equatorial e region electric fields at the dip equator 2 seasonal variabilities and effects over brazil due to the secular variation of the magnetic equator

formation of lava tubes and extensive flow field during the 1991 1993 eruption of mount etna detailed mapping during the 1991 1993 eruption of mount etna has shown that there is a relationship between tumuli ephemeral vents lava tubes and their parent lava flows during this eruption many tubes formed in stationary inflated a a lava flows ephemeral vents at the fronts of these stationary flows and above lava tubes fed secondary lava flows many of which subsequently developed new tubes the resulting complex network of tubes ephemeral vents and secondary flows was responsible for most of the widening thickening and lengthening of the 1991 1993 etna lava flow field the supply of relatively uncooled lava via tubes to distal parts of this flow field allowed lava to flow 3 km farther from the vent than the longest channel fed lava flow our observations suggest that lava tubes play a more important role in the formation of extensive a a flow fields on etna than has previously been recognized

a model for the formation of lava tubes by the growth of the crust from the levees 1 we propose a model to explain lava tube formation by the growth of crust slabs from the levees of a channel toward its center involving solid surface fragments the flow dynamics are described with the steady state solution of the navier stokes equation in a rectangular channel for a newtonian homogeneous isotropic and incompressible fluid the cooling of a lava flow is described by the mechanism of heat conduction into the atmosphere the presence of levees is taken into account both in the dynamical and in the thermal model as long as the flow cools a solid layer forms at the surface much thicker near the levees than at the center of the channel the crust that has formed breaks under the effects of the applied stresses solid blocks slow the fluid down the shear stress at the interface between crust and fluid lava increases and the flow thickens using the thin elastic plate approximation we determine conditions allowing a crust to resist both the action of the shear stress due to the drag of the underlying fluid and the tensile stress due to the weight of the crust itself detecting the required crust thickness and distances from the eruptive vent where the tube can form

ground motion relations for eastern north america predictive relations are developed for ground motions from eastern north american earthquakes of 4 0 m 7 25 at distances of 10 r 500 km the predicted parameters are response spectra at frequencies of 0 5 to 20 hz and peak ground acceleration and velocity the predictions are derived from an empirically based stochastic ground motion model the relations differ from previous work in the improved empirical definition of input parameters and em pirical validation of results the relations are in demonstrable agreement with ground motions from earthquakes of m 4 to 5 there are insufficient data to adequately judge the relations at larger magnitudes although they are consistent with data from the saguenay m 5 8 and nahanni m 6 8 earthquakes the underlying model parameters are constrained by empirical data for events as large as m 6 8

on the relationship between weakening of the northern polar vortex and the lunar tidal amplification in the equatorial electrojet enhanced lunar tidal effects in the equatorial electrojet eej during northern winters in the form of big l days have been known for a long time recent studies suggest that the changes in the tidal propagation conditions due to stratospheric sudden warmings ssw could be responsible for this phenomenon in this work we have used the h component of the magnetic field recorded at huancayo from 1997 2013 to study the relation between the timing and magnitude of the semi monthly lunar tide in the eej and the stratospheric polar vortex weakening pvw we prefer a definition of pvw by taking into account the atmospheric conditions from december to february for each winter our results indicate that the semi monthly lunar tide in the eej gets enhanced during northern winters when a significant pvw occurs and its peak timing and magnitude is correlated with the timing and intensity of pvw the timing of lunar tidal peaks and pvw correlate better than their respective magnitudes our results suggest that the initiation of the lunar tidal enhancement in most of the cases is closely related to a pvw event furthermore we discuss events where the semi monthly lunar tidal enhancements are not well timed with respect to pvw we also suggest that the amount of tropospheric forcing into the stratosphere plays a major role in the enhancement of the lunar tides in the eej

variabilities of the equatorial electrojet in brazil and peru 1 this report presents seasonal and longitudinal variabilities of the equatorial electrojet in the east brazil sao luis 2 3 s 315 8 e 0 5 s dip latitude and west jicamarca peru 11 95 s 283 13 e 0 6 n dip latitude coasts of the continent of south america ground based magnetic field perturbation measurements h for solar maximum 2001 2002 and solar minimum 2006 2007 conditions from the two equatorial stations sao luis and jicamarca have been used for the study the h signal which is a measure of the strength of the equatorial electrojet is spectrally analyzed using wavelet analysis the results of our analysis show that 1 the equatorial electrojet has maxima around equinoxes in jicamarca peru but it has a prominent maximum during southern hemisphere summer centered about december january in sao luis brazil the observed seasonal behavior of the equatorial electrojet in sao luis is highly likely due to the large magnetic declination angle about 20 west there 2 the equatorial electrojet is stronger in the west coast jicamarca compared to the east coast sao luis irrespective of solar activity condition 3 the magnitude of the equatorial electrojet is more variable with season and solar cycle over sao luis than over jicamarca

simulations of the 2004 lava flow at etna volcano using the magflow cellular automata model since the mechanical properties of lava change over time lava flows represent a challenge for physically based modeling this change is ruled by a temperature field which needs to be modeled magflow cellular automata ca model was developed for physically based simulations of lava flows in near real time we introduced an algorithm based on the monte carlo approach to solve the anisotropic problem as transition rule of ca a steady state solution of navier stokes equations was adopted in the case of isothermal laminar pressure driven bingham fluid for the cooling mechanism we consider only the radiative heat loss from the surface of the flow and the change of the temperature due to mixture of lavas between cells with different temperatures the model was applied to reproduce a real lava flow that occurred during the 2004 2005 etna eruption the simulations were computed using three different empirical relationships between viscosity and temperature

site amplifications for generic rock sites seismic shear wave velocity as a function of depth for generic rock sites has been estimated from borehole data and studies of crustal velocities and these velocities have been used to compute frequency dependent amplifications for zero attenuation for use in simulations of strong ground motion we define a genetic rock site as one whose velocity at shallow depths equals the average of those from the rock sites sampled by the borehole data most of the boreholes are in populated areas for that reason the rock sites sampled are of particular engineering significance we consider two genetic rock sites rock corresponding to the bulk of the borehole data and very hard rock such as is found in glaciated regions in large areas of eastern north america or in portions of western north america the amplifications on rock sites can be in excess of 3 5 at high frequencies in contrast to the amplifications of less than 1 2 on very hard rock sites the consideration of unattenuated amplification alone is computationally convenient but what matters for ground motion estimation is the combined effect of amplification and attenuation for reasonable values of the attenuation parameter k 0 the combined effect of attenuation and amplification for rock sites peaks between about 2 and 5 hz with a maximum level of less than 1 8 the combined effect is about a factor of 1 5 at 1 hz and is less than unity for frequencies in the range of 10 to 20 hz depending on t using these amplifications we find provisional values of about ao 70 bars and k 0 0 035 sec for rock sites in western north america by fitting our empirically determined response spectra for an m 6 5 event to simulated values the borehole data yield shear velocities 033o of 618 and 306 rrdsec for rock and soil sites respectively when averaged over the upper 30 m from this we recommend that v30 equals 620 and 310 m sec for applications requiring the average velocity for rock and soil sites in western north america by combining the amplifications for rock sites and the site factors obtained from our analysis of strong motion data we derive amplifications for sites with 17 3o 520 m sec nehrp class c corresponding to a mix of rock and soil sites and v3o 310 and 255 m sec average soil and nehrp class d sites respectively for the average soil site the combined effect of amplification and attenuation exceeds a factor of 2 0 for frequencies between 0 4 and about 4 hz with a peak site effect of 2 4 the peak of the nehrp class d site effect is 2 7

mechanisms of formation of lava tubes 1 we propose a model to describe lava tube formation considering lava as a newtonian fluid moving downslope in a rectangular channel we obtain flow velocity using an analytical steady state solution of the navier stokes equation shear stress is also calculated from velocity for a newtonian incompressible and isotropic fluid a 2 d model with heat flux assigned at the upper surface is introduced to describe lava cooling by radiation into the atmosphere and to obtain the flow temperature lava crust is considered as a plastic body and its rheology is described through the introduction of the yield strength as a function of temperature it describes the capacity of crustal structure to prevent shear deformation for lower shear stress values when lava temperature becomes lower than the solidus value ts a superficial thin solid layer develops in regions where shear stress xy is smaller than yield strength the model shows how the competition between these two functions xy and controls the development of crust width and the possible transition from a mobile crust to a stationary roof for typical parameter values of lava channels on mount etna crust develops in the central part of the flow laterally limited by two crust free regions we analyze the effects of some typical channel irregularities on surface shear stress and as a consequence on crust width growth we consider a variation of channel width and ground slope finding that crust widening is favored by channel widening or slope reduction in both cases the decrease in shear stress produces an increase in the fraction of channel width occupied by solid crust given a set of initial conditions defining eruptive parameters and channel features the model provides critical values of channel width and ground slope that allow tube formation the effect of different effusion rates on crust development is also studied with the result that tube formation is favored by low flow rates corresponding to lower values of xy

seasonal and longitudinal variations of the solar quiet sq current system during solar minimum determined by champ satellite magnetic field observations 1 vector magnetometer observations from the challenging minisatellite payload champ satellite are used to determine the solar quiet sq current system during the recent solar minimum observations from 2006 to 2008 are combined and after removal of a main field model and accounting for field aligned currents the longitudinal and seasonal variation of the sq currents are determined through the method of spherical harmonic analysis comparison with sq currents derived from ground based magnetometers in the african european longitude sector reveals similar amplitudes and seasonal variations indicating that the champ observations can reliably determine the sq current system the seasonal variation is consistent with prior observations during solar minimum conditions and in the northern hemisphere exhibits a primarily annual variation with peak currents during local summer the seasonal variation in the southern hemisphere is characterized by a semiannual variation with the maxima occurring around the equinoxes significant longitudinal variations are also observed and they display a seasonal variability during northern hemisphere summer the predominant feature at local noon is a wave number 1 variation in longitude during the remainder of the year a wave 3 longitudinal structure is observed at this local time the longitudinal variations are considered to be due to a combination of the orientation and strength of the geomagnetic field as well as the tidal winds in the lower thermosphere variations in tidal winds due to nonmigrating tides may influence the dynamo generated electric fields and currents resulting in the observed longitudinal variations of the sq current function

the influence of nonmigrating tides on the longitudinal variation of the equatorial electrojet 1 the climatological model of the equatorial electrojet eejm 1 derived from orsted champ and sac c satellite measurements provides the opportunity to investigate the longitudinal variation of the current strength in detail special emphasis is put in this study on the effect of nonmigrating tides we have found that the influence of the diurnal eastward propagating mode with wavenumber 3 de3 is particularly strong in polar orbiting satellite observations the de3 tidal signal appears as a four peaked longitudinal structure we have put special emphasis in our analysis to isolate the de3 contribution from other sources contributing to the wavenumber 4 structure in satellite data the amplitude of the de3 signature in the eej not only peaks during equinox seasons but is also strong around the june solstice when looking at the modulation of the eej intensity the de3 accounts for about 25 during the months of april through september it is thus the dominant cause for longitudinal variations during december solstice months the influence of de3 is negligible a secondary three peaked longitudinal pattern emerges during solstice seasons when the de3 influence is removed from the data available it is however not clear whether this pattern is related to any tidal drivers

longitudinal variation of the lunar tide in the equatorial electrojet the atmospheric lunar tide is one known source of ionospheric variability the subject received renewed attention as recent studies found a link between stratospheric sudden warmings and amplified lunar tidal perturbations in the equatorial ionosphere there is increasing evidence from ground observations that the lunar tidal influence on the ionosphere depends on longitude we use magnetic field measurements from the champ satellite during july 2000 september 2010 and from the two swarm satellites during november 2013 february 2017 to determine for the first time the complete seasonal longitudinal climatology of the semidiurnal lunar tidal variation in the equatorial electrojet intensity significant longitudinal variability is found in the amplitude of the lunar tidal variation while the longitudinal variability in the phase is small the amplitude peaks in the peruvian sector 285 e during the northern hemisphere winter and equinoxes and in the brazilian sector 325 e during the northern hemisphere summer there are also local amplitude maxima at 55 e and 120 e the longitudinal variation is partly due to the modulation of ionospheric conductivities by the inhomogeneous geomagnetic field another possible cause of the longitudinal variability is neutral wind forcing by nonmigrating lunar tides a tidal spectrum analysis of the semidiurnal lunar tidal variation in the equatorial electrojet reveals the dominance of the westward propagating mode with zonal wavenumber 2 sw2 with secondary contributions by westward propagating modes with zonal wavenumber 3 sw3 and 4 sw4 eastward propagating waves are largely absent from the tidal spectrum further study will be required for the relative importance of ionopsheric conductivities and nonmigrating lunar tides

high frequency earthquake ground motion scaling in utah and yellowstone velocity seismograms from the university of utah seismograph stations are used to quantify high frequency ground motion scaling for the yellowstone region and the wasatch front in utah this study uses a data set consisting of over 3000 waveforms from 93 stations and 506 regional earthquakes and mining associated seismic events that occurred in the years 1995 2001 all events lie within the upper crust with magnitudes less than 5 5 the signals were processed to examine the peak ground velocity and fourier velocity spectra in the frequency range of 1 0 16 0 hz regression results for utah are characterized by rapid decreases of amplitude at short distances which requires low q and a rapid geometrical spreading g r for the forward modeling q f 160 f 0 75 eff 0 05 sec and 300 bars are selected to predict the excitation terms when combined with the derived geometrical spreading the frequency dependent excitation of mining associated events differs significantly from that of earthquakes because of either an additional attenuation due to shallow source depth or apparent low stress drops associated with the slow collapse of long tunnels a q f 140 f 0 70 and geometrical spreading less rapid than r 1 0 at short distance ranges are used to describe the wave propagation distance dependence in the yellowstone region the yellowstone attenuation functional d r f is very different from that of utah perhaps because a shallow wave guide in the caldera traps more energy the yellowstone excitation spectra were modeled using 30 bars and eff 0 04 sec manuscript received 24 october 2003

the equatorial electrojet an integrated treatment of observations and models of the undisturbed equatorial electrojet is presented previous reviews have concentrated on particular aspects of the electrojet phenomenon such as ground magnetic variations the counterelectrojet or e region electron density irregularities and associated plasma instabilities here accomplishments during the past 15 years involving all aspects of the phenomenon are covered and where possible interrelated observational and theoretical studies during recent years have emphasized the local time longitude vertical and latitudinal structure of electric fields and currents in the electrojet this review similarly places its emphasis along these lines and by necessity involves a detailed examination of electrodynamic coupling with the neutral atmosphere tidal oscillations in temperature composition and winds the review concludes with an assessment of current knowledge concerning the equatorial electrojet and suggestions for the future direction of observational and theoretical research on electrodynamical processes in the equatorial ionosphere

longitudinal variation of the e region electric fields caused by atmospheric tides 1 polarization electric fields created by the e and f region dynamos cause the uplift of f region plasma the subsequent redistribution of that plasma along the magnetic field lines creates the equatorial ionospheric anomaly eia observations of the post sunset eia made by the image and timed satellites are compared here with champ orsted and sac c observations of the noontime equatorial electrojet eej during magnetically quiet periods around equinox the eia and eej show a remarkably similar four peaked wave like longitudinal variation its structure is consistent with the longitudinal variation in the strength of diurnal tides that drive the e region dynamo this indicates a strong vertical coupling between the ionosphere and troposphere because the four peaked tidal structure is driven by tropospheric weather furthermore the dayside ionospheric conditions are found to perform the global scale longitudinal structure of the post sunset ionosphere at low latitudes

variability of equatorial counter electrojet signatures in the indian region 1 the limited longitudinal extent of equatorial counter electrojet cej has been inferred by several workers based on the analysis of ground data however the scale length of cej characteristics at 2 hours or less has not been estimated so far the present study seeks to characterize the longitudinal variability of cej phenomena at a longitudinal separation of 15 using hourly averaged variations at two equatorial electrojet eej pairs of stations hyderabad vencode at 77 e and port blair campbell bay at 93 e the nature of cej events are classified by time of occurrence and studied using 12 months of concurrent data at the two longitudes from examination of 323 cej events at ven vencode and 239 at cby campbell bay over a period of 346 days the observations are i the occurrence of cej is not simultaneous at ven and cby for about 40 of events ii the amplitude and occurrence frequency of cej events is greater at ven than cby during both kp 2 and kp 2 iii the influence of westward currents on the eej peak was evidenced by early or late peak occurrences comprising about 175 days at ven and 89 days at cby it is established here that considerable variability of cej signatures is observed between the two longitudes at 15 separation revealing the impact of local electrodynamics these local processes therefore significantly influence the characteristics of eej

development of lava tubes in the light of observations at mauna ulu kilauea volcano hawaii during the 1969 1974 mauna ulu eruption on kilauea s upper east rift zone lava tubes were observed to develop by four principal processes 1 flat rooted crusts grew across streams within confined channels 2 overflows and spatter accreted to levees to build arched roofs across streams 3 plates of solidified crust floating downstream coalesced to form a roof and 4 pahoehoe lobes progressively extended fed by networks of distributaries beneath a solidified crust still another tube forming process operated when pahoehoe entered the ocean large waves would abruptly chill a crust across the entire surface of a molten stream crossing through the surf zone these littoral lava tubes formed abruptly in contrast to subaerial tubes which formed gradually all tube forming processes were favored by low to moderate volume rates of flow for sustained periods of time tubes thereby became ubiquitous within the pahoehoe flows and distributed a very large proportionof the lava that was produced during this prolonged eruption tubes transport lava efficiently once formed the roofs of tubes insulate the active streams within allowing the lava to retain its fluidity for a longer time than if exposed directly to ambient air temperature thus the flows can travel greater distances and spread over wider areas even though supply rates during most of 1970 1974 were moderate ranging from 1 to 5 m3 s large tube systems conducted lava as far as the coast 12 13 km distant where they fed extensive pahoehoe fields on the coastal flats some flows entered the sea to build lava deltas and add new land to the island the largest and most efficient tubes developed during periods of sustained extrusion when new lava was being supplied at nearly constant rates tubes can play a major role in building volcanic edifices with gentle slopes because they can deliver a substantial fraction of lava erupted at low to moderate rates to sites far down the flank of a volcano we conclude therefore that the tendency of active pahoehoe flows to form lava tubes is a significant factor in producing the common shield morphology of basaltic volcanoes

predicting the impact of lava flows at mount etna italy this work was sponsored by the italian ministry for education university and research firb project n rbau01rmz4 lava flow simulations by cellular automata and by the national civil defence department and ingv national institute of geophysics and volcanology project v3 6 09 v3 6 etna

the influence of viscous and latent heating on crystal rich magma flow in a conduit the flow dynamics of crystal rich high viscosity magma is likely to be strongly influenced by viscous and latent heat release viscous heating is observed to play an important role in the dynamics of fluids with temperature dependent viscosities the growth of microlite crystals and the accompanying release of latent heat should play a similar role in raising fluid temperatures earlier models of viscous heating in magmas have shown the potential for unstable thermal runaway flow as described by a gruntfest number using an arrhenius temperature dependence for the viscosity but have not considered crystal growth or latent heating we present a theoretical model for magma flow in an axisymmetric conduit and consider both heating effects using finite element method techniques we consider a constant mass flux in a 1 d infinitesimal conduit segment with isothermal and adiabatic boundary conditions and newtonian and non newtonian magma flow properties we find that the growth of crystals acts to stabilize the flow field and make the magma less likely to experience a thermal runaway the additional heating influences crystal growth and can counteract supercooling from degassing induced crystallization and drive the residual melt composition back towards the liquidus temperature we illustrate the models with results generated using parameters appropriate for the andesite lava dome forming eruption at soufriere hills volcano montserrat these results emphasize the radial variability of the magma both viscous and latent heating effects are shown to be capable of playing a significant role in the eruption dynamics of soufriere hills volcano latent heating is a factor in the top two kilometres of the conduit and may be responsible for relatively short term days transients viscous heating is less restricted spatially but because thermal runaway requires periods of hundreds of days to be achieved the process is likely to be interrupted our models show that thermal evolution of the conduit walls could lead to an increase in the effective diameter of flow and an increase in flux at constant magma pressure

a transform continental margin rich in hydrocarbons gulf of california conventional and near bottom geophysical surveys mapped shallow deformational structures and sediment accumulation patterns along part of the actively shearing continental margin of sonora including the intersection with a guaymas basin spreading center the principal strike slip faults occupy a zone 1 2 km 0 6 1 2 mi wide along the lower slope with a ridge of tightly folded sediments raised by uplift of sheared basement at the abrupt boundary between continental and oceanic crust this transform ridge and a continental rise on its seaward slope grows as the fault zone ages away from the spreading center intersection shoaling at a net rate of 500 m m y 1 600 ft m y despite erosion of its crest a clathrate horizon in the upper 80 m 260 ft of sediment is inferre from bottom simulating reflectors in the rise and lower slope hydrocarbon seeps occur at 1 600 m 1 mi below sea level along the crest of the transform ridge and patchy gas accumulation and seepage are recognized on a young marginal plateau

spatio temporal characterization of the equatorial electrojet from champ orsted and sac c satellite magnetic measurements received 4 may 2007 revised 20 june 2007 accepted 12 june 2007 published 13 september 2007 1 the equatorial electrojet eej is an eastward electric current on the day side flowing in a narrow band along the dip equator in the ionospheric e region recent magnetic observations from the champ orsted and sac c satellites comprising more than 95 000 dip equator crossings from 1999 to 2006 have provided an unprecedented longitudinal coverage of the eej magnetic signature we have used these data to construct an empirical model of the eej current climatological mean and day to day variability as a function of longitude local time season and solar flux our model has been successfully verified against vertical drift data from the julia radar at jicamarca we have also used the eej observations to estimate the self correlation of the eej confirming short longitudinal correlation lengths of 15 and finding a temporal correlation length of 2 4 h our model s predictions of the eastward electric field and its standard deviation may provide useful input to various kinds of ionospheric simulations coefficients and software are available online at http models geomag us eej html and http www earthref org

morphometric analysis of lava flow units case study over lidar derived topography at mount etna italy abstract high resolution lidar derived digital elevation models of volcanic areas can significantly improve knowledge of lava flow morphology and emplacement mechanisms here we focus on single flow units presenting a new semi automatic procedure which provides a quantitative analysis of their shape the method relies on the automatic processing of the elevation profiles obtained on transects orthogonal to the flow unit axis the initial phase of the mount etna flank eruption from september 2004 is taken as test case and the procedure is applied on an active lava flow which was emplaced on the eastern flank of the volcano the main topographic dataset used is a 2 m resolution digital elevation model obtained from a lidar survey starting from the axis of a lava flow unit our method yields morphometric data on the flow unit at a 2 m spacing calculating parameters including flow width channel width the heights of the levees inward and outward slope of levees and estimating pre emplacement slope along the axis the procedure is embedded in a customized gis which allows easy processing handling and displaying of data the procedure has also been applied to another flow unit emplaced during the october november 1999 overflow from the bocca nuova crater results show that the channel width seems to accommodate first order trends of the pre emplacement slope along the flow unit axis while it is little affected by high frequency changes in slope in contrast flow unit width and flow unit thickness are apparently influenced by small scale changes in slope the different emplacement conditions of the two flow units are reflected by the overall contrasting morphologies as shown by the different average thickness and by the different ratios between i flow width vs channel width and ii flow unit section area vs channel width the new method provides an enhanced systematic and thorough morphometric description of flow units which may improve the understanding of the emplacement mechanisms of lava flows on earth and other planets

waveform analysis of scholte modes in ocean sediment layers summary in an effort to determine the characteristics of seismic noise on the ocean bottom and its relationship to the structure of the sea floor we have adapted the method of nonlinear waveform fitting to accommodate multidimensional models shear velocity j and shear damping qs and have applied it to invert several records of interface waves scholte 1958 from the thumper experiment off southern california waveform fitting is a very powerful tool to determine the s velocity in the top few metres of the sediment starting from 30 m s l at the top clay layer the s velocity increases with a gradient of 2 8 m sk1 m over the first 150 m of sediment a theoretical estimation of the source strength gives coherent estimates of qs as a function of depth for distances between 400 and 1070m from the source the qs models are characterized by very low values 10 20 in the top three metres but by values in excess of 100 below that level the results confirm the identification of the noise as harmonics of interface waves in the area of this experiment the largest noise amplitudes belong to the fundamental mode and penetrate to a depth of about 20 m into the sediment the overtone energy can be appreciable too and is noticeable to about 80m depth the qs structure confirms the strong influence that the sea floor structure has on the noise spectrum the high attenuation at frequencies above 3 4 hz suppresses noise propagation and produces low noise at higher frequencies similarly high attenuation in the asthenosphere suppresses noise propagation below 0 1 hz

qp qs relations in the sedimentary basin of the upper mississippi embayment using converted phases abstract three component digital seismograms recorded by the 40 panda portable array for numerical data acquisition stations in the new madrid seismic zone were analyzed to study seismic wave attenuation in the sedimentary basin using the spectral ratio method a prominent s to p s p converted phase was generated at the boundary between the uppermost sedimentary basin and the underlying paleozoic rocks the direct s wave on the horizontal component is characterized by a lower frequency content than that of the converted s p wave on the vertical component the differences in frequency content between the direct s and the s p converted waves can be attributed to the different attenuation effects between p and s waves in the unconsolidated sediments the spectral ratio between the low frequency s wave and the high frequency converted s p wave from the bottom of the sediments can be used to yield a relationship between q p and q s in the sediments results from panda stations with well constrained spectral ratios in the frequency range from 2 to 25 hz give the q p value ranging from 25 to 60 and q s from 25 to 30 for the sedimentary basin in the upper mississippi embayment

principal components of quiet time temporal variability of equatorial and low latitude geomagnetic fields diurnal variations of the horizontal component of the geomagnetic field h on international quiet days of 1999 2012 measured hourly at two stations in the same longitude zone in the northern hemisphere near and away from the dip equator have been subjected to principal component analysis this technique is also applied to the difference heej of h at these two stations which is attributed to the equatorial electrojet eej the first three principal components pc1 pc2 and pc3 account for 91 96 of the variances in the data maximum contribution to the quiet day variations in h around its peak in the morning hours at both the stations and in the eej comes from the day to day variation of the amplitude of pc1 patterns of day to day variations of pc1 amplitudes for the equatorial station and the eej are essentially semiannual modulated by solar euv flux superimposed on a longer time scale solar euv flux dependent trend contributions from pc2 and to a lesser extent from pc3 are seen to be responsible for the absence of semi annual variations in h in the afternoon hours at the equatorial station distribution of amplitudes of pc2 and pc3 for heej for weak electrojet days shows seasonal features in accordance with greater occurrence of afternoon morning counter electrojet during june december solstice during the extended solar minimum pc3 amplitudes for h at the equatorial station and for the eej display annual variation possible sources for these seasonal features in the variations of equatorial h are discussed

estimating the diminution of shear wave amplitude with distance application to the los angeles california urban area the rate of decay with distance of shear wave amplitude computed from 20 sec s wave spectra is determined from terrascope records of small earthquakes in the greater los angeles area piecewise log linear interpolation functions and traditional diminution functions are used to fit spectral decay to a maximum distance of 150 km simultaneously isotropic source and receiver terms are determined separate branches of the spectral decay function are found for two categories of source depth greater than 10 km and less than 10 km in the hypocentral distance range of 20 to 150 km and in the frequency range of 0 5 to 8 0 hz an important result of the investigation is that the horizontal component decay rate associated with deeper crustal sources is generally greater than that associated with shallower sources and is greater than that which is estimated using more traditional models of spectral decay with distance the same behavior generally holds for vertical component spectra the variation in apparent attenuation rate with source depth should affect seismic hazard estimates associated with the rupture of blind thrust faults in the los angeles basin and vicinity the results of the inversions suggest that interpolation function representations of spectral decay are sensitive to perturbations of s wave amplitude due to crustal reflectors such as post critical s wave arrivals from mid crustal to deep crustal velocity interfaces

troposphere thermosphere tidal coupling as measured by the saber instrument on timed during july september 2002 1 coupling between the troposphere and lower thermosphere due to upward propagating tides is investigated using temperatures measured from the saber instrument on the timed satellite the data analyzed here are confined to 20 120 km altitude and 40 latitude during 20 july to 20 september 2002 apart from the migrating sun synchronous tidal components the predominant feature seen from the satellite frame during this period is a wave 4 structure in longitude with extrema of up to 40 50 k at 110 km amplitudes and longitudes of maxima of this structure evolve as the satellite precesses in local time and as the wave s responsible for this structure vary with time the primary wave responsible for the wave 4 pattern is the eastward propagating diurnal tide with zonal wave number s 3 de3 its average amplitude distribution over the interval is quasi symmetric about the equator similar to that of a kelvin wave with maximum of about 20 k at 5 s and 110 km de3 is primarily excited by latent heating due to deep tropical convection in the troposphere it is demonstrated that existence of de3 is intimately connected with the predominant wave 4 longitude distribution of topography and land sea difference at low latitudes and an analogy is drawn with the strong presence of de1 in mars atmosphere the predominant wave 2 topography on mars and the wave 2 patterns that dominate density measurements from the mars global surveyor mgs spacecraft near 130 km additional diurnal semidiurnal and terdiurnal nonmigrating tides are also revealed in the present study these tidal components are most likely excited by nonlinear interactions between their migrating counterparts and the stationary planetary wave with s 1 known to exist in the southern hemisphere during this period just prior to the austral midwinter stratospheric warming of 2002

on the day to day variation of the equatorial electrojet during quiet periods it has been known for a long time that the equatorial electrojet varies from day to day even when solar and geomagnetic activities are very low the quiet time day to day variation is considered to be due to irregular variability of the neutral wind but little is known about how variable winds drive the electrojet variability we employ a numerical model introduced by liu et al 2013 which takes into account weather changes in the lower atmosphere and thus can reproduce ionospheric variability due to forcing from below the simulation is run for may and june 2009 constant solar and magnetospheric energy inputs are used so that day to day changes will arise only from lower atmospheric forcing the simulated electrojet current shows day to day variability of 25 which produces day to day variations in ground level geomagnetic perturbations near the magnetic equator the current system associated with the day to day variation of the equatorial electrojet is traced based on a covariance analysis the current pattern reveals return flow at both sides of the electrojet in agreement with those inferred from ground based magnetometer data in previous studies the day to day variation in the electrojet current is compared with those in the neutral wind at various altitudes latitudes and longitudes it is found that the electrojet variability is dominated by the zonal wind at 100 120 km altitudes near the magnetic equator these results suggest that the response of the zonal polarization electric field to variable zonal winds is the main source of the day to day variation of the equatorial electrojet during quiet periods

geometric spreading functions and modeling of volcanic zones for strong motion attenuation models derived from records in japan abstract attenuation models derived from recorded ground motions are still important elements of probabilistic seismic hazard studies engineers use empirical attenuation models to derive the displacement demand for a site of interest from an earthquake at a given location many attenuation models have been published for different parts of the world and for different types of earthquakes most models have a simple function of constant or magnitude dependent geometric spreading and seldom consider well known seismological effects such as moho reflection for shallow crustal earthquakes multiple travel paths and constructive interference for subduction earthquakes and special characteristics of volcano zones the reason for not accounting for such effects may be the desire for simplicity in the attenuation functional forms for engineering applications and a lack of records from which to reliably identify these effects quantitatively in this article a large set of strong motion records obtained from dense recording networks in japan is used to derive geometric attenuation functional form and a possible manner to model the effect of volcanic zones a liberal approach is taken to introduce a relatively large number of parameters that can account for known seismological effects while retaining a fairly simple attenuation functional form based on analyses of residuals from simple models similar to those published previously preliminary results are reported here together with the proposed geometric attenuation function forms and plausible explanation of the physical process that leads to the proposed geometric attenuation functions the proposed model shows a large increase in the maximum likelihood from the random effects methodology the elimination of bias in the distribution of residuals with respect to source distance and much improved fitting for well recorded earthquakes

surface temperature measurements of active lava flows on kilauea volcano hawai i systematic hand held radiometer measurements of lava surface temperatures in active flows and tubes on kilauea volcano hawai i reveal complexities that cannot be resolved in remotely sensed data from aircraft or satellites using portable infrared minolta land cyclops radiometers we measured surface temperatures of flows at various distances from their sources and investigated cooling rates and the development of crust our measurements suggest that the upper surface of these lava flows can be split into a minimum of four thermal components core 1050 c visco elastic skin 750 900 c rigid solid crust 750 c and flow margins 175 c for the a a flows investigated a cool rigid crust characteristically developed in the central part of channels within 30 m of the source vent and incandescent lava was exposed in the marginal shear zones of channels this affects the heat loss and morphology of lava in active channels our investigations of temperature distributions on pahoehoe flow fields reveal temperature anomalies of up to 150 c above active tubes and tumuli

characterization of seasonal and longitudinal variability of eej in the indian region this paper presents the seasonal and longitudinal variability of the equatorial electrojet eej based on geomagnetic variation data from two electrojet stations in the northern indian ocean at a longitudinal separation of 15 i e at 77 e and at 93 e one complete year of data is used i e from november 2011 to october 2012 at the two longitudes and compared with the climatological model of the equatorial electrojet eejm 2 0 the results of our analysis show that i the monthly averaged hourly values of eej strength at 77 e and 93 e are overall in agreement with global characteristics of eej with significant departures over the year of study ii the monthly average hourly daytime values at campbell bay and vencode show poor correlation r 10 nt 20 nt for 30 of quiet days sorted by planetary index kp 1 and 2 this variability is reflected in monthly average values v mechanisms for persistent differences in eej on day to day basis are sought from perturbation of westward ion drifts by neutral winds caused by the upward propagation of gravity waves from troposphere stratosphere into the mesosphere these mechanisms have been identified theoretically and experimentally the four wave structure of ionospheric current densities obtained by eejm 2 0 and other contemporary models closely resembles atmospheric tidal signatures and has a common origin the magnitude and persistence of these differences at short spatial scales 15 are significant observation these effects are reflected in the monthly and seasonal signatures of eej and contribute to the contemporary models

the changing morphology of an open lava channel on mt etna an open channel lava flow on mt etna sicily was observed during may 30 31 2001 data collected using a forward looking infrared flir thermal camera and a minolta land cyclops 300 thermal infrared thermometer showed that the bulk volume flux of lava flowing in the channel varied greatly over time cyclic changes in the channel s volumetric flow rate occurred over several hours with cycle durations of 113 190 min and discharges peaking at 0 7 m3 s 1 and waning to 0 1 m3 s 1 each cycle was characterized by a relatively short high volume flux phase during which a pulse of lava with a well defined flow front would propagate down channel followed by a period of waning flow during which volume flux lowered pulses involved lava moving at relatively high velocities up to 0 29 m s 1 and were related to some change in the flow conditions occurring up channel possibly at the vent they implied either a change in the dense rock effusion rate at the source vent and or cyclic variation in the vesicle content of the lava changing its bulk volume flux pulses would generally overspill the channel to emplace p hoehoe overflows during periods of waning flow velocities fell to 0 05 m s 1 blockages forming during such phases caused lava to back up occasionally backup resulted in overflows of slow moving a that would advance a few tens of meters down the levee flank compound levees were thus a symptom of unsteady flow where overflow levees were emplaced as relatively fast moving p hoehoe sheets during pulses and as slow moving a units during backup small localized fluctuations in channel volume flux also occurred on timescales of minutes volumes of lava backed up behind blockages that formed at constrictions in the channel blockage collapse and or enhanced flow under around the blockage would then feed short lived wave like down channel surges real fluctuations in channel volume flux due to pulses and surges can lead to significant errors in effusion rate calculations

oceanic ridge subduction vs slab break off plate tectonic evolution along the baja california sur continental margin since 15 ma the interaction of the pacific farallon spreading centers with the north american convergent margin off baja california mexico supposedly ceased at 12 ma when plate convergence and seafloor spreading stopped we propose a new geodynamic evolution based on full bathymetry coverage and magnetic profiles from 23 n to 27 n famex cruise of the r v l9atalante april 2002 the data unveil a major clockwise rotation of the pacific farallon spreading direction starting ca 14 ma that formed a series of short spreading centers that became extinct ca 8 7 ma we suggest that the transcurrent motion between the pacific and north america along baja california was accommodated by seafloor spreading and oblique convergence along the trench this change in spreading direction was followed by a concomitant progressive demise of both pacific farallon seafloor spreading and farallon north america subduction that are attributed to the break off of the farallon slab this also resulted in the opening of a trench parallel slab window beneath baja california

do microplates in subduction zones leave a geological record active microplate boundaries in ocean continent subduction zones may induce deformation of the overlying plate and spatial or geochemical variations in the volcanic arc we discuss two modern cases the first is the south gorda juan de fuca plate boundary in the cascadia subduction zone where there is little or no effect on the overriding plate and the oceanic plate takes up much of the deformation the second case is the cocos rivera plate boundary in the middle america trench where the overlying colima graben contains substantial deformation in a zone extending from the trench to the volcanic arc and the sub duction related volcanism is spatially and geochemically complex we apply these observations to boundaries of the arguello monterey guadalupe and magdalena microplates which existed in the subduction zone west of baja california at various times from 20 to 12 5 ma the past positions of these boundaries relative to baja california are constrained by global plate reconstructions closure of the gulf of california and an estimate of extension in the mexican basin and range province existing regional mapping and our additional reconnaissance mapping show that paleocene to eocene fluvial and marine sedimentary rocks south of ensenada along the western baja california peninsula and eastward to the mid miocene volcanic arc are undeformed limited available data reveal no major spatial or geochemical variations in the mid miocene volcanic arc that might correlate with the past positions of the microplate boundaries thus these microplate boundaries had little to no effect on the overriding continental plate the nature of guadalupe and magdalena interactions with north america may have been closer to the south gorda juan de fuca example with possible internal deformation of the microplates the monterey and arguello microplates may have behaved like the modern explorer plate with largely strike slip motion relative to north america during their last stages of existence tectonic patterns similar to these examples may be expected from other plate boundaries where a plate is fragmenting as it enters a subduction zone e g the aluk plate in the trench beneath west antarctica in early tertiary time whether these microplates subsequently become attached to the overriding continental plate or to a larger oceanic plate and whether this causes deformation in the region of the former subduction zone may depend on the velocities of the nearby major plates and the relative orientations of the microplate boundaries

a detailed study of equatorial electrojet phenomenon using orsted satellite observations 1 detailed analysis of the scalar magnetic field data from orsted satellite for quiet days from april 1999 to march 2000 has been undertaken to study the equatorial electrojet eej phenomenon an objective technique has been adopted for the identification of the eej from the satellite data and estimation of the standard parameters associated with it eej strength computed using the satellite data and simultaneous ground magnetic observatory data for the indian and american sectors correlate very well authenticating the method used estimated zonal variation in the eej parameters such as peak current intensity j0 and total current i are broadly consistent with the earlier observations we however observe that the width of the eej varies considerably with longitude a feature not seen in the pogo data the study shows that the eej axis center of eej closely follows the dip equator at altitude of 106 km but there is a small departure that undergoes diurnal variation with a minimum at noon the globally averaged eej amplitude follows the expected diurnal pattern principal component analysis technique reveals that first four components can explain around two thirds of the electrojet variability the first component which contributes a little over 30 to the observed variance could be identified with the global variation of the eej emanating from the day to day variability of the migrating tides the second and fourth components which account for around 15 and 10 of the variance respectively are driven by forcing that depends on whether the location of the eej in that sector is in the northern or southern hemisphere the third component provides maximum contributions wherever the geomagnetic and dip equators are sufficiently close accounting for 12 5 of the variance the remaining components could be associated with contribution of nonmigratory tides or other unknown mechanisms thus the present study suggests that besides conductivity atmospheric tidal modes play important role in defining the zonal variability of the eej current system

a three dimensional bingham model for channeled lava flows we propose a three dimensional 3 d bingham model for channeled lava flow unlike from the 3 d newtonian models this model can be applied also far from the vent where the bingham rheology cannot be neglected as a consequence of the lava cooling we assume the lava to be an isothermal bingham liquid flowing in a rectangular channel down a constant slope the flow velocity is calculated by solving semianalytically the steady state navier stokes equation together with the 3 d bingham constitutive equation the flow vorticity is evaluated and used to define the plug shape and position for different flows a completely filled conduit a partially filled conduit and an open channel each component of the flow vorticity vector satisfies the laplace equation and has been evaluated by using the relaxation method the mass flow rate is evaluated for different values of the yield stress it appears that the bingham rheology causes a significant reduction in flow rate as the yield stress increases for the highest yield stress values the plug in the center of the flow welds with the plugs in the flow corners suggesting a possible rheological mechanism for the lava tube formation

near real time forecasting of lava flow hazards during the 12 13 january 2011 etna eruption we are grateful to eumetsat for seviri data to nasa for modis data and tonoaafor avhrr data the authors thank one anonymous reviewer and v acocella for their helpful and constructive comments this study was performed with the financial support from the v3 lava project ingv dpc 2007 2009 contract

longitudinal and seasonal structure of the ionospheric equatorial electric field 1 the daytime eastward equatorial electric field eef in the ionospheric e region plays an important role in equatorial ionospheric dynamics it is responsible for driving the equatorial electrojet eej current system equatorial vertical ion drifts and the equatorial ionization anomaly due to its importance there is much interest in accurately measuring and modeling the eef in this work we propose a method of estimating the eef using champ satellite derived latitudinal current profiles of the daytime eej along with h measurements from ground magnetometer stations magnetometer station pairs in both africa and south america were used for this study to produce time series of electrojet current profiles these current profiles were then inverted for estimates of the eef by solving the governing electrostatic equations we compare our results with the ion velocity meter ivm instrument on board the communication navigation outage forecasting system satellite we find high correlations of about 80 with the ivm data however we also find a constant offset of about 0 3 mv m between the two data sets in africa further investigation is needed to determine its cause we compare the eef structure in africa and south america and find differences which can be attributed to the effect of atmospheric nonmigrating tides this technique can be extended to any pair of ground magnetometer stations which can capture the day to day strength of the eej

seismicity and state of stress in the la paz los cabos region baja california sur mexico we present the results of an analysis of seismic data collected for seven years in the la paz los cabos region the data set includes earthquakes with magnitudes of up to 3 6 and focal depths mostly between 2 and 14 km the results show that some located epicenters correlated with known faults of the region but others did not suggesting faults that have not yet been recognized in addition even though earthquakes occurred all over the study area zones of stress concentration were identified in such zones the seismicity often developed as earthquake swarms composite fault plane solutions were prepared by using data of those areas the resulting mechanisms for events of the northern part of the study area indicated normal faulting east side down in such case the p axis had a mean vertical angle of 55 in the n12 w direction whereas the t axis was nearly horizontal and with a n68 e average trend this part of the study area is found to be under a predominant tensional stress regime to the southwest of the area the focal mechanisms showed predominant components of strike slip faulting there the t axes were still subhorizontal but the p axes were more horizontal resulting in a mean plunge of about 20 in the n38 w direction on the other hand highly consistent directions of p and t axes from 13 representative events of the gulf of california fault system led to average axes that are close approximations to the principal stresses that drive such a fault system a comparison of these axes with average p and t axes of our region shows that the latter are about 16 to 23 degrees more westerly than the former we propose then either that the earthquakes in the study area occur more in response to local tectonic forces or that our inferred stress axes are only approximations to the principal stresses the complex tectonic situation of the region makes the first possibility feasible but the fact that the earthquakes occurred on pre existing faults favors the second one future seismic data of the region will help to elucidate this uncertainty finally the microearthquakes studied were not generated by the gulf of california fault system that forms the boundary between the pacific and north america plates our results then are evidence of a wide zone of deformation across which subsidiary faulting accommodates part of the relative plates motion

viscous newtonian laminar flow in a rectangular channel application to etna lava flows we introduce a 3d model for near vent channelized lava flows we assume the lava to be an isothermal newtonian liquid flowing in a rectangular channel down a constant slope the flow velocity is calculated with an analytical steady state solution of the navier stokes equation the surface velocity and the flow rate are calculated as functions of the flow thickness for different flow widths and the results are compared with those of a 2d model for typical etna lava flow parameters the influence of levees on the flow dynamics is significant when the flow width is less than 25 m the model predicts the volume flow rate corresponding to the surface velocity taking into account that both depend on flow thickness the effusion rate is a critical parameter to evaluate lava flow hazard we propose a model to calculate the effusion rate given the lava flow width the topograhic slope the lava density the surface flow velocity and either the lava viscosity or the flow thickness

julia radar studies of electric fields in the equatorial electrojet first results from the julia radar at jicamarca are presented these include coherent scatter observations of the equatorial electrojet and of 150 km echoes interferometry is used to measure the zonal drift rate of kilometer scale waves in the electrojet as functions of altitude a technique for estimating the background zonal electric field from the interferometry data is described the electric field estimates can be calibrated against the doppler speed of the 150 km echoes when the latter are present the kilometer scale wave drifts sometimes exhibit large amplitude periodic height variations with vertical wavelengths of about 10 km these signatures are reminiscent of the wind profiles measured with chemical release techniques in the lower thermosphere during the guara campaign

flow and convective cooling in lava tubes tube fed basaltic lava flows with lengths ranging from 10 to 200 km are inferred to exhibit similar amounts of cooling to explain the wide range of implied cooling rates we consider forced convection as a dominant cooling process in lava tubes and present solutions that express mean temperature versus distance down the tube as a function of flow rate and flow cross section our models treat forced convective thermal losses in steady laminar flow through a lava tube with constant temperature walls and constant material properties we explore the effects of different wall temperature and heat flux rate boundary conditions for circular tube and parallel plate flows over a range of tube sizes plate spacings eruption temperatures and volume flow rates results show that nonlinear cooling rates over distance are characteristic of constant wall temperature for a piecewise parallel plate circular tube model this provides the best fit to temperature observations for hawaiian tubes such a model may also provide an explanation for the very low 10 c cooling observed in 10 km long hawaii tube flows and inferred in longer 50 to 150 km tube fed flows in queensland the forced convective cooling model may also explain similar flow morphologies for long tube fed basaltic lava flows in a wide variety of locations since small variations in eruption temperature or flow rate can accommodate the entire range of flow lengths and cooling rates considered our results are consistent with previous suggestions that long basaltic flows may be a reflection of low slopes a particularly steady moderate eruption rate and well insulated flow rather than of high discharge rates

noon time equatorial electrojet its spatial features as determined by the champ satellite 1 new observations obtained by the satellite champ reveal a detailed picture of the noon time equatorial electrojet eej the low orbit of champ and its high precision magnetometers reveal the spatial structure of the eej with unprecedented accuracy data from more than two and a half years have been used to investigate average features and also the global characteristics of the eej rather than interpreting the magnetic signatures we determined the horizontal current distribution by using a very general current model series of line currents this makes the results independent of satellite altitude and ambient field geometry the procedure for determining the structure of the electrojet is fully automated giving an objective response some of the spatial features of the noon time eej are as follows the electrojet current peaks right at the dip equator there is no deviation from it either on a seasonal basis or with longitude the width of the eej 4 in latitude at half the peak value of the current density profile is for a given longitude fairly constant independent of the amplitude return currents north and south of the eastward current are a common feature of the eej they peak at latitudes some 5 away from the dip equator the intensity of the eej varies strongly from day to day the average peak current density exhibits a clear dependence on longitude peaks show up over south america and indonesia the average current density follows closely the monthly mean of the solar flux index f10 7 the total eej eastward current is about three times as strong as the return current the total current and the peak current density are related to each other by a power law this suggests that the longitude dependence of the eej intensity can be explained by the varying cross sectional area of the cowling channel

evidence for short spatial correlation lengths of the noontime equatorial electrojet inferred from a comparison of satellite and ground magnetic data 1 the current density of the noontime equatorial electrojet eej as determined from champ data is highly variable between successive passes of the satellite which are separated by 23 in distance and 93 min in time an open question is to which extent this variability is caused by temporal or spatial variations in the ionosphere another important question is the connection between eej and global solar quiet sq current systems we try to answer these questions by comparing the eej current density estimated from highquality scalar magnetic field measurements of the champ satellite with the magnetic horizontal intensity variations at six equatorial observatory pairs distributed across the globe data taken during the period 2000 2002 were used for the present study we apply corrections for the effect of local time lt and sq fields by estimating the correlation coefficients between the ground and satellite data as a function of distances between measurements new insights into the spatial structure of the eej have been obtained the high correlation when champ passes directly over an observatory decays quickly in eastern and western directions typically within 15 of longitudinal separation between satellite and observatory the correlation falls well below the statistical significance level this observation holds for all longitude sectors interestingly the correlation between champ inferred eej strength and observatory differences breaks down for the observatory pairs outside of a 4 latitudinal band this implies that the eej and sq variations are uncorrelated for periods up to 1 hour additionally it was found that monitoring of the eej can be performed best if the reference observatory is 4 to 5 apart from the dip equator

evaluation of flow rate for a one dimensional lava flow with power law rheology 1 during the emplacement lava behaves as a non newtonian pseudoplastic fluid laboratory experiments on lava samples suggest that a power law constitutive equation may be appropriate we consider a horizontally unbounded isothermal layer of lava flowing down a slope driven by the gravity force we consider a constitutive equation where shear stress is proportional to strain rate raised to a power n ranging from 0 to 1 and we take into account the temperature dependence of the rheological parameters formulae are obtained relating the lava rheology to the geometric and dynamic parameters of a lava flow under the model assumptions if we know the temperature dependence of the rheological parameters these formulae allow to evaluate the flow rate from the field measurements of the temperature and the thickness or the surface velocity of a lava flow

flow and instability of a viscous current down a slope if viscous fluid is released on a horizontal surface it rapidly takes up a circular plan form as it spreads this form is observed1 2 to be stable to any small disturbances which are initiated on the front due for example to irregularities in the horizontal surface or to chance perturbations alternatively if some fluid is released onto a sloping surface for example some liquid detergent on a slanted plate a quite different plan form occurs one two or more extended regions of fluid develop downslope as shown in fig 1a b a situation intermediate between these two is now discussed consider a broad band of viscous fluid uniform in depth across a slope released so as to flow down a constant slope by following the motion which is initially independent of the cross slope coordinate the speed of advance and the depth of the flow before it breaks up into a series of waves of ever increasing amplitude can be determined i present an expression for the wavelength of the front which is determined by surface tension and is independent of the coefficient of viscosity

role of heat advection in a channeled lava flow with power law temperature dependent rheology 1 the cooling of a lava flow both in the transient and the steady state is investigated considering that lava rheology is pseudoplastic and dependent on temperature lava exits from the vent with constant velocity and flows down a slope under the effect of gravity force inside a channel of rectangular cross section we consider that cooling of lava is caused by thermal radiation into the atmosphere and thermal conduction at the channel walls and at the ground the heat equation is solved numerically in a 3 d computational domain and the solution is tested to evaluate the numerical errors we study the steady state and the initial transient period of lava cooling results indicate that the advective heat transport significantly modifies the cooling rate of lava slowing down the cooling process since the lava velocity depends on temperature the cooling rate depends on the effusion temperature velocity profiles are modified during cooling showing two marginal static zones where the crust can form and remain stable the fraction of crust coverage is calculated under the assumption that the solid lava is a plastic body with temperature dependent yield strength we numerically confirm that heat advection cannot be neglected in the mechanism of formation of lava tubes

seismic evidence of a ridge parallel strike slip fault off the transform system in the gulf of california 1 a left lateral strike slip fault perpendicular to the major transform fault that occurred at the extended continental crust in the middle of the gulf of california produced a remarkably active main shock and aftershock seismic sequence that began on 1 september 2007 in contrast to observations from oceanic transform fault systems this event induced unusually active seismicity by means of an inversion procedure we obtained the moment tensor solutions of all the events greater than mw 4 4 and we observed multiple types of faulting some very similar to the main event and others that included a tensional cracking mechanism with a significant nondouble couple component static stress change for optimally oriented left lateral faults predicts the seismic activity this event has implications for the californian peninsular geology especially for the late miocene fault systems that were optimally reoriented to promote active faulting

a model for the shape of lava flow fronts 1 the shape of the front of a lava flow is controlled by the forces acting on the lava and in turn controls the flow dynamics we present an analysis of the shape of the front of an advancing lava flow considering both a newtonian fluid and a bingham fluid which is the most commonly used non newtonian rheological model for lava we assume than the flow front is moving at constant velocity on a sloping plane the flow is considered as having an infinite extent perpendicularly to the flow direction so that the problem is two dimensional the forces producing the flow advance are the gravity force and the pressure gradient due to the curvature of the flow surface the differential equation for the shape of the front is solved analytically both in the case of a newtonian fluid and in the case of the bingham fluid since the fluid is considered as homogeneous and isothermal the calculated shape applies to the fluid core of the flow front the presence of a solid crust at the top of the flow producing variable amounts of solid debris at the flow snout alters the observable shape of the front and is taken into account in order to compare the model front shapes to those observed in the field

a comparison between p wave and s wave propagation characteristics in the southern part of the gulf of california mexico abstract we performed a regional study of p seismic wave attenuation and source excitation from moderate size earthquakes recorded at distances ranging from 23 to 120 km off the coast of la paz baja california sur from a remarkably productive earthquake sequence that occurred in 2007 data were recorded from four strong motion seismic stations using the la paz seismic network and two broadband stations located close to the bay of la paz we compared our results with a previously reported study in the same region with virtually the same method from peninsular earthquakes using s lg seismic waves the regional attenuation was carried out by measuring the maximum amplitude of the p waves after separating the excitation and site terms from the propagation term d r f our best model of the p quality factor is q p f 53 f 0 32 in addition offshore s and scholte modes in ocean sediment layers are discussed in this article

ground magnetic effects of the equatorial electrojet simulated by the tie gcm driven by timed satellite data quiet time daily variations of the geomagnetic field near the magnetic equator due to the equatorial electrojet are simulated using the national center for atmospheric research ncar thermosphere ionosphere electro dynamics general circulation model tie gcm and compared to those observed by ground based magnetometers simulations are run both with and without tidal forcing at the height of the model lower boundary 97 km when the lower boundary forcing is off the wind that generates an electro motive force in the model is primarily the vertically non propagating diurnal tide which is excited in the thermosphere due to daytime solar ultra violet heating the lower boundary tidal forcing adds the effect of upward propagating tides which are excited in the lower atmosphere and propagate vertically to the thermosphere the main objective of this study is to evaluate the relative importance of these thermospherically generated tides and upward propagating tides in the generation of the equatorial electrojet fairly good agreement is obtained between model and observations when the model is forced by realistic lower boundary tides based on temperature and wind measurements from the thermosphere ionosphere mesosphere energetics and dynamics timed satellite as determined by wu et al 2012 the simulation results show that the effect of upward propagating tides increases the range of the geomagnetic daily variation in the magnetic northward component at the magnetic equator approximately by 100 it is also shown that the well known semiannual change in the daily variation is mostly due to upward propagating tides especially the migrating semidiurnal tide these results indicate that upward propagating tides play a substantial role in producing the equatorial electrojet and its seasonal variability

effects of the curvature of a lava channel on flow dynamics and crust formation summary bends in lava channels are often observed in volcanic fields the curvature of a channel affects flow dynamics and surface morphology and may be a trigger for the formation of lava tube we propose a model to describe the effects of curvature on velocity shear stress and the formation of crust at the flow surface lava is described as a newtonian homogeneous isotropic and incompressible fluid the steady state solution of the navier stokes equation is found for a unidirectional flow in cylindrical coordinates the flow levees are described as arcs of concentric circumferences with their centres in the origin of the coordinate system under the assumption that the gravity force has no radial component in the bend the fluid moves parallel to the levees the velocity is assumed to depend on the radial coordinate only as an effect of curvature velocity and shear stress are asymmetric with respect to the centre of the channel the maximum of surface velocity is shifted toward the internal levee and the shear stress has larger values close to the internal levee this effect is greater for wider channels heatradiationandconvectionintotheatmosphereareconsideredasthemaincooling mechanisms and the temperature distribution along the channel is calculated crust formation at the flow surface is considered under the assumption that solid lava is a plastic body the amount of crust coverage is mainly controlled by the channel width narrow channels have a greater coverage than wide channels for a given radius of curvature the effect of a bend is to favour the crust growth toward the internal levee while the crust coverage toward the external levee decreases the presence of a bend in a lava channel may favour the formation of a lava tube the analytical solution will serve as a benchmark for numerical models understanding the mechanism of formation of lava tubes is crucial to the simulation of actual lava flows and to evaluation of the associated hazard

nonparametric description of peak acceleration as a function of magnitude distance and site in guerrero mexico this article describes the peak accelerations observed on a network of strong motion accelerographs above the subduction zone in guerrero mexico as a function of magnitude and hypocentral distance our empirical description differs from regression analysis however in that it produces a table of values of peak acceleration for selected values of m and r and an interpolation rule to obtain peak acceleration at intermediate values with this approach the existence and extent of saturation of peak acceleration as magnitude increases is dictated by the data and unlimited flexibility is allowed in the distance dependence of the peak acceleration this nonparametric approach does not allow extrapolation beyond the range of the data and is thus most useful when the data spans a large magnitude and distance range after 7 yr of recording the digital guerrero accelerograph network has obtained enough data to test the concept the records include events with magnitudes ranging from under 3 to 8 1 with all magnitudes recorded at distances ranging from nearly directly above the rupture to distances where acceleration has become too small to trigger the instruments the data used in this study consist of 528 recordings each three components from 146 earthquakes that occurred between 1985 and 1990 all but one station are on rock sites since all the accelerograms are recorded by one of 30 stations there is an average of about 18 records for each station the results suggest that at short distances about 14 to 25 km from the fault as magnitude increases the peak horizontal acceleration saturates at about 20 g however unlike small earthquakes peak accelerations decrease very slowly with increased distance from the rupture in a large magnitude station corrections for peak acceleration reduced the rms misfit by about 15 for the horizontal component by 12 for the vertical component and by 21 for the ratio for some stations horizontal corrections are close to vertical corrections but others show very different site effects on horizonal and vertical components the ratios of peak vertical acceleration to peak horizontal acceleration show a very weak tendency to decrease as magnitude increases and this tendency is further reduced at most distances after correction for average site effects the average value of this ratio is 0 70 before the station correction after these corrections for 55 events with known stress drop the residual between the predicted peak acceleration and the observed peak acceleration is correlated with stress drop although scattered the observations are consistent with a theoretical prediction that amax 0 80

lava dome growth and evolution with an independently deformable talus subduction zone volcanism occurs due to partial melting from subducting slabs which generally results in high viscosity magma containing a large amount of volatiles such volcanic eruptions can form a lava dome from which collapse events are a common and important part of their evolution collapse events can have devastating consequences in the form of block and ash avalanche deposits pyroclastic ows surges and the generation of tsunamis if they enter the sea in addition to this once a mass of lava dome has been removed during a collapse event this results in a drop in pressure in the remaining volatile rich magma which may then erupt explosively the internal structure of a lava dome and the extent of the surrounding carapace talus is unknown but likely to be critical for hazard assessment and is the motivation for this research presented is a computational model for the growth and evolution of an endogenous lava dome including an independently deformable talus using the finite element method dome growth is modelled to occur under two time scales continuous dome expansion via the addition of new magma into the molten core interior and relatively instantaneous talus readjustments due to rockfalls and the disintegration of the solid surface the continuous deformation of the dome is modelled as a uid with a yield strength in the talus region while talus deformation is modelled as a granular material that rests at angles below its angle of repose both surfaces dome and core talus interface are displaced using the level set method the model is axi symmetric and assumes that solidi cation and therefore talus growth occurs due to gas exsolution which promotes crystallisation rather than from surface cooling appropriate for intermediate composition lava ows for the purpose of this paper we consider and apply the model to the soufriere hills volcano montserrat but the techniques used are generic allowing the model to be applied to other dome forming eruptions the model provides information on the shape of the dome with the growth and extent of the talus and core found to be predominantly governed by the lava extrusion rate degree of solidi cation i e a solidus pressure the friction angle associated with the talus and lava dome viscosity

the 4 january 2006 mw 6 6 san pedro martir earthquake example of an earthquake for calibrating excitation and attenuation studiesthe mw 6 6 san pedro martir earthquake for calibrating excitation and attenuation studies

seismic wave attenuation and source excitation in la paz los cabos baja california sur mexico we present results from a regional study of seismic wave attenuation and source excitation from small magnitude earthquakes recorded at distances from 6 to 180 km in the la paz los cabos region at the south end of the baja california peninsula data were recorded using 32 strong motion seismic stations from the la paz network lap a least squares regression separating the excitation site and propagation effects was carried out we performed the analyses in the time and frequency domains and we compared these results with results from a coda normalization method the propagation term was parameterized to represent a geometrical spreading function and a frequency dependent q f at a reference distance of 40 km we estimated the regional attenuation by measuring the maximum amplitude of the s or lg waves as a function of frequency defining a continuous piecewise propagation term d r f after separating the excitation and site terms our results show that the attenuation is lower than that of central or northern mexico recorded data were of remarkably good quality despite the fact that the strong motion network recorded only small earthquakes our best model is that of a quality factor of q f 380 f 0 10 with a complex geometrical spreading function

electric fields and zonal winds in the equatorial ionosphere inferred from champ satellite magnetic measurements 1 the equatorial electrojet eej produces a strong magnetic signal in measurements of the low orbiting champ satellite six years of data with more than 30 000 dayside equator crossings provide a unique data basis to study this current system in addition to scalar measurements used in previous studies we have also inverted vector magnetic field measurements to gain accurate meridional profiles of the eastward current in the equatorial region by solving the relevant differential equation the champ derived current profiles can be inverted for the driving zonal electric fields and zonal winds as a result of this feasibility study we suggest an inversion of the complete set of individual champ eej current profiles which will provide valuable new information on dayside electric fields and thermospheric winds at low latitudes citation maus s p alken and

third generation of the potsdam magnetic model of the earth pomme the potsdam magnetic model of the earth pomme is a geomagnetic field model providing an estimate of the earth s core crustal magnetospheric and induced magnetic fields the internal field is represented to spherical harmonic sh degree 90 while the secular variation and acceleration are given to sh degree 16 static and time varying magnetospheric fields are parameterized in geocentric solar magnetospheric gsm and solar magnetic sm coordinates and include disturbance storm time dst index and interplanetary magnetic field imf by dependent contributions the model was estimated from five years of champ satellite magnetic data all measurements were corrected for ocean tidal induction and night side ionospheric f region currents the model is validated using an independent model from a combined data set of orsted and sac c satellite measurements for the core field to sh degree 13 the root mean square rms vector difference between the two models at the center of the model period is smaller than 4 nt at the earth s surface the rms uncertainty increases to about 100 nt for the predicted field in 2010 as inferred from the difference between the two models

pre pliocene extension around the gulf of california and the transfer of baja california to the pacific plate late miocene 12 5 ma extension around the edges of the gulf of california has been alternatively attributed to basin and range extension back arc extension or development of the pacific north america plate boundary this extension was ene directed and similar in structural style to extension in the basin and range province timing constraints permit nearly synchronous onset of this deformation in a belt extending sse from northernmost baja california to the mouth of the gulf where this extensional faulting continued through pliocene time to the present synchronous with motion on the modern transform plate boundary in the gulf of california no change in direction of extension can be resolved revised constraints on pacific north america plate motion support the development of this late miocene extension as a component of pacific north america displacement that could not be accommodated by strike slip displacement along the existing plate boundary west of the baja california peninsula this scenario implies that transfer of baja california from the north america plate to the pacific plate was a gradual process beginning about 12 10 ma when motion of the pacific plate relative to north america was partitioned into separate regimes of strike slip and dip slip displacement on opposite sides of baja california

a local magnitude scale for the western great basin eastern sierra nevada from synthetic wood anderson seismograms abstract we have computed synthetic wood anderson seismograms for over 1100 arrivals at 10 three component broadband digital stations in the unr western great basin eastern sierra nevada network these represent all the available records from local earthquakes over magnitude 3 5 between 1990 and june of 1993 plus selected events of smaller magnitude there were 77 events ranging in magnitude from 2 2 to 5 9 including four events over magnitude 5 the distances considered ranged from 15 to 600 km with the best represented range being from 30 to 450 km we invert these measurements to determine distance and station corrections appropriate for a local magnitude scale constrained by richter9s original definition that an earthquake of m l 3 will cause a 1 mm zero to peak deflection of the wood anderson seismogram at 100 km from the epicenter the results between 30 and 450 km were essentially independent of choice of curve fitting parameters in the 30 to 500 km distance region the smooth distance correction curves were very similar to that determined by richter 1958 which is still used for southern california earthquakes we propose to use richter9s distance correction curve in reporting amplitude magnitudes from our digital network

improved seismic tomography offshore northeastern taiwan implications for subduction and collision processes between taiwan and the southernmost ryukyu summary to improve the resolution in imaging the 3 d vp and vp vs structures in the taiwan region especially offshore eastern taiwan we combine the arrival times from eleven ocean bottom seismometers obss and from seismic stations of the japan meteorological agency jma with those from the permanent stations of taiwan central weather bureau seismic network cwbsn and taiwan strong motion instrumentation program tsmip by doing so we have obtained a new 3 d tomographic model for taiwan and its surrounding regions with a better resolution especially in the area offshore northeastern taiwan we also used this new tomography model to relocate the hypocentres of the earthquakes in northeastern taiwan and determined the focal mechanisms of relatively large events our tomography results indicate that in the region northeast of taiwan the subducting oceanic philippine sea plate beneath the eurasian continental lithosphere is characterized by a high vp layer surrounded by lower vp areas this p wave velocity characteristics of the subducting slab provides a better constraint on the geometry of the subduction interface especially in its shallower portion in the hangingwall eurasian block above the subduction interface a vertically elongated high vp vs body appears to originate from the interface at depths between 100 and 140 km we suggest that it represents the partially melted materials that are related to the magmatic activity of the ryukyu volcanic arc

a quiet time empirical model of equatorial vertical plasma drift in the peruvian sector based on 150 km echoes 1 equatorial vertical plasma drift is an important consequence of the e and f region dynamos understanding the climatology of vertical drift can provide significant insight into many ionospheric phenomena in this study we present the first empirical model of vertical plasma drifts at 150 km altitude observed by the jicamarca unattended long term studies of the ionosphere and atmosphere julia coherent scatter radar located in peru the model called julia vertical drift model jvdm describes the local time seasonal and solar flux behavior of the equatorial vertical drifts in the peruvian sector the model is valid from 0800 through 1600 local time which is typically when julia makes vertical drift measurements during very high solar flux conditions however the model is unreliable before 1000 local time owing to a lack of julia data the model includes a climatology of the 150 km equatorial vertical drifts as well as an estimate of the day to day variability which can be significant the daytime drifts typically peak between 1000 and 1200 lt and have amplitudes of 25 30 m s 10 m s the model has been validated against the global empirical model of scherliess and fejer with a total rms difference of under 4 m s for 1000 to 1600 lt this model will allow researchers to study daily variations in the equatorial electric field by subtracting the climatological mean model coefficients and software are available online at http geomag org models and http www earthref org

a model for the formation of lava tubes by roofing over a channel the formation of lava tubes is a common phenomenon on some basaltic volcanoes such as etna a model for tube formation by roofing of a channel is proposed and involves first describing lava as a bingham liquid flowing down a slope it is further assumed that lava flows in a channel with rectangular cross section as a result of heat loss into the atmosphere a crust is gradually formed on the upper surface of the flow and this crust eventually welds to the channel levees we assume that a lava tube is formed when such a crust is sufficiently thick to resist the drag of the underlying flow and to sustain itself under its own weight the minimum thickness of the crust satisfying such conditions depends on the tensile strength and shear strength of the crust itself assuming that the growth of the crust produces a downflow linear increase of the shear stress at the interface between flowing lava and the crust the distance is evaluated between the eruption vent and the point where the tube is formed the model predicts that if the flow rate is constant the thickness of the flow increases as the crust fragments grow and weld to each other and the velocity of the crust decreases to zero once the lava tube is formed the initial flow rate can be achieved by a flow thickness smaller than the vertical size of the tube with the same viscous dissipation this may explain why under steady state conditions the lava level inside a tube is frequently lower than the roof of the tube itself