estimation of coda wave attenuation for nw himalayan region using local earthquakes abstract the attenuation of seismic wave energy in nw himalayas has been estimated using local earthquakes most of the analyzed events are from the vicinity of the main boundary thrust mbt and the main central thrust mct which are well defined tectonic discontinuities in the himalayas the time domain coda decay method of a single back scattering model is employed to calculate frequency dependent values of coda q qc a total of 36 local earthquakes of magnitude range 2 1 4 8 have been used for q c estimation at central frequencies 1 5 3 0 6 0 9 0 12 0 and 18 0 hz through eight lapse time windows from 25 to 60 s starting at double the time of the primary s wave from the origin time the estimated average frequency dependence quality factor gives the relation q c 158 f 1 05 while the average q c values vary from 210 at 1 5 hz to 2861 at 18 hz central frequencies the observed coda quality factor is strongly dependent on frequency which indicates that the region is seismic and tectonically active with high heterogeneities the variation of the quality factor q c has been estimated at different lapse times to observe its effect with depth the estimated average frequency dependent relations of q c vary from 85 f 1 16 to 216 f 0 91 at 25 to 60 s lapse window length respectively for 25 s lapse time window the average q c value of the region varies from 131 36 at 1 5 hz to 2298 397 at 18 hz while for 60 s lapse time window its variation is from 285 95 at 1 5 hz to 2868 336 at 18 hz of central frequency the variation of q c with frequency and lapse time shows that the upper crustal layers are seismically more active compared to the lower lithosphere the decreasing value of the frequency parameter with increasing lapse time shows that the lithosphere acquires homogeneity with depth

long term development of short period gravity waves in middle europe 1 the long term development of short period gravity waves is investigated using the analysis of temperature fluctuations in the mesosphere the temperature fluctuations are quantified by their standard deviations based on data from oh measurements at wuppertal 51 n 7 e and hohenpeissenberg 48 n 11 e obtained from 1994 to 2009 at 87 km altitude the temperatures are fourier analyzed in the spectral regime of periods between 3 and 10 min the resulting oscillation amplitudes correlate very well with the standard deviations shortest periods are taken as ripples that are indicative of atmospheric instabilities breaking gravity waves in consequence the standard deviations are used as proxies for gravity wave activity and dissipation this data set is analyzed for seasonal intradecadal and interdecadal trend variations seasonal changes show a double peak structure with maxima occurring slightly before circulation turnaround in spring and autumn this is found to be in close agreement with seasonal variations of turbulent eddy coefficients obtained from waccm 3 5 the intradecadal variations show close correlations with the zonal wind and the annual amplitude of the mesopause temperature the long term trend 16 years indicates an increase of gravity wave activity of 1 5 per year correspondences with dynamical parameters such as zonal wind speed and summer length are discussed

two magmatic series with island arc affinities within the vourinos ophiolite within the vourinos ophiolite evidence of two magmatic series has been preserved in cognate cumulates and in effusive and hypabyssal rocks which constitute the earlier krapa sequence and the younger asprokambo sequence the asprokambo dyke basic magmas which are poor in incompatible elements and relatively ni and cr rich bear some resemblance to very low ti basalts transitional to boninites found in subduction related arcs or interarc basins krapa series magmas from sills massive and pillow lavas are best equated with low k tholeiites of island arc suites compositions of al and ti poor cpx in lavas from both series are comparable to those in island arc basalts the asprokambo cpx being richer in ca and cr than those from krapa the large volume of cumulates from the krapa sequence displays the following crystallization order ol sp cpx pl opx mt periodic influx of fresh magma batches into the magma chamber occurred mainly during the formation of the lower cumulates wehrlite ol clinopyroxenite and melagabbro the upper cumulates gabbronorite and leucogabbronorite with minor mt bearing gabbronorite crystallized in the upper levels of a magma chamber which became progressively smaller with time in the asprokambo sequence ol sp opx cpx pi and amph are the successively crystallizing phases the ortho to heteradcumulates consist of websterite pl websterite gabbronorite amphibole bearing leuconorite diorite and granophyre in cumulates especially in the lower krapa sequence significant subsolidus reaction was probably induced by the persistence of high geothermal gradients linked to continuous magmatism petrological features indicate that the evolution of the krapa series is more compatible with an intermediate fractional equilibrium crystallization history in an initially open system whereas nearly perfect fractional crystallization in closed system may have occurred in the small asprokambo magma chambers chemical variations in the lavas of both series can be explained in terms of crystallization of the observed cumulates significantly the asprokambo intrusives have igneous mg hornblende and vanadium bearing chromian aluminous titaniferous magnetite crystallization of which is responsible for the calcalkaline evolutionary trend of these rocks major and trace element modelling necessitates a two stage model for the petrogenesis of the vourinos parental melts involving high degree remelting of previously depleted mantle sources favoured by the influx of subduction derived hydrous fluids the primary magmas parental to the krapa and asprokambo series could have been derived respectively by 20 and 30 equilibrium partial fusion of variably depleted lherzolitic sources leaving residua having a harzburgitic to dunitic composition

first measurements of neutral wind and turbulence in the mesosphere and lower thermosphere over taiwan with a chemical release experiment 1 neutral winds and turbulence structure in the mesosphere and lower thermosphere were measured with a sounding rocket chemical release experiment carried out in taiwan trimethyl aluminum tma was used as a tracer of the drift of the background atmosphere the results show that the measured neutral wind had a maximum speed of 154 m s at a height around 105 km the wind vectors were found to rotate clockwise with height in the altitude range from about 98 to 121 km on the basis of the hodograph analysis of the measured neutral wind vectors an upward propagating inertio gravity wave with intrinsic period of 11 2 hours and vertical wavelength of 19 5 km was believed to be primarily responsible for the height variations of the neutral wind and the richardson number large vertical wind shears were observed near 100 km and 106 km turbulent structures were observed in much of the trail below 110 km but there were enhanced structures in the altitude range between the two large shears i e at and near the altitude of the maximum wind speed comparing the positions of the turbulent features with expected atmospheric stability zones induced by an upward propagating gravity wave indicates that the turbulence structures were primarily located within the wave induced convectively unstable zone the structures are therefore interpreted as counterrotating vortices within the convective instability zone of a breaking gravity wave moreover the relation between the horizontal separations l about 1 8 km of the turbulent structures and the vertical extent h about 0 7 and 1 5 km of the wind shear zones with richardson numbers less than 0 25 did not conform to the predicted l h ratio of a factor of approximately 8 predicted by simple linear kelvin helmholtz instability theory for the primary billow structures associated with the instability these results suggest that the observed structures were not the primary billows but were more likely associated with a secondary instability such as the counterrotating vortices that develop later in the evolution of the instability in general the observations reported here support the interpretation that the turbulence evident in the trail was very likely generated in the convectively unstable zone induced by the inertio gravity wave propagating through the region with large temperature gradients 32 k km produced by wave breaking processes

observations of the breakdown of mountain waves over the andes lidar observatory at cerro pachon on 8 9 july 2012

attenuation of high frequency seismic waves in eastern iran we investigated the frequency dependent attenuation of the crust in eastern iran by analysis data from 132 local earthquakes having focal depths in the range of 5 25 km we estimated the quality factor of coda waves q c and body waves q p and q s in the frequency band of 1 5 24 hz by applying the single backscattering theory of s coda envelopes and the extended coda normalization method respectively considering records from recent earthquakes rigan m w 6 5 2010 12 20 goharan m w 6 2 2013 5 11 and sirch m w 5 5 2013 1 21 the estimated values of q c q p and q s vary from 151 49 63 6 and 93 14 at 1 5 hz to 1 994 124 945 84 and 1 520 123 at 24 hz respectively the average frequency dependent relationships q q o f n estimated for the region are q c 108 10 f 0 96 0 01 q p 50 5 f 1 01 0 04 and q s 75 6 f 1 03 0 06 these results evidenced a frequency dependence of the quality factors q c q p and q s as commonly observed in tectonically active zones characterized by a high degree of heterogeneity and the low value of q indicated an attenuative crust beneath the entire region

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

qc qβ qi and qs attenuation parameters in the umbria marche italy region the attenuation of coda and s waves has been inferred for the umbria marche region central italy using seismic waveforms collected during the 1997 seismic crisis the selected dataset is composed of 343 small magnitude 1 4 ml 4 2 earthquakes recorded at a temporary array composed of 23 seismic stations the sato 1977 method based on the assumption of single isotropic scattering has been used to infer qc considering three different lapse times 20 30 and 40 s the coda normalization method aki 1980 has been used to infer q both qc and q show a clear frequency dependence with a different frequency dependent parameter the frequency dependence of qc is comparable with that previously found in the same area and around it using the method of wennerberg 1993 intrinsic and scattering attenuation have been separated intrinsic attenuation is found to be close to coda attenuation and dominates over scattering dissipation coda q increases with increasing lapse time but at a rate smaller than that observed in other areas of the earth coda and intrinsic attenuation in the umbria marche region are very high compared to other seismic active regions of the earth the retrieved high values of intrinsic attenuation may be explained in terms of the previously hypothesized fluid pressurized regime of the crust in the central apennines miller et al 2004

temporal variations of qc 1 and b values associated to the december 2000 january 2001 volcanic activity at the popocatepetl volcano mexico abstract we correlated temporal variations of coda attenuation q c 1 at 6 hz and b values with the 11 december 2000 23 january 2001 major eruptive activity at the popocatepetl volcano mexico we interpreted a total of 225 volcanic earthquakes with magnitudes between 1 9 and 3 3 located between 2 and 8 km from the summit of the volcano and registered from january 1999 to june 2001 q c 1 was estimated using a single scattering model and values of b were obtained applying the method of maximum likelihood our results indicate that from january 1999 to march 2000 period 1 q c 1 varied within the same range without significant changes then values of q c 1 steadily decreased during april mid december 2000 period 2 from about mid december 2000 onset of the major volcanic activity up to february 2001 period 3 q c 1 sharply increased reaching its peak value from march to june 2001 period 4 q c 1 decreased and increased in response to the post eruptive phase of dome formation and destruction process that took place during periods 2 and 3 average b values behaved opposite to the q c 1 trend within period 2 when q c 1 decreased b slowly increased at the start of period 3 b reached its peak value and returned to low values by the end of this time interval we associate the temporal changes of the two analyzed parameters to variations of pressure and or the variation in the degree of saturation of pore fluids that took place before during and after the major eruption during periods 2 and 3 q c 1 correlated negatively with b with a correlation coefficient of 0 61 and 0 83 respectively the significance of correlation cannot be rejected at the confidence level of 0 975 our observations may have important implications for future prediction studies of large eruptions at the popocatepetl volcano

role of the kopili fault in deformation tectonics of the indo burmese arc inferred from the rupture process of the 3 january 2016 mw 6 7 imphal earthquake the burmese arc is a peculiar plate boundary where there exists an eastward subducted indian slab but the current tectonics of the region are predominantly governed by a northward strike slip motion of the indian plate past the burmese plate as evidenced by seismic and global positioning system data the shallower portion of the dipping indian slab is characterized mostly by earthquakes with strike slip type focal mechanisms with roughly northwest and northeast trending fault planes although there is no clear evidence for the choice of rupture planes in the present study we use teleseismic broadband waveforms to model the rupture propagation of an m w 6 7 strike slip earthquake of 3 january 2016 that occurred in the indian city of imphal and infer the fault plane orientation the result indicates a right lateral strike slip motion along a n21 w plane which is confirmed by both waveform fitting and distribution of aftershocks interestingly this earthquake occurred at the intersection of three major faults in this region the churachandpur mao fault bounding the india and burma plates the dauki fault south of the shillong plateau and the kopili fault separating the shillong plateau from the brahmaputra valley this raises various possibilities for interpreting this event however based on the finite fault inversion we infer that this earthquake occurred on the kopili fault running northwest southeast from bhutan himalaya down to the burmese arc and manifested as a right lateral strike slip motion in response to the northward motion of the indian plate and a counterclockwise rotation of the brahmaputra valley we further interpret that the overall deformation in the burmese arc region is accommodated by northward slivering of the eastward subducted indian lithospheric slab along a series of northwest to north south trending right lateral strike slip faults from west to east as the indian plate moves northward past the burma and sunda blocks

in situ observations of instabilities in the mesopause region using foil chaff technique during the waves in airglow structures experiment wave campaigns 1 in order to investigate the dynamics of the mesopause region foil chaff experiments were carried out successfully during the wave2000 and wave2004 campaigns at kagoshima japan in the wave2004 campaign the height profiles of the horizontal and vertical wind speeds were obtained the wind shear layers of 40 m s km were located around the altitudes of 89 and 95 km and the profile of the richardson number reveals the existence of dynamically unstable layers at about the same height region ripple observations using the all sky imagers also support the possibility of dynamical instabilities in the wave2000 campaign a prominent small scale feature around an altitude of 90 5 km appeared in both the horizontal and vertical chaff motions these results demonstrate that the foil chaff technique is a valuable tool for in situ observation of small scale turbulence features around the mesopause

pmc turbo studying gravity wave and instability dynamics in the summer mesosphere using polar mesospheric cloud imaging and profiling from a stratospheric balloon the polar mesospheric cloud turbulence experiment pmc turbo was designed to observe and quantify the dynamics of small scale gravity waves gws and instabilities leading to turbulence in the upper mesosphere during polar summer using instruments aboard a stratospheric balloon the pmc turbo scientific payload comprised seven high resolution cameras and a rayleigh lidar overlapping wide and narrow camera field of views from the balloon altitude of 38 km enabled resolution of features extending from 20 m to 100 km at the pmc layer altitude of 82 km the rayleigh lidar provided profiles of temperature below the pmc altitudes and of the pmcs throughout the flight pmcs were imaged during an 5 9 day flight from esrange sweden to n canada in july 2018 these data reveal sensitivity of the pmcs and the dynamics driving their structure and variability to tropospheric weather and larger scale gws and tides at the pmc altitudes initial results reveal strong modulation of pmc presence and brightness by larger scale waves significant variability in the occurrence of gws and instability dynamics on timescales of hours and a diversity of small scale dynamics leading to instabilities and turbulence at smaller scales at multiple times the overall field of view was dominated by extensive and nearly continuous gws and instabilities at horizontal scales from 2 100 km suggesting sustained turbulence generation and persistence at other times gws were less pronounced and instabilities were localized and or weaker but not absent an overview of the pmc turbo experiment motivations scientific goals and initial results is presented here

moho geometry and upper mantle images of northeast india 1 images of the crust and mantle beneath northeast india obtained by 2d migration of 1000 broadband p receiver functions clearly trace a northward dipping moho from the himalayan foredeep reaching depths up to 50 km further north beneath the himalayan convergence zone also these images reveal presence of largely coherent 410 km and 660 km discontinuities that conform to the iasp91 model marginal variations in the depth of the 410 km interface are observed that appear region specific the thickness of the mantle transition zone does not deviate significantly from a global average of 250 km interestingly our results reveal consistent presence of a signal from an interface around 300 km origin of such a boundary known as x discontinuity and unrelated to the lehmann discontinuity is discussed possible presence of the x discontinuity from the indian region is reported here for the first time

attenuation of coda waves in new england abstract seismic wave attenuation was measured in new england from the time domain decay of coda wave amplitudes on narrow bandpass filtered seismograms of local earthquakes the frequency band of interest was 0 75 to 10 hz q c f was found to increase with frequency across this band but there was also a difference between the q c f values for short t t 100 sec lapse times of coda wave propagation for the short lapse time data corresponding to wave paths primarily in the upper crust q c f increases from 400 at 3 hz to 1300 at 10 hz for the large lapse time data corresponding to wave paths in the lower crust and upper mantle q c f was found to vary from 660 at 1 hz to 1500 at 10 hz if we interpret this dataset in terms of a model incorporating both scattering and anelastic attenuation we find that the mean free path of seismic waves over this frequency band is 80 km for short lapse times and 400 km for long lapse times if we assume that scattering is entirely responsible for the observed attenuation we find that the minimum mean free path for short lapse times is about 75 km over all frequencies whereas for long lapse times the minimum mean free path decreases from 400 km at 0 75 hz to 90 km at 10 hz

airglow imaging observations of small scale structures driven by convective instability in the upper mesosphere over tirunelveli 8 7 n 1 airglow imaging observations of broadband oh meinel band emissions made on the night of 20 january 2007 from the tropical indian site tirunelveli 8 7 n 77 8 e reveal large and small scale wave features that are aligned perpendicular to each other and that are associated with gravity wave dynamics the large scale waves were the signatures of propagating quasi monochromatic qm waves whereas the small scale features were identified to be ripples generated by convective instability in the mesosphere lower thermosphere mlt region the qm waves showed consistent propagation toward the northwest direction throughout the observation period of 4 5 hr whereas the ripples that manifested as short lived patches in the airglow images were transient and did not show any prominent phase propagation in addition to these well resolved structures in images we infer the presence of waves with relatively longer observed time periods compared with the observed time period of qm waves from the spectrum of the time series generated with zenith intensity values derived from the images from the complementary wind and temperature data obtained with co located mf radar and sounding of atmosphere with broad band emission radiometry on the thermosphere ionosphere mesosphere energetics and dynamics mission an attempt is made to understand the dynamic processes occurring in the vicinity of the mesopause during the night of 20 january 2007 the uniqueness of the present observations is that there were short lived ripple patches seen in various parts of the sky during the entire observation period of 4 5 hr the precipitation rates obtained by the tropical rainfall measuring mission satellite mission suggest that the deep convective activity occurring over the equatorial eastern indian ocean provided a plausible source mechanism for sustained generation of the waves observed over tirunelveli during this night

separation of intrinsic and scattering seismic attenuation in the southern apennine zone italy summary scattered waves observed at the seismographs of the national italy s seismic network have been used to investigate the intrinsic dissipation and scattering properties of the lithosphere under the southern apennines italy first we investigate the coda q properties then we apply the mltw analysis in the hypothesis of velocity and scattering coefficient constant with depth and finally we interpret these results with the aid of numerical simulations in a medium with depth dependent velocity and scattering coefficient results obtained in the hypothesis of a uniform model show that a low scattering q 1 and a relatively higher intrinsic q 1 characterize the lithosphere of the southern apennines numerical simulations of the seismogram energy envelopes were performed hypothesizing a strongly scattering crust and trasparent upper mantle both with reasonable intrinsic dissipation coefficients in these symplifying assumptions the theoretical curves calculated for the homogeneous model fit to the synthetic envelopes with scattering attenuation coefficients always greater than the synthetic values this results lead to the consideration that scattering q 1 obtained using mltw analysis under the assumption of uniform medium are overestimated the values of the scattering q 1 estimated for apennines at low frequency 1 2 hz in the hypothesis of uniform medium are of the same order of those obtained in several areas around the world the estimates obtained for frequencies ranging from 2 to 12 hz are very low if compared with those obtained in the same hypothesis for other areas around the world coda q 1 closely resembles intrinsic q 1

a frequency dependent relation of coda q c for koyna warna region india attenuation properties of the lithosphere around the koyna warna seismic zone is studied by estimating the coda q c from 30 local earthquakes of magnitude varying from 1 5 to 3 8 an average lapse time of 65 sec used in the single scattering model sampled a circular area with an average radius of 114 km the estimated q c values show a frequency dependent relation q c 169 f0 77 and range from 169 at i hz to 1565 at 18 hz a comparison of worldwide q studies reveals that for a large frequency range the q for active regions is low as compared to that for stable regions however south carolina and norway are exceptions in that their q is low in the low frequency range while new england and north iberia are exceptions as they have a q value similar to that for active regions like spain turkey italy and garhwal himalaya stih in the higher frequency range in contrast to this the q for the koyna warna area which belongs to a stable region is low in the entire frequency range as compared to the stable regions and similar to the active stih regions

regional variation of coda wave attenuation in northeast india an understanding of the physical state of the medium abstract in this study an attempt has been made to estimate spatial variation in attenuation characteristics in northeast india using coda q the entire study region is divided into three sub regions for this purpose estimated average frequency dependencies of coda wave attenuation for 30 s window length are qc f 135 7f0 99 0 03 qc f 109 7f1 10 0 03 and qc f 90 2f1 04 0 02 for shillong plateau mikir hills and surrounding river valley and indo burma ranges respectively it is observed that q0 is greater for the shillong plateau than the other sub regions this indicates lower attenuation due to more rigid high density material present in this area than the other sub regions the depth variations of the qc q0 and n values were also examined it is observed that the rate of increase of q0 with depth is not uniform for all the sub regions indo burma ranges has the smallest q0 and the largest n values at all depth levels among the three sub regions these results indicate that central part of indo burma ranges is the most attenuative seismically active and heterogeneous in nature however this region has smaller qc values than the other two sub regions for all window lengths up to the 6 hz this means at lower frequencies the subsurface beneath this area is more attenuative compared to the other two sub regions similar trends are observed at 8 10 and 12 hz up to 45 s window lengths for window lengths 55 s central part of indo burma ranges has higher qc values at 10 and 12 hz compared to shillong plateau qc values are lower for shillong plateau compared to the other two regions for window length 55 s at 10 and 12 hz which corresponds to depth levels 90 km such a complicated variation in qc values is a manifestation of complex nature of tectonic regime in northeast india

site dependent coda q at mono craters california abstract the coda q of the early coda of shear waves was determined from a network of seismic stations deployed in the mono craters area during the summer of 1982 coda amplitudes determined from a moving window analysis were fit to single scattering theory with an l1 norm for center frequencies from 1 5 to 12 0 hz we find that station to station variations in coda q observed for frequencies between 6 and 12 hz are well correlated with near site geology coda q for stations on crystalline rocks is larger and more frequency dependent than for stations sited on bishop tuff adjacent to mono craters coda q from sites on bishop tuff away from mono craters is still lower and less frequency dependent these observations suggest that site effects dominate the early coda in the mono craters region and that the single scattering model is inappropriate the mechanisms generating these site effects are inferred to be 1 multiple scattering from resonant structures such as sedimentary basins volcanic edifices variable basement topography and surface topography and 2 near site attenuation

coda wave attenuation for three regions of georgia sakartvelo using local earthquakes abstract seventy two local earthquakes were analyzed and the quality factor q c was calculated for three regions of georgia using the single scattering model in the frequency range of 1 32 hz standard international association of seismology and physics of the earth s interior iaspei routines for the coda q c determination have been used the coda window varied from 35 to 45 s and the lapse time was up to 63 s the epicenter distances and the focal depths of the earthquakes were up to 50 km and 20 km respectively local magnitudes ranged from 1 7 to 4 1 these earthquakes were recorded by three digital seismic stations equipped with broadband guralp cmg40t seismometers the q c values show strong frequency dependence for three regions the value of q c at frequency 1 hz varies from 35 1 5 3 to 83 8 2 and the frequency parameter n increases from 0 890 0 062 to 1 095 0 056 depending on the model of the coda generation and the considered region observed q c values reflect the average attenuation property of the whole crust beneath each region and are correlated with the seismicity pattern and geology in the studied regions

paleoseismic investigations in the kopili fault zone of north east india evidences from liquefaction chronology abstract we report the seismogenic liquefaction signatures observed in the kopili fault zone of the brahmaputra plains ne india this seismically active zone has previously been identified as the assam seismic gap and thus necessitates understanding its past seismicity and implied seismic hazard with this objective paleo seismic studies using seismogenic liquefaction features have been carried out in this region largely covered with the flood plain deposits of kopili and kalang rivers the trenches excavated at two locations revealed extensive liquefaction features with more than 20 sub parallel sand dykes having major orientation in ne sw direction a total of 29 samples from marker horizons have been processed to constrain chronology of the liquefaction features using optically stimulated luminescence osl and 14 c ams dating techniques the age constraints in terms of respective lower and upper bound age brackets for individual dykes suggest three time intervals of their formations i e i 250 25 yr bp ii between 400 to 770 yr bp and iii 900 50 yr bp these new ages of liquefaction features correspond to the occurrence timings of causative seismic events which are in addition to the known historical earthquakes and thus enhance our understanding of the paleoseismic history of this region during past 1000 years

coda q for the state of washington abstract frequency dependent coda q values for subregions of the state of washington have been determined using a time domain coda decay method a total of 95 earthquakes digitally recorded on a regional seismograph network of over 100 short period stations were selected to obtain 206 on scale high signal to noise ratio traces for analysis grouping the data by structural regions of the state showed only small variations in coda q by region other than in a very localized area at mount st helens at mount st helens coda q was significantly lower than for all other areas an average of all of the data except that from the local mount st helens area results in a q relationship of q c 63 f 0 97 for the frequency band 2 to 16 hz there is little variation of this coda q relationship when using sources down to 50 km depth and thereby uniformly sampling the top 50 to 100 km of the crust and upper mantle

characteristics of ripple structures revealed in oh airglow images small scale ripple structures observed in oh airglow images are most likely induced by either dynamic instability due to large wind shear or convective instability due to superadiabatic lapse rate using the data set taken in the mesopause region with an oh all sky imager at yucca ridge field station colorado 40 7 n 104 9 w from september 2003 to december 2005 we study the characteristics and seasonal variations of ripple structures by analyzing the simultaneous background wind and temperature observed by the nearby sodium temperature wind lidar at fort collins colorado 40 6 n 105 w and a nearby medium frequency radar at platteville colorado 40 2 n 105 8 w we are able to statistically study the possible relation between ripples and the background atmosphere conditions characteristics and seasonal variations of ripples are presented in detail in this study the occurrence frequency of ripples exhibits clear seasonal variability with peak in autumn the occurrence of ripples shows a local time dependence which is most likely associated with the solar tides the lifetime and spatial scale of these ripples are typically 5 20 min and 5 10 km respectively and most of the ripples move preferentially either southward or northward however more than half of the observed ripples do not advect with background flow they have higher richardson numbers than those ripples that advect with background flow it is possible that they are not instability features but wave structures that are hard to be distinguished from the real instability features

gravity wave characteristics in the mesopause region revealed from oh airglow imager observations over northern colorado using 5 years of all sky oh airglow imager data over yucca ridge field station co 40 7 n 104 9 w from september 2003 to september 2008 we extract and deduce quasi monochromatic gravity wave gw characteristics in the mesopause region the intrinsic periods are clustered between approximately 4 and 10 min and many of them are unstable and evanescent gw occurrence frequency exhibits a clear semiannual variation with equinoctial minima which is likely related to the seasonal variation of background wind the anomalous propagation direction in january 2006 with strong southward before major warming starting in 21 january and weak southward propagation afterward was most likely affected by stratospheric sudden warming the momentum fluxes show strongly anticorrelated with the tides with 180 out of phase in the zonal component while in the meridional component the easterly maximum occurred approximately 2 6 h after maximum easterly tidal wind however the anticorrelations are both weakest during the summer the dissipating and breaking of small scale and high frequency gw s components could have a potential impact on the general circulation in the mesopause region

climatology and modeling of quasi monochromatic atmospheric gravity waves observed over urbana illinois from analyzing nine months of airglow imaging observations of atmospheric gravity waves agws over adelaide australia 35 s walterscheid et al 1999 have proposed that many of the quasi monochromatic waves seen in the images were primarily thermally ducted here are presented 15 months of observations from february 1996 to may 1997 for agw frequency and propagation direction from a northern latitude site urbana illinois 40 n as adelaide urbana is geographically distant from large orographic features similar to what was found in adelaide the agws seem to originate from a preferred location during the time period around summer solstice in conjunction with these airglow data there exists mf radar data to provide winds in the 90 km region and near simultaneous lidar data which provide a temperature climatology the temperature data have previously been analyzed by states and gardner 2000 the temperature and wind data are used here in a full wave model analysis to determine the characteristics of the wave ducting and wave reflection during the 15 month observation period this model analysis is applied to this and another existing data set recently described by nakamura et al 1999 it is shown that the existence of a thermal duct around summer solstice can plausibly account for our observations however the characteristics of the thermal duct and the ability of waves to be ducted is also greatly dependent on the characteristics of the background wind a simple model is constructed to simulate the trapping of these waves by such a duct it is suggested that the waves seen over urbana originate no more than a few thousand kilometers from the observation site

computation of clear air radar backscatter from numerical simulations of turbulence 2 backscatter moments throughout the lifecycle of a kelvin helmholtz instability 1 franke et al 2011 describe a numerical simulation of the instability and turbulent breakdown of kelvin helmholtz kh billows at a high reynolds number numerical assessment of radar backscatter and accuracies of inferred doppler spectral moments for one test volume those results suggest a potential for significant measurement biases for radars that obtain backscatter from refractive index fluctuations we present in this paper the morphology of computed radar moments throughout the kh instability lifecycle for two radar configurations in order to reveal the evolving character of radar backscatter and compare the radar velocity estimates with true velocities throughout the evolution and to provide guidance and cautions for the interpretation of these dynamics in observational data results reveal strong variations in backscatter moments and character and dependence on radar measurement parameters that should be beneficial in the interpretation of such measurements in the atmosphere backscatter power predictions agree reasonably with observations of such events and their temporal evolutions our results also reveal a potential for significant measurement or sensitivity biases some of which were predicted previously examples include a lack of significant backscatter power in well mixed billow cores suggesting possibly weak turbulence where in fact it may be strongest maximum backscatter power in the billow exteriors where refractive index fluctuations are large but turbulence is weak underestimated vertical velocities within the kh billows at early times and inferred significant vertical velocities where true vertical velocities are near zero at late stages of restratification especially in the edge regions of the turbulence layer

estimation of coda wave attenuation in the east anatolia fault zone turkey in this study the attenuation of coda waves qc f has been estimated for different lapse times and frequencies in the east anatolian fault zone eafz in turkey using a single back scattering model of s coda envelopes the data include 255 earthquakes recorded by ten stations the frequency dependent qc values are estimated at central frequencies of 1 5 3 6 8 12 and 18 hz using 20 30 40 s lapse time windows along this fault zone the frequency dependent qc obtained for all data and lapse time is qc 57 5f0 82 the entire study area is divided into six subregions according to the magnitude of the earthquakes and the location of the fault segments the estimated average frequency dependent relation for all lapse times are q text c left text i right 3 4 3f 0 9 3 for bingol karliova erzincan triple junction q text c left text ii right 56 3f 0 71 for bingol lake hazar segment q text c left text iii right 68 5f 0 75 for lake hazar sincik segment q text c left text iv right 72 5f 0 78 hazar sincik and celikhan golbasi faults q text c left text v right 59 7f 0 87 for kahramanmaras triple junction and q text c left text vi right 67 4f 0 94 for amanos range and karasu basin the lowest qc is determined between bingol and malatya the highest qc value is along amanos range in addition qc values are calculated for each regions at different lapse times the average qc value of the study region varies from 53 11 at 1 5 hz to 498 41 at 18 hz for 20 s lapse time window as its variation is from 116 11 at 1 5 hz to 749 75 at 18 hz of central frequency for 40 s lapse time window the increase of qc with lapse times changes from one subregion to another along the fault zone the rate of increment is significantly higher in bingol karliova erzincan triple junction than in the other subregions this rapid increase of low qc values in the junction reaches the general attenuation characteristics of the fault at 40 s lapse time finally the low q0 and high n values can be attributed to the energy loss as a result of the heterogeneity and activity along the fault zone the increase of qc with frequency lapse time may be related to heterogeneity decreases with depth the rapid increase of qc with depth in bingol karliova erzincan triple junction may be interpreted that the effect of the northern anatolian fault zone is effective in the upper crust is not so deep compared to eafz

teleseismic p wave tomogram of the yellowstone plume 1 inversion of a new data set of teleseismic p wave travel times from three passcal seismic deployments around the yellowstone hotspot reveals a 100 km diameter upper mantle plume that extends from the yellowstone volcanic caldera to 500 km depth and dips 20 to the northwest a monotonic decrease in the velocity perturbation of the plume from 3 2 at 100 km to 0 9 at 450 km is consistent with a uniform thermal anomaly of 180 c where the plume crosses the 410 km discontinuity previous research shows a depression in the 410 km discontinuity consistent with a warm plume fee and dueker 2004 additionally a region of high velocities extends to 250 km beneath the wind river basin in nw wyoming that may represent a convective downwelling of the lithosphere

a fast propagating large scale atmospheric gravity wave observed in the wave2004 campaign 1 the waves in airglow campaign in 2004 wave2004 which aimed to elucidate the formation process of waves in airglow structures from both dynamical and chemical perspectives was conducted using rocket borne and ground based instruments in japan on 17 january 2004 in this experiment we observed a large scale atmospheric gravity wave agw which appeared in both the vertical profiles of sodium density obtained by a na lidar and the horizontal distributions of airglow emission obtained by an all sky imager asi vertical propagation of the agw accompanied by a shortening of its vertical wavelength was clearly visualized using the na lidar data the horizontal wavelength horizontal phase velocity period and propagation direction of the agw were estimated from the asi data as 673 774 km 107 122 m s 1 75 hours and north northeastward respectively using these parameters and the mf radar wind vertical wavelengths of the wave were calculated from the dispersion relation of gravity waves the calculated vertical wavelengths were comparable at altitudes of 85 5 km and 93 25 km to those estimated from the variation of the sodium density using a simple ray tracing technique the agw was traced back to the southern edge of the distorted jet stream near tropopause this result strongly suggests that an unstable baroclinic wave associated with ageostrophic motions in the jet stream was the wave source of the large scale agw observed in the wave2004

coda q in the charlevoix quebec region lapse time dependence and spatial and temporal comparisons coda q is determined in the seismically active charlevoix region quebec using 34 earthquakes recorded on the six station charlevoix local telemetered network for comparison an average value of coda q for southeastern canada is determined from 32 events that occur over a much larger region at lapse times of 20 to 40 sec coda q at 1 hz q at charlevoix and for southeastern canada is 91 4 and 125 10 respectively at a 40 to 80 sec lapse time it is 200 3 and 305 15 respectively the lower q value at charlevoix in comparison with other parts of southeastern canada is in agreement with jin and aki s 1988 finding that q is lower in the vicinity of large earthquakes no statistically significant temporal change in coda q at charlevoix is observed over the 11 yr of data studied a variation of as little as 15 would be statistically apparent ongoing monitoring of coda q in the area is planned using the local network in order to investigate any temporal changes prior to future large earthquakes coda q is found to increase with lapse time lapse time is defined as time elapsed after the origin time this dependence could be due to any of the following nonzero source receiver distance nonisotropic scattering scattering from below the crust multiple scattering or increase of q with depth or with distance from both source and receiver

empirical attenuation of ground motion spectral amplitudes in southeastern canada and the northeastern united states a database of 1700 digital seismograms from 186 earthquakes of mag nitude mn 2 5 5 6 that occurred in southeastern canada and the northeastern united states from 1990 to 2003 was compiled maximum likelihood regression analysis of the database was performed to determine a model for the attenuation of fourier spectral amplitudes for the shear window for the vertical and horizontal component of motion for frequencies from 0 2 to 20 hz fourier amplitudes follow a hinged trilinear attenuation model fourier spectral amplitudes decay as r 1 3 where r is hypocentral distance within 70 km of the source there is a transition zone from 70 to 140 km as the direct waves are joined by strong postcritical reflections where the attenuation is described as r 0 2 spectral amplitudes actually increase with distance in this range for low frequencies beyond 140 km the attenuation is well described by r 0 5 corresponding to geometric spreading in two dimensions the associated model for the regional quality factor for frequencies greater than 1 hz can be ex pressed as q 893f 032 q can be better modeled over a wider frequency range 0 2 20 hz by a polynomial expression log q 3 052 0 393 log f 0 945 log f 2 0 327 log f 3 the polynomial expression accommodates the observation that q values are at a minimum about 1000 near 1 hz and rise at both lower and higher frequencies correction factors for the spectral amplitude model that describe the effects of focal depth on the amplitudes and their attenuation are developed using the subset of events with known focal depth the attenuation model is similar to that determined from an earlier study with more limited data atkinson and mereu 1992 but the enlarged database indicates more rapid near source amplitude decay and higher q the attenuation model is used to play back attenuation effects to determine the apparent source spectrum for each earthquake in the database and hence determine moment magnitude m and brune stress drop the events have moment magnitude in the range from 2 5 to 5 stress drop increases with moment magnitude for events of m 4 3 then appears to attain a relatively constant level in the range from 100 to 200 bars for the larger events as previously noted in atkinson 1993b the results of this study provide a useful framework for improving regional ground motion relations in eastern north america they further our understanding of attenuation in the region through analysis of an enlarged ground motion database in particular the inclusion of the three component broadband data gathered over the last decade allows extension of attenuation models to both horizontal and vertical components over a broad frequency range 0 2 20 hz

concurrent oh imager and sodium temperature wind lidar observation of localized ripples over northern colorado 1 on 3 and 5 september 2002 the oh all sky imager at platteville colorado 40 2 n 104 7 w observed small scale wavelike patterns known as ripples with horizontal wavelengths of 9 km and 7 km and lifetimes of 9 min and 15 min respectively the colorado state university sodium lidar at nearby fort collins colorado 40 6 n 105 w also made concurrent observations of temperature and zonal and meridional winds which allowed us to determine the nature of the ripples observed our observations suggest that the 3 september ripple was induced by a convective instability located at 87 5 km and the 5 september ripple was induced by a dynamic instability at 88 5 km the ripples clearly advected as packets with the background wind lidar measurements also allowed us to relate the directions of wind shear to the phase front alignments of both the ripples and the nearby short period atmospheric gravity waves these spatial relationships provided a meaningful comparison with previously observed ripples as well as with current theoretical models using the 16 hour continuous lidar data set for each case we deduced that long period waves created an unusually large temperature perturbation at the ripple times on 3 september and an unusually large wind shear perturbation on 5 september these perturbations prepared the background atmosphere to be near the verge of local instability but as revealed again by lidar observation it was the superposition of smaller scale perturbations at the time of the ripples that helped to actually reach the conditions required for instability and generation of the ripples

attenuation of high frequency seismic waves in northeast india summary we studied attenuation of s and coda waves their frequency and lapse time dependencies in northeast india in the frequency range of 1 24 hz we adopted theories of both single and multiple scattering to bandpass filtered seismograms to fit coda envelopes to estimate q for coda waves qc and q for s waves qs at five central frequencies of 1 5 3 6 12 and 24 hz the selected data set consists of 182 seismograms recorded at ten seismic stations within epicentral distance of 22 300 km in the local magnitude range of 2 5 5 2 we found that with the increase in lapse time window from 40 to 60 s q0 qc at 1 hz increases from 213 to 278 while the frequency dependent coefficient n decreases from 0 89 to 0 79 both qc and qs increase with frequency the average value of qs obtained by using coda normalization method for ne india has the power law form of 96 8 21 5 f 1 03 0 04 in 1 24 hz we adopted energy flux model efm and diffusion model for the multiple scattered wave energy in three dimensions the results show that the contribution of multiple scattering dominates for longer lapse time close to or larger than mean free time of about 60 s the estimates of qc are overestimated at longer lapse time by neglecting the effects of multiple scattering some discrepancies have been observed between the theoretical predictions and the observations the difference could be due to the approximation of the uniform medium especially at large hypocentral distances increase in qc with lapse time can be explained as the result of the depth dependent attenuation properties and multiple scattering effect

3 d seismic structure of the northeast india region and its implications for local and regional tectonics abstract in this study we attempted to estimate 3 d p wave velocity structure of northeast india region using the first arrival data of local earthquakes that were recorded by about 77 temporary permanent local seismic stations the data set the published bulletins include 3494 p wave travel times and 3064 s p travel times from 980 local earthquakes that were located with a minimum of six observations the located earthquakes having a travel time root mean square rms residual 0 49 s and azimuthal gap 180 are selected to compute a 1 d velocity model for the region which is used as initial model for the subsequent 3 d inversions our results demonstrate that the computed 3 d velocity model has significantly improved hypocenter locations of the selected 980 earthquakes by reducing the rms error 0 06 by about 88 with respect to that by the 1 d velocity model the reconstructed p wave velocity v p structure with relocated events reveal strong heterogeneity in lateral as well as in vertical direction corresponding to the local and regional geology tectonics of the region high v p is mapped beneath the shillong plateau mikir hills and in the vicinity of indo burma ranges at shallower crust v p structure is imaged between the shillong plateau and mikir hills at 20 km depth which corresponds to the kopili fault the kopili fault system extends down to 30 km depth as evidenced by the low v p a high v p is imaged below the mikir hills at 40 km depth which is possibly the stress concentrator for high seismic activity along the kopili fault particularly at the fault end the bengal basin south of the shillong plateau is identified as a low v p zone extending down to a depth of about 20 km that indicates the thick alluvium sediments

coda q in southwestern british columbia canada abstract coda decay rates of 122 locally recorded earthquakes are used to infer frequency dependent coda q values at 21 short period stations in southwestern british columbia canada using the single scattering model coda q values q c are derived for a range of sampling volumes corresponding to maximum lapse times of 36 59 sec and maximum sampling depths of 70 110 km maps of q 0 q c inferred at 1 hz for different sampling volumes show a consistent trend of increasing q 0 to the northeast away from the subduction zone and into the coast belt batholith and decreasing q 0 toward the southeastern most stations near the vedder fault at the southern terminus of the coast belt q 0 increases gradually with sampling volume at all stations the dependence of q c on frequencies between 2 and 16 hz for different stations varies but on average ranges from 280 at 2 hz to 850 at 16 hz for sampling volumes that extend to depths of 90 km an average of all data for the same sampling volume size gives a relationship of q c 110 f 0 72 for frequencies in the 2 to 16 hz range which suggests significant differences in lithospheric coda attenuation properties in comparison with northwestern washington state where q c 63 f 0 97 changes in coda q correlate with the volume of brittle and fractured continental and subducting oceanic lithosphere sampled

the shape of ground motion attenuation curves in southeastern canada the shape of the attenuation curve of the fourier spectrum of acceleration is established for southeastern canada from empirical data the dataset is comprised of 1200 digital vertical component seismograms from 100 earthquakes recorded on 30 stations of the eastern canada telemetered network the distance range of the observations is 10 to 1700 km focal depths are from 5 to 30 km results indicate that the attenuation curve has three distinct sections at distances less than 70 km corresponding to attenuation of the direct wave amplitudes decay slightly more rapidly than 1 r r 1 1 between 70 and 130 km where the direct wave is joined by sms spectral amplitudes are approximately constant beyond 130 km corresponding to the lg phase amplitudes decay at a rate that is consistent with r 0 5 and q 670 f 0 33 the findings support the hypothesis of burger et al 1987 that postcritical reflections from the moho discontinuity play an important role in determining the shape of the attenuation curve however the influence of sms is subtle allowing the shape to be approximated by simple functional forms for example the commonly assumed bilinear form r 1 r 0 5 with frequency dependent q fits well if the transition from direct wave to lg spreading is placed at approximately 60 km a linear form r 1 over all distances with constant q 2000 also provides a satisfactory fit overall we find little evidence for the dependence of attenuation on focal depth or tectonic province

large and great earthquakes in the shillong plateau assam valley area of northeast india region pop up and transverse tectonics abstract the tectonic model of the shillong plateau and assam valley in the northeast india region the source area for the 1897 great earthquake ms 8 7 and for the four 1869 1923 1930 and 1943 large earthquakes m 7 0 is examined using the high precision data of a 20 station broadband seismic network about 300 selected earthquakes m 3 0 recorded during 2001 2009 are analysed to study the seismicity and fault plane solutions the dominating thrust reverse faulting earthquakes in the western plateau may be explained by the proposed pop up tectonics between two active boundary faults the oldham brahmaputra fault to the north and the dapsi dauki thrust to the south though the northern boundary fault is debated the more intense normal and strike slip faulting earthquakes in the eastern plateau mikir massif and in the assam valley on the other hand are well explained by transverse tectonics at the long and deep rooted kopili fault that cuts across the himalaya and caused the 2009 bhutan earthquake mw 6 3 it is conjectured that the complex tectonics of the shillong plateau and transverse tectonics at the kopili fault make the region vulnerable for impending large earthquake s

body wave crustal attenuation characteristics in the garhwal himalaya india we estimate frequency dependent attenuation of p and s waves in garhwal himalaya using the extended coda normalization method for the central frequencies 1 5 2 3 4 6 8 10 12 and 16 hz with earthquake hypocentral distance ranging from 27 to 200 km forty well located local earthquake waveforms were used to study the seismic attenuation characteristics of the garhwal himalaya india as recorded by eight stations operated by wadia institute of himalayan geology dehradun india from 2007 to 2012 we find frequency dependent p and s wave quality factors as defined by the relations q p 56 8f 0 91 0 002 and q s 151 8f 0 84 0 002 by fitting a power law frequency dependence model for the estimated values over the whole region both the q p and q s values indicate strong attenuation in the crust of garhwal himalaya the ratio of q s q p 1 obtained for the entire analyzed frequency range suggests that the scattering loss is due to a random and high degree of heterogeneities in the earth medium playing an important role in seismic wave attenuation in the himalayan crust

near infrared imaging of hydroxyl wave structure over an ocean site at low latitudes coordinated observations of wave structure in the near infrared hydroxyl oh nightglow emission have been made from maui hawaii using a suite of narrow angle and all sky tv cameras two sets of data were obtained the first in conjunction with the aloha 90 campaign and the second during the subsequent new moon period well formed short period 20 min wave patterns of comparable morphology dynamics and abundance to those regularly imaged from mid latitude mountain sites were detected on several occasions although the hawaiian islands comprise several high volcanic peaks the patterns were not consistent with gravity waves generated by the interaction of strong winds with the local island topography this suggests that other mid latitude wave patterns may also not be of mountain origin the wave patterns imaged during aloha 90 were of significantly lower contrast than those detected later this effect may be related to changes in the characteristics of the middle atmosphere that occur shortly after the spring equinox

variation of seismic coda wave attenuation in the garhwal region northwestern himalaya seismic coda wave attenuation q text c 1 characteristics in the garhwal region northwestern himalaya is studied using 113 short period vertical component seismic observations from local events with hypocentral distance less than 250 km and magnitude range between 1 0 to 4 0 they are located mainly in the vicinity of the main boundary thrust mbt and the main central thrust mct which are well defined tectonic discontinuities in the himalayas coda wave attenuation q text c 1 is estimated using the single isotropic scattering method at central frequencies 1 5 3 5 7 9 12 16 20 24 and 28 hz using several starting lapse times and coda window lengths for the analysis results show that the q text c 1 values are frequency dependent in the considered frequency range and they fit the frequency power law q text c 1 left f right q 0 1 f n the q0 qc at 1 hz estimates vary from about 50 for a 10 s lapse time and 10 s window length to about 350 for a 60 s lapse time and 60 s window length combination the exponent of the frequency dependence law n ranges from 1 2 to 0 7 however it is greater than 0 8 in general which correlates well with the values obtained in other seismically and tectonically active and highly heterogeneous regions the attenuation in the garhwal region is found to be lower than the qc 1 values obtained for other seismically active regions of the world however it is comparable to other regions of india the spatial variation of coda attenuation indicates that the level of heterogeneity decreases with increasing depth the variation of coda attenuation has been estimated for different lapse time and window length combinations to observe the effect with depth and it indicates that the upper lithosphere is more active seismically as compared to the lower lithosphere and the heterogeneity decreases with increasing depth

imaging subsurface structure of an urban area based on diffuse field theory concept using seismic ambient noise single station ambient noise measurement in campaign mode has of late gained a huge popularity among geo scientists herein we present results of ambient vibration analysis executed in a highly populated urban area covering 47 survey points the resonance frequency estimates range from 0 5 to 3 hz as found from h v taking h v curve as input for retrieving subsurface information we deploy diffuse field assumption dfa theory the obtained shear wave velocity from the inversion of h v curve through dfa approach provides evidence of the complex nature of the subsurface geological structures identifying six characteristic 2d cross sections of the entire area we attain prevalence of a low velocity intermediate layer with velocity ranging from 128 192 m s on the contrary a relatively high velocity layer is also obtained 279 471 m s which can be treated as sedimentary deposits may be for some sites as basin basement the attained results when extended to a 3d shear wave profile tally excellently with estimated frequency distribution and its corresponding links with depth wise strata accompanied by a topographical profile of the surveyed locations all findings are comprehensively analyzed and interpreted as a proof of concept of implementation of dfa approach towards retrieving subsurface information

studies of the seismic coda using an earthquake cluster as a deeply buried seismograph array loosely speaking the principle of green s function reciprocity means that the source and receiver positions in a seismic experiment can be exchanged without affecting the observed seismograms consequently the seismograms observed at a single observation location o and caused by a cluster of microearthquakes at locations ei are identical to the time series that would be measured by an array of stress meters emplaced at positions ei recording waves generated by a source acting at o by applying array analysis techniques like slant stacking and frequency wave number analysis to these seismograms we can determine the directions and velocities of the component waves as they travel in the earthquake focal region rather than at the surface we have developed a computationally rapid plane wave decomposition which we have applied to single station recordings of aftershocks of the 1984 morgan hill california earthquake the analysis is applied to data from three seismic stations having considerably different site geologies one is a relatively hard rock station situated on franciscan metamorphics one is within the calaveras fault zone and one is on semiconsolidated sand and gravels we define the early coda to be the part of the coda initiating immediately after the direct s wave and ending at twice the s wave lapse time the character of the s wave and early coda varies from being impulsive at the first station to highly reverberative at the last we examine waves in sequential time windows starting at the s wave and continuing through the early part of the coda at all seismic stations the early coda is dominated by a persistent signal that must be caused by multiple scattering probably within 2 km of each seismic station despite clear station to station differences in the character of the early coda coda q values measured in the late coda greater than twice the s lapse time agree well among stations implying that the mechanisms causing the varying behavior of the early coda do not control the coda decay rate at the stations we have considered coda q values measured on horizontal components of motion agree within a factor of 2 with those measured on vertical components we have not been able to determine the composition of the late coda because of a low signal to noise ratio our analysis technique however is quite appropriate for such a task

spatial distribution of scattering loss and intrinsic absorption of short period s waves in the lithosphere of japan on the basis of the multiple lapse time window analysis of hi net data summary propagation of short period s waves through the crust is strongly controlled by scattering loss and intrinsic absorption scattering loss controls the shape of the seismic envelope and the spatial distribution of the energy while intrinsic absorption produces an exponential decay as a function of time which is independent of the coordinates since both parameters have a different effect it is possible to compute them by means of the multiple lapse time window analysis mltwa in this paper high resolution maps of japan for both seismic s wave attenuation parameters are obtained by using the mltwa with data provided by the hi net seismic network the maps show strong regional variation of the parameters the variations depend mainly on the tectonic setting of each region and volcanism mechanisms in the scattering loss maps in the 1 2 hz map there is a very different behaviour between the northeast stronger scattering loss and the southwest much weaker scattering loss in the northeast of japan areas with strong scattering loss correspond mainly to the location of the volcanic arcs in southwest japan chugoku region and the west side of kii peninsula show strong scattering levels for the 4 8 hz and higher frequency bands in hokkaido strong scattering loss and intrinsic absorption can be observed for the lower frequency bands in the sendai plain we find strong scattering loss for all the frequency bands under all these areas low velocity anomalies have been detected in previous works in tohoku area the east side shows lower intrinsic attenuation than the west side this characteristic seems to extend to the southern part of hokkaido and to central japan in kanto area the values of intrinsic absorption are lower than in the surrounding areas but in the region around the itoigawa shizuoka tectonic line and in its western side strong absorption areas are observed the behaviour of each area for intrinsic absorption is similar to the behaviour observed in the q 1c maps the mltwa is based on the hypothesis of multiple isotropic scattering in a medium with the homogeneous distribution of scattering mean free path and intrinsic absorption although these hypotheses are very simple the results are very informative on the characteristics of each region and show the usefulness of studying the properties of scattered seismic waves in the understanding of the properties of the crust

attenuation of short period seismic waves at mt vesuvius italy we analysed short period seismograms from about 250 very local events recorded by a network of high dynamic range short period seismic stations deployed on mt vesuvius to estimate the site corrected short period seismic attenuation we calculated qc 1 the inverse of the quality factor for coda waves for short lapse times 12 s and qp 1 and qs 1 the inverse of the direct body wave quality factors for p and s waves follow ing shallow ray paths we used the single scattering assumption to fit the amplitude envelopes of the coda at different frequency bands obtaining a qc 1 slowly varying with frequency similar to values measured for other volcanoes at the same lapse time site corrected qp 1 and qs 1 were estimated using the frequency decay method for both p and s waves in two frequency bands 1 6 hz and 15 24 hz results show that qp 1 is 0 028 in both frequency bands and qs 1 is 0 015 and 0 017 at low and high frequencies respectively almost independent of the frequency and that the value of qp 1 is about twice that of qs 1 as measured worldwide a check was made by measuring the broadening of the first p wave pulse with station source distance finding qp 1 0 024 using the independent estimates of qc 1 and qs 1 we separated the intrinsic from the scattering quality factor at mt vesuvius obtaining a high scattering and a low intrinsi c q 1 as already observed for other volcanoes this result confirms the hypothesis of the predominant role of the scattering phenomena with respect to the intrinsic dissipation in the seismogram formation for volcanic earthquakes

intrinsic and scattering attenuation in the crust of the abu dabbab area in the eastern desert of egypt abstract fifty five microearthquakes recorded by a digital temporary seismic network in the abu dabbab area in the eastern desert of egypt were used to estimate the direct s wave q coda q c intrinsic q i and scattering quality factors q s sato s sato h 1977 single scattering assumption was used to fit the amplitude envelopes of the coda at seven central frequency bands 1 5 3 6 9 12 18 and 24 hz obtaining a q c varying with frequency as generally observed in tectonically active areas lapse time dependence was also studied for the area with the coda waves analyzed at window lengths ranging from 10 to 40 s starting from the onset of the s wave arrival the direct s wave q was estimated using the coda normalization method aki k 1980a the frequency dependence of q was investigated for the direct s waves and coda waves results show a low quality factor and a high frequency parameter indicating that the upper lithosphere of the abu dabbab area is seismically active and heterogeneous using the independent estimates of q c and q the intrinsic quality factor q i was separated from the scattering quality factor the results suggest that intrinsic dissipation plays a predominant role with respect to scattering phenomena in the area the obtained q values seem closer to those reported by analyzing volcano tectonic earthquakes this finding reflects that the cause of abu dabbab earthquake swarms might be igneous activity where the magma is ascending through joints or serpentinized joints that are dewatering

regional variation of coda q in kopili fault zone of northeast india and its implications abstract kopili fault has been experiencing higher seismic and tectonic activity during the recent years these kind of active tectonics can be inspected by examining coda wave attenuation and its dependence with frequency exploiting single back scattering model we have endeavored to measure coda q and its associated parameters such as frequency dependent factor n and attenuation coefficient covering seven lapse time windows spanning from 30 to 90 s and central frequencies 1 5 3 5 6 9 and 12 hz the average estimated values of qc increase s with frequency and lapse time window from 114 at frequency 1 5 hz to 1563 at frequency 12 hz for 30 s window length and from 305 at frequency 1 5 hz to 2135 at frequency 12 hz for 90 s window length the values of q0 and n are also estimated for the entire kopili fault zone for this study region the q0 values vary from 62 to 348 and n varies from 0 57 to 1 51 within the frequency range 1 5 to 12 hz furthermore depth variation of attenuation of this region reveals that there is velocity anomaly at depth 210 220 km as there arises sharp changes in and n which are supported by available data reported by other researcher for this region finally we have tried to separate the intrinsic and scattering attenuation for this area it is observed that the entire region is dominated by mainly scattering attenuation but we can see an increase in intrinsic attenuation with depths in two stations namely tzr and bkd furthermore the obtained results are comparable with the available global data

characteristics of short period wavelike features near 87 km altitude from airglow and lidar observations over maui 1 small scale less than 15 km horizontal wavelength wavelike structures known as ripples are a common occurrence in oh airglow images recent case studies attribute their origin to the presence of either convective or dynamical instabilities however little is known about their frequency of occurrence and period the maui malt observatory located at mt haleakala is instrumented with a na wind temperature lidar which allows the determination of whether the atmosphere is dynamically or convectively unstable and a fast oh airglow camera which takes images every 3 s with a sensitivity high enough to see the ripples this study reports on 2 months of observations in october november 2003 and in august 2004 eight nights of which also included na lidar measurements the imager results suggest that instability features occur in the 85 to 90 km region of the atmosphere for around 20 of the time the nominal observed period for the ripples is between 2 and 4 min while there are clear night to night variations the average observed period is similar for both the 2003 and 2004 observations in addition a few of the small scale structures are not ripples caused by instabilities but rather have features consistent with their being short horizontal wavelength evanescent waves their fractional intensity fluctuations are as large or larger than those of the ripple instabilities unlike the instabilities the origin of the evanescent waves is not determined

coda q estimates in the andaman islands using local earthquakes the attenuation property of andaman island has been investigated analyzing coda waves from 57 local earthquakes in the magnitude range of 2 0 4 9 using the single backscattering model these earthquakes waveforms recorded on five broadband seismographs sited over the island from north to south during nov 2003 to march 2004 have been used to calculate the frequency dependent coda q q c applying the time domain coda decay method the coda q computed at central frequencies from 0 5 12 hz and five lapse time windows from 40 to 80 s progressively increases from 105 f 0 88 in the north andaman to 135 f 0 79 in the south andaman with an average of 119 f 0 80 the average q c values vary from 75 42 at 0 5 hz to 697 54 at 12 hz central frequency for 40 s lapse time window while for 80 s lapse time window its variation is from 117 38 at 0 5 hz to 1256 115 at 12 hz the q c estimated at different lapse times manifests a significant variation from 122f 0 75 to 174f 0 73 corresponding to lapse time window lengths of 40 and 80 s respectively the variation of q c with frequency lapse time and also with the location of seismograph reflects the marked structural and compositional inhomogeneity with depth along the andaman islands these observations are well correlated with the seismicity pattern and distinct high angle subduction beneath the island

evidence of mesospheric gravity waves generated by orographic forcing in the troposphere 1 we report on the first imaging observations of stationary mesospheric gravity waves in the three nightglow emissions of oh 695 1050 nm na 589 3 nm and o 1s 557 7 nm the waves were observed in all sky images at the el leoncito observatory elo argentina 31 8 s 69 3 w during the period of 1 8 july 2008 over the course of each night the band like wave features exhibited a zero or near zero observed horizontal phase speed and had lifetimes of several hours these factors coupled with the winds measured locally and the orientation of the waves to the andes mountain range located nearby suggested that the waves were mountain waves generated by 70 ms 1 eastward winds flowing over the andes

spatial changes of seismic attenuation and multiscale geological heterogeneity in the baikal rift and surroundings from analysis of coda waves abstract the baikal rift system is undergoing an active tectonic deformation expressed by a high level of seismic activity this deformation leads to physical and mechanical changes of crustal properties which can be investigated by the seismic quality factor and its frequency dependence using a single backscattering model a seismic quality factor qc a frequency parameter n and an attenuation coefficient have been estimated by analyzing coda waves of 274 local earthquakes of the baikal rift system for nineteen lapse time windows w from 10 to 100 s every 5 s and for six central frequencies 0 3 0 75 1 5 3 6 and 12 hz the average qc value increases with the frequency and lapse time window from 46 52 at 0 75 hz to 502 109 at 12 hz for w 10 s and from 114 49 at 0 3 hz to 1865 679 at 12 hz for w 100 s the values of qc f and were estimated for the whole baikal rift system and for separate tectonic blocks the stable siberian platform main rift basins spurs and uplifts along the rift system the q0 value qc factor at the frequency f 1 hz varies within 72 109 and the frequency parameter n ranges from 0 87 to 1 22 whereas q0 is 134 and n is 0 48 for the stable siberian platform vertical variations of attenuation reveal that sharp changes of and n are confined to the velocity discontinuities the comparison of lateral variations of seismic wave attenuation and geological and geophysical characteristics of the baikal rift system shows that attenuation is correlated with both seismic activity and heat flow and in a lesser degree with the surface fault density and the age of the crust seismic wave attenuation found across the main shear zones of the south western baikal rift main sayan strike slip fault zone and tunka obruchev and primorsky normal faults is increased by more than 25 60 compared to the neighboring areas

lithospheric temperature estimates from seismic attenuation across range fronts in southern and central eurasia seismic attenuation 1 q changes abruptly between the stable eurasian craton and adjacent mountain belts associated with the alpine himalayan collision new attenuation measurements on local body and coda waves provide quantitative constraints on this contrast near the caucasus kopet dagh and tien shan mountains the 1 q estimates from all range fronts are similar the mountains being two to three times more attenuative than adjacent stable platforms these 1 q variations are a reasonable proxy for temperature variations and reveal crustal heating on the order of 100 c but probably not melting beneath the mountain ranges attenuation 1 q is high wherever high topography is seen implying that active mountains are typically hot hence processes that generate or transport heat dominate advective cooling due to lithospheric thickening even over the 10 20 m y lifetimes of these young mountain belts

maui mesosphere and lower thermosphere maui malt observations of the evolution of kelvin helmholtz billows formed near 86 km altitude 1 small scale less than 15 km horizontal wavelength structures known as ripples have been seen in oh airglow images for nearly 30 years the structures have been attributed to either convective or dynamical instabilities the latter are mainly due to large wind shears while the former are produced by superadiabatic temperature gradients dynamical instabilities produce kelvin helmholtz kh billows which have been known for many years however models and laboratory experiments suggest that these billows often spawn a secondary instability that is convective in nature while laboratory investigations see evidence of such structures the evolution of these instabilities in the atmosphere has not been well documented the maui mesosphere and lower thermosphere maui malt observatory located on mt haleakala is instrumented with a na wind temperature lidar that can detect dynamic or convective instabilities with 1 km vertical resolution over the altitude region from about 85 to 100 km the observatory also includes a fast oh airglow camera sensitive to emissions coming from approximately 82 to 92 km altitude which obtains images every 3 s at sufficient resolution and signal to noise to see the ripples on 15 july 2002 ripples were observed moving at an angle to their phase fronts after a few minutes structures appeared to form approximately perpendicular to the main ripple phase fronts the lidar data showed that a region of dynamical instability existed from approximately 85 5 to 87 km and that the direction of the wind shear in this region was consistent with the phase fronts of the ripple features the motion of the ripples themselves was consistent with the wind velocity at 85 9 km thus in this case the observed ripple motion was the advection of kh billows by the wind the perpendicular structures were seen to be associated with the kh billows they formed at the time when the atmosphere briefly became convectively unstable within the region where the kh billows most likely formed because of this and because the ripples were oriented approximately perpendicular to and moved with the billows we speculate that they are the secondary instabilities predicted by models of kh evolution the primary and perpendicular features were seen to decay into unstructured regions suggestive of turbulence while the formation and decay time appear consistent with models the horizontal wavelength of the perpendicular structures seems to be larger than models predict for the secondary instability features

simultaneous observations of the phase locked 2 day wave at adelaide cerro pachon and darwin the southern hemisphere summer 2 day wave tdw is the most dramatic large scale event of the upper mesosphere the winds accelerate over 1 week may attain 70 m s and are often accompanied by a near disappearance of the diurnal tide and stabilization of the period close to 48 h we denote this as the phase locked 2 day wave pl tdw we have examined airglow and meteor radar mr wind data from the andes lidar observatory cerro pachon chile 30 s 289 3 e mr data from darwin 12 5 s 131 e and airglow and medium frequency radar data from the university of adelaide 34 7 s 138 6 e for the behavior of the tdw during the austral summers of 2010 2012 and 2013 the cerro pachon and adelaide sites are located at similar latitudes separated in longitude by about 120 we find a remarkable coincidence between the tdw oscillations at chile and adelaide for the period january february 2010 the oscillations are nearly in phase in terms of local time and the minima and maxima repeat at nearly the same local time from cycle to cycle consistent with a phase locked wave number 3 tdw data for this and other years including darwin show that the amplitude of the diurnal tide decreases when the tdw is largest and that this occurs when the period is close to 48 h these observations support the proposal that the pl tdw is a subharmonic parametric instability wherein the diurnal tide transfers energy to a tdw that is resonant at nearly 48 h

attenuation of coda waves in the garhwal himalaya india abstract q c estimates have been obtained by analysing coda waves of seven local earthquakes recorded in the garhwal himalaya the earthquakes have their epicentral distances within 100 km focal depths up to 20 km with 2 4 m l 4 9 q c values have been computed at central frequencies of 1 5 3 0 6 0 12 0 and 18 0 hz for different earthquake stations falling in the lapse time window of 30 60 s using a single backscattering model the mean value of q c shows a dependence on frequency varying from 206 at 1 5 hz to 2090 at 18 hz the frequency dependence average q c relationship q c q 0 f n has been obtained for the region as q c 126 f 0 95 which indicates that attenuation at higher frequencies is less pronounced q c values estimated for the region represent the average attenuation properties for a surface area of about 20 000 km 2 in a circular shape with a radius of about 80 km assuming single backscattering

the attenuation mechanism of seismic waves in northwestern himalayas summary we analysed local earthquake waveforms recorded on a broad band seismic network in northwestern himalayas to compute the intrinsic and scattered attenuation parameters from coda waves similar to other tectonically active and heterogeneous regions attenuation frequency relation for western himalaya is q 1 113 7 f 1 01 0 05 where qc is the coda q parameter intrinsic q 1 and scattering q 1 attenuations was separated using qc and direct s wave q data qd it is observed that estimated q 1 is close to q 1 and both of them are much larger than q 1 suggesting that coda decay is predominantly caused by intrinsic attenuation at higher frequencies both the attenuation parameters qc and qd are similar indicating that coda is predominantly composed of back scattered s waves at these frequencies

a precursorlike change in coda excitation before the western nagano earthquake ms 6 8 of 1984 in central japan temporal variations of coda duration were studied in relation to a crustal earthquake september 14 1984 which took place near the nw corner of the kanto tokai microearthquake observation network of the national research center for disaster prevention in japan vertical seismograms recorded at station ger close to the main shock epicenter 24 km between february 1982 and december 1984 were analyzed a precursorlike change was found in the relation between coda duration and average magnitude for 185 earthquakes which occurred in a small volume in the middle of the aftershock region the average magnitude is the arithmetic mean of station magnitudes which are calculated from the maximum amplitudes of direct waves coda durations for earthquakes of the same average magnitude were significantly longer during the 16 month period preceding the main shock than those before and after this period with a confidence level of 99 9 the increase in coda durations was about 3 s on average in this period the coda duration anomaly was significant for lapse time shorter than 30 s which corresponds to a travel radius less than 50 km although no clear temporal change was found in the residuals of station magnitude measured at ger from average magnitude an attenuation change in the preevent period can not be ruled out due to the large scatter of data crack formation however is the most plausible mechanism for an increase in scattering intensity around the focal region in the stress accumulation stage and is consistent with other precursory observations clusters of cracks in the heterogeneous earth medium might be big enough to scatter high frequency seismic waves even though each individual crack may be very small

stability of coda q in the region of parkfield california view from the u s geological survey parkfield dense seismograph array many investigators have proposed that changes in the rate at which the coda decays may be an intermediate term precursor to moderate to large earthquakes parkfield california on the san andreas fault is a promising location for studying premonitory changes in coda q qc because a large earthquake is likely to occur there we have investigated qc using recordings from the u s geological survey parkfield dense seismograph array which is a digital array with 14 triaxial sensors and an aperture of about 1 km for each earthquake we can measure qc from up to 42 recordings their average is more stable than the measurement from a single station using clustered seismicity we have developed criteria for selecting events and reducing scatter in the measurement the qc value determined from a seismogram depends on the position and length of the analysis window thus qc should always be measured from the same length window starting at the same lapse time regardless of the source location in addition the band limited signal to noise ratio at the end of the analysis window is important qc determined in two frequency bands 4 8 hz and 8 16 hz from a tight cluster of 26 events which occurred between december 1989 and january 1994 has not changed despite m 4 7 and m 4 6 events in october 1992 and november 1993 qc measured from local events 60 km in three frequency bands shows larger scatter but has also not changed during this period for monitoring qc observations should include array averaged measurements from a single lapse time because qc measurements made using an analysis window that starts at a constant multiple of the s wave lapse time depend on epicentral distance a procedure combining the evaluation of the time and distance dependences of qc also gives stable observations

delineation of subsurface profiles beneath the kopili fault zone in northeast india utilizing coda portion abstract the kopili fault kf zone is witness to many seismic activities including the 1869 earthquake 7 8 ms the 1943 earthquake 7 3 ms and recent 2016 earthquake 6 7 mw which occurred at certain time intervals considerable portion of kf zone and its neighbouring is characterized by alluvial soils which have higher potential of trapping seismic waves this leads to intense amplification of ground shaking necessitating a detailed study of subsurface profile beneath kf the h v spectral ratio of strong motion recordings is an effective tool to evaluate such nonlinear site responses and to develop a subsurface velocity profile is an important step toward hazard mitigation in this work we used 14 seismic stations nearby this fault to construct the subsurface profile this study suggests that h v ratios obtained from coda portion of seismogram are almost independent of the coda window length we applied diffuse field concept to produce an inverted s wave as well as p wave velocity profile the inverted profiles show significant correlation with the underlying site class as well as exhibit an excellent match with already reported attenuation quality factors for this region for few selected sites inferred velocity estimates become 500 m s at a depth of 25 m or shallower interestingly it is observed that two nearby receiving sites are characterized by different shear wave velocity profiles at shallower depths however in deeper depths they are found to converge all results are comprehensively analyzed and their implications are accordingly outlined

energy flux model of seismic coda separation of scattering and intrinsic attenuation a new model of seismic coda is presented based on the balance between the energy scattered from the direct wave and the energy in the seismic coda this energy flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic anelastic attenuation of the medium this formula is valid for both weak and strong scattering and implicitly includes multiple scattering the model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity some of the simulations also included intrinsic dissipation the energy flux model explains the coda decay and amplitude observed in the synthetics for random media with a wide range of scattering q in contrast the single scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation scattering q less than or equal to 150 the simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate as predicted by the energy flux model the coda decay rate is sensitive however more to the intrinsic q of the medium the ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation thus analysis of the decay rate and amplitude of the coda can in principle produce separate estimates for the scattering and intrinsic q values of the crust we analyze the coda from two earthquakes near anza california intrinsic q values determined from these seismograms using the energy flux model are comparable to coda q values found from the single scattering theory the results demonstrate that coda q values are at best measures of the intrinsic attenuation of the lithosphere and are unrelated to the scatteing q less

intrinsic and scattering attenuation of the mt fuji region japan summary mount fuji is the focus of intense study because of its potential hazard signaled by seismic geologic and historical activity based on extensive seismic data recorded in the vicinity of mt fuji coda quality factor q 1c using a single scattering model hypothesis and intrinsic and scattering quality factor q 1i and q 1s using the multiple lapse time window mltw method were measured to focus the study on the magmatic structure below mt fuji the data were separated into two groups a near fuji region of rays traversing an area with radius 5 km around the summit r 20 km this classification shows the largest discrepancy of q 1c at a range of sampling volumes corresponding to overlapped sampling depth of about 80 km further the spatial division shows significant difference of q 1i and q 1s at hypocentral distance of 80 km the large difference of q 1s in bandwidths 2 4 and 4 8 hz indicates lithospheric heterogeneity beneath mt fuji with a characteristic heterogeneity scale length of about 1 km the results have a small error range due to the large data sample showing that all q 1 values in the near fuji area are greater than those of the far fuji area and q 1i for both the near and far fuji areas is higher than q 1s at high frequencies the q 1i and q 1s values for far fuji are in the range of values for typical non volcanic areas the q 1i values of the near fuji area are lower than those of other volcanic areas considered where as values of q 1s are not the low q 1i for the volcanic region of near fuji suggests that the magmatic activity indicated by percent partial melt in the vicinity of mt fuji is not as active as hot spot volcanoes such as kilauea hawaii

seismic attenuation in iberia using the coda q method summary coda wave analysis is used to obtain frequency dependent coda q values for different seismic zones of the iberian area seventeen source regions around the geophysical observatory of toledo and some four seismic events per region have been considered in this study we have used an iterative fourier analysis technique to see the variation of the frequency along the coda also taking into account the instrument response we have applied a suitable criterion to select the predominant frequency every 5 s along the coda the variation of the frequency with time for each region is averaged with a second degree polynomial which is compared to master curves obtained directly from the response of the seismograph system in order to determine the elastic quality factor q it has been observed that the frequency time curves thus obtained are better explained if q is considered as an exponential function of the peak frequency the main result of this work is a set of 1 hz q values with a clear indication that frequency dependence of q exists although the bandwidth from which our conclusions are reached is only 0 5 1 hz the coda q values obtained for the tectonically most stable areas north spain appear somewhat higher q 300 than those corresponding to the seismic active zones south spain q 250 thus a clear relationship is established between q values and the two major tectonic provinces in iberia these results may be helpful for seismic risk and earthquake engineering purposes

estimation of the coda wave attenuation and geometrical spreading in the new madrid seismic zone using the single backscattering method coda quality factor functions through coda window lengths of 20 30 40 50 and 60 s have been estimated for the new madrid seismic zone nmsz furthermore geometrical spreading functions for distances less than 60 km have been determined in this region at different center frequencies exploiting the coda normalization method a total of 284 triaxial seismograms with good signal to noise ratios snr 5 from broadband stations located in the nmsz were used the database consisted of records from 57 local earthquakes with moment magnitudes of 2 6 4 1 and hypocentral distances less than 200 km q factor values were evaluated at five frequency bands with central frequencies of 1 5 3 6 12 and 24 hz vertical components were utilized to estimate vertical coda q factor values horizontal coda q factor values were determined using the average amount of the q factor values estimated from two orthogonal horizontal components the coda q factor increases with increasing of the coda window length implying that with increasing the depth the coda q factor increases the intermediate values of the q factor and intermediate values of the frequency dependency indicate that the earth s crust and upper mantle beneath the entire nmsz is tectonically a moderate region with a moderate to relatively high degree of heterogeneities the geometrical spreading factors of s wave amplitudes are frequency dependent and determined to be 0 761 0 991 1 271 1 182 and 1 066 for center frequencies of 1 5 3 6 12 and 24 hz respectively at hypocentral distances of 10 60 km the geometrical spreading factors for lower frequencies are not recommended to be used due to the greater impact of the radiation pattern and directivity effect on low frequencies as well as the greater sensitivity of band pass filtered seismograms of small earthquakes to the noise in low frequencies

spatial and temporal correlation between coda q and seismicity in china a map of coda q at 1 hz q was constructed for china by analyzing more than 1000 seismograms from 80 seismic stations distributed throughout china the resultant contour map of q shows a strong correlation with the epicenters of historic great earthquakes in china the high q regions are devoid of the epicenters and the low q regions are full of them a remarkably linear relation was found between the logarithm of coda q and the maximum earthquake within the area sampled by coda waves radius of about 150 km from each station when we consider earthquakes which occurred from 1700 to present roughly speaking if q is 1000 m max is about 4 and if q is 100 m max is about 8 this relation will be very useful for siting critical facilities such as nuclear power plants and waste disposal sites we also found evidence in support of the migration of low q region coincident with the well known migration of high seismicity region over the distance of several hundred kilometers during the period of several hundred years if the migration is due to a diffusion process the diffusion constant is of the order of 100 km2 yr which agrees very well with those associated with the aftershock migration fluid injection and vp vs anomaly comparison of coda q with q1 estimated from the intensity data shows that they agree very well for q1 150 supporting the validity of the s to s single backscattering model for coda waves for q1 150 however coda q becomes constant independent of q1 this behavior is qualitatively consistent with numerical experiments of frankel and clayton and suggests that coda q may be measuring the intrinsic q of about 150 for these regions where q1 150 this limiting coda q value may depend on regions because coda q lower than 100 has been observed in some active regions in this study and also coda q as low as 30 to 40 has been reported in california mexico and italy

evaluation of a seismic event 12 may 2010 in north korea we assess seismological evidence bearing on claims that north korea conducted a small nuclear test on 12 may 2010 in the vicinity of known underground nuclear tests unts in 2006 2009 2013 and 2016 first we use lg wave cross correlation and more traditional methods to locate the 2010 event between about 4 and 10 km southwest of the 2009 test second we compare the relative sizes of regional p and s waves using stations within 400 km of the known north korean nuclear tests to assess the nature of the event we measured p s ratios at different frequencies at first using data from the open station mdj in northeast china for training sets of earthquakes and of explosions we developed a linear discriminant function ldf that in application to p s measured at mdj is most effective in separating the earthquake and explosion populations mdj lacks usable data for the event of interest but we obtained regional data from stations of the nearby dongbei broadband seismographic network dbsn for the 12 may 2010 event and for nearby unts conducted in 2006 and 2009 when our ldf is applied to dbsn data and to data from stations smt and ne3c in china the ldf values measured from p s ratios from known explosions are explosion like but for the 12 may 2010 event the ldf values are earthquake like for frequencies between 6 and 12 hz our method for characterizing earthquakes and explosions on the basis of their regional signals can be widely applied measurements of p s based on the three component waveform data provide better discrimination power than do those based on vertical component data alone electronic supplement 1 tutorial material on the mahalanobis distance squared measure three component linear discriminant function ldf analysis tables of measurements of the log10 p s spectral ratios obtained from waveforms recorded at station mdj for the two training sets and three component discrimination analysis and figures of log p s values measured at 8 hz from vertical component waveforms at station mdj for two training sets and probability distributions for d 1 http www bssaonline org lookup suppl doi 10 1785 0120160111 dc1

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

coda q estimates in the koyna region india the coda q q c have been estimated for the koyna region of india the coda waves of 76 seismograms from thirteen local earthquakes recorded digitally in the region during july august 1996 have been analyzed for this purpose at nine central frequencies viz 1 5 2 0 3 0 4 0 6 0 8 0 12 0 16 0 and 24 0 hz using a single backscattering model all events with magnitude less than 3 fall in the epicentral distances less than 60 km and have focal depths which range from 0 86 to 9 43 km for the 30 sec coda window length the estimated q c values vary from 81 to 261 at 1 5 hz and 2088 to 3234 at 24 hz whereas the mean values of q c with the standard error vary from 148 13 5 at 1 5 hz to 2703 38 8 at 24 hz both the estimated q c values and their mean values exhibit the clear dependence on frequency in the region and a frequency dependence average attenuation relationship q c 96f 1 09 has been obtained for the region covering an approximate area of 11 500 km2 with the surfacial extent of about 120 km and depth of 60 km

the effects of attenuation and site on the spectra of microearthquakes in the shillong region of northeast india microearthquake spectra from the shillong region are analyzed to observe the effect of attenuation and site on these spectra the spectral ratio method is utilized to estimate the q values for both p and s waves in the subsurface layer wherein the ratio of spectral amplitudes at lower and higher frequencies are taken into consideration for three stations at varying epicentral distances average estimates of qp and qs are 178 and 195 the ratio of qs to qp is estimated to be greater than 1 in major parts of the shillong area which can be related to the dry crust prevailing in the shillong region typically the variation in corner frequencies for these spectra is inferred to be characteristic of the site simultaneously observations from spectral content of local earthquakes recorded at two different stations with respect to the reference site yield greater amplification of incoming seismic signals in the frequency range of 2 5 hz which is found to be well supported by the existing local lithology pertinent to that region

characterization of exceptionally strong mesospheric wave events using all sky and zenith airglow observations 1 two unusually clear mesospheric gravity wave events were observed by the boston university all sky imager and the argentine airglow spectrometer on two consecutive nights at the el leoncito observatory argentina 31 8 s 69 3 w during august 2001 both events exhibited brightness amplitudes an order of magnitude above typical values the first event had the appearance of a large amplitude 60 in oh 6 2 22 in o 2 and 37 in o 1 s emissions peak to peak compared to 1 5 typically upward propagating gravity wave with pronounced nonlinear behavior the waves also showed noticeably curved wavefronts indicating that they had originated from a relatively small source region within 180 km of el leoncito estimates of the vertical flux of horizontal energy and momentum for the wave event in the oh and o 2 emissions were very large compared to typical values and they also indicated a high degree of flux divergence over the nominal 8 km altitude between the two layers the second event occurred on the following night and exhibited a frontal morphology and behavior consistent with an internal ducted gravity wave showing nonlinear behavior akin to a mesospheric bore the disturbance also had several interesting characteristics in particular the propagation speed decreased during its passage across the sky in addition a strong vertical temperature gradient due to the semidiurnal tide appeared to influence the occurrence of the bore event

the life cycle of instability features measured from the andes lidar observatory over cerro pachon on 24 march 2012 the aerospace corporation s nightglow imager ani observes nighttime oh emission near 1 6 m every 2 s over an approximate 73 field of view ani had previously been used to study instability features seen over maui here we describe observations of instabilities seen from 5 to 8 ut on 24 march 2012 over cerro pachon chile and compare them with previous results from maui with theory and with direct numerical simulations dns the atmosphere had reduced stability because of the large negative temperature gradients measured by a na lidar thus regions of dynamical and convective instabilities are expected to form depending on the value of the richardson number bright primary instabilities are formed with a horizontal wavelength near 9 km and showed the subsequent formation of secondary instabilities rarely seen over maui consistent with the primaries being dynamical instabilities the ratio of the primary to secondary horizontal wavelength was greater over chile than over maui after dissipation of the instabilities smaller scale features appeared with sizes in the buoyancy subrange between 1 5 and 6 km their size spectra were consistent with the model of weinstock 1978 if the turbulence is considered to be increasing the dns results produce secondary instabilities with sizes comparable to what is seen in the images although their spectra are somewhat steeper than is observed however the dns results also show that after the complete decay of the primary features scale sizes considerably smaller than 1 km are produced and these cannot be seen by the ani instrument

airglow observations of dynamical wind shear induced instabilities over adelaide australia associated with atmospheric gravity waves while several observations have been made in recent years of instability features in airglow images of atmospheric gravity waves agws such measurements are still rare to date these features are characterized by appearing to be aligned perpendicular to the agw wave fronts multi instrument observations confirm the theoretical prediction that such features are caused by convective instabilities where the agw induced temperature variation causes the total lapse rate to exceed the adiabatic lapse rate in february 2000 airglow observations were obtained at buckland park australia which showed instability features with a different characteristic these images showed small scale less than 10 km horizontal wavelength features aligned parallel to the larger scale agw wave fronts these features were only seen in oh images not in o2a images indicating that they originate below 90 km altitude simultaneous mf radar wind data reveal the presence of a mean wind shear which during the period of the small scale features was aligned nearly in the direction of agw propagation in addition the larger scale agw approached a critical level near 90 km altitude while the wind shear itself is not large enough to cause an instability an analysis of the data suggests that the small scale features are the result of a dynamic wind shear induced instability in the 87 90 km altitude region the instability was due to a combination of the background wind shear and the large shear induced by the passage of the larger scale agw as it approached the critical level