multi parametric climatological analysis associated with global significant volcanic eruptions during 2002 2017 in this work we search for physical and chemical climatological anomalies preceding major volcanic explosive eruptions mostly vei volcanic explosivity index 4 occurred from 2002 to 2017 by applying two specific algorithms i e capri and means the former algorithm has been already used for a multi climatological analysis of the amatrice norcia 2016 2017 earthquake preparatory phase piscini et al in pure appl geophys 174 3673 3688 2017 here we analyse some climatological parameters for a three month period before each volcanic explosive eruption then we compare the behavior with the typical one of the past the analysis is applied to an area with dimensions comparable to the volcano crater because it is the increase of the magmatic camera activity that in turn can cause a temperature increase whose evidence could be detected at the surface slezin in j volcanol geotherm res 122 1 2 7 50 2003 while the use of a larger area would provide a greater probability of occurrence of other events e g other volcano eruption meteorological storms etcetera therefore a smaller area of study reduces the risk to get false alarms in particular we considered thermal skin temperature skt and total water vapour content tcwv from ecmwf european centre and aerosol optical thickness aot sulphur dioxide so2 and atmospheric dimethylsulphide dms are obtained from nasa merra 2 global modeling and assimilation data archive the latter compound was added in the analysis to check the validity of the method since we did not expect significant anomalies from this parameter the models above described are used for their temporal spatial completeness allowing performing time series analyses and for a real time monitoring on a global scale by simultaneous analysis we found for almost all volcanic eruptions some anomalies in about all analyzed parameters that precede by 75 days to 20 days the explosion these anomalies are not always simultaneous but we find an interesting synchronicity that probably reveals a correlation among the different datasets in addition the agung volcano which has recently started an eruptive activity 25 november 2017 without reaching a vei4 explosion has also been investigated the data related to this volcano present a small number of anomalies much lower than all attributed to the other analyzed explosive volcanoes and this is in high agreement with the low explosive nature of the agung volcano eruption we find that the occurrence of thermal anomalies typically preceding stratovolcano caldera eruptions seems to take place some days after so2 emissions the climatological anomalies that precede eruptions at high latitudes usually surround the volcano in a wider area outside the volcanic edifice we verify that the number of positive anomalies is systematically greater in the year that precedes the investigated eruption with respect to a quiet year of comparison with accuracy from 91 to 100 suggesting that the applied methods detected climatological anomalies likely related to imminent volcanic eruptions

proving the age of a paleomagnetic pole the case of the ntonya ring structure malawi geological application of paleomagnetic data generally relies on equating radiometric or biostratigraphic age with that of the characteristic remanence yet the standard of proof of paleomagnetic age is often unsatisfactory and is extremely difficult to achieve where contact tests or conglomerate tests are unavailable in this study of the ntonya igneous ring complex the thermoremanent trm origin of one component of natural remanent magnetization nrm is confirmed by paleointensity determination and its carrier is identified mineralogically and the age of this trm is estimated by extrapolation from 40ar 39ar mineral ages the characteristic remanence in the ntonya ring structure which was determined by briden 1968 as d 311 i 43 95 1 9 pole 28 n 15 w is shown to be a trm in single domain pseudo single domain magnetite acquired in a field of approximately half the present geomagnetic field strength the 40ar 39ar mineral ages biotites 471 5 7 ma hornblendes 510 7 ma and the high precision of the paleomagnetic directions combine in a model of steady cooling 4 6 m y 1 that leads us to the conclusion that the thermoremanence was acquired over approximately 13 m y 522 13 m y ago in passing it is shown that the isothermal irm component that dominates the remanence is carried by multidomain magnetite the study shows how remanence age may be determined with precision in the absence of geological constraints it makes the ntonya pole a key point in the african and gondwanan apparent polar wander path correlating with middle cambrian glacial deposits in the sahara at about 80 s paleolatitude

geomagnetism and age study of tyrrhenian seamounts summary we discuss the results of measurements of the magnetic anomaly field of several seamounts located on the ocean floor and on the bordering continental slopes of the tyrrhenian sea this geomagnetic study of seamounts is based on joint 3 d analyses of the magnetic anomalies and the bathymetry on measurements of the magnetic properties of rock specimens and on geochronological data the 3 d analysis of the magnetic anomalies of large volcanoes emplaced in the small oceanic basins of vavilov and marsili serves to shed light on the spatial distribution of the magnetized bodies by eliminating the effect of topography a new magnetic anomaly map of the southern tyrrhenian sea is obtained by the merging of shipborne local data measured on topographic highs with data of regional type the study of the magnetic patterns and age of the oceanic seamounts indicates that the volcanic activity mainly developed prior to chron c2 2 02 ma bp on the vavilov and magnaghi edifices vavilov basin whereas the volcanism of a big oceanic seamount emplaced in the small basin of marsili took place mainly during the period of chron c1 0 0 78 ma bp

lightning associated with the 1992 eruptions of crater peak mount spurr volcano alaska abstract lightning occurred associated with the ash clouds of all three eruptions of mt spurr volcano in 1992 lightning was detected on seismograms as simultaneous spikes and simultaneous gain ranging a feature that normally lowers the gain at a station when the signal level begins to saturate spikes had typical durations of 0 04 0 05 s using uniform criteria we found 28 lightning flashes in the june 27th eruption 29 in the august 18th eruption and three in the september 17th eruption we measured peak voltages on station rso 94 km ssw to determine the relative strengths of lightning and found that the august lightning was strongest june weakest and september intermediate based on relative signal strengths at different stations we found evidence for different lightning geometries between the june and august eruptions during which prevailing winds blew the ash clouds to the north and east respectively for all three eruptions the first lightning was recorded 21 26 min after the onset of the eruption suggesting that charge separation occurred in the convecting cloud rather than at the vent data recorded by a bureau of land management lightning detection system for the august eruption showed negative polarities for the first 12 recorded flashes and a positive polarity for the last this suggests a charge separation based on particle size in which negative charge is found for larger particles which fall first and positive charge remains on smaller particles which remain suspended longer all three eruptions had similar durations of 3 5 4 h and tephra volumes of 44 56 million cubic meters the august eruption however produced stronger volcanic tremor 30 cm2 reduced displacement as compared with 16 cm2 for june and greater gas 400 120 kt so2 for august and 200 60 kt for june thus lightning strength correlates with both tremor amplitude and magmatic gas content the august eruption occurred during the lightest winds so the ash cloud and charge separation were vertically oriented and favored cloud to ground lightning the september eruption occurred during the coldest and driest atmospheric conditions which may explain the small amount of lightning in general volcanic lightning is important because it can help confirm that explosive eruptions are in progress although the value of the information may be limited by the long delay from eruption onset to first lightning and the variability of eruptive and atmospheric conditions

crustal features along a w e tyrrhenian transect from sardinia to campania margins central mediterranean abstract the tyrrhenian sea is a neogene back arc basin formed by continental extension at the rear of the eastward migrating apennine subduction system its central part generated from tortonian to pliocene includes the sardinia rifted margin to the west an area with large volcanoes in the deep central sector and the campania rifted margin to the east a reprocessing of some 2000 km of mcs lines a new swath bathymetric map and a review of previous geological and geophysical data allow to analyse the nature and distribution of continental vs oceanic crust in this area which evolved in a short time span the central portion of the southern tyrrhenian sea is characterized by moho at about 10 km depth north of magnghi and vavilov smts this thinned crustal domain include a wide continent ocean transition with the occurrence of extensional allochthons and of serpenitinzed sub continental mantle recalling other well known rifted margins as the iberia one sectors floored by oceanic crust should occur mainly in the southern part of the study area but they do not appear related to discrete spreading ridges the continent ocean boundary cannot be drawn unequivocally in the area due also to the occurrence of widespread and huge magmatic manifestations not related to oceanic spreading these portions of the southern tyrrhenian sea represents therefore a complex oceanic back arc basin surrounded by magma rich rifted continental margins the abundant igneous manifestations and the very high stretching rates observed in the area may be related to the fact that the present tyrrhenian area was occupied by an orogenic domain affected by shortening until middle miocene times which is just before the late miocene onset of back arc extension the lithosphere in the region had then to be rheologically weak abundant generation and ascent of magmas mostly of ocean island basalt type was favoured by the large lithospheric permeability induced by strong extensional deformations

paleomagnetism of the sierra de las animas complex southern uruguay its implications in the assembly of western gondwana global paleogeographies in the neoproterozoic are poorly known in particular the assembly of gondwana at the end of the proterozoic is controversial in order to constrain the kinematic evolution of the rio de la plata craton a paleomagnetic study was carried out in the vendian to cambrian sierra de las animas magmatic complex exposed in southeastern uruguay 34 7 s 55 3 w one hundred and forty seven samples from 23 sites were studied these included two sites on the vendian glaciogenic sediments of the playa hermosa formation after stepwise af and thermal cleaning a characteristic remanence was isolated at several sites according to the available isotopic data for the complex and the correlation between remanence directions and lithologic type and age two paleomagnetic poles were computed for the sierra de las animas complex sa1 338 1 e 5 9 n dp 19 6 dm 26 7 n 7 sites mean declination 44 5 mean inclination 58 0 95 18 1 with a likely age around 520 ma shows a distribution of vgps that suggests a remanence acquisition that spanned a long time during a period of fast apparent polar wander for gondwana sa2 250 9 e 16 9 s dp 15 9 dm 21 5 n 6 sites mean declination 95 3 mean inclination 58 5 95 14 5 corresponds to a likely age around 550 ma and falls close to a pole of similar age from the congo craton this suggests that the rio de la plata craton was at that time part of gondwana and confirms previous postulates that a single apwp can be defined for the supercontinent since 550 ma a preliminary mean geomagnetic pole obtained from the playa hermosa formation ph 198 4 e 43 0 s dp 8 6 dm 16 0 n 6 samples mean declination 226 0 mean inclination 24 2 95 15 0 is consistent with a previous pole of 595 ma from the campo alegre ca lavas and may suggest if confirmed that the glaciogenic deposits were produced at low to intermediate latitudes despite high uncertainties a new speculative model on the process of assembly of gondwana is proposed

limited true polar wander as evidence that earth s nonhydrostatic shape is persistently triaxial earth s spin axis follows the maximum moment of inertia axis of mantle convection with some delay due to adjustment of the rotational bulge here we compute this axis for geodynamic models based on subduction history assuming constant slab sinking speed with another contribution due to thermochemical piles for a wide range of parameters a large shift of 90 degrees is predicted around 80 90 ma it can be largely attributed to a change in circum pacific subduction from predominantly in the north and south towards east and west actual amounts of true polar wander are much smaller pointing towards additional inertia tensor contributions possibly due to slabs in the lowermost mantle below both polar regions these slabs would have been subducted before 150 ma when plate motions in the panthalassa basin are largely unknown matching predicted and observed true polar wander can serve at constraining such plate motions

new paleomagnetic results from the ediacaran doushantuo formation in south china and their paleogeographic implications abstract a new paleomagnetic pole is obtained from the top of member 3 of the doushantuo formation in the jiulongwan section of the yangtze gorges area in south china a total of 191 samples from 23 sites were collected and subjected to stepwise alternating field af and thermal demagnetization after the removal of a soft component sc of viscous magnetic remanence acquired in present geomagnetic field a high temperature component hc likely carried by magnetite was isolated the hc includes vectors from 147 samples using principal component analysis and arc constraints from 44 samples using remagnetization great circle analysis both the vectors only and the combined vectors and arc constraints of the hc passed a reversal test this is the first ediacaran paleomagnetic remanence from the south china block scb that passes a reversal test and it is interpreted as a primary remanence the hc vectors were thus used to calculate the paleomagnetic pole and in combination with arc constraints were used for polarity interpretation the vectors give a mean direction of d 75 2 i 41 0 95 2 5 n 147 after bedding correction and a corresponding paleomagnetic pole at 23 9 n 187 0 e dm dp 3 0 1 8 this pole differs significantly from previously published results of the doushantuo formation which may have been subjected to paleozoic remagnetization our results provide a 23 5 1 8 n paleolatitude for the yangtze gorges area of the scb and suggest several alternative paleogeographic options for the ediacaran cambrian amalgamation of east gondwana depending on chronostratigraphic correlations

a large self potential anomaly on unzen volcano shimabara peninsula kyushu island japan self potential sp observation was carried out in the summit area of unzen one of the active volcanoes in kyushu island japan we found a positive sp anomaly in the vicinity of the newly extruded lava dome the potential difference across the anomaly exceeds 1000mv per 500m streaming potentials associated with subsurface hydrothermal convection seem to be the most reasonable mechanism for the positive anomaly in association with the first emergence of the lava dome a sharp increase of sp was detected which is considered to be a result of the growth of the hydro thermal system

testing the occurrence of late jurassic true polar wander using the la negra volcanics of northern chile abstract true polar wander tpw is the reorientation of the crust mantle system driven by the redistribution of masses in the mantle and on the earth s surface in the ideal case characterization of tpw requires paleomagnetic constraints on the motion of all major plates and independent reconstructions of relative plate positions while such complete datasets are absent for pre mesozoic tpw inferences due to the absence of oceanic plates they are available for the late jurassic 165 145 ma monster shift a 30 amplitude proposed tpw event here we perform paleomagnetic sampling and ar ar geochronology on the la negra volcanics of northern chile producing two new paleomagnetic poles with ages 165 8 1 8 ma 1 84 3 n 0 9 e 95 7 6 n 28 and 152 8 0 8 ma 84 5 n 256 4 e 95 10 8 n 18 by combining these data with other recently published results we compute a net lithospheric rotation of 25 3 7 3 1 at a mean rate of 1 21 0 35 my 1 between 170 and 145 ma with a peak rate of 1 46 0 65 my 1 between 160 and 145 ma these rates are consistent with inferences from the pacific plate implying true whole lithosphere rotation given coherent motion involving the entire lithosphere we conclude that the earth underwent rapid tpw between approximately 165 and 145 ma potentially driven by the cessation of subduction along the western north american margin

reply to comment on pervasive remagnetization of detrital zircon host rocks in the jack hills western australia and implications for records of the early dynamo determining the history of earth s dynamo prior to the oldest known well preserved rock record is one of the ultimate challenges in the field of paleomagnetism tarduno et al 2015 argued that detrital zircons contain records of an active dynamo dating back to 4 2 billion years ago ga 700 million years earlier than previously identified biggin et al 2011 and tarduno et al 2010 however this extraordinary claim requires evidence that the zircons have not been remagnetized during the intervening time since their formation weiss et al 2015 argued that such evidence had yet to be provided a conclusion that we find still firmly holds

a search for elf vlf emissions induced by earthquakes as observed in the ionosphere by the de 2 satellite satellite observations of elf vlf wave activity by groups from both the soviet union and france have indicated the possibility of elf vlf radio emissions generated by earthquakes however an examination of elf vlf wave data from the low altitude apogee 1300 km perigee 300 km inclination 90 dynamics explorer 2 de 2 satellite showed no clearly distinguishable elf vlf signatures associated with earthquakes after an initial survey of approximately 5000 de 2 orbits elf and vlf wave data were selected from 63 satellite orbits called earthquake orbits in which the ionospheric footprint of the de 2 crossed the geographic latitude while passing within 20 geographic longitude of the epicenters of imminent or recent earthquakes of magnitude 5 0 elf vlf noise measured near the epicenters was analyzed for occurrence rates and average spectra as well as for peak and mean electric field intensities in three spectrometers covering a frequency range of 4 hz 512 khz in 20 channels the same analysis was then repeated for 61 carefully matched control orbits when there were no imminent or recent earthquakes within 20 geographic longitude or within 10 geographic latitude of the satellite footprint these control orbits resembled the earthquake orbits with respect to latitude longitude local time and geomagnetic index kp sixty three percent of the earthquake orbits showed an elf or vlf emission above 10 v m in at least one of the 20 channels when the satellite passed near an epicenter the same analysis performed on control orbit data yielded a 62 chance of observing similar emissions moreover these results did not change when geomagnetic latitudes instead of geographic latitudes were considered further analyses failed to indicate any significant differences between the elf vlf noise measured on earthquake orbits and control orbits with regard to the general nature of the spectra the frequency of occurrence of emissions and peak and mean values of the electric field of the emissions

magnetic reversal frequency and apparent polar wander of the siberian platform in the earliest palaeozoic inferred from the khorbusuonka river section northeastern siberia summary marly limestones that crop out along the khorbusuonka river northeastern siberian platform define a well dated lower and middle cambrian sequence which was sampled for magnetostratigraphy in the upper part of the section from the uppermost lower cambrian toyonian stage to the middle cambrian amgan and mayan stages thermal demagnetization isolates two magnetic components carried either by magnetite haematite or both the first is parallel to the recent geomagnetic field at the site and is removed in the low to middle temperature range the second component is isolated at higher temperatures and has dual magnetic polarities this component yields a positive but partial since we consider only two sites fold test with other middle cambrian data previously obtained from the distant kulumbe river section and was probably acquired during sedimentation or at an early stage of diagenesis it records a very high magnetic reversal frequency of at least six to eight reversals per myr during the entire middle cambrian assuming a 10 myr duration for this epoch a much more complex palaeomagnetic behaviour is observed within the upper tommotian lower atdabanian lower cambrian part of the khorbusuonka section demagnetization diagrams show large overlaps between magnetic components which prevents the isolation of a clear magnetic component at high temperatures analysis of these overlaps is however consistent with the existence of an ill determined primary magnetic direction for the lower cambrian which is very different from that isolated in the middle cambrian although still in need of further confirmation the possibility that a large drift in siberian apparent polar wander occurred over a rather short time during the lower cambrian appears to be supported by our data

rapid early cambrian rotation of gondwana based on the history of mesozoic cenozoic plate motions as well as simple dynamical considerations a speed limit for tectonic plates has been suggested at 20 cm yr previous paleomagnetic data from the early cambrian of gondwana are confl icting but generally imply rapid motions approaching that limit herein we describe results from a continuous paleomagnetic sampling of lower to middle cambrian strata from the amadeus basin central australia we fi characteristic remanence directions that show an 60 declination shift through the section assuming a tectonically assembled gondwana supercontinent by early cambrian time this large vertical axis rotation of its australian sector corresponds to an equally large translation across paleolatitudes for its brazilian and west african sectors analysis of all high quality paleomagnetic data from gondwana both confi rms and constrains the 60 rotation to have occurred toward the end of early cambrian time at rates exceeding 16 12 8 cm yr these observations suggest that either nonuniformitarian plate tectonics or an episode of rapid true polar wander occurred during the cambrian explosion of animal life

resistivity and self potential changes associated with volcanic activity the july 8 2000 miyake jima eruption japan abstract the miyake jima volcano abruptly erupted on july 8 2000 after 17 years of quiet and gave birth to a crater 1 km in diameter and 250 m deep this expected unrest was monitored during the years 1995 2000 by electromagnetic methods including dc resistivity measurements and self potential sp surveys beneath the 2500 yr old hatcho taira summit caldera audio magnetotelluric soundings made in 1997 98 identified a conductive medium 200 500 m thick within the 50 m isoline located at a few hundred metres depth it was associated with the active steady state hydrothermal system centred close to the 1940 cone and extending southward a dc resistivity meter set in a schlumberger array with 600 1000 and 1400 m long injection lines evidenced strong resistivity changes between september 1999 and july 3 2000 in the vicinity of the newly formed crater the apparent resistivity has reached about three times its initial values on the 1400 m long line and has lowered to about 20 on the 600 m line just prior to the july 8 2000 eruption sp mapping made inside the summit hatcho taira caldera revealed negative anomalies where positive ones had occurred during the previous tens of years the largest negative anomaly 225 mv in amplitude mainly took place above the 1940 cone which collapsed in the crater formation a permanent 1 km long sp line across the caldera suggests accelerating changes during the 3 months preceding the eruption on a larger scale the comparison between 1995 and 2000 surveys has shown a global increase of the hydrothermal activity beneath the volcano its source could have been 250 m to the south of the crater these observations suggest that the hydrothermal system was slowly disturbed in the months preceding the eruption while drastic changes have occurred during the 2 weeks before the summit collapse when tectonic and volcanic swarms have appeared

signals recorded by demeter satellite over active volcanoes during the period 2004 august 2007 december more than 1500 volcanoes can potentially enter into eruption but only some tens of them are equipped with monitoring networks most of volcanic eruptions can be predicted by the integration of continuous real time observations data processing and analysing in the electromagnetic field em a long history of ground observations shows that electric magnetic and electromagnetic signals may precede and accompany volcanic eruptions the possibility that volcanic eruptions may also be preceded by transient electromagnetic anomalies in the ionosphere can be analysed on the basis of demeter mission this microsatellite launched by cnes in 2004 covers 14 orbits per day over seismic and volcanic regions of the earth two complementary and systematic studies are presented over the time period 2004 august 2007 december the first study shows that three types of electric and or magnetic anomalies can be observed in the time window of 30 d preceding an eruption and 15 d after on the 74 eruptions occurring on 50 volcanoes under consideration 48 anomalies are recognised along 30 eruptions 41 per cent of the eruptions were accompanied by em signals on board of the satellite 81 per cent of the anomalies are observed before the eruptions for the period 30 d 15 d and 69 per cent for the period 15 d 15 d in the second study the anomalies above three nearby volcanoes lopevi ambrym and aoba are systematically looked for all orbits between 2004 august and 2006 december anomalies are only observed during periods of larger activity on each of them taking into account that no anomaly is observed a long time before an eruption on can allocate the anomalies to each volcano although the database is still limited the study shows that volcanic activity may be preceded by em perturbations of the ionosphere

spacecraft observations of electromagnetic perturbations connected with seismic activity 1 results of a statistical study of intensity of vlf electromagnetic waves observed in the vicinity of earthquakes are presented a unique set of data obtained by the micro satellite demeter altitude of about 700 km nearly sun synchronous orbit and a robust two step data processing has been used in the first step all the measured data are used to construct a map of electromagnetic emissions containing a statistical description of wave intensity at a given point of the satellite orbit under given conditions in the second step the intensity measured close to earthquakes is analyzed using the statistical distribution of background intensity obtained in the first step the changes of wave intensity caused by seismic activity are investigated and their statistical significance is evaluated altogether more than 2 5 years of satellite data have been analyzed and about 9000 earthquakes with magnitudes larger than or equal to 4 8 that occurred all over the world during the analyzed period have been included in the study it is shown that during the night there is a statistically significant decrease by 4 6 db of the measured wave intensity shortly 0 4 hours before an intense surface depth less than or equal to 40 km earthquake

paleozoic terranes of eastern australia and the drift history of gondwana abstract critical assessment of paleozoic paleomagnetic results from australia shows that paleopoles from locations on the main craton and in the various terranes of the tasman fold belt of eastern australia follow the same path since 400 ma for the lachlan and thomson superterranes but not until 250 ma or younger for the new england superterrane most of the paleopoles from the tasman fold belt are derived from the lolworth ravenswood terrane of the thomson superterrane and the molong monaro terrane of the lachlan superterrane consideration of the paleomagnetic data and geological constraints suggests that these terranes were amalgamated with cratonic australia by the late early devonian the lolworth ravenswood terrane is interpreted to have undergone a 90 clockwise rotation between 425 and 380 ma although the tamworth terrane of the western new england superterrane is thought to have amalgamated with the lachlan superterrane by the late carboniferous geological syntheses suggest that movements between these regions may have persisted until the middle triassic this view is supported by the available paleomagnetic data with these constraints an apparent polar wander path for gondwana during the paleozoic has been constructed after review of the gondwana paleomagnetic data the drift history of gondwana with respect to laurentia and baltica during the paleozoic is shown in a series of paleogeographic maps

magnetic interpretation related to geo magnetic provinces the italian case history abstract a comparison of the results obtained from the geophysical interpretation with the available information regarding the italian geological situation permitted us to establish our so called geo magnetic provinces the relationship between the magnetic characteristics and the tectonic evolution permitted the identification of each of the four following provinces that exist inside the global tectonic confines 1 1 the sardo corso block which represents the eastern boundary of stable europe this province is characterized by medium wavelength low amplitude anomalies that originate in an outcropping basement hercynian granites s l 2 2 the orogenic belt which constitutes the double alps apennines system from a magnetic standpoint this system is characterized by short wavelength low amplitude anomalies that are due to a paleozoic outcropping and or buried acid crystalline basement these anomalies are found to overlie long wavelength medium amplitude regional anomalies that are related to a deep apenninic basement central northern apennines 3 3 the foreland area which occurs from sicily hyblean plateau and apulia northwards to ancona and the po plain this area is characterized by a crystalline basement which is typically differentiated from the standpoint of basicity 4 4 the rifting zone which is represented by the part of the tyrrhenian sea lying south of the 41st parallel discontinuity the ionian abyssal plain and the pantelleria and linosa troughs in the sicily channel the main characteristic of this province is its extreme basicity differentiation in the crystalline basement which is induced by the geochemical processes connected with the deep geodynamic events these phenomena do not permit the correlation of the semioceanic basement of the rifting zone with the continental basement by means of interactive modeling a structural tectonic picture of the basement of the various italian geo magnetic provinces has been obtained the main result was found to be that the orogenic belt basement is undergoing intense tectonic compression and overlies the structural highs of the foreland area which mainly show tensive events

revisiting the paleomagnetism of the neoarchean uaua mafic dyke swarm brazil implications for archean supercratons abstract the original connections of archean cratons are becoming traceable due to an increasing amount of paleomagnetic data and refined magmatic barcodes the uaua block of the northern sao francisco craton may represent a fragment of a major archean craton here we report new paleomagnetic data from the 2 62 ga uaua tholeiitic mafic dyke swarm of the uaua block in the northern sao francisco craton eastern brazil our paleomagnetic results confirm the earlier results for these units but our interpretation differs we suggest that the obtained characteristic remanent magnetization for the 2 62 ga swarm is of primary origin supported by a provisionally positive baked contact test the corresponding paleomagnetic pole 25 2 n 330 5 e a95 8 1 n 20 takes the present northern part of the sao francisco craton to moderate latitudes based on the comparison of the paleolatitudes of cratons with high quality paleomagnetic data and magmatic barcodes we suggest that the northern part of the sao francisco craton could have been part of the proposed supervaalbara supercraton during the archean supervaalbara is proposed as including but not limited to the part of the sao francisco craton as well as the superior wyoming kola karelia zimbabwe kaapvaal tanzania yilgarn and pilbara cratons

magnetic and electric field observations during the 2000 activity of miyake jima volcano central japan magnetic and electric field variations associated with the 2000 eruption of miyake jima volcano are summarized for about 1 week prior to the july 8 phreatic explosion significant changes in the total intensity were observed at a few stations which indicated uprising of a demagnetized area from a depth of 2 km towards the summit this nonmagnetic source can be regarded as a vacant space itself electric and magnetic field variations were observed simultaneously associated with the tilt step event which was the abrupt v50 s inflation at a few km depth within the volcano followed by gradual recovery vseveral hours the electric field is ascribed to the electrokinetic effect most probably due to forced injection of fluids from the source while the magnetic field to the piezomagnetic effect due to increased pressure large magnetic variations amounting to a few tens of nt were observed at several stations since july 8 and they turned almost flat after the august 18 largest eruption magnetic changes are explained mostly by the vanishing of magnetic mass in the summit and additionally by the thermal demagnetization at a rather shallow depth a large increase in the self potential by 130 mv was also observed near the summit caldera associated with the august 18 eruption which suggests that the hydrothermal circulation system sustained within the volcano for the past more than 10 years was destroyed by this eruption 9 2002 published by elsevier science b v

structural pattern and co2 ch4 degassing of ustica island southern tyrrhenian basin brittle tectonics and ground degassing including fracture field soil gas and exhalation flux analyses of co2 and ch4 were studied at ustica island a pleistocene volcanic complex in the southern tyrrhenian sea the mesoscopic fracture pattern perfectly fits an e w trending left lateral strike slip master fault in agreement with the main morpho structural submarine alignment including ustica island and anchise seamount along the sw ne high angle normal arso fault geological evidence of reactivation with different kinematics left to right lateral displacements was recognised major co2 and ch4 degassing with fluxes up to 93 750 and 20 t km 2 a 1 respectively and soil gas concentrations of 11 3 and 5 7 ppm occur over the arso fault although this fault is mapped just in the sw sector of the island soil gas co2 anomalies point out its clear continuation up to the ne margin of the island these data together with those of previous geophysical and geochemical results from off shore ustica suggest that the arso fault is the local evidence of a more important active gas bearing structure this tectonic feature is interpreted as a reactivation of a preexistent sw ne trend inherited as a second order structure of the e w deep shear zone the reactivation is related to the interplay among different structures of the southern tyrrhenian basin

paleomagnetism of a well dated marine succession in south china a possible late cambrian true polar wander tpw abstract the cambrian true polar wander tpw hypothesis remains controversial largely because of the uncertainties in the quality and or fidelity of the paleomagnetic data as well as their chronological control testing the tpw hypothesis requires high quality paleomagnetic data of sufficient spatial and temporal resolutions here we present paleomagnetic results of a continuous cambrian shallow marine succession from south china where available detailed biostratigraphy provides exceptional chronological constraints forty three sites of paleomagnetic samples were collected from this limestone dominated succession stepwise thermal demagnetization generally reveals three component magnetizations low and intermediate temperature components can be cleaned by 330 c and the high temperature component htc was isolated typically from 350 to 450 c a positive fold test and the presence of reversed polarity in the strata together with rock magnetic data as well as the scanning electron microscopic sem and transmission electron microscopic tem results collectively suggest that the htcs are likely primary a directional shift of the htcs occurs between the lower middle cambrian and the upper cambrian strata in the succession and is tentatively interpreted to indicate a 57 polar wander from 500 5 to 494 ma because the rate of polar wander is too fast to be a tectonic origin this polar wander is interpreted to represent a late cambrian tpw this tpw appears coeval with the steptoean positive carbon isotope excursion spice and the major trilobite mass extinctions suggesting a potential link between the tpw and the late cambrian biotic and climatic changes because the proposed tpw event is exceptionally well dated it should be testable through examination of other worldwide sections

volcanomagnetic signals associated with the 2001 flank eruption of mt etna italy 1 geomagnetic changes were observed during the 2001 flank eruption at mt etna after differential magnetic fields were filtered from the seasonal thermic noise by using temperature data we recognized three stages in the total intensity changes related to different volcanic events a rapid variation of 4 nt associated with july 12 seismic swarm recorded beneath the summit craters b step like variation of 7 nt occurring during the quick propagation of fractures in the south flank which was followed by the off set of 2 nt before july 17 when the lava outpoured from fissures and c quick variation of 3 nt coincident with july 19 eruptive fissures opening up in the valle del leone these observations are consistent with those calculated from volcanomagnetic models in which the magnetic changes are generated by stress redistribution due to magmatic intrusions at different depth and by the thermal demagnetization at a rather shallow depth

volcanomagnetic changes accompanying the onset of the 2002 2003 eruption of mt etna italy abstract remarkable changes in the local magnetic field were associated with the onset of the 2002 2003 flank eruption at mt etna after differential magnetic field measurements were filtered from the external noise by using adaptive filters we recognized two stages in the total intensity changes which are closely related to different volcanic events a rapid variations of about 4 5 nt associated with october 26 seismic swarm recorded beneath the summit craters b step like variations of 9 10 nt coincident with october 27 eruptive fissures opening up in the north flank these observations are generally consistent with those calculated from simple magnetic models of these volcanic processes in which the magnetic changes are generated by stress redistribution due to magmatic intrusions at different depth the magnetic data not only allow the timing of the intrusive event to be described in greater detail but also together with other volcanological and geophysical evidences permit some constraints to be set on the characteristics of propagation of a shallow dike firstly at around midnight on 26 october magma was rapidly injected to a depth of 3 4 km just below the summit craters secondly after 1 00 on 27 october continued intrusion magma occurred upward and culminated a few hundred meters below the free surface fractured along a n e direction thirdly at about 2 28 magma gave rise to an explosive fissural vent at the northern base of the ne crater near 3000 m a s l finally at about 5 00 the first eruptive fissure became active along the eastern border of the ne rift at 2500 m a s l the rate of growth of the magnetic anomalies moreover leads to the interpretation that the magmatic intrusion travelled northward from base of the ne crater to the ne rift at approximately 14 m min

extreme geomagnetic reversal frequency during the middle cambrian as revealed by the magnetostratigraphy of the khorbusuonka section northeastern siberia abstract we present new magnetostratigraphic results obtained for the drumian stage 504 5 500 5 ma epoch 3 middle cambrian from the khorbusuonka sedimentary section in northeastern siberia they complement previous data that did not allow the determination of a reliable estimate of the geomagnetic reversal frequency during this time magnetization of the samples is carried by a mixture of magnetite and hematite in various proportions thermal demagnetization makes it possible to distinguish two magnetization components the low unblocking temperature 20 reversals per myr during the drumian to 1 5 reversals per myr during the furongian upper cambrian such a sharp decrease is consistent with a transition at a 1 myr timescale probably caused by threshold effects in core processes between two geodynamo modes one characterized by reversals occurring at frequencies ranging from 1 to 5 reversals per myr and the other marked by hyperactivity of the reversing process with reversal rates 15 reversals per myr

paleomagnetic insights into the cambrian biogeographic conundrum did the north china craton link laurentia and east gondwana

low frequency magnetic field measurements near the epicenter of the ms 7 1 loma prieta earthquake the authors report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the m sub s 7 1 loma prieta earthquake of 17 october 1989 their measurements cover 25 narrow frequency bands in the more than six decade frequency range 0 01 hz 32 khz with a time resolution varying from a half hour in the ulf range 0 01 10 hz to one second in the elf vlf range 10 hz 32 khz the ulf system is located near corralitos about 7 km from the epicenter the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf data has revealed no precursor activity that they can identify at this time however the ulf data have some distinctive and anomalous features first a narrow band signal appeared in the range 0 05 0 2 hz around september 12 and persisted until the appearance of the second anomalous feature which consisted of a substantial increase in the noise background starting on 5 october and covering almost the entire frequency range of the ulf system third there was an anomalousmore dip in the noise background in the range 0 2 5 hz starting one day ahead of the earthquake finally and perhaps most compelling there was an increase to an exceptionally high level of activity in the range 0 01 0 5 hz starting approximately three hours before the earthquake there do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase further while the systems are sensitive to motion seismic measurements indicate that there were no significant shocks preceding the quake thus the various anomalous features in the data and in particular the large amplitude increase in activity starting three hours before the quake may have been magnetic precursors less

an explanation for earth s long term rotational stability paleomagnetic data show less than approximately 1000 kilometers of motion between the paleomagnetic and hotspot reference frames that is true polar wander during the past 100 million years which implies that earth s rotation axis has been very stable this long term rotational stability can be explained by the slow rate of change in the large scale pattern of plate tectonic motions during cenozoic and late mesozoic time provided that subducted lithosphere is a major component of the mantle density heterogeneity generated by convection therefore it is unnecessary to invoke other mechanisms such as sluggish readjustment of the rotational bulge to explain the observed low rate of true polar wander

ionospheric disturbances observed during the period of mount pinatubo eruptions in june 1991 a series of climatic eruptions of mount pinatubo occurred in june 1991 many quasi periodic ionospheric disturbances were observed in the virtual height variations of the ionosphere at chungli in the total electron content variations at lunping kaohsiung and chihpen and in the differential doppler shift data recorded at lunping these ionospheric disturbances were characterized by quasi periodic wavelike trains lasting for several cycles with periods around 16 to 30 min wavelengths between 160 and 435 km and propagation speeds ranging from 131 to 259 m s from the direction of mount pinatubo to the observation sites the oscillation periods downward movement of distortion and inclined phase fronts all show that these ionospheric disturbances were manifested by the gravity waves that arrived from the direction of mount pinatubo by use of a simplified isothermal atmosphere model the propagation mode is interpreted as the freely propagating gravity waves 26 refs

magnetic monitoring at merapi volcano indonesia abstract merapi volcano located 30 km north of the heavily populated city of yogjakarta java is one of the most active of the 129 volcanoes in indonesia about every 2 years a new phase of activity is observed depending on the past activity the unrest gives rise either to an endogenous dome which partly collapses in the southwest direction or to pyroclastic flows which travel as far as 15 km the 1990 1997 period has involved a plume emission on 30 august 1990 an extrusion on 20 january 1992 and a pyroclastic eruption on 22 november 1994 the intensity of the earth magnetic field has been measured simultaneously and digitally recorded at four stations since 1990 two overhauser magnetometers with resolution of 0 01 nt have been installed in the summit area to strengthen the volcano monitoring outstanding magnetic changes appear to correlate with volcanic activity three types of volcanomagnetic signals can be identified long term trends up to 15 nt with period 10 years medium term cyclic variations at most 3 nt in amplitude and with 1 2 years period and small events reaching 1 5 nt lasting a few months and associated with any remarkable volcanic activity merapi volcano began a new cycle of activity in 1995 leading to a dome growth in july 1996 and accompanied by 27 nuees ardentes in august the comparison between magnetic data seismicity and surface phenomena suggests that some long term trends of decade periods could be of thermomagnetic origin while mid term volcanomagnetic variations associated with the cycles of merapi activity could be of piezomagnetic origin short term variations of a few weeks duration less than 1 5 nt are well correlated with the 1995 1996 seismic activity

explosion energy of the 2004 eruption of the asama volcano central japan inferred from ionospheric disturbances 1 the japanese dense array of global positioning system recorded ionospheric disturbances as changes in total electron content 12 minutes after the september 1 2004 eruption of the asama volcano central japan the disturbance had a period of one and a quarter minutes and propagated as fast as 1 1 km s suggesting its origin as the acoustic wave generated by the explosion by comparing the disturbance amplitudes with those by a surface mine blast with a known energy the overall asama explosion energy is inferred to be about 2 1014 j

vlf emissions associated with earthquakes and observed in the ionosphere and the magnetosphere abstract several electromagnetic phenomena recorded at the time of earthquakes were recorded independently by the geostationary satellite geos 2 above africa longitude 37 e and the polar orbiting satellite aureol 3 apogee 2012 km perigee 408 km inclination 82 5 period 109 5 min the observations were made with magnetic and electric antennae in the frequency range 10 hz 15 khz characteristics of the emissions and differences between low and high altitude observations are presented some geos 2 very low frequency data can be correlated with ionospheric measurements made on ground at the djibouti station latitude 11 n longitude 42 e where increases of the critical frequency f 0 e s of the sporadic e s layer are observed when earthquakes occur nearby time differences between disturbance at ionospheric level and at the height of geos 2 seem to indicate that earthquakes cause two distinct types of electromagnetic disturbance an electromagnetic wave in the ionosphere and a density increase of the e s layer

changes of the earth s rotation axis owing to advection of mantle density heterogeneities polar wander the secular motion of the earth s rotation axis relative to its surface has been studied for many years dynamical arguments1 3 show that polar wander can arise from the redistribution of mass in a plastic deformable earth the rate depending on both the rate of mass redistribution and the rate at which the earth s rotational bulge can readjust to the changing rotation axis here we use a viscosity structure obtained through geoid modelling4 a mantle flow field consistent with tomographic anomalies5 and time dependent lithospheric plate motions6 to calculate the advection of mantle density heterogeneities and corresponding changes in the degree two geoid during the cenozoic era we show that the rotation axis will follow closely any imposed changes of the axis of maximum non hydrostatic moment of inertia the resulting path of the rotation axis agrees well with palaeomagnetic results7 with the model predicting a current rate of polar motion that explains 40 of that observed geodetically8

electric and magnetic phenomena observed before the volcano seismic activity in 2000 in the izu island region japan significant anomalous changes in the ultra low frequency range 0 01 hz were observed in both geoelectric and geomagnetic fields before the major volcano seismic activity in the izu island region japan the spectral intensity of the geoelectric potential difference between some electrodes on niijima island and the third principal component of geomagnetic field variations at an array network in izu peninsula started to increase from a few months before the onset of the volcano seismic activity culminating immediately before nearby magnitude 6 class earthquakes appearance of similar changes in two different measurements conducted at two far apart sites seems to provide information supporting the reality of preseismic electromagnetic signals

the influence of true polar wander on glacial inception in north america abstract the impact that long term changes in earth s rotation axis relative to the surface geography or true polar wander tpw and continental drift have had in driving cooling of high latitude north america since the eocene is explored recent reanalyses of paleomagnetic pole positions suggest a secular drift in earth s rotation axis of 8 over the last 40 myr in a direction that has brought north america to increasingly higher latitudes using modern temperature data in tandem with a simple model a reduction in the annual sum of positive degree days pdds driven by this polar and plate motion over the last 20 myr is quantified at sites in baffin island the tpw and continental drift driven decrease in insolation forcing over the last 20 myr rivals changes in insolation forcing caused by variations in earth s obliquity and precession using conservative pdd scaling factors and an annual snowfall equal to modern station observations the snowiest location in baffin island 20 myr ago had a mass balance deficit of 0 75 2 m yr 1 water equivalent thickness relative to its projected mass balance at 2 7 ma this mass balance deficit would have continued to increase as one goes back in time until 40 myr ago based on adopted paleopole locations tpw and continental drift that moved arctic north america poleward would have strongly promoted glacial inception in baffin island at 3 ma a location where the proto laurentide ice sheet is thought to have originated

rapid precise and high sensitivity acquisition of paleomagnetic and rock magnetic data development of a low noise automatic sample changing system for superconducting rock magnetometers among earth sciences paleomagnetism is particularly linked to the statistics of large sample sets as a matter of historical development and logistical necessity because the geomagnetic field varies over timescales relevant to sedimentary deposition and igneous intrusion while the fidelity of recorded magnetization is modulated by original properties of rock units and by alteration histories ideal paleomagnetic results measure remanent magnetizations of hundreds of samples at dozens of progressive demagnetization levels accompanied by tests of magnetic composition on representative sister specimens we present an inexpensive open source system for automating paleomagnetic and rock magnetic measurements using vacuum pick and place technology and a quartz glass sample holder the system can in one hour measure remanent magnetizations as weak as a few pam2 of 30 specimens in two vertical orientations with measurement errors comparable to those of the best manual systems the system reduces the number of manual manipulations required per specimen 8 fold

electrical activity during the 2006 mount st augustine volcanic eruptions by using a combination of radio frequency time of arrival and interferometer measurements we observed a sequence of lightning and electrical activity during one of mount st augustine s eruptions the observations indicate that the electrical activity had two modes or phases first there was an explosive phase in which the ejecta from the explosion appeared to be highly charged upon exiting the volcano resulting in numerous apparently disorganized discharges and some simple lightning the net charge exiting the volcano appears to have been positive the second phase which followed the most energetic explosion produced conventional type discharges that occurred within plume although the plume cloud was undoubtedly charged as a result of the explosion itself the fact that the lightning onset was delayed and continued after and well downwind of the eruption indicates that in situ charging of some kind was occurring presumably similar in some respects to that which occurs in normal thunderstorms