm was an order of magnitude larger than that of the companion thellier estimation therefore the nrm sirm ratio can only provide crude estimations on the absolute planetary magnetic field intensity in practice anisotropy correction is advisable to reduce the scatter of nrm sirm

ancient stable magnetism of the richardton h5 chondrite investigating mineral magnetic properties of meteorites is essential to understanding the formation and evolution of planetary bodies in the solar system in order to decipher ancient magnetic records demagnetization experiments were carried out for the 4550 ma richardton h5 chondrite alternating field demagnetization revealed a soft fraction as well as a hard fraction conventional thermal demagnetization in air showed severe alterations but a few thermal demagnetizations in vacuum were successful in isolating a stable paleomagnetic record on the basis of microscopic analysis we found that fine grained clinopyroxene hosted kamacite is abundant responsible for the stable and permanent magnetic record of richardton the experimental data imply a thermal or thermochemical origin for the stable paleomagnetic record of richardton however the possibility of pressure re magnetization cannot be evaluated because the effect of pressure on magnetization for the fe ni system is unknown

high temperature characteristics of a natural titanomagnetite summary continuous recordings were made of thermal demagnetizations of isr arm and trm induced in artificial rock specimens the artificial rock specimens contained well defined grain size fractions of a natural titanomagnetite which under an optical microscope was homogeneous using a transmission electron microscope it was shown that submicroscopic inclusions exist within the titanomagnetite screening of the remanence of these inclusions by the surrounding titanomagnetite is thought to be responsible for the occurrence of peaks in the continuous thermal decay curves of isr and arm higher peaks observed in the case of trm are thought to be caused by the combined effects of screening and an anti parallel remanence in the titanomagnetite further submicroscopic exsolution processes which occur in the titanomagnetite as a result of repeated heating can be deduced from the development of new peaks from changes in the temperature at which the peak s occur their shape and their relative height the use of stepwise demagnetization techniques on the titanomagnetite yielded erroneous directional results due to the screening in the titanomagnetite the biasing effects due to screening could be avoided by using continuous thermal demagnetization techniques

a linear field dependence of thermoremanence in low magnetic fields abstract we tested a linear field dependence of thermoremanent magnetization trm to saturation isothermal remanent magnetization sirm ratio for magnetite containing natural samples the trm sirm shows a linear field dependence to very low field ranges

trm in low magnetic fields a minimum field that can be recorded by large multidomain grains abstract thermally acquired remanent magnetization is important for the estimation of the past magnetic field present at the time of cooling rocks that cool slowly commonly contain magnetic grains of millimeter scale this study investigated 1 mm sized magnetic minerals of iron iron nickel magnetite and hematite and concluded that the thermoremanent magnetization trm acquired by these grains did not accurately record the ambient magnetic fields less than 1 t instead the trm of these grains fluctuated around a constant value consequently the magnetic grain ability to record the ambient field accurately is reduced above the critical field trm acquisition is governed by an empirical law and is proportional to saturation magnetization m s the efficiency of trm is inversely proportional to the mineral s saturation magnetization m s and is related to the number of domains in the magnetic grains the absolute field for which we have an onset of trm sensitivity is inversely proportional to the size of the magnetic grain these results have implications for previous reports of random directions in meteorites during alternating field demagnetization or thermal demagnetization of trm extraterrestrial magnetic fields in our solar system are weaker than the geomagnetic field by several orders of magnitude extraterrestrial rocks commonly contain large iron based magnetic minerals as a common part of their composition and therefore ignoring this behavior of multidomain grains can result in erroneous paleofield estimates

isotopic constraints of sedimentary inputs and organic carbon burial rates in the saguenay fjord quebec abstract the saguenay fjord quebec has exceptionally high sedimentation rates resulting in up to 100 m thick holocene sequences filling some of its basins partly due the frequent occurrence of rapidly deposited layers landslides seismic events floods in the present study special attention is paid on the incidence of such events on organic carbon oc fluxes sources and burial rates using physical sedimentological geochemical and isotopic measurements on 4 sediment cores raised from the inner basin of the fjord and the adjacent baie des ha ha in these cores rapidly deposited layers rdl include notably a turbidite linked to a major earthquake in 1663 a landslide layer dating from 1971 saint jean vianney landslide and a flood layer from 1996 compared with background sediments rdl are characterized by low oc contents 3 contents 2 and low 13 c values in oc 13 c oc values 26 8 0 2 and c n ratios 17 7 1 7 in the pre industrial pre 1663 fjord sediments indicate that most sedimentary organic matter om was then of terrigenous origin paper mill activity during the 20th century has resulted in om fluxes growing almost exponentially until the mid 1960s when major changes in industrial practices and the implementation of environmental regulations during the 1970s and later on reduced the amount of industrial om discharged into the fjord this industrial om shows an isotopic signature of 26 34 0 02 and c n ratios 20 not unlike those of the regional terrestrial om oc burial rates since the 1663 earthquake varied between 20 and 290 gc m 2 yr 1 rdl seem to favour oc preservation in the fjord by reducing bioturbation and both oxic and anoxic oc degradation and by contributing themselves to higher carbon burial rates therefore transitional environments such as the saguenay fjord could represent significant long term carbon sinks

a variety of aftershock decays in the rate and state friction model due to the effect of secondary aftershocks implications derived from an analysis of real aftershock sequences the model based on rate and state dependent friction law reproduces the temporal decay of an aftershock sequence with the p value of the omori utsu law equal to 1 if we simply assume a constant stress rate over time however because p values vary in real aftershock sequences this model requires some modification this study examined the effect of secondary aftershocks on the variety of the p value a large aftershock causes a stepwise stress increase in the aftershock area and the expected seismicity rate derived from the friction law also increases abruptly these multiple increases in the seismicity rate during its decay following a mainshock could cause variation in the apparent p value in this study a model incorporating this idea is applied to two aftershock sequences observed in japan and is shown to substantially modify the modeling of aftershock activity