new relationships between vs thickness of sediments and resonance frequency calculated by the h v ratio of seismic noise for the cologne area germany noise measurements were carried out in the cologne area germany and the resonance frequency of each site was estimated from the main peak in the spectral ratio between the horizontal and vertical component for 32 of these sites the thickness of the sedimentary cover was known from boreholes and a clear correlation between resonance frequency and sediment thickness was observed a formula that correlates cover thickness with frequency of the main peak in the horizontal to vertical spectral ratio was derived in addition a best fitting shear wave velocity distribution with depth vs z as well as a relationship between average shear wave velocity vs and thickness of the sedimentary cover was calculated by using all of the noise measurements and applying the derived relationships we obtained a subsoil classification for the cologne area

analysing the topographic form of stratovolcanoes abstract the goal of this study is to explore ideal analytic functional forms that best fit the topographic shape of n 190 isolated stratovolcanoes from around the world using a stochastic model for the piling of lava flows to demonstrate one set of physical processes that give rise to a stratovolcano s topography we find that although the ideal form fits well for many stratovolcanoes there exist deviations from this shape particularly where the edifice is more protuberant than expected we explore sub surface factors such as the emplacement of magma beneath a volcano edifice that may be responsible for these deviations and estimate the relative contribution of dyke intrusions on the height and shape of a volcanic edifice versus the constructional piling of lava from this comparison we are able to gain more insight into the role of important subsurface physical factors such as chamber depth and total intruded volume we find that low basal ellipticity is a characteristic of nearly all volcanoes that fit the ideal stratovolcano form by fitting along each quadrant bisected by either a semi major or semi minor ellipse axis we find that the volcanoes chosen in this study fall into four groups 1 volcanoes that are axisymmetric and fit the ideal form well 2 volcanoes that are not axisymmetric but may be fit to the ideal form using different fitting parameters in each quadrant 3 volcanoes that have axisymmetric protuberant deviations in all quadrants and 4 volcanoes that have non axisymmetric protuberant deviations that are only present in a couple of quadrants we show that in some cases the non axisymmetry of volcanoes in category 2 may be understood as the result of the piling of eruptive products along a regional planar trend for edifices in categories 3 and 4 we model protuberant deviations as the result of a statistical distribution of elastic tensile dislocations representing dykes which emanate from a magma reservoir and cause uplift at the surface we support this interpretation of the excess topography in a few case studies where independent geologic and geophysical data corroborate our model results

source parameters and tectonic implications of aftershocks of the mw 7 6 bhuj earthquake of 26 january 2001 we present and discuss the spatial distribution of more than 1000 aftershocks of the largest continental intraplate earthquake to occur during the modern seismological period the data were recorded on a network of eight portable digital seismographs deployed for 3 weeks starting 17 days after the mainshock we have calculated high quality single event locations based on a 1d velocity model determined for the region for earthquakes with magnitudes between 2 and 5 aftershock locations reveal activity concentrated on a nearly east striking south dipping plane trapezoidal in outline the active zone tapers from about 45 km along strike at the shallow end which is about 5 km deep to no more than 25 km long at a depth of 35 km the total rupture area was about 1300 km 2 we estimate the static stress drop of the mainshock at 16 2 mpa aftershocks extend nearly through the entire crust with concentrations in the lower crust at about 26 km and in the upper crust at about 10 km the fault that ruptured was not mapped at the surface and not known to have been active prior to the 2001 earthquake the aftershock data are consistent with the bhuj earthquake resulting from reactivation in contraction of a fault formed under extension within a failed rift

geometrical form of aseismic ridges volcanoes and seamounts many volcanic structures have a regular geometrical form that suggests a simple and universal mechanism for the growth we suggest that the surface of these volcanic structures is a surface of constant hydraulic potential when an eruption begins it follows a path to the point on the surface that has the minimum hydraulic resistance this resistance includes both the frictional resistance to the flow and the gravimetric potential associated with elevation we determine the shape of a two dimensional volcanic edifice formed from a line source and compare the shape with bathymetric profiles across several aseismic ocean ridges we also compare the predicted shape of an axisymmetric volcanic edifice formed from a point source with several profiles from the cascade range in the western united states and with a number of volcanic islands and seamounts in the pacific

the morphologies of volcanic landforms at central elysium planitia evidence for recent and fluid lavas on mars abstract this paper focuses on physical parameters flow rates and rheological properties of lava flows observed in the central elysium planitia cep region of mars the flows are modeled as newtonian fluids using the jeffrey s equation and the concept of graetz number or alternatively as bingham fluids in addition to these approaches a theoretical model of the shape of shield volcanoes based on the solution for the porous flow of an unconfined aquifer is applied to 5 shields providing independent quantifications of rheological variations between the shields this analysis indicates that of the five volcanoes studied two are partially buried by lava postdating their formation a result which has been confirmed independently in one case by high resolution images our observations reveal that two types of lava flows may be found in the cep region the first group is composed of large lava flows with viscosities around 2 5 10 5 pa s or yield strengths ranging from 100 to 500 pa the second group includes small lava flows of the shield volcanoes and large leveed lava channels on the plains with viscosities below 103 pa s or yield strengths less than 200 pa when compared with other volcanic regions on mars investigated with similar approaches these latter values are at present the lowest inferred for martian lava flows several hypotheses for the formation of these lavas are discussed in the context of cep given that low viscosity can be the result of 1 high temperature 2 low crystal content 3 low si abundance of the liquid phase and or 4 the presence of dissolved volatiles two scenarios are considered in the first one it is demonstrated that low viscosity lavas of low silica content can be produced in the context proposed by schumacher and breuer schumacher s breuer d 2007 geophys res lett 34 l12202 for recent volcanism however geochemical maps derived from grs measurements do not provide support for anomalously low silica concentrations in this region in the second scenario a water rich magma is proposed although arguments in favor of a water rich mantle source below the cep are not available at the present time

site effect evaluation in the basin of santiago de chile using ambient noise measurements summary we performed extensive ambient vibration measurements in the basin of santiago de chile chile and we look for testing the reliability of the horizontal to vertical amplitude spectra ratio method h v as a tool to provide qualitative and quantitative information of site effects in complex geological media the interpretation of the h v data was carried out conformably to the sesame project consensus criteria and outlines three major patterns 1 clear peaked h v curves related to sharp underground velocity contrast 2 h v peak of low amplitude and flat curve related to weak contrast and 3 broad h v peak indicating the presence of strong lateral variations of underground structure h v measurements however reveal a discrepancy between the computed soil resonance frequencies and the expected building resonance therefore not leading to a straight interpretation of the intensity distribution derived from observed damage to one storey houses in santiago after the 1985 valparaiso earthquake indeed the h v technique mostly maps the first fundamental frequency however it fails to show higher resonance modes in the case of the city of santiago this method works well for assessing the seismic hazard for high rise buildings but is questionable for smaller structures as is the case of a great percentage of constructions in the city

shape analysis of pacific seamounts abstract shape statistics have been compiled from 85 profiles of well surveyed pacific seamounts in the height range 140 3800 m a flat topped cone was fit to each seamount s cross sectional profile maintaining the slopes of the sides as closely as possible on each profile a basal width d b a summit width d t and a maximum height h were measured the height to basal radius ratio is h is estimated by the ratio 2hd b and flatness f by the ratio d t d b slope angle arctan e is estimated from e 2h d b d t summit height and basal radius are found to be highly correlated r 0 93 the 85 point sample mean of the height to basal radius ratio is h 0 21 0 08 implying that a seamount s summit height is typically one fifth its basal radius despite the high correlation individual points show some scatter and there may be groupings into different morphological types for example all but one of the seamounts with summit heights above 1000 m have values of h that are larger than the sample mean the 85 point sample mean of flatness is f 0 31 0 18 data points show a large scatter with values of f varying between 0 a pointy cone and 0 69 a flat topped cone a histogram representation of flatness however indicates that certain values of f may be more common than others the histogram shows a bimodal distribution with maxima occurring at values of f in the ranges 0 10 0 20 and 0 35 0 50 moreover there is some evidence that the mean flatness decreases with summit height so that the preferred shape of a large sized seamount may be a pointy cone slope angle has an 85 point sample mean of 18 6 individual values of vary between 5 and 36 in addition to having a lower than average mean flatness seamounts with heights above 2600 m also have a lower than average mean slope angle 15 to determine which variables account for most of the observed variation in the seamount shapes a multivariate principal component analysis was performed on the data using five shape variables summit height basal radius summit radius flatness and slope the analysis indicates that most of the variation is described by two variables flatness and summit height

comparison of the shapes and sizes of seafloor volcanoes on earth and pancake domes on venus the fact that flat topped pancake domes observed on venus resemble flat topped volcanoes on earth s seafloor suggests that volcanic processes on the seafloor and on venus may operate to construct volcanic forms with similar characteristics to test this the shapes and size distributions of terrestrial submarine volcanoes seamounts from several magmatic and tectonic provinces are quantitatively compared with those of venusian pancake domes seamount heights and diameters are highly correlated suggesting that there may be a universal mechanism for their growth the 2014 point sample mean of the height to diameter ratio is d 0 10 0 04 in contrast heights and diameters of 52 pancake domes exhibit no obvious trend and values of d are as much as three orders of magnitude smaller with a 52 point sample mean of d 0 02 0 03 seamounts with basal diameters db 10 km have flatness values ratio of top to bottom diameter that span the entire range between 0 pointed cone and 1 truncated cone larger sized seamounts tend to have small values of flatness and more pointed tops this is not true for pancake domes which show large flatnesses at all sizes additionally seamounts have distinctive profiles with their flank slopes increasing in gradient toward the summit flank slopes of pancake domes however commonly increase in gradient toward the base with respect to sizes the diameter distributions of the different seamount populations are consistent with a model in which the number of seamounts decreases exponentially with increasing diameter the diameter distribution of 126 pancake domes by contrast is more uniform its mean is db 22 13 km this size is at least an order of magnitude larger than the estimated characteristic diameters of the seamount populations based on the above results i conclude that seamounts have significantly different shapes and size distributions than venusian pancake domes that have been identified and measured to date this suggests that one or more of the variables e g magma composition crystallinity magma volume effusion rate cooling rate pre existing topography governing their formation differs in terms of shapes and size distributions the small db 20 km volcanic edifices first identified from venera data are good morphologic matches to seamounts and should be the focus of future work investigating the formation of comparable volcanic features in these two different planetary environments

on the geometrical form of volcanoes abstract many volcanic edifices have a remarkably symmetric geometrical form an example is mount fuji in japan we model this form assuming that the surface of the volcano is a surface of uniform hydraulic potential that an erupting magma will follow the path of minimum resistance to the surface in order to model the resistance to fluid flow we assume the volcanic edifice is a uniform porous medium the vertical flow of magma is also resisted by the gravitational body force if the volcano becomes too tall flank eruptions will widen it if the volcano becomes too wide summit eruptions will increase its elevation using the dupuit approximation for an unconfined aquifer it is shown that the percolation equation is applicable as magma reaches the surface it is assumed to extend the solid porous matrix a similarity solution is obtained to this moving boundary problem the solution predicts a uniform shape for all volcanoes this shape is shown to be in excellent agreement with the geometrical form of mount fuji

characteristics of deformation and past seismicity associated with the 1819 kutch earthquake northwestern india the 1819 earthquake in kutch northwestern india is one of the most significant events to have occurred in a plate interior setting despite being the second largest among the stable continental region scr earthquakes this event has not been analyzed within the context of present day understanding of earthquake seismology coseismic changes related to this earthquake include massive ground deformation in a wide low lying tidal flat area although detailed historic accounts of this earthquake exist many questions regarding the mode of deformation and the seismic history of the region remain unresolved we explored the region nearly 180 years after the earthquake and the information gathered adds to our understanding of this event and provides a fresh perspective on this unique intraplate seismogenic zone a 90 km long tract of elevated land with a peak height of 4 3 m is the most visible surface expression of this earthquake we surveyed and analyzed the morphological features of this scarp and also carried out exploratory trenching in this region the scarp morphology is suggestive of a growing fold related to a buried north dipping thrust rather than a discrete fault that could have resulted from a surface rupture the extensive liquefaction field associated with the earthquake offered an ideal setting to explore the paleoearthquake history age data of liquefaction features suggest that a previous event of comparable size must have occurred 800 1000 years ago seismic activity appears to be related to the reactivation of an ancient rift in a stress regime that is dominated by nearly north south compression

assessing the previous activity at the source zone of the 2001 bhuj earthquake based on the near source and distant paleoseismological indicators 1 the m w 7 7 2001 bhuj kachchh earthquake was not associated with any primary surface rupture but it produced secondary faulting folding and liquefaction this study highlights the potential of a secondary rupture and proxies like lateral spreads and sandblows in unraveling the past activity related to the 2001 source chronological constraints of an older lateral spread and far field paleoliquefaction features combined with archeological data provide evidence for occurrences of two previous earthquakes at the 2001 source zone about 4000 and 9000 years ago distinct stratigraphic evidence for at least one previous offset dated at 4424 656 years could be detected at a stepover zone associated with a dextral secondary fault reactivated during the 2001 earthquake the studies imply longer interseismic intervals for the 2001 source zone in comparison with the source zone of the 1819 earthquake located toward the northwestern part of the rann of kachchh the spatial and temporal correlation of previous events derived on the basis of the available paleoseismic data from the region suggest not only repeated activity at the 2001 source but possibility for additional potential sources in parts of kachchh and cambay basins although we infer a longer recurrence interval for the 2001 bhuj earthquake source our study points to the fact that these additional sources may have the potential to rupture in the future considering the long elapsed time

a comparison of site response techniques using earthquake data and ambient seismic noise analysis in the large urban areas of santiago de chile summary situated in an active tectonic region santiago de chile the country s capital with more than six million inhabitants faces tremendous earthquake risk macroseismic data for the 1985 valparaiso event show large variations in the distribution of damage to buildings within short distances indicating strong effects of local sediments on ground motion therefore a temporary seismic network was installed in the urban area for recording earthquake activity and a study was carried out aiming to estimate site amplification derived from horizontal tovertical h v spectral ratios from earthquake data ehv and ambient noise nhv as well as using the standard spectral ratio ssr technique with a nearby reference station located on igneous rock the results lead to the following conclusions 1 the analysis of earthquake data shows significant dependence on the local geological structure with respect to amplitude and duration 2 an amplification of ground motion at frequencies higher than the fundamental one can be found this amplification would not be found when looking at nhv ratios alone 3 the analysis of nhv spectral ratios shows that they can only provide a lower bound in amplitude for site amplification 4 p wave site responses always show lower amplitudes than those derived by s waves and sometimes even fail to provide some frequencies of amplification 5 no variability in terms of time and amplitude is observed in the analysis of the h v ratio of noise 6 due to the geological conditions in some parts of the investigated area the fundamental resonance frequency of a site is difficult to estimate following standard criteria proposed by the sesame consortium suggesting that these are too restrictive under certain circumstances

precise location of unsurveyed seamounts in the austral archipelago area using seasat data summary seasat altimetric geoid data are used to detect uncharted seamounts in the austral archipelago area the various physical parameters which affect the geoid signature of a seamount are inspected to analyse their influence on the precision of the location these parameters are the shape of the seamount its density the crustal model the effective elastic thickness of the lithosphere and the distance between the seamount and sub satellite tracks respectively the results of the tests performed on synthetic data as well as on charted structures show that when a seamount is detected on at least two neighbouring tracks it is possible to locate it with good confidence and to give an estimation of its height if the correct elastic thickness is assumed the precision on the location is order 15 km ten previously unsurveyed seamounts have been located in the austral archipelago it appears that they are emplaced along two well defined azimuths n 1 10 e and n 150 e and that two parallel distinct volcanic chains form the austral archipelago

shape rheology and emplacement times of small martian shield volcanoes abstract this paper focuses on the shape of 31 shield volcanoes of small to intermediate size a few tens of kilometers in diameter in 5 regions of mars tempe terra syria planum pavonis mons arsia mons and central elysium planitia a model for the shape of these shield volcanoes is applied based upon the concept of porous flow of an unconfined aquifer proposed by lacey et al lacey a ockendon j r turcotte d l 1981 on the geometrical form of volcanoes earth planet sci lett 54 1 139 143 and developed by turcotte and schubert turcotte d schubert g 2002 geodynamics cambridge university press second edition the agreement between the topographic profiles and the theoretical shape suggests that the model is appropriate and can be used to derive the product of flow rate and viscosity q estimates of q are found to be homogeneous within a given volcanic region but show large differences from one region to another values generally decreasing with age from oldest to youngest intrinsically the method cannot separate the flow rate from the viscosity but independent observations on individual lava flows in syria planum and central elysium planitia suggest that this evolution may be explained by decreasing magma viscosity with age independent constraints on the viscosity are used to interpret q variations between volcanic regions except for tempe terra and within error bars relative effusion rates are essentially independent of volcano volumes suggesting that the size of a shield volcano is principally controlled by the duration of volcanic activity the specificity of central elysium planitia is emphasized with highest flow rates associated with lowest lava viscosity however the lower viscosities at central elysium planitia cannot totally explain low q values considering the equation of magma flow through a dike from a magma chamber at depth to the shield we suggest that lower volatile contents and or deeper magma chambers may contribute to the decrease of q values with time finally the emplacement times of the 31 shield volcanoes were calculated using a calibration based upon terrestrial volcanoes mauna loa eldborgir and skjalbrei ur emplacement times of martian volcanoes calculated in this way range from a few hundred thousand years tempe terra to a few tens of thousands of years central elysium planitia despite the simplicity of the model the quality of the fits and the internal consistency of the results are reasonable encouraging development of more advanced models linking shield volcano shape to rheological properties of lavas and their characteristic time scales of emplacement

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

use of microtremor in liquefaction hazard mapping this study shows how microtremor measurements can be used as an aid to liquefaction hazard mapping and zonation as demonstrated in laoag city northern philippines from microtremor measurements qualitative information on subsoil conditions was obtained and a site classification map was generated the map was combined with the geomorphology based liquefaction susceptibility map to produce an integrated liquefaction hazard zonation map this integrated map is deemed to be more accurate in depicting relative liquefaction susceptibility since it combines information on the distribution of potentially liquefiable soils in terms of geology and grain characteristics with information on the stiffness and thickness of these soils with information about the thickness of the deposits an idea of the severity of liquefaction related damage can also be gathered since thicker deposits relate to more serious damage plots of historical liquefaction cases as well as borehole data and resistivity profiles in the study area support the validity of the integrated map the use of microtremor therefore constitutes an effective and inexpensive approach to liquefaction hazard zonation and as such is very useful in less developed countries like the philippines and other areas where funds for more rigorous investigations are not always available

geochemical characterization of a marine sediment core from the joides basin ross sea antarctica abstract the chemical fractionation of ten metals al ti cr fe cd cu mn pb zn and ni is reported for a marine sediment collected in the joides basin ross sea antarctica to evaluate their mobility and availability the bcr sequential extraction procedure was applied on 11 sections of the sediment the analyses performed both by icp oes and gf aas highlighted that most of the elements were in the residual phase showing a strong binding with the matrix and a low availability the bcr sequential procedure allowed us to have an insight into the chemical properties of the sediment and provided useful information about the redox state of the sediment itself and important indication on the availability and partitioning of different metals a chemometric treatment was applied on the dataset and it showed a separation between the superficial and the deep sections of the core the first being more influenced by the presence of mn and the second by an increase in al ti fe cr and pb concentrations

implications of new data on mesozoic rocks of kachchh western india a lack of detailed facies studies has resulted in a false impression of the mesozoic depositional setting in kachchh western india previously kachchh has been termed kutch or cutch in addition designation of part of this sequence as gondawana implies by tradition a predominantly non marine origin recently we examined these jurassic cretaceous units and found numerous wave built sedimentary structures that have been previously overlooked or unreported abundant marine trace fossils and highly bioturbated and glauconite rich beds thus we now propose a marine origin for the entire kachchh succession this interpretation has important implications regarding similar sequences around the indian plate margin

site effects in the city of lourdes france from h v measurements implications for seismic risk evaluation abstract the pilgrimage city of lourdes in the french pyrenees has been heavily damaged by earthquakes in the seventeenth and eighteenth centuries assessments of local seismic hazard have been performed through a seismic microzonation of the city a campaign of urban noise recording has been conducted at about 180 points to determine seismic wave amplification by means of spectral ratios of the horizontal to vertical h v components a comparison of this ratio obtained from ambient noise measurements with spectral ratios obtained from earthquake s wave recording h href reveals that the fundamental resonance frequency is well estimated but that the site amplification is generally underestimated resonance frequencies and amplitudes exhibit coherent patterns that relate to the geological structure bedrock sites are generally characterized by flat spectra whatever the geological nature of bedrock unless topography or karst are present along the river in particular at the pilgrimage site thick sediments induce low resonance frequencies with large amplifications along and across valleys north and east of the city h v spectra show systematic variations according to sediment filling properties finally on the hill flanks east of the city h v spectra rather relate to topography an additional issue with h v spectral ratios based on ambient noise is whether this indicator reflects meaningful geological variations this question is tested on sites where the s wave ground velocity structure is known a first test consists of estimating h v spectral ratios by means of simulation of urban noise through the summation of synthetic seismograms with random properties a second test consists of estimating h href spectral ratios by propagating an earthquake record through a 1d soil profile these two modelings successfully predict most of the observed spectrum characteristics in addition they give some information on the nature of the urban noise which may include a significant amount of shear energy

characterizing surface geology liquefaction potential and maximum intensity in the kachchh seismic zone western india through microtremor analysis abstract this study presents results of microtremor analysis carried out over diverse geological formations and liquefaction sites in the kachchh seismic zone of western india which is host to the deadliest intraplate earthquake m w 7 7 microtremors were recorded at 36 sites with single stations and 7 sites with an array the microtremor array measurements were made using triangular arrays with sensors kept at 30 90 m radii the rayleigh wave velocities are estimated from the array data using high resolution frequency wavenumber f k analysis and the 1d shear wave velocity structure is determined by inversion we found a good correlation between surface geology resonant frequency and amplitude of the horizontal to vertical spectral ratio hvsr curve and shear wave velocity the ground vulnerability index k g values in the liquefied areas are found to be higher than those in the adjacent areas devoid of liquefaction broad or multiple peaks in the hvsr curves and large variations in the shear velocity models could be attributable to the structural and tectonic complexity in the maximum intensity area further our results show that the average fundamental frequencies are around 0 32 hz for the quaternary 0 80 hz for tertiary 1 8 hz for cretaceous 1 8 hz for jurassic and 2 3 hz for the deccan trap formations the inverted s wave velocity varies from 190 to 1350 m s down to a depth of 200 m for the quaternary 220 to 680 m s down to 100 m for tertiary 236 to 1160 m s for cretaceous 670 to 1780 m s for jurassic and 260 to 2440 m s for the deccan trap sites the results of microtremor analysis corroborate the observations from the available geophysical geological and borehole data

shallow velocity structure and site effects at mt vesuvius italy from hvsr and array measurements of ambient vibrations abstract ambient vibrations were recorded by two dense short period seismic arrays located on mount vesuvius the aim of this study is to derive the surface velocity structure through the application of array techniques and to interpret it in terms of resonance effects mount vesuvius which is located in proximity to the apennines earthquake source zone is one of the most dangerous volcanoes of the world we compared different array techniques to derive the dispersive properties of the surface waves composing the noise wave field the frequency wavenumber f k spectral method applied to the data recorded by array a furnished the rayleigh waves and love waves dispersive functions and proved the time space stationarity of the noise wave field the existence of a stochastic wave field justifies the use of the spatial autocorrelation spac method and the time stationarity autocorrelation tsac method which appear to be most effective at the lowest frequencies the tsac method which time averages is confirmed as the most user friendly because it does not require circular geometries the knowledge of the surface structure is an important goal in site effects studies and is used to determine the frequency response of the near surface geology velocity models have been derived from the dispersion curves using both trial and standard inversion procedure the results are compared with those obtained from array measurements in adjacent areas scarpa et al 2003 revealing similar mechanical properties in the cover deposits and heterogeneities down to 40 m of depth the shear wave velocity profiles derived at the array sites are used to model the 1d transfer functions for vertically incident shear waves the fundamental resonance frequencies agree with the peak frequencies observed in the microtremor horizontal to vertical spectral ratios the frequency band of amplification is also compatible with the results obtained from local earthquakes at sites located at the same elevation on mount vesuvius galluzzo et al 2009

comparison of phase velocities from array measurements of rayleigh waves associated with microtremor and results calculated from borehole shear wave velocity profiles shear wave velocities vs are widely used for earthquake ground motion site characterization vs data are now largely obtained using borehole meth ods drilling holes however is expensive nonintrusive surface methods are inex pensive for obtaining vs information but not many comparisons with direct borehole measurements have been published because different assumptions are used in data interpretation of each surface method and public safety is involved in site character ization for engineering structures it is important to validate the surface methods by additional comparisons with borehole measurements we compare results obtained from a particular surface method array measurement of surface waves associated with microtremor with results obtained from borehole methods using a 10 element nested triangular array of 100 m aperture we measured surface wave phase veloci ties at two california sites garner valley near hemet and hollister municipal air port the garner valley site is located at an ancient lake bed where water saturated sediment overlies decomposed granite on top of granite bedrock our array was deployed at a location where seismic velocities had been determined to a depth of 500 m by borehole methods at hollister where the near surface sediment consists of clay sand and gravel we determined phase velocities using an array located close to a 60 m deep borehole where downhole velocity logs already exist because we want to assess the measurements uncomplicated by uncertainties introduced by the inversion process we compare our phase velocity results with the borehole vs depth profile by calculating fundamental mode rayleigh wave phase velocities from an earth model constructed from the borehole data for wavelengths less than 2 times of the array aperture at garner valley phase velocity results from array measure ments agree with the calculated rayleigh wave velocities to better than 11 mea surement errors become larger for wavelengths 2 times greater than the array aper ture at hollister the measured phase velocity at 3 9 hz near the upper edge of the microtremor frequency band is within 20 of the calculated rayleigh wave veloc ity because shear wave velocity is the predominant factor controlling rayleigh wave phase velocities the comparisons suggest that this nonintrusive method can provide vs information adequate for ground motion estimation

constructing the upper crust of the mid atlantic ridge a reinterpretation based on the puna ridge kilauea volcano the volcanic morphology of a number of segments of the slow spreading mid atlantic ridge mar have been reinterpreted based on our understanding of dike emplacement dike propagation and eruption at the east rift zone of kilauea volcano hawaii and its submarine extension the puna ridge the styles of volcanic eruption at the submarine puna ridge are remarkably similar to those of the axial volcanic ridges avrs constructed on the median valley floor of the mar we use this observation to relate volcanic processes occurring at kilauea volcano to the mar we now consider that volcanic features e g seamounts and lava terraces built on the flanks of the avrs are secondary features that are fed from lava tubes or channels not primary features fed directly from an underlying dike we examine simple models of pipe flow and conclude that lava tubes can transport lava down the flanks of submarine rifts to build all of the volcanic features observed there in addition deep water lava tubes are strong enough to withstand the pressures of a few megapascals that the building of a volcanic structure 150 m high at the end of the tube would generate the volumes of individual volcanic terraces and seamounts on the puna ridge and at the mar are large 0 1 1 km3 and similar to the volumes of lava flows that are broadly distributed at the subaerial east rift zone of kilauea this striking difference in the volcanic morphology on a scale of 1 2 km producing terraces and seamounts underwater and low relief flows on land must be related to the enhanced cooling and to the greater mechanical stability of tubes in the submarine environment we suggest that at the mar a crustal magma reservoir most likely located beneath shallow flat sections of the segment provides magma to the rift axis through dikes that propagate laterally tens of kilometers the zone of dike intrusion at least in the neighborhood of the magma body is likely narrower than the width resurfaced by flows yielding a crustal structure that has a rapid vertical transition from lavas to sheeted dikes at segment ends the zone of dike intrusion is likely to be wider giving a resulting structure with a more gradual transition from lavas to dikes