simultaneous determination of alteration and eruption ages of volcanic rocks by electron spin resonance abstract the alteration and eruption ages of japanese welded tuffs were estimated by the method of esr using ge ohc and al centers in quartz whose stabilities are different the ages obtained from the ge and ohc centers were 1 2 ma however the ages from the al center varied from 0 059 to 1 36 ma the comparison of these ages with thermoluminescence tl and fission track ft ages proves that the esr age of the al center which agrees with the tl age shows the thermal history and in an ideal case gives the alteration age those of the ge and ohc centers which agree with ft age indicate the eruption age therefore this method enables us to describe the thermal history of a rock

the challenging retrieval of the displacement field from insar data for andesitic stratovolcanoes case study of popocatepetl and colima volcano mexico abstract despite the ability of synthetic aperture radar sar interferometry to measure ground motion with high resolution application of this remote sensing technique to monitor andesitic stratovolcanoes remains limited specific acquisition conditions characterizing andesitic stratovolcanoes mainly vegetated areas with large elevation ranges induce low signal coherence as well as strong tropospheric artefacts that result in small signal to noise ratio we propose here a way to mitigate these difficulties and improve the sar measurements we derive ground motions for two of the most active mexican stratovolcanoes popocatepetl and colima volcano from the time series of sar data acquired from december 2002 to august 2006 the sar data are processed using a method that combines both persistent scatterers and small baseline approaches stratified tropospheric delays are estimated for each interferogram using inputs from the global atmospheric model narr up to a maximum of 10 rad km these delays are validated using spectrometer data as well as the correlation between the wrapped phase and the elevation the tropospheric effect is removed from the wrapped phase in order to improve the unwrapping process on popocatepetl we observe no significant deformation the colima summit area exhibits a constant subsidence rate of more than 1 cm year centered on the summit but enhanced reaching more than 2 cm year around the 1998 lava flow we model this subsidence considering both a deflating magma source at depth and the effect of the eruptive deposits load

energy transport by nonlinear internal waves wintertime stratification on oregon s continental shelf often produces a near bottom layer of densefluid that acts as an internal waveguide on which nonlinear internal waves propagate shipboard profiling and bottom lander observations capture disturbances that exhibit properties of internal solitary waves bores and gravity currents wave like pulses are highly turbulent instantaneous bed stresses are 1 n m 2 resuspending bottom sediments into the water column and raising them 30 m above the seafloor the waves cross shelf transport of fluid counters the time averaged ekman transport in the bottom boundary layer in the nonlinear internal waves we have observed the kinetic energy is roughly equal to the available potential energy and is o 0 1 mj per m of coastline the energy transported by these waves includes a nonlinear advection term huei that is negligible in linear internal waves unlike linear internal waves the pressure velocity energy flux hupi includes important contributions from nonhydrostatic effects and surface displacement it is found that statistically huei 2hupi vertical profiles indicate that up z is more important in transporting energy near the seafloor while ue z dominates farther from the bottom with the wave speed c estimated from weakly nonlinear wave theory it is verified experimentally that the total energy transported by the waves hupi huei chei the high but intermittent energyflux by the waves is in an averaged sense o 100 w per m of coastline this is similar to independent estimates of the shoreward energy flux in the semidiurnal internal tide at the shelfbreak

synthetic aperture radar observations of resonantly generated internal solitary waves at race point channel cape cod 1 synthetic aperture radar images revealed the two dimensional propagation characteristics of short period internal solitary waves in race point channel in massachusetts bay the images and in situ measurements of the flow in the channel are used to infer the likely generation mechanism of the waves the solitary waves are generated during the ebb phase of the tide within the channel on some occasions two trains of internal waves are generated presumably at the same location but at slightly different phases of the ebb tide the main characteristics of the two layer flow are described based on the criticality of the froude number it is suggested that these two individual packets of waves result from flow passage through resonance where the froude number is one one packet is generated as the flow passes through the transcritical regime during the acceleration phase of the ebb tidal current and another packet is generated during the deceleration phase both packets propagate upstream when the tide slacks but with slightly different propagation directions

seafloor pressure measurements of nonlinear internal waves highly resolved pressure measurements on the seafloor over new jersey s continental shelf reveal the pressure signature of nonlinear internal waves of depression as negative pressure perturbations the sign of the perturbation is determined by the dominance of the internal hydrostatic pressure p 0 due to isopycnal displacement over the contributions of external hydrostatic pressure 0gh h is surface displacement and nonhydrostatic pressure p 0 each of opposite sign to p 0 this measurement represents experimental confirmation of the wave induced pressure signal inferred in a previous study by moum and smyth

esr dating in quaternary geology abstract electron spin resonance esr a relatively new dating technique was first suggested by zeller et al 1967 zeller 1968 and levy 1968 it has made substantial progress in frequent applications in the last few years esr dating is based on the direct measurement of the amount of radiation induced paramagnetic electrons trapped in crystal defects these free electrons were generated by alpha beta and gamma radiation of natural radioelements e g u th k and have accumulated in the minerals over geologic time the esr age is obtained by dividing the total amount of accumulated radiation dose archaeological dose ad by the dose per year annual dose this review comprises four major parts the principles of the method the determination of the archaeological dose ad the determination of the annual dose and a compilation of datable materials several questions remain the evaluation of the ad the determination of the annual dose and particularly with respect to the nature and stability of the electron traps used for dating

observation of very large and steep internal waves of elevation near the massachusetts coast 1 we report on near bottom waves of elevation with amplitude nearly half the 25 m water column very steep and propagating into a sheared turbulent wave guide the waves contained trapped cores transporting parcels of water shoreward these large waves depart strongly from weakly nonlinear and weakly nonhydrostatic conditions and challenge established paradigms they can also represent an important factor in the across shore transport of plankton and contaminants

a large silent earthquake in the guerrero seismic gap mexico 1 geodetic measurements from a network of permanent gps stations along the pacific coast of mexico reveal a large silent earthquake along the segment of the cocos north american plate interface identified as the guerrero seismic gap the event began in october of 2001 and lasted for 6 7 months average slip of 10 cm produced measurable displacements over an area of 550 250 km2 the equivalent moment magnitude of the event was mw 7 5 recognition of this and previous slow event here indicate that the seismogenic portion of the plate interface is not loading steadily as hitherto believed but is rather partitioning the stress buildup with episodic as opposed to steady state or periodic slip downdip of the seismogenic zone this process increases the stress at the base of the seismogenic zone bringing it closer to failure these results call for a reassessment of the seismic potential of guerrero and other seismic gaps in mexico

deformation of popocatepetl volcano using gps regional geodynamic context and constraints on its magma chamber we have operated a gps network on popocatepetl volcano since 1994 consisting of a total of 7 continuous gps stations on its northern and southwestern flanks and one additional station in the vicinity of the volcano the overall characteristic behavior of popocatepetl volcano during this period can be described as a minimally deforming system in sharp contrast with its essentially continuous visible eruptive activity a north component motion analysis assuming a fixed north american plate shows a close correspondence of the popocatepetl sites to those of other regional gps sites most of the large deformation transients observed on the popocatepetl sites are therefore not of magmatic origin but instead reflect aseismic transients that have been recognized recently as part of the mid american trench subduction process the surface deformation record of popocatepetl volcano therefore suggests a magmatic system that lacks a well defined shallow magma chamber where most of the magma storage transport and ascent is carried out via a network of deep rooted conduits that eventually extend to the summit crater in most cases popocatepetl seems to operate as a semi open system thereby preventing any significant pressure build up

timing magma ascent at popocatepetl volcano mexico 2000 2001 abstract magnetic anomalies may be used to constrain magma ascent and are useful as precursors to eruptions especially when correlated with other geophysical and geochemical data in this paper we present multiparameter data on the magnetics dome morphology geochemistry and seismicity associated with the december 2000 january 2001 eruptions the largest of the recent eruptions at popocatepetl volcano a 6 month data period was studied in order to evaluate the precursors and post eruption processes several cycles of dome construction and destruction occurred from september 2000 through february 2001 in december large amplitude tremor associated with a higher effusion rate resulted in the formation of a large dome which filled the crater to within about 50 m of the lowest part of the crater rim seismic activity in december was marked by many volcanotectonic earthquakes and both high frequency and harmonic tremor on december 12 and 13 an increase in the tremor amplitude was followed by ash eruptions with 1 7 5 km high columns tremor amplitude increased again on december 15 and oscillated for the next four days activity remained high until the end of the month on january 22 an 18 km high plume produced ash and pumice fall to the east as well as pyroclastic flows and mudflows which reached 6 km from the crater the eruption left three concentric explosion pits partially destroying the december dome mixing of a mafic olivine bearing melt with a more evolved magma triggered the larger eruption on january 22 as can be seen from the higher mgo concentrations in some of the ejecta and the presence of a dark andesitic scoria with lower silica content and a white andesitic pumice with higher silica content precursory negative magnetic anomalies up to 5 nt 3 2 nt 5 nt 2 9 nt were associated with the ascent of the larger batches of magma which preceded the increases in seismicity before the december 2000 january 22 vei 3 4 eruptions no significant increases in seismicity were observed prior to the january 22 eruption except for a magnitude 2 4 earthquake on the day of the eruption there was however a 0 8 nt magnetic anomaly which lasted from january 10 to 12 and possibly to january 17 most of the magma ascended in three large batches and several smaller ones from october 22 through december 10 short lived crater domes with small volumes were formed at popocatepetl in september october and november 2000 and in march 2001 even the smaller negative anomalies from september to february were associated with the ascent of several batches of magma they preceded the increases observed in the seismicity and growth of a dome by several days

modelling ground deformation patterns associated with volcanic processes at the okataina volcanic centre abstract the okataina volcanic centre ovc is one of two large active rhyolite centres in the modern taupo volcanic zone tvz in the north island of new zealand it is located in a complex section of the taupo rift a tectonically active section of the tvz the most recent volcanic unrest at the ovc includes the 1315 ce kaharoa and 1886 tarawera eruptions current monitoring activity at the ovc includes the use of continuous gps receivers cgps lake levelling and seismographs the ground deformation patterns preceding volcanic activity the ovc are poorly constrained and restricted to predictions from basic modelling and comparison to other volcanoes worldwide a better understanding of the deformation patterns preceding renewed volcanic activity is essential to determine if observed deformation is related to volcanic tectonic or hydrothermal processes such an understanding also means that the ability of the present day cgps network to detect these deformation patterns can also be assessed the research presented here uses the finite element fe modelling technique to investigate ground deformation patterns associated with magma accumulation and diking processes at the ovc in greater detail a number of fe models are produced and tested using pylith software and incorporate characteristics of the 1315 ce kaharoa and 1886 tarawera eruptions summarised from the existing body of research literature the influence of a simple ring fault structure at the ovc on the modelled deformation is evaluated the ability of the present day continuous gps cgps geonet monitoring network to detect or observe the modelled deformation is also considered the results show the modelled horizontal and vertical displacement fields have a number of key features which include prominent lobe based regions extending northwest and southeast of the ovc the results also show that the ring fault structure increases the magnitude of the displacements inside the caldera in particular in the vicinity of the southern margin as a result some of the cgps stations in the vicinity of the ovc are more important for measuring deformation related to volcanic processes than others the results have important implications for how any future observed deformation at the ovc is observed and interpreted

crustal deformation measurements in guerrero mexico 1 gps measurements of crustal deformation in guerrero southern mexico include surveys collected between 1992 and 2001 as well as continuous gps measurements at a few sites these geodetic observations are used to calculate interseismic deformation rates and assess the presence and possible location of transient deformation during the period encompassing 1992 25 to 2001 75 the data are used to examine transient deformation in 1998 previously described from data at a single site by lowry et al 2001 survey measurements and continuous data from a site near popocatepetl volcano confirm the 1998 transient and survey data also suggest another transient occurred following the 14 september 1995 mw 7 3 copala earthquake all of the available gps position estimates have been inverted for a combined model of slip during each event plus the steady state slip on the plate interface modeling of the steady state deformation rates confirms that the guerrero seismic gap is partially frictionally locked at depths shallower than about 25 km and accumulating strain that may eventually be released in a great earthquake the data also suggest that there is frictional coupling to much greater 40 km depths which releases more frequently in aseismic slip events the locations and sizes of the transient events are only partially constrained by the available data however the transient models which best fit the gps coordinate time series suggest that aseismic slip was centered downdip of the seismogenic portion of the plate bounding thrust in both events and the moment release had equivalent magnitudes mw 7 1 1 3 1 0 in 1995 1996 and 7 1 0 4 0 1 in 1998

observations of polarity reversal in shoaling nonlinear internal waves observations off the new jersey coast document the shoaling of three groups of nonlinear internal waves of depression over 35 km across the shelf each wave group experienced changing background conditions along its shoreward transit despite different wave environments a clear pattern emerges nearly symmetric waves propagating into shallow water develop an asymmetric shape in the wave reference frame the leading edge accelerates causing the front face to broaden while the trailing face remains steep this trend continues until the front edge and face of the leading depression wave become unidentifiable and a near bottom elevation wave emerges formed from the trailing face of the initial depression wave and the leading face of the following wave the transition from depression to elevation waves is diagnosed by the integrated wave vorticity which changes sign as the wave s polarity changes sign this transition is predicted by the sign change of the coefficient of the nonlinear term in the kdv equation when evaluated using observed profiles of stratification and velocity

contemporary ground deformation in the taupo rift and okataina volcanic centre from 1998 to 2011 measured using gps the taupo volcanic zone tvz is one of the world s most productive regions of rhyolitic volcanism and contains the highly active okataina volcanic centre ovc within the tvz intra arc extension is expressed as normal faulting within a zone known as the taupo rift the ovc is located within a complex part of the rift where volcanism and deformation is considered influenced by rift structure and kinematics there has been significant research on the structural volcanic and geophysical properties of the rift and ovc but less focus on deformation using geodetic data the limited studies that have utilized geodetic data do not clearly resolve the distribution of deformation and strain rates within the rift and ovc this is essential to ensure that deformation signals from volcanic processes at the ovc are correctly identified and distinguished from those related to regional tectonic or local hydrothermal processes within the rift in this paper we present a picture of contemporary deformation at the ovc and within the surrounding rift in detail using existing and new gps campaign and continuous gps cgps data collected between 1998 and 2011 the results show a highly heterogeneous deformation and strain rate field both extension and shortening through the study area partitioned into different parts of the rift our results agree well with earlier geodetic studies as well as identify new features but some deformation patterns conflict with long term geological observations in the ovc we observe a locally rotated horizontal velocity field significant vertical deformation and variable strain rates across the caldera in the tarawera rift we identify elevated extension and shear rates which may have significant implications for volcanism there a shortening pattern is identified through the central rift which is unexpected in an intra arc rifting environment we attempt to explain the source s of shortening and extension and discuss their implications for geodetic monitoring efforts in the ovc

the pressure disturbance of a nonlinear internal wave train observations from a lander fixed to the seafloor over the continental shelf in 124 m of water provide highly resolved velocity measurements through nonlinear internal waves of elevation from these measurements we determine for the first time the non hydrostatic pressure disturbance p nh in nonlinear internal waves for near bottom waves of elevation ranging in amplitude a from 12 to 33 m the value of p nh evaluated at the seafloor changes sign from 0 to and back in accordance with weakly nonlinear theory peak values of vert p nh vert range from 25 to 90 n m 2 the external hydrostatic pressure disturbance due to the surface displacement eta h is inferred from horizontal accelerations for elevation waves eta h peak values range from 0 1 to 9 mm 1 to 90 n m 2 the internal hydrostatic pressure perturbation p wh caused by isopycnal displacement is inferred from measured streamlines and an ambient density profile its value at the seafloor is 0 for elevation waves peak values range from 100 to 300 n m 2 vert eta h vert and seafloor values of vert p nh vert p wh all increase monotonically with a since vert p nh vert and p wh increase at roughly the same rate with a no clear trend arises in the degree to which waves become more or less non hydrostatic as a changes a distinct bottom pressure signature is determined for bottom trapped nonlinear waves of elevation a wave train consisting of a sequence of positive pressure perturbations dominated by p wh by inference a train of surface trapped nonlinear internal waves of depression will consist of a sequence of negative pressure perturbations a result of this analysis is that significant properties of the waves can be discerned from a simple adequately resolved bottom pressure measurement

shoaling of nonlinear internal waves in massachusetts bay 1 the shoaling of the nonlinear internal tide in massachusetts bay is studied with a fully nonlinear and nonhydrostatic model the results are compared with current and temperature observations obtained during the august 1998 massachusetts bay internal wave experiment and observations from a shorter experiment which took place in september 2001 the model shows how the approaching nonlinear undular bore interacts strongly with a shoaling bottom offshore of where kdv theory predicts polarity switching should occur it is shown that the shoaling process is dominated by nonlinearity and the model results are interpreted with the aid of a two layer nonlinear but hydrostatic model after interacting with the shoaling bottom the undular bore emerges on the shallow shelf inshore of the 30 m isobath as a nonlinear internal tide with a range of possible shapes all of which are found in the available observational record

a nonhydrostatic version of fvcom 2 mechanistic study of tidally generated nonlinear internal waves in massachusetts bay 1 the generation propagation and dissipation processes of large amplitude nonlinear internal waves in massachusetts bay during the stratified season were examined using the nonhydrostatic finite volume coastal ocean model fvcom nh the model reproduced well the characteristics of the high frequency internal waves observed in massachusetts bay in august 1998 the model experiments suggested that internal waves over stellwagen bank are generated by the interaction of tidal currents with steep bottom topography through a process of forming a large density front on the western slope of the bank by the release of an initial density perturbation near ebb flood transition nonlinear steepening of the density front into a deep density depression and disintegrating of the density depression into a wave train earth s rotation tends to transfer the cross bank tidal kinetic energy into the along bank direction and thus reduces the intensity of the density perturbation at ebb flood transition and density depression in the flood period the internal wave packet propagates as a leading edge feature of the internal tidal wave and the faster propagation speed of the high frequency internal waves in massachusetts bay is caused by earth s rotation the model experiments suggested that bottom friction can significantly influence the cross bank scale of the density perturbation and thus the density depression during wave generation and the dissipation during the wave s shoaling inclusion of vertical mixing using the mellor yamada level 2 5 turbulence closure model had only a marginal effect on wave evolution the model results support the internal wave theory proposed by lee and beardsley 1974 but are in disagreement with the lee wave mechanism proposed by maxworthy 1979

generation of internal waves in massachusetts bay observations of stratified tidal flow over a submarine ridge indicate that the large amplitude and asymmetry of the topography are critical in determining the type of flow response the observations consist of hydrographic current meter and echo sounding data and are used as a basis for inferring the generation mechanism of previously observed trains of internal waves the flow response on ebb and flood tide is categorized according to the froude number classification of sill flows proposed by farmer and smith 1980a the calculated froude numbers response length scale and duration differ markedly between the two phases of the tide due to the asymmetry of the bank the development of two features in the acoustic imagery related to wave formation is followed

horizontal variability of high frequency nonlinear internal waves in massachusetts bay detected by an array of seafloor pressure sensors a two dimensional array of fourteen seafloor pressure sensors was deployed to measure properties of tidally generated nonlinear high frequency internal waves over a 14 km by 12 km area west of stellwagen bank in massachusetts bay during summer 2009 thirteen high frequency internal wave packets propagated through the region over 6 5 days one packet every semidiurnal cycle propagation speed and direction of wave packets were determined by triangulation using arrival times and distances between triads of sensor locations wavefront curvature ranged from straight to radially spreading with wave speeds generally faster to the south waves propagated to the southwest rotating to more westward with shoreward propagation linear theory predicts a relationship between kinetic energy and bottom pressure variance of internal waves that is sensitive to sheared background currents water depth and stratification by comparison to seafloor acoustic doppler current profiler measurements observations nonetheless show a strong relationship between kinetic energy and bottom pressure variance this is presumably due to phase locking of the wave packets to the internal tide that dominates background currents and to horizontally uniform and relatively constant stratification throughout the study this relationship was used to qualitatively describe variations in kinetic energy of the high frequency wave packets in general high frequency internal wave kinetic energy was greater near the southern extent of wavefronts and greatly decreased upon propagating shoreward of the 40 m isobath this article is protected by copyright all rights reserved

monitoring the volcanic unrest of el hierro canary islands before the onset of the 2011 2012 submarine eruption 1 on 10 october 2011 a submarine volcanic eruption started 2 km south from el hierro island spain since july 2011 a dense multiparametric monitoring network was deployed all over the island by instituto geografico nacional ign by the time the eruption started almost 10000 earthquakes had been located and the deformation analyses showed a maximum deformation of more than 5 cm earthquake migration from the north to the south of the island and acceleration of seismicity are in good correlation with changes in the deformation pattern as well as with some anomalies in geochemical and geomagnetic parameters an earthquake of local magnitude 4 3 at 12 km depth 8 october 2011 and shallower seismicity a day after preceded the onset of the eruption this is the first time that a volcanic eruption is fully monitored in the canary islands data recorded during this unrest episode at el hierro will contribute to understand reawakening of volcanic activity in this region and others of similar characteristics

analysis of source characteristics of experimental gas burst and fragmentation explosions generated by rapid decompression of volcanic rocks gas burst and fragmentation explosions induced by rapid decompression of volcanic rocks in a high pressure autoclave have been analyzed we performed experiments from 4 to 20 mpa on 1 loose pyroclasts and 2 pumice from recent eruptions of popocatepetl volcano our aim is to characterize the source mechanism distinguishing the physical processes that operate in the conduit which determine the dynamics of explosive volcanoes for this aim we have analyzed experimentally the parameters that indicate the state and behavior of the conduit i e decompression time fragmentation threshold and speed forces and the partitioning of energy using microseismic monitoring the decompression time curves and the sample rheological properties the initial available potential energy in the system and its partitioning into different types of energies are correlated in space and time with specific stages of the explosive phenomenon such correlations taken together with the energy distribution enable the distinction of the individual physical processes involved and their causal sequence and relationships our observations suggest that in volcanic conduits with regular explosive activity a source mechanism may operate whereby a causal sequence of processes results in a system that undergoes both rapid and stable transitions such behavior may persist over long periods of time

continuous monitoring of surface deformation at long valley caldera california with gps continuous global positioning system gps measurements at long valley caldera an active volcanic region in east central california have been made on the south side of the resurgent dome since early 1993 a site on the north side of the dome was added in late 1994 special adaptations for autonomous operation in remote regions and enhanced vertical precision were made the data record ongoing volcanic deformation consistent with uplift and expansion of the surface above a shallow magma chamber measurement precisions 1 standard error for absolute position coordinates i e relative to a global reference frame are 3 4 mm north 5 6 mm east and 10 12 mm vertical using 24 hour solutions corresponding velocity uncertainties for a 12 month period are about 2 mm yr in the horizontal components and 3 4 mm yr in the vertical component high precision can also be achieved for relative position coordinates on short 10 km baselines using broadcast ephemerides and observing times as short as 3 hours even when data are processed rapidly on site comparison of baseline length changes across the resurgent dome between the two gps sites and corresponding two color electronic distance measurements indicates similar extension rates within error 2 mm yr once we account for a random walk noise component in both systems that may reflect spurious monument motion both data sets suggest a pause in deformation for a 3 5 month period in mid 1995 when the extension rate across the dome decreased essentially to zero three dimensional positioning data from the two gps stations suggest a depth 5 8 1 6 km and location west side of the resurgent dome of a major inflation center in agreement with other geodetic techniques near the top of a magma chamber inferred from seismic data gps systems similar to those installed at long valley can provide a practical method for near real time monitoring and hazard assessment on many active volcanoes

magma storage and diking revealed by gps and insar geodesy at pacaya volcano guatemala gps measurements from a campaign network at pacaya volcano guatemala occupied from 2009 to 2015 were combined with insar data from 2013 to 2014 to model deformation sources for two eruptive time periods 2009 2011 and 2013 2014 the gps data for both of these time periods show downward vertical and outward horizontal deformation greater than 25 cm at several stations surrounding the volcano while insar data shows up to 15 cm line of sight displacement to better understand the dynamics of the magma storage system and sources of deformation we inverted available geodetic data for these two periods our analytical modeling suggests that horizontal deformation was dominated by inflation of a shallow subvertical dike high within the volcanic edifice while deflation of a deeper spherical source embedded below the nw flank of the volcano occurred during at least part of the observation period the source parameters for the dike feature are in good agreement with the observed alignment of recent eruptive vents while parameters for the deeper spherical source accommodate the downward vertical deformation observed at stations on and around the volcano

esr dating of quaternary tephra from mt osore zan using al and ti centres in quartz abstract quaternary tephra of mt osore zan was dated by electron spin resonance quartz grains were separated from the tephra and esr signals of al and ti centres were measured at 77 k the signals of al and ti centres which have a complicated hyperfine structure were simplified by using wider field modulations width 5 gauss than usually used 0 5 1 gauss the influence of 5 gauss modulation width on the measurement of the signal intensity of al and ti centres was investigated the intensity of the signal increases linearly with gamma irradiation and total doses obtained were 178 to 273 gy and esr ages were 0 19 to 0 32 ma these ages agree with the estimated age of about 0 3 ma from the correlation of volcanic ash and terrace level

speed and evolution of nonlinear internal waves transiting the south china sea abstract in the south china sea scs 14 nonlinear internal waves are detected as they transit a synchronous array of 10 moorings spanning the waves generation site at luzon strait through the deep basin and onto the upper continental slope 560 km to the west their arrival time speed width energy amplitude and number of trailing waves are monitored waves occur twice daily in a particular pattern where larger narrower a waves alternate with wider smaller b waves waves begin as broad internal tides close to luzon strait s two ridges steepening to o 3 10 km wide in the deep basin and o 200 300 m on the upper slope nearly all waves eventually develop wave trains with larger steeper waves developing them earlier and in greater numbers the b waves in the deep basin begin at a mean speed of 5 greater than the linear mode 1 phase speed for semidiurnal internal waves computed using climatological and in situ stratification the a waves travel 5 10 faster than b waves until they reach

transient fault slip in guerrero southern mexico the guerrero region of southern mexico has ac cumulated more than 5 m of relative plate motion since the last major earthquake in early 1998 a continuous gps site in guerrero recorded a transient displacement modeling indicates that anomalous fault slip propagated from east to west along strike of the subduction megathrust campaign gps and leveling data corroborate the model the moment release was equivalent to an mw 6 5 earthquake no m 5 earthquakes accompanied the event indicating the frictional regime is velocity strengthening at the location of slip

seismic tomography at popocatepetl volcano mexico abstract we performed the first 3d seismic tomography of the popocatepetl volcano mexico from the inversion of the p wave arrival times of nearly 1500 earthquakes recorded by up to 11 seismic stations of the permanent cenapred ssn network we used the bayesian tomographic algorithm developed by monteiller et al 2005 to perform this p wave travel time tomography and carefully choose optimal regularization hyper parameters sensitivity tests show that the inversion is correctly constrained under the volcano from 1 to 4 km depth b s l at these depths the optimal tomographic model mainly shows low velocity volumes surrounded by higher velocity volumes lateral heterogeneity is strong the variation of the p wave velocity may reach up to 20 of the average value at a given depth low velocity volumes correlate well with results from former geological and geophysical studies

generation and propagation of nonlinear internal waves in massachusetts bay 1 during the summer nonlinear internal waves nliws are commonly observed propagating in massachusetts bay the topography of the area is unique in the sense that the generation area over stellwagen bank is only 25 km away from the shoaling area and thus it represents an excellent natural laboratory to study the life cycle of nliws to assist in the interpretation of the data collected during the 1998 massachusetts bay internal wave experiment mbiwe98 a fully nonlinear and nonhydrostatic model covering the generation shoaling region was developed to investigate the response of the system to the range of background and driving conditions observed simplified models were also used to elucidate the role of nonlinearity and dispersion in shaping the nliw field this paper concentrates on the generation process and the subsequent evolution inthe basin themodel was foundtoreproducewell the range of propagation characteristics observed arrival time propagation speed amplitude and provided a coherent framework to interpret the observations comparison with a fully nonlinear hydrostatic model shows that during the generation and initial evolution of the waves as they move away from stellwagen bank dispersive effects play a negligible role thus the problem can be well understood considering the geometry of the characteristics along which the riemann invariants of the hydrostatic problem propagate dispersion plays a role only during the evolution of the undular bore in the middle of stellwagen basin the consequences for modeling nliws within hydrostatic models are briefly discussed at the end

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

high resolution observations of subsurface fronts and alongshore bottom temperature variability over the inner shelf author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 53 3 2019 1639 1649 doi 10 1029 2018jc014454

esr dating of ancient flints natural radioactivity can produce measurable amounts of radiation damage in rocks and glasses and the gradual accumulation of this damage with time provides a built in clock that can be used as a dating tool for geology and archaeology although a studied technique for estimating this damage involves measurements of stored thermoluminescent tl activity1 4 several authors have reported the direct observation of natural radiation damage by esr5 7 we describe here esr measurements on a damage signal which we have found to be present without exception in a wide variety of natural flints the point defect responsible for the signal is identified and the samples are calibrated with an artificial damage simulation preliminary age determinations are presented for several natural flints flint artefacts heated in antiquity will have their clock reset to zero and measurements on one sample suggest that the esr technique may have applications in the study of early cultures

observations of shoaling nonlinear internal bores across the central california inner shelf abstractwe present observations of shoaling nonlinear internal bores off the coast of central california the dataset includes 15 moorings deployed during september october 2017 and cross shore shi