test ban treaty verification with regional data a review this paper summarizes the use of regional 30 seismic data in a test ban context for detecting locating identifying and determining the yield of underground nuclear explosions in many areas of the world eastern north america africa eastern ussr lg is the largest amplitude wave recorded on standard seismograph systems and thus is the most appropriate phase for monitoring small magnitude events excellent location capability for near regional events has been demonstrated at the norwegian small aperture array noress using lg and p waves lg and other regional phases may contain information on source depth but such information has not been exploited to date fifteen classes of regional discriminants have been identified including 1 1 first motion 2 2 ms mb 3 3 p2 p1 ratio 4 4 excitation of short period sh waves 5 5 lg rg amplitude ratios 6 6 pn lg pg lg and pmax lg amplitude ratios 7 7 lg group velocity and energy ratios in lg 8 8 excitation of sn 9 9 third moment of frequency 10 10 generation of higher mode surface waves 11 11 peak amplitudes of love and rayleigh waves and long period surface wave energy density 12 12 prevailing period of long period love waves 13 13 spectral ratio long period s waves to rayleigh waves 14 14 spectral ratio long period love waves to rayleigh waves 15 15 frequency of the peak spectral amplitudes and spectral ratios in pn pg s and lg each of these proposed discriminants has with differing degrees of success separated some explosions from some earthquakes however most have been tested only on limited data usually from one geographic region and only one or two recording stations no systematic analyses have been done to determine the best individual discriminant or combination of them preliminary evaluation of the use of lg for yield determination suggests that regional waves hold promise in this application theoretical studies have contributed significantly to the understanding of propagation characteristics of regional waves but further studies are required emphasizing modeling for realistic anisotropic sources the major conclusion of this study is that a systematic and comparative evaluation of all the proposed regional discriminants is now required utilizing a common data base derived from all present day test sites this evaluation would suggest the optimal discrimination procedure using regional waves and would also define areas of needed research without such an integrated evaluation it is still possible to speculate using existing results on the most promising regional discriminants

paleolatitudes of the tibetan himalaya from primary and secondary magnetizations of jurassic to lower cretaceous sedimentary rocks the tibetan himalaya represents the northernmost continental unit of the indian plate that collided with asia in the cenozoic paleomagnetic studies on the tibetan himalaya can help constrain the dimension and paleogeography of greater india the indian plate lithosphere that subducted and underthrusted below asia after initial collision here we present a paleomagnetic investigation of a jurassic limestones and lower cretaceous volcaniclastic sandstones section of the tibetan himalaya the limestones yielded positive fold test showing a prefolding origin of the isolated remanent magnetizations detailed paleomagnetic analyses rock magnetic tests end member modeling of acquisition curves of isothermal remanent magnetization and petrographic investigation reveal that the magnetic carrier of the jurassic limestones is authigenic mag netite whereas the dominant magnetic carrier of the lower cretaceous volcaniclastic sandstones is detrital magnetite our observations lead us to conclude that the jurassic limestones record a prefolding remagnetiza tion whereas the lower cretaceous volcaniclastic sandstones retain a primary remanence the volcaniclastic sandstones yield an early cretaceous paleolatitude of 55 5 s 52 5 s 58 6 s for the tibetan himalaya suggesting it was part of the indian continent at that time the size of greater india during jurassic time cannot be estimated from these limestones instead a paleolatitude of the tibetan himalaya of 23 8 s 21 8 s 26 1 s during the remagnetization process is suggested it is likely that the remagnetization caused by the oxidation of early diagenetic pyrite to magnetite was induced during 103 83 or 77 67 ma the inferred paleolatitudes at these two time intervals imply very different tectonic consequences for the tibetan himalaya

an inversion of lg wave attenuation and site response in the north china region a joint inversion method for determining the lg wave attenuation along the propagation path and site response based on seismic spectral ratios was developed and applied to invert the lg wave attenuation and site response in the north china region is related to the quality factor q by f uq where u is the velocity waveform data of 200 earthquakes during 2006 2008 with m l 1 7 5 5 in the area of 38 41 n 114 120 e were selected for this study more than 1500 three component records chosen from 81 stations on the basis of the signal to noise ratio were used in the inversion the waveform data were processed in the frequency range of 1 6 hz with an interval of 0 2 hz the results indicate that there is remarkable heterogeneity in lg wave attenuation in the study area we divided the area into four regions according to the lg wave propagation paths lower values are found in the tectonic mountain region higher values occur in the tectonic basin region and moderate values are found for the propagation paths passing through both the mountain and basin regions on the vertical component was found to be frequency dependent and in the form graphic 1 and graphic 2 for propagation paths in the mountain and basin regions respectively and graphic 3 and graphic 4 for paths passing through both mountain and basin regions with seismic ray direction from the mountain to the basin and vise versa respectively the absolute quality factor q ranges from 125 to 306 the response of rock sites is smooth and flat and less than five at low frequency while that for soil sites is higher than for rock sites for soil sites the amplification of low frequency waves is higher than that for high frequency waves for both site response and attenuation no significant differences were observed between different components online material source parameters of the studied earthquakes 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif 4 embed inline graphic 4 gif

characteristics of surface waves generated by events on and near the chinese nuclear test site our goal is to characterize surface waves at intermediate periods 5 30s generated by nuclear explosions and natural earthquakes occurring in and around the chinese nuclear test site at lop nor observed at epicentral distances between 10 and 20 we present observations of rayleigh and love wave group velocities spectral amplitudes and polarizations for eight nuclear explosions and nine earthquakes recorded at iris and geoscope broad band digital stations and at the kirghiz telemetered seismic network knet the wave paths studied cross complex geological regimes waveforms are extremely complicated yet observations made with frequency time analysis are robust and repeatable 1 group velocity and spectral amplitude measurements vary strongly across the studied region but display understandable systematics related to known tectonic features 2 both group velocity and spectral amplitude measurements across the knet array are generally similar at periods above 10s but differences are striking at shorter periods stacking methods dependent on waveform coherence across the network should only succeed at periods above 10 s for this large scale array 3 group velocity measurements for earthquakes and nuclear explosions that share a common wave path agree well but spectral amplitudes differ appreciably especially for rayleigh waves typically earthquake spectra are enriched in longer periods 12 20s relative to explosion spectra for events of the same magnitude 4 higher modes are observed on frequency time diagrams for rayleigh waves generated by earthquakes but are not observed for explosions 5 multipathing is observed in both frequency time diagrams and polarization analyses but again is qualitatively understandable in terms of known structural features in particular the channelling of love waves by the tarim basin is documented 6 large amplitude love waves are generated by nuclear explosions at lop nor indicative of significant tectonic release we discuss the relevance of the differences in spectral amplitudes between earthquakes and explosions and of the appearance of higher modes on earthquake frequency time diagrams to the problem of discriminating nuclear explosions from earthquakes

paleomagnetism of early paleogene marine sediments in southern tibet china implications to onset of the india asia collision and size of greater india article i nfo we report a paleomagnetic study of paleocene marine sediments in the gamba area of the tethyan himalayan terrane southern tibet which aims to accurately locate the position of the northern margin of greater india and further constrain timing of initial contact between india and asia following detailed rock magnetic and paleomagnetic experiments on a total of 675 drill core samples collected from the zongpu and upper jidula formations characteristic remanent magnetizations chrms were successfully isolated from most samples following alternating field af or integrated thermal and af demagnetization the chrms are of dual polarity and pass fold and reversal tests indicating a pre folding origin together with detailed biostratigraphic investigation of the sampling section a magnetic polarity sequence is constructed from data at 167 sampled horizons and satisfactorily correlates with polarity chrons c24r to c27r dating the zongpu formation between 56 2 and 61 8 ma on the geomagnetic polarity time scale the chrm directions from the zongpu formation are grouped stratigraphically into 33 sites and yield two paleopoles of 71 6 n 277 8 e a95 2 5 and 67 3 n 266 3 e a95 3 5 for the time intervals comprising 56 to 59 ma and 59 to 62 ma respectively these new paleopoles imply that the tethyan himalayan terrane was sited at low latitudes in the northern hemisphere during the interval 62 56 ma suggestingthatinitial contact between thetethyanhimalayaand lhasa terranes was established before60 5 1 5 ma and verylikelyoccurred nearthecretaceous tertiary boundary at least in the central partof the suturezone the results alsoindicate that atleast 1500 480 kmof post collisionalcrustal shortening occurred within the himalayas from the analysis of available paleomagnetic data obtained on both sides of the suture zone we propose a conceptional collision model for the india asia collision

spectral discrimination between nts explosions and western united states earthquakes at regional distances spectral ratio disciminants are applied to 72 western united states earthquakes and 64 nts explosions recorded at four broadband seismic stations surrounding nts the ratio of the energy in the 1 to 2 and 6 to 8 hz bands for pn pg and lg is calculated and a simple distance correction applied to the data the spectral ratio appears to have potential as a disciminant at relatively small magnitudes 3 0 4 5 to 5 0 this may be due to uncertainties in the apparent source time function for explosions these complications may be due to changes in the dynamic response of the material in the near source region as a function of overburden pressure effects of secondary sources or to variations in regional phase excitation with depth

what was the paleogene latitude of the lhasa terrane a reassessment of the geochronology and paleomagnetism of linzizong volcanic rocks linzhou basin tibet the paleogene latitude of the lhasa terrane southern tibet can constrain the age of the onset of the india asia collision estimates for this latitude however vary from 5 n to 30 n and thus here we reassess the geochronology and paleomagnetism of paleogene volcanic rocks from the linzizong group in the linzhou basin the lower and upper parts of the section previously yielded particularly conflicting ages and paleolatitudes we report consistent 40ar 39ar and u pb zircon dates of 52 ma for the upper linzizong and 40ar 39ar dates 51 ma from the lower linzizong are significantly younger than u pb zircon dates 64 63 ma suggesting that the lower linzizong was thermally and or chemically reset paleomagnetic results from 24 sites in lower linzizong confirm a low apparent paleolatitude of 5 n compared to the upper part 20 n and to underlying cretaceous strata 20 n detailed rock magnetic analyses end member modeling of magnetic components and petrography from the lower and upper linzizong indicate widespread secondary hematite in the lower linzizong whereas hematite is rare in upper linzizong volcanic rocks of the lower linzizong have been hydrothermally chemically remagnetized whereas the upper linzizong retains a primary remanence we suggest that remagnetization was induced by acquisition of chemical and thermoviscous remanent magnetizations such that the shallow inclinations are an artifact of a tilt correction applied to a secondary remanence in lower linzizong we estimate that the paleogene latitude of lhasa terrane was 20 4 n consistent with previous results suggesting that india asia collision likely took place by 52 ma at 20 n

spectral discrimination of nts explosions and earthquakes in the southwestern united states using high frequency regional data a high frequency seismic station has been operating since march 1987 near nelson nv records of earthquakes at regional distances from the station show substantially more energy at frequencies above 10 hz than records of nuclear tests of comparable magnitude on the nevada test site this contradicts the predictions made by investigators who have advocated high frequency monitoring for nuclear test detection and identification measuring the slopes of the pg velocity spectra between 4 and 30 hz successfully discriminates 11 nts explosions from 36 earthquakes recorded in the first seven months of operation the spectral differences may result from the respective source depths with the earthquakes occurring deeper and in faster material than the explosions

multispectral bathymetry using a simple physically based algorithm a simple method for estimating water depths from multispectral imagery is described and is applied to several ikonos data sets for which independent measurements of the water depth are available the methodology is based on a physical model for the shallow water reflectance and is capable of correcting for at least some range of water quality and bottom reflectance variations corrections for sun glint effects are applied prior to the application of the bathymetry algorithm the accuracy of the depth algorithm is determined by comparison with ground truth measurements and comparisons between the observed and calculated radiances are presented for one case to illustrate how the algorithm corrects for water attenuation and or bottom reflectance variations

palaeomagnetism of cretaceous to tertiary sediments from southern tibet evidence for the extent of the northern margin of india prior to the collision with eurasia abstract palaeomagnetic studies have been carried out on mid cretaceous to latest palaeocene sediments from the tethyan himalaya on the northern margin of the indian plate near the localities of gamba 28 3 n 88 5 e and duela 28 0 n 89 2 e in southern tibet a total of 61 sites more than 700 cores have been sampled mainly from limestones zongshan formation jidula formation member ii zongpu formation sandstones jidula formation member iii and graywackes gamba group member ii with ages well defined from detailed lithological and biostratigraphic analyses carriers of characteristic remanences are magnetite in limestones and graywackes and hematite in sandstones reliable palaeodirections were obtained from 35 sites 356 specimens positive fold tests antiparallel normal and reverse polarities a northward trend of the palaeolatitudes with decreasing age and absence of any metamorphic overprint indicate a primary origin for the characteristic remanences the results have been compared with expected palaeodirections according to available data for the indian subcontinent based on its present day geometry the late maastrichtian sites fourteen sites 156 specimens and the middle late palaeocene sites fourteen sites 113 specimens yield palaeolatitudes of 5 7 s and 4 0 n for the sampling localities in southern tibet respectively these palaeolatitudes are much further north than expected and imply that crustal shortening between the tethyan himalaya and the indian shield since the time of india eurasia collision has occurred on the order of 1500 km at the longitude of gamba duela comparison of our observed palaeolatitudes with palaeolatitudes for the lhasa block during cretaceous and palaeocene times indicate that initial contact of the northern indian margin with the lhasa block was already established at 65 60 ma with suturing completed at about 55 50 ma

analysis of seismic discrimination capabilities using regional data from western united states events additional studies have been conducted to help verify the findings of previous investigations cf murphy and bennett 1982 which indicated that spectral differences in short period regional phases may be diagnostic of source type for nevada test site nts explosions and nearby earthquakes recorded at tonto forest observatory in arizona regional phase signals from two additional stations the uinta basin observatory array in utah and the blue mountains observatory array in oregon and from supplemental events including aftershocks of the 1966 caliente nevada earthquake have been analyzed these stations are at epicentral distances of 430 to 530 km for tonto forest observatory 520 to 670 km for uinta basin observatory and 870 to 880 km for blue mountains observatory with the near ranges representing the distances to the caliente source area and the far ranges to the average nts source receiver distances this enhanced data base included 50 earthquakes within about 150 km of nts and 35 nts explosions recorded at one or more stations the events cover a magnitude range from about 2 8 to 5 2 mb with the majority of earthquakes concentrated in the lower half of that range the current investigation essentially corroborated our previous findings that comparison of simple peak amplitude measurements of regional p and lg phases did not consistently discriminate between earthquakes and explosions this discriminant breakdown appears to be related to variability in excitation of regional phases from similar sources which has been dramatically illustrated by observations from the 1966 caliente aftershocks these events produced large variations in the relative amplitudes of pg and lg signals even though the events were spatially restricted to a small zone in contrast the lg spectral ratio discriminant measure defined in the previous study continued to provide reliable distinction between the earthquake and explosion sources for data observed at all three stations the discrimination capability of the spectral ratio prevails in spite of the evident mechanism variability between earthquakes and shifts in the discrimination threshold between stations apparently related to attenuation differences along the propagation paths

the timing of india asia collision onset facts theories controversies abstract the timing of initial collision between india and asia has remained controversial for half a century this paper attempts to review this crucial and hotly debated argument describing first the different methods used to constrain the age of collision and discussing next the rationale results inferences and problems associated with each we conclude that stratigraphy represents the best direct way to unravel collision chronology other methods focusing on the magmatic metamorphic or paleomagnetic record provide additional fundamental constraints but cannot provide a robust direct estimate of collision onset initial collision in the central eastern himalaya is dated directly at the middle paleocene 59 1 ma by the abrupt change in sediment provenance recorded in trench settings the quasi synchronous unconformities documented along both tethyan passive margin of india and active margin of asia from tibet to zanskar ladakh confirm that orogeny was underway at the close of the paleocene 56 ma well before the disappearance of marine seaways in the himalaya during the early middle eocene 50 45 ma sedimentary evolution and provenance changes in marine to fluvio deltaic successions are recorded synchronously within error from the western to the central eastern himalaya failing to provide conclusive evidence for diachronous collision these coherent observations are hard to reconcile with three widely cited hypotheses invoking either paleogene arc continent collision or late cretaceous ophiolite obduction or the protracted existence of a greater india basin which are all not favored after discussing the geological evidence critically point by point a scenario no more complex than the one involving solely the passive continental margin of india and the active continental margin of asia is needed to explain the geological evolution of the nascent himalaya the collision between the tethys himalaya and the transhimalayan arc trench system does represent the collision between india and asia because the yarlung zangbo ophiolite is the forearc basement of the asian active margin its obduction onto india could not have preceded the initial closure of neo tethys ophiolite obduction began when collision began in the middle paleocene

regional seismic waveform discriminants and case based event identification using regional arrays abstract in this study we have investigated regional phase spectra spectral ratios and amplitude ratios as discriminants for case based regional seismic event identification using western norway explosions and earthquakes recorded at the noress array all events were in a comparable local magnitude range 2 to 3 and distance range 300 to 500 km from the noress array thus the propagation paths from the earthquakes and explosions were similar but not identical many of the events previously not identified as blasts had time independent spectral modulations indicative of ripple firing these include a number of offshore events which appear to be underwater explosions the modulations for the offshore events may have been caused by bubble pulse interference effects and or underwater reverberations amplitude ratios of pn sn and pn lg measured off of incoherent beams were examined on a region by region basis for a group of confirmed blasts events strongly suspected to be earthquakes and other events that had time independent spectral modulations the blast and earthquake groups were well separated by both ratios with the blasts producing more p wave energy relative to s wave energy than the earthquakes however the lg spectral ratio provided no separation this result agrees with others in shield regions that amplitude ratios between compressional and shear waves discriminate better than low frequency to high frequency spectral ratios for individual phases the converse holds for events in orogenic regions such as the basin and range tectonic region of the western united states for reasons that are not well understood but may relate to differences in crustal attenuation this fact argues in favor of using a case based approach to event identification where events are identified by comparing them to previous events or cases that occur in the same or similar tectonic environments in the absence of a well understood unifying theory for regional event identification characterizing events on the basis of geophysical and signal similarities to previous cases may be the only way of providing meaningful event identifications

a real time discrimination system of earthquakes and explosions for the mainland spanish seismic network different waveform based discrimination parameters were tested using multivariate statistical analysis to develop a real time procedure for discriminating explosions from earthquakes at regional distances in the iberian peninsula this work enabled a purge of the spanish national seismic catalogue for the period 2003 2014 the training data consisted of waveform based signal properties in the time and frequency domain for events earthquakes and explosions recorded during the selected time period by the spanish broadband national network and sonseca short period array of the instituto geografico nacional ign for each station and its associated training dataset a discriminant function was defined as a linear combination of the measured variables all station specific discriminant functions were then combined with a weighting scheme to test the training events revealing that 86 of the events were consistent with the analysts judgement the application of this method to the whole of the ign s seismic database for the studied period gave an 83 success rate however a 91 success rate is reached if events are classified using at least three stations and 100 confidence levels

on the nature of regional seismic phases ii on the influence of structural barriers summary the blockage of the lg wave by crustal barriers such as continental margins and graben structures has long been recognized as providing a very useful tool for mapping large scale lateral crustal variations along the propagation path numerical simulation of lg wave propagation in complex anelastic media using the pseudospectral method provides insight into the nature of the propagation process using both snapshots of the wavefield and synthetic seismograms a variety of 2 d structures have been investigated including the influence of sediments crustal thickness and attenuation thick sedimentary basins covering a graben structure can have a major influence since they remove lg energy by generating p conversion and scattering the principal mechanisms for strong lg attenuation across a graben the reduction of the lg energy is reinforced by anelastic attenuation in the sediments as well as the influence of the gradually thinning crustal waveguide associated with an elevated moho the extinction of lg in a sequence of explosions fired across the central graben of the north sea can be simulated by numerical calculations for the structure derived from refraction experiments

new paleomagnetic results from the lhasa block revised estimation of latitudinal shortening across tibet and implications for dating the india asia collision knowing how and when the tibetan plateau formed is of global concern as high topography modifies climate circulation patterns and alters species migration paths previous paleomagnetic work suggested that intracontinental shortening from deformation related to the india asia collision played a major role in building the tibetan plateau however these studies were derived from red bed facies which are often afflicted by inclination shallowing leading to overestimates of continental shortening we report new paleomagnetic data from the lhasa block the southern continental margin of asia before the india asia collision a high temperature characteristic remanent magnetization chrm was isolated from 43 sites of late cretaceous red beds 32 sites of late cretaceous lava flows and nine sites of eocene tuffs all the chrm directions are significantly different from the present day geomagnetic field and the mean directions of red beds lava flows and tuffs pass the fold test the distribution patterns of chrm directions derived from volcanic rocks are consistent with a secular variation model suggesting that secular variation was likely averaged out in contrast the red bed chrm directions exhibit an east west elongated distribution pattern indicative of inclination flattening the mean chrm inclination of the red beds 23 5 degrees 2 5 degrees is consistent with previous results but significantly shallower than that of 41 9 degrees 4 4 degrees carried by the coeval lava flows an elongation inclination analysis of the red bed chrm directions yielded an unflattened mean inclination of 39 7 degrees with 95 confidence limits between 37 7 degrees and 41 9 degrees the paleolatitudes of the late cretaceous volcanic rocks and inclination corrected sediments suggest about 10 degrees less shortening occurred between lhasa and siberia than previous estimates with total shortening lying between 3 3 degrees 2 6 degrees and 7 3 degrees 5 4 degrees since the late cretaceous the mean chrm inclination derived from the eocene tuffs 51 8 degrees 5 2 degrees is indistinguishable from the expected reference direction our new results imply that india asia convergence was accommodated mainly through consumption of the india plate and yield a much younger age ca 43 ma for the initial india asia collision than previously estimated by paleomagnetic data c 2010 elsevier b v all rights reserved

discriminating quarry blasts from earthquakes using coda waves abstract a new quarry blast earthquake discrimination method is presented based on the analysis of seismic coda waves quarry blasts and local earthquakes in the area encompassing the south central mojave desert and eastern transverse ranges were used to test this method we found that the coda decay rate q c 1 is significantly higher for quarry blasts than earthquakes for lower frequencies 1 5 and 3 hz for lapse time up to about 30 sec this result is attributed to the greater contribution of surface waves to quarry blasts due to the shallowness of their source depth the difference in q c 1 however disappears for lapse time greater than 30 sec for the same frequency range as well as for higher frequencies 6 and 12 hz for lapse time greater than 20 sec this suggests that the coda waves at the lapse time greater than these critical values are dominated by the same type of body waves probably s waves for both quarry blasts and earthquakes the power spectrum p 0 obtained after the correction for attenuation was compared between earthquakes and quarry blasts at the same stations and a significant difference was found in the spectral shape between these two data sets the curves of power spectrum p 0 versus frequency for quarry blasts decrease more sharply than for earthquakes at high frequencies indicating a lack of energy in high frequencies for quarry blasts as compared to earthquakes the different frequency dependence of power spectrum p 0 between quarry blasts and earthquakes is attributed to their different source properties and can be used for seismic discrimination of quarry blasts from earthquakes

seismic event detection and source location using single station three component data the seismic event detection and source location scheme presented in this paper uses single station seismic data to analyze seismic events to detect events the detection scheme combines the signals on the horizontal components in a manner analogous to beam steering once an event is detected the location scheme estimates the location of the source with respect to the receiver by estimating the polarization direction of the pn phase the range estimate is then obtained from the relative timing of different phases

the distance dependence of regional phase discriminants abstract amplitude ratios of p and s phases recorded at regional distances have been suggested as potential discriminants for the character of seismic sources because of the differences expected in the radiation patterns of earthquakes and well contained explosions the most useful reference phase for p waves beyond 200 km from the source is pn and for s possible choices are the mantle phase sn and the crustally guided wave lg each of these phases has a different interaction with the seismic structure of the crust and mantle and such structural effects will impose their own patterns on the radiation characteristics from the source the range dependent component in lg pn and sn pn ratios have been investigated for a dense set of three component records covering the distance range out to 700 km for an explosive shot in water in southern sweden which formed part of the 1979 fennolora experiment a stable measure of amplitudes and amplitude ratios is provided by using the vector resultant of ground motion the square root of the total energy however even for a common source there are significant variations in the amplitude ratios for lg pn and sn pn of a factor of three or more as a function of range three component record sections allow a detailed examination of the way in which individual records relate to the whole wavefields the role of multiple reflections in building the pg and lg phases can be clearly seen as well as the complex substructure of the pn and sn phases returned from the uppermost mantle

propagation of lg waves in the north australian craton influence of crustal velocity gradients abstract aftershocks of three large earthquakes near tennant creek in the northern territory of australia provide a unique opportunity to study regional seismic phases in the north australian craton three portable digital seismographs were operated near the source zone to provide control on earthquake locations and seven recorders formed a line between tennant creek and the seismic array at alice springs which is 430 km to the south eleven earthquakes of sufficient size for analysis were recorded during a one week deployment two months following the main shocks the group velocity observed for lg waves along this profile of 3 7 km sec is at the high end of the normal range and appropriate for a stable continental interior we estimate attenuation in discrete frequency bands by measuring the decay of amplitude as a function of distance from the source and assuming the common r 5 6 relationship for geometrical spreading however this assumption leads to frequency dependent q values q 230 36 f 0 66 0 12 that are abnormally low for a stable continental region the apparent q is also not consistent with other observations such as the high lg group velocity the positive bias in m l estimates obtained for other parts of australia using standard attenuation relations the size of felt areas for large central australian earthquakes nor with the high frequency content of seismic reflection data collected near our profile some crustal models for northern australia derived from seismic refraction work show a gradient zone between 30 and 55 km rather than a sharp moho discontinuity we therefore investigate the effect of gradient zones at the crust mantle transition on the decay of lg amplitudes using synthetic seismograms calculated with the wavenumber integral method the modeling suggests that some of the s wave energy that would be trapped in a crustal wave guide with a sharp lower boundary can leak out in the presence of a gradient and so enhance the attenuation in addition there are focusing effects due to the formation of caustics from the gradient zones which cannot be represented by a single analytic amplitude correction

comparative analysis of teleseismic p coda and lg waves from underground nuclear explosions in eurasia this study has investigated the characteristics of p coda and lg waves recorded at the norsar and graefenberg arrays from presumed nuclear explosions in western russia lg waves were found to be more energetic relative to the preceding coda in the mid band frequency range 0 2 to 1 0 hz recorded on the broadband graefenberg instruments than in the high frequency band 0 6 to 3 0 hz at either array comparison of the log rms coda envelopes at the two arrays revealed that the early high frequency p coda at norsar is stronger relative to lg than at graefenberg also the amplitudes of p waves and early p coda waves within 55 sec after p recorded at the centers of the norsar subarrays are positively correlated indicating the effect of focusing defocusing on the p and coda waves however for subarrays which cluster spatially there is an inverse correlation which seems to be due to scattering attenuation suggesting that much of the early p coda is generated by local p wave scattering beneath the norsar array also the norsar coda envelopes flatten between about 219 and 352 sec after p whereas the graefenberg coda decays monitonically from the p wave out to the sn and lg arrival times the standard deviation across the norsar array of the log rms amplitudes of lg and s coda phases are higher by about 0 05 to 0 06 magnitude units than those of p coda phases these differences are probably related to differential site and propagation path effects on p s and lg waves in the p coda the flattening of the norsar coda envelopes appears to be a burst of energy not associated with any known regional phases the burst may be caused by forward scattering of lg to p waves along the path between the source and norsar based on a regional travel time curve for western russia the start and end time of the coda flattening is consistent with lg to p scattering in the distance range of 23 to 29 from norsar which brackets the ural mountains the lg propagation path from the source region to graefenberg does not appear to traverse the ural mountains which may explain why the coda flattening is not observed at graefenberg

high frequency spectra of regional phases from earthquakes and chemical explosions abstract we analyze the high frequency 1 to 50 hz spectra of chemical explosions and earthquakes at local and regional distances in the northeastern united states and in norway to understand the seismic signal characteristics of single explosions multiple hole instantaneous explosions ripple fired quarry blasts and earthquakes our purpose is to evaluate practical discriminants and to obtain a physical understanding of their successes and failures high frequency spectra from ripple fired blasts usually show clear time independent frequency bands due to the repetitive nature of the source and are distinctively different from the spectra of instantaneous blasts or earthquakes however like other discriminators based on spectral estimates the spectrogram method requires data with high signal to noise ratios at high frequencies for unambiguous discrimination in addition banding is not seen in spectrograms for shots with small delay times less than 8 msec and short total durations we have successfully modeled the observed high frequency spectral bands up to about 45 hz of the regional signals from quarry blasts in new york and adjacent states using information on shot hole patterns and charge distribution we find that ripple firing results in an enrichment of high frequency s waves and efficient excitation of the rg phase there is an azimuthal dependence of p wave amplitude associated with orientation of the path with respect to local topography ridges benches in which the shots are emplaced to discriminate instantaneous explosions from earthquakes we find the p s spectral amplitude ratio at high frequencies is complementary to the use of spectrogram methods a high p s spectral ratio above 10 hz is a stable characteristic of instantaneous explosions

calibration of regional s p amplitude ratio discriminants s p amplitude ratios have proven to be a valuable discriminant in support of monitoring a comprehensive nuclear test ban treaty regional s and p phases attenuate at different rates and the attenuation can vary geographically therefore calibration is needed to apply the s p discriminant in new regions calibration includes application of frequency dependent source and distance corrections for regional pn pg sn and lg phases jenkins et al 1998 developed pn pg sn and lg amplitude models for nine geographic regions and two global composite models stable and tectonic they determined frequency dependent source and attenuation corrections from a large data set obtained from the prototype international data center pidc we use their corrections to evaluate calibrated s p discriminants our discrimination data set includes 1000 amplitude ratios from earthquakes industrial explosions chemical explosions and nuclear explosions from lop nor india and pakistan we find that the calibrated s p ratio is largest for earthquakes and smallest for the nuclear explosions as expected however the discriminant is not universally valid in particular the s p ratio for the pakistan nuclear explosion fell within the normal range for the earthquakes this event was recorded by only a few stations at far regional distances and appears to have an anomalously high sn amplitude the industrial explosions overlap with the earthquake population however the buried chemical explosions generally register lower s p ratio than earthquakes

analysis of high frequency pg lg ratios from nts explosions and western u s earthquakes the high frequency pg lg discriminant is studied between frequencies of 0 5 and 10 hz using 294 nts explosions and 114 western u s earthquakes recorded at four broadband seismic stations operated by lawrence livermore national laboratory the stations are located at distances of about 200 to 400 km from the nevada test site nts event magnitudes ranged from about 2 5 to 6 5 and propagation paths for the earthquakes range from approximately 175 to 1300 km the discriminant is shown to be very effective and displays improved separation between earthquakes and explosions as frequency is increased because of propagation effects it is important to apply distance corrections directly to the amplitude ratios or to the magnitude corrected amplitudes prior to computing the ratios multivariate discrimination analysis using both maximum likelihood gaussian classifiers and a backpropagation neural network show that approximately 95 of the events can be correctly identified both classification procedures were designed to handle missing data filled in using a nearest neighbor algorithm except for a few notable exceptions most of the earthquake misclassifications occur for mb 4 which is expected for events having reduced signal to noise ratios all of the explosion misclassifications occur for mb 4 suggesting a source or near source effect rather than an effect of poor signal to noise ratio the explosions that were misclassified were typically of magnitude large enough to be classified correctly by mb ms or love wave energy the main drawback of the pg lg discriminant is that because of signal to noise considerations and propagation effects the number of measurements are reduced considerably at higher frequencies it is expected that the problem will be amplified as magnitudes are reduced and event receiver distances are increased

basin formation in the high himalaya by arc parallel extension and tectonic damming zhada basin southwestern tibet 1 the late miocene pleistocene zhada basin in southwestern tibet provides a record of subsidence and basin formation within an active collisional thrust belt the 800 m thick basin fill is undeformed and was deposited along an angular unconformity on top of tethyan strata that were previously shortened in the himalayan fold thrust belt modal sandstone petrographic data conglomerate clast count data and detrital zircon u pb age spectra indicate a transition from detritus dominated by a distal northern source to a local southern source this transition was accompanied by a change in paleocurrent directions from uniformly northwestward to basin centric at the same time the depositional environment in the zhada basin changed from a large braided river to a closed basin lake sedimentation in the zhada basin was synchronous with displacement on the qusum and gurla mandhata detachment faults which root beneath the basin and exhume midcrustal rocks along the northwestern and southeastern flanks of the basin respectively these observations indicate that accommodation for zhada basin fill was produced by a combination of tectonic subsidence and damming as midcrustal rocks were evacuated from beneath the zhada basin in response to arc parallel slip on crustal scale detachment faults

effects of crustal structure under the barents and kara seas on short period regional wave propagation for novaya zemlya explosions empirical relations abstract short period seismic recordings at regional and upper mantle distances from underground explosions at novaya zemlya demonstrate that propagation across the continental shelf under the barents and kara seas appears to modify the partitioning of energy between l g and s n phases relative to purely continental paths in the eurasian crust while the underwater segments of the paths are relatively short variations in bathymetric characteristics from path to path influence the regional wave field with systematic behavior that can be used to establish empirical amplitude corrections for regional phases we analyze a large set of eurasian recordings to explore the relationship between regional phase energy partitioning and bathymetric characteristics maximum water depth along the path is the most influential factor for the novaya zemlya data it has strong linear correlations with the logarithmic rms amplitude of l g and the ratios s n l g and p l g the maximum water depth probably reflects the extent of necking of the crustal wave guide under the continental margin which may disrupt l g modes resulting in l g to s n scattering but there is surprising sensitivity to small variations in bathymetry empirical relations like those found here may be useful for nuclear yield estimation and discrimination for regions such as the korean peninsula and persian gulf where many seismic phases traverse water covered continental shelf with poorly known crustal structure

on the nature of regional seismic phases i phase representations for pn pg sn lg summary an operator development of the seismic wavefield is used to generate descriptions of the propagation processes contributing to the main regional seismic phases pn pg sn lg these operator forms are valid for laterally heterogeneous crust and mantle models and include the major processes of interconversion between wavetypes these representations of the regional phases are used to examine the theoretical basis for discriminants between earthquakes and underground explosions based on the relative amplitudes of p and s phases the ratio of sn to pn amplitude looks promising as a high frequency discriminant however the ratio of lg to pn amplitudes is not as useful because of the complex nature of the propagation characteristics of lg

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

a novel technique for measuring lg attenuation results from eastern canada between 1 to 10 hz spectral amplitudes of regionally recorded lg waves are studied in detail between 0 6 and 10 hz using vertical component velocity seismograms of the eastern canada telemetered network stations and a supplementary seismic research observatory type station at glen almond gac quebec we find that the site responses vary among these stations by more than a factor of 3 within the frequency range of interest furthermore they are found to be strongly frequency dependent consequently it is essential that they be taken into consideration in studies of lg wave attenuation and lg source spectra of regionally recorded seismic events we present a new method of measuring interstation surface wave attenuation which is closely related to the conventional two station method while retaining all the desirable features of the conventional two station method the new technique which we will call the reversed two station method allows simple direct one parameter determination of the lg wave attenuation from sparse spectral data in a manner unaffected by station site effects and associated instrument error the reversed two station method is successfully tested over weakly attenuating short 53 to 210 km interstation paths in eastern canada a difficult experimental condition by normal standards the lg attenuation coefficient 0 6 to 10 hz in eastern canada is found to be frequency dependent and of the form f 0 0008 f 0 81 km 1 at higher frequencies the lg attenuation appears to be essentially frequency independent this latter finding is preliminarily interpreted as evidence that regionally recorded lg waves in the canadian shield are as in the case of lg waves propagating through the structurally complex appalachian province contaminated by the high frequency coda of sn waves the lg contamination over the shield paths becomes severe starting at 14 hz twice the frequency above which the lg signal propagating over the appalachian province becomes completely dominated by non lg arrivals

a comparison of the high frequency 1 hz surface and subsurface noise environment at three sites in the united states abstract surface and subsurface high frequency 1 hz noise data were recorded using nearly identical instrumentation at three widely separated sites in the united states amarillo texas datil new mexico and pinedale wyoming for extended periods of time under varying wind conditions while the sites are geologically distinct the near surface noise environments have many common features that we believe may be due in large part to the presence of a surficial layer of highly attenuative unconsolidated material at each site noise levels seen at or near the surface 5 m or less are much higher up to 30 db and much more variable power range up to 44 db than those seen at depth the smallest range was 9 db for 1951 m at amarillo the greatest gains in noise level reduction are realized within the first 100 m and probably much shallower

on the nature of regional seismic phases iii the influence of crustal heterogeneity on the wavefield for subduction earthquakes the 1985 michoacan and 1995 copala guerrero mexico earthquakes summary the most prominent feature of the regional seismic wavefield from about 150 to over 1000 km is usually the lg phase this arrival represents trapped s wave propagation within the crust as a superposition of multiple reflections and its amplitude is quite sensitive to the lateral variation in the crust along a propagation path in an environment where the events occur in a subduction zone such as the western coast of mexico quite complex influences on the character of the regional wavefield arise from the presence of the subduction zone the great 1985 michoacan earthquake mw 8 1 which occurred in the mexican subduction zone was one of the most destructive earthquakes in modern history and its notable character was that at mexico city located over 350 km from the epicentre there was strong ground shaking almost comparable to that in the epicentral region that lasted for several minutes considerable effort has been expended to explain the origin of the unusual observed waves that caused the severe damage in the capital city during the destructive earthquake the nature of the propagation process in this region can be understood in part by using the detailed strong motion records from the 1995 copala guerrero mw 7 4 earthquake near the coast to the south of mexico city which also had an enhanced amplitude in the valley of mexico numerical modelling of both p and s seismic waves in 2 d and 3 d heterogeneous crustal models for western mexico using the pseudospectral method provides direct insight into the nature of the propagation processes through the use of sequences of snapshots of the wavefield and synthetic seismograms at the surface a comparison of different models allows the influences of different aspects of the structure to be isolated 2 d and 3 d modelling of the 1985 michoacan and 1995 copala earthquakes clearly demonstrates that the origin of the long duration of strong ground shaking comes from the sn and lg wave trains these s wave arrivals are produced efficiently from shallow subduction earthquakes and are strongly enhanced during their propagation within the laterally heterogeneous waveguide produced by the subduction of the cocos plate beneath the mexican mainland the amplitude and duration of the lg coda is also strongly reinforced by transmission through the mexican volcanic belt from the amplification of s waves in the low velocity surficial layer associated withs to p conversions in the volcanic zone the further amplification of the large and long lg wave train impinging on the shallow structure in the basin of mexico city with very soft soil underlain by nearly rigid bedrock with a strong impedance contrast gives rise to the destructive strong ground shaking from the mexican subduction earthquakes

the seismic disturbance on 1986 august 1 near novaya zemlya a source of concern summary on 1986 august 1 a small seismic disturbance occurred to the east of a soviet nuclear test site at novaya zemlya reported attempts to identify the nature of the source using only short period seismological data recorded at regional distances were unsuccessful however by using teleseismic p wave data it is possible to identify the source as an earthquake which occurred within the crust at a depth of 24 km the source is shown to have a double couple mechanism with a well constrained fault plane solution the identification as an earthquake is supported by the mb ms evidence

regional wave propagation in china and its surrounding regions a comprehensive study of the gross characteristics of high frequency seismic wave propagation in china and its surrounding regions was accomplished to learn more about how regional geology affects high frequency phases amplitudes of the regional seismic waves sn and lg relative to p coda were used to map lateral variations of shear wave attenuation in the crust and upper mantle over 7000 digital seismograms from 13 broadband stations of the chinese digital seismic network and global seismic network in the frequency range 0 5 to 5 0 hz were visually examined propagation efficiencies of sn and lg were qualitatively analyzed by ranking their amplitudes relative to the p wave coda efficient sn propagation is observed in the tien shan tarim platform southern tibet yangzi paraplatform and sino korean platform we have confirmed results of previous studies by finding a lack of sn transmission in north central tibet the ryukyu and japan arcs burma and the baikal rift an important observation which has not been previously reported is that sn does not propagate across mongolia the elimination of sn and the occurrence of recent volcanism in north central tibet and mongolia suggest that there is partial melt in the uppermost mantle beneath those regions high frequency lg waves propagate efficiently for most of china indochina and mongolia lg signals are attenuated within central tibet as well as along its southern boundary crustal structure variations along with an anomalously low q crust are primarily responsible for weakened lg amplitudes in tibet propagation paths across oceanic crust in the sea of japan and the andaman sea show blockage of the lg phase as well this investigation has relevance to comprehensive test ban treaty monitoring by showing where certain regional phases will or will not propagate efficiently

seismic event discrimination abstract discrimination of small events begins with detection association and location recent advances in detection include use of updated measures of the noise variance to control the false alarm rate and updating the noise amplitude spectrum n for application of the optimum detection filter s n 2 where s is the signal spectrum postdetection processes of interest include determination of signal azimuth and emergence angle from linear three component processing association programs have recently been improved by implementation of techniques taking advantage of information provided by arrays location advances include modification of the a priori travel time residual covariance matrix to account for the fact that travel time residuals are correlated at stations near to each other simultaneous determination of location and phase velocity when using regional phases and direct use of phases other than p e g pg lg s pp and pkpbc according to most source theories small earthquakes and explosions have the same flat displacement spectrum for p waves at teleseismic frequencies aside from location discrimination therefore rests on focal mechanism differences and generation of shear waves by earthquakes the m s m b discriminant rests on the shear wave generation but there is overlap of explosions and earthquakes at low magnitudes for dip slip earthquakes low frequency 0 3 hz p waves are weak from explosions due to the surface pp reflections p pp amplitude ratios for earthquakes vary over the focal sphere in a way impossible for a pair of explosions regional discrimination shows promise in the ratio of maximum amplitudes before and after sn and in the observed fact that shear phases from explosions detonated near high impedance contrasts are of lower frequency than those from earthquakes in the same region possibly due to the generation of the explosion shear phases by p to s scattering recent experimental analyses show that there is almost no decoupling at high frequencies in agreement with earlier theories these frequencies may be observable at regional distances

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

contamination of seismicity catalogs by quarry blasts an example from istanbul and its vicinity northwestern turkey abstract scientists have proposed two fault systems of different ages in the sea of marmara the thrace eskisehir fault zone of early miocene early pliocene age and the north anatolian fault zone of late pliocene recent age different seismicity rates and extensions of these faults onto land near istanbul have been suggested one of the reasons for these differences is the contamination of seismicity catalogs by seismic events from quarries operated in istanbul and its vicinity including gaziosmanpasa cebeci and kemerburgaz catalca omerli gebze and hereke in this study we investigated waveforms of 179 seismic events 1 8

single station location of seismic events a review and a plea for more research abstract traveltime based location methods are ineffective for locating regional seismic events which are recorded by few stations however the comprehensive test ban treaty ctbt makes it imperative that we monitor sparsely observed events this paper reviews the current status of single station location ssl methods the location of seismic events using records from one three component broadband digital station we argue here that ssl methods may ultimately provide the most effective and economical means for monitoring small magnitude m 3 seismic events over most of the earth potentially station event distance and focal depth may be determined accurately by utilizing broadband three component data and matching observed and synthetic waveforms station event azimuth is determinable from the polarization of the p wave arrival and p coda however more research is required before ssl methods become a practical alternative to traveltime based methods currently the most significant problem is that regional seismograms are strongly dependent on regional crustal structure thus future research efforts should focus both on determining appropriate crustal models in specific regions and also on improved methods for dealing with regional variations in crustal structure a second important problem concerns location errors with ssl they may involve 180 errors in station event azimuth or other highly non gaussian blunders

on the attenuation of lg waves in western and central asia and their use as a discriminant between earthquakes and explosions data from earthquakes and explosions in the western and central parts of the soviet union are used to determine the values of the coefficient of anelastic attenuation of 1 sec period lg waves from the russian uplands region and for the region from the caspian sea to the southern perimeter of the soviet union for the former region the value is approximately 0 15 deg 1 and for the latter 0 35 deg 1 using the empirical veith and clawson 1972 curve for the amplitude of p waves at regional distances and theoretical curves for the attenuation of higher mode surface waves for lg curves are constructed which show the variation of the amplitude ratio of lg to p with epicentral distance with the coefficient of anelastic attenuation as a parameter when data from explosions and earthquakes in the soviet union are compared with the calculated curves the amplitude ratios of lg and p on the average are larger for earthquakes than explosions however there is much overlap so that this ratio by itself does not appear to be a useful discriminant between earthquakes and explosions

developing local to near regional explosion and earthquake discriminants abstract we develop local to near regional 0 200 km amplitude discriminants using earthquakes single fired explosions and delayed fired explosions we use the source phenomenology experiment spe broadband data collected across the colorado plateau during the summer of 2003 which recorded explosions in hard and soft rock mines we optimized a local surface wave magnitude scale derived from a stable regional surface wave magnitude russell 2006 for the sources however the magnitude of the source and the distance to the station limit the surface wave energy which can cause instability in the surface wave magnitudes magnitude scales for the local phases pg lg sg and rg were also tested and compared when an azimuthal station correction was applied to each magnitude scale there was an average reduction of standard deviation by 16 58 regional and teleseismic discrimination techniques were optimized for local distance and our results show that lithology of the source is a critical component in discriminating events at local distances we also found that magnitude and amplitude ratios are effectively used to discriminate between small earthquakes and explosions at local distances with each performing the best in the hard rock lithology furthermore the ratio techniques perform equally in both lithologies if multiple stations are used to establish the ratio values we find that an average of four or five stations will generally have a 90 or better correct identification for both types of ratios finally we find that the source lithology local site effects and large scale geologic features control most of the variability in the amplitude measurements

regional phase development of the non proliferation experiment within the western united states abstract to effectively monitor a comprehensive test ban treaty seismologists must be able to confidently detect and identify low yield explosions this requires the use of short period regional phases which can be extremely complicated the non proliferation experiment npe was a low yield chemical explosion detonated at the nevada test site nts and recorded at more than 50 broadband seismic stations located throughout the western united states these data were used to investigate the development of lg and pn two seismic phases used in regional discriminants the frequency dependent attenuation for lg recorded at 43 stations is described by the relation q lg vertical 238 f 1 28 the amplitude decay for pn recorded at 38 stations is proportional to 1 29 0 05 f for the frequency window of 1 to 6 hz after removing the effects of distance and attenuation we found the values of the spectral ratio lg 4 6 2 4 to group according to the geologic terrain associated with the path traveled stations located within the basin and range had lower ratio values than stations located outside the basin and range however for the spectral ratio pn 2 4 4 6 geologic terrain had an indirect effect pn is affected by moho structure associated with the backazimuth causing an azimuthal dependence of course moho structure can be a function of geologic terrain furthermore the pn arrival may be large or small independent of azimuth the values of the discriminant phase ratio pn 1 2 lg 2 4 have an order of magnitude more scatter than lg lg or pn pn nonetheless the values are both a function of geologic terrain the lg contribution as well as moho structure pn contribution

regional mb ms lg pg amplitude ratios and lg spectral ratios as criteria for distinguishing between earthquakes and explosions a theoretical study summary theoretical seismograms for point explosion and double couple sources in a uniform plane layered earth are used to evaluate the likely effectiveness of three criteria that have been proposed for distinguishing between earthquakes and explosions the criteria are regional ms ms lg pg amplitude ratios and lg spectral ratios for explosions in material with a high wave speed the near regional mb ms discriminant gives only marginal separation between the two types of source ranging from zero for strike slip earthquakes to on average 0 4 magnitude units for 45d dip slip mechanisms only for explosions in material with a low wave speed do the theoretical data show an overall separation lg pg amplitude ratios successfully separate the source types except for strike slip earthquakes where there is overlap with shallow explosions theoretical lg spectra for deep 1 5 km explosions are depleted in high frequencies when compared with those for earthquakes and shallow explosions discrimination between earthquakes and these deep explosions is therefore possible using the spectral ratio method an important mechanism underlying these lg based discriminants is the interaction of the spherical p wavefront from an explosion with the free surface which generates shear waves with amplitude depending both on frequency and source depth of burial

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

enhanced seismic source discrimination using noress recordings from eurasian events summary the problem of discriminating between earthquakes and underground nuclear explosions is formulated as an exercise in pattern recognition approach analysis an advantage of our procedure is flexibility by combining both adaptive noise suppression and event classification incorporating feature selection criteria the analysis has been applied to a learning set of 44 nuclear explosions eight test sites and 35 earthquakes in eurasia recorded at the noress array fig 1 the signal features considered were the normalized power in eight spectral bands in the 0 2 5 0 hz range of the p wave 6 s and the p coda 30 s physically it means that we exploit potential differences in the shape of earthquake and explosion spectra respectively other features included are peak p and p coda amplitude frequencies and relative p p coda power these 19 features were extracted either from conventional array beam traces or the optimum group filtered traces ogf removal of coherent low frequency noise using the feature selection algorithm based on estimates of the expected probability of misclassification epmc only two to four features were needed for optimum discrimination performance the dominant features were coda excitation and p and p coda power at lower signal frequencies furthermore feature parameters extracted from the ogf traces had a slightly better performance in comparison to those extracted from beam traces finally there were no misclassifications for ogf derived features when the explosion population was limited to east kazakh events while including events from the other test sites lead to a decrease in discrimination power

source inversion of seismic waveforms the koyna india earthquakes of 13 september 1967 abstract the treatment of the seismic source inverse problem when diverse forms of waveform data are available is simple and elegant using a moment tensor formalism if earth structure is known and its effects predictable in terms of vertically inhomogeneous elastic layered models then all types of wave phenomena e g surface waves body waves leaky modes etc for a purely deviatoric moment tensor point source may be represented by at most a sum of three green9s functions for an arbitrary symmetric moment tensor point source one additional green9s function is needed for the p sv system however elegant this formalism may be for posing the linear inverse problem the major difficulties lie in earth structure unknowns and resultant nonlinearities in the green9s functions which can cause significant trade offs with source parameters a hybrid inversion procedure is set up to gain insight into the probable unknowns in particular problems by incorporating both a linearized least squares gradient method for the moment tensor or double couple and smoothed time function parameters and a nonlinear systematic trial and error search for moment tensor or double couple parameters for several assumptions of green9s function the inversion technique is applied to near regional waveform data from a small earthquake associated with the koyna reservoir which occurred 13 september 1967 as the second in a group of three events with very similar waveshapes but differing amplitudes the magnitudes of the second and third events are smaller by 0 2 and 0 8 units respectively compared to the first the absolute magnitude for the first event is poorly constrained but is estimated to be 4 0 to 4 5 rather than the previously published value of 5 5 to 6 0 from the similarity of waveshapes all three events are inferred to have the same mechanism and occurred within about 2 km of the same hypocenter the results from moment tensor and double couple inversions for event 2 data indicate that source depth was 5 km and that left lateral faulting occurred on a plane with a strike of n20 e 5 dip of 90 15 and a rake of 0 35 the inferred far field time function is approximately 3 sec in duration unusually long for the seismic moment of 9 10 22 dyne cm yielding a possible stress drop of about 0 05 bars a fault map was constructed from landsat image interpretation and shows a predominance of nnw to nne striking faults in the koyna area which is used to infer the appropriate nodal plane in the inversion results these faults tend to define a broad en echelon zone which parallels the western ghats in this area

single station spectral discrimination using coda waves spectral discrimination methods applied at regional distances are based on the observation that there is a difference in the frequency content of the seismic waves radiated from the source region of earthquakes and explosions we have investigated a spectral discrimination method that exploits the scattered energy contained in the event codas of seismograms to measure the relative source excitation of earthquakes and explosions as a function of frequency key strengths of the coda method include the following 1 it is not affected by source radiation pattern because the scattering process averages the radiation over the focal sphere 2 path corrections are not required with the coda method because coda waves are scattered throughout a common crustal volume 3 it can be successfully applied using data from only a single station and 4 it can be successfully applied using data with clipped direct arrivals to implement the coda method we first estimate a type curve which represents the average shape of all the individual coda decay curves for a particular frequency band the shape of the type curve as well as the shape of all individual coda decay curves is controlled by the scattering and attenuation properties of the crustal volume sampled by the coda waves a common path effect the amplitude of the type curve is not defined and we arbitrarily adjust it to have a zero mean the amplitude difference between an individual event coda decay curve and the type curve provides a relative measure of the event s source size within the particular frequency band we define this amplitude difference as the relative source factor our approach exploits all of an event s usable coda for each spectral measurement thus providing a more stable measure of relative source size than could be obtained from using a predefined fixed length time window analysis of 27 nevada test site explosions and 15 southern great basin earthquakes 3 1 m 4 7 shows that the source factor difference between the 0 5 to 1 and 2 to 4 hz bands plotted against the 1 to 2 hz source factor is a stable event discriminant the method reliably distinguishes small explosions from small earthquakes 3 0 m 3 5 even if the explosions are overburied because the coda method requires only one seismic station we believe that it would be especially useful in identifying small clandestine underground nuclear tests that occur far from established networks

observations in support of rg scattering as a source for explosion s waves regional and local recordings of the 1997 kazakhstan depth of burial experiment abstract in august and september of 1997 three 25 ton chemical explosions were detonated at nominal depths of 550 300 and 50 m in boreholes at the former soviet test site at balapan kazakhstan one objective of this experiment was to evaluate the effect of differing source depth on the regional wave field analysis of regional seismic phases lead to the observation that regional p s wave amplitude ratios in the 1 to 5 hz band increase as a function of source depth however at frequencies greater than about 5 hz the relative amplitudes of p and s waves remain approximately constant for the differing depth shots similarly regional coda spectra are amplified in the 1 to 5 hz band for the shallow shots at local distances rg is the dominant seismic phase with peak amplitudes in the 0 7 to 5 hz range and rg is strongest for the shallower shots within the short distance spanned by the local stations rg is rapidly attenuated and the attenuation is accompanied by a significant shift in peak amplitude toward lower frequency at regional distances rg is below the noise level the coincident frequency band in which local rg rapidly loses energy and regional s phases are amplified points toward rg scattering as the dominant mechanism causing the discrepancies between p s amplitude ratios in this study these observations are particularly relevant to the understanding of physical processes affecting regional p s discriminants and may lead to improvements in discriminant methods

expanse of greater india in the late cretaceous abstract knowing the original size of greater india is a fundamental parameter to quantify the amount of continental lithosphere that was subducted to help form the tibetan plateau and to constrain the tectonic evolution of the india asia collision here we report paleomagnetic data from upper cretaceous rocks of the western tethyan himalaya that are consistent with a model that greater india extended 2700 km farther north from its present northern margin at the longitude of 79 6 e before collision with asia our result further suggests that the indian plate together with greater india acted as a single entity since at least the early cretaceous the pre collision geometry of greater india s leading margin helped shape the india asia plate boundary the proposed configuration produced right lateral shear east of the indenter thereby accounting for the clockwise vertical axis block rotations observed there

spectral analysis of underwater explosions in the dead sea the present study utilizes the israel seismic network isn as a spatially distributed multichannel system for the discrimination of low magnitude events ml 2 5 namely earthquakes and underwater explosions in the dead sea in order to achieve this we began with the application of conventional single station methods such as spectral short period ratios we then applied a newly developed network oriented algorithm based on different spectral features of the seismic radiation from underwater explosions and earthquakes i e spectral semblance statistics twenty eight single shot underwater explosions uwes and 16 earthquakes in the magnitude range ml 1 6 2 8 within distances of 10 150 km recorded by the isn were selected for the analysis the analysis is based on a smoothed 0 5 hz window fourier spectrum of the whole signal defined by the signal to noise criterion without picking separate wave phases it was found that the classical discriminant of the seismic energy ratio between the relatively low frequency 1 6 hz and high frequency 6 11 hz bands averaged over an isn subnetwork showed an overlap between uwes and earthquakes and cannot itself provide reliable identification we developed and tested a new multistation discriminant based on the low frequency spectral modulation lfsm method in our case the lfsm is associated with the bubbling effect in underwater explosions the method demonstrates a distinct azimuth invariant coherency of spectral shapes in the low frequency range 1 12 hz of short period seismometer systems the coherency of the modulated spectra for different isn stations was measured by semblance statistics commonly used in seismic prospecting for phase correlation in the time domain the modified statistics provided an almost complete separation between earthquakes and underwater explosions

single station seismic event detection and location a seismic event detection and source location sedsl scheme which uses single station three component seismic data to analyze seismic event is presented each station monitors ground motion along three orthogonal directions vertical north and east to detect events sedsl combines the signals on the three components in a manner analogous to beam steering once an event is detected sedsl estimates the bearing of the source with respect to the receiver by estimating the polarization direction of the initial compressional phase the range estimate is then obtained from the relative times of arrival of the different phases

hypocenter constraint with regional seismic data a theoretical analysis for the natural resources defense council network in kazakhstan ussr source depth and epicenter determination remains a simple but key method for discrimination between earthquakes and nuclear explosions at near regional distances a variety of secondary body wave arrivals can be observed that may be useful for constraining source depth and epicenter in this paper we study the source location problem using regional arrival time and arrival azimuth data from a sparse seismic network a theoretical analysis of the source location inverse problem provides estimates of the stability and uncertainty of the solution for a particular suite of data as a function of epicenter and depth as well as evaluating the importance of each datum to the solution an empirical analysis with actual data complements the theoretical analysis our approach is applied to the three station natural resources defense council soviet academy of sciences network in kazakhstan the theoretical analysis indicates that reasonable constraint on depth and epicenter is possible whenever three distinct phases p pn pg pzp and pmp or equivalent s phases are observed at two or three stations our theoretical analysis for two station locations shows that the epicenter constraints are extremely poor for sources along the line passing through the two observing stations the use of arrival azimuth in two station locations results in improvement in epicenter constraint for events occurring in the vicinity of the line connecting the two stations but there is no significant improvement elsewhere an empirical analysis of data from two of the september 1987 chemical explosions and data from an explosion in an active mining area supports the theoretical analysis showing that two station locations both epicenter and depth are quite reliable furthermore the theoretical analysis also indicates that even with data from a single observing station satisfactory results are obtained if three or more phases plus arrival azimuth are available

spectral characteristics of regional phases recorded at noress abstract the spectral characteristics of pn and lg are studied for regional events recorded at the noress array in norway the emphasis is on the potential value of spectral ratios for identifying events as earthquake chemical explosions and nuclear explosions the events studied include a suite of explosions from the titania mine in southwest norway a suite of events of unknown source type from a site offshore about 90 km from this mine suites of explosions from several mines in the soviet union about 1000 km from noress events from several locations along the 90 azimuth from noress an apparent earthquake in the north atlantic and a nuclear explosion pne at a range of 1560 km the event identification issues addressed are as follows 1 can earthquakes and explosions be identified based on the ratio of high and low frequency energy in their signal spectra 2 do spectral ratios separate mine blasts from earthquakes for all source areas 3 will spectral ratio discriminants be effective for identifying decoupled underground nuclear explosions we conclude that spectral ratios can sometimes separate events an example is separation of the titania mine blasts from the events at the nearby offshore locations although we cannot be sure how much this is due to path differences however in general spectral ratios vary as much within classes of events as they do among different classes the pne in our data set allows the simulation of spectra from a decoupled nuclear explosion by simply applying the frequency dependent decoupling factor to the observed pn spectrum for this event after applying a distance correction the spectrum for this simulated decoupled nuclear explosion is similar to those for the soviet union mine blasts in our data set

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

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

numerical modelling of sh lg waves in and near continental margins summary the effect of transition regions between continental and oceanic structures on the propagation of l waves from continental sources is examined in particular the attenuation due to variations in layer thickness in such transition regions is calculated and explained for a suite of simple models the measured attenuation due tq the geometry of the transition regions between the oceanic and continental structures within a partially oceanic path with source and receiver in a continental structure is at most a factor of four for frequencies from 0 01 to 1 hz this is inadequate to explain the observed extinction of l along such paths this extinction has previously been attributed to the effects of the transition region geometry the method used to calculate the results presented in this study is developed and its validity and accuracy are demonstrated propagator matrix seismograms are coupled into a finite element calculation to produce hybrid teleseismic sh mode sum seismograms these hybrid synthetics can be determined for paths including any regional transition zone or other heterogeneity that exists as part of a longer mostly plane layered path numerical results presented for a suite of transition models show distinct trends in each of the regions through which the wavefield passes the wavefield passes through a continent ocean transition region then a region of oceanic structure and finally through an ocean continent transition region when an l wavefront passes through a continent ocean transition the amplitude and coda duration of the l wave at the surface both increase at the same time much of the modal l energy previously trapped in the continental crust is able to escape from the lower crust into the subcrustal layers as body waves the magnitude of both these effects increases as the length of the transition region increases when the wavefront passes through the region of oceanic structure further energy escapes from the crustal layer and produces a decrease in l amplitude at the surface the rate of amplitude decrease is maximum near the transition region and decreases with distance from it when the wavefield passes through the oceancontinent transition region a rapid decrease in the l amplitude at the surface of the crust results the energy previously trapped in the oceanic crustal layer spreads throughout the thickening crustal layer some of the body wave phases produced when the wavefield passes through the continent ocean transition region are incident on the continental crust in the ocean continent transition region these waves are predominantly transmitted back into the crust the other body wave phases reach depths below the depth of the base of the continental crust before reaching the ocean continent transition and thus escape from the system

evidence for early 44 ma himalayan crustal thickening tethyan himalaya southeastern tibet abstract comprehensive understanding of himalayan orogenesis is limited in part by a poor knowledge of the eohimalayan episode a phase of tectonic activity predating the better understood neohimalayan crustal thickening associated with coaxial deformation along the main central thrust the cambo ordovician to tertiary metasedimentary sequences outcropping within the tethyan himalaya are the structurally highest units of the himalayan fold and thrust belt they and are inferred to have been the first to have accreted to asia a compilation of data from transects along the length of the main himalayan arc shows that the tethyan sequences have experienced at least five deformation events although the timing of these episodes is poorly constrained emplacement of a series of undeformed granitoid bodies following the second of these events which accounts for the majority of crustal thickening in the tethyan himalayan units is constrained by u pb zircon dating to be older than 44 1 1 2 ma thus significant crustal thickening had occurred along the length of the proto himalayan arc by the mid eocene or within 10 to 20 myr of the initiation of himalayan orogenesis

greater india basin hypothesis and a two stage cenozoic collision between india and asia cenozoic convergence between the indian and asian plates pro duced the archetypical continental collision zone comprising the himalaya mountain belt and the tibetan plateau how and where india asia convergence was accommodated after collision at or be fore 52 ma remains a long standing controversy since 52 ma the two plates have converged up to 3 600 35 km yet the upper crustal shortening documented from the geological record of asia and the himalaya is up to approximately 2 350 km less here we show that the discrepancy between the convergence and the shortening can be explained by subduction of highly extended continental and oceanic indian lithosphere within the himalaya be tween approximately 50 and 25 ma paleomagnetic data show that this extended continental and oceanic greater india promontory resulted from 2 675 700 km of north south extension between 120 and 70 ma accommodated between the tibetan himalaya and cratonic india we suggest that the approximately 50 ma india asia collision was a collision of a tibetan himalayan microconti nent with asia followed by subduction of the largely oceanic greater india basin along a subduction zone at the location of the greater himalaya the hard india asia collision with thicker and contiguous indian continental lithosphere occurred around 25 20 ma this hard collision is coincident with far field deforma tion in central asia and rapid exhumation of greater himalaya crys talline rocks and may be linked to intensification of the asian monsoon system this two stage collision between india and asia is also reflected in the deep mantle remnants of subduction imaged with seismic tomography

discrimination of chemical explosions and earthquakes in central europe a case study both natural and artificial seismicity is observed in the vogtland area at near regional distance 180 km from the geress array this setting offers the opportunity to test various discrimination criteria using a uniform data set of 39 earthquakes and 22 chemical explosions strip mine and quarry blasts from a single epicentral region mostly eliminating wave path and distance effects discriminants used include lg pg and lg rg maximum amplitude ratios spectral peaks and slopes extracted by autoregressive moving average arma modeling master event correlation and the search for time independent frequency structures in sonograms although no single discrimi nant achieves a perfect separation of the two populations a joint discrimination scheme employing simple majority voting reduces misclassifications to 2 future research will focus on possible generalization and the physical basis of the discriminants

lg attenuation near the north korean border with china part ii model development from the 2006 nuclear explosion in north korea an underground nuclear explosion was set off on 9 october 2006 in north korea the event was recorded at near regional to regional distances over purely continental paths by a network of broadband seismographs located along the northern edge of the korean peninsula the event provided the first window of opportunity to make a reliable measurement of lg wave attenuation in northernmost north korea where the regional phase propagation characteristics are poorly known the results of our analysis show q0 317 14 and 0 343 0 024 in close agreement with the corresponding values obtained of late using a completely different methodology and an independent set of seismic recordings in an adjacent region to the northwest in southern jilin and in liaoning provinces in china

paleomagnetic results from the early cretaceous lakang formation lavas constraints on the paleolatitude of the tethyan himalaya and the india asia collision abstract to better constrain the early cretaceous paleogeographic position of the tethyan himalaya and the india asia collision process a paleomagnetic study was performed on the lakang formation lava flows in the cuona area in the southeastern tethyan himalaya stepwise thermal and alternating field demagnetizations successfully isolated reliable characteristic remanent magnetization chrm directions that include antipodal dual polarities and pass positive fold tests at the 99 confidence level and reversal tests at 95 confidence level indicating prefolding primary magnetizations the distribution patterns of chrm directions from the lakang formation lava flows are consistent with young lava flows at similar latitudes suggesting that secular variation has likely been averaged out the tilt corrected site mean direction for 31 sites is d 261 6 i 68 5 with 95 3 6 which provides a paleopole at 26 8 s 315 2 e a 95 5 7 corresponding to a paleolatitude of 52 2 5 7 s for the study area comparison of the paleolatitude observed from the lakang formation lava flows with that expected from the apparent polar wander paths of india at 130 ma show a paleolatitude difference of 2 1 230 km indicating that neither a great north south continental crustal shortening occurred between the indian craton and the tethyan himalaya after 130 ma nor that a wide ocean separated them at that time comparison with reliable cretaceous paleocene paleomagnetic results observed from the tethyan himalaya and the lhasa terrane indicates that the latitudinal width of the neo tethyan ocean could have been up to 7000 km at 134 130 ma and an extension should have existed between the indian craton and the tethyan himalaya during the late cretaceous and paleocene furthermore reliable paleomagnetic results suggest that the india asia collision was a dual collision process consisting of a first collision of the tethyan himalaya with the lhasa terrane asia at 54 9 2 3 ma and a final continent continent collision of the indian craton with the tethyan himalaya at 40 0 3 3 ma

a system to mitigate deep mine tremor effects in the design of civil infrastructure deep mining may induce quakes reaching magnitude ml of 4 5 to 5 5 and leading to surface ground motion with modified mercalli intensities up to viii such strong ground motions may cause serious damages in civil infrastructure in the vicinity of mines however any adaptation of a classic seismic code in design faces an impending problem of differences in spectral content and duration between the surface records of the rockbursts and natural earthquakes as well as in their different risk definitions this paper presents a system to define design seismic load based on forecasted surface horizontal particle velocity from the rockbursts expected during the planned mining activities such forecasts are routinely prepared by the geophysical mine services respective seismic load may then be applied in the design of buildings and other structures to mitigate the rockburst induced seismic effects on them for this purpose the european seismic code eurocode 8 is adapted

propagation efficiency of long period lg waves in the south american continent summary we investigate the propagation efficiency characteristics of long period 3 12 s lg waves in continental south america as recorded in the last few years on stations of the gtsn iris usgs irisiida and geoscope networks this paper reports the results of a first look at the available lg data for events with m 5 0 from 1990 to 1995 in this period seven main seismic events and aftershocks along the length of the andes produced a total of 29 usable paths from which preliminary results indicate that 1 long period lg waves are unusually prominent in seismograms of continental paths covering the shield areas of south america and are clearly observed on broad band instruments at epicentral distances exceeding 3500 km 2 lg propagation is substantially attenuated weak or absent for paths along the strike of the andes and along the three active volcanic chains of chile peru and colombia 3 away from the active volcanoes the data show lg propagating more efficiently across than along the strike of the andes and 4 in general the ratio of the transverse to the vertical components of the lg phase decreases with decreasing propagation efficiency these first results also raise a number of exciting questions regarding the exploration of the crustal waveguide in south america such as the potential for lgbased tomography to detect a postulated fossil plume in southeastern brazil or how the propagation efficiency of high frequency lg in volcanically active areas may be used to detect magma chambers consequently we intend to carry out a systematic study of lg in the continent as part of the ongoing surface wave inversion for the south american lithosphere sisal project a collaborative effort vdovin et al 1996 to determine the crustal and lithospheric structure of the south american plate from measurements of surface wave dispersion in the period range 2 200 s

discrimination of earthquakes and explosions in southern russia using regional high frequency three component data from the iris jsp caucasus network high frequency regional records from small earthquakes magnitude 4 5 and comparable magnitude chemical explosions are analyzed to find a reliable seismic discriminant in southern russia near kislovodsk the digital three compo nent seismograms recorded during 1992 by the caucasus network operated by la mont doherty earth observatory since 1991 in the distance ranges 15 to 233 km are used mean vertical component pg lg spectral amplitude ratios in the band 8 to 18 hz are about 1 3 and 3 2 for earthquakes and explosions respectively in this region we find that the vertical component pg lg spectral ratio in the frequency band 8 to 18 hz serves quite well for classifying these events a linear discriminant function analysis indicates that the pg lg spectral ratio method provides discrimination power with a total misclassification probability of about 7 the pg lg spectral ratios of rotated three component regional records improve the discrimination power of the spectral ratio method over the vertical component pg lg ratios preliminary analysis indicates that distance corrected vertical component pg lg ratios improve the dis crimination power by about 4 over uncorrected ratios but we find that an even better discriminant is the pg lg spectral ratio of the three component regional records corrected for the free surface effect in the frequency band 8 to 18 hz the free surface corrected three component pg lg spectral ratio provides discrimination power with a total misclassification probability of only 2 6 free surface corrected and network averaged pg lg spectral ratios provide transportability of the spectral ratio method to various regions worldwide

regional seismic discriminants using wave train energy ratios we have examined broadband regional waveforms of recent since 1988 nevada test site nts underground explosions and earthquakes throughout the southwestern united states and baja mexico recorded by terrascope and other iris stations in order to characterize seismic sources for the purposes of event identification as expected earthquakes tended to be richer in long period surface wave and short period shear wave energy relative to explosions of comparable p wave strength also explosions in general were found to be richer in 1 to 6 sec surface wave rg energy and other late arriving coda energy than were earthquakes most earthquakes show relatively little long period t 6 sec rg and surface wave coda energy which we attribute to their deeper source depths whereas known shallow earthquakes do exhibit these phases we have developed several seismic discriminants based on our observations the most promising discriminant is the ratio of short period f 1 0 hz vertical component pnl wave train energy esppz to long period 0 05 to 0 167 hz three component surface wave energy e lp 3 for this ratio explosions tend to have a higher value than do earthquakes this discriminant works on the same premise as the teleseismic mb ms ratio for which earthquakes are richer in long period surface wave energy relative to explosions with the same body wave magnitude the long period passband was chosen to limit the effect of longer period noise and to remove the effect of the coda surface waves another potential discriminant examined is the ratio of short period f 1 0 hz vertical component p wave to s wave energy esppz espsz we find that this criterion only yields marginal separation of the source populations but becomes more effective at higher frequency bands f 4 0 hz or when looking at single station observations it does however help to quantify significant short period waveform differences between the three test subsites with pahute mesa shots generating relatively little s wave energy compared to those of yucca flat for which the s wave or lg is often the largest phase while rainier s shots are intermediate in character with distinct but less prominent s waves this s wave generation is thought to be caused by near source scattering to converted phases and appears to be highly dependent on the near source geology these two discriminants are useful in that they are simple and fast to calculate using regional stations for sources 200 to 1300 km away the magnitude threshold for the esppz e lp 3 discriminant is roughly ml 4 0 the limiting factor being the signal level of the airy phase while that for the esppz espsz discriminant is roughly ml 3 0 for the same distance ranges

an investigation of discriminants for events in western ussr based on regional phases recorded at station kabul short period vertical component records at the wwssn station kabul for 13 earthquakes and 8 nuclear explosions occurring within a region of efficient propagation of lg are examined to explore the possibility of using ratios of amplitudes in different group velocity windows as a discriminant each seismogram is divided into 10 windows with boundaries representing pn and group velocities of 6 0 5 0 4 5 4 0 3 8 3 6 3 4 3 2 3 0 and 2 8 km sec the first three windows include crustal phases pn pg and sn respectively whereas the six windows from 4 0 to 2 8 km sec encompass the expected group velocity of higher mode rayleigh waves that include lg the ratio of the maximum amplitude before the arrival of sn to the maximum amplitude thereafter is significantly larger for explosions than for earthquakes and provides the largest separation between earthquake and explosion populations considerable separation is also shown by amplitude ratios pn lg and pn pg amplitude ratios based on earlier and later arriving lg phases and the amplitude ratio sn lg show insignificant discrimination the ratio maximum before sn maximum after sn is expected to be a useful regional discriminant for events in the western ussr

magnetic properties of pelagic marine carbonates abstract pelagic carbonates are deposited far from continents usually at water depths of 3000 6000 m at rates below 10 cm kyr and are a globally important sediment type recent advances with recognition of widespread preservation of biogenic magnetite the inorganic remains of magnetotactic bacteria have fundamentally changed our understanding of the magnetic properties of pelagic carbonates we review evidence for the magnetic minerals typically preserved in pelagic carbonates the effects of magnetic mineral diagenesis on paleomagnetic and environmental magnetic records of pelagic carbonates and what magnetic properties can tell us about the open ocean environments in which pelagic carbonates are deposited we also discuss briefly late diagenetic remagnetisations recorded by some carbonates despite recent advances in our knowledge of these phenomena much remains undiscovered we are only at early stages of understanding how biogenic magnetite gives rise to paleomagnetic signals in sediments and whether it carries a poorly understood biogeochemical remanent magnetisation recently developed techniques have potential for testing how different magnetotactic bacterial species which produce different magnetite morphologies respond to changing nutrient and oxygenation conditions future work needs to test whether it is possible to develop proxies for ancient nutrient conditions from well calibrated modern magnetotactic bacterial occurrences a tantalizing link between giant magnetofossils and paleogene hyperthermal events needs to be tested much remains to be learned about the relationship between climate and the organisms that biomineralised these large and novel magnetite morphologies rather than being a well worn subject that has been studied for over 60 years the magnetic properties of pelagic carbonates hold many secrets that await discovery

phase and spectral ratio discrimination between nts earthquakes and explosions part i empirical observations seismic discrimination of small magnitude mb 0 5 hz regional measurements in this study we evaluate the most promising short period discriminants p wave to s wave phase amplitude ratios and low to high frequency spectral amplitude ratios for a data set from the nevada test site the data consist of 130 underground nuclear explosions one very large chemical explosion and 50 earthquakes ranging from magnitude 2 to 6 recorded at two broadband digital seismic stations operated by lawrence livermore national laboratory in contrast with much previous discrimination work in the western united states the common stations and paths for all the events in this study allow the discriminants to be evaluated without applying propagation corrections and differences between events can be ascribed to very near source effects the source effects found to have the most influence on the discriminants in this study are depth for the earthquakes and the source medium properties of gas porosity density and velocity for the explosions the phase amplitude ratio discriminants tested are pn lg and pg lg both show little dependence on magnitude and work better at higher frequencies and when averaged over the two stations at 6 to 8 hz pn lg discriminates all except the shallowest earthquakes while pg lg discriminates all but the high gas porosity explosions low to high frequency spectral amplitude ratio discriminants were tested in each of the phases pn pg lg and lg coda the explosions show significant dependence on source material properties such as gas porosity all the spectral ratios show dependence on magnitude and for 1 2 hz 6 8 hz none performs well below magnitude 3 5 of the spectral ratios lg coda performs the best at least in part because of its extremely small interstation variability discriminating all but the low gasporosity explosions the best discriminant performance is given by combining phase and spectral ratios a sum of the logarithmic values of pn lg pg lg and the lg coda discriminates all but two of the shallowest earthquakes the source medium dependence of the discriminants suggests that discrimination performance differences between the western united states and other regions of the world may be due more to source property differences than differences in the regional path simply put western united states discriminant studies differ from those in the rest of the world because of the lack of explosions in very high gas porosity low velocity materials outside of the nevada test site

paleomagnetism and u pb zircon geochronology of lower cretaceous lava flows from the western lhasa terrane new constraints on the india asia collision process and intracontinental deformation within asia to better understand the india asia collisional process and intracontinental deformation within asia a paleomagnetic study has been conducted on the qushenla formation lava flows dated at 132 120 ma from the yanhu area in the western lhasa terrane stepwise thermal demagnetization isolates stable characteristic remanent magnetizations which include dual polarity and pass fold tests at a 99 confidence level indicating primary magnetizations the tilt corrected site mean direction for 51 sites is d 28 2 i 34 5 and k 74 3 with 95 2 3 corresponding to a paleopole at 61 4 n 192 9 e a95 2 1 our new paleomagnetic data combined with previous cretaceous volcanic paleomagnetic data from the lhasa terrane show that the precollisional southern margin of asia was at 16 8 n with a relatively e w alignment and that the lhasa terrane did not experience significantly discrepant north south movement although local vertical axis rotations did take place after the cretaceous comparison with the apparent polar wander paths apwps of india and the cretaceous paleocene paleopoles of the tethyan himalaya shows that the india asia collision was at 54 3 ma and the greater india during the paleocene had a large northern extent of 2000 km 18 1 beyond its present northern margin comparison with the cretaceous eurasian apwp indicates that a latitudinal convergence of 1000 km has taken place between the lhasa terrane and eurasia since the india asia collision the amount of north south shortening deduced from cretaceous paleomagnetic data is consistent with that accommodated by the cenozoic fold and thrust belts between the lhasa terrane and the hexi corridor

a preliminary study of regional seismic discrimination in central asia with emphasis on western china abstract in support of a comprehensive test ban treaty we have started to evaluate regional seismic event discrimination capabilities for central asia emphasizing western china we have measured noise and signal levels of over 260 earthquakes and 26 underground nuclear explosions recorded at the broadband digital station wmq in western china and over 120 earthquakes and five nuclear explosions at station aak in kyrgyzstan the explosions are from the kazakh test site kts and lop nor china the earthquakes are mostly from northwest china event magnitudes measured as either m b or m l range between 2 5 and 6 5 and maximum event station distance is about 1700 km we formed phase spectral cross spectral short period long period and long period ratios to test many possible event discriminants all ratios were corrected for distance effects before forming ratio versus magnitude discrimination plots the most consistent discriminants for separating earthquakes from explosions are p s phase ratios for frequencies above 3 to 4 hz p wave f 1 hz to rayleigh wave 0 03 hz f p s ratios separation between earthquakes and explosions increases with frequency and for the p r ratios separation increases with increasing p frequency the p 3 to 6 hz s 0 75 to 1 5 hz cross spectral ratios also separate earthquakes and explosions these cross spectral ratios may prove quite useful because due to weak high frequency l g signals from explosions the high frequency p l g ratio sometimes cannot be evaluated but the p 3 to 6 hz l g 0 75 to 1 5 hz can be evaluated successfully p spectral ratios 3 to 6 hz 0 75 to 1 5 hz also separate earthquakes and explosions but not quite as consistently as the p s ratios however p spectral ratios may prove useful in cases where path effects block or highly attenuate s n and l g waves rendering the p s ratios unavailable in contrast to nevada test site nts events the l g 3 to 6 hz 0 75 to 1 5 hz spectral ratio does not separate earthquakes and nuclear explosions in central asia this observation may be a source effect as asian explosions are thought to be detonated in highly lithified rocks below the water table while most of the smaller m b for station aak the short period spectral and cross spectral ratios identify a few earthquakes not recorded at wmq from the north pamir region that plot with the lop nor explosions the waveforms from these earthquakes lack surface waves and a distinct l g phase these events which we interpret as having occurred in a subducted slab do separate from the explosions on high frequency f 4 hz p s discrimination plots for station wmq long period r l rayleigh wave love wave ratios separate kts explosions and asian earthquakes however r l ratios fail to identify the large lop nor explosions recorded at station aak because the love waves are as large as the rayleigh waves suggesting that strong tectonic release occurs with these explosions because we have examined only one path at a single station for these explosions source radiation pattern may be influencing this observation

aspects of pn and pg propagation at regional distances generalized ray theory models are calculated for a moment tensor point source in two idealized structure models appropriate for the eastern united states to study the wave propagation of regional pn and pg the models are analyzed to determine useful discriminants between earthquakes and explosions pg is composed of multiply reflected postcritical rays trapped in the upper crustal layer the amplitude decay with distance of pg is found to be source dependent and may be useful as a discriminant in well calibrated earth structures pg waves from dip slip sources fall off r 0 5 to r 0 9 faster than those from isotropic and vertical strike slip sources where r is the horizontal distance in conjunction with previously published refraction results and magnitude studies it is shown that regional pn along many profiles in eastern north america consists principally of high amplitude turning rays rather than head waves as observed in the western united states these turning rays are as large or larger than the pg phase explaining why pg is not as commonly observed as a distinct phase in the east as compared with observations in the western united states