crustal deformation of the eastern tibetan plateau revealed by magnetotelluric imaging the ongoing collision of the indian and asian continents has created the himalaya and tibetan plateau through a range of deformation processes these include crustal thickening detachment of the lower lithosphere from the plate delamination and flow in a weakened lower crust 1 6 debate continues as to which of these processes are most significant 7 in eastern tibet large scale motion of the surface occurs but the nature of deformation at depth remains unresolved a large scale crustal flow channel has been proposed as an explanation for regional uplift in eastern tibet 6 8 9 but existing geophysical data 10 11 do not constrain the pattern of flow magnetotellurics uses naturally occurring electromagnetic waves to image the earth s subsurface here we present magnetotelluric data that image two major zones or channels of high electrical conductivity at a depth of 20 40 km the channels extend horizontally more than 800 km from the tibetan plateau into southwest china the electrical properties of the channels imply an elevated fluid content consistent with a weak crust 12 13 that permits flow on a geological timescale these findings support the hypothesis that crustal flow can occur in orogenic belts and contribute to uplift of plateaux our results reveal the previously unknown complexities of these patterns of crustal flow many previous studies of the indiaasia

dynamic topography produced by lower crustal flow against rheological strength heterogeneities bordering the tibetan plateau summary dynamic stresses developed in the deep crust as a consequence of flow of weak lower crust may explain anomalously high topography and extensional structures localized along orogenic plateau margins with lubrication equations commonly used to describe viscous flow in a thin gap geometry we model dynamic stresses associated with the obstruction of lower crustal channel flow due to rheological heterogeneity dynamic stresses depend on the mean velocity u viscosity and channel thickness h uniquely through the term u h 2 these stresses are then applied to the base of an elastic upper crust and the deflection of the elastic layer is computed to yield the predicted dynamic topography we compare model calculations with observed topography of the eastern tibetan plateau margin where we interpret channel flow of the deep crust to be inhibited by the rigid sichuan basin model results suggest that as much 1500 m of dynamic topography across a region of several tens to a hundred kilometres wide may be produced for lower crustal material with a viscosity of 2 10 18 p asfl owing in a 15 km thick channel around a rigid cylindrical block at an average rate of 80 mm yr 1

monitoring nuclear test sites with geress abstract since the installation of the 25 element german experimental seismic system geress array in southeastern germany in 1990 36 presumed nuclear tests were recorded by this system 16 from nevada 12 from the tuamotu archipelago 7 from lop nor and 1 from novaya zemlya also a chemical calibration experiment at nevada test site npe was observed at the array in 1993 in addition two presumed nuclear events from nevada four from the tuamotu archipelago and six from eastern kazakhstan were recorded on temporary stations close to the geress array during the site survey 1988 to 1989 these latter 12 events were carefully included in this study to broaden the data set this has been done since the number of underground nuclear tests observable at the geress site is not expected to increase significantly in the future because most nuclear powers have adhered to a moratorium on nuclear testing in addition we also do not expect that peaceful nuclear explosions pne will be detonated in the future due to reasons of environmental hazard concentrating on nevada test site and the tuamotu archipelago a cross correlation method and a cluster analysis indicate subgroups of the data these empirical methods clearly discriminate presumed nuclear tests on the islands of mururoa and fangataufa in addition detection thresholds at geress were estimated based on bodywave magnitudes published by isc m b 4 3 for the nevada test site m b 3 9 for the tuamotu archipelago m b 4 6 for lop nor m b 4 3 for novaya zemlya and m b 4 4 for eastern kazakhstan clearly these path specific detection thresholds deviate substantially from those derived from global amplitude distance relations i e gutenberg richter this indicates that a network of seismic stations used for global monitoring purposes may need careful calibration

the seismogenic structure of the southern segment of the longmen shan thrust belt eastern tibetan plateau sw china a comprehensive analysis of surface geology and deep structure abstract since the ms 7 0 earthquake occurred in lushan on april 20 2013 five years after the wenchuan ms 8 0 earthquake the seismogenic potential of southern longmen shan has been a considerable concern comparative studies of active faults and deep structures of the lushan and wenchuan earthquakes are important to evaluate longmen shan potential terrace measurements geophysical surveys and borehole drilling reveal that late quaternary fault activity in the southern segment of the longmen shan thrust belt is weaker than that along the central segment magnetotelluric data across the southern segment of the longmen shan thrust belt show that the central fault and the front range fault are the electrical boundaries of the crust and that the longmen shan thrust belt is a high resistivity body the lushan earthquake occurred at the boundary zone between the high and low resistivity bodies and the crustal structure of the southern longmen shan thrust belt matches the multiunit combination seismogenic model indicating a potential large earthquake in longmen shan compared to conditions along the central segment the low resistivity layer of the upper and lower crust on the western side of the songpan ganzi block develops along the xianshuihe fault which may reduce the strain accumulated from the songpan ganzi block to the southern longmen shan thrust belt this interpretation suggests that the main crustal shortening is accommodated by foreland thin fold structures whereas the structural deformation accommodated by the thrust belt accounts for only a small proportion thus the seismogenic potential of southern longmen shan is weaker than that of the central segment

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

theoretical study of the excitation spectral characteristics and geometrical attenuation of regional seismic phases abstract we present a theoretical study of the generation and geometrical attenuation of regional crustal phases we do this through the computation of seismograms in the epicentral distance range from 60 to 500 km the geometrical attenuation of lg waves with epicentral distance is of the form r 0 83 pg wave amplitudes display a much stronger decay of the form r 1 5 the spectral density of the crustal transfer function for pg waves is relatively flat for frequencies between 0 1 and 5 hz while lg wave spectra strongly fall off beyond 2 to 3 hz the excitation of pg wave is insensitive to the depth of the source within the crust while the lg amplitude is about 50 per cent higher for a source in the upper and middle crust than in the lower crust the amplitudes of these two phases drastically decrease when the source is below the moho these results illustrate the important role of wave guide played by the crust for the propagation of lg and pg we find that the geometrical attenuation of pg and lg waves is independent of source mechanisms in the case of an explosion the excitation of pg is insensitive to the source depth the lg wave amplitude is small in comparison to pg and rayleigh waves and depends on the closeness of the source to an interface or to the free surface

teleseismic lg of semipalatinsk and novaya zemlya nuclear explosions recorded by the grf grafenberg array comparison with regional lg brv and their potential for accurate yield estimation acomparison of regional and teleseismic log rms root mean square lgamplitude measurements have been made for 14 underground nuclear explosions from the east kazakh test site recorded both by the brv borovoye station in kazakhstan and the grf grafenberg array in germany the log rmslgamplitudes observed at the brv regional station at a distance of 690 km and at the teleseismic grf array at a distance exceeding 4700 km show very similar relative values standard deviation 0 048 magnitude units for underground explosions of different sizes at the shagan river test site this result as well as the comparison of brv rmslgmagnitudes which were calculated from the log rms amplitudes using an appropriate calibration with magnitude determinations forpwaves of global seismic networks standard deviation 0 054 magnitude units point to a high precision in estimating the relative source sizes of explosions from lg based single station data similar results were also obtained by other investigators patton 1988 ringdalet al 1992 usinglgdata from different stations at different distances

shear waves from explosions in granite revisited lessons learned from the new england damage experiment abstract we studied seismic wave generation from five small 60 122 kg fully contained explosions detonated in barre granite as a part of the new england damage experiment nede the explosions were conducted using three types of explosives with different velocities of detonation vod black powder ammonium nitrate fuel oil anfo emulsion and composition b comp b empirical evidence suggests that the low vod explosives produce more shear wave energy than high vod explosives the proposed mechanisms to explain this effect include a inhibition of gas driven fracture propagation by thicker pulverized zone for high vod explosions and b fracture toughness increase at higher loading rate the main objective of the experiment was to study differences in shear wave generation between different types of explosives and to determine the likely mechanism responsible for these differences seismic amplitude analysis revealed that comp b releases more energy and larger amplitude p waves for the same weight of explosives while producing smaller amplitude s waves furthermore large radial cracks were observed on the surface after the anfo and black powder shots while there was no surface fracturing after the comp b shots thus longer fractures correlate with higher s wave amplitudes however drilling into the source region indicates that high vod explosions may actually produce a smaller pulverized zone which means that fracture inhibition is a less plausible explanation therefore we hypothesize that increase in loading rate in combination with shorter impulse duration for high vod explosives inhibits fracture processes and subsequently reduced s wave radiation

calibration of mb pn mb lg scales and transportability of the m0 mb discriminant to new tectonic regions we have developed mo mb relationships for earthquakes and explosions in central asia using regional waveform data from the chinese broadband digital station wmq regional magnitude scales mb pn and mb lg were established by 1 determining the attenuation rates of pn and lg waves 2 calibrating the mb pn against the teleseismic rob and 3 applying nuttli s method to determine m b from the lg waves seismic moments for earthquakes and explosions were obtained by applying the bolt and herraiz 1983 method calibrated using cmt moments for earthquakes and regional moment estimates of the soviet joint verification experi ment jve explosion the results show that mo mb pn relationships for central asian earthquakes and explosions are in excellent agreement with the relationships for the western united states this demonstrates that the mo r discriminant is transportable to other regions and supports theoretical claims patton and walter 1993 that mo m b are directly comparable for explosions detonated in different emplacement media successful application depends upon correcting the mb pn for the magnitude bias known to exist between the shagan river test site and the nevada test site nts in general region specific mb bias must be accounted for whenever regional mag nitude scales are calibrated against teleseismic rob as pointed out by douglas and marshall 1996 transporting mo mb lg can be problematic because attenuation rates based on coda waves or lg waves from earthquakes may not necessarily apply to lg waves from explosions and vice versa this is demonstrated for the western united states where the coda q measured from explosion data is much lower than the coda q from earthquake data we show that mb lg for earthquakes located close to nts is greatly overestimated using the q values determined from the coda of nts explosions this is apparently not a problem for lg calibration in central asia perhaps because of differences in velocity and or q structures for the two regions other important considerations are the character of lg propagation on short paths 400 km for nts explosions versus long paths 1000 kin for east kazakh explosions and the properties of coda wave spreading as a function of distance and velocity structures for different tectonic regions

paleoseismic events and recurrence interval along the beichuan yingxiu fault of longmenshan fault zone yingxiu sichuan china abstract prior to the 2008 wenchuan earthquake mw 7 9 sichuan china no earthquake of magnitude larger than m 7 0 had been reported in the historical record for the longmenshan region to reveal paleoseismic behaviors in this region we conducted a paleoseismic study along the 2008 wenchuan earthquake fault scarp at the town of yingxiu along the beichuan yingxiu fault through a trench investigation geomorphic analysis and radiocarbon dating we interpret the occurrence of three paleoseismic events including the wenchuan earthquake within the past 6000 years the cumulative vertical displacement resulting from the three seismic events is 7 6 m the coseismic uplift for the wenchuan earthquake is 2 4 m integrated with previous paleoseismic results along the fault the age of the penultimate event is constrained between 3300 and 2300 cal bp we suggest the antepenultimate event occurred later than 5920 5730 cal bp an average vertical slip rate of 0 88 0 91 mm year is calculated from the vertical displacement of u2 since 5940 5730 cal bp we estimate that an average recurrence interval of large earthquakes is at most 3000 years furthermore the three paleoseismic events revealed at yingxiu show similar coseismic vertical displacements we propose that the strain accumulation and deformation across the longmenshan fault zone is a relatively stable and continuous process since late quaternary

paleoceanography of surface waters in the gulf of mexico during the late quaternary abstract late quaternary paleotemperatures and paleosalinities of surface waters of the gulf of mexico were estimated using a multivariate statistical analysis of census data of planktonic foraminifera two climatic extremes were selected for detailed basinwide study the climatic optimum 125 000 yr ago and the glacial maximum 18 000 yr ago in addition patterns of climatic change were examined in seven piston cores from 127 000 yr ago to the present day during the climatic optimum 125 000 yr ago temperature distributions in surface waters were similar to those of the present the 22 c winter isotherm trended northeastward across the central basin and paleotemperatures decreased northward summer distributions were nearly homogeneous and ranged between 28 and 29 c winter salinities were 1 fresher than present values in the northmost gulf and 0 4 fresher in the central basin summer salinities were similar during both times in contrast during the last glacial maximum temperatures were 1 to 2 c cooler in winter and 1 c cooler in summer and isotherms formed a circular pattern in the gulf during both seasons salinity was 0 3 fresher in winter than at present but 0 6 saltier in summer conditions deteriorated from the climatic optimum to the glacial maximum in the mexico basin winter temperatures were 2 c cooler from 75 000 to 45 000 yr ago y6 to y3 subzones summer temperatures reached a minimum 3 c cooler 32 000 yr ago y2 y3 boundary and seasonality reached minimal values 5 c from 45 000 to 15 000 yr ago all three parameters became similar in value to those in the straits of florida from 45 000 to 15 000 yr ago suggesting that the exchange of surface waters was enhanced at this time between the two regions summer salinities remained similar to present conditions in the mexico basin whereas winter salinities increased 2 by 32 000 yr ago and then fell 0 5 until the glacial maximum ended the westerlies may have migrated southward over the mexico basin in winter from 32 000 to 15 000 yr ago

regional seismic characteristics of the 9 october 2006 north korean nuclear test we investigate the regional seismic signature of the 9 october 2006 north korean nuclear test broadband regional data for the nuclear test and a group of earthquakes close to the test site were obtained between december 2000 and no vember 2006 epicentral distances from the stations to the test site are between 371 and 1153 km we first use these regional events to calibrate the lg wave magnitude in the network then the network is used to calculate mblg 3 93 for the north ko rean nuclear explosion using a modified fully coupled magnitude yield relation the yield of the north korean nuclear test is estimated to be 0 48 kt because of large uncertainties in the source depth the estimate is preliminary the p s type spectral ratios pg lg pn lg and pn sn are calculated for the nuclear explosion and a group of earthquakes close to the test site at frequencies above 2 hz the network averaged p s spectral ratios clearly separate the 9 october 2006 explosion from the regional earthquakes our result indicates that a single blast explosion in the north korea re gion shows different seismic characteristics from an earthquake any well coupled single blast explosion detonated in this region with yield similar to that for the north korean nuclear test has a large probability of being identified by a regional seismic network such as the one adopted in this study

phenomenology and modeling of explosion generated shear energy for the source physics experiments abstract we present a mechanism for shear wave generation from buried explosions as part of the source physics experiment spe series the spe series includes sensitized heavy ammonium nitrate fuel oil sources of various sizes detonated in a borehole in the jointed climax stock granite the cylinder shaped shots were grouted in the borehole to couple the energy to the rock a high fidelity site model with explicit inclusion of the cylindrical explosive the grout filled borehole and site joint sets was included in a numerical simulation that mimics the near field velocity environment measured by an array of in ground accelerometers this approach was accommodated through a coupled euler lagrange code that allows simultaneous solving of a euler domain to model the high deformation source region and a lagrange domain that includes the complex geology with full contact specific laboratory measured geomechanical properties for the rock and the joint sets were included in the model the simulations compare favorably to the data and provide a possible physical mechanism for unexpected shear motion through the release of stored shear strain on the joints this research will advance our understanding of explosion generated shear wave energy from low yield nuclear tests

analysis of historical seismograms root mean square lg magnitudes yields and depths of explosions at the semipalatinsk test range summary magnitudes mb lg based on rms amplitudes of lg waves recorded at nine internal soviet stations for 83 underground nuclear explosions at the semipalatinsk test range were analysed network magnitudes based on a combination of station magnitudes were formed as weighted averages over the station magnitudes after adjusting for variations among station magnitudes in scaling with source strength combining the station magnitudes into network magnitudes although the number of stations was small less than six appeared to reduce scatter in magnitude yield relations the correlation between network mb lg and announced explosion yields was very high and mb lg closely approximated simple proportionality with the logarithm of yield throughout the yield interval 2 165 kt the error of misfit was about 0 04 magnitude units excluding data for the explosion of 1972 august 16 8 kt at 139m the yield of which appeared high compared to mb lg the close correlation between network mb lg and explosion yield together with the fact that several of the explosions were not at scaled depths indicates that mb lg may not be critically dependent on depth of burial at least for depth ranges within a factor of two

contemporary crustal deformation around the southeast borderland of the tibetan plateau 1 we derive a detailed horizontal velocity field for the southeast borderland of the tibetan plateau using gps data collected from the crustal motion observation network of china between 1998 and 2004 our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes separated by strike slip and transtensional faults most notably the regional deformation includes 10 11 mm yr left slip across the xianshuihe fault 7 mm yr left slip across the anninghe zemuhe xiaojiang fault zone 2 mm yr right slip across a shear zone trending northwest near the southern segment of the lancang river fault and 3 mm yr left slip across the lijiang fault deformation along the southern segment of the red river fault appears not significant at present time the region south and west of the xianshuihexiaojiang fault system whose eastward motion is resisted by the stable south china block to the east turns from eastward to southward motion with respect to south china resulting in clockwise rotation of its internal subblocks active deformation is detected across two previously unknown deformation zones one is located 150 km northwest of and in parallel with the longmenshan fault with 4 6 mm yr right slip and another is continued south southwestward from the xiaojiang fault abutting the red river fault with 7 mm yr left slip while both of these zones are seismically active the exact locations of faults responsible for such deformation are yet to be mapped by field geology comparing our gps results with predictions of various models proposed for tibetan plateau deformation we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger highly fragmented upper crust

geodetic measurement of crustal motion in southwest china global positioning system measurements performed over a 2 4 yr period confirm the xianshuihe xiaojiang fault system as one of the primary active structures in southwest china stations southwest of these faults show southerly motions of 5 15 mm yr relative to the western sichuan basin and stations in a 200 km geodetic network located northwest of the basin move at only 0 5 mm yr these results are consistent with clockwise rotation of southwestern sichuan and western yunnan about the eastern tibetan syntaxis accommodated by left lateral slip of 12 4 mm yr on the xianshuihe xiaojiang fault system the results imply that if eastward extrusion of crustal material from the plateau occurs at present it is not accommodated by east west shortening along the margin of the plateau and must involve wholesale eastward motion of low lying regions to the east

a comparison of regional phases from underground nuclear explosions at east kazakh and nevada test sites abstract analysis of regional data from east kazakh ussr and nevada test site nts underground nuclear explosions suggests possible mechanisms for the generation of both low and high frequency lg spectral characteristics of pn and lg phases from 25 soviet nuclear shots recorded at the chinese digital seismic network cdsn station wmq are analyzed for their dependence on parameters such as m b generally related to shot depth and spatial location shagan versus degelen test sites the observed results are compared with those from the nevada test site nts where the near source conditions are better known the average amplitude ratio pn lg is found to be stable with m b but to vary strongly with frequency for both shagan and yucca flat explosions of similar yield the reduction in amplitude over the frequency range of about 1 to 5 hz is considerably larger for lg than for pn the low frequency lg appears to be generated by the scattering of explosion generated rg into s especially for the shagan river explosions for which good agreement between observation and theory is observed this mechanism also provides a possible explanation for the stability of lg as an estimator of explosive yields because the scattering should be expected to occur over a large region of the shallow crust another important result supported by theory is that the higher frequency lg is strongly dependent on the source medium velocity at higher frequencies 3 to 7 hz the amplitude ratios pn lg for explosions from shagan degelen pahute mesa and yucca flat test sites show significant differences that appear related to differences in their source medium velocities the observed large differences in the relative spectral content of pn and lg from east kazakh and nts explosions are mainly due to the vast differences in the crustal structure of the two test sites

application of nuttli s method to estimate yield of nevada test site explosions recorded on lawrence livermore national laboratory s digital seismic system methods utilizing lg waves for estimating yields of underground nuclear explosions have attracted considerable attention for their accuracy claims of portability and suitability for low yield test ban verification in this study the method developed by nuttli is applied to a large dataset of nevada test site explosions recorded on livermore s digital seismic system the purpose was to check the reproducibility of nuttli s results and to verify the accuracy of mb lg to estimate yield at high and low yield levels portability of the method is examined from the perspective of variability of the magnitude yield relations as a function of station site and source geology the results of this study show accuracies of about a factor of 1 6 in yield at the two sigma level for shots below the water table in source regions exhibiting more or less uniform coupling at nevada test site there are three such source regions pahute mesa areas 19 and 20 northern yucca including areas 2 and 9 and southern yucca including areas 3 4 and 7 there is no apparent degradation in accuracies at low yields 1 to 10 kt variations in source coupling were observed as a function of shot location and as a function of the medium s gas porosity for shots in tuff the effect of gas porosity was not observed for shots in alluvium which have uniformly low coupling compared to shots in tuff variations in magnitude yield relations were observed from station to station while the four station network average magnitudes are more robust and agreed well with nuttli s magnitude yield relations thus portability to other test sites should be considered guardedly optimistic requiring geologic and seismic data related to coupling in each source region and sufficient numbers of stations four or five to estimate a robust network magnitude taken all together the findings of this study lend support to this method as a viable means of monitoring a threshold test ban or low yield threshold test ban

spectral characteristics of the excitation and propagation of lg from underground nuclear explosions in central asia the nonlinear inverse method of xie 1993 is applied to analyze lg spectra from many recent underground nuclear explosions in central asia the analysis simultaneously determines lg seismic moments m0 and corner frequencies fc of events as well as path variable lg q values and their frequency dependences at 1 hz lg q at 1 hz estimated for many paths from the lop nor and balapan test sites to various broadband incorporated institution for seismology chinese digital seismic network and kyrghizstan network stations agree well with path averaged lg coda q values from previously obtained tomographic maps for eurasia this suggests that the lg q values obtained in this inversion have not been significantly affected by focusing defocusing or other effects of three dimensional structural complexities the logarithms of lg m0 values obtained in this study correlate linearly with a slope of about 1 2 with international seismological centre isc body wave magnitudes mb the linear relationship is consistent with a previous empirical relationship found between the logarithm of p wave seismic moments and isc mb values the slope of the linear relationship also suggests that the logarithm of lg m0 is a more direct measure of event size than is mb which for larger events is affected by high frequency amplitude falloff another important finding of this study is that the m0 values for the explosions scale with fc 4 rather than with fc 3 as would be expected if stress drops were constant this is consistent with previous scaling relations derived using lg from earthquake sources and suggests that the difference between lg and local s excitation by the same source types explosion or earthquake may overwhelm that between the excitation of lg by different source types a comparison between lg m0 and fc values obtained using an explosion source model with those obtained using an earthquake source model suggests that the m0 values estimated using the explosion source model are systematically lower by a factor of 0 27 than those estimated using the earthquake source model this occurs even though the data used are the same in the inversions with the two types of source model the factor of 0 27 is therefore due to the source model dependence of the m0 fc estimates the overshoot and lower spectral levels at lower frequencies in the explosion source model tend to reduce both the estimated m0 and fc values this suggests that in any nuclear monitoring program the same type of source model either an earthquake or explosion should always be used to discriminate explosions using lg the source model dependence also suggests that more effort should be made to estimate the amount of overshoot in the lg excitation caused by various source types

simulation of topographic effects on seismic waves from shallow explosions near the north korean nuclear test site with emphasis on shear wave generation 1 we performed high resolution 8 hz three dimensional simulations of ground motions from shallow explosions in the presence of rough surface topography near the north korean nuclear test site to study elastic propagation effects with emphasis on theoretical aspects of shear wave generation interaction with rough topography causes significant p to rg scattering along the surface with amplification of high frequency 2 8 hz shear waves relative to the flat earth case shear waves of different polarizations are coupled by topographic scattering rg precursors composed of p to rg conversions traveling as surface waves have the spectral amplitudes comparable to the p wave while the rg phase has the low frequency 0 5 3 hz spectral shape of the rg from the flat case plus the high frequency 3 8 hz p wave spectra motions at near vertical takeoff angles corresponding to teleseismic propagation are increased or decreased indicating that waves are focused or defocused by topographic features above the source topographic roughness has a dramatic effect as short wavelength features 2 5 km are included higher frequencies are amplified by topography including frequencies corresponding to wavelengths shorter than the shortest topographic scale length overall topography enhances energy propagating along the surface near the source amplifies surface waves and tends to balance sv and sh polarized motions all of which impact shear wave observations used for nuclear explosion monitoring further simulation studies could elucidate how the wavefield emerging from a topographically rough area ultimately propagates to regional and or teleseismic distances

lg magnitudes and yield estimates for underground novaya zemlya nuclear explosions abstract lg wave amplitudes of 30 novaya zemlya underground nuclear explosions as recorded by short period seismographs in denmark finland germany norway spitsbergen and sweden are used to determine m b lg values assuming that the m b lg versus explosion yield relation derived from nevada test site data applies to all continental areas the yields of the explosions are estimated they cover a large range of values from 2 5 to 4900 kt the largest explosion since april 1976 had an estimated yield of 145 kt the m b lg values when subtracted from the m b p values can be used to estimate the m b p bias between two test sites in this way the m b p bias between novaya zemlya and the nevada test site is estimated to be 0 20 magnitude units

structural setting of the 2008 mw 7 9 wenchuan china earthquake the 2008 m w 7 9 wenchuan earthquake ruptured an imbricate thrust system in the longmen shan range which forms the eastern boundary of the tibetan plateau we use seismic reflection data and surface geology to construct geologic cross sections and a three dimensional 3d fault model in the range front the rupture was complex with slip on both the steeply dipping beichuan fault and the more shallowly dipping pengguan fault which appear to merge at depth in contrast only the beichuan fault ruptured in the north with the transition near a lateral fault offset thus the earthquake involved multiple thrust splays and breached a significant segment boundary to investigate the tectonic setting of the earthquake we extend our previous measurements of crustal shortening hubbard and shaw 2009 into the interior of the range and show that shortening correlates with topography this suggests that upper crustal shortening can produce the high topography of the longmen shan without calling on other uplift mechanisms based on this understanding we model the thrust belt as a critical taper wedge to assess what rock and fault strengths are required to explain the topographic slopes within the range front and basin the low taper within the basin is consistent with a weak detachment f 0 1 while a slightly stronger f 0 3 0 4 detachment is necessary to explain the higher taper of the range front this difference may relate to the localization of the detachment within a triassic evaporite sequence within the basin while the faults beneath the range front are rooted in precambrian metasedimentary or igneous rocks critical taper theory implies that shortening in the range front where the 2008 wenchuan earthquake occurred is many times greater than in the basin consistent with our shortening measurements we examine the implications of these findings for seismic hazard assessment in the region and in other active mountain belts around the world

three dimensional velocity field of present day crustal motion of the tibetan plateau derived from gps measurements 1 using the measurements of 750 gps stations around the tibetan plateau for over 10 years since 1999 we derived a high resolution 3 d velocity field for the present day crustal movement of the plateau the horizontal velocity field relative to stable eurasia displays in details the crustal movement and tectonic deformation features of the india eurasia continental collision zone with thrust compression lateral extrusion and clockwise rotation the vertical velocity field reveals that the tibetan plateau is continuing to rise as a whole relative to its stable north neighbor however in some subregions uplift is insignificant or even negative the main features of the vertical crustal deformation of the plateau are the following a the himalayan range is still rising at a rate of 2 mm yr the uplift rate is 6 mm yr with respect to the south foot of the himalayan range b the middle eastern plateau has a typical uplift rate between 1 and 2 mm yr and some high mountain ranges in this area like the longmen shan and gongga shan have surprising uplift rates as large as 2 3mm yr c in the middle southern plateau there is a basin and endorheic subregion with a series of ns striking normal faults showing obvious sinking with the rates between 0 and 3 mm yr d the present day rising and sinking subregions generally correspond well to the cenozoic orogenic belts and basins respectively e at the southeastern corner of the plateau there is an apparent trend that the uplift rate is gradually decreasing from between 0 8 and 2 3 mm yr in the inner plateau to between 0 5 and 1 6 mm yr outside the plateau with the decrease of terrain height

crustal structure and rheology of the longmenshan and wenchuan mw 7 9 earthquake epicentral area from magnetotelluric data the longmenshan forms the eastern margin of the tibetan plateau adjacent to the sichuan basin this range is anomalous because it formed despite low convergence and slip rates and without the development of a foreland basin the devastating a d 2008 wenchuan earthquake mw 7 9 has renewed debate about the tectonics of the longmenshan a magnetotelluric mt study was undertaken subsequent to the earthquake to investigate the crustal structure of the longmenshan and inversion of the data reveals a low resistivity high conductivity layer at a depth of 20 km beneath the eastern tibetan plateau that terminates 25 km west of the wenchuan maoxian fault its electrical properties are consistent with it being fluid rich and mechanically weak beneath the longmenshan and sichuan basin a high resistivity zone extends through the entire crust but with a zone of low resistivity in the vicinity of the wenchuan hypocenter we show that the mt data combined with other geological and geophysical observations support geodynamic models for the uplift of eastern tibet being caused by southeast directed crustal flow that is blocked by stable lithosphere beneath the sichuan basin and longmenshan leading to inflation of the songpan ganzi terrane this rigid high resistivity backstop not only provided a block to flow but also may have accumulated stress prior to the earthquake the mt observations provide new insights into the generation of the wenchuan earthquake which occurred in a region with low convergence rates prior to the earthquake

active tectonics of the beichuan and pengguan faults at the eastern margin of the tibetan plateau the steep high relief eastern margin of the tibetan plateau has undergone rapid cenozoic cooling and denudation yet shows little evidence for large magnitude shortening or accommodation generation in the foreland basin we address this paradox by using a variety of geomorphic observations to place constraints on the kinematics and slip rates of several large faults that parallel the plateau margin the beichuan and pengguan faults are active dominantly dextral slip structures that can be traced continuously for up to 200 km along the plateau margin both faults offset fluvial fill terraces that yield inheritance corrected cosmogenic 10be exposure ages of 15 kyr indicating latest pleistocene activity the pengguan fault appears to have been active in the holocene at two sites along strike latest quaternary apparent throw rates on both faults are variable along strike but are typically 1 mm yr 1 rates of strike slip displacement are likely to be several times higher probably 1 10 mm yr 1 but remain poorly constrained late quaternary folding and dextral strike slip has also occurred along the western margin of the sichuan basin particularly associated with the present day mountain front these observations support models for the formation and maintenance of the eastern plateau margin that do not involve major upper crustal shortening they also suggest that activity on the margin parallel faults in eastern tibet may represent a significant seismic hazard to the densely populated sichuan basin

upper crustal folding of the 2013 lushan earthquake area in southern longmen shan china insights from late quaternary fluvial terraces abstract a thrust earthquake of mw6 6 occurred on april 20 2013 near lushan county in the southern longmen shan at the east margin of tibetan plateau this earthquake did not produce a surface rupture zone and the late quaternary activities of the outcropped faults in the earthquake area were not obvious which increased the difficulty of studying the seismogenic structure this article took as the research target the middle reach of the qingyijiang river which traverses the earthquake area by surveying correlating the fluvial terraces studied quantitatively the late quaternary tectonic deformation and further discussed the seismotectonics the longitudinal profile of river terraces along the middle reach of the qingyijiang river reveals that the principal deformation style in the late quaternary was anticline type folding the folding is a typical fault bend fold involving the basement which is controlled by the newest flat ramp flat structure possibly formed in the pliocene or the early pleistocene across the fold the average shortening rate in the late quaternary is 0 6 1 3 mm yr about one third of the crustal shortening rate by gps data across the longmen shan fold and thrust belt and its foreland the foreland thin skinned structure developed in the cretaceous to paleogene strata in the earthquake area was passively involved into the fault bend folding in the late quaternary which commend the thrust ramp developing in a piggyback style the newest ramp appears to have controlled the rupture and the surface deformation of the 2013 lushan earthquake in the process of thrust sheet sliding toward foreland along the flat ramp flat detachment the ramp acts as a locking structure where earthquake ruptures the coseismic surface deformation seems to be passive folding of the thrust sheet climbing the ramp

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

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

lg magnitudes of selected east kazakhstan underground explosions abstract the amplitude of 1 sec period lg waves as recorded on seismograms of wwssn stations in southern asia and scandinavia are used to determine m b lg values for 62 underground nuclear explosions in the eastern portion of the east kazakhstan test site the explosions were selected to be of m b p 5 5 or greater in the period 1965 to 1985 the yields of the explosions are estimated assuming that a nevada test site derived relation between m b lg and yield for water saturated rock is also applicable to the east kazakhstan test site assuming that lateral variations in crustal structure and in depth of emplacement of the explosion do not affect m b lg values the lg data indicate that the m b p bias between the nevada test site and east kazakhstan is 0 35 magnitude units

determination of seismic energy from lg waves seismic energy is a physical concept related to broadband information on the source radiation this is different from seismic moment which is related to low frequency information improved estimates of seismic moment and radiated energy can improve the scientific framework for interpreting observed seismicity in terms of physical source processes this study evaluates the utility of regional lg waves the dominant feature of seismograms for regional earthquakes for the estimation of radiated seismic energy the rms lg which is defined as the root mean square of lg wave ground velocity within a certain group velocity range is proportional to the square root of lg wave radiated energy flux we find that rms lg is a good quantity for estimating the energy release of earthquakes because a large fraction of the total seismic energy is radiated as lg waves we scale the network averaged rms lg value to a reference distance of 100 km for a set of 52 earthquakes in the northeastern united states using an empirically derived relation between rms lg and epicentral distance we apply the source parameters estimated for these earthquakes to boatwright s deceleration source model and calculate the total seismic energy expected to have been radiated by each event assuming it can be modeled by this source we then obtain for earthquakes in the northeastern united states the scaling of the total radiated seismic energy of earthquakes with network averaged rms lg values from synthetic seismograms it is found that different velocity structures have an effect on the efficiency of lg wave radiation using measurements of rms lg made from synthetics we find that the vertical strike slip source tends to radiate less lg wave energy than other source mechanisms manuscript received 4 february 1998

identification of earthquakes and explosions using amplitude ratios the vogtland area revisited identification of seismic events is a major scientific issue in the framework of verification of the comprehensive nuclear test ban treaty ctbt of special interest in this context is the identification of the numerous low yield mining or blasting events especially those occurring in the same area as earthquakes such as the vogtland area in the border region of germany and the czech republic seismic events in this area were investigated by wuster 1993 1995 who achieved complete discrimination using measures of spectral decay and spectral variance at the geress array and a quadratic discrimination function

regional wave propagation in tanzania east africa 1 crust and upper mantle structure under tanzania east africa is investigated using broadband waveforms and phase travel times collected from regional events recorded by the 1994 1995 tanzania broadband seismic experiment broadband displacement waveforms from the ml 5 9 rukwa graben earthquake 18 august 1994 are modeled using a wave number integration algorithm and a new phase time inversion technique to infer a very simple crustal and upper mantle model that can be used for waveform studies of other regional earthquakes in the area displacement amplitudes for all phases in the data are predicted quite well using source parameters determined from a previous study of teleseismic waveforms the crust is parameterized by a linear gradient in velocity defined by surface and moho p velocities poisson s ratio and crustal thickness this simple parameterization is sufficient to explain arrival times and waveshapes of the three component waveforms recorded between 200 and 800 km at stations located on the craton and mozambique belt the s wave train consists of sn multiple sn and critically reflected s wave multiples in the crustal waveguide in addition to the fundamental mode rayleigh wave high phase velocity critical s wave reflections are seen to form the low group velocity lg phase prominent sp depth phases are seen in the regional waveform data which can be used to infer accurate source depths for events in the region the tanzania craton and adjacent mozambique belt crustal structure is simple and laterally homogeneous showing few effects of rift disruption high wave velocities in the uppermost mantle suggest little thermal modification from rifting processes of the east african rift

regional observations of the second north korean nuclear test on 2009 may 25 summary the suspicious seismic event that occurred in the northern korean peninsula on 2009 may 25 was declared to be the second underground nuclear test nk2nd by north korea we investigated the characteristics of nk2nd using seismic signals recorded at regional distance stations in south korea and china the pn lg ratios of nk2nd definitely discriminate this event from two nearby natural earthquakes at frequencies above 4 hz full moment tensor inversion of full waveform data shows that nk2nd had a very large isotropic component pure isotropic moment tensor inversion also resulted in good recovery of observed waveforms with clear indication that nk2nd was explosive in origin the moment magnitude mw from the full moment tensor inversion was estimated to be 4 5 and network averaged values of 4 6 and 3 6 were calculated for rms mb lg and ms vmax respectively although mb ms signature has been considered one of the most reliable discriminants for separating explosions and earthquakes this signature showed poor discrimination in the case of nk2nd the pn lg ratios and moment tensor inversion give more reliable evidence than does the mb ms for classifying the suspicious event in the northern korean peninsula as a possible explosion the characteristics of nk2nd are also quite similar to those of the first north korean nuclear test on 2006 october 9

characteristics of the fault related rocks fault zones and the principal slip zone in the wenchuan earthquake fault scientific drilling project hole 1 wfsd 1 abstract scientific drilling in active faults after a large earthquake is ideal to study earthquake mechanisms the wenchuan earthquake fault scientific drilling project wfsd is an extremely rapid response to the 2008 ms 8 0 wenchuan earthquake which happened along the longmenshan fault eastern margin of the tibetan plateau in order to better understand the fault mechanism and the physical and chemical characteristics of the rocks the wfsd project will eventually drill 5 boreholes along the two main faults this paper focuses on the first hole wfsd 1 which started just 178 days after the earthquake down to a final depth of 1201 15 m petrological and structural analyses of the cores allowed the identification of fault related rocks in the yingxiu beichuan fault fault gouge cataclasite and fault breccia and the principle slip zone psz location of the wenchuan earthquake was determined we found 12 fault zones in the entire core profile with at least 10 including the yingxiu beichuan fault zone with a multiple cores structure and minimum width of 100 m the co seismic slip plane of the wenchuan earthquake at depth corresponding to the yingxiu beichuan fault zone at the outcrop as well as its psz was expected to be located at the bottom of the fault zone at 759 m depth instead it was found at 590 m depth with 1 cm wide fresh fault gouge as determined by logging data such as temperature natural gamma ray p wave velocity and resistivity combined with the fresh appearance magnetic susceptibility and microstructure of the gouge the wenchuan earthquake slip plane has a dip angle of 65 showing the high angle thrust feature the distribution of fault gouge with several meters thick the location of the wenchuan earthquake s psz and the thickness of fresh gouge all imply a correlation between the width of the fault zone and the number of seismic events

yield estimation of the 25 may 2009 north korean nuclear explosion we collect nine vertical component broadband seismograms from the 25 may 2009 north korean nuclear explosion for a regional seismic network in which eight stations also recorded the 9 october 2006 north korean nuclear test comparing the observed waveforms and spectra from the two events we estimate that the amplitudes of the records from the second event are approximately five times those from the first one additionally we use 599 vertical broadband seismograms from 82 regional events recorded on the regional network between december 1995 and may 2009 to calibrate the network lg wave magnitude the calibrated network is used to calculate the lg wave body wave magnitude m b lg 4 53 for the 25 may 2009 north korean nuclear explosion based upon 15 first arrivals from the two north korea nuclear explosions the regional pn velocity in the northeast china north korea region is calculated to be 8 0 km s this result along with the regional geological structures suggests that the north korean test site nkts is located at a relatively stable continental region we thus use a modified fully coupled magnitude yield relation to estimate the explosion yield and the result shows that the yield of the 25 may 2009 north korean nuclear test is approximately 2 35 kt under the minimum burial depth assumption online material epicentral parameters computed m b lg and corrected m b lg for 82 events used in the study

robust and reliable epicenter determinations envelope processing of local network data local event recordings are complex in the sense that relevant p and s phases vary in an unpredictable manner even between closely spaced stations thus manual analysis of such records is still commonplace our approach to solving this long standing problem of observational seismology is to bandpass filter 3 to 6 hz to ensure good signal to noise ratio snr and then form envelopes to ensure simple signals across a seismograph network the physical basis is that pg and lg are crustal wave guide phases reflecting p and s energy propagation extensive tests on envelope analysis of local records from different areas found that arrival times of the maxima of pg and lg envelopes increase very consistently with distance even in different tectonic regimes typical velocities being 6 1 and 3 5 km sec respectively these arrival time parameters are easy to extract in a semi automatic manner and are highly suitable for local epicenter determinations extensive tests on locating mining explosions were conducted and on average the envelope location errors relative to true locations were similar to those in bulletins that are based on conventional phase pickings occasionally the pg pn envelope may be very weak but can be replaced by the easily pickable non envelope pn phase additional advantages with envelope locations are transportability not overly sensitive to details of crustal structure and that envelope amplitudes can be directly converted to ground motion and magnitudes for modern stations envelopes can be formed in situ with low sampling rates of 1 to 2 hz thus greatly reducing transmission costs

crustal structure of western tibet revealed by lg attenuation tomography abstract the lateral lg wave attenuation in western tibet and surrounding regions is studied a total of 706 two station method tsm and 533 reverse two station method rtsm pairs are generated from 282 regional earthquakes the earthquakes are recorded at 48 seismic stations operated across western kunlun and western tibet regions the lg phases are extracted from the vertical component of seismograms with magnitude greater than 4 6 mb and focal depth less than 50 km to measure the tsm and rtsm lg q at 1 hz q0 the lgq0 tomography map is generated with grid size 0 5 0 5 using the least squares orthogonal factor decomposition lsqr algorithm lateral variation of lg attenuation is found to exist across the region the results provide new insights into the attenuation properties of the crust and its linkage with regional geodynamics the low lgq0 200 is revealed in the central part of lhasa terrane in western tibet from both tsm and rtsm images the high lgq0 values complemented with the high pn velocities beneath the central part of lhasa terrane reveal the trace of underthrusting indian lithosphere beneath the western tibet

characteristics of short period wave propagation in regions of fennoscandia with emphasis on lg abstract wave propagation of crustal phases in particular lg near the arcess array in northern norway is examined and compared to propagation characteristics near the noress array in southern norway relying on array analysis we show that ray theory explanations of arrivals in local and regional seismograms are very useful in deducing the composition of the crustal wave trains frequency wavenumber analysis is applied to the array data to identify the arrivals then a composite of array beams is used to approximate each event record sections of composite seismograms are constructed for different directions from arcess to study propagational characteristics with distance and azimuth and then compared to composite seismogram record sections from noress to study different regional characteristics to model the observed character of lg and rg synthetic record sections are constructed by wavenumber integration in velocity models representative of structure in the different regions the results show that rg propagation distance varies significantly between regions and that the velocity gradient in the lower crust is the dominant factor in specifying lg characteristics in the baltic shield region lg is dominated by several discrete arrivals representing multiple moho reflections or by multiple moho reflections and turning waves with each multiple confined to a small distance range so that only one multiple set dominates at each distance furthermore we demonstrate that incomplete knowledge of the propagation characteristics leads to mislocations of local and regional events and inhibits source depth discrimination of events we identify three earthquakes in the arcess data set based on source depths these are constrained by phase velocities and depth phases none of which were properly identified by the automatic array detection software

slip maxima at fault junctions and rupturing of barriers during the 2008 wenchuan earthquake the devastating wenchuan earthquake in 2008 struck along a fault zone that showed low rates of deformation analysis of gps and insar data suggests that as structural barriers failed during a single earthquake the rupture cascaded across multiple fault segments which may explain the high magnitude of the event

coseismic reverse and oblique slip surface faulting generated by the 2008 mw 7 9 wenchuan earthquake china the mw 7 9 wenchuan china earthquake ruptured two large thrust faults along the long menshan thrust belt at the eastern margin of the tibetan plateau this earthquake generated a 240 km long surface rupture zone along the beichuan fault and an additional 72 km long surface rupture zone along the pengguan fault maximum vertical and horizontal offsets of 6 5 m and 4 9 m respectively were measured along the beichuan fault a maximum vertical offset of 3 5 m was measured along the pengguan fault coseismic surface ruptures integrated with aftershocks and industry seismic profiles show that two imbricate structures have ruptured simultaneously resulting in the largest continental thrust event ever documented large oblique thrusting observed during this earthquake indicates that crustal shortening is an important process responsible for the high topography in the region as everywhere along the edge of tibetan plateau

implications for upper mantle structure in the western united states from complete far regional seismograms abstract nuclear explosions from the nevada test site and earthquakes in southern and central california are recorded with offsets of 800 to 2000 km at the lajitas seismic station in texas these broadband far regional data are from a single high dynamic range station with three component instruments at an exceptionally quiet site and bridge the distance range between regional refraction studies of the crust and uppermost mantle and teleseismic investigations with long period data seismograms from 15 events were used to constrain the upper mantle structure to a depth of about 250 km by matching the complete waveforms including body and surface waves a simple one dimensional model is proposed that is consistent with the broadband body and surface waveforms as well as arrival times while the p wave velocity structure is well constrained by a model similar to that proposed by olsen et al 1980 the shear wave velocity structure is less controlled since the only identifiable shear arrivals are the l g phase trapped in the crustal wave guide there are no identifiable s n or mantle s waves below a distance of 1900 km in contrast mantle p waves turning in the depth range below 120 to 150 km are the p wave arrivals that dominate beyond 1200 km although p n is observed in cases of good signal to noise ratios to distances of 1400 to 1500 km as an emergent phase preceding these mantle arrivals due to the emergent p n wave packet observed at all distances the mantle lid p wave velocities are believed to exhibit a negative gradient zone as proposed by olsen et al 1980 in contrast to the model developed by burdick and helmberger 1978 the medium parameters for s waves can only be constrained by the observed dominant l g energy by introducing a strong velocity contrast across the crust mantle boundary including a high velocity s lid the l g energy can be efficiently trapped in the crust this effect is further enhanced by including a laminated structure for the lower crust surface waves are most sensitive to the velocities in the uppermost crust which consists of low velocity gradient layers typical for sediments starting at 4 and 2 km sec for p and s waves respectively for the basin and range province low q values 20 to 50 in the shallow crustal layers are further required to match these waves

seismic wave theory in the us 1991 1994 the early 1990s saw many interesting contributions to the field of seismic wave propagation from a variety of us researchers even as many wave propagation specialists shifted their research focus away from new methods for seismogram synthesis toward data acquisition and inversion in part this shift was a natural consequence of the explosive growth in the amount and availability of high quality digital seismic data ready to be processed with interpretation tools developed in previous decades as a result observational seismology has recently made dramatic contributions toward imaging global geodynamics revealing the great variety of crustal structures and laying the foundation for a collaborative global network of broadband seismometers to monitor earthquakes and other seismic events however recent observational studies have brought to light new problems in wave propagation theory and have made some older problems more difficult to ignore

seismic yield determination of soviet underground nuclear explosions at the shagan river test site summary a study of p and lg based source size estimators has been conducted for 101 presumed underground nuclear explosions at the shagan river test site near semipalatinsk ussr a systematic variation in the relative patterns across the test site has been observed when comparing the p wave estimators world wide mb and ulm and the lg based observations rms lg determined from norsar and grafenberg array recordings these variations correlate well with geological features determined from satellite imagery and suggest in particular that the northeast and southwest portions of the test site divided by the chinrau fault are characterized by distinct geophysical properties a difference in m p mlg bias of as much as 0 15 magnitude units exists between these two subareas available data indicate that the mlg observations are very consistent with published yields and suggest that the magnitude yield relationship for p wave based estimators can be significantly improved by introducing regional bias corrections we have determined such corrections for three subareas of the test site and used the corrected mh and ym observations in combination with the lg data in a weighted averaging scheme to arrive at yield estimates for all events in the database for the explosion of 1988 september 14 we obtain yield estimates from the three estimators ranging from 106 to 118 kt which is consistent with the independently derived estimates of 115 122 kt quoted by sykes ekstrom 1989 a further assessment of the validity of our results would require access to independently measured yields of additional explosions

the kaliningrad west russia earthquakes on the 21st of september 2004 surprise events in a very low seismicity area abstract the earthquakes in kaliningrad west russia on the 21st of september 2004 were unexpected in a seismically quiet area the main shock of magnitude m b 5 was widely felt around the baltic sea a comparison with some historic earthquakes in northern europe shows that its perceptibility area is smaller than that of the 1904 oslo graben earthquake of an estimated magnitude m l 5 4 but larger than those of the 1759 kattegat and 1819 luroy earthquakes the latter are claimed to have had magnitudes m s in the range of 5 7 6 0 an analysis of the lg phase of the kaliningrad earthquakes as recorded at a number of european stations accords only weakly with the macroseismic intensity pattern that shows fast attenuation towards west northwest and southeast the strike slip focal mechanism of the main shock is discussed in the context of remnant glacial rebound stresses in generating present day seismicity in n europe

rupture mechanism and seismotectonics of the ms6 5 ludian earthquake inferred from three dimensional magnetotelluric imaging a three dimensional 3 d resistivity model around the 2014 ms6 5 ludian earthquake was obtained the model shows that the aftershocks were mainly distributed in a shallow inverse l shaped conductive angular region surrounded by resistive structures the presences of this shallow conductive zone may be the key factor leading to the severe damage and surface rupture of the ludian earthquake a northwest trending local resistive belt along the baogunao xiaohe fault interrupts the northeast trending conductive zone at the zhaotong lianfeng fault zone in the middle crust which may be the seismogenic structure of the main shock based on the 3 d electrical model combining with gps thermal structure and seismic survey results a geodynamic model is proposed to interpret the seismotectonics deep seismogenic background and deformation characterized by a sinistral strike slip with a tensile component of the ludian earthquake

the stability of rms lg measurements and their potential for accurate estimation of the yields of soviet underground nuclear explosions data on underground nuclear explosions have recently become available from modern digital seismic stations installed within the soviet union and china observations of root mean square rms lg wave signals for soviet underground nuclear explosions at the shagan river test site in east kazakhstan show that the relative amplitudes of the rms signals at stations in norway the ussr and china are very similar for different explosions the standard deviation of the differences being only about 0 03 in logarithmic units i e magnitude units this is consistent with earlier observations comparing norsar and graefenberg array data and the observed scatter is significantly lower than has been reported for lg data from nevada test site explosions in view of the excellent correspondence found by nuttli 1986 and patton 1988 for lg versus yield at nevada this indicates that rms lg has a potential for yield estimation with very high accuracy at shagan river our study has shown that a selected stations in the ussr and china situated at regional distances provide a much improved signal to noise ratio of the lg phase for events at shagan river as compared to norsar array data b the scaling of rms lg amplitudes between different sized events recorded at the same single station site appears to be consistent with that of norsar indicating a remarkable degree of precision in single station measurements of lg signal c rms lg amplitude measurements for the best of these stations may be made at 1 5 to 2 0 magnitude units lower than at norsar or graefenberg allowing a much lower threshold for lg based yield determination and d the p wave detection capabilities of these single stations do not match those of the noress and arcess arrays thus teleseismic signals continue to be important for detection of small nuclear explosions our conclusion is that lg signals appear to provide an excellent basis for supplying estimates of the yields of nuclear explosions even down to below 1 kt when such signals are recorded at high quality digital in country seismic stations and when calibrated by access to independent nonseismic yield information for a few nuclear explosions at the test sites of interest in the context of monitoring a low yield threshold test ban treaty it will in addition be important to take into consideration various environmental conditions in the testing area such as the possible presence of cavities and to devise appropriate procedures for on site observations in this regard

broad band lg attenuation modelling in the middle east summary we present a broad band tomographic model oflg attenuation in the middle east derived from source and site corrected amplitudes absolute amplitude measurements are made on handselected and carefully windowed seismograms for tens of stations and thousands of crustal earthquakes resulting in excellent coverage of the region a conjugate gradient method is used to tomographically invert the amplitude data set of over 8000 paths over a 45 40 region of the middle east we solve for q variation as well as site and source terms for a wide range of frequencies ranging from 0 5 to 10 hz we have modified the standard attenuation tomography technique to more explicitly define the earthquake source expression in terms of the seismic moment this facilitates the use of the model to predict the expected amplitudes of new events an important consideration for earthquake hazard or explosion monitoring applications the attenuation results have a strong correlation to tectonics shields have low attenuation whereas tectonic regions have high attenuation with the highest attenuation at 1 hz found in eastern turkey the results also compare favourably to other studies in the region made using lg propagation efficiency lg pg amplitude ratios and two station methods we tomographically invert the amplitude measurements for each frequency independently in doing so it appears the frequency dependence of attenuation in all regions is not compatible with the power law representation of q f an assumption that is often made

an improved uk local magnitude scale from analysis of shear and lg wave amplitudes the amplitudes of shear and lg waves recorded at uk seismograph stations from local earthquakes in the range 0 600 km have been subjected to an analysis of variance allowing separation of the effects of earthquake size distance and station corrections for each recording site the propagation paths sample mainly the central to western part of the uk with good north south coverage the analysis of 385 amplitude readings at 28 stations from 40 earthquakes showed that the effects of both distance and station site corrections were statistically significant tables of corrections for both distance and station effects have been derived to allow local magnitude ml to be determined more accurately from horizontal and vertical component records one set of tables allows the estimation of an ml which is consistent with the original richter definition of ml with a standard deviation which is smaller than that produced by the theoretical attenuation curve defined according to attenuation in southern california which has customarily been used to calculate ml in the uk the reduction in standard deviation is mainly due to the incorporation of station terms to correct for station effects since the theoretical and observed variations of attenuation with distance are similar this similarity implies that southern california and the uk show a similar variation of distance dependent attenuation for lg waves which was not expected in view of the differences in geology and tectonics another set of tables is provided to calculate an ml which is consistent with the body wave magnitude mb determined by the international data centre from station records of the comprehensive test ban treaty organization s global monitoring network the decay with distance of the predominantly lg wave amplitude values gives a value of 440 50 for lg q at a frequency of 3 hz in agreement with estimates obtained from spectral displacement amplitudes of lg waves in the uk

teleseismic event detection using the noress array with special reference to low yield semipalatinsk explosions abstract the small aperture noress array in norway has been designed for improving signal to noise ratios at high frequencies 1 to 15 hz while the main motivation for this has been to enhance the capabilities for detecting and characterizing weak seismic events at regional distances it has been found that the array is also very effective in the teleseismic distance range in particular for eurasia this results from a combination of two factors 1 due to high q paths eurasian earthquake and explosion recordings generally show high dominant frequencies typically in the range of 1 5 to 4 0 hz where the noise level at the site is low and 2 the array provides a particularly high signal to noise ratio gain of 12 to 14 db 0 6 to 0 7 m b units at these frequencies analysis of noress on line detection performance shows that there are large regional variations even within small epicentral areas this is interpreted as resulting mainly from signal focusing effects underneath the source areas in analogy to the receiver focusing effects earlier observed across large arrays a detailed study of noress recordings of underground nuclear explosions at the semipalatinsk test site has shown that relative to worldwide m b noress has a significant positive m b bias it is highest 1 0 m b units for the eastern part shagan river and somewhat lower 0 4 m b units for the western parts degelen konystan although there is a fair amount of scatter within each area analyzing observed signal to noise ratios at the noress site for a set of low yield nuclear explosions at semipalatinsk with published yields available in the soviet literature it is estimated that fully coupled explosions of yields as low as 0 1 kt would be detectable by noress under normal noise conditions however to give a precise threshold is difficult because of the low number of reference events available and the significant amount of extrapolation involved it is emphasized that this detection level will not be achieved in cases when the noise level is abnormally high e g in the coda of a large earthquake or if coupling conditions are not optimal e g in the case of full or partial cavity decoupling it must also be noted that the event identification threshold is necessarily higher than the signal detection threshold

seismotectonics of the 2013 lushan mw 6 7 earthquake inversion tectonics in the eastern margin of the tibetan plateau on 20 april 2013 an unexpected mw 6 7 earthquake occurred in lushan county at the southern longmen shan the eastern margin of the tibetan plateau a high resolution seismic reflection profile was combined with near surface geological data earthquake relocation and geodetic measurements and a recent deep artificial seismic reflection profile to identify the active fault and seismotectonics of this earthquake three dimensional imaging of the aftershocks was used to identify two planar faults that together form a y shape f1 and f2 seismic interpretations suggest that fault f1 did not break through the overlying mesozoic and cenozoic rocks and is a typical blind fault geodetic measurements suggest that the coseismic deformation is consistent with the geometry and kinematics of shear fault bend folding deep seismic data indicate the syndepositional nature of fault f1 a preexisting normal fault older than the triassic which underwent positive inversion tectonics during the late cenozoic a thrust fault f3 converges with f1 at a depth of approximately 12 km with an accumulated slip 3 6 km this 2013 lushan earthquake triggered by blind faults is a hidden earthquake blind and reactivated faults increase the potential risk and uncertainty related to earthquakes in the eastern margin of the tibetan plateau

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

analysis of short period regional phase path effects associated with topography in eurasia propagation of regional seismic phases is highly dependent on path effects but we have a limited understanding of these effects and no general procedure for accounting for path variation influence on regional waveforms thus there is strong regional variability in the effectiveness of regional wave discriminants used to identify small earthquakes and nuclear explosions motivated by many observations of correlation between surface geology and regional phase behavior we empirically explore the relationship between short period regional and upper mantle distance signal energy and statistics of topography along different travel paths using data for underground nuclear explosions at semipalatinsk kazakhstan we find strong linear correlations of the logarithmic rms amplitude ratio sn lg and to a lesser extent p lg with mean altitude rms roughness rms slope and skewness of topography along the paths to receivers in eurasia this indicates that energy partitioning in the regional wave field is controlled by wave guide structure and attenuation variations that are manifested in surface topography this suggests that it is feasible in many cases to directly calibrate regional discriminants for path effects in terms of observable surface topography as a surrogate for overall path properties the relationships also help to understand the nature of regional phase propagation

on finding and using repeating seismic events in and near china 1 a comprehensive search for repeating seismic events was performed using cross correlation on waveforms for 17 898 seismic events in and near china reported in the annual bulletin of chinese earthquakes from 1985 to 2005 we define a repeat as an event pair having a high cross correlation 0 8 for a particular bandwidth 0 5 to 5 hz and time window 5 s before p arrival to 40 s after lg arrival such events typically have hypocenters separated by no more than about 1 km this result enables a determination of median relative location error of around 15 km for global and regional catalogs that locate events in this study one at a time using phase picks the maximum location error is on the order of hundreds of kilometers we use nonnormalized cross correlation values to measure relative amplitudes of event pairs the standard deviation is about 0 06 magnitude units much better than the precision of relative magnitudes for doublet events which we estimate for the chinese catalog to have a standard deviation of 0 36 magnitude units two thousand three hundred and seventy nine events out of the 17 898 or 13 of the events in this catalog are classified as repeats with later years showing an increase in the percentage about half the repeats occur as isolated doublets the rest as multiplets of three or larger up to a 92 event multiplet most of the events appear to be triggered or are due to some earthquake interaction since their recurrence intervals are significantly shorter than would be estimated from tectonic loading

deep crustal deformation of the longmen shan eastern margin of the tibetan plateau from seismic reflection and finite element modeling rivaling the himalaya in relief the longmen shan is probably one of the most enigmatic mountain ranges in the world high mountains reach more than 4000 m relief but without adjacent foreland subsidence and with only slow active convergence what are geological and geodynamic processes that built the longmen shan coseismic deformation associated with the 2008 wenchuan earthquake could hold clues to answer these questions the primary features associated with the 2008 wenchuan earthquake rupture have been narrowly distributed coseismic deformation and predominantly vertical displacements that could be interpreted as the result of slips on high angle listric seismogenic faults deep sounding seismic reflection profiling across the seismogenic faults indeed reveals high angle listric reverse faulting in the brittle upper crust and east dipping reflectors that we interpret as ductile shearing in the viscous lower crust in conjunction with a visco elastic finite element modeling of coseismic displacements associated with the wenchuan earthquake we show that the high angle listric nature of earthquake faults produces insignificant horizontal shortening across the fault and facilitates upward slips along the fault that both explain the localized coseismic deformation and vertical displacement as well as the presence of high mountains without adjacent foreland flexure we suggest that the formation of the longmen shan may be better understood in terms of partitioned lithospheric pure shear thickening in which upward high angle listric faulting of brittle upper crust is linked to thickening of the more viscous lithospheric mantle through downward ductile shearing of rheologically deformable lower crust

lg body wave magnitude scaling for the continental margin around korea and japan regional body wave magnitude scalings are essential for quantification of small and moderate size earthquakes that are observed only up to regional distances crustally guided shear waves lg develop stably at regional distances in continental crusts and are minimally influenced by the source radiation patterns lg body wave magnitude scalings m b lg are widely used for assessment of sizes of regional crustal events the m b lg scaling has rarely been tested in continental margins where lg waves are significantly attenuated due to abrupt lateral variation of crustal structures we test the applicability of m b lg scaling to the eastern margin of the eurasian plate around the korean peninsula and japanese islands both third peak and root mean square rms amplitudes of lg vary significantly according to the crustal structures along raypaths causing apparent underestimation of m b lg implementation of raypath dependent quality factors q allows accurate estimation of m b lg retaining the transportability of m b lg in the continental margin around korea and japan the calibration constants for an rms amplitude based m b lg scaling are not determined to vary by region in the continental margin due to complicated crustal structures the calibration constants are determined to be distance dependent both the third peak amplitude based and rms amplitude based m b lg scalings yield accurate magnitude estimates when raypath dependent quality factors are implemented

the excitation of lg waves by explosions a finite difference investigation several mechanisms have been proposed to explain the excitation of the regional lg phase by explosions we examine some of these mechanisms with finite difference simulations an energy flux technique is used to analyze the synthetic signals the method is adapted from conventional array analysis techniques and gives a clear characterization of wave field intensity wave slow ness and propagation direction the vector energy flux in the model is studied instead of the scalar distribution of energy in the space time domain the cal culations show that for an explosive source in a high p wave velocity crust p wave energy cannot be effectively trapped in the crust and the nongeomet rical phase s may be the primary contributor to thelg phase for an explosive source buried in a low velocity upper crust i e where the p wave velocity is lower than the upper mantle s wave velocity part of the ps wave can be trapped in the crustal wave guide to form the lg phase the relative lg excitation de pends on the ratio between the p wave velocity in the source region and the s wave velocity in the uppermost mantle scattering effects can transfer p wave or surface wave energy into lg but the efficiency strongly depends on both the wave frequency and the characteristic size of the scatterers any source process that directly excites s waves is more efficient for generating lg than the afore mentioned mechanisms spall directly generates s wave energy and conse quently is an efficient source for lg for actual explosions all of these factors may simultaneously contribute to lg excitation determining their relative im portance and interactions requires additional observations

late quaternary vegetational dynamics and community stability reconsidered abstract defining the spatial and temporal limits of vegetational processes such as migration and invasion of established communities is a prerequisite to evaluating the degree of stability in plant communities through the late quaternary the interpretation of changes in boundaries of major vegetation types over the past 20 000 yr offers a complementary view to that provided by migration maps for particular plant taxa north of approximately 43 n in eastern north america continual vegetational disequilibrium has resulted from climatic change soil development and species migrations during postglacial times between 33 and 39 n stable full glacial vegetation was replaced by a relatively unstable vegetation during late glacial climatic amelioration stable interglacial vegetation developed there after about 9000 yr b p late quaternary vegetation has been in dynamic equilibrium with a relatively constant flora south of 33 n on upland interfluves along the northern gulf coastal plain peninsular florida and west central mexico

oblique high angle listric reverse faulting and associated development of strain the wenchuan earthquake of may 12 2008 sichuan china the 2008 wenchuan earthquake occurred on imbricate oblique steeply dipping slowly slipping listric reverse faults measurements of coseismic slip the distribution of aftershocks and fault plane solution of the mainshock all confirm this style of deformation and indicate cascading earthquake rupture of multiple segments each with coseismic slip occurring in the shallow crust above a depth range of 10 to 12 km interactions among three geological units eastern tibet the longmen shan and the sichuan basin caused slow strain accumulation in the longmen shan so that measurable preearthquake slip was minor coseismic deformation however took place mostly within the interseismically locked longmen shan fault zone the earthquake may have initiated from slip on a fault plane dipping 30 40 northwest in a depth range from 15 to 20 km and triggered oblique slip on the high angle faults at depths shallower than 15 km to form the great wenchuan earthquake

a study of small magnitude seismic events during 1961 1989 on and near the semipalatinsk test site kazakhstan official russian sources in 1996 and 1997 have stated that 340 underground nuclear tests unts were conducted during 1961 1989 at the semipalatinsk test site sts in eastern kazakhstan only 271 of these nuclear tests appear to have been described with well determined origin time coordinates and magnitudes in the openly available technical literature thus good open documentation has been lacking for 69 unts at sts

yield estimates of nevada test site explosions obtained from seismic lg waves a methodology is presented for determining the yield of underground nuclear explosions from lg wave amplitudes the methodology is applied to nevada test site nts explosions for which the data from short period vertical component analog seismographs at three stations are used to develop calibration curves for unsaturated material and water saturated rock source conditions the latter curves are found to provide reasonably accurate estimates of the yields of explosions in other areas of the united states and in the french sahara suggesting that they may be applicable to all continental areas if so they also can provide an estimate of the bias of mb p magnitudes between different continental sites for example the lg data from nts explosions indicate a 0 31 0 02 magnitude unit bias between nts and eastern north america similar to the approximately 0 33 unit bias found between western and eastern north america previously by use of earthquake data

excitation and propagation of lg from earthquakes in central asia with implications for explosion earthquake discrimination broadband lg records from 52 shallow earthquakes that occurred near the balapan and lop nor nuclear test sites have been used to study spectral characteristics of the excitation and propagation of the lg phase in central asia using a source model that falls off as 2 at high frequencies and a nonlinear inversion method we simultaneously inverted for lg seismic moments m0 corner frequencies fc and path variable values of q0 and qlg at 1 hz and its power law frequency dependence the logarithms of m0 obtained using lg correlate linearly with logarithms of fc the slope being about 3 56 when all data are used and 4 04 when data were sufficient that full inversions could be performed these slopes differ only slightly from the slope of 3 83 obtained in our earlier studies using underground nuclear explosions the fc values in this study are systematically lower than those found for explosions at the same m0 level a comparison of corner frequencies and lg moment values for unknown events with the plots for known events of this study therefore provides means to discriminate between earthquakes and explosions the mb values are systematically lower for earthquakes of this study than for previously studied explosions at the same seismic moment moreover the logarithms of lg moments obtained in this study correlate linearly with a slope of 1 04 with mb values when all data are used and 1 21 when only well recorded events are used these slopes are close to the slope of 1 19 obtained for explosions the average qlg values along the paths used in this study agree well with those obtained using explosion data in central asia and with reported lg coda q values

exhumation history and faulting activity of the southern segment of the longmen shan eastern tibet abstract the longmen shan lms which constitutes the eastern border of the tibetan plateau is about 400 km in length and characterized by a steep topographic transition from the sichuan basin to the plateau the 2008 mw7 9 wenchuan earthquake and 2013 mw6 6 lushan earthquake were associated with the central to northern segments and southern segment of the lms fault belt respectively in this paper zircon and apatite fission track zft and aft respectively dating in combination with previously published low temperature thermochronology studies are used to constrain both the exhumation history and fault activity along the lms with a special focus on the southern segment in the southern segment of the lms the zft ages in the hanging wall of the wulong yanjing fault 10 14 ma increasing to ca 30 ma to the northwest of the faults and to 100 200 ma in the plateau region the aft ages are 3 5 ma at the mountain front and increase to 8 26 ma in the plateau we show that these age distributions are controlled by fault geometry two stages of rapid exhumation were identified using apatite fission track length modeling and the age distributions in the southern segment of the lms the first stage is from ca 30 ma and the second stage is from 3 5 ma to present in contrast with the middle segment of the lms the cenozoic exhumation rate is higher in the southern segment of the lms which may be due to the influence of the collision between the india and eurasia plates and or different faulting mechanisms in the different segments

numerical simulation of high and low frequency lg wave propagation summary lg waves are sometimes extinguished when traversing geological structures such as mountain ranges or grabens previous investigations have applied numerical full waveform simulations at relatively low frequencies on the order of 1 hz to investigate the relationship of different structural models and the amplitude anomalies of the lg waves these studies often fail to link specific known structures to the amplitude anomalies however the observed waveforms also often contain data of significantly higher frequency than the full waveform simulations we compare such low frequency simulations computed with the boundary integral equation bie technique with synthetic seismograms generated by dynamic ray tracing drt beginning with a plane layered model of the crust in central france we show that the general characteristics of the lg wave train over distances ranging from 100 km to around 500 km can be modelled by computing a relatively small number of rays reflected between the free surface and the moho matching the details of the waveforms is more difficult but can be improved by the addition of reflections between other interfaces in the model considering a one layer model of the crust with a step like change in moho depth that leads to a rapid decrease in crustal thickness we show again that the bie and drt solutions are very similar in character significantly both solutions predict that the lg wave will not be extinguished on traversing the moho step finally we consider a more complete and detailed model of the pyrenees though it is more difficult to match exactly the ray and integral equation solutions the general trends continue to be the same and the lg waves are still predicted to cross the tectonic structures associated with the mountains therefore it appears that observed amplitude changes must be caused by something other than the general structure of the pyrenees such as scattering by smaller scale features within the lower crust

a transportable mb lg scale for central europe and implications for low magnitude ms mb discrimination summary we have extended the mb lg method of nuttli using root mean square rms amplitudes corrected for noise and a 1 dependence for geometrical spreading lg waves recorded on the german regional seismic network grsn for earthquakes in south central europe were used to develop an mb lg formula requiring a new calibration constant crms to keep rms mb lg on the same baseline as nuttli s traditional formula based on 3rd peak amplitudes grsn stations had to be calibrated for site terms and for lg attenuation lateral variations in lgq appear to be significant across the study area and a regional q model consisting of constant q partitions north south and in the central alps was developed using measurements based on interstation and two event single station methods when plotted against surface wave estimates of mw rms mb lg measurements in central europe are found to be consistent with mw mb lg relationships for north america and southern asia thus supporting the transportability of our mb lg formula frequency wavenumber processing of grafenberg array data enabled us to extract rayleigh waves for small events and regional ms were measured using the marshall and basham formula our ms mb lg relationship extends to ms 2 5 and agrees well with observations in other regions including the western united states the discrimination potential of ms mb lg observations was examined under realistic monitoring conditions where path corrections were inferred from earthquake data and applied uniformly to natural sources and explosions under these conditions mb pn p are greater than mb lg for large nts explosions however ms mb scaling slopes are steeper for p waves than they are for lg and ms mb observations for nts explosions converge near mb 4 thus allowing for measurement errors and additional uncertainty in mb pn due to regional bias there is little difference in the discrimination potential for pn and lg waves at small magnitudes as such a regional ms mb discriminant based on lg might be preferred owing to the better detectability of lg waves for small earthquakes these results need to be confirmed for explosions at other test sites compared to teleseismic experience regional ms mb observations extend the discrimination capability to lower magnitudes by at least one ms unit