the time averaged paleomagnetic field we review indications of persistent deviations from the geocentric axial dipole model of the time averaged geomagnetic field and present a zonal harmonic model derived from 185 deep sea sediment piston cores taken from low to middle latitudes to approximately 45 analysis of the paleomagnetic inclination recorded in these cores for the brunhes normal polarity 0 73 ma and matuyama reverse polarity 0 73 2 47 ma chrons after plate motion correction gives well constrained estimates of the dominant long term nondipole contributions the axial quadrupole and axial octupole and shows no significant deviation from axial symmetry the amplitude of the axial quadrupole is found to vary with polarity 2 6 of the geocentric axial dipole for normal 4 6 for reverse while the axial octupole does not show appreciable change 2 9 for normal 2 1 for reverse these estimates of the quadrupole contribution agree well with prior determinations for the plio pleistocene 0 5 ma however the octupole contribution we find is opposite in sign to previous estimates we suggest that a negative octupole is representative of the actual time averaged paleomagnetic field while prior positive octupole estimates probably reflect spurious inclination shallowing the lack of polarity asymmetry in the octupole suggests that this nondipole component may be more closely linked to the main dipole field than is the quadrupole and so supports models of the geodynamo in which dipole and quadrupole families do not interact

the time averaged geomagnetic field global and regional biases for 0 5 ma summary palaeodirectional data from lava flows and marine sediments provide information about the long term structure and variability in the geomagnetic field we present a detailed analysis of the internal consistency and reliability of global compilations of sediment and lava flow data time averaged field models are constructed for normal and reverse polarity periods for the past 5 ma using the combined data sets nonzonal models are required to satisfy the lava flow data but not those from sediments alone this is in part because the sediment data are much noisier than those from lavas but is also a consequence of the site distributions and the way that inclination data sample the geomagnetic field generated in the earth s core different average field configurations for normal and reverse polarity periods are consistent with the palaeomagnetic directions however the differences are insignificant relative to the uncertainty in the average field models thus previous inferences of non antipodal normal and reverse polarity field geometries will need to be re examined using recently collected high quality palaeomagnetic data our new models indicate that current global sediment and lava flow data sets combined do not permit the unambiguous detection of northern hemisphere flux lobes in the 0 5 ma time averaged field highlighting the need for the collection of additional high latitude palaeomagnetic data anomalous time averaged field structure is seen in the pacific hemisphere centred just south of hawaii the location of the anomaly coincides with heterogeneities in the lower mantle inferred from seismological data the seismic observations can be partly explained by lateral temperature variations however they also suggest the presence of lateral compositional variations and or the presence of partial melt the role of such heterogeneities in influencing the geomagnetic field observed at the earth s surface remains an unresolved issue requiring higher resolution time averaged geomagnetic field models along with the integration of future results from seismology mineral physics and numerical simulations

equatorial paleosecular variation of the geomagnetic field from 0 to 3 ma lavas from the galapagos islands abstract complete progressive thermal demagnetization of nearly 400 oriented samples from 58 sites lava flows from the galapagos islands of santa cruz san cristobal and floreana provide data for the statistical characterization of the time averaged geomagnetic field near the equator for the past few million years estimates of vgp dispersion due to paleosecular variation range from 9 2 to 11 8 depending on site selection criteria our preferred estimate based on 64 site vgps 51 accepted from this study and 13 from the 1971 study by cox is 11 4 95 confidence interval 10 2 13 0 consistent with previous estimates from the galapagos islands as well as paleosecular variation model g and confirming that angular dispersion of vgps near the equator is relatively low the mean direction is not significantly different from a geocentric axial dipole field when account is taken of southward plate motion over the galapagos hotspot preliminary paleointensity results from a comparison of the natural remanence with a total thermal remanence produced in a lab field of 15 t on a subset of 321 samples from 48 sites that had relatively small changes in magnetic susceptibility after laboratory heating suggest that the time averaged field was about 21 t or only two thirds the present strength in agreement with some other recent estimates

long term geometry of the geomagnetic field for the last five million years an updated secular variation database lee 1983 assembled more than two thousand paleomagnetic directional data from lava flows in 65 sampling sites with ages spanning the last 5 million years constable 1992 recently suggested that the virtual geomagnetic poles vgp derived from this data base have been preferentially located within two antipodal bands of longitude we have reanalyzed and updated the lee data base yielding a total of 3179 data from 86 distinct sites neither the total data set nor various subsets of the data unambiguously show any large and clear maxima in the longitude distribution of vgps the shape of the common site longitude distribution is far more striking with a pronounced and robust minimum close to the common site longitude and secondary maxima about 120 o away from it the former first order feature is equivalent to the far sided effect discovered by wilson 1970 and corresponds to a persistent axial quadrupole amounting to about 5 of the axial dipole as previously found by several authors the latter second order feature could correspond to the vgp biasing effect described by egbert 1992 although its observed amplitude appears larger than predicted part of this effect an asymmetry in the maxima may also correspond to wilson s 1971 right handed effect given only a small axial quadrupolar component and the very uneven actual site distribution the expected longitude distribution of vgps can be calculated this is found to be in good agreement with the paleomagnetic observations i e rather flat with a moderate maximum near 120oe this study emphasizes problems related to the unsatisfactory distribution of sites the amplitude and significance of other terms beyond the dominant axial dipole and significant axial quadrupole contribution remain to be assessed

paleomagnetism of miocene volcanics on sao tome paleosecular variation at the equator and a comparison to its latitudinal dependence over the last 5 myr a collection was made in january 2009 of 10 oriented samples from each of 54 sites in lavas on sao tome island nominal location 0 3o n 6 5o e some sites were affected by lightning leaving a total of 42 sites for analysis of paleosecular variation overall magnetic properties were excellent highly stable magnetizations carried by pseudo single domain magnetite after principal component analysis of progressive alternating field demagnetization data for the samples twenty two sites had normal polarity magnetizations d 0 6o i 8 3o 95 4 3o 53 1 and 20 had reverse magnetizations d 176 0o i 4 2o 95 7 3o 20 8 the directions are within 5 of antiparallel yielding a positive reversal test the combined data set of 42 site mean virtual geomagnetic poles converted to common normal polarity yields a pole position at 86 0 n 211 5oe a95 3 1o ar ar and k ar dating reveals that these rocks are miocene in age 5 11 ma old enough to allow northerly plate motion to help explain the slightly far sided pole position the between site dispersion in virtual geomagnetic poles was estimated as the angular standard deviation sb and equaled 11 4 with 95 confidence interval between 9 9 and 13 4 this article is protected by copyright all rights reserved

paleomagnetic directions and k ar dating of 0 to 1 ma lava flows from la guadeloupe island french west indies implications for time averaged field models twenty six lava flows spanning the last million years were sampled in la guadeloupe french west indies because of the lack of continuous volcano stratigraphic sections in la guadeloupe dating is necessary in order to describe the temporal evolution of the geomagnetic field in this time interval new k ar ages ranging from 50 ka to 1 ma have been obtained on andesites using the cassignol gillot technique at the universite paris sud institut de physique du globe de paris orsay laboratory additional flows with k ar ages obtained using the same dating technique were also sampled for paleomagnetic investigations more than 200 samples were analyzed using both alternating field af and thermal stepwise demagnetization techniques duplicate samplings of two flows at three different sites demonstrate that within flow dispersion is negligible for the andesitic lava flows sampled in this study direct comparison with an earlier paleomagnetic study performed on the island indicates that for the three investigated flows modern demagnetization techniques yield much better defined paleomagnetic directions the matuyama brunhes transition was recorded in a three flow section and is dated at 781 18 ka in good agreement with other recent radiometric age determinations the mean paleomagnetic pole calculated from the 23 normal polarity flows is indistinguishable from geographic north which implies that no significant persistent axial quadrupole term can be identified at this site for the last million years this result contradicts earlier results and has important implications for models of the time averaged field taf an occam algorithm was used to construct a taf model from the global volcanic database from the last 5 ma substitution of the mean direction calculated from the earlier study for the lesser antilles by our new mean value reduces the quadrupole term by more than 30 this effect which was produced by changing data from a single site demonstrates that older paleomagnetic sites may need to be reinvestigated furthermore it also highlights the limitations of taf models that can be inferred from paleomagnetic databases in their present state

paleomagnetic directions from mid latitude sites in the southern hemisphere argentina contribution to time averaged field models back arc volcanism located to the east of the andean cordillera was sampled in the argentina provinces of mendoza and neuquen for paleomagnetic time average field and paleosecular investigations the activity ranges from 2 ma to very recent time with a large variety of products from basalts to highly differentiated lavas after removal of sites affected by lightning those with 95 higher than 10 and combining of nearby sites displaying close directions we present new paleomagnetic results from 31 flows units belonging to two volcanic massifs the payun matru and the cerro nevado previous and new k ar age determinations constrain the volcanic activity of these massifs from 300 to 0 ka and from 1 9 to 0 9 ma respectively most paleomagnetic samples have nrm intensities between about 1 and 20 a m and depict progressive removal of magnetization components in a consistent fashion during stepwise af or thermal demagnetization nineteen flows yielded a normal direction declination 354 8 inclination 53 0 95 6 8 and 12 flows a reverse direction declination 181 0 inclination 52 3 95 5 9 the combined data yielded a mean direction declination 357 3 inclination 52 8 95 4 6 which is not statistically different from the axial dipole field g10 expected at this latitude 36 s the angular dispersion of virtual geomagnetic poles calculated from flows with normal directions asd 16 5 compares well with the observed value from global datasets for this site latitude but flows with reverse directions display a surprisingly low dispersion asd 12 5 since most reverse directions were sampled from flows ranging between 1 9 and 0 9 ma this can be interpreted as an interval of low paleomagnetic secular variation additional data also with accurate time constraints are obviously needed to better support this observation finally no convincing evidence for a complex time average field significantly different from the axial dipole can be supported by this study for the last 2 myr

palaeosecular variation in java and bawean islands indonesia during the brunhes chron summary a palaeomagnetic study has been conducted from indonesian lava flows and dykes sampling was concentrated to the merapi and merbabu volcanoes central java the bromo tengger volcanic complex the lurus volcano both east of java and the bawean island numerical dating indicates that the rock units sampled have ages that are well distributed within the brunhes chron only a few reverse polarity flows were probably emplaced during the late matuyama chron alternating field af and thermal demagnetization treatments were routinely used for all sites results from both methods were generally in good agreement demonstrating the reliability and the reproducibility of the palaeomagnetic determinations obtained from 36 independent sites the large dispersion of the directions and the age distribution indicate that a large spectrum of the secular variation has been sampled our best estimate of the mean brunhes field direction in java is characterized by a zero declination and an inclination anomaly of 4 7 with a 95 per cent confidence angle of 5 3 this value agrees with an axial dipolar field model or a model to which a persisting zonal quadrupolar term of a few per cent of the geocentric axial dipole is added this study adds new constraints to recent results which suggested that a large zone of negative inclination anomalies may have persisted in the southwestern pacific ocean over the past 500 kyr and possibly extended toward the eastern indian ocean the present results do not support such an extension they also suggest that the inclination anomaly may have varied over 100 kyr and that it was more pronounced in recent times

a map of the pacific geomagnetic anomaly during the brunhes chron abstract the persistence of an anomaly of the geomagnetic field in the central pacific ocean has been suggested by many authors however the amplitude and the extent of this feature remain poorly constrained due to insufficient spatial and temporal coverage of the volcanic database records from marine sediments are appropriate to document the long term behavior of the geomagnetic field we studied 11 piston cores from the central and southwestern pacific in order to document the anomaly during the past 800 kyr ten records were retained after applying selection criteria dealing with physical disturbances deformations and any possible sources of inclination errors the results have been integrated into a new data set for the pacific ocean and the eastern indian ocean which combines sedimentary and volcanic records a strong negative inclination anomaly 10 in the southwestern pacific is the main characteristic of the new map in contrast the sedimentary records from the hawaiian area do not indicate any stable feature but rather alternating positive and negative anomalies the new inclination map of the brunhes chron bears striking similarities with the configuration of the historical field particularly the presence of a negative anomaly centered in the eastern indian ocean and southwestern pacific ocean detailed records constraining the archeological period in the southwestern pacific and documenting the spatial extension of the anomaly are now needed to establish a direct link with the present field

palaeosecular variation recorded by 9 ka to 2 5 ma old lavas from martinique island new evidence for the la palma aborted reversal 617 ka ago

gps determined eastward sundaland motion with respect to eurasia confirmed by earthquakes slip vectors at sunda and philippine trenches abstract gps measurements acquired over southeast asia in 1994 and 1996 in the framework of the geodyssea program revealed that a large piece of continental lithosphere comprising the indochina peninsula sunda shelf and part of indonesia behaves as a rigid sundaland platelet a direct adjustment of velocity vectors obtained in a eurasian frame of reference shows that sundaland block is rotating clockwise with respect to eurasia around a pole of rotation located south of australia we present here an additional check of sundaland motion that uses earthquakes slip vectors at sunda and philippine trenches seven sites of the geodyssea network are close to the trenches and not separated from them by large active faults two at sumatra trench three at java trench and two at the philippine trench the difference between the vector at the station and the adjacent subducting plate vector defines the relative subduction motion and should thus be aligned with the subduction earthquake slip vectors we first derive a frame free solution that minimizes the upper plate or sundaland motion when corrected for australia eurasia and philippines eurasia nuvel1 a motion the misfit between gps and slip vectors azimuths is significant at 95 confidence indicating that the upper plate does not belong to eurasia we then examine the range of solutions compatible with the slip vectors azimuths and conclude that the minimum velocity of sundaland is a uniform 7 10 mm a eastward velocity however introducing the additional constraint of the fit of the geodyssea sites with the australian igs reference ones or tie with the ntus singapore station leads to a much narrower range of solutions we conclude that sundaland has an eastward velocity of about 10 mm a on its southern boundary increasing to 16 18 mm a on its northern boundary

10 000 years of explosive eruptions of merapi volcano central java archaeological and modern implications abstract stratigraphy and radiocarbon dating of pyroclastic deposits at merapi volcano central java reveals 10 000 years of explosive eruptions highlights include 1 construction of an old merapi stratovolcano to the height of the present cone or slightly higher our oldest age for an explosive eruption is 9630 60 14 c y b p construction of old merapi certainly began earlier 2 collapse s of old merapi that left a somma rim high on its eastern slope and sent one or more debris avalanche s down its southern and western flanks impoundment of kali progo to form an early lake borobudur at 3400 14 c y b p hints at a possible early collapse of merapi the latest somma forming collapse occurred 1900 14 c y b p the current cone new merapi began to grow soon thereafter 3 several large and many small buddhist and hindu temples were constructed in central java between 732 and 900 a d roughly 1400 1000 14 c y b p explosive merapi eruptions occurred before during and after temple construction some temples were destroyed and or buried soon after their construction and we suspect that this destruction contributed to an abrupt shift of power and organized society to east java in 928 a d other temples sites though were occupied by caretakers for several centuries longer 4 a partial collapse of new merapi occurred 14 c y b p eruptions 700 800 14 c y b p 12 14th century a d deposited ash on the floors of still occupied candi sambisari and candi kedulan we speculate but cannot prove that these eruptions were triggered by the same partial collapse of new merapi and that the eruptions in turn ended caretaker occupation at candi sambisari and candi kedulan a new or raised lake borobudur also existed during part or all of the 12 14th centuries probably impounded by deposits from merapi 5 relatively benign lava dome extrusion and dome collapse pyroclastic flows have dominated activity of the 20th century but explosive eruptions much larger than any of this century have occurred many times during merapi s history most recently during the 19th century are the relatively small eruptions of the 20th century a new style of open vent less hazardous activity that will persist for the foreseeable future or alternatively are they merely low level background activity that could be interrupted upon relatively short notice by much larger explosive eruptions the geologic record suggests the latter which would place several hundred thousand people at risk we know of no reliable method to forecast when an explosive eruption will interrupt the present interval of low level activity this conclusion has important implications for hazard evaluation

paleomagnetism of pleistocene volcanic rocks from pantelleria island sicily channel italy abstract a paleomagnetic investigation has been carried out on pleistocene volcanic rocks from pantelleria in the sicily channel this island is characterised by a bimodal volcanism of peralkaline rhyolite to trachyte and basalt composition the radiometric data indicate that volcanic activity started around 324 ka bp samples have been collected from 30 sites in 16 volcanic units spanning activity during the last 150 ka magnetic properties vary systematically with lithotype and indicate high ti titanomagnetite to magnetite as the main carriers of magnetisation stable characteristic remanent magnetisation chrm directions isolated by alternating fields af demagnetisation show normal polarity consistent with emplacement during the brunhes chron and vary within the paleosecular variation psv range however the inclinations are low as compared with the geocentric axial dipole gad inclination at pantelleria especially for volcanic units younger than 50 ka the mean chrm direction computed from 27 sites is d 358 8 i 46 9 k 30 95 5 2 and the inclination anomaly is i 8 1 both tectonic movements and the presence of large magnetic anomalies around the island of pantelleria fail to explain this low inclination which may therefore be related to a significant long lived non dipolar field contribution in the area over the past 150 kyr

persistently anomalous pacific geomagnetic fields a new average geomagnetic field model for the past 3kyr als3k helps bridge a large temporal sampling gap between historical models and more traditional paleo magnetic studies spanning the last 5 myr a quasi static feature seen historically in the central pacific has the oppo site sign in als3k its structure is similar to but of larger amplitude than that in the time averaged geomagnetic field for the last 5 myr anomalous geomagnetic fields exist be neath the pacific over timescales rangingfrom 10 2 10 6 years it is unlikely that bias over such long time scales arises from electromagnetic screening but conceivable that the lorentz force is influenced by long wavelength thermal variations and or localized regions of increased electrical conductiv ity associated with compositional anomalies and possibly partial melt this is consistent with recent seismic obser vations of the lower mantle

anisotropic paleosecular variation models implications for geomagnetic field observables abstract we present a family of statistical models for paleosecular variation psv of the geomagnetic field that are compatible with paleodirectional and paleointensity variations in lava flows sampling the last 5 ma and explore what paleomagnetic observables might be used to discriminate among the various family members we distinguish statistical models with axial anisotropy which provide a suitable description for an earth with homogeneous boundary conditions at the core mantle interface from those with more general anisotropy corresponding to geographically heterogeneous boundary conditions the models revise and extend earlier ones which are themselves descendants of cp88 devised by constable and parker constable c g parker r l 1988 statistics of the geomagnetic secular variation for the past 5 m y j geophys res 93 11569 11581 in cp88 secular variation is described by statistical variability of each gauss coefficient in a spherical harmonic description of the geomagnetic field with each coefficient treated as a normally distributed random variable the gauss coefficients of the non dipole part of the field exhibit isotropic variability and the variances are derived from the present field spatial power spectrum the dipole terms have a special status in cp88 with a non zero mean for the axial dipole and lower variance than predicted from the spatial power spectrum all non dipole terms have zero mean except the axial quadrupole cp88 is untenable for two reasons it fails to predict the observed geographic dependence of directional variability in the magnetic field and it grossly underpredicts the variance in paleointensity data the new models incorporate large variance in the axial dipole and in the non axial quadrupole gauss coefficients g21 and h21 the resulting variance in paleomagnetic observables depends only on latitude zonal models unless the variance in h21 is different from that in g21 non zonal models non zonal longitudinal variations in psv such as the flux lobes seen in the historical magnetic field are simulated using the non zonal models both the zonal and non zonal models fit summary statistics of the present dataset we investigate the influence of persistent non zonal influences in psv on various paleomagnetic observables it is shown that virtual geomagnetic pole vgp dispersion is rather insensitive to longitudinal variations in structure of psv and that inclination dispersion has the potential to be more informative given the right site distribution there is also the possibility of using paleointensity and geographic variations in the frequency of occurrence of excursional directions to identify appropriate psv models

persistent patterns in the geomagnetic field over the past 2 5 myr historical geomagnetic measurements covering the past 400 years reveal a symmetrical pattern of four relatively stationary flux concentrations lobes at the surface of the liquid core and regions of rapid change extending from the atlantic to the indian ocean1 palaeomagnetic data define a time average over several thousand years2 which might reflect the stationary parts of the present field but unfortunately the historical record is too short to provide a satisfactory average3 here we model palaeomagnetic directions from the past 2 5 myr using the same methods as for modern data4 and find the two northern lobes in the same position as today over arctic canada and siberia in southern regions by contrast the field appears to have been smoothed out as might be expected from the current rapid secular variation1 we propose that the present geomagnetic field morphology and pattern of secular variation have persisted for several million years as would occur if the solid mantle controls flow at the top of the core

analysis of the current field in the new yellow river entrance sea area a hydrographic and sand content survey was conducted in the new yellow river entrance sea area in september 1996 it is shown from the survey results that the tide in the entrance sea area belongs to irregular semidiurnal tide the current speed in front of the entrance is higher than those on either side of the entrance with that on the left side of the entrance being the lowest the current speed is higher in the deep water area than in the shallow water area and the current speed is vertically nonuniform with the surface one being mostly higher than the bottom one the sand content increases with increasing depth the sand transport direction at the river entrance is consistent with the runoff direction and that in other entrance sea area is in correspondence with the tidal current direction the sand dispersion range is as large as 500km 2

evidence from geoid data of a hotspot origin for the southern mascarene plateau and mascarene islands indian ocean a high resolution geoid map of the madagascar and mascarene basins is constructed from geos 3 and seasat satellite altimetric data with an accuracy of 0 7 m large positive anomalies are due to topographic highs and their regional compensation the deflection of the lithosphere under volcanic loads and its effect on the geoid are modeled for the southern mascarene plateau mauritius reunion and rodriguez islands assuming a purely elastic lithospheric model the effective flexural rigidity is estimated for the four zones rigidity varies from 1 10 21 to 2 10 23 n m increasing from north to south the highest rigidity occurs under reunion island and suggests a recent origin for the volcanism 3 5 ma the southern mascarene plateau shows the lowest rigidity suggesting a near ridge origin rodriguez island shows the same trend but in another tectonic framework the topographic and geoid swell is studied as an effect of a thermal mantle plume using a conductive model of lithospheric heating we confirm the assumption of hotspot migration for the origin of the southern mascarene plateau and the mascarene islands

merapi central java indonesia an outline of the structural and magmatological evolution with a special emphasis to the major pyroclastic events abstract merapi volcano in the central part of java is regarded as the most active and most dangerous volcano in indonesia on the basis of field studies and geochronological data its history is divided into four periods ancient middle recent and modern merapi according to our preliminary age data the ancient period may have begun around 40 000 y bp and lasted until 14 000 y bp when the middle period begun the recent period begun around 2200 y bp and was replaced by the modern period after the eruption of 1786 during the middle merapi stage a mount st helens type edifice collapse occurred our data suggest that his event is younger than 6700 y bp and older than 2200 y bp during the recent merapi stage violent magmatic to phreatomagmatic eruptions twice interrupted the growth of the volcano the older gumuk phreatoplinian deposits cover the entire cone charcoal found within these deposits gave 14c ages of 2200 and 1470 y bp the overlying sambisari ash deposits were emplaced by violent pyroclastic surges directed towards the south i e to the present location of the town of yogyakarta they buried the shivaitic temple of sambisari at the start of the 15th century modern merapi is characterised by the persistent growth of a summit dome periodically interrupted by partial or total collapse of the dome to generate frequent merapi type nuees ardentes blocks and ash flows and associated surges or more exceptionally fall back st vincent type nuees ardentes scoria flows in contrast previous stages were characterised by effusion of long lava flows alternating with violent explosive phases generating essentially st vincent type nuees ardentes merapi lavas are calc alkaline with a compositional range between 49 5 and 60 5 wt sio2 moreover high k basaltic andesites represent about 90 of merapi lavas disequilibrium features are common in the mineralogical assemblage plagioclase orthopyroxene clinopyroxene olivine amphibole titanomagnetite scarce alkali feldspar macroscopic and microscopic textural heterogeneities are related to magma mixing that may have buffered the compositions of lavas and caused the restricted range of compositions our studies of past activity at merapi provide some insights into future activity and to related volcanic hazards it is clear that merapi has the potential of eruptions much more powerful than observed during the historic period

a detailed tephrostratigraphic framework at merapi volcano central java indonesia implications for eruption predictions and hazard assessment abstract the upper part of merapi volcano is characterised by a summit crater breached to the southwest and occupied by an unstable lava dome episodes of dome growth have usually resulted in partial dome collapse events that have generated pyroclastic flows in recent years these have inundated the southwestern lower flanks and in the past other sectors of the volcano have been affected this recent pattern of volcanic activity since the 1880s is well known from direct observations in this study the eruptive record extending back to mid holocene times is deduced from the stratigraphy and chronology of volcaniclastic deposits this record forms an important basis from which the average periodicity of eruptions at merapi and the severity and the extent of future eruptions can be assessed the most complete record of eruptive activity from merapi volcano is found in the deeply dissected volcaniclastic fans of the lower flanks here successions of numerous coarse ash and lapilli beds are interbedded with andic soil material thin pyroclastic flow and surge deposits and a hitherto unrecognised inter regional tephra marker bed many of these tephra beds can be reliably correlated around the flanks of merapi volcano and can be distinguished on the basis of physical appearance and stratigraphic association these formations can be reliably used to correlate units around the flanks of the volcano in the deeper parts of this stratigraphic succession pyroclastic products originating from the adjacent merbabu volcano are also recognised and provide evidence of concurrent activity at both volcanoes it is clear from the stratigraphic record that relatively large magnitude eruptive volume to 3 7 108 m3 eruptions have been generated at merapi volcano these eruptive deposits are typically produced from pyroclastic flow and or pyroclastic fall events most of the fall beds are characterised by single to multiple upward fining pumiceous or scoriaeous units sometimes overlain by ash cloud surge beds isopach maps have been produced for several of these tephra beds and most of them show either west southwest south and southeast dispersion except for the ngrangkah tephra which shows no systematic direction or distribution sub plinian or plinian to vulcanian open vent styles of activity appear to have been common at merapi volcano such eruptive episodes are in contrast with the style of activity that had been occurring at merapi volcano in the last two centuries clearly the range of eruptive events likely to be experienced at merapi volcano needs to be more critically considered in any existing or future hazard assessment and contingency planning programme

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