modelling the lower crust by simulation of the in situ conditions an example from the saxonian erzgebirge abstract seismic data supply an image of the earth s interior with more detail than other geophysical methods however interpretation of the data is a complicated process laboratory investigations of rock properties under simulated in situ conditions can make a valuable contribution for the material interpretation of the seismic profile dekorp 3 mve 90 along the saxonian erzgebirge in germany rock samples from this area were investigated under high pressure high temperature conditions the aim of the investigations was to find relations between longitudinal and shear wave velocities v p and v s and the mineral composition of the rocks under extreme conditions of pressure and temperature the experiments with different pressure chambers were made using two types of pressure apparatus one allows numerous experiments at relatively low pressure for measurements at extreme conditions up to 2 gpa and 1000 c with partial melting a special arrangement inside a gas pressure chamber was used the experimental data are used for the construction of velocity vs depth curves together with seismic velocity models and the geological interpretation of reflections these data allow the construction of a crustal model of the erzgebirge it can be shown that there are indications of partial melting zones in the lower crust the results provide an example of the importance of this method for the material interpretation of seismic data in general

importance of small earthquakes for stress transfers and earthquake triggering 1 we estimate the relative importance of small and large earthquakes for static stress changes and for earthquake triggering assuming that earthquakes are triggered by static stress changes and that earthquakes are located on a fractal network of dimension d this model predicts that both the number of events triggered by an earthquake of magnitude m and the stress change induced by this earthquake at the location of other earthquakes increase with m as similar to 10 dm 2 the stronger the spatial clustering the larger the influence of small earthquakes on stress changes at the location of a future event as well as earthquake triggering if earthquake magnitudes follow the gutenberg richter law with b d 2 small earthquakes collectively dominate stress transfer and earthquake triggering because their greater frequency overcomes their smaller individual triggering potential using a southern california catalog we observe that the rate of seismicity triggered by an earthquake of magnitude m increases with m as 10 alpha m where alpha 1 05 0 05 we also find that the magnitude distribution of triggered earthquakes is independent of the triggering earthquake s magnitude m when alpha approximate to b small earthquakes are roughly as important to earthquake triggering as larger ones we evaluate the fractal correlation dimension d of hypocenters using two relocated catalogs for southern california the value of d measured for distances 0 1 r 5 km is d 1 54 for the shearer et al catalog and d 1 73 for the hauksson et al catalog the value of d reflects both the structure of the fault network and the nature of earthquake interactions by considering only those earthquake pairs with interevent times larger than 1000 days we can largely remove the effects of short term clustering then d approximate to 2 close to the value d 2 alpha 2 1 predicted by assuming that earthquake triggering is due to static stress the value d approximate to 2b implies that small earthquakes are as important as larger ones for stress transfers between earthquakes and that considering stress changes induced by small earthquakes should improve models of earthquake interactions

low frequency electrical impedance of partially molten gabbro the effect of melt geometry on electrical properties abstract electrical impedance of partially molten gabbro was measured as a function of the frequency of the applied electric field the impedance of the partially molten gabbro was mainly controlled by the volume and geometry of partial melt which were observed with an optical microscope study of the quenched sample the experimental results are interpreted by a theory that formulates the electrical property of rocks containing partial melt taking ionic diffusion in the melt into account the theory evaluates the contributions from two types of melt geometry distributed in the rock matrix namely 1 a nearly isolated melt pockets and 2 b connected melt along grain boundaries according to the theory connected melt mainly contributes to the increase of net conductivity while melt pockets increase displacement current and cause the frequency dependence of impedance the characteristic ionic diffusivity in melt pockets was determined from the peak frequency of the imaginary part of impedance the magnitude of diffusion coefficient is estimated to be of the order of 10 7 to 10 6 cm 2 sec this suggests that sodium iron magnesium and or calcium ions mainly carry the electric charge in partial melt the observed frequency dependence of impedance is considered to reflect ionic polarization in melt pockets due to the migration of these alkali ions toward solid melt interfaces the present experimental and theoretical work suggests that electrical properties of the earth s upper mantle may involve an intrinsic frequency dependence associated with ionic diffusion in the frequency range of geomagnetic observation if a partial melt zone exists the analysis of the earth s conductivity structure may be inadequate if such intrinsic frequency dependence of mantle media is neglected

earthquake clusters in southern california i identification and stability 1 we use recent results on statistical analysis of seismicity to present a robust method for comprehensive detection and analysis of earthquake clusters the method is based on nearest neighbor distances of events in space time energy domain the method is applied to a 1981 2011 relocated seismicity catalog of southern california having 111 981 events with magnitudes m 2 and corresponding synthetic catalogs produced by the epidemic type aftershock sequence etas model analysis of the etas model demonstrates that the cluster detection results are accurate and stable with respect to 1 three numerical parameters of the method 2 variations of the minimal reported magnitude 3 catalog incompleteness and 4 location errors application of the method to the observed catalog separates the 111 981 examined earthquakes into 41 393 statistically significant clusters comprised of foreshocks mainshocks and aftershocks the results reproduce the essential known statistical properties of earthquake clusters which provide overall support for the proposed technique in addition systematic analysis with our method allows us to detect several new features of seismicity that include 1 existence of a significant population of single event clusters 2 existence of foreshock activity in natural seismicity that exceeds expectation based on the etas model and 3 dependence of all cluster properties except area on the magnitude difference of events from mainshocks but not on their absolute values the classification of detected clusters into several major types generally corresponding to singles burst like and swarm like sequences and correlations between different cluster types and geographic locations is addressed in a companion paper

recent seismicity and tomographic modeling of the mount etna plumbing system the monitoring of seismic activity in eastern sicily southern italy has been recently improved in the framework of the poseidon project to investigate both tectonics and volcanic processes of mount etna this effort has produced a homogeneous and complete data set which we use to image the deep structure of the volcano and to define the space and time distribution of the recent seismicity encompassing the 1995 eruption diffuse eruptions between 1995 and 1997 a further magma intrusion started in 1997 and an increase of volcanic activity in july 1998 we inverted p wave arrival times from 307 selected local earthquakes to obtain a three dimensional velocity model of the volcano with a simultaneous inversion for hypocenters and velocity parameters the new tomographic images permit us to define the structure beneath the volcano from the surface down to 18 km depth the main structural feature revealed by our inversion is a high velocity body located beneath the central craters whose lateral extent increases from 6 km between 18 and 9 km depth to 12 km between 9 and 3 km depth near the surface the fast anomaly branches in two separate high vp regions which are located below the summit craters and the eastern flank valle del bove respectively the high velocity features are interpreted as high density cumulates of solidified magma that intruded the shallow crust we hypothesize that magma ascends the crust within the relatively small high velocity conduit below 9 km depth and is stored at depth shallower than 9 km within the broad high velocity region as also suggested by petrological data a sharp increase of seismicity in 1997 with earthquakes occurring at the border of the high velocity body suggests that mount etna sustained recent episodes of intrusions which possibly herald future eruptions no large low velocity anomaly interpretable as a melted magma chamber is imaged in the upper 18 km of the crust while a broad low velocity anomaly in the uppermost mantle revealed by regional seismic data possibly indicates the magma source region at depth earthquake occurrence from the deep source to the shallow intrusive area helps to trace the magma migration and the feeding of the volcanic system

a strong correlation between induced peak dynamic coulomb stress change from the 1992 m7 3 landers california earthquake and the hypocenter of the 1999 m7 1 hector mine california earthquake the 1992 m7 3 landers earthquake may have played a role in triggering the 1999 m7 1 1 hector mine earthquake as suggested by their close spatial 20 km proximity current investigations of triggering by static stress changes produce differing conclusions when small variations in parameter values are employed here i test the hypothesis that large amplitude dynamic stress changes induced by the landers rupture acted to promote the hector mine earthquake i use a flat layer reflectivity method to model the landers earthquake displacement seismograms by requiring agreement between the model seismograms and data i can constrain the landers main shock parameters and velocity model a similar reflectivity method is used to compute the evolution of stress changes i find a strong positive correlation between the hector mine hypocenter and regions of large 4 mpa dynamic coulomb stress changes peak f t induced by the landers main shock a positive correlation is also found with large dynamic normal and shear stress changes uncertainties in peak f t 1 3 mpa are only 28 of the median value 4 6 mpa determined from an extensive set 160 of model parameters therefore the correlation with dynamic stresses is robust to a range of hector mine main shock parameters as well as to variations in the friction and skempton s coefficients used in the calculations these results imply dynamic stress changes may be an important part of earthquake trigging such that large amplitude stress changes alter the properties of an existing fault in a way that promotes fault failure

electrical conductivity of polycrystalline olivine containing a silicate glass the complex impedance of a polycrystalline sample of san carlos olivine including 5 vol of a synthetic silicate glass containing sodium magnesium and iron has been measured as a function of temperature under controlled oxygen fugacity at a c frequencies of 10 sup 2 10 sup 3 and 10 sup 4 hz below approximately 800 degrees c the conductivity of the sample is at least 5 to 10 times higher than that of single crystal and polycrystalline san carlos olivine respectively and has an activation energy half that of the single crystal the sample conductivity increases dramatically as a function of the measurement frequency hysteresis and time dependent changes in sample conductivity are observed above the liquidus of the glass approximately 900 degrees c the data suggest that the electrical conductivity of partially molten samples is characterized by parallel conduction of the solid and melt phases and is a sensitive indicator of melt distribution as well as the kinetics of melt re equilibration 20 refs 6 figs 1 tab

the 10 october 1999 hip 9369 occultation by the northern polar region of jupiter ingress and egress lightcurves analysis abstract the occultation of bright star hip9369 by the northern polar region of jupiter was observed from four locations in north and south america providing four data sets for ingress and egress the inversion of the eight occultation lightcurves provides temperature profiles at different latitudes ranging from 55 n to 73 2 n we estimate the errors on the profiles due to the uncertainties of the inversion method and compare the value of the temperature at the deepest level probed 50 bar with previous observations the shape of the temperature gradient profile is found similar to previous investigations of planetary atmospheres with propagating and breaking gravity waves we analyze the small scale structures in both lightcurves and temperature profiles using the continuous wavelet transform the calculated power spectra of localized fluctuations in the temperature profiles show slopes close to 3 for all eight profiles we also isolate and reconstruct the three dimensional geometry of a single wave mode with vertical and horizontal wavelengths of respectively 3 and 70 km the identified wave is consistent with the gravity wave regime with a horizontal phase speed nearly parallel to the planetary meridian nevertheless the dissipation of the corresponding wave in jupiter s stratosphere should preclude its detection at the observed levels and an acoustic wave cannot be ruled out

triggering of seismicity at short timescales following californian earthquakes 1 a method for measuring seismicity rate changes caused by the occurrence of major earthquakes in the surrounding crust is proposed it is based on a nonstationary poisson modeling of earthquake activity an estimate of the seismicity rate change and a probability measure of seismicity triggering following a large shock are derived and the removal of the influence of independent aftershock sequences of other nearby previous earthquakes is attempted without using more traditional declustering techniques the seismicity rate change estimator is corrected for its natural bias in favor of positive changes at short timescales that has so far strongly hindered measures of seismicity quiescences three californian earthquakes are examined using this method the 1989 m7 1 loma prieta the 1992 m7 3 landers and the 1994 m6 7 northridge earthquakes positive triggering is very commonly observed as expected but quiescence is however more seldomly obtained for timescales up to 100 days after the main shock this relative absence of quiescence as compared to typical predictions of coulomb modeling for example is also independently observed through direct correlation analyses of californian seismicity the possibility that the stresses caused by the main shock are spatially highly variable may explain these observations

comments on comparisons of vertical winds measured with the chatanika and poker flat radars by b j watkins and k jayaweera discussion de l erreur introduite dans la mesure des vents verticaux et due a l erreur de pointage des antennes

fine doppler resolution observations of thin turbulence structures in the tropostratosphere at millstone hill the 440 mhz radar at millstone hill 42 6 n 71 5 w was employed to examine the detailed evolution of turbulence structures in the tropostratosphere with a very fine doppler resolution of 0 12 hz corresponding to 4 cm s 1 radial velocity resolution the measurement technique involved directing the antenna downwind at a low elevation angle 15 or 20 and processing the echos from a range where the background wind shear was high although no attempt was made to obtain good range resolution a wide variety of turbulence structures were evident by virtue of their different doppler shifts in the presence of a high wind shear using arguments based on the dominance of shear broadening and the required velocity gradient to create instabilities maximum layer thicknesses in the vicinity of 20 300 m were inferred the implication of these observations to bulk transport of passive contaminants in the stratosphere is briefly discussed

small earthquakes tectonic forces earthquake scaling and frequency of occurrence relations require that small earthquakes be just as important as larger ones in redistributing the forces that drive relative displacements across active faults of any dimension including plate boundaries

electrical conductivity of a phonotephrite from mt vesuvius the importance of chemical composition on the electrical conductivity of silicate melts the bulk electrical conductivity of the phonotephritic lava from the 1944 eruption of mt vesuvius was measured using complex impedance spectroscopy in a multianvil apparatus at 1 gpa and temperatures up to 700 c melting experiments prior to the electrical measurements were also performed on this sample in a piston cylinder apparatus in order to gauge how bulk conductivity varies as a function of its melt fraction unlike the behaviour found in basaltic rocks in which conductivity increases with increasing melt fraction we observe a conductivity decrease of the order of a factor of ten for samples at 700 c ranging in melt fraction from 32 vol to completely molten we attribute this anomalous behaviour to the progressive loss of highly conductive leucite upon melting the addition of potassium to the melt phase however does not result in an increase of the total alkali concentration due to the melting of other mineral components we also present an empirical model to predict the electrical conductivity of fully molten silicate liquids as a function of temperature and chemical composition based on conductivity data for natural silicate liquids found in the literature the inclusion of compositional terms reduces the error by more than a factor of four with respect to a composition independent temperature only parameterization

electrical conductivity of magma in the course of crystallization controlled by their residual liquid composition 1 the electrical conductivity of a magma in the course of crystallization was experimentally investigated in the temperature range of 1350 1018 c large samples of basaltic composition with a homogeneous crystal content were synthesized in a gas mixing furnace at 1 atm pressure the samples were analyzed by electron microprobe the relative proportions of the phases as a function of temperature were determined depending on temperature the phase assemblies included quenched silicate liquid plagioclase pyroxene fe ti oxides the crystal content varied from 0 to 80 wt in response to partial crystallization the residual liquid changed composition from basalt to andesite to dacite liquid the electrical conductivity of the partially crystallized basaltic samples was measured in addition above liquidus conductivity measurements were conducted on compositions matching the residual liquid at different temperature these supplemental electrical measurements allowed us to discriminate the effect of crystal content from the effect of changing liquid composition associated with partial crystallization combining with the modified archie s law a set of constraints describing the conductivity of the residual liquid versus chemical composition and temperature we propose an equation to calculate changes in conductivity associated with partial magma crystallization we showed how the composition of the residual liquid is critical on the electrical behavior of crystal liquid system the model overcomes the previous difficulties in finding a robust model for describing the electrical behavior of crystal liquid systems the effect of liquid composition on the electrical conductivity is related to diffusion mechanisms and transport properties in molten silicate combining known constraints on na tracer diffusion and our conductivity results confirms the statements that sodium is the dominant charge carrier silicate liquids from basalt to rhyolite these findings revealed that we need a comprehensive model that can predict the conductivity of molten silicate as a function of chemical composition

electrical conductivity of molten basalt and andesite to 25 kilobars pressure geophysical significance and implications for charge transport and melt structure electrical conductivities of molten hawaiian tholeiite and crater lake andesite were measured between 1200 c and 1400 c at atmospheric pressure and at pressures up to 17and 25 kbar respectively isobaric plots of log versus 1 t is electrical conductivity are linear with the exception of the zero pressure tholeiite melt data conductivities decrease with increasing pressure in both melts with the andesitic melt exhibiting a greater pressure dependence between 5 and 10 kbar abrupt decreases in the slopes of isothermal log versus p plots i e decreases in activation volume are observed for both rock melts this discontinuity probably reflects changes in melt structure as opposed to changes in conduction mechanism in each pressure range the data for each rock melt can be described reasonably well by an equation of the form 0 exp ea p v kt where 0 is a preexponential constant ea is the activation energy and v is the activation volume a qualitative model involving depolymerization of the melt with increased pressure leading to increased efficiency of packing can explain the observed discontinuity in activation volume as well as the observed pressure dependences of other melt physical properties such as viscosity and density conductivity versus melt fraction curves for partially molten peridotite are reevaluated using high pressure tholeiitic melt conductivities and crystalline conductivity values recently determined by other workers minimum melt fraction estimates of 5 10 are required to explain upper mantle regions of anomalously high electrical conductivity in terms of a partial melting hypothesis

viscoelastic stress triggering of the 1999 hector mine earthquake by the 1992 landers earthquake the 1999 mw 7 1 hector mine earthquake occurred only 20 km from the 1992 mw 7 3 landers earthquake fault the close spacing between the two earthquakes suggests that the landers earthquake trigger the hector mine event based on an elastic half space model scientists from the usgs scec and cdmg 2000 have found a negative coulomb stress change at the hector mine hypocenter due to landers this negative stress change is inconsistent with the hypothesis of static stress triggering in this paper i show evidence of stress triggering of the hector mine earthquake by landers due to a process governed by viscoelastic flow in the lower crust this visoelastic flow has produced broad scale postseismic rebound observed by gps and insar measurements the result of this study is that viscoelastic flow has significantly modified the regional stress field in the mojave desert after the landers earthquake the evolving stress field including viscoelastic flow has gradually moved the coulomb stress change at the hector mine hypocenter to a positive level the increase in coulomb stress exceeded 1 bar right before the hector mine earthquake bringing the hector mine ruptures to the proximity of catastrophic failure

fractal analysis of three dimensional spatial distributions of earthquakes with a percolation interpretation although many studies have shown that faults and fractures are self similar over a large range of scales none have tested the fault structure for self similarity in three dimensions in this study earthquake hypocentral locations in central and southern california were used to illuminate three dimensional 3 d fault structures for which we measured the fractal capacity dimension d0 3 d hypocentral distributions from the joshua tree big bear and upland aftershock sequences as well as background seismicity at parkfield were found to be fractal where d0 3 d increased with increasing event density asymptotically approaching a stable value the joshua tree data set stabilized at d0 3 d 1 92 0 02 the parkfield data set asymptotically approached d0 3 d 1 82 and the big bear data set approached d0 3 d 2 01 as a test of the effects of location errors upon the measured value of d0 3 d the upland aftershock data were located with both the southern california hadley and kanamori 1977 h k velocity model and the more accurate hauksson and jones 1991 h j velocity model events located with the h k model asymptotically approached d0 3 d 2 07 and events located with the h j model approached d0 3 d 1 79 suggesting that improved hypocentral locations may decrease the measured fractal dimension one interpretation of our results of d0 3 d 2 0 for all of the hypocentral data is that earthquakes only occur on the percolation backbone of a fault network i e the active part of the network that accommodates finite strain deformation sahimi et al 1993 we show that a percolation model that allows for healing of previously broken bonds is consistent with this interpretation

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

electrical conductivity and partial melting of mafic rocks under pressure we demonstrate the importance of electric conductivity measurements of partially molten mafic rocks by examining of oman gabbro karelia olivinite ronda and spitzbergen peridotites the electrical conductivities of these rocks were estimated using the impedance spectroscopy at temperatures between 800 c and 1450 c and at pressures between 0 3 and 2 gpa in experiments performed in a piston cylinder apparatus at temperatures below and above melting samples were equilibrated during durations on the order of 200 h our results show that a jump in electrical conductivity can be correlated with the temperature range slightly above the solidus due to the delayed formation of an interconnected melt phase thin sections of quenched samples were used to estimate volume fractions and chemical compositions of the partial melts the increase of the electrical conductivity compares well with the connectivity of melt in partially molten samples above the solidus the electrical conductivity increases by 1 to 2 orders of magnitude in comparison with the conductivity of non melted rock below solidus when a complete melt connectivity is established the charge transport follows the network of the formed melt films at grain boundaries durations of up to 200 h are required in order to reach a steady state electrical resistance in a partially molten rock sample the experimental results were compared with the conductivity data obtained from magnetotelluric mt and electromagnetic em measurements in the northern part of the mid atlantic ridge where a series of axial magma chambers amc are presumably located there is good agreement between the measured electric conductivity of gabbroic samples with a melt fraction of 10 to 13 vol and the conductivity estimated at amc beneath the central part of reykjanes ridge as well as between the conductivity of partially molten peridotites and the source zone beneath the mid atlantic ridge at 60 km

electrical conductivity measurements on synthetic olivines and on olivine enstatite and diopside from dreiser weiher eifel germany under defined thermodynamic activities as a function of temperature and pressure abstract results of electrical conductivity measurments on synthetic olivines of the system mg 2 sio 4 fe 2 sio 4 and on minerals of dreiser weiher peridotite nodule ib 8 eifel germany are discussed in relation to the measuring procedure and to the variation of thermodynamic parameters the measurements were performed in solid state high pressure vessels between 340 and 1100 c and at a pressure of 10 kbar it is shown that for ternary olivines and for pyroxenes the control of two further variables like the chemical activities of the components is needed besides temperature and pressure control the experimental set up for the control of chemical activities and oxygen partial pressure is shown from the slopes of the lines of log against 1 t the activation energies were calculated though in most cases the same oxygen fugacity o 2 is applied the results reveal different values for synthetic and natural samples since the chemical activities of sio 2 are different

the use of laboratory velocity data for estimating temperature and partial melt fraction in the low velocity zone comparison with heat flow and electrical conductivity studies peridotite is widely considered to be the dominant component of the upper most mantle seismic velocities of a dry peridotite determined in the laboratory at high pressure and hypersolidus temperature show a rapid decrease with increasing temperature the strong temperature dependence of velocities can be used to estimate temperature and melt fraction in the low velocity zone of the earth the laboratory results show that the pressure dependence of both velocity and melt fraction appears to be well accounted for by the pressure dependence of the solidus temperature of the peridotite i e homologous temperature dependence this observation allows us to extrapolate laboratory results to higher pressures greater depths with some confidence requiring only a knowledge of the solidus as a function of pressure using the ratios of lithospheric to asthenospheric velocities temperature and melt fraction in the asthenosphere the low velocity zone can be determined from laboratory velocity data examples of thermal structures of the upper mantle beneath oceanic plates are presented we choose three locations of geophysical interest iceland plateau pacific ocean and philippine sea where reliable seismic velocities have been determined in the upper mantle from surface wave studies a large amount of partial melt 5 vol and a higher temperature than the dry peridotite solidus are inferred in 0 5 m y asthenosphere under the iceland plateau and the active marginal basin of the east philippine sea the partial melt zone appears to extend deeper 100 km and to greater ages 20 m y in the pacific ocean region than under the slowly spreading iceland plateau partial melting is not expected in the asthenosphere older than 5 m y under the iceland plateau even though the volume fraction of partial melt is not so large 3 vol beneath the pacific plate the melting zone may extend to a distance of above 2000 km from the ridge many seamounts observed in the pacific ocean may result from this vast region of melting under the plate we suggest a linear relation between the width of melting zone and the plate velocity the laboratory results are also applied to other low velocity zones it is suggested that a velocity drop up to about 6 in the asthenosphere does not necessarily require the existence of partial melt but can be explained by high subsolidus temperature this implies that partial melt may not exist generally but only in limited areas in the low velocity zone comparison of seismic results with theoretical models may overestimate the temperature and melt fraction if the velocity drop at subsolidus temperature is neglected temperature and melt fraction obtained in this study are discussed together with results from heat flow and electrical studies almost the same temperatures as inferred from seismic velocity and a dry peridotite solidus are calculated from heat flow data indicating that the upper mantle under mid ocean ridges may be fairly dry even a water or co2 undersaturated solidus 0 1 wt does not give a temperature consistent with the lithospheric geotherm and laboratory velocity results it is noted that electrical conductivity studies generally yield lower temperatures and larger melt fractions than this study unknown pressure frequency and impurity effects on laboratory conductivities of partially molten mantle rocks are suggested as possible reasons for this discrepancy

high pressure and high temperature measurements of electrical conductivity in basaltic rocks from mount etna sicily italy 1 we have investigated the electrical properties of etnean rocks by in situ complex impedance spectroscopy using a multianvil apparatus from these measurements we determined the electrical conductivity of a lava flow sample whose basaltic composition can be considered close to that of the parent magma and also that of a mafic nodule representative of the high density cumulates interpreted as responsible for the main high velocity anomaly observed beneath the volcano the electrical conductivities of the two samples were measured at pressures of 0 9 and 1 5 gpa and temperatures from 400 to 1100 c at frequencies from 0 1 to 105 hz to investigate the electrical properties of the etnean products as a function of partial melting a few experiments were performed in a piston cylinder apparatus prior to the electrical measurements the obtained data were approximated using an equivalent circuit fitting technique for the lava flow sample electrical conductivity displays arrhenian behavior over the entire investigated temperature range with an activation energy of 0 8 ev within the uncertainties of our measurements we do not observe any effect of pressure on conductivity between 0 9 and 1 5 gpa on the contrary experiments performed on the series of partially molten samples indicate that conductivity increases with increasing quantity of glass while conductivities of samples with minor amounts of glass are comparable to that of the lava flow starting material with increased melting conductivity can increase by as much as a factor of 3 the mafic nodule was observed to have a conductivity higher than the lava flow sample e g at 800 c and 0 9 gpa a factor of 4 higher however scatter in the data is somewhat higher in comparison to the lava flow sample most likely because of the coarse texture of the samples and a consequence to their chemical and structural heterogeneity using our results we illustrate the effects that a layer of hot magma surrounded by a cooler wall rock has on apparent resistivities determined by one dimensional forward calculations our modeling demonstrates that both size and depth of magmatic intrusions strongly influence apparent resistivity and that these parameters can be extracted from field data if the electrical properties of the rocks below the surface are well understood

velocity structure and seismicity of the garm region central asia summary we have examined arrival time data from two seismic networks operating within the pamir tien shan region of central asia in order to evaluate crustal structure and earthquake distribution in one of the most seismically active zones in the region the data are from two networks surrounding the soviet earthquake prediction laboratory at garm tadjikistan a 15 station local network operated by the soviet complex seismological expedition cse since the mid l950s and a dense telemetered network nested within the larger cse network operated jointly by the us geological survey usgs and the cse since 1975 a simultaneous inversion procedure was used to calculate l d layered velocity models and station corrections independently for each of the two networks using a variety of data subsets and starting models we obtained stable estimates of the velocity structure independent of the initial velocity models for both the cse and the usgs network data the velocities of two upper crustal layers proved to be indistinguishable from a model with a single layer over a half space for the cse network the best p wave velocity model comprises an 8 km thick upper crustal layer of 5 2 km sk overlying a 5 9 km sk half space using data from the usgs network alone a similar velocity model was obtained with the exception of a significantly higher velocity v 6 3 km sk for the mid crustal half space these results contradict previously published velocity models featuring anomalously low or high seismic velocities in the upper to mid crust hypocentral parameters were redetermined for approximately 26 000 events occurring during the period 1975 82 using the newly obtained velocity models and station corrections most of the seismicity in the study area is associated with active deformation of the sedimentary rocks of the peter the first range the distribution of hypocentres within the range suggests the presence of a southeastdipping zone of seismicity that can be traced updip to the petrovsky thrust fault beneath this upper crustal seismicity at a depth of 12 17 km is an aseismic zone that may be related to the presence of low strength evaporites at the base of the sedimentary section this aseismic zone is in turn underlain by anomalously deep crustal seismicity at a depth of 17 30 km the deeper seismicity appears to be associated with a southeast dipping feature approximately 10 km in thickness this dipping seismic zone is interpreted as a zone of intracontinental subduction whose surface expression is the vakhsh thrust fault at the frontal edge of the peter the first range

sensitivity of static stress calculations to the earthquake slip distribution 1 the apparent strong correlation between coulomb stress changes and the spatial distribution of aftershocks suggests the possibility of making near real time estimations of areas at risk of experiencing off fault aftershocks in order to do this in practice a number of issues must first be addressed including the extent to which the main shock slip must be known in detail before a meaningful stress map can be constructed here we investigate this issue by constructing a time ordered sequence of slip solutions for the landers earthquake computing coulomb stress changes for each solution and quantitatively comparing the stress field with the observed aftershocks by 1 resolving the coulomb stress change onto the aftershock nodal planes and calculating the percentage of events consistent with triggering and 2 constructing a two dimensional map of coulomb stress and computing the correlation coefficient between the positive and negative areas and the locations of the aftershocks we find that slip solutions based on empirical relations and either focal mechanism or moment tensor data produce stress fields inconsistent with the observed spatial distribution of aftershocks whereas slip solutions incorporating the correct rupture geometry but greatly simplified slip produce stress fields consistent with the aftershock distribution when very near fault events are excluded we further find that resolving stress perturbations onto earthquake nodal planes and computing the percentage of events experiencing positive coulomb stress provides a poor measure of success because of the limited range of structures on which events occur and the compatibility of the main shock stress field with these structures our results support the hypothesis that coulomb stress changes affect the spatial distribution of aftershocks and suggest that meaningful calculations of coulomb stress can be made as soon as an earthquake s rupture geometry is well constrained

earthquake spatial distribution the correlation dimension summary we review methods for determining the fractal dimensions of earthquake epicentres and hypocentres paying special attention to the problem of errors biases and systematic effects among effects considered are earthquake location errors boundary effects inhomogeneity of depth distribution and temporal dependence in particular the correlation dimension of earthquake spatial distribution is discussed techniques for its evaluation presented and results for several earthquake catalogues are analysed we show that practically any value for the correlation dimension can be obtained if many errors and inhomogeneities in observational data as well as deficiencies in data processing are not properly considered it is likely that such technical difficulties are intensified when one attempts to evaluate multifractal measures of dimension taking into account possible errors and biases we conclude that the fractal dimension for shallow seismicity asymptotically approaches 2 20 0 05 for a catalogue time span of decades and perhaps centuries the value of the correlation dimension declines to 1 8 1 9 for intermediate events depth interval 71 280 km and to 1 5 1 6 for deeper ones

experimental study on the electrical conductivity of pyroxene andesite at high temperature and high pressure the electrical conductivity of pyroxene andesite was in situ measured under conditions of 1 0 2 0 gpa and 673 1073 k using a yj 3000t multi anvil press and solartron 1260 impedance gain phase analyzer experimental results indicate that the electrical conductivities of pyroxene andesite increase with increasing temperature and the electrical conductivities decrease with the rise of pressure and the relationship between electrical conductivity and temperature t conforms to an arrhenius relation within a given pressure and temperature range when temperature rises up to 873 923 k the electrical conductivities of pyroxene andesite abruptly increase and the activation enthalpy increases at this range which demonstrates that pyroxene andesite starts to dehydrate by the virtue of the activation enthalpy 0 35 0 42 ev and the activation volume 6 75 1 67 cm3 mole which characterizes the electrical properties of sample after dehydration we consider that the conduction mechanism is the small polaron conduction before and after dehydration and that the rise of carrier concentration is the most important reason of increased electrical conductivity

statistical model for standard seismicity and detection of anomalies by residual analysis abstract a statistical point process model is derived to describe the standard activity of earthquake occurrences by assuming that general seismicity is given by the superposition of aftershock sequences the parameters are estimated ty the maximum likelihood method using the estimated model the residual point process of the data is defined and used to find the anomalies which are included in the data set but not captured in the considered model for the standard seismicity for instance seismic quiescences can be measured quantitatively by using the residual process some examples are provided to illustrate such analyses furthermore a time series of the magnitudes on the residual point process is considered to investigate its dependence either on the time or on the history of the seismicity by assuming the exponential distribution at each time and modelling of the b value we can examine such dependences and estimate them two practical examples are shown

magnitude of completeness b value and spatial correlation dimension of earthquakes in the south baikal basin baikal rift system abstract magnitude of completeness b value and correlation dimension of spatial epicenter distribution were estimated for the south baikal basin using earthquake catalogue for the period of digital observations all estimated parameters were mapped with a one for all approach that allowed revealing their spatial variability the value of the completeness magnitude which was evaluated on the frequency magnitude distribution was found to range from mc 1 0 to 1 6 over the basin depending on network configuration change with the average value of 1 1 0 1 then b value in the gutenberg richter relation was estimated by maximum likelihood method based on the catalogue with m 1 1 earthquakes the lower b value 0 81 0 03 was revealed for the southern part of the basin which is under transtension stress regime in contrast to pure extension characteristic for the rest of the territory the higher b value 1 01 0 01 was obtained for the area to the north east of the selenga delta where two of the largest baikal earthquakes occurred in the last 150 years and which is characterized by more heterogeneous crust structure correlation dimension in the southern part of the basin was found to be closed to 1 that is interpreted as a tendency of epicenters to be distributed along a line whereas the central part is characterized by a higher value that corresponds to a tendency of epicenters to be distributed over a plane rather than along lineaments a comparison of the southern and central basins which make up the tectonically single south baikal basin shows that seismicity of the central basin is characterized by higher b values and correlation dimension that may imply different stress level and or faulting type

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

crustal structure of the ionian margin of sicily etna volcano in the frame of regional evolution abstract crustal imaging could be achieved on normal incidence reflection profiles offshore eastern sicily by using industrial grade reflection seismic with improved marine sources thick recent sediments a reflective pile including the mesozoic deposits a transparent upper crust and a band of low frequency reflections attributed to the lower crust are imaged in the seismic sections the structure of the crust and its thickness show features inherited from the mesozoic evolution as a passive margin by which ionian basin crust was formed around the hyblean continental promontory of africa to constitute the southern plate in the later convergence with europe the seismic images are also marked by the lithospheric deformation due to the neogene overriding of the northern part of this paleomargin by the calabro peloritan block of european continental crust this transpressive motion may have been guided along the northern part of this paleomargin where the seismic profiles evidence a hinge line between the northward upslope of the moho of that old passive margin and its downslope to the present slab under the tyrrhenian sea etna volcano is located at the intersection of this mantle upwarp by a zone of active sea bottom normal faults which cut across the formerly constructed compressional belt the onset of its volcanic activity is roughly coeval with that of the cessation of interplate thrusting and could hence be related to a change of the coupling of the ionian slab this slab is now probably disconnected from the overriding plate and rolled back in front of the expanding hot tyrrhenian asthenospheric dome with the mobilisation of a viscous mantle material at depth an active lithospheric fault is here imaged which cuts over more than 100 km into the ionian basin the fault runs from the tyrrhenian margin in the sse direction of etna updip of the southwestern lateral edge of this slab leaving north eastward the extruded calabrian block and on its south westward edge the uplifted crust and mantle structures of etna along it the crust including the mesozoic and deeper layers has sagged vertically in the segment in front of the slab with a finite throw across the fault increasing from the basin towards etna

artificial and natural changes in the rates of seismic activity a case study of the garm region tadjikistan cis summary seismicity rate variations observed in earthquake catalogues can be natural i e associated with temporal variations in the seismic process or they can be artificial i e related to changes in the networks of seismic stations used to create these catalogues such artificial changes must be identified and corrected before real variations can be reliably examined this paper demonstrates techniques for modelling of the observed changes in seismicity rates in order to determine their origin the main technique used here has been previously applied to a number of catalogues to identify times of rate changes it can be used to demonstrate the magnitude dependence of these changes and the existence of two major types of possible artificial rate variations detection changes and magnitude shifts in addition two new techniques are applied one of them the variable window technique makes use of windows of different sizes to sample the data thus addressing some of the shortcomings of the original approach the other new technique catalogue randomization helps analyse the cause of some of the rate changes it is most helpful in the cases of pure magnitude shifts the use of these techniques is demonstrated examining data from the garm region tadjikistan former soviet union the garm earthquake catalogue includes more than 85 000 events for the period 1955 january 1989 april and covers an 80 km x 100 km area in the collisional zone between the indian and eurasian plates known changes in the garm network recently documented in detail were compared with the rate changes identified with the above techniques of the 18 main rate variations identified at least two thirds were found to be artificial most of them were readily associated with reported changes in the network such as closure and opening of stations and or changes in instrumentation of the rate changes determined to be natural most prominent were the ones associated with a possible quiescence preceding a m6 3 event and its aftershock sequence finally other authors reports of linear trends and annual periodicity in the seismic activity at garm are critically examined

quantifying a potential bias in probabilistic seismic hazard assessment seismotectonic zonation with fractal properties the accurate definition and characterization of relevant seismic sources are critical steps in probabilistic seismic hazard assessment psha this is particu larly challenging in low seismicity regions because observation periods are relatively short seismicity is often diffuse and active faults are difficult to identify in such regions seismogenic sources are typically represented as areal sources zones with equal seismic potential however observed seismicity is never truly uniformly dis tributed but clusters at all scales a reflection of the seismotectonic forces and tectonic structures in this study we use a fractal scaling approach to explore a more realistic characterization of the seismicity distribution within each source zone for a hypothe tical square source zone we compute hazard curves and hazard maps resulting from simulations of uniformly distributed seismicity fractal dimension d 2 0 and we compare these with those resulting from simulations of clustered seismicity 1 0 d 2 0 we find that the assumption of uniform distribution of events leads systematically to a higher estimate of hazard within the source zone this overestima tion is increasing for lower probability levels equally important the assumed uniform distribution underestimates the uncertainty of the hazard by up to a factor of three we perform an extensive sensitivity study of psha input parameters illustrating the complexity of the interaction between the specific setup and the resulting impact on the psha we apply the fractal scaling approach to the seismicity of switzerland and measure the fractal dimension of instrumental seismicity for the past 30 yr d 1 5 using this value for synthetic catalogs we build a fractal seismic zonation and hazard model we find that in general the assumption of uniform distribution of events over estimates the mean hazard in switzerland by 3 to 20 and the uncertainty distribu tion estimation is 50 to 100 narrower than in fractal distribution depending on the location and the probability level of interest

electrical conductivity of dry and hydrous naalsi 3 o 8 glasses and liquids at high pressures we report the first study of electrical conductivities of silicate melts at very high pressures up to 10 gpa and temperatures up to 2 173 k impedance spectroscopy was applied to dry and hydrous albite naalsi3o8 glasses and liquids with 0 02 5 7 wt h2o at 473 1 773 k and 0 9 1 8 gpa in a piston cylinder apparatus using a coaxial cylindrical setup measurements were also taken at 473 2 173 k and 6 10 gpa in two multianvil presses using simple plate geometry the electrical conductivity of albite melts is found to increase with temperature and water content but to decrease with pressure however at 6 gpa conductivity increases rapidly with temperature above 1 773 k so that at temperatures beyond 2 200 k conductivity may actually increase with pressure moreover the effect of water in enhancing conductivity appears to be more pronounced at 6 gpa than at 1 8 gpa these observations suggest that smaller fractions of partial melt than previously assumed may be sufficient to explain anomalously high conductivities such as in the asthenosphere for dry melt at 1 8 gpa the activation energy at t 1 073 k is higher than that at t 1 073 k and the inflection point coincides with the rheological glass transition upon heating at 6 10 gpa dry albite glass often shows a conductivity depression starting from 1 173 k due to crystallization followed by rapid conductivity enhancement when temperature approaches the albite liquidus for hydrous melts at 0 9 1 8 gpa the activation energies for conductivity at 1 373 k are lower than those at 973 k with a complex transition pattern in between electrical conductivity and previously reported na diffusivity in albite melt are consistent with the nernst einstein relation suggesting the dominance of na transport for electrical conduction in albite melts

the influence of partial melting on the electrical behavior of crustal rocks laboratory examinations model calculations and geological interpretations abstract the complex electrical impedance of a granulite has been determined over the frequency range 10 1 to 105 hz at temperatures between 600 and 1200 c at normal pressure and different oxygen fugacities in the stability field of magnetite the impedance spectroscopic is measurements are compared with the results of melting experiments performed under the same experimental conditions and with the same rock sample as the is measurements a strong increase in the electrical conductivity of about one and a half orders of magnitude is observed during partial melting this increase is explained by the formation of an interconnected network of melt the wetting of the grain surfaces starts slightly above the solidus however complete interconnection of the network is detected at higher temperatures 1070 c and hence higher melt fractions 10 vol this is explained by deviations from the equilibrium fabric of the partially molten sample with a modified brick layer model mblm the electrical conductivity is calculated as a function of the observed melt portion this model is valid if the melt forms a complete interconnected network at the grain boundaries the electrical conductivity at different temperatures was modeled using the results of the melting experiments and the mblm melt 10 s m with ea melt 1 ev solid 0 01 s m with ea solid 1 4 ev the results of the laboratory examinations were applied to different crustal regions where partially molten rocks are assumed to exist the same mblm is used to estimate the melt fraction that is necessary to explain the high conducting zones hczs observed in the crust beneath the andean orogen the pyrenees and the tibetan plateau at least 14 4 and 4 vol of interconnected melt are necessary to produce the observed conductivity respectively the actual amount of melt should be higher due to perturbation problems and melt trapped in pockets

application of gravity and deep dipole geoelectrics in the volcanic area of mt etna sicily abstract the structural pattern of the basement of the mt etna volcano is studied by combining results from new gravity and deep dipole geoelectric field data at first the bouguer map was separated into regional and residual contour maps by a 50 km cut off wavelength then by the geoelectric interpretation n s and e w resistivity cross sections were elaborated which were used as guidelines for modelling gravity residuals after observing a close correspondence between bouguer anomalies and resistivity classes by a trial and error adjustment to the relationship between resistivity and density a 3 d block model of the basement was finally constructed which consistently matched with both gravity and geoelectric information content two main conclusions emerged from the combined interpretation the first is the presence of diffuse inhomogeneities in the upper portion of the basement down to an average depth of 2 km below sea level in contrast with the regularity of the explored underlying portion the second is the absence of geophysical markers suggesting the existence of a large magmatic chamber down to about 3 km below sea level

comparisons of vertical winds measured with the chatanika and poker flat radars the poker flat alaska mst radar and the chatanika incoherent scatter radar operated in an st mode were simultaneously operated to compare vertical air motions in the troposphere and lower stratosphere the two nearby radars were operated with their antennas pointed vertically with 750 m range resolutions the radars have widely differing operating frequencies 50 mhz and 1290 mhz for the long wavelength radar returned signals are thought to result from combination of specular reflection and turbulence scattered signals with either mechanism possibly being dominant at various heights the short wavelength radar is expected to receive only turbulence scattered signals both radars were able to detect motions of a few centimeters per second and detect the presence of similar short period wave motions however when the data were averaged for an hour or more significant differences in the averaged data were observed we suggest that the differences are probably due to either experimental errors or apparent vertical motions observed with the poker flat radar as a result of off vertical specular echoes from horizontally moving tilted layers an estimate of an apparent antenna pointing direction of 0 27 off vertical has been made for the poker flat radar with the available data we are unable to determine if this is a true antenna pointing error or the result of horizontally moving tilted layers on the specular echoing mechanism at heights where specular echoes are dominant the physical pointing direction of the antenna is not critical the effective pointing angle of the antenna is determined by the normal to the specular reflection layer in this case a component of the horizontal wind may be interpreted as a vertical wind component because small tilts in the atmospheric layers control the effective antenna pointing direction for the other heights where nonspecular scattering is dominant the physical pointing direction of the antenna is important for vertically directed antennas small pointing errors may cause a component of the horizontal wind to be interpreted as a vertical motion

observations of clear air turbulence and winds with the millstone hill radar the millstone hill 440 mhz radar at westford massachusetts has been upgraded for studies of turbulence and winds in the troposphere and lower stratosphere useful data have been obtained up to 20 km altitude the radar has been operated with a peak pulse power of 1 1 5 mw a pulse length of 10 s and a pulse repetition of 500 hz the 150 foot diameter steerable antenna has been used differently in three types of experiments 1 antenna azimuth scans with fixed elevation 2 elevation scan with fixed azimuth and 3 fixed antenna azimuth scan experiments can obtain both the horizontal and the vertical wind components antenna elevation scans have been used to investigate the horizontal structure of turbulence the fixed antenna experiments provide maximum time resolution and are useful for studying the occurrence of waves waves in both the velocity and cn2 the refractive index turbulence structure constant have been frequently observed at heights near the tropopause and below the waves have periods 10 20 min and have been interpreted as internal gravity waves the largest amplitude waves have been found to occur 1 2 km below the level of a velocity shear waves generally persist for several cycles by using the antenna elevation scan method the level of turbulence as measured by the cn2 value has been measured at points separated by 10 20 km horizontal patches of turbulence have been found that appear to move with the wind

northeastern pacific mantle conductivity profile from long period magnetotelluric sounding using hawaii to california submarine cable data we present results of a long period magnetotelluric mt investigation of the electrical structure beneath the eastern north pacific the electric field data consist of 2 years of continuously recorded voltages across an unpowered 4000 km long submarine telephone cable haw 1 extending from point arena california to oahu hawaii the electric field measurements are coherent to some degree with magnetic field measurements from honolulu observatory at periods of 0 1 to 45 days this coherence is enhanced at long periods over that observed with point electric field sensors due to horizontal averaging of the motional electric fields of spatial scale smaller than the cable length significantly diminishing their effect robust controlled leverage mt response estimates and their jacknife confidence limits are computed for the haw 1 to honolulu data an equivalent scalar mt response obtained from honolulu magnetic variations data is used to correct the haw 1 mt response for static shift and to extend the mt response estimate to periods of 100 days the composite response function satisfies necessary and sufficient conditions for consistency with a one dimensional conductivity structure and is most sensitive to structure between 150 and 1000 km inversion of the mt response reveals a conductive zone 0 05 0 1 s m between 150 and 400 km depth and a positive gradient below 500 km these observations are consistent with previous mt studies in the north pacific this upper mantle conductivity is too high to be explained by solid state conduction in dry olivine using reasonable mantle geotherms calculations based on measurements of hydrogen solubility and diffusivity in olivine indicate that h dissolved in olivine possibly combined with a lattice preferred orientation consistent with measured seismic anisotropy provide sufficient conductivity enhancement to explain the inversion results the high conductivity may also be explained by the presence of gravitationally stable partial melt comparison of the haw 1 results with long period mt studies conducted on land reveals differences in upper mantle conductivity between different tectonic regimes in particular the upper mantle beneath the pacific ocean is considerably more conductive than that beneath the canadian shield and similar in conductivity to that beneath the basin and range

geothermal evolution of an intruded dike in the rift zone of kilauea volcano hawaii from vlf and self potential measurements abstract self potential sp and vlf measurements were made in 1973 1975 1995 1997 and 2012 across a basaltic dike that intruded into the koae fault zone of kilauea volcano hawaii in may 1973 the sp anomaly remained strong throughout in 2012 it was at about 60 of the strength it had in 1973 in contrast the vlf anomaly though diminished was still observable in 1995 1997 but by 2012 it had disappeared a hydrothermal dike model with parameters calibrated by modeling the solidification of kilauea iki lava lake is used to calculate temperatures and conductivity variation following jaeger s 1957 method we find that the time in years for a dike of width w m to solidify is 0 0075w2 thus a 1 m dike solidifies within the first few days and after 39 years is only tens of degrees above ambient given the orders of magnitude difference between the conductivities of wet and dry basalt we infer that after solidification the vlf anomalies were caused by induction in a localized veil of wet hot basalt enveloping the dike that was generated initially by condensation of steam and subsequently by condensation of evaporated water as temperatures reduced the conductivity anomaly persisted until the mid nineties by 2012 temperatures and condensation were too small for a vlf signal the persistent sp anomaly is attributed to localized fluid disruption with evaporation mainly at the water table and in the vadose zone streaming potentials are associated with evaporative circulation in the vadose zone next to the dike a positive potential is generated by upward flow of moisture laden air with a smaller negative potential on its flanks from downward infiltrating rainwater the analysis indicates that the combination of sp and vlf measurements can characterize the evolving geothermal regime of intrusions above the water table

global omori law decay of triggered earthquakes large aftershocks outside the classical aftershock zone 1 triggered earthquakes can be large damaging and lethal as evidenced by the1999 shocks in turkey and the 2001 earthquakes in el salvador in this study earthquakes with ms 7 0 from the harvard centroid moment tensor cmt catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected about 61 of earthquakes that occurred near defined as having shear stress change 0 01 mpa the ms 7 0 shocks are associated with calculated shear stress increases while 39 are associated with shear stress decreases if earthquakes associated with calculated shear stress increases are interpreted as triggered then such events make up at least 8 of the cmt catalog globally these triggered earthquakes obey an omori law rate decay that lasts between 7 11 years after the main shock earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid omori s law is one of the few time predictable patterns evident in the global occurrence of earthquakes if large triggered earthquakes habitually obey omori s law then their hazard can be more readily assessed the characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of ms 7 0 i show an example application to the m 7 7 13 january 2001 el salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than coulomb stress change calculations

volcanic structure of the southern sector of mt etna after the 2001 and 2002 eruptions defined by magnetotelluric measurements two magnetotelluric mt surveys were carried out on the mt etna volcano after two of the most intense eruptions of the last 30 years which took place in summer 2001 and winter 2002 2003 surveying was pursued for two main reasons first we sought to contribute to the definition of the first order structure and physico chemical state temperature fluids melts of a volcano that has been extensively explored and monitored by means of various geophysical methods but where only few electrical and electromagnetic surveys have been performed secondly we acquired mt data in the same sites in the two different surveys with the aim of monitoring the possible changes of the first order structure since conditions are expected to vary on an active volcano such as etna and are supposed to be linked to the eruptive events soundings have been acquired in an e w 10 km long profile across the southern flank of mt etna at a distance of almost 6 km south from the central crater the first survey was carried out three months after the 2001 eruption inverse models define a pronounced 4 km thickness low resistivity section at a depth of about 1 km b s l to the west to the east a low resistivity section is still present but appears deeper thinner and more resistive and a shallow low resistivity anomaly also exists the shallow anomaly to the east is tentatively correlated with altered and clayey volcanic units and or temporary groundwater storage the deep anomalies are interpreted as being due to melt storage at shallow depths which was not exhausted during the eruption this would be confirmed by the abundance of lava erupted within one year from the end of the survey the few good sites retrieved in the second survey carried out a few weeks after the eruption of 2002 2003 confirm the picture defined in the first survey and provide a better definition of the bottom of the deep anomaly located in the sedimentary basement

the fractal description of seismicity summary the stable estimation of multifractal characteristics of seismicity is considered the data are world and accessible regional catalogues of m 2 4 events our attention is focused on the range of scales in which the renyi functionals admit of scale invariant behaviour we find that the stable fractal analysis of hypocentres is generally difficult as to epicentres we have carried out a stable analysis for seven regions worldwide in the range of scales 1 1 7 decades the estimates of generalized dimensions admit of tectonic interpretation

theory of time dependent rupture in the earth at a velocity x which is a well defined function of k this propagation is stable and quasi static and is referred to as subcritical crack growth we shall use the terms stable quasistatic and subcritical to mean propagation at velocities much less than the sonic velocities of the medium this behavior results from stress induced corrosion at the crack tip the principal corrodent for the present application being h20 this behavior has been firmly established in the laboratory for mode i tensile cracks in a wide variety of materials ineluding silicates and silicate glasses see cholz 1968a 1972a martin 1972 wiederhorn and bolz 1970 atkinson 1979 lawn and wilshaw 1975 knott 1973 the form of the relationship between k and x does not vary significantly with the material only the parameters in the law vary as an example we show in figure 1 data on subcritical crack growth in quartz after atkinson 1979 the empirical relationship is found to take the form