eccentricity paced monsoon like system along the northwestern tethyan margin during the valanginian early cretaceous new insights from detrital and nutrient fluxes into the vocontian basin se france high resolution changes in terrigenous and nutrient fluxes into the vocontian basin northwestern tethyan margin were investigated for the late berriasian late valanginian time interval in order to assess the precipitation patterns in the source areas and to evaluate the effect of orbital forcing on the strength of the hydrological cycle in this study new high resolution mineralogical bulk rock and clay fraction and geochemical phosphorus and oxygen isotope data are used from the astronomically calibrated orpierre section for the first time kaolinite detrital and phosphorus accumulation rates kar dar and par are calculated and compared to a set of 547 geochemical and 260 mineralogical published data from other vocontian sections it appears that three regional increases in the kar document three successive humid episodes during the valanginian this is confirmed by contemporaneous increases in dar and partly also in par which highlight higher terrigenous and nutrient fluxes to the vocontian basin during these episodes concomitant decreases in the 18owhole rock signals may reflect higher sea surface temperatures during the early valanginian and the early late valanginian transition the occurrence of the three humid episodes is interpreted to relate to an orbital paced monsoonal circulation pattern through seasonally reversing movements of air mass heat and precipitation over the northwestern tethyan margin in particular based on the correlation between the 405 kyr eccentricity cycles and the kar signal obtained at orpierre an eccentricity influenced monsoonal circulation is proposed as the possible forcing factor behind these climatic patterns the average duration between the climaxes of the three regional wetter episodes is approximately 2 43 myr the wetter and likely also warmer episode at the early late valanginian transition is in step with the onset of the weissert episode in this regard the intensification of monsoonal driven precipitations appears as a possible external forcing factor leading or at least accelerating the important perturbation in the global carbon cycle associated with the weissert episode

the correction for sediment loading on the seafloor available measurements of sediment velocity and density indicate that a factor of 600 m s 1 of two way sediment reflection time will correct seafloor depth to yield basement depth in the absence of sediment loading this simple linear relation is derived from the results of six deep drill holes in abyssal sediments of the north and south atlantic oceans the relation predicts the sediment correction with an accuracy of about 50 m regardless of the lithology sampled down to a depth of 1 5 s of reflection time the cost wells on the u s continental shelf and empirical relations among velocity density porosity and depth provide estimates of the deeper behavior of abyssal sediments and suggest that the 600 m s 1 factor continues to provide a satisfactory sediment correction to a depth of 3 s

effects of latent heat release at phase boundaries on flow in the earth s mantle phase boundary topography and dynamic topography at the earth s surface abstract mantle flow models that do not consider the effects of latent heat on phase boundaries typically predict dynamic surface topography too large to be compatible with observations here these effects were implemented in a mantle flow model and resulting changes in dynamic topography and topography of phase boundaries were computed inclusion of these effects was found to reduce the rms amplitude of dynamic topography by about 50 60 m still leaving a substantial misfit from observations in most cases considered generally it also leads to a slight improvement of correlation with dynamic surface and phase boundary topography constrained by observations results thus indicate that the model implemented here is applicable to the earth but that other effects need to be considered as well in order to fully explain phase boundary and dynamic surface topographies

a telemetric system for measuring electrotelluric variations in greece and its application to earthquake prediction abstract a detailed description of the telemetric system that records variations in the earth s electrical field from sixteen field stations in greece is presented each field station measures potential differences between eight pairs of electrodes inserted into the ground in two orthogonal directions n s and e w two techniques have been applied the first one is real time where the field station takes the information digitizes it and transmitts it via telephone line to a central station in athens which decodes the information offsets it automatically and displays on chart recorders the small variations in the telluric current the resolution of the system is 0 1 mv for a total gain of 200 the second technique uses dataloggers where the information is digitized and stored in the datalogger memory the central station has a commercial personal computer which communicates with the datalogger takes the information via a standard telephone line and plots the recordings every 4 h the data are stored in compressed mode on a tape back up streamer for future reference the system works unattended

seismic electric signals ses and earthquakes a review of an updated van method and competing hypotheses for ses generation and earthquake triggering abstract electromagnetic phenomena are sometimes associated with seismic events but earthquake prediction using seismic electric signals ses has not been seriously considered since the early 1990s there are several causes 1 false alarms that have created panics in greece and 2 a strong critique of the varotsos alexopoulos nomicos van method used there an updated van method that includes time series analysis has made successful medium range predictions and short range predictions when coupled with seismic time series analysis four types of potential mechanisms to create precursory ses relying on deformation effects temperature effects ore mineral movement or groundwater variation are reviewed data relevant to each are insufficient to favor a single mechanism records of the number of false positive and missed events for an updated van method have not been well maintained false positives appear to be abundant and render the method unusable co seismic groundwater fluctuations are addressed and two novel hypotheses of earthquake trigger mechanism are also presented ionospherically induced electric and resultant magnetic fields to weaken rock thereby causing failure and volatiles liberated from minerals additionally promoting rock failure recommendations for further study are included

partial melting zones in the crust in southern tibet from magnetotelluric results magnetotelluric studies in southern tibet along a north south traverse 200 km long crossing the yarlung zangbo suture zone near lhasa have enabled us to construct a two dimensional model in which layers of anomalously high conductivity exist at depths shallower than 33 km the electrical properties of these layers are different on the two sides of the suture zone we show here that the most plausible explanation of the high conductivity is the existence of partial melting zones in the upper part rather than the lower part of a crust 70 km thick this represents a powerful constraint for thermo mechanical models of continental collisions

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

latest aspects of earthquake prediction in greece based on seismic electric signals ii abstract since 1983 continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in greece the basic physical properties of the transient changes seismic electric signals ses in the electrotelluric field that are forerunners of earthquakes were first described six years ago since then a large body of data has been collected resulting in new insight into various aspects of the method the present paper reviews the latest developments in ses based earthquake prediction and describes the current procedures used to predict the epicenter and magnitude of an impending earthquake a detailed list of the predictions officially issued in greece during the past 3 years january 1 1987 november 30 1989 is also given public warnings were issued well before the most destructive seismic activity

on the difficulty of detecting streaming potentials generated at depth in order to investigate how a streaming potential coefficient measured in the laboratory at a typical scale of 10 cm can be incorporated into a field model with a typical scale of 1 to 10 km we measured the electric field induced by water flows forced at 150 m depth through a 10 m wide granite fractured zone the water flows were obtained by pumping cyclically 10 m of water from a borehole that cut the fractured zone at depth and contemporaneously reinjecting it into another borehole located 50 m away after one day a steady state fluid flow regime was reached with pumping cycles lasting 45 minutes indicating a hydraulic conductivity of 10 5 m s 1 and a specific storage coefficient of 3 25 10 6 m 1 the expected self potential at the surface was an anomaly with two maxima of opposite sign and 2 v amplitude each both located 160 m away from the middle of the borehole heads the signal being divided by two 500 m away from the middle of the borehole heads in agreement with wurmstich and morgan 1994 instead we observed an electrical signal of 8 mv midway between the borehole heads and smaller than 5 mv 33 m away from the borehole heads the discrepancy observed between the data and the model can be explained by fluid flow leakages that occurred close to the water table head represented about 20 of the total water flow and activated smaller but closer electric sources this experiment thus illustrates the practical difficulty of detecting streaming potentials generated at depth it shows in particular that in fractured zones and hence in the vicinity of a major active fault small water flows located distantly from an energetic targeted source but close to some of the electrodes of the network can sometimes drastically distort the shape of the expected anomaly models of possible electrical earthquake precursors therefore turn out to be more speculative than expected

seismic stratigraphy and geological evolution of the cenozoic cool water eucla platform great australian bight seismic images of the continental margin in the western great australian bight reveal the internal anatomy of a long lived cenozoic cool water carbonate shelf the cenozoic succession is divisible into seven seismic sequences that reflect four depositional phases phase a paleocene middle eocene is a progradational siliciclastic wedge deposited in a depositional sag and represents lowstand and transgressive sedimentation phase b middle eocene earliest middle miocene contains cool water ramp carbonates with biogenic mounds eocene oligocene overlain by a warm water flat topped platform rimmed by the early middle miocene little barrier reef coeval deep water carbonate deposition formed a multi lobed sediment apron this phase was terminated by gentle uplift and tilting throughout southern australia in the late middle miocene phase c late miocene early pliocene represents cool water lowstand wedge and ramp deposition and contains numerous biogenic mounds in the youngest sequence this phase is terminated by an unconformity attributed to marine erosion phase d pliocene quaternary is a thick succession of cool water carbonates with spectacular clinoform ramp geometry that forms most of the modern outer shelf and contains large deep water biogenic mounds this platform the first large cool water carbonate shelf imaged by high quality seismic reflection data demonstrates the interaction between regional tectonic and local and global paleo oceanographic processes as australia drifted northward during the cenozoic the great australian bight moved from high to middle latitudes and the regional oceanographic regime remained cool water largely because of coeval development of the antarctic circumpolar current in the evolving southern ocean short episodes of warm water deposition probably reflect incursions of a proto leeuwin current from the indian ocean whereas growth of the miocene coral algal little barrier reef resulted from a short term global increase in sea surface temperatures this platform dominated by stacked carbonate ramps is most similar to the west florida shelf but contains many more biogenic mounds the western great australian bight carbonate platform is an excellent modern analog for the mesoscale structure of cool water platforms in the older geologic record

cretaceous tertiary inversion history of the dampier sub basin northwest australia insights from quantitative basin modelling abstract seismic sequence analysis has been combined with a kinematic and flexural model for the deformation of the lithosphere to define the history distribution and magnitude of inversion within the dampier sub basin northwest australia during the cretaceous and tertiary inversion tends to be focused along the trend of pre existing border fault systems and or internal to the basin across the roll over anticlines of collapsed hangingwall blocks the spatial distribution of inversion varied with different faults involved in the inversion process at different times whereas cretaceous inversion concentrated along major boundary faults of the northeast southwest oriented rankin madeleine and rosemary legendre trends the locus of miocene inversion was located adjacent to the northwest limits of the rosemary legendre trend total shortening of the lithosphere during the santonian and tertiary was modelled to be 2 6 and 0 16 km respectively with northeast southwest trends being preferentially reactivated the amplitudes of inversion structures range from 1000 m over the eastern rankin trend to hundreds of metres for inversion structures comprising the rosemary legendre trend although responsible for the development of relatively subtle features inversion has critically controlled the major structures for trapping hydrocarbons within the dampier sub basin

evolution of deep water rifted margins testing depth dependent extensional models 1 a general understanding of rifted margins which form by thinning of the continental lithosphere exists nevertheless the exact form of thinning is unclear this debate has been stimulated by acquisition of dense seismic wide angle and deep reflection surveys from atlantic ocean margins a central issue concerns the way in which thinning changes with depth we have tackled this issue by developing a generalized inverse model this model attempts to fit subsidence and crustal thinning observations by varying strain rate as a function of time and space depth dependent thinning is permitted but we do not prescribe its existence or form here the algorithm is applied to six margins including two of the most contentious conjugate margins newfoundland iberia and brazil angola calculated strain rate histories predict thinning estimates which broadly match estimates inferred from normal faulting the eastern indian and beaufort sea margins formed by largely uniform lithospheric thinning in contrast the newfoundland iberian conjugate margins formed by a pattern of strongly depth dependent strain rate to account for the paucity of syn rift decompression melting of the underlying asthenosphere the lithospheric mantle close to oceanic continent transition must thin more slowly than the overlying crust this form of depth dependency is not common for example the brazil angolan conjugate margin could have formed by uniform lithospheric thinning provided thick layers of salt were deposited in a preexisting 400 m deep topographic depression depth dependent thinning is not required to account for rapid subsidence of presalt strata

time resolved study of charge generation and propagation in igneous rocks electrical resistivity changes ground potentials electromagnetic em and luminous signals preceding or accompanying earthquakes have been reported many times in addition to ground uplift and tilt and other parameters however no concept exists that would tie these diverse phenomena together into a physically coherent model using low to medium velocity impacts to measure electrical signals with microsecond time resolution it is observed that when gabbro and diorite cores are impacted at relatively low velocities 100 m s highly mobile charge carriers are generated in a small volume near the impact point they spread through the rocks causing electric potentials exceeding 400 mv em and light emission as the charge cloud spreads the rock becomes momentarily conductive when a granite block is impacted at higher velocity 1 5 km s the propagation of the p and s waves is registered through the transient piezoelectric response of quartz after the sound waves have passed the surface of the granite block becomes positively charged suggesting the same charge carriers as observed during the low velocity impact experiments expanding from within the bulk during the next 2 3 ms the surface potential oscillates indicating pulses of electrons injected from ground and contact electrodes the observations are consistent with positive holes e g defect electrons in the o2 sublattice traveling via the o 2p dominated valence band of the silicate minerals the positive holes propagate as charge clouds rather than as classical em waves before activation they lay dormant in form of electrically inactive positive hole pairs php chemically equivalent to peroxy links o3x oo xo3 with x si4 al3 etc phps are introduced into the minerals by way of hydroxyl o3x oh which all nominally anhydrous minerals incorporate when crystallizing in h2o laden environments the fact that positive holes can be activated by low energy impacts and their attendant sound waves suggests that they can also be activated in the crust by microfractures during the dilatancy phase depending on where in the stressed rock volume the charge carriers are activated they will form rapidly moving or fluctuating charge clouds that can account for earthquake related electrical signals and em emission wherever such charge clouds intersect the surface high fields are expected causing electric discharges and earthquake lights

cenozoic eucla basin and associated palaeovalleys southern australia climatic and tectonic influences on landscape evolution sedimentation and heavy mineral accumulation abstract the eucla basin including the vast nullarbor plain lies on the margins of the yilgarn musgrave and gawler cratons in southern australia and owes its distinctive landscape to a unique set of interactions between eustatic climatic and tectonic processes over the last 50 ma understanding of the history of the basin and the palaeovalleys that drained from the surrounding cratons are important because they contain major mineral deposits and the sediments derived from them contain remobilised gold uranium and heavy minerals in particular a remarkably preserved palaeoshoreline sequence along the north eastern margin of the eucla basin is highly prospective for heavy mineral placer deposits the record of marine marginal marine estuarine fluvial and lacustrine environments as constrained mainly by an extensive borehole dataset reflects major depositional events during the palaeocene early eocene middle late eocene oligocene early miocene middle miocene early pliocene and pliocene quaternary these events reflect the key role of eustatic sea level variation which during highstands inundated the craton margins flooding palaeovalleys to up to 400 km inboard of the present coastline however a systematic eastward migration of the depocentre across the eucla basin during the neogene together with apparent flow reversals in a number of palaeovalley systems draining the gawler craton suggest that the eucla basin has also been subject to differential vertical movements expressed as a west side up east side down tilting of 100 200 m this differential movement forms part of a broader north down southwest up dynamic topographic tilting of the australian continent associated with relatively fast 6 7 cm yr northward plate motion since fast spreading commenced in the southern ocean at 43 ma we suggest that the evolving dynamic topography field has played a key role in facilitating development of placer deposits largely through multistage eastward reworking of near shore sequences during highstand transgressive cycles on a progressively tilting platform under the influence of persistent westerly weather systems

densities and porosities in the oceanic crust and their variations with depth and age we have used drilling and downhole logging results from deep sea drilling project holes 395a and 418a measured properties of core samples from the seafloor and from ophiolites and seismic velocity structure models of the oceanic crust to constrain empirical statistical relationships between in situ densities porosities and seismic velocities and to estimate densities and porosities in the oceanic crust with the following principal results our review of drilling results and studies of ophiolites suggests that the velocity structure of the oceanic crust is more closely related to changes in porosity and alteration or metamorphic grade than to its igneous structure the transition from layer 2a 3 7 0 4 km s 1 to 2b 5 2 0 4 km s 1 occurs within the extrusive pile the top of layer 2c 6 2 0 2 km s 1 is associated with the top of the sheeted dike complex and with the first appearance of greenschist facies alteration products ophiolite studies have shown that the top of layer 3 occurs within the sheeted dikes where the metamorphic grade of alteration products increases from greenschist to amphibolite facies a comparison of reprocessed and corrected downhole logs from holes 395a and 418a indicates that in situ densities and fractional porosities differ by 0 2 mg m 3 and 0 07 respectively these differences are consistent with prevailing views of the progressive alteration of the upper oceanic crust statistical relationships between in situ density porosity and slowness are highly linear and indicate that the density slowness relation estimated from laboratory samples pb 3 81 0 02 6 0 0 1 s applies to in situ properties as well we obtained a similar empirical relationship for porosities from the hole 418a log data f 0 35 0 03 2 37 0 15 s r2 0 84 s e 0 015 applying these empirical models to seismic velocity structure models yields the following crustal densities and porosities layer 2 2 62 2 69 mg m 3 0 10 0 12 and layer 3 2 92 2 97 mg m 3 the estimated average density of the oceanic crust is 2 86 0 03 mg m 3 densities and porosities estimated from a seismic crustal structure model for old atlantic crust agree very well with the logging data from hole 418a suggesting that in situ densities and porosities can be estimated from seismic velocities high density and porosity gradients are characteristic of the upper oceanic crust increasing densities reflect both a progressive decrease of porosity and increasing grain density with depth based on the seismic properties of layer 2a we estimate that the layer thins at an approximate rate 20 to 45 m m y 1 while the velocity increases by 0 040 km s 1 m y 1 the corresponding rates of change of density and porosity are 0 016 0 009 mg m 3 m y 1 and 0 005 0 003 m y 1 respectively

1 fα fluctuations in geoelectrical signals observed in a seismic area of southern italy abstract recent studies have shown that many natural systems display temporal fluctuations with long range power law correlations suggesting a fractal geometry of the underlying dynamical system four geoelectrical time series measured in a seismic area of southern italy are investigated by means of spectral tools in order to evidence the existence of power law correlations results show the scaling behaviour for all the signals recorded pointing to the presence of fractal features expressing a long term correlation with scaling exponents which indicate stabilizing mechanisms furthermore our findings suggest an observational evidence of correlations between the variation of parameters describing the temporal fluctuations of geoelectrical signals and earthquakes that occurred in the area investigated

subducted slabs and the geoid constraints on mantle rheology and flow geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion the total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself these boundary deformations and hence the total gravity field depend on the radial distribution of effective viscosity if the internal density contrasts can be estimated as is the case for subducted slabs useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system the degree 4 9 components of the observed long wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs the positive sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more the amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs however the amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long wavelength geoid anomalies over subduction zones

a new approach to investigate the correlation between geoelectrical time fluctuations and earthquakes in a seismic area of southern italy we propose a new approach to investigate the possible correlation between electrical signals and earthquakes good correlation has been found between the spectral power law exponent of geoelectrical signals and the hurst exponent of the seismicity of the area investigated a tendency of both parameters to converge toward unity typical of self organized critical dynamics is evident before the occurrence of the major event recorded in the area during the observation period

development of the australian antarctic depth anomaly the oceanic australian antarctic discordance aad contains two unusual features 1 n s trending anomalously deep bathymetries and 2 rough basement morphologies in young 45 spreading obliquities

can electromagnetic disturbances related to the recent great earthquakes be detected by satellite magnetometers abstract on december 26 2004 the world s fourth largest earthquake since 1900 and the largest since the 1964 prince william sound alaska earthquake occurred off the west coast of northern sumatra with a magnitude of 9 3 on march 28 2005 another event of magnitude 8 7 took place in the same region the december 26 2004 earthquake has prompted scientists to investigate possible electromagnetic signatures of this event using ground magnetic observations iyemori et al iyemori t et al 2005 geomagnetic pulsations caused by the sumatra earthquake on december 26 2004 geophys res lett 32 l20807 doi 10 1029 2005gl024083 have suggested that a 3 6 min long geomagnetic pulsation observed shortly after this event was generated by the earthquake they have speculated that a 30 s magnetic pulsation was also caused by the earthquake here for the first time champ satellite magnetic and electron density data are examined to find out if electromagnetic signatures which are possibly related to these recent megathrust earthquakes are observed in satellite magnetic data we have shown that some specific features are observed after the two earthquakes with periods of about 16 and 30 s our results favor an external source origin for the 30 s pulsation moreover after more than 1 h champ magnetic data indicate the existence of a feature characterized by the same parameters duration amplitude and frequency content which could be associated with each earthquake respectively further investigations are required in order to answer the question of whether these signals can be associated with earthquakes and to assign their possible usefulness with respect to earthquake development

characteristics of electromagnetic noise in the ioannina region greece a possible origin for so called seismic electric signal ses the study of electromagnetic noise in the ioannina region nw greece shows the existence of long transient electric signals duration 10 s without measurable correlated magnetic signals as is the case for seismic electric signal ses observed in the van network of short term earthquake prediction our signals have an artificial origin and are emitted by different kinds of transmitters implanted in the ioannina region this origin can be clearly ascertained from simultaneous observation at stations in direct sight of the transmitters of four electromagnetic components two electric and two magnetic in a broad band of frequencies 10 3 10 hz relying on these observations it is proposed that the april 18 and 19 1995 electric signals interpreted by the van group as ses precursors to the may 13 kozani earthquake are due to some transmitter located far to the north of the ioa station of the van network the transmitters of this area would be of digital type as is increasingly common in radio telecommunication networks we believe that careful studies of electromagnetic noise in a broad range of frequencies should precede lengthy discussions of the statistical significance of recorded signals

reply to comment on seismomagnetic effects from the long awaited 28 september 2004 m 6 0 parkfield earthquake by m j s johnston y sasai g d egbert and r j mueller by p varotsos and s uyeda the comment by varotsos and uyeda 2008 vu hereafter does not have much to do with our article which reports electromagnetic data and their implications prior to during and following the 2004 m 6 parkfield earthquake eq in fact our article did not include any extensive discussion of the possible flaws in the seismic electric signal ses approach to eq prediction the four main points vu discuss in their comment are from a summary sentence in the introduction that is preceded by the phrase controversy about these ses results exists because 1 2 4 where 1 4 are the specific points that vu list we respond to each of these points in the following discussion a final comment made by vu concerns our observation that ses type signals are not seen in the data that we have we could have provided more detailed evidence about the lack of ses in the months preceding the earthquake but see little point in including long data plots that show nothing note that all of these data are freely available from the northern california earthquake data center ncedc www ncedc org last accessed october 2007 in our article we presented null results from sites above the parkfield eq rupture without extrapolating to the conclusion that sess do not exist anywhere in fact park et al 2007 report additional data from 10 20 km lines over the entire region that also show no evidence for ses type signals preceding the parkfield eq such signals were also not seen in 16 yr of previous monitoring with these lines park 1991 1997 furthermore no signals were seen in 2 yr of data on 10 km lines both along and within the fault and orthogonal to the fault a little farther to the north johnston 1989 to suggest that all of these observations resulted from an

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

identification and analysis of electromagnetic signals in greece the case of the kozani earthquake van prediction an electric station was installed in july 1993 4 5 km away from the van station of ioannina and recorded in the following two years a number of anomalous signals including those of april 18 and 19 1995 interpreted by the van group as seismic electric signals precursors to the may 13 kozani earthquake west macedonia a magnetic station was also installed and clearly recorded the magnetic components of the same events the amplitude shape characteristic pattern and duration magnetic characteristics and polarisation of the anomalous signals suggest that they are generated by artificial industrial sources

spatial and temporal patterns of cenozoic dynamic topography around australia 1 despite its importance the spatial and temporal pattern of dynamic topography generated by mantle convective circulation is poorly known we present accurate estimates of dynamic topography from oceanic basins and continental margins surrounding australia our starting point is measurement of residual depth anomalies on the oldest oceanic floor adjacent to the continental shelf these anomalies were determined from a combined dataset of 200 seismic reflection and wide angle images of well sedimented oceanic crust they have amplitudes of between 1 km and 0 5 km and their spatial variation is broadly consistent with long wavelength free air gravity and shallow seismic tomographic anomalies along the northwest shelf a regional depth anomaly of 300 to 700 m intersects the adjacent continental shelf the temporal evolution of this anomaly was determined by analyzing the stratigraphic architecture of an extensive carbonate platform which fringes the shelf and records a dramatic switch from progradation to aggradation during neogene times three dimensional seismic mapping calibrated by boreholes was used to calculate water loaded subsidence histories at rollover points of clinoforms along the shelf at 9 3 ma the rate of subsidence increases from 5 to up 75 m myr 1 generating a subsidence anomaly of 300 to 700 m the amplitude of this anomaly varies along the shelf and cannot be generated by glacio eustatic sea level variation instead we propose that a regional subsidence episode which affects both the proximal shelf and the distal oceanic basin was generated by convective drawdown by combining our results with other published estimates of uplift and subsidence a map of australia which shows the spatial and temporal pattern of dynamic topography is presented most but not all of australia s epeirogeny can be attributed to rapid northward motion of the australian plate over a pre existing pattern of convective circulation

seismomagnetic effects from the long awaited 28 september 2004 m 6 0 parkfield earthquake precise measurements of local magnetic fields have been obtained with a differentially connected array of seven synchronized proton magnetometers located along 60 km of the locked to creeping transition region of the san andreas fault at parkfield california since 1976 the m 6 0 parkfield earthquake on 28 september 2004 occurred within this array and generated coseismic magnetic field changes of between 0 2 and 0 5 nt at five sites in the network no preseismic magnetic field changes exceeding background noise levels are apparent in the magnetic data during the month week and days before the earthquake or expected in light of the absence of measurable precursive deformation seismicity or pore pressure changes obser vations of electric and magnetic fields from 0 01 to 20 hz are also made at one site near the end of the earthquake rupture and corrected for common mode signals from the ionosphere magnetosphere using a second site some 115 km to the northwest along the fault these magnetic data show no indications of unusual noise before the earthquake in the ulf band 0 01 20 hz as suggested may have preceded the 1989 ml 7 1 loma prieta earthquake nor do we see electric field changes similar to those suggested to occur before earthquakes of this magnitude from data in greece uni form and variable slip piezomagnetic models of the earthquake derived from strain displacement and seismic data generate magnetic field perturbations that are con sistent with those observed by the magnetometer array a higher rate of longer term magnetic field change consistent with increased loading in the region is apparent since 1993 this accompanied an increased rate of secular shear strain observed on a two color edm network and a small network of borehole tensor strainmeters and increased seismicity dominated by three m 4 5 5 earthquakes roughly a year apart in 1992 1993 and 1994 models incorporating all of these data indicate increased slip at depth in the region and this may have played a role in the final occurrence of the 28 september 2004 m 6 0 parkfield earthquake the absence of electric and magnetic field precursors for this and other earthquakes with m 5 7 3 elsewhere in the san andreas fault system indicates useful prediction of damaging earthquakes seems unlikely using these electromagnetic data

electromagnetic signals generated in the solid earth by digital transmission of radio waves as a plausible source for some so called seismic electric signals abstract claims by the van group varotsos p alexopoulos k 1984 physical properties of the variations of the electric field of the earth preceding earthquakes i tectonophysics 110 73 98 and later works to have developed a short term earthquake prediction technique in greece continue to arouse contentious debates claims of success in using geoelectrical precursors to predict earthquakes are criticized and defended 1998 letters phys today 51 6 15 100 great debates in seismology the van method of earthquake prediction 1998 eos 79 573 580 this is partly because of the unknown origin of the so called seismic electric signals ses precursors their particular characteristics are not those of the usual electromagnetic noise cultural noise or of the natural electromagnetic field magnetotelluric field in this paper we show that transient electric signals looking like ses can be generated by digital transmitters of the radio telecommunication network such signals have been observed in different regions of the world including greece and vietnam their characteristics have been analyzed in a broad band of frequencies 10 3 103 hz in the ioannina greece site which is considered as the most sensitive area of the van network it is concluded that some of the signals recorded at this site and identified as ses are probably of artificial origin and that the criteria used by the van group are not sufficient to guarantee that the so called ses are not man made without an extended and thorough study of the ambient electromagnetic noise in a broad band of frequencies and better information about the electrical properties of the deep structure beneath the monitoring station earthquake predictions issued on the basis of signals recorded by the van network are of dubious significance

buried inset valleys in the eastern yilgarn craton western australia geomorphology age and allogenic control abstract a contributory network of narrow fluvially incised valleys filled with a distinctive sequence of tertiary continental to shallow marine sediments is widespread throughout the eastern yilgarn craton in southwestern australia previously referred to as deep leads or paleochannels these are herein termed inset valleys to more accurately reflect their geomorphic expression and emphasize their subordinate and entrenched position with the bedrock surface of a much broader and older system of primary valleys owing to minimal denudation and tectonic deformation during the late cenozoic the inset valleys are excellently preserved and can be readily traced in boreholes and open cut mines throughout the eastern yilgarn craton and possibly also adjacent parts of southwestern australia with a combined catchment areal extent of at least documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmary

crustal thickness variations along the southeast indian ridge 100 116 e from 2 d body wave tomography 1 axial morphology along the southeast indian ridge seir systematically changes from an axial high to a deep rift valley at a nearly uniform intermediate spreading rate between 100 116 e west of the australian antarctic discordance aad basalt geochemistry has a consistent indian mid ocean ridge basalt morb type isotopic signature so changes in axial topography are attributed to variations in both mantle temperature and melt supply wide angle seismic refraction lines were shot to four ocean bottom hydrophones within seir segments p1 p2 s1 and t where each segment is characterized by a different morphology we constructed 2 d crustal velocity models by jointly inverting hand picked p wave refraction pg and moho reflection pmp traveltime data using a top down minimum structure methodology the results show a 1 5 km eastward decrease in crustal thickness across the study area with segment averages ranging from 6 1 km at p1 to 4 6 km at t melt generation models require a 30 c decrease in mantle temperature toward the aad to account for the crustal thickness trend significant changes in axial morphology accompany small scale variations in crustal thickness consistent with models of crustal accretion where ridge topography is determined by a balance between mantle temperature melt supply and cooling from hydrothermal circulation layer 3 thins by 3 0 km as layer 2 thickens by 1 4 km between segments p1 and t reflecting the eastward decrease in melt supply and increase in melt lens depth the trade off in seismic layers may be explained by models relating the increase in overburden pressure on a deepening melt lens to the volume of magma erupted into the upper crust rather than cooling at depth to form new lower crustal material

quest for dynamic topography observations from southeast asia transient dynamic topography is maintained by time varying density anomalies deep within earth9s mantle there is considerable interest in predicting and measuring dynamic topography because its spatial and temporal variation will help to track changes in the pattern of mantle convection despite the availability of increasingly elaborate predictive models there is little agreement about the amplitude wavelength and rate of change of dynamic topography here we analyze a hybrid data set of subsidence observations from continental and oceanic basins in southeast asia where published dynamic models predict 1 2 km of regional subsidence residual subsidence was isolated by removing the well defined effects of lithospheric extension and or cooling at long wavelengths 10 3 km the amplitude of residual subsidence i e maximum permissible dynamic subsidence has an upper bound of only 300 m the spatial distribution of permissible dynamic topography has no simple spatial or temporal relationship to the pattern of subduction over the past 65 m y anomalous subsidence commenced 5 10 m y ago accelerating to a present day rate of 100 m m y our results show that density anomalies within the lower mantle have little apparent influence at earth9s surface instead the distribution of residual subsidence reported here can be accounted for by minor variations in lithospheric thickness or by transient density variations beneath the lithospheric plate the absence of measurable dynamic topography is surprising and indicates that mantle mass anomalies are supported elsewhere presumably at internal boundaries within earth our hybrid data set can thus be used as an independent constraint on the viscosity structure of the mantle

arc continent collision in papua guinea constraints from fission track thermochronology the papua new guinea png mobile belt adjacent to the finisterre arc was formerly the leading ne corner of the australian plate that converged obliquely with the pacific plate forty new apatite and zircon fission track analyses of mobile belt rocks previously dated by k ar and rb sr analyses constrain neogene time temperature paths and tectonic models the paleogene arc along the southern margin of the caroline plate was juxtaposed against png in the early miocene coeval with locking up of the west dipping solomon subduction zone by the ontong java plateau these events initiated wrenching along the northern png margin and increased westward subduction of the solomon sea plate beneath the eastern margin the mobile belt underwent extension above the downgoing slab with rapid cooling of metamorphic rocks at 17 ma immediately prior to emplacement of the maramuni arc from 17 to 12 ma a change in plate motion at 12 10 ma terminated the arc and caused png caroline plate convergence creating the orogenic belt in new guinea from 12 to 4 ma this resulted in 4 5 km of uplift and 3 km of denudation and cooling of the entire mobile belt in the late miocene propagating westward along the mobile belt at 8 5 ma and southward into the fold belt at 5 4 ma the compression caused thrusting of miocene strata within the mesozoic type section a further change in plate motion at 4 3 ma returned the margin to transpression with local compression along strike slip faults and ongoing collision of the finisterre arc terrane