along strike variations of earthquake apparent stress at the nicoya peninsula costa rica subduction zone oceanic plates vary in temperature topography and sediment load as they enter subduction zones these variations persist along the subduction interface causing perturbations in coupling and earthquake rupture processes we explore the effects of variable subducting plate structure on microseismicity rupture characteristics along the nicoya peninsula costa rica the subducting cocos plate has low relief along the northern and central portion of the peninsula with seamounts present at the southern tip of the peninsula we compute apparent stresses for 94 ml 2 5 4 2 earthquakes along the plate interface using waveform coda and find along strike variations that mimic bathymetric variability median stress values are higher 3 2 mpa in the smooth northern region with lower values in the central 2 1 mpa and southern 0 7 mpa segments higher apparent stresses along a zone of little suspected subduction topography imply increased coupling or higher friction along the interface these results agree with geodetic and other seismic studies that suggest variable plate coupling along the nicoya peninsula

satellite remote sensing of surface oceanic fronts in coastal waters off west central florida abstract two algorithms designed to detect deepwater oceanic features and arbitrary edge profiles were tuned to automatically delineate fronts in coastal waters off west central florida using satellite derived sea surface temperature sst chlorophyll a concentration chl normalized water leaving radiance nlw and fluorescence line height flh images during select periods in the spring and fall of 2004 and 2005 the dates correspond to recreational king mackerel scomberomorus cavalla tournaments a histogram based algorithm was useful to detect coastal surface sst nlw and flh fronts specifically a gradient based algorithm with a smaller kernel box of 3 3 pixels best identified nearshore

gradual fault weakening with seismic slip inferences from the seismic sequences of l aquila 2009 and northridge 1994 we estimate seismological fracture energies from two subsets of events selected from the seismic sequences of l aquila 2009 and northridge 1994 57 and 16 selected events respectively including the main shocks following abercrombie and rice geophys j int 162 406 424 2005 we postulate that fracture energy g represents the post failure integral of the dynamic weakening curve which is described by the evolution of shear traction as a function of slip following a direct wave approach we compute mainshock aftershock source spectral ratios and analyze them using the approach proposed by malagnini et al pure appl geophys this issue 2014 to infer corner frequencies and seismic moment our estimates of source parameters including fracture energies are based on best fit grid searches performed over empirical source spectral ratios we quantify the source scaling of spectra from small and large earthquakes by using the mdac formulation of walter and taylor a revised magnitude and distance amplitude correction mdac2 procedure for regional seismic discriminants 2001 the source parameters presented in this paper must be considered as point source estimates representing averages calculated over specific ruptured portions of the fault area in order to constrain the scaling of fracture energy with coseismic slip we investigate two different slip weakening functions to model the shear traction as a function of slip i a power law as suggested by abercrombie and rice geophys j int 162 406 424 2005 and ii an exponential decay our results show that the exponential decay of stress on the fault allows a good fit between measured and predicted fracture energies both for the main events and for their aftershocks regardless of the significant differences in the energy budgets between the large main and small earthquakes aftershocks using the power law slip weakening function would lead us to a very different situation in our two investigated sequences if the aftershock scaling is extrapolated to events with large slips a power law a la abercrombie and rice would predict unrealistically large stress drops for large main earthquakes we conclude that the exponential stress evolution law has the advantage of avoiding unrealistic stress drops and unbounded fracture energies at large slip values while still describing the abrupt shear stress degradation observed in high velocity laboratory experiments e g di toro et al fault lubrication during earthquakes nature 2011

potential atmospheric impact of the toba mega eruption 71 000 years ago an approx 6 year long period of volcanic sulfate recorded in the gisp2 ice core about 71 000 5000 years ago may provide detailed information on the atmospheric and climate impact in the toba mega eruption deposition of these aerosols occur beginning of an approx 1000 year long stadial event but not immediately before the longer glacial period beginning approx 67 500 years ago total stratospheric loading estimates over this approx 6 year period range from 2200 to 4400 mt of h sub 2 so sub 4 aerosols the range in values is given to compensate for uncertainties in aerosol transport magnitude and longevity of the atmospheric loading may have led directly to enhanced cooling during the initial two centuries of this approx 1000 year cooling event 25 refs 2 fig 1 tab

evidence for non constant energy moment scaling from coda derived source spectra 1 we present two lines of evidence showing the ratio of seismically radiated energy er to seismic moment mo increases with increasing moment for crustal events spanning 5 orders in seismic moment this ratio often referred to as the scaled energy er m0 has been elusive and the subject of recent debate within the seismological community because significant frequency dependent corrections must be made to account for source and path heterogeneity it is not uncommon that energy estimates of the same event by different researchers have significantly different values to minimize some of the potential problems we used the regional coda methodology outlined by mayeda et al 2003 on 4 large earthquake sequences mw 7 4 and 7 2 izmit duzce mw 7 2 gulf of aqaba mw 7 3 landers and mw 7 2 hector mine this methodology has been shown to provide the lowest variance estimate of the source spectrum when compared against traditional direct wave estimates in our first approach we made energy estimates from coda derived spectra and observed that increases with increasing moment for 3 7 mw 7 4 in our second approach we used the simple idea outlined by prieto et al 2004 to directly test for self similarity under self similarity earthquake source spectra scaled by 3 should have the same shape to test this one needs very stable spectra either through spectral stacking of direct wave spectra or by the use of stable coda derived spectra for all sequences we found that the mainshocks and larger aftershocks had significantly different spectral shapes than the smaller events the scaled 3 spectra of the larger events represented an upper bound having larger amplitudes near the corner frequency in fact an 3 5 scaling moved the larger events closer to the mean of the spectral population though the spectral shape differences persisted these results strongly suggest that earthquakes are not scaling self similarly and that complexities in the rupture process such as variable slip velocity exist between small and large events

ground motion scaling in eastern sicily italy we describe the characteristics of crustal wave propagation in eastern sicily by using the background seismicity of the area we follow the approach de scribed by malagnini hermann and di bona 2000 and malagnini et al 2002 our data set consists of 106 earthquakes recorded by nine three component digital seismic stations between 1994 and 2001 we used only crustal events depths shal lower than 25 km with local magnitudes ranging from 1 0 to 4 3 and hypocentral distances from 10 to 130 km peak ground velocities from 1311 narrow bandpass filtered waveforms are mea sured in thefrequency range 1 0 16 0 hz and regressedtodefinecrustalpropagation excitation and site characteristics with respect to a reference station a subsequent modeling effort is carried out through the use of random vibration theory rvt for obtaining a quantitative evaluation of the apparent geometrical spreading g r and of the crustal quality factor q f an attenuation parameter j0 is also evaluated relative to a reference rock site the attenuation and source parameters estimated in this study are used through the rvt in order to predict the peak horizontal ground acceleration pga and the 5 damping pseudoacceleration spectra psa

response of vietnam coastal upwelling to the 1997 1998 enso event observed by multisensor data abstract in this paper we examine the behavior of the vietnam coastal upwelling during the 1997 1998 el nino southern oscillation enso event the baseline is 4 years of national oceanic and atmospheric administration noaa satellite advanced very high resolution radiometer avhrr sea surface temperature sst data taken from 1997 to 2000 comparison of upwelling images to simultaneous ers 2 european remote sensing satellite wind fields indicates that the summer monsoon winds constitute a major generation forcing during the 1997 el nino the monsoon winds enhanced the upwelling and induced the upwelling center to move southward during the 1998 la nina the monsoon winds weakened the upwelling in contrast with the tropical pacific in the study area la nina implies a warm event and el nino a cold event we use empirical orthogonal function eof methods to analyze the spatial and temporal variance of the upwelling the three principal modes account for 37 15 and 8 of the total variance respectively the first eof modes reveal that the sst variance in the north and south subregions underwent a positive negative sign switch in summer 1997 the second eof modes represent the monthly evolution in normal years the third modes seem to be sensitive to the 1998 la nina event simultaneous topex poseidon and ers 2 altimeter data provide further evidence for our analysis comparison with california coastal upwelling and mid atlantic bight mab coastal upwelling indicates that the vietnam coastal upwelling is the most intensive one

zooplankton distributions and transport across the northeastern tidal front of georges bank tidal fronts are important sites of contact and mixing between zooplankton populations on and off georges bank in the northwest atlantic this study a component of the us globec program examined crossfrontal distributions of zooplankton especially the copepod calanus finmarchicus across the northeastern tidal front of georges bank relative to the tidal cycle frontal structure flow field and day night cycle a unique feature was a precisely executed sampling strategy designed to isolate spatial tidal and day night effects vertically stratified zooplankton sampling was done along tidally coordinated crossfrontal transects and during time series studies at specific locations zooplankton taxa differed in their spatial and vertical distributions relative to the front and the hydrographic structure of the water column there were significant associations between zooplankton assemblages and spatial location depth and water mass zooplankton distributions generally tracked water masses but usually showed crossbank abundance gradients consistent differences between day and night distributions were not apparent for most taxa meroplankton larvae of benthic animals were derived primarily from onbank populations the zooplankton community was advected with the tidal flow crossfrontal distributions characteristic of onbank and offbank flow regimes clearly differentiated tidal phases and interacted with the flow field and topography salinity a proxy for water mass and depth interacted in controlling vertical distributions as tidal forcing sloshed water masses up and down the bank slope some taxa followed isohalines through depth changes while other taxa maintained themselves within a relatively limited depth or salinity regime surface convergence and downwelling tidal upwelling of bottom water and mid depth tidal pumping influenced crossfrontal exchange

high frequency ground motion in the erzincan region turkey inferences from small earthquakes this study has been supported by istituto nazionale di geofisica e vulcanologia ingv internal project attenuazione e leggi di scala nei paesi dell area mediterranea internally funded r b herrmann s participation was supported by ingv and by the earthquake engineering research centers program of the national science foundation under award number eec 9701785

dependence of sediment filled valley response on input amplitude and valley properties abstract for three sediment filled valleys average site responses were experimentally determined and found to apply to within 0 25 log units to earthquakes at any azimuth and to s waves and coda waves for one of these valleys ground accelerations were measured over the range 10 5 to 0 2 g and no significant differences in site responses were apparent in two valleys with sediment basement impedance contrasts of 5 1 and 6 1 average site amplification is as much as a factor of five in certain frequency bands in another valley with a sediment basement impedance contrast of 3 1 sediment amplification is about a factor of two the duration of motion on the valley sediments in narrow frequency bands is equal to that on the bordering rock implying that the observed amplification is not due to a high q resonance of the sediments

spectral ratio estimates for site effects on the horst graben system in west turkey recordings of micro and moderate size local earthquakes have been used to quantify site effects in the central west turkey which contains one of the world s best examples of a rapid intra continental extension with its high population and industrial potential we analyzed 436 earthquakes with local magnitudes ranging between 2 0 and 5 6 using three component digital recordings from 32 stations site functions were obtained using two different spectral ratio approaches horizontal to vertical spectral ratio hvsr and standard spectral ratio ssr hvsr estimates of transverse and radial s waves were compared with one another epicentral distance magnitude and back azimuth dependencies of site functions were also evaluated in general hvsr values from transverse and radial s waves are similar within a factor of 2 the back azimuth dependencies of transverse s wave hvsr results are more significant than distance and magnitude dependencies on the other hand averaging of transverse and radial s wave hvsr results eliminates systematic back azimuth dependencies caused by source radiation effects distributions of hvsr estimates along n s linear array which traversed main grabens in the region with a station spacing of 3 4 km reflect subsurface geological complexities in the region the sites located near the basin edges are characterized by broader hvsr curves broad hvsr peaks could be attributed to the complexity of wave propagation related to significant 2d 3d velocity variations at the sediment bedrock interface near the basin edges the results also show that even if the site is located on a horst the presence of weathered zones along the surface could cause moderate frequency dependent site effects comparison of hvsr and ssr estimates for the stations on the graben sites showed that ssr estimates give larger values at lower frequencies which could be attributed to lateral variations in regional velocity and attenuation values caused by basin geometry and edge effects

the front on the northern flank of georges bank in spring 1 tidal and subtidal variability 1 during march april 1999 2 weeks of undulating ctd and shipboard acoustic doppler current profiler surveys revealed the variability of the intense internal tide on the northern edge of georges bank the nature of the internal tide was modulated by episodic surface intrusions of cool fresh scotian shelf water ssw stratifying the otherwise vertically well mixed outer bank the introduction of ssw created a system analogous to that in summer when the outer bank is thermally stratified and separated from well mixed regions by a tidal mixing front during ssw intrusions internal tidal behavior is characterized by tidal advection that is significantly faster than internal wave propagation speeds on the bank supercritical flow and slower than the lowest internal modes in deeper water to the north subcritical flow a large amplitude internal lee wave develops over the slope during off bank tidal flow this stalled energy is released to propagate on bank as a high frequency internal wave when the tide reverses it is suggested by analogy with the summer case that a portion of this energy is used by mixing at the on bank limit of ssw the presence of ssw thus modifies the internal tidal response enabling a mechanism that contributes to its assimilation with ambient bank water the off bank propagating internal tide is dominated by a mode 1 internal wave at the m2 frequency with cross bank velocities comparable to the barotropic tide

high frequency attenuation in the lake van region eastern turkey we provide a complete description of the characteristics of excitation and attenuation of the ground motion in the lake van region eastern turkey using a data set that includes three component seismograms from the 23 october 2011 m w 7 1 van earthquake as well as its aftershocks regional attenuation and source scaling are parameterized to describe the observed ground motions as a function of distance frequency and magnitude peak ground velocities are measured in selected narrow frequency bands from 0 25 to 12 5 hz observed peaks are regressed to define a piecewise linear regional attenuation function a set of excitation terms and a set of site response terms results are modeled through random vibration theory see cartwright and longuet higgins 1956 in the log log space the regional crustal attenuation is modeled with a bilinear geometrical spreading graphic 1 characterized by a crossover distance at 40 km graphic 2 fits our results at short distances r is better at larger distances 40 r 200 km a frequency dependent quality factor q f 100 f f ref 0 43 in which f ref 1 0 hz is coupled to the geometrical spreading because of the inherent trade off of the excitation attenuation parameters and their specific values strongly depend on the choice made for the stress drop of the smaller earthquakes after choosing a brune stress drop brune 4 mpa at m w 3 5 we were able to define 1 an effective high frequency distance and magnitude independent roll off spectral parameter eff 0 03 s and 2 a size dependent stress drop parameter which increases with moment magnitude from brune 4 mpa at m w 3 5 to brune 20 mpa at m w 7 1 the set of parameters mentioned here may be used in order to predict the earthquake induced ground motions expected from future earthquakes in the region surrounding lake van 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif

predictions of high frequency ground motion in taiwan based on weak motion data summary following a recent paper we use weak motion waveforms to calibrate a model for the prediction of earthquake induced ground motion in taiwan in the 0 25 5 0 hz frequency range valid up to mw 7 6 the excitation attenuation model is given in terms of frequency dependent seismic wave attenuation qs f geometrical spreading g r a magnitude dependent stress parameters for the excitation terms and a site term for each seismic station used in the study a set of weak motion data was gathered from about 170 aftershocks of the chi chi earthquake mw 7 6 of 1999 september 20 17 47 utc recorded by 10 broad band seismic stations the moment magnitudes of the registered aftershocks ranged from mw 3 0 to 6 5 and the hypocentral distances from a few kilometres to about 250 km a frequency dependent crustal quality factor q f 350f0 32 was obtained to be coupled with the geometrical spreading function earthquake related excitation spectra were calibrated over our empirical results by using a magnitude dependent brune model with a stress drop value of 8 0 1 0 mpa for the largest event of mw 6 5 in our data set and with a near surface attenuation parameter of 0 05 s results on region specific crustal attenuation and source scaling were used to generate stochastic simulations both for point source and extended fault ruptures through the computer codes stochastic model simulation smsim and extended fault model simulation exsim the absolute peak ground accelerations pga peak ground velocities pgv and 5 per cent damped spectral accelerations sa at three different frequencies 0 33 hz 1 0 hz and 3 0 hz for several magnitudes and distance ranges were predicted at large magnitudes well beyond magnitude mw 6 5 the upper limit for the events of our weak motion data set the performance of the stochastic model was then tested against the strong motion data recorded during the mw 7 6 chi chi earthquake and against several other empirical ground motion models

physical oceanography of the western iberia ecosystem latest views and challenges the present review is focused on the mesoscale physical processes recognized in the western iberia ecosystem complementing earlier reviews dedicated to larger scales recent studies support the idea that the mesoscale processes superimposed on the larger scale variability are the major factor controlling the ecosystem functioning in the region a complex structure of interleaved alongshore slope shelf and coastal currents that interact with eddies buoyant plumes upwelling filaments and fronts surface layer expressions of the subsurface circulation and internal waves is revealed by the latest research all of these contribute in different ways to have an effect on the ecosystem the supposedly less variable winter circulation also exhibits significant mesoscale activity in the form of eddy shedding from the poleward slope current intermittent upwelling events and transient nearshore poleward flows the present incomplete knowledge of this complex system presents a number of challenges and questions that must be addressed if we are to arrive at a satisfactory understanding and predictive capability for the system as a whole 2007 elsevier ltd all rights reserved

frequency dependent site amplifications with f 0 01 hz evaluated from velocity and density models in central taiwan the frequency dependent site amplifications at 87 free field strong motion station sites in central taiwan are evaluated from the velocity and density structures constructed from borehole data measured at shallow depths and the veloc ity models inferred from earthquake data at great depths results based on the quarter wavelength approximation method proposed by boore and joyner 1997 show that the site amplifications increase with frequency and are larger in the western plain with thick holocene alluvium than in the western foothill with pleistocene and miocene formations considering wave attenuation site amplification first increases and then decreases with increasing frequency the turning frequency ft associated with the maximum amplification varies site by site

tidal and atmospheric forcing of the upper ocean in the gulf of california 1 sea surface temperature variability two years of satellite infrared imagery 1984 1986 are used to examine the sea surface temperature sst variability in the northern gulf of california empirical orthogonal functions eofs of the temporal and spatial sst variance for 20 monthly mean images show that the dominant sst patterns are generated by spatially varying tidal mixing in the presence of seasonal heating and cooling these patterns are modified in the fall and winter when shelf temperatures south of tiburon island cool in response to upwelling favorable winds these same winds bring cold dry air from off the continental united states causing local cooling of the shallow northern shelf during the rest of the year the broad shallow shelves are warmer than offshore the seasonally reversing temperature patterns are consistent with recent hydrographic observations which show a cyclonic surface circulation in the summer and a weaker anticyclonic circulation during the rest of the year atmospheric forcing of the northern gulf appears to occur over large spatial scales area averaged ssts for the guaymas basin island region and northern basin show significant fluctuations which are highly correlated these fluctuations in sst correspond to similar fluctuations in the air temperature which are related to synoptic weather events over the gulf during periods of particularly low wind speeds the air temperature over the gulf increases dramatically by afternoon intense heating of the sea surface results in the appearance of warm sst anomalies in the satellite data these ssts are approximately 2 c warmer than surrounding ssts and most likely occur as a result of a spatially varying wind field a regression analysis of the sst relative to the fortnightly tidal range shows that tidal mixing occurs over the sills in the island region as well as on the shallow norther shelf mixing over the sills however occurs as a result of large breaking internal waves or internal hydraulic jumps which mix water over the upper 300 500 m this mixing pumps heat away from the surface deep into the water column there by maintaining the cool ssts since mixing occurs over greater depths in the island region the temperatures there are much colder than those generated by tidal mixing on the shallow shelves resulting in the persistent pool of cool water evident in the satellite data this cooler water is mixed horizontally by the basin scale circulation lowering the ssts over much of the northern gulf these reduced ssts have a large impact on the surface heat flux by lowering the saturation vapor pressure of the air as a result the amount of heat lost to the atmosphere through the latent or evaporative heat flux is reduced this may explain why the gulf of california gains heat on an annual average rather than losing heat as occurs in the mediterranean and red seas where tidal mixing is not significant

ground motions for earthquakes in southwestern british columbia and northwestern washington crustal in slab and offshore events regional ground motion generation and propagation must be charac terized to adequately assess seismic hazard in the cascadia region of southwestern british columbia and northwestern washington the ground motion issues are par ticularly complex because of the contributions to hazard from five distinct types of events all of which behave differently in terms of their ground motion propagation characteristics 1 shallow earthquakes occurring in the continental crust 2 shallow earthquakes occurring offshore in oceanic crust 3 earthquakes occurring within the subducting juan de fuca slab beneath the continent e g puget sound 4 earth quakes occurring within the subducting juan de fuca slab at the edge of the continent e g transitional events along the west coast of vancouver island and 5 great subduction earthquakes on the interface between the subducting juan de fuca plate and the overriding north american plate in this study empirical data recorded within the cascadia region are used to evaluate the source and attenuation characteristics of ground motion amplitudes from the first four of these event types crustal off shore in slab and transitional and examine their implications for regional ground motion relations for crustal earthquakes in cascadia a simple application of the hybrid empirical approach is used to suggest appropriate regional ground motion relations the ground motions are obtained by multiplying california ground motion relations by a frequency dependent factor to account for regional differences in crustal amplifica tion the developed ground motion relations for cascadia earthquakes are in rea sonable agreement with recorded ground motions in the region the proposed rela tions are the first region specific ground motion relations to be developed for the cascadia region and they provide a useful alternative to california relations for use in seismic hazard analysis

a 200 ka pollen and oxygen isotopic record from two sediment cores from the eastern arabian sea abstract we present here a pollen record from the northern indian ocean that goes back to 200 ka the boundary between marine isotopic stages mis 7 and 6 pollen oxygen isotopic composition and organic carbon have been examined for two sediment cores from the eastern arabian sea 15 02 n and 71 41 e 13 16 n and 71 00 e to reconstruct the long term palaeoclimate and palaeovegetation of the indian subcontinent oxygen isotope data suggest that glacial periods mis 2 4 and 6 are characterised by low precipitation because of a weak southwest monsoon and a strong northeast monsoon in contrast interglacial periods mis 1 3 and 5 are marked by high fresh water input resulting from a strong southwest monsoon during the last glacial interglacial cycle sea surface temperature and surface salinity changed as a result of variations in the evaporation precipitation e p balance throughout the core the dominant pollen types are poaceae and chenopodiaceae and or amaranthaceae 50 their dominance during glacial periods mis 2 4 and 6 suggests that the climate was cold and dry this dominance is also suggestive of salinity tolerant vegetation colonizing large areas near seashore due to lower sea level or high e p conditions during interglacial periods mis 1 3 and 5 when there was high precipitation the arid taxa were sparse whereas poaceae and piperaceae were abundant hence chenopodiaceae and or amaranthaceae and artemisia are suggestive of cold and arid semi arid climate and poaceae and piperaceae of warm and wet conditions mangrove pollen is not well represented in the cores

unbiased moment rate spectra and absolute site effects in the kachchh basin india from the analysis of the aftershocks of the 2001 mw 7 6 bhuj earthquake what can be learned about absolute site effects on ground motions with no geotechnical information available in a very poorly instrumented region in addition can reliable source spectra be computed at a temporary deployment these challenges motivated our current study of aftershocks of the 2001 m w 7 6 bhuj earthquake in western india where we decouple the ambiguity between absolute source radiation and site effects by first computing robust estimates of coda derived moment rate spectra of about 200 aftershocks in each of two depth ranges crustal attenuation and spreading relationships based on the same data used here were determined in an an earlier study using our new estimates of source spectra and our understanding of regional wave propagation for direct s waves we isolate the absolute site terms for the stations of the temporary deployment absolute site terms for each station were determined in an average sense for the three components of the ground motion via an l1 norm minimization results for each site were averaged over wide ranges of azimuths and incidence angles the bhuj deployment is characterized by a variable shallow geology mostly of soft sedimentary units vertical site terms in the region were observed to be almost featureless i e flat with amplifications slightly 1 0 within wide frequency ranges as a result the horizontal to vertical h v spectral ratios observed at the deployment mimic the behavior of the corresponding absolute horizontal site terms and they generally overpredict them this differs significantly from results for sedimentary rock sites limestone dolomite obtained by malagnini et al 2004 in northeastern italy where the h v spectral ratios had little in common with the absolute horizontal site terms spectral ratios between the vector sum of the computed horizontal site terms for the temporary deployment with respect to the same quantity computed at the hardest rock station available bac1 are seriously biased by its nonflat nonunitary site response this indicates that occasionally the actual behavior of a rock outcrop may be far from that of an ideal reference site steidl et al 1996

an inversion of lg wave attenuation and site response from seismic spectral ratios in the eastern china region abstract both lg wave attenuation and site responses are determined in the eastern china region the region ranges from 26 n to 33 n and 117 e to 124 e we analyze over 1360 three component seismograms from 92 local and regional earthquakes the seismograms are recorded in the distance range of 100 600 km the earthquakes occurred between 2002 and 2012 in the region and varied in magnitude between 2 0 and 4 7 m l a combined inversion method which can simultaneously estimate attenuation and site response from seismic spectral ratios is implemented in the study modeling errors are determined using a delete j jackknife resampling technique fourier spectral amplitudes are measured from lg phases windowed between the group velocity limits 2 6 and 3 6 km s the inversion are performed in a frequency range of 1 6 hz with an interval of 0 2 hz the frequency dependent quality factor is modeled in the form of q q 0 f the eastern china region displays high q 0 and a weaker frequency dependence characterized by the functions q 335 16 f 0 45 0 02 q 411 21 f 0 26 0 01 and q 432 26 f 0 24 0 01 for vertical north south and east west components respectively the values are similar to the average for other stable regions of the globe site responses from 32 stations are estimated in the region most stations do not show obvious amplification the site responses are mainly smooth flat and less than 5 in the frequency range of 1 6 hz

2d coda and direct wave attenuation tomography in northern italy abstract a 1d coda method was proposed by mayeda et al 2003 in order to obtain stable seismic source moment rate spectra using narrowband coda envelope measurements that study took advantage of the averaging nature of coda waves to derive stable amplitude measurements taking into account all propagation site and s to coda transfer function effects recently this methodology was applied to microearthquake data sets from three subregions of northern italy i e western alps northern apennines and eastern alps because the study regions were small ranging between local to near regional distances the simple 1d path assumptions used in the coda method worked very well the lateral complexity of this region would suggest however that a 2d path correction might provide even better results if the data sets were combined especially when paths traverse larger distances and complicated regions the structural heterogeneity of northern italy makes the region ideal to test the extent to which coda variance can be reduced further by using a 2d q tomography technique the approach we use has been developed by phillips et al 2005 and is an extension of previous amplitude ratio techniques to remove source effects from the inversion the method requires some assumptions such as isotropic source radiation which is generally true for coda waves our results are compared against direct s wave inversions for 1 q and results from both share very similar attenuation features that coincide with known geologic structures we compare our results with those derived from direct waves as well as some recent results from northern california obtained by mayeda et al 2005 that tested the same tomographic methodology applied in this study to invert for 1 q we find that 2d coda path corrections for this region significantly improve upon the 1d corrections in contrast to california where only a marginal improvement was observed we attribute this difference to stronger lateral variations in q for northern italy relative to california

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

all toba tephra occurrences across peninsular india belong to the 75 000 yr b p eruption abstract a controversy currently exists regarding the number of toba eruptive events represented in the tephra occurrences across peninsular india some claim the presence of a single bed the 75 000 yr old toba tephra others argue that dating and archaeological evidence suggest the presence of earlier toba tephra resolution of this issue was sought through detailed geochemical analyses of a comprehensive suite of samples allowing comparison of the indian samples to those from the toba caldera in northern sumatra malaysia and importantly the sedimentary core at odp site 758 in the indian ocean a core that contains several of the earlier toba tephra beds in addition two samples of toba tephra from western india were dated by the fission track method the results unequivocally demonstrate that all the presently known toba tephra occurrences in peninsular india belong to the 75 000 yr b p toba eruption hence this tephra bed can be used as an effective tool in the correlation and dating of late quaternary sedimentary sequences across india and it can no longer be used in support of a middle pleistocene age for associated acheulian artifacts

sedimentological analysis of the tephra from the 12 15 august 1991 eruption of hudson volcano the tephra fallout from the 12 15 august 1991 explosive eruption of hudson volcano cordillera de los andes 45 54 s 72 58 w chile was dispersed on a narrow elongated ese sector of patagonia covering an area on land of more than 100 000 km2 the elongated shape of the deposit together with the relatively coarse mean and median values of the particles at a considerable distance from the vent were the result of strong winds blowing to the southeast during the eruption the thickness of the fall deposit decreases up to 250 km ese from hudson volcano where it begins to thicken again secondary maxima are well developed at approximately 500 km from the vent secondary maxima together with grainsize bimodality in individual layers and in the bulk deposit suggest that particle aggregation played an important role in tephra sedimentation the fallout deposit is well stratified with alternating fine grained and coarsegrained layers which is probably a result of strong eruptive pulses followed by relatively calm periods and or changes in the eruptive style from plinian to phreatoplinian the tephra is mostly composed of juvenile material the coarse mode mostly pumice shifts to finer sizes with distance from the volcano the fine mode mostly glass shards is always about 5 6 phi glass shards and pumice are mostly light gray to colorless however considerable amounts of dark poorly vesiculated blocky shards suggest a hydromagmatic component in the eruption a land based tephra volume of 4 35 km3 was estimated and a total volume of 7 6 km3 arose from an extrapolation which took into account the probable volume sedimented in the sea bulk density ranges from 0 9 to 1 10 gr cm3 beyond 110 km from the vent rather uniform density values measured in crushed samples 2 45 2 50 gr cm3 at all distances from the vent reveal a relatively homogeneous composition mean and median sizes decrease rapidly up to 270 km from the vent beyond that point they are more or less constant whereas the maximum size 1 phi shows a steady decrease up to 550 km a concomitant improvement in sorting is observed this is attributed to sorting due to wind transport combined with particle aggregation at different times and distances from the vent the hudson tephra fallout shares some strikingly similar features with the mount st helens 18 may 1980 and quizapu 1932 eruptions

seasonal variability of sea surface temperature fronts on georges bank abstract sea surface temperature sst fronts extracted from archived 1985 1996 advanced very high resolution radiometer avhrr data are determined in the georges bank region resulting frontal locations clearly show the tidal mixing front on georges bank the probability of detecting an sst front at an individual pixel on georges bank is presented as a monthly climatology variations in the probability position and associated water depth of sst fronts in the georges bank region show the development of the tidal mixing front during the summer as well as the presence of a persistent front near the shelfbreak from the 12 yr time series of fronts 144 individual monthly frontal probability images are decomposed into the mean frontal position and empirical orthogonal functions eof using singular value decomposition svd spatial and temporal information from the first eof mode reveals the seasonal development of the tidal mixing front spatial patterns associated with the first mode also reveal the winter occurrence of fronts on the northeast peak area of georges bank which is most likely associated with scotian shelf water flow across the northeast channel the second mode also indicates the development of the hot spot often observed over georges bank during the late summer and early fall further evidence indicates that the mean position of detected sst fronts on southern georges bank changes approximately 10 km on bank from late spring to mid summer monthly mean positions are also compared to the distribution of simpson and hunter s 1974 tidal mixing parameter with resultant positions compared to historical stratification at those locations comparison of detected sst fronts to historical hydrographic data on georges bank points to the fronts being located in increasingly stratified water from may through august

elastohydrodynamic lubrication of faults the heat flow paradox provides evidence that a dynamic weakening mechanism may be important in understanding fault friction and rupture we present here a specific model for dynamic velocity weakening that uses the mechanics of well studied industrial bearings to explain fault zone processes an elevated fluid pressure is generated in a thin film of viscous fluid that is sheared between nearly parallel surface this lubrication pressure supports part of the load therefore reducing the normal stress and associated friction across the gap the pressure also elastically deforms the wall rock the model is parameterized using the sommerfeld number which is a measure of the lubrication pressure normalized by the lithostatic load for typical values of the material properties slip distance and velocity the sommerfeld number suggests that lubrication is an important process if the lubrication length scales as the slip distance in an earthquake the frictional stress during dynamically lubricated large earthquakes is 30 less than the friction with only hydrostatic pore pressure elastohydrodynamic lubrication also predicts a decrease in high frequency 1 hz radiation above a critical slip distance of a few meters this prediction is well matched by the strong motion data from the 1999 taiwan earthquake the observed 2 orders of magnitude variation in scaled radiated energy between small m w 6 is also predicted by the lubrication model

volcanic winter and accelerated glaciation following the toba super eruption the eruption of toba in sumatra 73 500 years ago was the largest known explosive volcanic event in the late quaternary1 it could have lofted about 1015 g each of fine ash and sulphur gases to heights of 27 37 km creating dense stratospheric dust and aerosol clouds here we present model calculations that investigate the possible climatic effects of the volcanic cloud the increase in atmospheric opacity might have produced a volcanic winter 2 a brief pronounced regional and perhaps hemispheric cooling caused by the volcanic dust followed by a few years with maximum estimated annual hemispheric surface temperature decreases of 3 5 c the eruption occurred during the stage 5a 4 transition of the oxygen isotope record a time of rapid ice growth and falling sea level3 we suggest that the toba eruption may have greatly accelerated the shift to glacial conditions that was already underway by inducing perennial snow cover and increased sea ice extent at sensitive northern latitudes as the onset of climate change may have helped to trigger the eruption itself4 we propose that the toba event may exemplify a more general climate volcano feedback mechanism

river response to quaternary climatic fluctuations evidence from the son and belan valleys north central india abstract the last glacial period was cold and dry in peninsular india in north central india the interval from 39 9 to 16 3 ka was associated with widespread and prolonged aggradation in the son and belan valleys the aggradation ended with sustained vertical incision after 16 3 ka and reflects a return to warmer wetter conditions in this region it would appear that terminal pleistocene to holocene river incision was broadly synchronous with a strong summer monsoon regime and higher levels of river discharge and the preceding river aggradation with lower discharge and a weaker or more variable summer monsoon regime two older phases of prolonged aggradation followed by vertical incision are evident in the son and belan valleys before 39 ka one of these phases is centred towards 73 4 ka when ash from the toba mega eruption in sumatra was deposited across peninsular india the following phase of aggradation has yielded infrared stimulated luminescence ages of 58 6 and 45 12 ka the youngest phase of aggradation began towards 5 5 ka and seems to mark a return to a weaker summer monsoon regime

an application of the coda methodology for moment rate spectra using broadband stations in turkey a recently developed coda magnitude methodology was applied to selected broadband stations in turkey for the purpose of testing the coda method in a large laterally complex region as found in other albeit smaller regions coda envelope amplitude measurements are significantly less variable than distance corrected direct wave measurements i e l sub g and surface waves by roughly a factor 3 to 4 despite strong lateral crustal heterogeneity in turkey they found that the region could be adequately modeled assuming a simple 1 d radially symmetric path correction after calibrating the stations isp iskb and malt for local and regional distances single station moment magnitude estimates m sub w derived from the coda spectra were in excellent agreement with those determined from multistation waveform modeling inversions exhibiting a data standard deviation of 0 17 though the calibration was validated using large events the results of the calibration will extend m sub w estimates to significantly smaller events which could not otherwise be waveform modeled the successful application of the method is remarkable considering the significant lateral complexity in turkey and the simple assumptions used in the coda method

source scaling and site effects at vesuvius volcano the site corrected source scaling pattern is estimated for local earthquakes 0 9 m d 3 6 at mt vesuvius the dataset comprises 35 low to moderate local earthquakes recorded by 14 three component seismic stations during 1993 1996 and 1999 site transfer functions in the frequency range 1 hz 25 hz are estimated from the spectra of s waves and coda waves and from the horizontal to vertical h v spectral ratios we applied the direct spectral ratios method to s waves considering as a reference the average spectrum and the inversion method to s waves and coda waves the site amplification on the coda waves was also compared with that evaluated using the wavelet transform the standard deviation associated with the experimental results is computed for all of the used methods results indicate a general agreement among the methods and the site transfer functions show interesting features the highest amplifications are found for frequencies lower than 12 hz for sites located at lower altitude the methods based on coda waves show highest amplification with respect to the methods based on s waves for most of the sites located in the summit part of the volcano this can be a phenomenon of coda localization which consists in the trapping inside the upper part of the volcano of scattered waves the h v spectral ratios do not show total agreement with the other methods mostly for the sites located in the summit part of the volcano the discrepancies among the results obtained in this work are also due to the different normalization applied in the methods of analysis generalized inversion method allowed us to estimate the source scaling of the site corrected source seismic spectrum for the investigated area the source scaling obtained in terms of seismic moment and source radii shows that the seismicity of mt vesuvius is characterized by stress drop as low as a few bars 10 bars except for the event of graphic 1 graphic 2 the scaling pattern shows an apparent linear relationship between source size and seismic moment for m d 3 3 but the statistical test shows that the linear trend has low reliability 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif

sea surface temperature fronts in the california current system from geostationary satellite observations 1 sea surface temperature sst fronts are determined for the 2001 2004 time period from geostationary operational environmental satellites goes data in the california current system ccs the probability of detecting a sst front at an individual pixel location in the ccs is presented as a bi monthly climatology fronts clearly indicate the seasonal evolution of coastal upwelling as well as meanders and filaments that are often linked with irregularities in coastline geometry winter is characterized by low frontal activity along the entire coast fronts first appear close to the coast during spring particularly south of cape blanco where upwelling favorable winds are already persistent the area of high frontal activity continues to increase during summer especially between monterey bay and cape blanco extending more than 300 km from the coast the region with high frontal activity widens at 2 6 km day 1 off northern baja california a band with persistent fronts is found close to the coast year round but there is no evidence of a seasonal widening of the area of higher activity during fall the weakening of upwelling favorable winds leads to a gradual decrease in frontal activity an empirical orthogonal function eof decomposition reveals the development of sst fronts associated with seasonal upwelling for locations north of monterey bay with less summer intensification to the south the first appearance of fronts close to the coast during spring and the occurrence of the fronts offshore later in the season are represented by additional statistically significant eof modes

fallout and distribution of volcanic ash over argentina following the may 2008 explosive eruption of chaiten chile 1 the major explosive eruption of chaiten volcano chile in may 2008 provided a rare opportunity to track the long range dispersal and deposition of fine volcanic ash the eruption followed 10 000 years of quiescence was the largest explosive eruption globally since hudson chile in 1991 and was the first explosive rhyolitic eruption since novarupta alaska in 1912 field examination of distal ashfall indicates that 1 6 1011 kg of ash dense rock equivalent volume of 0 07 km3 was deposited over 2 105 km2 of argentina during the first week of eruption the minimum eruption magnitude estimated from the mass of the tephra deposit is 4 2 several discrete ashfall units are identifiable from their distribution and grain size characteristics with more energetic phases showing a bimodal size distribution and evidence of cloud aggregation processes ash chemistry was uniform throughout the early stages of eruption and is consistent with magma storage prior to eruption at depths of 3 6 km deposition of ash over a continental region allowed the tracking of eruption development and demonstrates the potential complexity of tephra dispersal from a single eruption which in this case comprised several phases over a week long period of intense activity

effects of frictional heating on the thermal hydrologic and mechanical response of a fault the mechanical response of a fault zone during an earthquake may be controlled by the diffusion of excess heat and fluid pressures generated by frictional heating in this study we formulate a fault model which incorporates the effects of frictional heating on the thermal hydrologic and mechanical response of a small patch of the failure surface this model is used to examine the parameters that control the fault response and to determine their critical range of values where thermal pressurization is significant the problem has two time scales a characteristic slip duration and a characteristic time for thermal pressurization the slip duration is set by the fault geometry the characteristic time for thermal pressurization is set by the slip rate the friction coefficient and the thermal and hydraulic characteristics of the medium the response of the fault depends on the relative magnitude of these two times results suggest that the fault width and hydraulic characteristics of the fault zone and adjacent medium are the primary parameters controlling the mechanical response for earthquakes occurring across zones of low porous medium compressibility 10 9 pa 1 and permeability 10 18 m2 the characteristic time for thermal pressurization is small in this case frictional heating can cause fluid pressures to approach lithostatic values the shear strength to approach zero and the temperature rise to stabilize at a maximum value dependent on the pore dilatational and transport properties of the porous medium whether the patch acts as a barrier to slip or exhibits substantial strain weakening is dependent on the shear strain across the fault moderate slip events where shear strains exceed two cause substantial strain weakening and consequently large stress drops accelerations and displacements thus it is possible for the patch to act as a barrier for small earthquakes but not for large ones both the dynamic stress drop and total displacement decrease for zones with larger compressibility permeability or width if the compressibility or permeability exceeds 10 8 pa 1 or 10 14 m2 or the shear strain is less than one then the effects of frictional heating may be negligible and the fault will exhibit no strain weakening characteristics consequently the patch acts as barrier that halts or resists further fault motion extrapolation of these results suggests that spatial variations in fault width and hydraulic characteristics will cause a heterogeneous stress drop and fault slip over the failure surface explaining many of the features of active faulting e g barriers nonuniform slip rupture stoppage random ground accelerations strong motions and frequency magnitude relations

estimating absolute site effects the authors use previously determined direct wave attenuation functions as well as stable coda derived source excitation spectra to isolate the absolute s wave site effect for the horizontal and vertical components of weak ground motion they used selected stations in the seismic network of the eastern alps and find the following 1 all hard rock sites exhibited deamplification phenomena due to absorption at frequencies ranging between 0 5 and 12 hz the available bandwidth on both the horizontal and vertical components 2 hard rock site transfer functions showed large variability at high frequency 3 vertical motion site transfer functions show strong frequency dependence and 4 h v spectral ratios do not reproduce the characteristics of the true horizontal site transfer functions 5 traditional relative site terms obtained by using reference rock sites can be misleading in inferring the behaviors of true site transfer functions since most rock sites have non flat responses due to shallow heterogeneities resulting from varying degrees of weathering they also use their stable source spectra to estimate total radiated seismic energy and compare against previous results they find that the earthquakes in this region exhibit non constant dynamic stress drop scaling which gives further support for a fundamental difference in rupture dynamics between small and large earthquakes to correct the vertical and horizontal s wave spectra for attenuation they used detailed regional attenuation functions derived by malagnini et al 2002 who determined frequency dependent geometrical spreading and q for the region these corrections account for the gross path effects i e all distance dependent effects although the source and site effects are still present in the distance corrected spectra the main goal of this study is to isolate the absolute site effect as a function of frequency by removing the source spectrum moment rate spectrum from the distance corrected s wave spectra typically removing the s wave source spectrum is difficult because of inadequate corrections for the source radiation pattern directivity and random interference in addition to complexities near the source 2 d and 3 d structure beneath the recording site will result in an azimuth dependent site effect since the direct wave only samples a narrow range in take off and back azimuth angles multi station averaging is needed to minimize the inherent scatter to minimize these complicating effects they apply the coda methodology outlined by mayeda et al 2003 to obtain stable moment rate spectra this methodology provides source amplitude and derived source spectra that are a factor of 3 to 4 times more stable than those derived from direct waves since the coda is commonly thought of as scattered energy that samples all ray parameters and back azimuths it is not very sensitive to the source radiation pattern and 3 d structure this property makes it an excellent choice for use in obtaining average properties of the source site and path effects in a region due to the characteristics of the techniques used in this study all the inverted quantities are azimuthally averaged since the aximuthal information is lost in the processing

how to invert multi band regional phase amplitudes for 2 d attenuation and source parameters tests using the usarray we inverted for laterally varying attenuation absolute site terms moments and apparent stress using over 460 000 lg amplitudes recorded by the usarray for frequencies between 0 5 and 16 hz corner frequencies of wells nevada aftershocks obtained by independent analysis of coda spectral ratios controlled the tradeoff between attenuation and stress while independently determined moments from st louis university and the university of california constrained absolute levels the quality factor q was low for coastal regions and interior volcanic and tectonic areas and high for stable regions such as the great plains and colorado and columbia plateaus q increased with frequency and the rate of increase correlated inversely with 1 hz q with highest rates in low q tectonic regions and lowest rates in high q stable areas moments matched independently determined moments with a scatter of 0 2 nm apparent stress ranged from below 0 01 to above 1 mpa with means of 0 1 mpa for smaller events and 0 3 mpa for larger events stress was observed to be spatially coherent in some areas for example stress was lower along the san andreas fault through central and northern california and higher in the walker lane and for isolated sequences such as wells variance reduction relative to 1 d models ranged from 50 to 90 depending on band and inversion method parameterizing frequency dependent q as a power law produced little misfit relative to a collection of independent multi band q models and performed better than the omega square source parameterization in that sense amplitude residuals showed modest but regionally coherent patterns that varied from event to event even between those with similar source mechanisms indicating a combination of focal mechanism and near source propagation effects played a role an exception was the wells mainshock which produced dramatic amplitude patterns due to its directivity and was thus excluded from the inversions the 2 d q plus absolute site models can be used for high accuracy broad area source spectra magnitude and yield estimation and in combination with models for all regional phases can be used to improve discrimination in particular for intermediate bands that allow coverage to be extended beyond that available for high frequency p to s discriminants

moment tensor estimation using regional seismograms from a tibetan plateau portable network deployment the authors present the results of moment tensor inversions using regional seismograms recorded during the 1991 1992 passcal passive seismic experiment on the tibetan plateau using data recorded over a one year period they estimate the source mechanisms for 38 earthquakes within and near the tibetan plateau with moment magnitudes m sub w ranging from 3 8 to 5 0 with only one exception all the events within the plateau but away from the plateau boundary indicate either strike slip or extensional faulting a result consistent with previous studies three fourths of all the events occurred at depths less than 10 km and all but two at depths less than 15 km several events located near the southeastern section of the plateau exhibit an unusual m sub b m sub w difference of approximately one magnitude unit 19 refs 3 figs

empirical orthogonal function analysis of sea surface temperature patterns in delaware bay empirical orthogonal functions eofs are used to study a time series of ir images from the delaware bay region to determine the dominant patterns of sea surface temperature sst variance thirty two months of avhrr imagery from february 1992 to september 1994 were used in the study the sst images were averaged into monthly means for the analysis eof analysis decomposed the time series into its component parts for delaware bay the seasonal solar heating cycle dominated the results accounting for 95 3 of the total variance higher modes in this area are interpreted as the result of spring heating and fall cooling of shallow river and bay waters ahead of offshore waters the eof results provide independent satellite derived evidence for lateral variability in the circulation of the estuary which had previously been found in in situ studies the lateral variability in the bay circulation is a result of delaware bay s drowned river valley bathymetry

application of an edge detection method to satellite images for distinguishing sea surface temperature fronts near the japanese coast abstract this study applies an edge detection method to satellite sea surface temperature sst images in order to distinguish sst fronts frequently occurring near the japanese coast first we develop a new set of edge detection algorithms the method is based on an entropic approach using jensen shannon divergence which is certified as a robust technique for detecting edge pixel candidates additionally we incorporate ridge line extraction morphological filter to obtain edge pixels which is suited to delineate intricate frontal features the methodology allows us to detect reasonable amount of possible fronts to the fullest extent according to the original image resolution therefore it enables us to analyze finer scale fronts near the coast as well as larger scale fronts associated with major currents then we present four case study examples of sst fronts near the japanese coast by applying the method to advanced very high resolution radiometer avhrr sst images with a grid size of 0 01 we describe the configuration and seasonal variability of the sst frontal systems from the viewpoint of occurrence probability sst gradient magnitude and orientation to the local bathymetry as compared with the previous observational studies consequently it is demonstrated that application of the method can derive new views of finer scale and highly variable sst fronts moreover this study first verifies the capability of comprehensive and statistical description of sst front configurations and variations near the japanese coast by applying edge detection method to sequences of satellite sst images

moment magnitudes of local regional events from 1d coda calibrations in the broader middle east region abstract reliable moment magnitude estimates for seismic events in the middle east region can be difficult to obtain due to the uneven distribution of stations the complex tectonic structure and regions of high attenuation in this study we take advantage of the many new broadband seismic stations that have become available through improved national networks and numerous temporary deployments we make coda envelope amplitude measurements for 2247 events recorded by 68 stations over 13 narrow frequency bands ranging between 0 03 and 8 hz the absolute scaling of these spectra was calculated based on independent waveform modeling solutions of the moment magnitudes for a subset of these events to avoid circularity using our 1d path calibrations we determined coda based magnitudes for a majority of the events we obtain fairly good agreement with waveform modeled seismic moments for the larger events m w 4 5 at low frequencies 0 7 hz because of unaccounted 2d path effects as well as mixing of both sn coda and lg coda which have different attenuation behavior this scatter leads to increased variance in the magnitudes estimated for smaller events in which low frequency amplitudes are below the noise levels and the higher frequencies are the only signals available we quantify the expected variance in coda envelope amplitudes as a function of frequency using interstation scatter as our metric the net results of this study provide thousands of new 1d coda magnitude estimates for events in the broad region as well as the necessary initial starting model for use in a new related 2d coda study pasyanos et al 2016 online material table of site terms and moment magnitudes

what is a reference site many methods for estimating site response compare ground motions at sites of interest to a nearby rock site that is considered a reference motion the critical assumption in these methods is that the surface rock site record reference is equivalent to the input motion at the base of the soil layers data collected in this study show that surface rock sites can have a site response of their own which could lead to an underestimation of the seismic hazard when these sites are used as reference sites data were collected from local and regional earthquakes on digital recorders both at the surface and in boreholes at two rock sites and one basin site in the san jacinto mountains southern california the two rock sites keenwild and pinon flat are located on granitic bedrock of the southern california peninsular ranges batholith the basin site garner valley is an ancestral lake bed with watersaturated sediments on top of a section of decomposed granite which overlies the competent bedrock ground motion is recorded simultaneously at the surface and in the bedrock at all three sites when the surface rock sites are used as the reference site i e the surface rock motion is used as the input to the basin the computed amplification underestimates the actual amplification at the basin site for frequencies above 2 to 5 hz this underestimation by a factor of 2 to 4 depending on frequency and site results from the rock sites having a site response of their own above the 2 to 5 hz frequencies the near surface weathering and cracking of the bedrock affects the recorded ground motions at frequencies of engineering interest even at sites that appear to be located on competent crystalline rock the bedrock borehole ground motion can be used as the reference motion but the effect of the downgoing wave field and the resulting destructive interference must be considered this destructive interference may produce pseudo resonances in the spectral amplification estimates if one is careful the bedrock borehole ground motion can be considered a good reference site for seismic hazard analysis even at distances as large as 20 km from the soil site

historical and recent evidence of scotian shelf water on southern georges bank abstract historical data from 1912 1987 indicate that low salinity less than 32 0 psu near surface water occurs occasionally on southern georges bank during may while none occurs during april composite monthly plots of historical near surface salinity and estimated advection rates show that the southwestern scotian shelf is the immediate upstream source of this low salinity water optimally interpolated satellite derived sst and hydrographic data reveal that very cold less than 2 0 c low salinity less than 32 0 psu scotian shelf water ssw initially located south of the 200 m isobath off southern georges bank in early march 1992 moved north onto southern georges bank during april 1992 ssw was not as extensive during the same period in 1993 as evidence by significantly higher temperatures and salinities these differences show large interannual variability in the transport and or properties of ssw flowing onto georges bank lower higher salinities measured during spring 1992 1993 on southern georges bank are consistent with higher lower st lawrence river discharge noted during spring 1991 1992 and the nine month lag between annual discharge maxima from rivers located upstream and minimum salinity at cape sable in february however comparisons between historical occurrences of low salinity less than 32 0 psu ssw on southern georges bank noted for may 1966 1971 and 1978 and cumulative st lawrence river discharge from the spring prior to each occurrence show no relationship this suggests that the occurrence of low salinity water on southern georges bank is not directly related to variations in upstream river discharge although an idealized model of wind forcing on a bank trapped density front shows that near surface flow is related to superposition of an ekman layer and the along bank gyral circulation evidence from late winter spring 1992 and 1993 on georges bank shows that except for on bank movement of the shelf slope front during late spring 1992 simple ekman theory does not explain on bank movement of the ssw plume during 1992 nor the immobile nature of the shelf slope front during late winter 1992 and late winter spring 1993 surface heat flux and satellite derived sst from georges bank and the scotian shelf together with a slab mixed layer model allows estimation of the advective heat flux and transport of ssw flowing onto georges bank from the scotian shelf during late winter spring 1992 mean advective heat flux onto georges bank during march may 1992 is 14 5 mw cm 2 with an estimated error of 3 5 mw cm 2 demonstrating that advection of cold ssw onto georges bank is required mean velocity and transport of ssw flowing onto georges bank during march may 1992 are 13 4 cm s 1 and 0 21 sv assuming a ssw depth width of 40 m 40 km demonstrating that flow of ssw onto georges bank was robust during the period at this time the dynamics that control the flow of ssw across northeast channel are unknown

seasonal variability of alongshore winds and sea surface temperature fronts in eastern boundary current systems seven years of satellite observations 2003 2009 are used to describe variability in sea surface temperature sst fronts and in the alongshore component of ocean winds and to investigate their relations in four eastern boundary current systems ebcs the general patterns of sst frontal activity are remarkably similar in all ebcs with high frontal probabilities along the coast decreasing with distance from the coastline results from empirical orthogonal function decompositions reveal that the seasonal evolution of sst fronts and wind stress are significantly correlated with intensified upwelling favorable winds associated with an increase in frontal probabilities an offshore migration of the region of high frontal activity is observed during the period of upwelling favorable alongshore wind stress in ebcs in all regions the seasonal variability of frontal activity and wind stress is stronger at mid than at low latitudes the width of the region of high frontal activity is relatively broader in the california and benguela current systems and narrower in the canary and humboldt current systems the width of the band of high frontal activity may be influenced by multiple factors including wind forcing flow topography interactions and mesoscale dynamics while seasonal variability in frontal activity in the california current system acts to reinforce or weaken the average pattern they are substantially different in the canary current system where there is little overlap in the areas characterized by persistent and seasonally varying front activity

moment energy stress drop and source spectra of western united states earthquakes from regional coda envelopes we present a new method to estimate stable seismic source parameters such as energy moment and orowan stress drop using regional coda envelopes from as few as one broadband station we use the method to compute path and site corrected seismic moment rate spectra for 117 recent western united states earthquakes empirical green s function corrections were applied to our surface and body wave coda envelope measurements to generate s wave source spectra these source spectra provide stable single station estimates of radiated seismic energy es and seismic moment mo that for common events are in excellent agreement with network averaged estimates obtained using local and regional data teleseismic moment estimates are compatible with our regional results but teleseismic energy estimates appear to be nearly an order of magnitude low we estimated the seismic moment of events ranging between mw 2 2 and 7 3 and energy estimates for which we had measured at least 70 of the total energy generally events above mw 3 3 we use these estimates to examine the behavior of derived parameters such as the orowan stress drop 2 es mo while the earthquakes we studied have a small range in orowan stress drop generally between 0 1 and 20 mpa they show a strong tendency for orowan stress drop to increase with moment approximately as mo0 25 we believe this is a source effect and is not due to inadequate bandwidth or attenuation correction and note that this trend appears to continue for microearthquakes as described in a recent deep borehole study in southern california many of the large high stress drop earthquakes show complexity in their moment rate spectra near the corner frequency and cannot be fit by a simple square model instead above the first corner frequency the spectral decay ranges between f 1 0 and f 1 5 this leads to larger estimates of radiated energy than predicted with a simple square model and has implications for seismic hazard estimation coda envelopes have three main advantages over direct arrivals for estimating seismic moment and energy 1 coda amplitudes vary little with geology and source radiation anisotropy and allow accurate single station applications 2 path corrected coda amplitude measurements can be applied to very large regions allowing a comparison of source parameters throughout the western united states using a common methodology and stations 3 because long period coda can last for hours for large local and regional events it allows the analysis of seismograms with clipped early arrivals

characterization of earthquake induced ground motion from the l aquila seismic sequence of 2009 italy summary based only on weak motion data we carried out a combined study on region specific source scaling and crustal attenuation in the central apennines italy our goal was to obtain a reappraisal of the existing predictive relationships for the ground motion and to test them against the strong motion data peak ground acceleration pga peak ground velocity pgv and spectral acceleration sa gathered during the mw 6 15 l aquila earthquake 2009 april 6 01 32 utc the l aquila main shock was not part of the predictive study and the validation test was an extrapolation to one magnitude unit above the largest earthquake of the calibration data set the regional attenuation was determined through a set of regressions on a data set of 12 777 high quality high gain waveforms with excellent s n ratios 4259 vertical and 8518 horizontal time histories seismograms were selected from the recordings of 170 foreshocks and aftershocks of the sequence the complete set of all earthquakes with ml 3 0 from 2008 october 1 to 2010 may 10 all waveforms were downloaded from the iside web page http iside rm ingv it iside standard index jsp a web site maintained by the istituto nazionale di geofisica e vulcanologia ingv weak motion data were used to obtain a moment tensor solution as well as a coda based moment rate source spectrum for each one of the 170 events of the l aquila sequence 2 8 mw 6 15 source spectra were used to verify the good agreement with the source scaling of the colfiorito seismic sequence of 1997 1998 recently described by malagnini et al 2008 finally results on source excitation and crustal attenuation were used to produce the absolute site terms for the 23 stations located within 80 km of the epicentral area the complete set of spectral corrections crustal attenuation and absolute site effects was used to implement a fast and accurate tool for the automatic computation of moment magnitudes in the central apennines

modulation and amplification of climatic changes in the northern hemisphere by the indian summer monsoon during the past 80 k y high frequency suborbital variations dansgaard oeschger cycles characterize the climatic history of the northern hemisphere as observed in greenland ice cores deep sea sediments of the north atlantic the californian borderland the arabian sea the south china sea and the chinese loess area paleoceanographic data from core kl126 from the bay of bengal in combination with data from the other asian monsoonal areas indicate that the feedback processes involving snow and dust of the tibetan plateau vary the summer monsoon capacity to transport moisture into central south asia and into the atmosphere we postulate that the summer monsoon initiates amplifies and terminates these cycles in the northern hemisphere

observed variations of earthquake motion across a sediment filled valley the response to earthquake motion of a site in one sediment filled valley was observed to depend strongly on frequency and the position of the site within the valley and weakly on the input signal s azimuth and incidence angles the observed input motion was weak varying between 10 5 and 10 3 g measurements of ground velocity were made on profiles across and along the valley and simultaneously on two nearby rock sites the valley was 400 m wide and 700 m long with a maximum sediment thickness of 60 m the average seismic impedance contrast between the sediments and underlying basement rock was about 6 1 ratios of fourier spectra from soil sites to spectra from nearby rock sites showed apparent site amplifications of as much as a factor of ten depending strongly on frequency and the distance of the site from the valley edge the scatter in spectral ratios for earthquakes with different azimuths and angles of incidence was about a factor of two thus local site effects that changed the amplitude of incident motion by a factor of two or more could be identified in the records of most earthquakes ground motion at valley edge and mid valley sites separated by less than 100 m differed by as much as a factor of five this difference could cause large differential motion in structures spanning these sites a theoretical flat layer model of sediment response predicts the average behavior of the middle of the valley but not that of the valley edge the lowest frequency responance apparently involves the sediments across the width of the valley not just the vertical column of soil beneath each site

limited global change due to the largest known quaternary eruption toba 74 kyr bp abstract the 74 kyr bp super eruption of toba volcano in sumatra is the largest known quaternary eruption on the basis of preserved deposits the eruption magnitude has been estimated at 7 10 15 kg 2800 km 3 of dense magma the largest sulphate anomaly in the greenland ice sheet project 2 core has been identified as fallout from toba s stratospheric aerosol veil correlation of the sulphate and oxygen isotope stratigraphy of the ice core suggests that the toba eruption might have played a role in triggering a millennium of cool climate prior to dansgaard oeschger event 19 although a comparable stadial preceded event 20 a possible 6 yr duration volcanic winter immediately following the eruption has also been proposed as the cause of a putative bottleneck in human population supporting in a general way the garden of eden model for the origin of modern humans however along with counter arguments regarding the timing of any demographic crash there remain major gaps in our understanding of the 74 kyr bp toba eruption that hinder attempts to model its global atmospheric and climatic and hence human consequences the tephra record reveals basic aspects of the eruption style but calculations of the duration and hence intensity and plume height of the event are poorly constrained furthermore estimates of the sulphur yield of the erupting magma central to predictions of its atmospheric and climatic impacts vary by two orders of magnitude 3 5 330 10 10 kg previous estimates of globally averaged surface cooling of 3 5 c after the eruption are probably too high a figure closer to 1 c appears more realistic the volcanological uncertainties need to be appreciated before accepting arguments for catastrophic consequences of the toba super eruption

the mean and seasonal circulation off southwest nova scotia abstract long term measurements off southwest nova scotia reveal the following features of the mean circulation a a westward longshore coastal current 4 10 cm s 1 b an anticyclonic gyre around brown bank 5 15 cm s 1 and c an upwelling circulation off cape sable 1 2 cm s 1 at bottom the gyre circulation appears permanent but the coastal current and upwelling exhibit annual variations of the same order as the means there is a distinct annual signal in the longshore transport at cape sable maximum westward in winter whereas the mean transport 0 14 106 m4 s 1 is consistent with both geostrophic estimates and budget requirements in the gulf of marine strong seasonal cycles are also found in the salinity and density fields at cape sable which appear to be controlled both by buoyancy input from the coastal current and local mixing effects a linear diagnostic model indicates that the primary dynamical balance for the circulation is between a longshore pressure gradient and longshore mean

stratigraphy of the toba tuffs and the evolution of the toba caldera complex sumatra indonesia during the past 1 2 m y a magma chamber of batholithic proportions has developed under the 100 by 30 km toba caldera complex four separate eruptions have occurred from vents within the present collapse structure which formed from eruption of the 2800 km3 youngest toba tuff ytt at 74 ka eruption of the three older toba tuffs alternated from calderas situated in northern and southern portions of the present caldera the northern caldera apparently developed upon a large andesitic stratovolcano the calderas associated with the three older tuffs are obscured by caldera collapse and resurgence resulting from eruption of the ytt samosir island and the uluan block are two sides of a single resurgent dome that has resurged since eruption of the ytt samosir island is composed of thick ytt caldera fill whereas the uluan block consists mainly of the oldest toba tuff ott in the past 74000 years lava domes have been extruded on samosir island and along the caldera s western ring fracture this part of the ring fracture is the site of the only current activity at toba updoming and fumarolic activity the toba eruptions document the growth of the laterally continuous magma body which eventually erupted the ytt repose periods between the four toba tuffs range between 0 34 and 0 43 m y and give insights into pluton emplacement and magmatic evolution at toba

the respiratory health hazards of volcanic ash a review for volcanic risk mitigation studies of the respiratory health effects of different types of volcanic ash have been undertaken only in the last 40 years and mostly since the eruption of mt st helens in 1980 this review of all published clinical epidemiological and toxicological studies and other work known to the authors up to and including 2005 highlights the sparseness of studies on acute health effects after eruptions and the complexity of evaluating the long term health risk silicosis non specific pneumoconiosis and chronic obstructive pulmonary disease in populations from prolonged exposure to ash due to persistent eruptive activity the acute and chronic health effects of volcanic ash depend upon particle size particularly the proportion of respirable sized material mineralogical composition including the crystalline silica content and the physico chemical properties of the surfaces of the ash particles all of which vary between volcanoes and even eruptions of the same volcano but adequate information on these key characteristics is not reported for most eruptions the incidence of acute respiratory symptoms e g asthma bronchitis varies greatly after ashfalls from very few if any reported cases to population outbreaks of asthma the studies are inadequate for excluding increases in acute respiratory mortality after eruptions individuals with pre existing lung disease including asthma can be at increased risk of their symptoms being exacerbated after falls of fine ash a comprehensive risk assessment including toxicological studies to determine the long term risk of silicosis from chronic exposure to volcanic ash has been undertaken only in the eruptions of mt st helens 1980 usa and soufriere hills montserrat 1995 onwards in the soufriere hills eruption a long term silicosis hazard has been identified and sufficient exposure and toxicological information obtained to make a probabilistic risk assessment for the development of silicosis in outdoor workers and the general population a more systematic approach to multi disciplinary studies in future eruptions is recommended including establishing an archive of ash samples and a website containing health advice for the public together with scientific and medical study guidelines for volcanologists and health care workers

toba ash on the indian subcontinent and its implications for correlation of late pleistocene alluvium the toba ash occurs extensively in the indian subcontinent and marks a ca 74 000 yr old event in the bay of bengal and indian ocean it is about 10 cm thick whereas in several alluvial basins it is usually 1 3 m thick the latter occurs in a partly reworked state but as nearly chemically pure first cycle sediments the ash has a broad northwesterly dispersal pattern samples of ash from the indian subcontinent compare closely with the youngest 74 000 yr b p toba tuff and the deep sea toba ash in bulk chemical composition ree signature and bubble wall shard morphology however a more proximally located and thicker 2 5 m ash bed from the alluvial basins in the gneissic area and close to east coast has a lower magnitude negative eu anomaly possibly because of minor contamination by feldspathic silt quaternary sediments in the central narmada and middle son basins contain rich late and middle pleistocene mammalian and cultural records based on the presence of the ash layer marker and stratigraphic relations late pleistocene sediments within the subcontinent can be correlated with those from central india and the deep sea

coda derived source parameters of earthquakes and their scaling relationships in the korean peninsula we applied the coda derived source spectrum method of mayeda et al 2003 to earthquakes in and around the korean peninsula after empirical calibra tions we derived source spectra of the earthquakes from the coda derived spectra we estimated valuable source parameters such as the seismic moment corner frequency and radiated energy for small events with mw 3 5 we derived simple linear relation ships between the coda spectral amplitudes and local magnitudes reported from the korea meteorological administration and korea institute of geoscience and mineral resources these relationships can be used to estimate stable local magnitudes for future earthquakes using a small number of stations to investigate whether the earth quakes occurring in this region obey self similarity we examined the scaling relation ships between dynamic and static source parameters such as the corner frequency radiated energy and scaled energy versus seismic moment the scaling relationship between the corner frequency and seismic moment showed clear nonself similarity with a scaling parameter of 0 54 this value is more or less consistent with previous results for different regions scaling relations of radiated energy and scaled energy versus the seismic moment also show size dependent behavior that cannot be explained by self similarity this result implies that the rupture dynamics of small and large earthquakes are different in this region our observation provides further evidence supporting the nonself similarity of earthquakes

circulation hydrographic structure and mixing at tidal fronts the view from georges bank and discussion the steep slope on the northern side of georges bank and its location in the fundy maine tidal system result in a persistent summertime frontal system comprising a tidal mixing front and a stratified tide topography interaction at the bank edge recent field studies have provided a high resolution description of the circulation hydrographic structure and mixing in the region frontal features include an along front residual jet a surface convergence zone regular variations in frontal structure and position over the tidal period and tidal modulation cycle large amplitude internal waves and strong spatial and temporal variations in small scale turbulence the observations suggest that the magnitude of cross front and vertical exchange in frontal regions can be site specific depending on the relative importance of the underlying physical processes

palaeoenvironmental response to the 74 ka toba ash fall in the jurreru and middle son valleys in southern and north central india distal deposits of rhyolitic volcanic ash from the 74 ka supervolcanic eruption of toba in northern sumatra are preserved in numerous river valleys across peninsular india the toba eruption is hypothesized to have resulted in climate change and the devastation of ecosystems and hominin populations this study reports the results of the analysis of sediments and stratigraphical sequences from sites in the jurreru and middle son valleys in southern and north central india the aim of the study is to determine the extent of palaeoenvironmental change in both valleys as a result of the ash fall inferences based on evidence from the jurreru valley are more detailed where pre and post toba palaeoenvironmental changes are divided into seven phases the results indicate that ash fall deposits in both valleys underwent several phases of reworking that possibly lasted for several years indicating that ash was mobile in the landscape for a considerable period of time prior to burial this could have enhanced and lengthened the detrimental effects of the ash on vegetation and water sources as well as animal and hominin populations