inversion of rg waveforms recorded in southern spain abstract group velocity dispersion measurements of r g waves generated either by blasts or by local earthquakes are used to investigate the shallow crustal structure of almeria southern spain in principle the usable frequency range of 250 to 2000 mhz allows determination of structures to depths of about 4 km for this purpose the main operations are a detailed dispersion analysis of high frequency rayleigh waves propagating along very short paths and the inversion of r g wave group velocities a total of 21 seismic events were studied these events had small magnitudes 2 0 to 2 5 approximately and very shallow focal depths about 100 m and were taken from a set of 214 events that occurred in 1991 during a spanish italian seismic experiment the events were recorded at seven single component stations belonging to the regional seismic network of andalucia at approximate distances of between 15 and 57 km from the source these events were grouped into six seismic sources according to specific criteria we used digital filtering techniques providing a significant improvement in signal to noise ratio to determine ray path group velocities and we inverted dispersion data via generalized inversion in order to obtain refined dispersion data we have carried out a further regionalization of group velocities and thus six small subregions have been resolved in group velocities the highest group velocity values from 1 93 to 2 25 km sec 1 correspond to the filabres mountain range which is an area containing materials of the nevado filabride complex of paleozoic and triassic age on the other hand low velocity values between 1 39 and 1 56 km sec 1 correspond to the alhamilla mountain range which belongs to the alpujarride complex and contains conglomerates of the cambrian and tortonian periods the velocities obtained for the neogene quaternary basin of the andarax river with materials of the tortonian and pliocene periods are also very low between 1 35 and 1 68 km sec 1 we inverted the regionalized group velocities in order to obtain the shear velocity structure of the region for depths down to 4 km according to the regional earth models that we obtained we find clear variations in velocity both laterally and vertically for several zones with different composition the filabres mountain range shows high shear velocity values 2 14 to 2 83 km sec 1 in the opposite end we have the andarax basin that presents the lowest shear velocity values consistent with its sedimentary structure 1 56 to 2 55 km sec 1 intermediate shear wave velocities characterize the remaining regions the tabernas sorbas basin the gador mountain range and the volcanic region of nijar cape of gata although the relationship between lateral changes in r g dispersion and geologic structure may not be straightforward in this study we have observed a correlation between those changes and the sharply contrasting geology between adjacent geological formations

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

synthesis of realistic oceanic pn wave trains the synthesis of realistic oceanic pn phases was accomplished using wave number integration wave trains with durations of the order of 100 s following the initial compressional wave arrival were generated for a laterally homogeneous vertically inhomogeneous oceanic lithosphere model the excitation of these long wave trains is primarily a result of near receiver water and sediment reverberations and does not involve scattering a late arriving wave train with a group velocity of 1 6 km s having an emergent onset and substantial duration characteristic of oceanic abyssal t phases was also generated even with phase velocities restricted to be greater than 5 5 km s the synthetic pn wave train was compared to data collected in the southwest pacific during the ngendei seismic experiment many of the spectral characteristics associated with sediment and water reverberation observed in the synthetics were also observed in the data first it was found that the amplitude falloff rate of the pn wave train is a strongly increasing function of frequency in direct contrast to results predicted for forward scattered coda this leads to a predominance of low frequencies late in the wave train which is easily interpreted in terms of the constructive interference of different modes of reverberation second the presence of spectral peaks at frequencies associated with both sediment and water reverberations was observed the predicted frequencies were computed using values of the water depth sediment thickness and sediment velocity obtained in an independent study strong alignment of the spectral peaks with the predicted frequencies illustrates the reverberating nature of the pn wave train the presence of substantial power in excess of 15 hz can be attributed to the confinement of pn to the oceanic lithosphere the oceanic pn phase is thus characterized as a refraction from the lower lithosphere with multiple reverberations in the oceanic water column and sediment layer comprising the subsequent coda complicated oceanic lithosphere models are not needed to explain the gross characteristics of pn propagation

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

an evaluation of seismic decoupling and underground nuclear test monitoring using high frequency seismic data an effective solution to the problem of the detection and identification of low yield coupled and fully decoupled underground nuclear explosions appears available via use of high frequency seismic data ranging up to 30 or 40 hz in order to evaluate detection identification capabilities when using such data it is necessary to estimate 1 spectral characteristics and relative amplitudes of both p and s waves from explosions and earthquakes over the frequency band from 5 to 40 hz 2 signal transmission characteristics over this band through pertinent types of earth structure and 3 recording system and ground noise characteristics over this frequency band in this study each of these topics is considered in turn as they relate to detection and discrimination of the signals from low yield coupled and decoupled explosions in the regional and teleseismic distance ranges estimates of the capabilities of specific hypothetical networks to detect and identify insofar as signal to noise ratio is an important factor in identification explosions within the ussr are then considered these estimates of signal detection capability provide the central focus for the study as they serve to translate diverse and rather complex sets of observational data and theory into concrete predictions of monitoring capability following the assessment of detection capabilities the problem of identification of small events is considered with particular emphasis on discrimination at regional distances where the network is calculated to provide signals of high signal to noise ratio the principal results and conclusions of this study are as follows 1 seismic system noise can be suppressed to levels well below ground noise at quiet sites up to frequencies at least as high as 30 40 hz when using presently available hardware 2 average amplitudes of high frequency noise in a variety of geological environments are very low and change little with time or season 3 transmission of high frequency p and s wave signals in the regional distance range in stable continental areas and shields is nearly as efficient as at 1 hz with effective q factors in shield areas being about 9000 and 4000 for high frequency pn and sn respectively while the effective q for pn waves in tectonic areas is about 1000 4 a properly designed and deployed network of 25 simple three component nonarray stations internal to the ussr and 15 similar stations surrounding the ussr is predicted to be capable of multistation detection at high signal to noise ratio of fully decoupled 1 kt explosions located at all potential decoupling sites within the ussr 5 by inference from the quantitative agreement of empirical observations and theoretical predictions when using lower frequency data over a great range of explosion yields we conclude that procedures based on the use of both detectable p and s waves will serve to identify explosion generated seismic signals at least as small as those expected from a fully decoupled 1 kt explosion

using group velocities of seismic phases for regional event discrimination we examined over the israel seismic network isn the seismogram envelopes vs group velocity v r t where r is the epicenter distance and t the travel time and found out a persistent difference between quarry blasts and earthquakes the data include 53 seismic events occurring in northern israel with magnitudes of ml 1 0 2 6 and at distances of 15 310 km within the 1 4 km s range we measured the velocity vms at which the envelope reaches its maximum for each isn station a simple linear discrimination function c b 0 33a based on an empirical relationship between the vms and r vms a b ln r provides effective separation between the regional earthquakes and explosions these results are attributed to different excitation of regional surface waves from these two types of seismic events

the 1983 goodnow earthquake in the central adirondacks new york rupture of a simple circular crack on 7 october 1983 a magnitude 5 1 mb earthquake occurred in the central adirondack mountains near the town of goodnow new york the earthquake was well recorded both by regional stations and by a large number of digital and analog seismographs in north and south america and europe these regional and teleseismic data are complemented by accurate locations of aftershocks recorded by a portable network from 17 hours after the main shock providing an unusually complete dataset to study the source process of an intraplate earthquake the results of an analysis involving the formal inversion of the vertical component rayleigh waves and of short period p waves show that the earthquake was due to reverse faulting with a centroidal depth of 7 5 km striking north south and dipping at 60 to the west the scalar seismic moment is 1 9 1023 dyn cm for p waves for paths from northeastern united states plausible values of t attenuation range from 0 4 to 0 7 sec and for these values the estimates of source duration range from 0 60 to 0 35 sec assuming a circular crack model with a rupture velocity of 3 0 km sec the bounds on source duration give upper and lower limits for the fault radius of 0 9 and 0 5 km and for the stress drop of 670 and 115 bars the preferred value of t 0 6 sec yields a source duration of 0 45 sec a radius of 0 7 km and a stress drop of 265 bars this fault radius agrees with that inferred from the spatial distribution of aftershocks the inferred stress drop of the goodnow earthquake is higher than generally observed for interplate events if the goodnow earthquake is representative of events in eastern north america the high stress drop may partially explain the large felt areas produced by these relatively small intracontinental earthquakes

rg as a depth discriminant for earthquakes and explosions a case study in new england fundamental mode rayleigh waves with periods between about 0 4 and 2 5 sec rg are often observed on seismograms of explosions and very shallow focus earthquakes the rg phase is particularly prominent on seismograms of quarry blasts in this study rg waves generated by small earthquakes and explosions in new england are investigated to evaluate the extent to which rg waves can be used to estimate depths of events in the upper crust the data were recorded by the new england seismic network nesn operated by weston observatory the strongest rg signals recorded by the nesn are generally in the period range of 0 5 to 1 5 sec in that period range rg displacement is essentially confined to the upper 5 km of the crust with most of the rg wave energy in the upper 2 or 3 km sources deeper than about 4 km would not be expected to generate strong rg signals at these periods and so if rg can be clearly identified on a seismogram the source is most likely very shallow observed rg waves can therefore be used to discriminate very shallow focus events from deeper events provided that rg can be identified and distinguished from other phases a method for identifying rg waves at distances up to about 170 km is presented in this paper rg is identified and distinguished from other phases by measuring amplitudes at particular periods and arrival times using a narrow bandpass filter analysis rg p and rg lg ratios are estimated by forming the ratios of amplitudes in the appropriate group velocity frequency windows on vertical component seismograms the phase referred to as lg is actually a complicated wave train recorded on short period seismograms that travels with group velocities appropriate for s and lg waves an rg lg ratio appears to be a better measure of the presence of rg on a seismogram than an rg p ratio observed rg lg ratios are used to estimate depths of two earthquakes recorded by the nesn

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

discrimination of small earthquakes and artificial explosions in the korean peninsula using pg lg ratios summary the purpose of this study is to develop a technique to discriminate artificial explosions from local small earthquakes m4 0 in the time frequency domain in order to obtain spectral features of artificial explosions and earthquakes 3 d spectrograms frequency time and amplitude have been used they represent a useful tool for studying the frequency content of entire seismic waveforms observed at local and regional distances kim simpson richards 1994 p and s l g waves from quarry blasts show that the frequency content associated with the dominant amplitude appears above 10 hz and rg phases are observed at close distances p and s l g waves from the tongosan earthquake have strong amplitudes below 10 hz for the munkyong earthquake however a broader frequency content up to 20 hz is found for discrimination between small earthquakes and explosions pg l g spectral ratios are used below 10 hz and through spectrogram analysis we can see diverent frequency contents of explosions and earthquakes unfortunately because explosion data recorded at ksrs array are digitized at 20 sps we cannot avoid analysing below 10 hz because of the nyquist frequency in order to select time windows the group velocity was computed using multiple filter analysis mfa and free surface evects have been removed from all three component data in order to improve data quality using fft a log average spectral amplitude is calculated over seven frequency bands 0 5 to 3 2 to 4 3 to 5 4 to 6 5 to 7 6 to 8 and 8 to 10 hz the best separation between explosions and earthquakes is observed from 6 to 8 hz in this frequency band we can separate explosions with log pg l g above 0 5 except exp1 recorded at sihy1 1 and earthquakes below 0 5 except the munkyong earthquake record at station kmh

identification of mining blasts at mid to far regional distances using low frequency seismic signals this paper reports results from two recent monitoring experiments in wyoming broadband seismic recordings of kiloton class delay fired cast blasts and instantaneous calibration shots in the black thunder coal mine were made at four azimuths at ranges from 1 to 2 the primary focus of this experiment was to observe and to explain low frequency signals that can be seen at all azimuths and should routinely propagate above noise to mid regional distances where most events will be recorded by international monitoring system ims stations

kinematic multistation discriminator between local quarry blasts and earthquakes it has long been known that s waves on seismograms of local explosions are often accompanied by strong low frequency low velocity rg surface wave trains often significantly diminished for earthquakes we utilize this fact to construct a new formal discriminator between earthquakes and explosions by measuring the s surface wave group velocity the method is based on analysing the velogram that is the display of the envelope of ground motion versus group velocity v r t where r is the epicentral distance and t the traveltime we examine the distribution of seismic energy in time and space using envelopes of records from the israel seismic network isn from which we compute the velograms and observe differences in the velograms of quarry blasts and earthquakes the data include 143 seismic events occurring in three areas galilee dead sea and gilad monitored by the isn the magnitude range is ml 1 0 2 8 at distances of 15 310 km from the velograms we measure the group velocity vms within the 1 4 km s 1 range at which the velogram reaches its maximum for each available station the resulting vms r function is closely fitted by the empirical relationship a b ln r with a and b coefficients varying from event to event a simple linear function c b 0 33a at a threshold c 0 69 completely separates a b pairs for the 67 galilee events and for the 76 remaining events one earthquake and four explosions are wrongly classified after data validation and application of the fisher linear discriminator adapted to the events from galilee only two misidentified events remain for the whole data set

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

shear velocity and intrinsic q structure of the shallow crust in southeastern new england from rg wave dispersion in this study we analyzed 0 5 2 0 s period rayleigh waves rg generated by quarry and construction blasting in southern new england cne we investigated group velocity dispersion and attenuation of the observed rg waves the paths crossing the hartford rift basin hrb show an obvious correlation between geology and rg dispersion the entire region in the southeastern new england comprising a wide range of geological structures and rock types from the bronson hill anticlinorium to the avalonian terrane can be represented as one dispersion region therefore the relationship between lateral changes in geologic structures mapped on the surface and rg dispersion is not as straightforward as might be expected for a best fitting flat layered model of the shallow crust the shear wave velocities appear to vary between 2 55 and 3 63 km s within the upper 2 5 km except for the central hrb where the variation is between 2 12 and 2 7 km s intrinsic q structure is considered to be the primary means for the loss of energy in the shallow crust and was analyzed by modelling the waveforms of several of the observed seismograms for this aspect of our study we used a modal summation of rayleigh waves assuming a far field radiation approximation the observed seismograms were dominated primarily by contributions from the fundamental mode but higher modes were also included in the synthesis of the waveform we were unable to model the absolute amplitudes of the waveforms because of the problems with the instrument calibration it is clear however that to predict correct waveforms the shear wave q values in the upper few tenths of a kilometer of the crust must be about an order of magnitude smaller than q values at the depth of 1 3 km which is of order of 100 250

wide angle seismic imaging of the elberton granite georgia a pilot study using instantaneous blasts at dimension stone quarries abstractwide angle recordings of small multiple hole blasts at dimension stone quarries in the elberton granite show coherent reflections at offsets between 7 and 15 km in contrast with much larger blasts at crushed stone quarries this type of blast is fired without delays between holes the data were recorded with an array of twenty portable seismographs using three component 4 5 hz geophones migration of source gathers for two of the blasts shows a number of subhorizontal interfaces at depths between 2 and 4 km that may represent a layered complex near the base of the granite other reflectors include southeast dipping interfaces at depths between 6 and 9 3 km and a more gently southeast dipping complex at 9 5 11 km that may represent the master decollement the results of the pilot study show that this type of quarry blast can be useful for imaging structure within the upper crust although preliminary the wide angle results support the interpretation that the elberton granite is a tabular body l

discrimination of earthquakes and explosions in the eastern united states using regional high frequency data high frequency regional records from small earthquakes 1 3 magnitude 4 and comparable magnitude explosions are analyzed to find a reliable seismic discriminant in the eastern u s over 500 digital vertical component seismograms recorded by the new york state seismic network in the distance ranges 10 to 610 km are used mean p lg spectral ratios in the band 1 25 hz are about 0 5 and 1 25 for earthquakes and explosions respectively in the eastern united states we find that the high frequency p lg spectral amplitude ratio in the frequency band 5 25 hz is a reliable and robust discriminant for classifying these events a linear discriminant function analysis indicates that the p lg spectral amplitude ratio method provides discrimination power with a total misclassification probability of about 1 single hole instantaneous explosions and ripple fired quarry blasts have somewhat different p lg spectral ratios but as a group are distinctly different from earthquakes

spectral evidence for source multiplicity in explosions application to regional discrimination of earthquakes and explosions abstract spectral and cepstral analysis were performed on regional array noress recordings of mining explosions in scandinavia and russia in order to detect the effects of delayed explosions or ripple firing commonly used in mine blasting practice noress array stacked spectra corrected for instrument and noise were computed in windows on pn pg sn and lg waves from the mine blasts by averaging individual channel spectra frequency by frequency across the array for comparison spectra were also computed for six western norway earthquakes located near the blasjo and titania norwegian mines also stack spectra of p coda sn and lg were computed using norsar seismograms for presumed peaceful nuclear explosions pnes located at near regional distances 10 in western russia the norsar spectra were determined in the same manner as the noress spectra except that an individual source correction was applied to the spectra comparison of western norway mine blast spectra and nearby earthquakes shows that the earthquake pn spectra are peaked in the 8 to 16 hz band with little energy below 6 hz whereas the explosion spectra have flatter spectra from 3 to 16 hz this difference in the pn spectra may be caused by the earthquakes occurring at greater depths than the explosions differences in the near source media or source mechanism effects in the earthquake spectra the main difference between earthquake and explosion spectra is that the explosion spectra exhibit marked scalloping or modulation patterns not observed in the earthquake spectra the modulation patterns are identical in spectra of all phases indicating that they are caused by multiple shot sequences or ripple firing simulated multiple source spectra determined using the noress seismograms for one of the western norway earthquakes resulted in spectra that resembled many of the explosion modulation patterns based on the simulation studies and cepstral analysis of the spectra the mine explosions appear to be composed of two to three separate explosions delayed by between 80 to 150 msec moreover the norsar spectra of pnes indicate that these signals are also produced by multiple explosions although they have larger delay times of between 0 9 to 1 5 sec these results show that spectral modulations in seismogram spectra of economic explosions including mine explosions and nuclear explosions fired for peaceful economic purposes can be used to distinguish them from earthquakes and nuclear explosion weapons tests

imaging of the near surface shear wave velocity structure of the granada basin southern spain the seismic velocity structure of the granada basin southern spain at depths of 1 4 km is investigated by dispersion analysis of 0 5 to 5 9 sec rayleigh waves we have used records from 12 quarry blasts detonated between 1990 and 2000 and 16 local earthquakes with magnitudes between 2 6 and 3 8 that occurred between 1990 and 1997 all events were recorded on the regional seismic network of andalucia spain and on the national seismic network p s and rg phases were recorded at 13 stations at distances between 10 and 72 km from the source the analysis and inversion of rg waveforms is performed using multiple filtering techniques and a generalized inversion approach we measured ray path group velocities from 0 83 to 2 15 km sec in the 0 6 to 5 8 sec period interval and obtained shear wave velocity profiles for 29 source station paths the shear velocities lie between 0 8 and 3 34 km sec within a standard deviation band of 0 05 0 14 km sec from these models it is possible to infer the most conspicuous features in the upper 4 km of the region and the existence of some degree of lateral variation in velocity after applying an imaging method aimed at volumetric modeling and data visualization we present the first velocity images obtained for the granada basin our results characterize the basin and are correlated with the surface geology manuscript received 7 september 2001

seismological constraints on source properties of the mb 4 0 1985 ardsley new york earthquake a characteristic rupture on october 19 1985 a magnitude 4 0 earthquake occurred in southern westchester county new york approximately 30 km north of central manhattan barstow et al 1988 concluded that this earthquake consisted of two sub events with the larger sub event occurring 0 6 s after the first one we present analysis of data for the main shock as well as aftershocks and foreshocks which were recorded on the new york state seismic network because this data set includes a range of source magnitudes from less than 2 to 4 recorded for virtually identical source receiver pairs an empirical green s function technique can be used to study the source characteristics of the larger events the corner frequency of the main shock and an attenuation parameter t are resolved from the initial portion of the seismogram at station pal in palisades new york 8 km northwest of the epicenter spectra of small foreshocks and aftershocks can then be corrected for attenuation using t following an iterative procedure it is then possible to make reliable determinations of seismic corner frequency for these events several conclusions are obtained 1 the spectrum of the first subevent in the main shock can be well modelled by a brune spectrum from 1 to 10 hz with a corner frequency of 7 1 hz at higher frequencies the source spectrum contains sharp peaks which do not fit an omega square model and may reflect complexities in the rupture process 2 the average stress drop of the sequence is 205 bars the stress drop of the main event is 540 bars but no stress drop dependency on moment is resolved over the magnitude range 1 8 4 0 3 attenuation parameters t are obtained for the 8 km northwestward path from ardsley to palisades and for a 52 km westward path to a station in the hudson highlands and their similarity suggests an increase of q with depth 4 assuming that the two main shock sub events did not rerupture the same area but were contiguous a maximum rupture dimension is 440 680 m the rupture diameter of the largest aftershock mb 3 is determined to be approximately 320 meters the combined rupture for the sequence inferred from spectral methods is consistent with the size of the rupture inferred from the area surrounded by the early aftershocks 700 m diameter the rupture dimension of the ardsley sequence may be characteristic of the dobbs ferry fault and other seismogenic faults in the manhattan prong which are segmented with characteristic dimensions of 0 5 2 km seeber and dawers 1989 assuming that the range of stress drops in the ardsley sequence is also characteristic of the manhattan prong this range of dimensions corresponds to a range of characteristic magnitudes between mb of 3 3 and 5 5 we note that this magnitude range encompasses the five largest known earthquakes in the new york city seismic zone the 1985 ardsley main shock and events in 1737 1783 1884 and 1895

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

high frequency seismic observations and models of chemical explosions implications for the discrimination of ripple fired mining blasts discrimination of large chemical explosions e g mining blasts from possible clandestine nuclear tests e g decoupled explosions is a significant issue for seismic verification unless discrimination is possible the numerous mining blasts within the ussr would give ample opportunity for concealing a clandestine test evernden et al 1986 advocate high frequencies as a means to detect these clandestine tests however mining blasts must still give a unique signature for their discrimination specific conditions are also necessary for high frequency verification low attenuation and quiet seismic stations are among the most important in this study we address these problems under conditions representing a best case scenerio during the summer of 1985 lawrence livermore national laboratory llnl deployed a regional array and high frequency seismic station near rson red lake ontario canada to study regional seismic signals at a low noise site with excellent propagation characteristics the continental shield one objective was to evaluate the performance of regional seismic arrays and high frequency stations in this geological environment using high frequency data from mining blasts within the mesabi iron range in northern minnesota distance of 380 km we also observed the high frequency pn phase of ripple fired blasts modeled their source properties and evaluated a possible discriminant for chemical explosions this study suggests the existence of a distinctive signature for large chemical explosions strong high frequency spectral peaks in the p spectra introduced by delay shooting or ripple firing its application depends however on a frequency band extending to at least 35 hz at regional distances reasonably uniform delay times in the blast pattern predictably quiet seismic sites and minimal path attenuation for high frequencies at 380 km we observe good propagation to 30 hz at 50 hz the evidence suggests severe attenuation or scattering which is consistent with a total q between 1500 and 2500 attenuation estimates assuming a simple source behavior e g f 2 or f 3 at high frequencies for mining explosions would give incorrect values of q unless corrected for the blast pattern these attenuations will limit the value of high frequencies for the detection of small decoupled explosions at regional distances

estimation of response spectra and simulation of nonstationary earthquake ground motions abstract italian strong motion data were used to study the attenuation of response spectra and to simulate artificial accelerograms as a function of magnitude distance and site geology the database has already been utilized for the study of the atten uation of peak ground acceleration pga and velocity and consists of 95 accelero grams from 17 earthquakes of magnitudes ranging from 4 6 to 6 8 using multiple regressions we developed empirical predictive equations for the vertical and hori zontal components of response spectra corresponding to 14 frequencies ranging from 0 25 to 25 hz predictive equations aimed at the ground motion simulation were also estimated for time dependent frequency parameters strong ground motion du ration and arias intensity the shape of the predicted spectra is strongly dependent on magnitude and nearly independent of distance alluvium sites show an amplification effect with respect to stiff sites in different frequency ranges according to the thickness of the soil deposit the vertical horizontal spectral ratio in far field varies with magnitude and frequency from 0 35 to 0 85 the resulting response spectra are compared with the predictions of some recent attenuation relationships and with those proposed by the eurocode ec8 the simulation of nonstationary strong ground motions is achieved through an empirical method where time and frequency features of the motion are represented through the physical spectrum extending the spectral moments theory to the nonsta tionary case the simulated time histories fit the recorded accelerograms in terms of several ground motion amplitude measures such as peak acceleration peak velocity fourier spectra and response spectra the principal advantage of the proposed method consists in correlating the simulation parameters with earthquake magnitude source distance and soil conditions introduction in the field of seismic risk assessment the prediction of shaking intensity in future earthquakes plays a key role re liable estimates of the ground motions that structures must be designed to withstand are obtained mainly through em pirical predictive relationships developed after statistical analysis of data recorded during strong earthquakes many predictive equations are by now available in dif ferent regions of the world campbell 1985 1993 for the prediction of peak ground acceleration pga many fewer are the relationships developed for the prediction of response spectral values idriss 1991 boore

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

depth of faulting during the 1968 meckering australia earthquake sequence determined from waveform analysis of local seismograms waveforms for 11 foreshocks and 48 aftershocks of the ms 6 8 meckering earthquake recorded at the world wide standard seismograph network station mundaring are analyzed to determine the depth distribtion of faulting during this unusual intraplate earthquake sequence clear depth phases including sp and rg are seen in the local seismograms at distances of 60 95 km and are studied using synthetic seismograms computed using generalized ray theory and wave number integration techniques large rg s ratios seen on the vertical component short period data for many events imply source depths less than 2 km the short period p waveform contains the best depth estimator in the form of sp so that depth can be estimated to within an uncertainty of about 1 km for most events the foreshocks cluster at less than 2 km depth and most aftershocks occur within 1 km of the surface a few aftershocks occur as deep as 7 km these results are consistent with a previous teleseismic waveform study in which faulting was inferred to start near the surface at 1 5 km depth with rupture proceeding downward and not exceeding 6 km depth these results coupled with previous stress studies in the australian shield and models of crustal strength show that faulting in a cold shield area is a near surface phenomenon and implies that most of the crust is too strong to be fractured

discriminating earthquakes from quarry blasts based on shakemap ground motion parameters abstract we use shakemap ground motion parameters from small seismic events in the western alberta region to develop a reliable seismic discriminant that can be used in an automated procedure to distinguish blasts from earthquakes in comparison with earthquakes quarry blasts have higher vertical to horizontal v h ratio of ground motion parameters at high frequencies 8 15 hz and at close distances

a discrimination analysis of short period regional seismic data recorded at tonto forest observatory abstract a new seismic discriminant based on spectral differences of regional phases from earthquakes and explosions recorded at a single station has been tested and found to work remarkably well the test data consisted of a well constrained set of 30 nevada test site nts explosions and 21 earthquakes located within about 100 km of nts which were recorded on short period seismographs at the tonto forest observatory in central arizona at an epicentral distance averaging 530 km the events in the data set cover a magnitude range from 3 3 to 4 8 m b for which p n p g and l g phases have been analyzed we found that although l g phases from earthquakes are typically more prominent than for explosions with comparable p wave amplitude levels simple time domain l g p amplitude ratios do not result in a separation of the earthquake and explosion samples consistent enough to provide reliable discrimination however spectral analyses of the data over the frequency band from 0 5 to 5 0 hz revealed significant differences in the spectra of certain regional phases which proved to be a quite reliable discriminant in particular both the p g and l g spectra from earthquakes have been found to be richer in high frequency content than corresponding explosion spectra a discriminant measure defined as the ratio of average l g spectral amplitude level in the 0 5 to 1 0 hz passband to that in the 2 0 to 4 0 hz passband provides good separation of earthquake and explosion populations

tectonic synthesis of the taconian orogeny in western new england a tectonic synthesis based on stratigraphic and structural analysis of western new england is proposed for the ordovician taconian orogeny it emphasizes arc continental collision in which ocean floor continental margin and ensialic rift rocks were imbricated westward in a repeatedly deformed accretionary wedge continued compression displaced segments of the north american sialic crust to the west and deformed the earlier emplaced slices of the taconic allochthons which were derived from the continental margin critical arguments for this synthesis are 1 the west to east stratigraphic relations among the basal rift clastic rocks of the dalton pinnacle and hoosac formations of late precambrian to early cambrian age 2 the stratigraphic and sedimentological similarities between the rocks of the lower taconic sequence and rocks in the pinney hollow and underhill slices to the east and north of the green mountain massif 3 the environmental similarities between the cambrian and lower ordovician section of the giddings brook slice and the age equivalent section in the st albans synclinorium 4 the presence of carbonate platform rocks as slivers between each of the successively higher and younger premetamorphic slices groups 1 and 2 of the taconic allochthons 5 the presence of synmetamorphic fault related structures in the youngest and highest slices group 3 of the taconic allochthons 6 the recognition of extensive thrust zones in the pre silurian eugeoclinal sequence east of the middle proterozoic basement of the housatonic berkshire green mountain and lincoln massifs 7 the location of the taconic root zone within the pre silurian eugeoclinal sequence 8 the recognition of numerous faults in the serpentinite belt 9 the similarity between the rocks of the moretown formation and modern fore arc basin sequences 10 the recognition that the volcanic arc continental complexes of the ascot weedon and bronson hill have been displaced westward over the moretown and or hawley formations along such faults as the bristol and coburn hill thrusts 11 the allochthonous and internally imbricated nature of the north american basement in the berkshire massif 12 the proposition that the housatonic green mountain and lincoln massifs as well as the middle proterozoic cored domes of southeastern vermont are also thick sialic slices of north american basement 13 the recognition of medium high to high pressure metamorphic mineral assemblages in the pre silurian eugeoclinal rocks of vermont and 14 the recent synthesis of isotopic age data by sutter and others 1985 on the basis of an analysis of the foregoing arguments and relationships a chronological sequence of seven structural sections between albany new york and the bronson hill anticlinorium in central massachusetts is used to depict the evolution of the taconian orogeny retrodeformed distances are based on structural overlap and restoration of the taconic slices to their depositional setting along the ancient north american continental margin these easterly younging diverticulated slices formed as a result of horizontal compression rather than gravity sliding this palinspastic analysis implies the following 1 approximately 1 000 km of shortening has occurred during the emplacement of the taconic allochthons and the subsequent imbrication of north american basement as thick sialic slices approximately 330 km of this shortening is attributed to multiple cleavage generations 2 repeated movement along such major surfaces as the cameron9s line whitcomb summit belvidere mountain thrust zone has buried the taconic root zone we suggest that the northern extension of this root zone is exposed to the east of the lincoln massif in vermont where the underhill pinney hollow and hazens notch formations are exposed these formations here considered thrust slices disappear along the belvidere mountain whitcomb summit thrust zone as it is traced southward into western massachusetts and western connecticut 3 taconian metamorphic rocks particularly the older medium high pressure rocks in northern vermont have been transported westward on such reactivated surfaces as the belvidere mountain thrust 4 the anticlinorial form of the middle proterozoic basement in the green mountain and lincoln massifs may have resulted from fault bend folding on deep mantle involved thrusts that developed late in the taconian orogeny

origin and salinity of groundwater from interpretation of analysis data in the mining area of oumjrane southeastern morocco under the arid climate in the southern sub saharan catchments of morocco groundwater is the only permanent water supply usually the groundwater is scarce because of the low recharge however the mining activities in oumjrane area eastern anti atlas mountains reveal that water resources are relatively abundant in the fissured ordovician aquifer to understand this phenomenon geochemical and isotopic investigations were carried out in the region the results show that the quality of water is variable in superficial and deep aquifers the specific conductivities range from 0 44 to 10 ms cm most groundwater samples from the deep aquifer indicate high salinity low ph and co2 anomalies geochemical analyses show that groundwater concentrations are mainly controlled by i evaporite dissolution halite and gypsum ii cation exchange with clay minerals iii silicate hydrolysis and iv dedolomitisation carbonate precipitation takes place in the groundwater issuing from the mine sector the discharge is estimated at 386 t year downstream of the bounhass mine moreover stable isotope 2h and 18o and chemical analyses reveal a clear difference between the alluvial and deep aquifers they also show a local recharge for the alluvial aquifer from saghro inliers low isotope ratios are found in the ordovician formation aquifer indicating a deep water circulation these waters could originate from the high atlas and or saghro mountains and flow through fissures and fault networks connections to regional faults and veins may play a role in it as well as the proximity of the major contact with the high atlas

source classification in the northern caucasus abstract regional records of well documented mine blasts in the area of caucasian mineral water northern caucasus russia are analyzed to test the efficiency of the spectrogram method and pg lg spectral ratios as discriminants between small earthquakes magnitude

the time frequency characteristics of quarry blasts and calibration explosions recorded in kazakhstan ussr summary in this paper we consider two fundamentally different processes that can be responsible for the organization of energy in seismic coda into discrete time independent frequency bands one process involves the resonance of energy in low velocity horizons and the other requires the interaction of time offset wavefields produced by subevents within multiple event mine explosions ripple fired quarry blasts we examined data collected by high frequency seismometers in kazakhstan ussr and observed regular time independent spectral modulations in coda resulting from events strongly suspected to be soviet quarry blasts but not in the coda from single event calibration explosions detonated at similar ranges we conclude these modulations are a source effect and due to ripple firing this modulation is independent of the source receiver azimuth and we infer that the spatial array of subshots in each event must be small we demonstrate that simple linear superposition theory can be used to reproduce effectively the spectral modulation observed in real quarry blasts on the basis of these observations we attempt to discriminate between the two types of events using a spectral pattern based algorithm that seeks time independent features we consider the detrimental effect that resonant energy in low velocity horizons can have on the successful application of our algorithm

palaeoclimate and the formation of sapropel s1 inferences from late quaternary lacustrine and marine sequences in the central mediterranean region abstract synchronous responses to climatic changes during the late pleistocene holocene transition are inferred from marine and lacustrine stratigraphic records in the central mediterranean region new stratigraphic data are presented from well dated sequences in the meso adriatic depression mad two crater lakes in the lazio region and in the tyrrhenian sea the sequences all span the last termination and the holocene but we focus here on the evidence in each record for the time period during which sapropel s1 formed in the mediterranean ca 9 0 to 6 8 cal kyr b p the new records provide evidence of palaeoenvironmental changes on land and sea that can be reconstructed at a high temporal resolution and which throw some light on the processes which led to the formation of s1 the collective evidence indicates that i organic rich sediments occurred in both the marine and the crater lake sites during the time of formation of the s1 sapropel ii there is evidence of increased stratification and anoxia in the sea water column during the period of s1 formation iii the s1 period in the study area is divisible into two sub phases s1a and s1b which reflect short term variations in oceanographic conditions stratification and anoxia iv changes in stratification in the marine column were contemporaneous with regional climate variations that are inferred from the terrestrial records we conclude that the key factor that initiated the formation of s1 was increased discharge of freshwater into the mediterranean following a change post 9 0 cal kyr b p to a warmer and wetter climate furthermore the period of s1 formation was interrupted by a short lived episode ca 500 years of comparatively cooler and drier conditions during the early middle holocene transition emht

spectral discrimination between quarry blasts and earthquakes in southern california we compare p wave spectra of quarry blasts and earthquakes recorded by the southern california seismic network scsn between 2000 and 2005 with the goal of developing methods to discriminate between these events we process the spectra using an iterative robust least squares method to isolate source receiver and propagation path contributions this corrects for first order attenuation structure as well as near receiver site effects and any errors in the instrument response functions using the earthquake spectra and a simple omega 2 source model we compute an empirical green s function egf to remove the trade off between the source terms and other parameters in our model a constant stress drop model gives a good fit to the observed average earthquake spectra over a wide range of moment magnitude but provides a mediocre fit to the average quarry blast spectra which have a generally steeper fall off at high frequencies than omega 2 we also compare p and s wave amplitudes and find modestly smaller average s amplitudes for the explosions compared to the earthquakes for southern california the root mean square rms misfit of p wave spectra to an omega 2 source model is a more reliable explosion discriminant than the s to p amplitude ratio and works for about 90 of the events

small aperture seismo acoustic arrays design implementation and utilization a four element 1 km aperture seismo acoustic array has been designed and installed northeast of seoul korea each element of the array consists of a gs 13 vertical seismometer 1 hz in a shallow borehole 10 m and a low frequency acoustic gauge connected to an 11 element hose array 7 6 m hoses at the surface the array is being used to assess the importance of colocated seismic and acoustic sensors for the purposes of 1 quantifying wind as a source of seismic and acoustic noise 2 constraining propagation path effects in the atmosphere and solid earth 3 locating the sources of the waves and 4 characterizing the source type seismic noise estimates illustrate a level that is only slightly above the low noise model on average acoustic noise levels resolve the microbaroms during low noise times but document a nearly 50 db increase in noise during the windiest periods infrasonic noise in the 0 01 to 5 hz band increases rapidly with wind velocity the seismic noise shows little or no dependence on wind velocity analysis of the data from a 2 month time period suggests that there are many more acoustic signals than seismic 4 10 times as many approximately 1 4 of all seismic signals are associated with an acoustic arrival the vast majority of seismo acoustic observations come from sources in the 30 to 200 km range and occur during working hours local time the 30 to 200 km observation distance is surprising in that average atmospheric velocity models predict no acoustic returns in this range average atmospheric models modified by meteorological data for the troposphere indicate the possibility of ducting in the troposphere as an explanation for these arrivals event location is based upon regional seismic phase identification p n p g p m p l g r g using the array and backazimuth estimates from both the seismic and acoustic data many of the infrasound signals have good signal to noise ratios from 1 to beyond 4 hz despite the small size of the array event clusters are identified at regional distances events associated with acoustic signals are presumed to be from mining regions the existence of rg arrivals and dominance of p energy at high frequency are consistent with this interpretation ground truth in the form of in mine observations has validated that two of the clusters come from construction and mine blasts

modelling short period crustal phases at regional distances for the seismic source parameter inversion abstract waveforms of short period crustal phases observed at regional distances are modelled in an attempt to retrieve the source parameters of small earthquakes for a simple shield type crustal structure the synthetic seismograms calculated for elementary source mechanisms show that the waveforms of crustal phases are quite distinct for different source mechanisms and suggest that these features can be used to constrain the source mechanisms waveforms of the crustal phases are also strongly affected even by small variations in the crustal thickness as well as in the focal depth a generalized linearized waveform inversion technique is used to invert the regional crustal phases for a deviatoric moment tensor source the inversion technique is applied to regional short period records from a small earthquake in central sweden for determining its source parameters the waveform inversion which mainly used lg waves produced a satisfactory fit between the observed and synthetic records suggesting that the source mechanism and focal depth estimates were reasonable the focal depth of 40 km obtained for the event studied suggests the occurrence of a deep crustal earthquake and demonstrates the usefulness of crustal phases in studying small intraplate earthquakes

analysis of local seismo acoustic events in the korean peninsula 1 in order to discriminate between man made explosions and earthquakes a preliminary seismo acoustic analysis was performed in the korean peninsula from august 1999 to december 2000 during this time 202 seismo acoustic events were identified as blasts these events were concentrated in specific regions a rock quarry an open pit mine and a construction site which were identified by field survey all of these events occurred within 200 km of a seismo acoustic array we applied ray tracing methods to the atmosphere using local meteorological observations to understand the short distance propagation characteristics of infrasonic signals calculated infrasonic traveltime using a local meteorological model fits well with observed traveltime from a quarry local winds make possible infrasonic wave ducts in the lower atmosphere and allow infrasonic wave arrival at short distances ray tracing using a local meteorological model has been used for the association between seismic and infrasonic signals