the miocene roof mapping using microtremor recording and electrical survey method in blida city algeria bedrock depths in the mitidja basin in general and in the blida region in particular are still poorly known despite the existence of some relatively deep hydraulic boreholes that intersect only superficial alluvial formations to assess the seismic risk of blida town knowledge of soil amplification requires the thickness and properties of sedimentary formations that cover the substratum for the purposes of our study the thicknesses obtained by the vertical electric soundings carried out in the hydrogeological study of the basin were combined with horizontal to vertical spectral ratio hvsr microtremor recordings this combination made it possible to determine an empirical relationship between frequency and thickness specific to the blida site area which enabled the roof of the miocene to be mapped and shows slight undulations with directions compatible with the tectonic constraints of the region the boundaries between the low and high frequencies obtained by hvsr are well materialized at south by sidi el kebir river at west by chiffa river and in the central part by a line of direction se nw corresponding to the old passage of sidi el kebir river the presence of low frequencies attributed to the old alluvial deposits with significant thicknesses that originate just after sidi el kebir river confirms that the south mitidjian contact is subvertical

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

the chemistry of geothermal waters in iceland ii mineral equilibria and independent variables controlling water compositions abstract the major element chemistry of icelandic geothermal waters is predictable provided two parameters are known this follows from an attainment of or a close approach to an overall chemical equilibrium in the geothermal systems at temperatures as low as 50 c it is considered that the geothermal system composition temperature and kinetic factors determine which alteration minerals form the system composition is not so much fixed by rock composition as by the rate of leaching of the various constituents from the fresh rock and the composition of inflowing water the water chemistry is determined by the system composition and the external variables acting on the system they include temperature and the mobility of chloride pressure which theoretically should be regarded as an external variable has insignificant effect on water compositions in the range 1 200 bars occurring in the geothermal systems

estimating bedrock depth in the case of regolith sites using ambient noise analysis abstract subsurface geometry particularly the depth of bedrock is crucial in seismic hazard studies because the basin geometry has been shown to play an important role in the altering of seismic waves estimating the bedrock surface using ambient seismic noise analysis has been undertaken by many researchers with most studies focusing on sites with a strong impedance contrast between the bedrock and the overlying materials the application of this technique at regolith sites which is subjected to impedance contrasts in the low to high range is underdeveloped and requires further attention this study seeks to address this need and is focused on the city of adelaide in south australia which exhibits site amplification and is associated with various impedance contrasts analyses of ambient noise data are carried out using the generic function gf of the classic horizontal vertical spectral ratio hvsr method and the spatial autocorrelation spac technique to estimate the depth to bedrock comparison of the bedrock depth predictions from the seismic methods with boreholes drilled in close proximity to the measured sites demonstrate that the spac method provides superior estimates especially to those obtained from the other approach this work demonstrates that the microtremor spac method is an effective tool for estimating bedrock structure at regolith sites

building a three dimensional model of the active plio quaternary basin of argostoli cephalonia island greece an integrated geophysical and geological approach abstract this work is a multidisciplinary approach from geological and geophysical surveys to build a 3d geological model of argostoli basin cephalonia island greece aiming to be used for computational 3d simulation of seismic motion cephalonia island is located at the north western end of the aegean subduction frontal thrust that is linked to the dextral cephalonia transform fault west of cephalonia where the seismic hazard is high in terms of earthquake frequency and magnitude the plio quaternary koutavos argostoli basin site was selected within the french research agency pia sinaps project www institut seism fr projets sinaps last accessed on november 25th 2019 to host a vertical accelerometer array the long term goal is to validate three dimensional nonlinear numerical simulation codes to assess the site specific amplification and nonlinearity herein the geological and geophysical surveys carried out from 2011 to 2017 are presented and in particular the complementary investigations that led to the identification of the main stratigraphic units and their structures in addition coral debris sampled from the vertical array deep borehole cores were used for 230th 234u measurements which confirmed the pleistocene age of the koutavos basin the characterization of the three dimensional structure of the stratigraphic units was achieved by coupling geological cross sections i e depth geometry and geophysical surveys based of surface wave analysis

overview of local site effects and seismic microzonation mapping in metropolitan vancouver british columbia canada abstract a multi year seismic microzonation project to map local variations of site response across metropolitan metro vancouver british columbia canada is currently underway this paper presents our progress in one dimensional site amplification hazard mapping of metro vancouver following our first field campaign we initiated our microzonation study by assembling relevant geological geophysical and geotechnical datasets from online and private sources to develop a regional 3d geodatabase we perform site characterization near 20 strong motion stations located on soft and stiff sediments using multiple non invasive in situ seismic methods including surface wave array and microtremor horizontal to vertical spectral ratio mhvsr techniques to retrieve shear wave velocity vs depth profiles we also compile all available earthquake recordings from 6 events of moment magnitude m 3 9 to assess earthquake site amplification across metro vancouver comparison of the limited earthquake horizontal to vertical spectral ratio ehvsr data with mhvsrs demonstrates consistent empirical site amplification supporting the use of mhvsrs as a valid proxy for earthquake site amplification in british columbia vertical array recordings in soft sediments from a m 4 7 earthquake further demonstrate consistency between these amplification measures to achieve spatial coverage for regional microzonation mapping the same vs profiling methods are applied in available open areas and more than 1100 mhvsr measurements are collected in a 600 m resolution grid three additional field campaigns will target validation of our non invasive seismic methods with co located invasive testing and fill in any spatial gaps this paper summarizes the developed and applied methodologies and challenges encountered in seismic amplification hazard mapping for the metro vancouver region

lithology and shear wave velocity in memphis tennessee we have derived a new three dimensional model of the lithologic struc ture beneath the city of memphis tennessee and examined its correlation with measured shear wave velocity profiles the correlation is sufficiently high that the better constrained lithologic model may be used as a proxy for shear wave velocities which are required to calculate site amplification for new seismic hazard maps for memphis the lithologic model and its uncertainties are derived from over 1200 newly compiled well and boring logs some sampling to 500 m depth and a moving least squares algorithm seventy six new shear wave velocity profiles have been measured and used for this study most sampling to 30 m depth or less all log and velocity observations are publicly available via new web sites

unusual mixed silica carbonate deposits from magmatic hydrothermal hot springs savo solomon islands abstract the volcanic island of savo solomon islands hosts an active hydrothermal system discharging unusual alkaline ph 7 8 sulphate rich chloride poor fluid with variable admixtures of ca mg hco 3 rich fluid hot springs and their outflow streams precipitate a variety of deposits including travertine silica sinter and unusual mixed silica carbonate rocks travertine fabrics are dominated by ray crystal calcite associated with rapid abiotic precipitation from a supersaturated solution sinter is produced by evaporation of thermal waters and downstream samples contain preserved traces of micro organisms which potentially acted as templates for precipitation trace element chemistry of sinters and travertines includes anomalously high levels of te indicating a magmatic origin for a component fluid in the hydrothermal system springs are close to or at saturation with both calcite and amorphous silica increased contributions from the ca mg hco 3 end member favours calcite formation this fluid is of low temperature origin and as such is favoured by high rainfall mixed samples show cyclical changes between silica and carbonate precipitation potentially as a result of seasonal variation in rainfall supplementary material a spreadsheet of water and deposit chemical analyses is available at www geolsoc org uk sup18495

comment on microtremor observations of deep sediment resonance in metropolitan memphis tennessee by paul bodin kevin smith steve horton and howard hwang abstract bodin et al eng geol 62 2001 159 reported three sets of maxima in observed h v particle motion spectra where the longest period set of peaks provided clear mapping information on the thickness of post cretaceous sediments in the mississippi embayment but the remaining peaks remained largely unexplained a review of microtremor array studies for similar sites and similar frequencies suggests that the microtremor field is best interpreted in terms of rayleigh wave energy use of this approach with modeling of particle motion h v ratios for realistic models of the mississippi embayment shows that the eng geol 62 2001 159 second set of spectral maxima can be associated with higher mode rayleigh wave energy and may contain information on a possible velocity inversion in the shear velocity profile of the site a third spectral maximum appears to be associated with soft soils loess and may be able to be used for mapping the near surface thickness order 15 m of this unit

tectonic evolution and copper gold metallogenesis of the papua new guinea and solomon islands region papua new guinea and the solomon islands are in one of the most prospective regions for intrusion related mineral deposits however because of the tectonic complexity of the region and the lack of comprehensive regional geological datasets the link between mineralization and the regional scale geodynamic framework has not been understood here we present a new model for the metallogenesis of the region based on a synthesis of recent studies on the petrogenesis of magmatic arcs and the history of subduction zones throughout the region combined with the spatio temporal distribution of intrusion related mineral deposits and six new deposit ages convergence at the pacific australia plate boundary was accommodated from at least 45 ma by subduction at the melanesian trench with related melanesian arc magmatism the arrival of the ontong java plateau at the trench at ca 26 ma resulted in cessation of subduction immediately followed by formation of cu au porphyry epithermal deposits at 24 20 ma throughout the melanesian arc late oligocene to early miocene tectonic reorganization led to initiation of subduction at the pocklington trough and onset of magmatism in the maramuni arc the arrival of the australian continent at the pocklington trough by 12 ma resulted in continental collision and ore deposit formation from 12 to 6 ma this is represented by cu au porphyry deposits in the new guinea orogen and epithermal au systems in the papuan peninsula from 6 ma crustal delamination in papua new guinea related to the prior pocklington trough subduction resulted in adiabatic mantle melting with emplacement of diverse cu and au porphyry and epithermal deposits within the papuan fold and thrust belt and papuan peninsula from 6 ma to the present day subduction at the new britain and san cristobal trenches from ca 10 ma resulted in an escalation in tectonic complexity and the onset of microplate tectonics in eastern papua new guinea and the solomon islands this is reflected in the formation of diverse and discrete geodynamic settings for mineralization within the recent to modern arc setting primarily related to upper plate shortening and extension and the spatial relationship to structures within the subducting slab

study of the h v spectral ratio method for determining average shear wave velocities in the mississippi embayment abstract the shear wave velocity v s structure of the deep sediments in the mississippi embayment is of interest to engineers and seismologists due to its influence on seismic wave propagation and site response during an earthquake although the shallow v s structure top 30 to 60 m is generally well characterized information on the v s structure at greater depths to 1000 m in some regions is very limited past studies have developed relationships between the average v s v s ave of post paleozoic sediments in the embayment as a function of sediment thickness one of these studies used converted body wave arrivals while the other used ambient noise measurements processed with the horizontal to vertical spectral ratio hvsr method interestingly these two approaches yielded relationships that differed by about 25 to 30 the objective of this study is to investigate the cause of the discrepancy between these relationships and identify the more reliable relationship for the v s structure in the mississippi embayment experimental measurements of ambient noise were performed at eleven deep soil sites in the mississippi embayment and analyzed using the hvsr method the results from the experimental study yielded v s ave values that were consistent with findings from the previous hvsr study however simulations of body and surface wave propagation performed using estimated full depth v s profiles at each site showed that the methodology used to develop the velocity thickness relationship specifically the approximate relationship used to relate site frequency sediment thickness and v s produces an overestimation of the true v s ave for the profile by 25 to 30

microtremor recordings in northern mississippi abstract this paper presents the results of 305 single point microtremor recordings covering northern mississippi that is situated within the upper mississippi embayment area both long and short term recordings were obtained by a le 3d 20s seismometer over a large network of points where the unconsolidated sediment thickness ust varies from zero to 1400 m applying the nakamura method the recordings were processed to determine predominant frequency f0 and its relation to ust initial results of wind influence on the frequency spectra particularly in low frequency band 0 05 0 2 hz and dominant vibration direction are also presented it is shown that analysis of systematic microtremor recordings can provide a stable and reliable estimation of the predominant frequency from which estimates of average shear wave velocity of overall sediment profile can be derived predominant frequency and average shear wave velocity is reasonably well correlated with ust wind and human activities are found to produce peaks over the low frequency band

measuring the sediment thickness in urban areas using revised h v spectral ratio method abstract for the sake of safety it is crucial for civil engineers to determine the thickness of the sediment layers in the urban areas however the noisy detection environment in a city presents a significant challenge to the traditional artificial source geophysical methods which are used to estimate and monitor of sediment thickness given this otherwise challenging detection environment the h v spectral ratio method provides an effective and cheap means of detecting sediment thickness it exploits microtremor signals to obtain the resonant frequency of the surface layer which is then used to determine site sediment thickness with an empirical equation using the data from a single observation station in this study we collected microtremor data at 109 locations in the aoshan bay area of the shandong peninsula and determined the resonant frequency and analysed the morphological features of the h v spectral ratio curves in order to calibrate the frequency bedrock depth equation accurately to the local conditions vs profile estimation is used to fine tune the frequency bedrock depth equation by comparing the s wave velocity structure obtained using the microtremor spac method with that found from borehole samples we were able to verify the reliability and accuracy of application of the microtremor spac method by using the h v spectral ratio method and the modified equation that transforms resonance frequencies to sediment thickness we generated a thickness map of the sedimentary layers in the aoshan bay area of the shandong peninsula the map provides useful information for ensuring the safe construction of the city s infrastructure we conclude that the use of microtremor signals can provide important geological information as a cheaper and quick way for the construction and development of urban infrastructure

the basic ingredients of the north atlantic storm track part ii sea surface temperatures abstractthe impact of north atlantic sst patterns on the storm track is investigated using a hierarchy of gcm simulations using idealized aquaplanet and semirealistic boundary conditions in the atmospheric component hadam3 of the third climate configuration of the met office unified model hadcm3 this framework enables the mechanisms determining the tropospheric response to north atlantic sst patterns to be examined both in isolation and in combination with continental scale landmasses and orography in isolation a gulf stream sst pattern acts to strengthen the downstream storm track while a north atlantic drift sst pattern weakens it these changes are consistent with changes in the extratropical sst gradient and near surface baroclinicity and each storm track response is associated with a consistent change in the tropospheric jet structure locally enhanced near surface horizontal wind convergence is found over the warm side of strengthened sst gradients associated with ascending air and i

intraplate type magmatism in a continent island arc collision zone porgera intrusive complex papua new guinea cogenetic volatile rich alkali basalts and gabbros hawaiites and mugearites occur in the late miocene age epizonal porgera intrusive complex which is temporally and spatially associated with rich gold silver mineralization the least evolved rocks show enrichments in light rare earth elements la yb sub cn 15 19 and other incompatible elements e g ba la approx 8 10 la nb approx 0 6 0 7 sr nd approx 25 characteristic of intraplate alkalic basalts and have isotopic compositions sup 87 sr sup 86 sr approx 0 7035 epsilon sub nd approx 6 sup 206 pb sup 204 pb approx 18 66 sup 207 pb sup 204 pb approx 15 56 sup 298 pb sup 204 pb approx 38 55 consistent with derivation from a time averaged depleted mantle source the porgera intrusive complex was emplaced at 6 ma in jurassic cretaceous shelf facies sedimentary rocks near the edge of the australasian plate intrusion appears to have occurred in a back arc environment during subduction of an oceanic microplate segment on two sides beneath the continental margin and an island arc we suggest that this unusual tectonic setting promoted partial melting of asthenospheric source materials that were perhaps modified by deep 150 km subduction processes to form alkalic magmas with intraplate character

using h v measurements to determine depth to bedrock and vs30 in boston massachusetts abstract seismic microzonation is an important step in seismic risk and loss studies for densely populated urban regions ambient noise studies using h v measurements to determine the fundamental site period fsp can be an inexpensive and efficient method to map site effects for a microzonation study ambient noise studies are particularly effective in high impedance contrast environments like boston massachusetts where the soil depth ranges from 1 to 80 m and the soil shear wave velocity vs 200 m s overlays hard glacial till or bedrock vs 2000 3000 m s in this study ambient noise data were collected from 570 locations in the greater boston area nakamura s technique taking the ratio of the fast fourier transform fft of horizontal components to vertical components is applied to determine the fsp the fsp data are mapped across the region and show a consistent pattern with the local geologic and geomorphologic conditions the fsp data are then paired with depth to bedrock and vs30 drawn from 2403 boring logs and 25 vs profiles vs30 is defined as the time weighted average of the vs in the upper 30 m of the soil profile the depth to bedrock and fsp are correlated as are fsp and vs30 measurements fsp depth to bedrock and fsp vs30 correlations are reported with 95 confidence bounds for use in regional planning the resulting fsp vs30 correlation is comparable with similar studies from high impedance contrast regions in canada and japan and show lower vs30 for sites with fsp 0 2 s where the fsp predicts depth to bedrock 18 m than previously reported for the nga west2 database the accuracy of single station ambient noise results is also confirmed with single station and vertical array earthquake spectral ratios an fsp 0 74 s was calculated from ambient noise data at the northeastern university neu vertical array site in the back bay of boston at this site the sediment thickness is 51 m and is consistent with the fsp 0 73 s calculated for the site using earthquake records from the 2011 mw 5 8 mineral virginia earthquake overall the outcomes of this study demonstrate that ambient noise studies can be used in high impedance contrast environments to reliably and consistently estimate the fsp when the fsp estimates are paired with additional data such as depth to bedrock vs30 estimates and recorded ground motion data the spatial distribution of regional site effects can be characterized

dense array recordings in the san bernardino valley of landers big bear aftershocks basin surface waves moho reflections and three dimensional simulations abstract fourteen geos seismic recorders were deployed in the san bernardino valley to study the propagation of short period t 1 to 3 sec surface waves and moho reflections three dense arrays were used to determine the direction and speed of propagation of arrivals in the seismograms the seismograms for a shallow d 1 km m 4 9 aftershock of the big bear earthquake exhibit a very long duration 60 sec of sustained shaking at periods of about 2 sec array analysis indicates that these late arrivals are dominated by surface waves traveling in various directions across the valley some energy is arriving from a direction 180 from the epicenter and was apparently reflected from the edge of the valley opposite the source a close in aftershock 25 km depth 7 km displays substantial short period surface waves at deep soil sites a three dimensional 3d finite difference simulation produces synthetic seismograms with durations similar to those of the observed records for this event indicating the importance of s wave to surface wave conversion near the edge of the basin flat layered models severely underpredict the duration and spectral amplification of this deep soil site i show an example where the coda wave amplitude ratio at 1 to 2 hz between a deep soil and a rock site does not equal the s wave amplitude ratio because of the presence of surface waves in the coda of the deep soil site for one of the events studied 90 km there are sizable phases that are critically reflected from the moho pmp and sms at one of the rock sites the sms phase has a more peaked spectrum that the direct s wave

late cretaceous and cenozoic geology of the new madrid seismic zone structure contour maps constructed from well seismic reflection and outcrop data of the tops of the paleozoic section upper cretaceous section paleocene midway group and eocene section illustrate the post paleozoic structure of the new madrid seismic zone region isopach maps of the late cretaceous section midway group and eocene section help constrain the timing of the structural events these maps which encompass much of the northern mississippi embayment reveal reactivation of the underlying late precambrian cambrian reelfoot rift during midway group deposition but no reactivation during late cretaceous or eocene deposition the structure contour maps also indicate a subtle south plunging depression on the tops of the paleozoic upper cretaceous and midway group along the axis of the northern mississippi embayment that we have called a trench this trench is 50 km wide has a maximum depth of 100 m and appears to have formed during the eocene the trench s western boundary coincides with the blytheville arch lake county uplift and its southeastern margin underlies memphis tennessee the blytheville arch lake county uplift is the structure responsible for the new madrid seismic zone and thus it is possible that the southeastern margin of the trench is also a fault zone northern mississippi embayment post paleozoic stratigraphy consists of sands silts and clays that thicken from 477 m at new madrid missouri to 987 m near memphis tennessee the uniformity of these sediments indicates their elastic properties and therefore seismic velocities are very similar however variations in cementation and unconformities within the section may influence seismic wave propagation manuscript received 17 june 1999

microtremor observations of deep sediment resonance in metropolitan memphis tennessee we measured site resonance periods throughout metropolitan memphis tennessee the site resonance was derived from recordings of ambient microtremor and is a direct measurement of seismic ground shaking in the memphis metropolitan area the period t0 in s is predicted by the empirical relation t0 0 39899 7 8922 10 3h 3 0634 10 6h2 350 h 1100 m where h is the thickness in m of the unconsolidated sediments that overly hard paleozoic rocks assuming that a quarter wavelength relationship governs the relationship between resonant period sediment thickness and average shear wave speed we estimate the average shear wave speed of unconsolidated sediments as a function of sediment thicknesses vs 521 15 0 37459h 350 h 1100 m the scatter in the observations and discordance with earlier work suggests that caution is warranted in applying these values of wave speed indiscriminately to sites in the absence of further detailed work

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

the basic ingredients of the north atlantic storm track part i land sea contrast and orography understanding and predicting changes in storm tracks over longer time scales is a challenging problem particularly in the north atlantic this is due in part to the complex range of forcings land sea contrast orography sea surface temperatures etc that combine to produce the structure of the storm track the impact of land sea contrast and midlatitude orography on the north atlantic storm track is investigated through a hierarchy of gcm simulations using idealized and semirealistic boundary conditions in a highresolution version of the hadley centre atmosphere model hadam3 this framework captures the largescale essence of features such as the north and south american continents eurasia and the rocky mountains enabling the results to be applied more directly to realistic modeling situations than was possible with previous idealized studies the physical processes by which the forcing mechanisms impact the large scale flow and the midlatitude storm tracks are discussed the characteristics of the north american continent are found to be very important in generating the structure of the north atlantic storm track in particular the southwest northeast tilt in the upper tropospheric jet produced by southward deflection of the westerly flow incident on the rocky mountains leads to enhanced storm development along an axis close to that of the continent s eastern coastline the approximately triangular shape of north america also enables a cold pool of air to develop in the northeast intensifying the surface temperature contrast across the eastern coastline consistent with further enhancements of baroclinicity and storm growth along the same axis

the eruptive history and volcanic hazards of savo solomon islands savo island is the 6 km diameter emergent summit of an andesitic dacitic stratovolcano rising from the iron bottom sound 35 km nw of honiara solomon islands savo has erupted at least three times within recorded history and the 3 000 inhabitants maintain extensive oral traditions of past events through description and interpretation of the volcaniclastic sequences on the island in conjunction with historical accounts and oral traditions we reconstruct the eruptive processes on savo block and ash flow baf deposits are volumetrically dominant on the island within three main depositional environments near vent sequences thick medial channel sequences and distal fan sequences the deposits comprise universally non vesicular and highly porphyritic 40 70 phenocrysts high silica andesite and dacite clasts these appear to have been derived from collapsing lava domes during an 1560 1570 a d eruption however eyewitness descriptions and crater morphology suggest that similar deposits formed from dome explosions or collapses of eruption columns during later eruptions 1830 1840 a d the high sodium magmas ca 5 7 wt na2o apparently crystallised and strongly degassed prior to eruption shallow explosions were possibly caused by entrapment of magmatic gases beneath a dome or conduit plug of highly crystalline near solid magma repeated sealing of the vent may have been due to inward collapse of the highly altered rocks of the surrounding hydrothermal system these rocks probably were saturated due to contemporaneous high intensity rainfall events bafs were hot enough to char vegetation and attain aligned clast trm thermal remnant magnetism up to 3 km from the vent many being accompanied by ash cloud surges changes with distance in the baf deposits appear mostly dependent on flow confinement and are limited to an overall decrease in thickness and maximum clast size and an increased definition of weak planar fabrics in distal fan sequences there is strong evidence for syn and post eruptive redeposition of primary deposits since the savo population is concentrated on coastal volcaniclastic fans we consider the greatest volcanic risk to life is from bafs associated ash cloud surges and lahars hence the main channels and fans are designated as the highest of three relative hazard zones on a simple map prepared to aid local education and planning initiatives on savo

evaluation of deep sediment velocity structure in the new madrid seismic zone detailed knowledge of the physical properties of the sediments filling the mississippi embayment has proven critical to both unravel the tectonic frame work operating in the region and assess the seismic hazards posed by the new madrid seismic zone in this article we show that independent geotechnical estimates for p and s wave velocities are compatible with a sedimentary model of k feldspar clasts embeded in water and we test its validity by modeling receiver functions at a number of broadband stations by constraining the bulk sediment thicknesses beneath each station from independent reflection profiling estimates we have been able to recover the depth to the top of the cretaceous from the receiver function data at individual stations our receiver function modeling thus provides confidence in the velocity and density structures extrapolated from in situ geotechnical measurements in the upper mississippi embayment

quantifying the uncertainty in site amplification modeling and its effects on site specific seismic hazard estimation in the upper mississippi embayment and adjacent areas the mississippi embayment located in the central united states and its thick deposits of sediments over 1 km in places have a large effect on earthquake ground motions several previous studies have addressed how these thick sediments might modify probabilistic seismic hazard maps the high seismic hazard associated with the new madrid seismic zone makes it particularly important to quantify the uncertainty in modeling site amplification to better represent earthquake hazard in seismic hazard maps the methodology of the memphis urban seismic hazard mapping project cramer et al 2004 is combined with the reference profile approach of toro and silva 2001 to better estimate seismic hazard in the mississippi embayment improvements over previous approaches include using the 2002 national seismic hazard model fully probabilistic hazard calculations calibration of site amplification with improved nonlinear soil response estimates and estimates of uncertainty comparisons are made with the results of several previous studies and estimates of uncertainty inherent in site amplification modeling for the upper mississippi embayment are developed i present new seismic hazard maps for the upper mississippi embayment with the effects of site geology incorporating these uncertainties

comprehensive ambient noise analyses for seismic microzonation of sarpol e zahab after the mw 7 3 2017 iran earthquake abstract this study is intended to investigate ambient noise recordings in form of array and single station measurements at sarpol e zahab city after the destructive mw 7 3 earthquake of 12 november 2017 in kermanshah province iran the espac f k hvtfa and hvsr methods are applied to analyze the ambient noise and obtain useful information on three key factors of site seismic properties i e the geometry of ground layers their mechanical characteristics and site resonance frequencies the results of this study are presented as maps of the fundamental frequency of the ground depth of bedrock the thickness of top cover materials as well as the average shear wave velocity vs 700 and vs 30 for sarpol e zahab the analyses show that the single value of vs 30 does not represent seismic ground response and the depth of competent bedrock which dominates the low frequency seismic response amplifications is located far beyond 30 m in this city the most effective grade ii seismic microzonation of sarpol e zahab is provided by combining the results of these analyses

the chemistry of fumarolic vapor and thermal spring discharges from the nevado del ruiz volcanic magmatic hydrothermal system colombia on the basis of three sets of gas samples taken during the three months preceding the november 13 1985 eruption of nevado del ruiz from fumaroles on the crater floor the composition of the vapors discharged following minor eruptive activity in september corresponded to that of an essentially magmatic gas during the subsequent quiet period in october the proportion of a hydrothermal component in the vapor discharge increased steadily up until the major eruption the gases were found to be exceptionally high in total sulfur and are super saturated with respect to elemental sulfur their thermodynamic equilibration temperatures range from 200 to 600 c gases and waters from fumaroles and thermal springs on the flanks of the volcano are likely to be derived from a two phase vapor brine envelope surrounding the magmatic system the chemistry of the fumarole discharges is compatible with the assumption of an eruptive mechanism involving the build up of pressure in an extensive vapor zone by gas released from an essentially stagnant already extensively degassed body of magmatic material at depth production of such a residual gas over extended periods may account for the large amount of so2 discharged from the volcano in relation to the small amount of ejected solids

geochemistry of the magmatic hydrothermal system of kawah ijen volcano east java indonesia samples from kawah ijen crater lake spring and fumarole discharges were collected between 1990 and 1996 for chemical and isotopic analysis an extremely low ph 0 3 lake contains so 4 cl waters produced during absorption of magmatic volatiles into shallow ground water the acidic waters dissolve the rock isochemically to produce immature solutions the strong d and 18 o enrichment of the lake is mainly due to enhanced evaporation at elevated temperature but involvement of a magmatic component with heavy isotopic ratios also modifies the lake d and 18 o content the large so4 s d 23 8 26 4 measured in the lake suggest that dissolved so 4 forms during disproportionation of magmatic so 2 in the hydrothermal conduit at temperatures of 250 280 c the lake 18 o so4 and 18 o h2o values may reflect equilibration during subsurface circulation of the water at temperatures near 150 c significant variations in the lake s bulk composition from 1990 to 1996 were not detected however we interpret a change in the distribution and concentration of polythionate species in 1996 as a result of increased so 2 rich gas input to the lake system thermal springs at kawah ijen consist of acidic so 4 cl waters on the lakeshore and neutral ph hco 3 so 4 cl na waters in blawan village 17 km from the crater the cation contents of these discharges are diluted compared to the crater lake but still do not represent equilibrium with the rock the so 4 cl ratios and water and sulfur isotopic compositions support the idea that these springs are mixtures of summit acidic so 4 cl water and ground water the lakeshore fumarole discharges t 170 245 c have both a magmatic and a hydrothermal component and are supersaturated with respect to elemental sulfur the apparent equilibrium temperature of the gas is 260 c the proportions of the oxidized so 2 dominated magmatic vapor anti of the reduced h 2 s dominated hydrothermal vapor in the fumaroles varied between 1979 and 1996 this may be the result of interaction of so 2 bearing magmatic vapors with the summit acidic hydrothermal reservoir this idea is supported by the lower h 2 s so 2 ratio deduced for the gas producing the so 4 cl reservoir feeding the lake compared with that observed in the subaerial gas discharges the condensing gas may have equilibrated in a liquid vapor zone at about 350 c elemental sulfur occurs in the crater lake environment as banded sediments exposed on the lakeshore and as a subaqueous molten body on the crater floor the sediments were precipitated in the past during inorganic oxidation of h 2 s in the lake water this process was not continuous but was interrupted by periods of massive silica poorly crystallized precipitation similar to the present day lake conditions we suggest that the factor controlling the type of deposition is related to whether h 2 s or silica rich volcanic discharges enter the lake this could depend on the efficiency with which the lake water circulates in the hydrothermal cell beneath the crater quenched liquid sulfur products show 34 s values similar to those found in the banded deposits suggesting that the subaqueous molten body simply consists of melted sediments previously accumulated at the lake bottom

downstream self destruction of storm tracks the northern hemisphere storm tracks have maximum intensity over the pacific and atlantic basins their intensity is reduced over the continents downstream here simulations with an idealized aquaplanet general circulation model are used to demonstrate that even without continents storm tracks have a self determined longitudinal length scale their length is controlled primarily by the planetary rotation rate and is similar to thatofearth sstormtracksforearth srotationrate downstream stormtracksself destruct thedownstream eddy kinetic energy is lower than it would be without the zonal asymmetries that cause localized storm tracks likely involved in the downstreamself destruction ofstormtracks arethe energyfluxesassociatedwiththem the zonalasymmetries that causelocalized stormtracksenhancetheenergytransport throughthe generation of stationary eddies and this leads to a reduced baroclinicity that persists far downstream of the eddy kinetic energy maxima

neotectonics of the upper mississippi embayment abstract although the upper mississippi embayment is an area of low relief the region has been subjected to tectonic influence throughout its history and continues to be so today tectonic activity can be recognized through seismicity patterns and geological indicators of activity either those as a direct result of earthquakes or longer term geomorphic structural and sedimentological signatures the rate of seismic activity in the upper mississippi embayment is generally lower than at the margins of tectonic plates the embayment however is the most seismically active region east of the rocky mountains with activity concentrated in the new madrid seismic zone this zone produced the very large new madrid earthquakes of 1811 and 1812 geological and geophysical evidence of neotectonic activity in the upper mississippi embayment includes faulting in the benton hills and thebes gap in missouri paleoliquefaction in the western lowlands of missouri subsurface faulting beneath and tilting of crowley s ridge in northeastern arkansas and southeastern missouri subsurface faulting along the crittenden county fault zone near memphis tennessee faulting along the east flank of the tiptonville dome and numerous indicators of historic and prehistoric large earthquakes in the new madrid seismic zone paleoearthquake studies in the new madrid seismic zone have used trenching seismic reflection shallow coring pedology geomorphology archaeology and dendrochronology to identify and date faulting deposits of liquefied sand and areas of uplift and subsidence the cause of today s relatively high rate of tectonic activity in the mississippi embayment remains elusive it is also not clear whether this activity rate is a short term phenomenon or has been constant over millions of years ongoing geodetic and geological studies should provide more insight as to the precise manner in which crustal strain is accumulating and perhaps allow improved regional neotectonic models

the central role of ocean dynamics in connecting the north atlantic oscillation to the extratropical component of the atlantic multidecadal oscillation abstractthe relationship between the north atlantic oscillation nao and atlantic sea surface temperature sst variability is investigated using models and observations coupled climate models are used in which the ocean component is either a fully dynamic ocean or a slab ocean with no resolved ocean heat transport on time scales less than 10 yr nao variations drive a tripole pattern of sst anomalies in both observations and models this sst pattern is a direct response of the ocean mixed layer to turbulent surface heat flux anomalies associated with the nao on time scales longer than 10 yr a similar relationship exists between the nao and the tripole pattern of sst anomalies in models with a slab ocean a different relationship exists both for the observations and for models with a dynamic ocean in these models a positive negative nao anomaly leads after a decadal scale lag to a monopole pattern of warming cooling that resembles the atlantic multidecadal oscillation amo although with sma

bulk sediment qp and qs in the mississippi embayment central united states we have estimated p wave ands wave anelastic attenuation coefficients for the thick unconsolidated sediments of the mississippi embayment central united states using the spectral distance decay of explosion p and rayleigh waves the sediment trapped p wave psed is observed to ranges of 80 km at 10 hz and 1 hz rayleigh waves are observed out to 130 km from a 5000 lb borehole explosion in the northern part of the embayment rayleigh waves of 4 hz are seen to distances of 3 km from a smaller 50 lb explosion analysis of the group velocity and amplitude distance decay of both waves yields an average qs of 100 and qp of 200 for embay ment sediments that are independent of frequency scatter in the q estimates comes from interference of multiple p wave reverberations and rayleigh wave modes the attenuation model is self consistent in that it is the same as obtained by the analysis of synthetic seismograms using the inferred q values inferred qp and qs values are more than three times higher than previous estimates and imply that unconsolidated sediments of the embayment do not significantly attenuate small strain earthquake ground motions these estimates represent a lower bound to q of the sediments since significant scattering is observed in the waveform data that contributes to the distance decay of wave amplitude higher q values also imply that the unconsolidated sedi ments of the embayment will form an efficient wave guide for surface waves radiated from shallow earthquakes or large earthquakes that rupture into the sediments pro ducing high amplitude long duration wave trains that should be considered in earth quake hazard assessments

variations in north american summer precipitation driven by the atlantic multidecadal oscillation understanding the development and variation of the atmospheric circulation regimes driven by the atlantic multidecadaloscillation amo isessentialbecausethesecirculationsinteractwithotherforcingsondecadaland interannual time scales collectively they determine the summer june july and august precipitation variations for north america in this study a general circulation model gcm is used to obtain such understanding with a focus on physical processes connecting the amo and the summertime precipitation regime change in northamerica twoexperimentalrunsareconductedwithseasurfacetemperature sst anomaliesimposedin the north atlantic ocean that represent the warm and cold phases of the amo climatological ssts are used elsewhere in the oceans model results yield summertime precipitation anomalies in north america closely matching the observed anomaly patterns in north america suggesting that the amo provides a fundamental control on summertime precipitation in north america at decadal time scales the impacts of the amo are achieved by a chain of events arising from different circulation anomalies during warm and cold phases of the amo during the warm phase the north atlantic subtropical high pressure system nash weakens and the north american continent is much less influenced by it a massive body of warm air develops over the heated land in north america from june august associated with high temperature and low pressure anomalies in the lowertroposphereandhighpressureanomaliesintheuppertroposphere incontrast duringthecoldphaseofthe amo the north american continent particularly to the west is much more influenced by an enhanced nash cooler temperatures and high pressure anomalies prevail in the lower troposphere and a frontal zone forms in the upper troposphere these different circulation anomalies further induce a three cell circulation anomaly pattern over north america in the warm and cold phases of the amo in particular during the cold phase the three cell circulation anomaly pattern features a broad region of anomalous low level southerly flow from the gulf of mexico into the u s great plains superimposed with an upper troposphere front more frequent summertime storms develop and excess precipitation occurs over most of north america a nearly reversed condition occurs during the warm phase of the amo yielding drier conditions in north america this new understandingprovides a foundation for further studyand better prediction of the variations of north american summer precipitation especially when modulated by other multidecadal variations for example the pacific decadal oscillation and interannual variations associated with the enso and the arctic oscillation

anomalous alkaline sulphate fluids produced in a magmatic hydrothermal system savo solomon islands abstract in magmatic hydrothermal and associated geothermal systems acidic magmatic derived fluids ph 5 geothermal fluids are typically limited to lateral outflows some distance from the main vent here we describe an unusual hydrothermal system associated with savo volcano a recently eruptive 1830 1840 ad trachyte dominated island arc stratovolcano in the solomon islands hot springs 100 c near to the volcanic crater discharge alkaline waters instead of the more commonly recognised acidic fluids the hydrothermal system of savo dominantly discharges sinter and travertine forming alkaline sulphate ph 7 8 waters at hot springs on its upper flanks in addition to a small number of lower discharge acid sulphate springs ph 2 7 alkaline sulphate fluids are dilute chloride poor 600 mg l and silica rich 250 mg l they have restricted 34sso4 5 4 1 5 and 18oh2o values 4 local non thermal groundwater is 8 acid sulphate springs discharge low chloride geochemical modelling shows that water rock reaction and dilution in the presence of secondary anhydrite pyrite and quartz leads to chloride being diluted to low concentrations whilst maintaining high sulphate and silica concentrations in the fluid strontium oxygen and hydrogen isotopes confirm water rock reaction and mixing with groundwater as primary controls on the composition of the alkaline sulphate springs the highly unusual dilute chemistry of all discharges at savo is a consequence of high regional rainfall i e climatic control and results from open system mixing at depth between hydrothermal and meteoric waters

evaluation of site effect within the tectonic basin in the northern side of ankara abstract this study mainly concentrates on the determination of site effects for the plio quaternary and especially alluvial soils of the cubuk district and its close vicinity in ankara turkey in the study area particularly in the vicinity of the asymmetric graben that has formed due to the tectonic activities along the ne sw trending normal faults a microtremor survey was implemented to identify the local site response under a possible seismic event the results were compared and correlated by using passive and active surface wave measurements engineering geological and geotechnical deep borehole logs along with information on local geology and geological tectonic setting regarding the microtremor results larger fundamental periods were acquired than expected over the area and the effect of the tectonic deformation on the stiffness of the soils was also observed at either the h v curves or the shear wave velocity profiles the results have demonstrated that geotechnical information down to a depth of 30 m may not be compared with the h v parameters the h v amplitudes were not always accompanied with the higher periods in the quaternary sediments this could be due to the basin and basin edge effects observed particularly at the center and boundary of the basin respectively additionally the microtremor survey showed that the spectral ratio amplitudes derived by the h v ratio are debatable and are not a direct indicator of local soil behavior under a seismic excitation

sequence stratigraphy structural style and age of deformation of the malaita accretionary prism solomon arc ontong java plateau convergent zone possibilities for the fate of oceanic plateaus at subduction zones range from complete subduction of the plateau beneath the arc to complete plateau arc accretion and resulting collisional orogenesis deep penetration multi channel seismic reflection mcs data from the northern flank of the solomon islands reveal the sequence stratigraphy structural style and age of deformation of an accretionary prism formed during late neogene 5 0 ma convergence between the 33 km thick crust of the ontong java oceanic plateau and the 15 km thick solomon island arc correlation of mcs data with the satellite derived free air gravity field defines the tectonic boundaries and internal structure of the 800 km long 140 km wide accretionary prism we name this prism the malaita accretionary prism or map after malaita the largest and best studied island exposure of the accretionary prism in the solomon islands mcs data gravity data and stratigraphic correlations to islands and odp sites on the ontong java plateau ojp reveal that the offshore map is composed of folded and thrust faulted sedimentary rocks and upper crystalline crust offscraped from the solomon the subducting ontong java plateau pacific plate and transferred to the solomon arc with the exception of an upper sequence of quaternary island derived terrigenous sediments the deformed stratigraphy of the map is identical to that of the incoming ontong java plateau in the north solomon trench

the influence of wind on measurements of seismic noise summary the horizontal to vertical spectral ratio hvsr technique of microtremor measurement is widely applied in microzonation and site response studies given the small amplitude of the measured signal unwanted disturbances may adversely affect the results we analysed the influence of local wind on microtremor measurements as follows first we studied variation in hvsr at a permanent three component seismological station under various wind patterns second we conducted an experiment under controlled condition in a wind room equipped with a laser particle image velocimeter analysing the effect of increasing wind speed on various sensor digitizer configurations third we undertook numerical modelling to explain the observed data our main conclusions are that wind increases the amplitude of all components of the microtremor wavefield but does not affect hvsr however certain sensor digitizer configurations can be adversely affected by instrumental noise due to turbulence at the air instrument ground interface

winter cold of eastern continental boundaries induced by warm ocean waters in winter northeastern north america and northeastern asia are both colder than other regions at similar latitudes this has been attributed to the effects of stationary weather systems set by elevated terrain orography and to a lack of maritime influences from the prevailing westerly winds however the differences in extent and orography between the two continents suggest that further mechanisms are involved here we show that this anomalous winter cold can result in part from westward radiation of large scale atmospheric waves nearly stationary rossby waves generated by heating of the atmosphere over warm ocean waters we demonstrate this mechanism using simulations with an idealized general circulation model with which we show that the extent of the cold region is controlled by properties of rossby waves such as their group velocity and its dependence on the planetary rotation rate our results show that warm ocean waters contribute to the contrast in mid latitude winter temperatures between eastern and western continental boundaries not only by warming western boundaries but also by cooling eastern boundaries

geophysical and geomorphological investigations of a quaternary karstic paleolake and its underground marine connection in cassis bestouan cassis se france an original karstic system in a coastal alluvial plain located in a carbonate environment cassis provence se france was studied using a multi method approach electrical resistivity tomography gravimetric passive seismic survey combined with geomorphologic methods surface observations and drilling limestone dissolution and or cavity collapse led to the development of a polje which was filled rapidly by erosion of aptian marls the combination of several dating and paleoenvironmental proxies indicates that the polje was filled during a glacial period mis 6 8 or 10 i e in the 130 360 ka age range this discovery has implications for the understanding of karst processes the connection between the polje and the three km long bestouan underwater karstic conduit with submarine outlet is strongly suggested by sedimentological studies and geophysical prospections

the influence of atlantic variability on asian summer climate is sensitive to the pattern of the sea surface temperature anomaly we simulate the response of asian summer climate to atlantic multidecadal oscillation amo like sea surface temperature sst anomalies using an intermediate complexity general circulation model igcm4 experiments are performed with seven individualamosst anomalies obtained from cmip5 pmip3 global climate models as well as their multimodel mean globally and over the north atlantic ocean only for both the positive and negative phases of the amo during the positive warm amo phase a rossby wave train propagates eastward causing a high pressure and warm and dry surface anomalies over eastern china and japan during the negative cool phase of the amo the midlatitude rossby wave train is less robust but the model does simulate a warm and dry south asian monsoon associated with the movement of the intertropical convergence zone in the tropical atlantic the circulation response and associated temperature and precipitation anomalies are sensitive to the choice of amo sst anomaly pattern a comparison between global sst and north atlantic sst perturbation experiments indicates that east asian climate anomalies are forced from the north atlantic region whereas south asian climate anomalies are more strongly affected by the amo related sst anomalies outside the north atlantic region experiments conducted with different amplitudes of negative and positiveamoanomalies show that the temperature response is linear with respect to sst anomaly but the precipitation response is nonlinear

atmospheric responses to north atlantic sst anomalies in idealized experiments part i northern hemispheric circulation abstractidealized model experiments using the ncar cesm1 0 5 under equinox conditions are designed and performed to address two fundamental questions about the effects of the sea surface temperature sst variation associated with the atlantic multidecadal oscillation amo on circulation and precipitation in north america and europe 1 is the observed relationship between the amo sst and the warm season precipitation in north america a statistical coincidence and 2 why is the response of negative precipitation anomaly to warm sst in the amo fairly uniform across most of north america whereas the positive precipitation anomaly in the cold sst rather spotty model experiments are done with either a warm or cold sst anomaly in an aquaplanet a planet with idealized continents and a planet with both idealized continents and orography major results show that the atmospheric response to warm sst anomaly in the north atlantic is fairly similar among the three sets of experiments in the lower troposphere

microtremor survey in talchir india to ascertain its basin characteristics in terms of predominant frequency by nakamura s ratio technique abstract the talchir basin one of india s oldest basins has been a subject of interest because of its rich coal deposits the maximum thickness of the basin is about 1500 m beyond the basin is the hard metamorphic rocks of precambrian age the ambient noise survey data have been analyzed for the talchir basin using nakamura s technique of horizontal vertical spectral ratio hvsr to ascertain the basin structure in terms of the predominant frequency the predominant frequency varies from 0 25 hz to 7 8 hz but a major portion of the basin comes under the range of 0 3 hz 2 4 hz while on the metamorphic rocks it is as high as 7 8 hz the variation in predominant frequency shows a good correlation with the sediment thickness of the basin the results have been compared with the previous studies by other researchers and it shows consistency with the northerly dip of the basin the present study has also been compared with the results of the synthetic seismogram that was performed for the talchir basin the predominant frequency obtained from hvsr technique complements well with the frequency at which the peak response spectra ratio is observed the present study of the predominant frequency identifies quite well the characteristics of talchir basin and is in good agreement with the synthetic ground motion modeling of the region

stochastic seismic response of a slope based on large scale shaking table tests abstract slopes should be regarded as stochastic dynamic systems when investigating the uncertainty of ground motions in engineering this involves the propagation and spatial evolution of physical quantities e g acceleration that can be assessed with some probability more specifically stochastic stability and amplification effects are important issues under random seismic inputs in studying the above a large scale shaking table test is carried out to investigate the slope seismic response under random earthquake ground motions where 144 ground motion samples are generated using a time evolution power spectrum model in this test acceleration evolves in a way that its pdf changes with time and space in the time domain the pdf variability first increases and then decreases with the progression of the earthquake in the spatial domain the pdf variability increases upslope indicating that the mean and standard deviation of amplification factors increase with elevation moreover the stability of the upper part of the slope stochastic dynamic system is poor meanwhile the de amplification effect of the slope toe is identified under random seismic inputs finally we discuss different amplification factors and consider applications of the research results in slope engineering

three dimensional simulation of earthquakes on the los angeles fault system we have used a 3d finite difference method to simulate ground motion from elastodynamic propagating ruptures with constant slip on faults in the metropolitan area of los angeles california simulations are carried out for hypothetical m 6 75 earthquakes on the palos verdes and elysian park faults and for comparison an approximation to the 17 january 1994 m 6 7 northridge earthquake the dominant subsurface features of this area are the deep sedimentary los angeles basin and the smaller and shallower san fernando basin simulated ground motions are restricted to the frequency range 0 0 to 0 4 hz ground motion time histories show that in general sites associated with the largest particle velocities and cumulative kinetic energies are located 1 in the epicentral area 2 above the deepest parts of the basins and 3 near the steepest edges of the los angeles basin we find maximum particle velocities for the palos verdes elysian park and northridge simulations of 0 44 0 67 and 0 58 m sec respectively in each case both the directivity of the rupture and the lower impedance of the basins significantly amplify the ground motion although the gross radiation pattern from these ruptures is observable the 3d basin structure distorts the wave field and becomes a source for edge generated waves signal durations at some basin sites last beyond 90 sec due to love waves and refracted s waves that propagate into the sediments from the basin edges compared with the palos verdes event the durations are generally smaller for the elysian park earthquake due to a smaller amount of love waves generated at the basin edges a simple approximation to the northridge earthquake reproduces the overall spatial pattern of the long period particle velocities successfully predicts the timing of late arriving waves and matches the peak velocities with discrepancies generally less than a factor of 2 however for localized areas immediately north and south of the santa monica mountains the computed ground motion underpredicts the observed horizontal peak velocities but matches the vertical ones the pattern of simulated total cumulative kinetic energies is similar to that for the damage intensities observed near the epicenter of the northridge event while the northridge earthquake caused damage in the los angeles area the 3d simulations show that earthquakes with the same magnitude on the palos verdes or elysian park faults produce more severe ground shaking in the los angeles basin

automated procedure for estimating vs30 utilizing p wave seismograms and its application to japan abstract we develop an automated procedure to estimate time averaged shear wave velocities in the upper 30 m of soil deposits vs30 rapidly and objectively based on initial p wave seismogram amplitudes in the radial and vertical directions we apply this procedure to 630 kiban kyoshin network stations in japan utilizing 9207 records it is clear that the estimates are in good agreement with real world measurements filtering records based on signal to noise ratio snr thresholds slightly improves vs30 estimation but a decrease in the number of records results in an inability to estimate vs30 at certain sites we propose bias correction models based on snrs and take off angles to facilitate vs30 estimation at numerous sites while maintaining suitable prediction performance we observe that the performance of the proposed method is similar to that of methods utilizing different types of proxies for various regions we successfully apply the proposed method to 989 kyoshin network stations utilizing 18 454 records and create a vs30 map for the entire area of japan

site effect evaluation using spectral ratios with only one station the spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity the purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station the technique originally proposed by nakamura to analyze rayleigh waves in the microtremor records is presented briefly and it is discussed why it may be applicable to study the intense s wave part in earthquake records results are presented for three different cities in mexico oaxaca oax acapulco gro and mexico city these cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city each time we compare the results of nakamura s technique with standard spectral ratios in all three cases the results are very encouraging we conclude that if site effects are caused by simple geology a first estimate of dominant period and local amplification level can be obtained using records of only one station

geological tectonic framework of solomon islands sw pacific crustal accretion and growth within an intra oceanic setting the solomon islands are a complex collage of crustal units or terrains herein termed the solomon block which have formed and accreted within an intra oceanic environment since cretaceous times predominantly cretaceous basaltic basement sequences are divided into 1 a plume related ontong java plateau terrain ojpt which includes malaita ulawa and northern santa isabel 2 a normal ocean ridge related south solomon morb terrain ssmt which includes choiseul and guadalcanal and 3 a hybrid makira terrain which has both morb and plume plateau affinities the ojpt formed as an integral part of the massive ontong java plateau ojp at c 122 ma and 90 ma respectively was subsequently affected by eocene oligocene alkaline and alnoitic magmatism and was unaffected by subsequent arc development the ssmt initially formed within a normal ocean ridge environment which produced a morb like basaltic basement through which two stages of arc crustal growth subsequently developed from the eocene onwards the makira terrain records the intermingling of basalts with plume plateau and morb affinities from c 90 ma to c 30 ma and a contribution from late miocene present day arc growth two distinct stages of arc growth occurred within the solomon block from the eocene to the early miocene stage 1 and from the late miocene to the present day stage 2 stage 1 arc growth created the basement of the central part of the solomon block the central solomon terrain cst which includes the shortland florida and south isabel islands stage 2 arc growth led to crustal growth in the west and south the new georgia terrain or ngt which includes savo and the new georgia and russell islands both stages of arc growth also added new material to pre existing crustal units within other terrains the solomon block terrane collage records the collision between the alaska sized ojp and the solomon arc initial contact possibly first occurred some 25 20 ma but it is only since around 4 ma that the ojp has more forcefully collided with the solomon arc and has been actively accreting since that time continuing to the present day we present a number of tectonic models in an attempt to understand the mechanism of plateau accretion one model depicts the ojp as splitting in two with the upper 4 10 km forming an imbricate stack verging to the northeast over which the solomon arc is overthrust whilst deeper portions of the ojp beneath a critical detachment surface are subducted the subduction of young 5 ma hot oceanic lithosphere belonging to the woodlark basin at the ssts has resulted in a sequence of tectonic phenomena including the production of unusual magma compositions e g na ti rich basalts and an abundance of picrites an anomalously small

site amplification in the san fernando valley california variability of site effect estimation using the s wave coda and h v methods during the months that followed the 17 january 1994 m 6 7 northridge california earthquake portable digital seismic stations were deployed in the san fernando basin to record aftershock data and estimate site amplification factors this study analyzes data recorded on 31 three component stations from 38 aftershocks ranging from m 3 0 to m 5 1 and depths from 0 2 to 19 km site responses from the 31 stations are estimated from coda waves s waves and ratios of horizontal to vertical h v recordings for the coda and the s waves site response is estimated using both direct spectral ratios and a generalized inversion scheme results from the inversions indicate that the effect of qs can be significant especially at high frequencies site amplifications estimated from the coda of the vertical and horizontal components can be significantly different from each other depending on the choice of the reference site the difference is reduced when an average of six rock sites is used as a reference site in addition when using this multi reference site the coda amplification from rock sites is usually within a factor of 2 of the amplification determined from the direct spectral ratios and the inversion of the s waves however for nonrock sites the coda amplification can be larger by a factor of 2 or more when compared with the amplification estimated from the direct spectral ratios and the inversion of the s waves the h v method for estimating site response is found to extract the same predominant peaks as the direct spectral ratio and the inversion methods the amplifications determined from the hiv method are however different from the amplifications determined from the other methods finally the stations were grouped into classes based on two different classifications general geology and a more detailed classification using a quaternary geology map for the los angeles and san fernando areas average site response estimates using the site characterization based on the detailed geology show better correlation between amplification and surface geology than the general geology classification

the seismic response of the los angeles basin california using strong motion data recorded in the los angeles region from the 1992 mw 7 3 landers earthquake we have tested the accuracy of existing three dimensional 3d velocity models on the simulation of long period 2 sec ground motions in the los angeles basin and surrounding san fernando and san gabriel valleys first the overall pattern and degree of long period excitation of the basins were identified in the observations within the los angeles basin the recorded amplitudes are about three to four times larger than at sites outside the basins amplitudes within the san fernando and san gabriel valleys are nearly a factor of 3 greater than surrounding bedrock sites then using a 3d finite difference numerical modeling approach we analyzed how variations in 3d earth structure affect simulated waveforms amplitudes and the fit to the observed patterns of amplification significant differences exist in the 3d velocity models of southern california that we tested magistrale et al 1996 graves 1996a hauksson and haase 1997 major differences in the models include the velocity of the assumed background models the depth of the los angeles basin and the depth location and geometry of smaller basins the largest disparities in the response of the models are seen for the san fernando valley and the deepest portion of the los angeles basin these arise in large part from variations in the structure of the basins particularly the effective depth extent which is mainly due to alternative assumptions about the nature of the basin sediment fill the general ground motion characteristics are matched by the 3d model simulations validating the use of 3d modeling with geologically based velocity structure models however significant shortcomings exist in the overall patterns of amplification and the duration of the long period response the successes and limitations of the models for reproducing the recorded ground motions as discussed provide the basis and direction for necessary improvements to earth structure models whether geologically or tomographically derived the differences in the response of the earth models tested also translate to variable success in the ability to successfully model the data and add uncertainty to estimates of the basin response given input scenario earthquake source models

shear wave velocity of the sedimentary basin in the upper mississippi embayment using s to p converted waves from mid october 1989 to august 1992 40 three component panda portable array for numerical data acquisition stations were deployed in the central new madrid seismic zone three component digital seismograms recorded by the panda stations in the region are characterized by 1 the very weak direct s arrivals on the vertical component which can be identified unambiguously from the two horizontal components and 2 at least two prominent secondary arrivals between the direct p and s arrivals one sp dominant on the vertical component and another ps with smaller amplitude on the two horizontal components travel time differences between the sp and s and between the p and ps are the same for different earthquakes recorded at the same station but are different at different stations even for the same event polarization analyses of three component seismograms and travel time measurements confirm the interpretation that these two secondary arrivals are the p to s ps and s to p sp converted waves that occur at the bottom of the sedimentary basin beneath each station since abundant well log data are available in the upper mississippi embayment the thickness of the sediments beneath each seismic station can be estimated travel time differences between the direct and the converted waves can be used to calculate average shear wave velocity for the sediments beneath each station the estimated shear wave velocities of the sediments beneath panda stations vary from 0 45 to 0 67 km sec the higher shear wave velocity associated with thicker sediments can be interpreted as a consequence of increasing compaction of unconsolidated sediments due to increasing overburden

dynamic deformations of shallow sediments in the valley of mexico part i three dimensional strains and rotations recorded on a seismic array abstract we study the spatial variation in earthquake ground motions or equivalently the dynamic displacement gradient field using a novel analysis procedure borrowed from geodesy seismic data recorded in the valley of mexico by a microarray of three three component surface accelerographs and two three component accelerographs at depths of 30 m and 102 m constrain our estimates of the dynamic displacement gradient field from which strains and rotations derive for four moderate earthquakes at distances of 250 to 300 km our study focuses on the effects of low velocity surface materials on the deformation at the surface the gradients corresponding to deformation across vertical planes dominate and vertical axis rotations are of similar magnitudes as strains the greatest peak surface gradient we observed was 206 strain for the 14 september 1995 m w 7 5 earthquake at a distance of 300 km however much larger gradients occur across horizontal planes u z where u is a horizontal displacement and z is depth at some depth between 0 and 30 m these values are about a factor 10 greater than the corresponding gradient components at the surface u z for the 14 september earthquake equaled or exceeded 665 strain at depth the dynamic deformations experienced in mexico city undoubtedly have occurred before and will occur again in other densely populated areas however in many other regions the sediment response will not remain linear and elastic resulting instead in liquefaction and ground failure

array observations of microseismic noise and the nature of h v in the mississippi embayment abstract ambient ground motion data were collected using phased seismic arrays in fall 2002 and spring 2007 within the mississippi embayment and at a single station external to the embayment these data allowed us to determine the wave field composition of ambient noise for understanding wave propagation mechanisms giving rise to spectral peaks using nakamura s h v technique ambient ground motions in the frequency band of 0 1 0 33 hz 10 3 sec period were dominated by spatially localized rayleigh and love wave microseisms generated by high ocean waves along the north american seaboard in the time periods of analysis seismic waves important in forming the h v peak near 4 sec period are composed of relatively high phase velocity rayleigh and love waves that convert to propagating homogeneous shear waves in the thick unconsolidated sediments of the embayment the h v resonant period is controlled by both constructive and destructive interference of these shear waves a simple relationship for the h v peak is given using a propagator matrix formulation that predicts the resonance frequency of a layered medium for surface wave motion at the base of the system the amplitude of the observed h v peak however does not give an accurate estimate of shear wave amplification because it depends on the slowness of the incident wave the inconsistency in estimated average shear wave velocities using the h v method and differential travel times of local earthquake sp phases in the mississippi embayment may be explained by misidentification of sp wave conversion points from deeper interfaces

seismic ground motions from a bolide shock wave 1 an intensely brilliant bolide accompanied by an audible sonic boom occurred on the night of 3 november 2003 2150 lt or 4 november 2003 0350 ut in northeastern arkansas the sonic boom was well recorded by 22 three component stations of the center for earthquake research and information cooperative seismic network arrival times and wave polarizations were used to reconstruct the acoustic wave front propagating across the network and to estimate trajectory parameters of the bolide a grid search location technique constrains the trajectory and gives a reference height of 50 100 km above the southern edge of the network an azimuth of propagation of 270 290 toward the northwest and a plunge of 38 48 downward the trajectory and date of the bolide event are consistent with a taurid shower meteor transient ground motions from the sonic boom were studied using plane wave cagniard dehoop and propagator matrix theory for an incident pressure pulse impinging on a layered elastic earth model general characteristics of the vertical and radial polarization and wave frequency content require acoustic coupling within a thin 10 m near surface layer with low p wave 0 25 km s and s wave 0 125 km s velocities ground motions are generally confined to this near surface layer are not sensitive to deeper earth structure within the mississippi embayment unconsolidated sediments and display both leaky mode pl a type of dispersed p type seismic wave and locked mode rayleigh wave propagation acoustic wave ground motion coupling studies may be a useful way to analyze near surface site responses to determine velocity structure in earthquake shaking hazard studies

investigation of 3 d basin structures in the izmit bay area turkey by single station microtremor and gravimetric methods summary we investigate 3 d basin structures and site resonance frequencies in the izmit bay area of turkey by new geophysical surveys based on 239 single station microtremor and 405 point gravity measurements a fundamental resonance frequency map of the izmit bay was produced from the main peak in the horizontal to vertical component spectral ratio hvsr of microtremors the hvsr analysis of the microtremor data reveals single double broad peaked or no peak type hvsr curves varying in accordance with the surface geology and spatial extent of the three basins present in the izmit bay area in the deepest sections of the izmit golcuk and derince basins of the izmit bay the fundamental resonance frequencies are dominantly 0 24 0 30 hz these resonance frequencies should be taken into consideration along with higher mode frequencies to construct earthquake resistant structures in the izmit bay area the 3 d gravimetric bedrock depth map of the izmit basin shows that the basin has an asymmetric shape with its deepest section coinciding with the surface trace of the north anatolian fault the northern shoulder of the basin has a gentle dip on the kocaeli peneplain side and the southern shoulder is much steeper and it is bounded by the samanli mountains we derive a power law relationship that correlates the fundamental site resonance frequencies with the sedimentary cover thickness obtained from the gravity and shear wave velocity data in the izmit bay we use this relationship to estimate bedrock depths beneath golcuk and derince basins our estimation of maximum basin depths is 1400 m for the izmit and is 800 m for the golcuk and derince basins finally we have analysed a converted sp phase from a local earthquake recording made at site cmp to calculate and verify the sediment thickness estimations obtained from our gravimetric and microtremor analyses this calculation shows close agreement with that of the gravimetric and microtremor results our results show that the basins in the izmit bay area have a very thick sedimentary cover with very low shear velocities underlined by hard bedrock forming a sharp impedance contrast we anticipate that these results will be a key contribution to the quantitative assessment of seismic hazard for the izmit bay area before the occurrence of strong earthquakes in the marmara region

are microtremors useful in site response evaluation we have reviewed the applicability of microtremor measurements to evaluate site response of soft soils to this end we evaluated three different techniques commonly used to estimate site effects from microtremor measurements interpretation of fourier amplitude spectra computation of spectral ratios relative to a firm reference station and finally computation of spectral ratios of horizontal components relative to the vertical component of ground motion nakamura s technique these techniques are applied to microtremor records obtained in three cities in mexico mexico city oaxaca and acapulco these cities differ in their local geological conditions and in their seismotectonic environment in order to evaluate the results obtained from microtremor measurements we compare them with standard spectral ratios of the intense s wave part of weak or strong motion records obtained at the same sites our results showed that microtremor measurements can be used to estimate the dominant period of a site with very acceptable reliability in the range 0 3 to 5 hz the best results were obtained with nakamura s technique which also gives a rough estimate of amplification of seismic waves when the local geology is relatively simple simple numerical simulations indicate that the underlying assumptions of nakamura s technique are consistent with the propagation of rayleigh waves these simple numerical simulations also explain why different researchers have been able to successfully characterize 1d site effects using microtremor records regardless of whether they consider microtremors to consist of surface or body waves our results strongly suggest that the technique by nakamura effectively compensates for source effects in microtremor measurements which eliminates a major limitation to their application in earthquake engineering

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

microtremor measurements used to map thickness of soft sediments the observations about the behavior of microtremor spectra presented here show that noise measurements can be used as a powerful tool to determine the thickness of soft cover layers the most suitable method for this determination is nakamura s technique which is the ratio of the horizontal component noise spectrum and that of the vertical component i i v spectrum the frequency of the main peak in these spectral ratios correlates well with the sediment thickness at the site using an extensive database of microtremor measurements carried out in the western lower rhine embayment germany it was possible to show that this correlation is clearly valid for a wide range of thickness namely from tens of meters to more than 1000 m a simple formula was derived that for the sediments to be found in the area investigated directly calculates the cover thickness from the frequency of the main peak in the h v spectrum a comparison with calculated resonant frequencies sug gests the relation derived from the noise measurements depending on the velocity depth function of the shear wave classical spectral ratios are shown to be strongly influenced by the noise level and are therefore less reliable in determining the res onant frequency of the subsoil the practical relevance of the investigation is illus trated by means of cross sections constructed from results of the microtremor anal yses which provide a convincing image of the surficial structure of the areas investigated

geochemistry of the volcano hydrothermal system of el chichon volcano chiapas mexico the 1982 eruption of el chichon volcano ejected more than 1 km3 of anhydrite bearing trachyandesite pyroclastic material to form a new 1 km wide and 300 m deep crater and uncovered the upper 500 m of an active volcano hydrothermal system instead of the weak boiling point temperature fumaroles of the former lava dome a vigorously boiling crater spring now discharges 20 kg s of cl rich 15 000 mg kg and sulphur poor 200 mg kg of so4 almost neutral ph up to 6 7 water with an isotopic composition close to that of subduction type magmatic water d 15 18o 6 5 this spring as well as numerous cl free boiling springs discharging a mixture of meteoric water with fumarolic condensates feed the crater lake which compared with values in 1983 is now much more diluted 3000 mg kg of cl vs 24 030 mg kg less acidic ph 2 6 vs 0 56 and contains much lower amounts of s 200 mg kg of so4 vs 3550 mg kg with 34s 0 5 4 2 17 in 1983 agua caliente thermal waters on the southeast slope of the volcano have an outflow rate of approximately 100 kg s of 71 c na ca cl water and are five times more concentrated than before the eruption b r molina unpublished data relative n2 ar and he gas concentrations suggest extensional tectonics for the el chichon volcanic centre the 3he 4he and 4he 20ne ratios in gases from the crater fumaroles 7 3ra 2560 and agua caliente hot springs 5 3ra 44 indicate a strong magmatic contribution however relative concentrations of reactive species are typical of equilibrium in a two phase boiling aquifer sulphur and c isotopic data indicate highly reducing conditions within the system probably associated with the presence of buried vegetation resulting from the 1982 eruption all cl rich waters at el chichon have a common source this water has the appearence of a partially matured magmatic fluid condensed magmatic vapour neutralized by interaction with fresh volcaniclastic deposits and depleted in s due to anhydrite precipitation shallow ground waters emerging around the volcano from the thick cover of fresh pumice deposits red waters are ca so4 rich and have a negative oxygen isotopic shift probably due to ongoing formation of clay at low temperatures

microseisms observations in the santa clara valley california we have investigated ground motion amplification in the santa clara valley scv using microseisms observed during the 1998 deployment of 41 short period seismometers the santa clara valley seismic experiment scvse lindh et al 1999 fletcher et al 2003 recorded many local regional and teleseismic events in our previous work we investigated the 3d velocity structure of the scv by modeling the teleseismic p waves recorded during the scvse dolenc et al 2005 to complement these results we now focus on the microseisms that were recorded during the same period and relate these observations to local earthquake wave amplification it is found that the seismic noise is related to the ocean wave heights measured on the weather buoy west of half moon bay california the spectral ratio of the horizontal to vertical h v microseisms at each scvse site is stable with time and the period of the dominant peak in the h v ratio is related to the basin depth the results of this study show that seismic noise can be used in the assessment of the effects of deep sediments on long period earthquake ground motions

broadband microtremor observation of basin resonance in the mississippi embayment central us we report systematic variations in the fundamental period of seismic site resonance within the mississippi embayment the resonance periods are revealed by peaks in horizontal to vertical h v spectral ratios of microtremor measurements and increase with the depth to the sediment basement interface the sediment depth varies slowly enough spatially that at any site it can be modeled as a one dimensional problem revealing structural details of the sedimentary column the strong impedance contrast and gentle dip of the base of the embayment sediments may trap seismic energy within the soft sediments increasing durations and amplitudes of strong ground motions broadband recordings of microtremor within the mississippi embayment provide a simple method to study the seismic response of the basin

watching the wind seismic data contamination at long periods due to atmospheric pressure field induced tilting abstract following the installation of a new broadband seismic station near the pacific coast of the olympic peninsula washington the pacific northwest seismic network recorded elevated background seismic noise at periods exceeding 30 s we observed power spectral density variations of about 15 20 db in the horizontal component seismograms between times of high and low noise and differences of up to about 25 db between the horizontal and vertical components during noisy intervals the amplitude of the signal at long periods exhibited clear correlations with cyclic daytime fluctuations of air temperature and wind speed our observations provided measurable evidence that the variations of the local atmospheric pressure field associated with local wind systems represents an effective source of ground displacements and rotations the rotational component of the pressure field induced motion is recorded by horizontal component seismometers that below their low frequency corner are sensitive to surface tilts the response of seismometers to ground rotations is characterized by a transfer function which we use to estimate the amplitude of tilt we measured a pressure field induced surface tilt of the order of several tenths of rad based on simple modeling tilt contamination is expected to attenuate rapidly with depth and to become negligible just a few hundreds of meters below the surface removal of this unwanted effect from seismograms remains a challenging task as the details of tilting depend on the nonstationary character of the pressure field the compliance of the near surface to pressure variations and the design and construction of the seismic station online material animated time sequenced plots of daily seismic noise pdfs

atmospheric responses to north atlantic sst anomalies in idealized experiments part ii north american precipitation abstractthis is the second part of a two part paper that addresses deterministic roles of the sea surface temperature sst anomalies associated with the atlantic multidecadal oscillation amo in variations of atmospheric circulation and precipitation in the northern hemisphere using a sequence of idealized model runs at the spring equinox conditions this part focuses on the effect of the sst anomalies on north american precipitation major results show that in the model setting closest to the real world situation a warm sst anomaly in the north atlantic ocean causes suppressed precipitation in central western and northern north america but more precipitation in the southeast a nearly reversed pattern of precipitation anomalies develops in response to the cold sst anomaly further examinations of these solutions reveal that the response to the cold sst anomaly is less stable than that to the warm sst anomaly the former is dynamically charged in the sense that positive eddy kinetic energy eke

the crater lake and hydrothermal system of mount pinatubo philippines evolution in the decade after eruption the june 1991 eruption of mount pinatubo philippines breached a significant pre eruptive magmatic hydrothermal system consisting of a hot 300 c core at two phase conditions and surrounding cooler 260 c liquid outflows to the n and s the eruption created a large closed crater that accumulated hydrothermal upwellings near surface aquifer and meteoric inflows a shallow lake formed by early september 1991 and showed a long term increase in level of 1 m month until an artificial drainage was created in september 2001 comparison of the temporal trends in lake chemistry to pre and post eruptive springs distinguishes processes important in lake evolution the lake was initially near neutral ph and dominated by meteoric influx and cl so4 and cl hco3 hydrothermal waters with peaks in so4 and ca concentrations resulting from leaching of anhydrite and aerosol laden tephra magmatic discharge acidity ph 2 and rock dissolution peaked in late 1992 during and immediately after eruption of a lava dome on the crater floor since cessation of dome growth trends in lake ph increase from 3 to 5 5 temperature decline from 40 to 26 c and chemical and isotopic composition indicate that magmatic degassing and rock dissolution have declined significantly relative to the input of meteoric water and immature hydrothermal brine higher concentrations of cl na k li and b and lower concentrations of mg ca fe so4 and f up to 1999 highlight the importance of a dilute hydrothermal contribution as do stable isotope and tritium compositions of the various fluids however samples taken since that time indicate further dilution and steeper trends of increasing ph and declining temperature present gas and brine compositions from crater fumaroles and hot springs indicate boiling of an immature cl so4 geothermal fluid of near neutral ph at approximately 200 c rather than direct discharge from magma it appears that remnants of the pre eruptive hydrothermal system invaded the magma conduit shortly after the end of dome emplacement blocking the direct degassing path this along with the large catchment area 5 km2 and the high precipitation rate of the area led to a rapid transition from a small and hot acid lake to a large lake with near ambient temperature and ph this behavior contrasts with that of peak activity lakes that have more sustained volcanic gas influx e g kawah ijen indonesia poas and rincon de la vieja costa rica

evaluation of gases condensates and so2 emissions from augustine volcano alaska the degassing of a cl rich volcanic system after the march april 1986 explosive eruption a comprehensive gas study at augustine was undertaken in the summers of 1986 and 1987 airborne cospec measurements indicate that passive so2 emission rates declined exponentially during this period from 380 45 metric tons day t d on 7 24 86 to 27 6 t d on 8 24 87 these data are consistent with the hypothesis that the augustine magma reservoir has become more degassed as volcanic activity decreased after the spring 1986 eruption gas samples collected in 1987 from an 870 c fumarole on the andesitic lava dome show various degrees of disequilibrium due to oxidation of reduced gas species and condensation and loss of h2o in the intake tube of the sampling apparatus thermochemical restoration of the data permits removal of these effects to infer an equilibrium composition of the gases although not conclusive this restoration is consistent with the idea that the gases were in equilibrium at 870 c with an oxygen fugacity near the ni nio buffer these restored gas compositions show that relative to other convergent plate volcanoes the augustine gases are very hcl rich 5 3 6 0 mol hcl s rich 7 1 mol total s and h2o poor 83 9 84 8 mol h2o values of d and 18o suggest that the h2o in the dome gases is a mixture of primary magmatic water pmw and local seawater part of the cl in the augustine volcanic gases probably comes from this shallow seawater source additional cl may come from subducted oceanic crust because data by johnston 1978 show that cl rich glass inclusions in olivine crystals contain hornblende which is evidence for a deep source 25km for part of the cl gas samples collected in 1986 from 390 642 c fumaroles on a ramp surrounding the inner summit crater have been oxidized so severely that restoration to an equilibrium composition is not possible h and o isotope data suggest that these gases are variable mixtures of seawater fmw and meteoric steam these samples are much more h2o rich 92 97 h2o than the dome gases possibly due to a larger meteoric steam component the 1986 samples also have higher cl s s c and f cl ratios which imply that the magmatic component in these gases is from the more degassed 1976 magma thus the 1987 samples from the lava dome are better indicators than the 1986 samples of degassing within the augustine magma reservoir even though they were collected a year later and contain a significant seawater component future gas studies at augustine should emphasize fumaroles on active lava domes condensates collected from the same lava dome fumarole have enrichments ot 107 102 in cl br f b cd as s bi pb sb mo zn cu k li na si and ni lower temperature 200 650 c fumaroles around the volcano are generally less enriched in highly volatile elements however these lower termperature fumaroles have higher concentration of rock forming elements probably derived from the wall rock

meteoric interaction with magmatic discharges in japan and the significance for mineralization the andesitic volcanoes kirishima kyushu and esan hokkaido discharge 94 to 225 c hcl bearing vapors from summit fumaroles at kirishima a geothermal system exists on the flanks of the large volcanic massif 1500 m relief and 12 km radius in contrast esan is a small dome 600 m relief and 1 km radius with ephemeral hot springs the chemical and isotopic compositions of the fumarole gases and condensates and of waters from hot springs indicate that esan discharges are dominated by magmatic water and gases whereas those at kirishima are mainly meteoric the kirishima geothermal system contains acid fluids that are neutralized by interaction with the host rock and dilution by meteoric ground water the acidity is probably of magmatic origin a large ground water carapace at kirishima condenses a majority of magmatic volatiles and metals before they can discharge to the surface in contrast to esan where the volatiles including metals degas to the atmosphere this suggests that a meteoric system may be necessary to condense metals in this high level volcanic environment to provide a situation conducive to hydrothermal mineralization at epithermal depths

investigating the reliability of h v spectral ratio and image entropy for quantifying the degree of disintegration of weak rocks abstract characterization and quantification of disintegration behavior of weak rocks such as shales claystones mudstones and siltstones are usually a difficult task because of their extremely diverse nature these rocks present numerous stability problems along cut slopes around the world because they can change rapidly from rock like to soil like materials upon exposure to natural climatic conditions engineers often overestimate the design parameters for cut slopes in these rocks when laboratory tests are performed on fresh samples adjusting the design parameters for the anticipated amount of disintegration can be problematic because of the complex and time dependent nature of disintegration behavior in this study we investigate the reliability of using microtremor h v spectral ratio derived from microtremor signals and image entropy obtained from image analysis techniques for quantifying the varying degrees of disintegration during 2011 2014 both techniques were used to study disintegration of slopes cut through claystones mudstones and limestones along the 80 km stretch of a highway between bogota and tunja in central colombia for image analysis a new algorithm was developed to discriminate between varying degrees of disintegration across the complete color structure of the image avoiding the gray scale transformation that is usually time consuming the results indicate significant correlations between the degree of disintegration of the cut face the dominant frequency estimated from the microtremor h v ratio and the image entropy values suggesting that h v ratio and image entropy can be reliable techniques for quantifying the degree of disintegration