a teleseismic analysis of the new brunswick earthquake of january 9 1982 the analysis of the new brunswick earthquake of january 9 1982 has important implications for the evaluation of seismic hazards in eastern north america although moderate in size mb 5 7 it was well recorded teleseismically source characteristics of this earthquake have been determined from analysis of data that were digitally recorded by the global digital seismograph network from broadband displacement and velocity records of p waves we have obtained a dynamic description of the rupture process as well as conventional static properties of the source the depth of the hypocenter is estimated to be 9 km from depth phases the focal mechanism determined from the broadband data corresponds to predominantly thrust faulting from the variation in the waveforms the direction of slip is inferred to be updip on a west dipping nne striking fault plane the steep dip of the inferred fault plane suggests that the earthquake occurred on a preexisting fault that was at one time a normal fault from an inversion of bodywave pulse durations the estimated rupture length is 5 5 km average properties of the rupture process were examined by a moment tensor analysis of long period p and sh body waves the long period moment of this earthquake was 5 3 1024 dyne cm the static and dynamic stress drops are 41 and 65 bars respectively similar to those of many earthquakes with similar moment in regions that are more seismically active the joint epicenter determination algorithm was used to locate relative to the mainshock the three teleseismically recorded aftershocks that occurred through march 31 1982 the relocated hypocenters of the aftershocks are significantly different from each other and from that of the mainshock they provide additional support for the source dimensions inferred from the waveform analysis

source parameters and scaling relations for small earthquakes in the matsushiro region southwest honshu japan abstract using near field broadband data from a suite of crustal earthquakes which occurred in a small homogeneous source region we examine the scaling relationships among source parameters for earthquakes in the critical 1 5 to 4 5 magnitude range we take special precautions to insure that our conclusions are not biased by local structure seismic moment fault radius and stress drop relations were determined for 32 small shallow strike slip earthquakes 1 6 m l 4 3 in the matsushiro region of southwest honshu japan spectral and cepstral analyses of short period arrivals exhibit structure interpreted as resulting from reverberations within thin low velocity surface layers below the recording site furthermore calculated crustal transfer functions for sh predict a peak over the range of 2 to 4 hz this type of site response can bias estimates of spectral parameters particularly corner or characteristic frequencies for simple sources such a bias can be reduced by filtering in the cepstral domain the effect of cepstral filtering on corner frequency determinations is generally less than 20 per cent and tends to decrease them particularly for larger events where the structurally induced spectral enhancement is at frequencies above the source related corner frequencies estimates of the seismic moment brune stress drop and fault radius for each event were calculated from sh displacement amplitude spectra the seismic moments range from 10 18 to 10 22 dyne cm the stress drops range from 0 008 to 16 bars the relationship between log stress drop and log moment is approximately linear with a slope of 1 up to a moment of 2 10 21 dyne cm but for higher moments the slope is not significantly different from zero fault radii range from 0 3 to 1 2 km there is a physical scatter in radius for any given moment up to a factor of 1 5 for moments less than 2 10 21 dyne cm there is no significant trend in the radius as a function of moment but for higher moments the radius increases with moment the main conclusion is that the stress drop is the dominant scaling factor for moments less than 10 21 dyne cm for higher moment the source dimension becomes the controlling factor

a comparison between the tectonic stress measured in situ and stress parameters from induced seismicity at monticello reservoir south carolina during may and early june 1979 five three component digital seismographs were deployed near the monticello reservoir south carolina to determine the stress drops of reservoir induced earthquakes and compare them with earlier hydrofracture stress measurements of zoback and hickman this issue records for 327 events were obtained 10 of these events each recorded on four or more stations were analyzed to determine stress drops depths for the 10 events ranged from 0 5 to 1 4 km fault plane orientations were calculated from an inversion of the body wave displacements individual radiation pattern corrections were applied in calculating the moments at each station final estimates of seismic moment were obtained by averaging logarithmically the estimates from each component for each event an arithmetic moment was obtained from the individual estimates of the source radius and stress drop was then calculated once from the final estimates of seismic moment and source radius for each event moments of the 10 digitally recorded earthquakes ranged from 2 5 1017 to 2 7 1018 dyne cm for the p wave data and from 4 6 1017 to 4 6 1018 dyne cm for the s wave data the stress drops s wave data only generally ranged from about 0 2 to 4 bars four earthquakes were recorded by a strong motion instrument at the dam site magnitudes m for these events ranged from 2 8 to 3 0 moments taken as averages of the values from each component ranged from 1 7 to 3 4 1020 dyne cm and the stress drops from 13 to 92 bars large differences between the corner frequencies of the two components factors of 2 5 and 4 for two of the events correspond to a large relative uncertainty for these stress drop values nevertheless tens of bars of stress are apparently released for the largest events in the monticello sequence but only a few bars are released for the smaller magnitude events in comparison the in situ stress data measured in two holes give an estimate of shear stress of about 45 bars at 0 2 km depth and 30 to 70 bars at 1 km depth in the northern hole and from 15 20 bars near the surface to almost 70 bars at depth in the southern hole the variation in shear stress inferred from in situ measurements at the deeper levels indicates an inconsistency between the thrust faulting mechanisms of the earthquakes and the state of stress which is more consistent with thrust faulting at 0 2 km depth and strike slip or normal faulting below thus the estimates of shear stress from in situ measurements are of the same order as the stress drops of the m 2 8 3 0 events but about 1 order of magnitude larger than the stress drops obtained for the smaller events

the effect of crustal scattering on observed high frequency earthquake seismograms summary a comparison of high frequency 1 100 hz local out to 40 km earthquake seismograms at stations of the southern black forest digital seismic network is made in an attempt to isolate the effects of near receiver structure and of crustal scattering on the waveforms of the direct body waves and on the coda waves angle of incidence and azimuth of approach analyses from lower crustal earthquakes show that near surface weathering layers with low body wave velocities and with laterally varying thicknesses exist under all of the stations even those at hard rock sites of the black forest the similarity of direct p wave pulse shapes at each site for events of different sizes the time domain form of the so called fmax phenomenon is attributed to the response from this weathering zone the amplitude of the p wave coda of an event is found to be independent of the earthquake radiation pattern and to depend only on the absolute size of the event and on epicentral distance to the receiver furthermore the high frequency p wave coda is found to be generated at least in part from random crustal scattering including that within 100 m of the earthquake focus direct s waveforms are shown to be more complicated than their p wave counterparts probably due to the same near receiver and crustal scattering phenomena however in the case of s waves scattered energy can arrive before as well as at and after the direct s arrival making the identification of the direct s difficult especially for nodal arrivals

high frequency site effects at two parkfield downhole and surface stations abstract using stacked ratios of microearthquake source spectra recorded at the surface and 200 m downhole we have established the p and s wave site effect at two locations in parkfield california the frequency responses of both sites are bimodal being completely dominated by multiples and amplification below 10 hz and by attenuation above 30 hz the low frequency amplification factors show roughly three to five times more uphole motion compared to that downhole the multiples produce peaks with a maximum of nearly 10 times more uphole motion above 50 hz the downhole motion is always larger approaching a factor of 5 at the high frequency limits of our study when fit with a linear attenuation model the high frequency ratios yield compressional and shear q values between 6 and 19 the data were divided into subsets based on event location and time of year statistical comparison of these subsets shows no systematic variation with azimuth or season the results of our study accounts for the lack of high frequency surface reflections in the parkfield downhole data but not for the lack of source scaling of parkfield microearthquakes

necessity of normalization to aluminum to assess the contamination by heavy metals and arsenic in sediments near haiphong harbor vietnam abstract while assessing many different aspects of contamination by heavy metals and arsenic in sediments the natural variability in element contents which depends on the grain size and mineralogical composition of sediments needs to be taken into account in previous studies the normalization of element contents to a reference element such as al was commonly applied to compensate for granulometric and mineralogical effects in the present study through the investigation on the contamination of heavy metals and arsenic in sediments near haiphong harbor the necessity of the normalization towards al is assessed the results indicate that before al normalization the occurrences on the source and historical trend of contamination by heavy metals and arsenic can be masked by the distribution of clay

a finite difference simulation of wave propagation in two dimensional random media a finite difference algorithm is used to generate synthetic seismograms for waves propagating through two dimensional random media the media have a significant component of their material properties varying randomly over length scales smaller than the seismic wavelength and are meant to approximate the heterogeneity of the crust and upper mantle the finite difference technique retains all multiply scattered and diffracted waves and also accounts for transmission losses the synthetic seismograms clearly exhibit coda and apparent attenuation caused by scattering for a medium with a white wavenumber spectrum of velocity fluctuations the coda is higher frequency than the initial pulse the apparent attenuation is greatest when the scatterer size is comparable to the seismic wavelength the spectra of the coda generally increase in frequency as the scatterers decrease in size examples demonstrate how scattering can produce spectra with broad peaks and sharp fall offs that can make the determination of the source spectra and corner frequencies of small earthquakes extremely difficult

source parameters for small events associated with the 1986 north palm springs california earthquake determined using empirical green functions using small events as empirical green functions which include path site and instrument effects on the p waveforms source parameters were estimated for 25 ml 3 4 to 4 4 events associated with the 1986 north palm springs earthquake the static stress drops ranged from 3 to 80 bars for moments of 0 7 to 11 1021 dyne cm there was a spatial pattern to the stress drops of the aftershocks which showed increasing values along the fault plane toward the northwest compared to relatively low values near the hypocenter of the mainshock the highest values were outside the main area of slip and are believed to reflect a loaded area of the fault that still has an higher level of stress which was not released during the main shock the relatively high stress drop of a preshock in 1983 located close to the hypocenter of the main shock is also interpreted as evidence that stress drops of magnitude 3 and 4 events can be used as indicators of the stress level in a particular area

short period strain 0 1 105 s near source strain field for an earthquake m l 3 2 near san juan bautista california measurements of dilational earth strain in the frequency band 25 10 5 hz have been made on a deep borehole strainmeter installed near the san andreas fault these data are used to determine seismic radiation fields during nuclear explosions teleseisms local earthquakes and ground noise during seismically quiet times strains of less than 10 10 on these instruments can be clearly resolved at short periods 10 s and are recorded with wide dynamic range digital recorders this permits measurement of the static and dynamic strain variations in the near field of local earthquakes noise spectra for earth strain referenced to 1 strain 2 hz show that strain resolution decreases at about 10 db per decade of frequency from 150 db at 10 4 hz to 223 db at 10 hz exact expressions are derived to relate the volumetric strain and displacement field for a homogeneous p wave in a general viscoelastic solid as observed on colocated dilatometers and seismometers a rare near field recording of strain and seismic velocity was obtained on may 26 1984 from an earthquake ml 3 2 at a hypocentral distance of 3 2 km near the san andreas fault at san juan bautista california while the data indicate no precursory strain release at the 5 10 11 strain level a coseismic strain release of 1 86 nanostrain was observed this change in strain is consistent with that calculated from a simple dislocation model of the event ground displacement spectra determined from the downhole strain data and instrument corrected surface seismic data suggest that source parameters estimated from surface recordings may be contaminated by amplification effects in near surface low velocity materials

geophone ground coupling for frequencies much lower than the coupling resonant frequency the geophone accurately follows the ground motion but for higher frequencies the coupling can alter both the amplitude and phase of the seismic signal the normal planting of vertical geophones in the field results in coupling adequate for conventional recording that uses frequencies less than 100 hz however for very loose soils or for high frequency seismic recording i recommend that the geophones be buried to place the geophones in firmer soil the coupling resonant frequency for vertical geophones is determined by the firmness of the soil and i have measured resonant frequency ranging from 100 to 500 hz at different locations because the firmness of the soil increases with depth the coupling resonant frequency can be increased by burial of the geophones or by the use of longer spikes the rocking of horizontal geophones causes a low frequency coupling resonance it is crucial that horizontal geophones be planted with their bases firmly contacting the soil geophones so planted have a resonance around 130 hz whereas those 1 cm off the ground can have a resonance of 30 hz or lower soil conditions have little effect on the resonant frequency horizontal geophones with 1 inch spikes are as well coupled as those with longer spikes but the best coupling is achieved by burial of the geophones modified journal abstract

empirical green s functions from small earthquakes a waveform study of locally recorded aftershocks of the 1971 san fernando earthquake seismograms from 52 aftershocks of the 1971 san fernando earthquake recorded at 25 stations distributed across the san fernando valley are examined to identify empirical green s functions and characterize the dependence of their waveforms on moment focal mechanism source and recording site spatial variations recording site geology and recorded frequency band recording distances ranged from 3 0 to 33 0 km hypocentral separations ranged from 0 22 to 28 4 km and recording site separations ranged from 0 185 to 24 2 km the recording site geologies are diorite gneiss marine and nonmarine sediments and alluvium of varying thicknesses waveforms of events with moment below about 1 5 1021 dyn cm are independent of the source time function and are termed empirical green s functions waveforms recorded at a particular station from events located within 1 0 to 3 0 km of each other depending upon site geology with very similar focal mechanism solutions are nearly identical for frequencies up to 10 hz there is no correlation to waveforms between recording sites at least 1 2 km apart and waveforms are clearly distinctive for two sites 0 185 km apart the geologic conditions of the recording site dominate the character of empirical green s functions even for source spatial separations of up to 20 0 km the empirical green s functions at a particular site are consistent in frequency content amplification and energy distribution therefore it is shown that empirical green s functions can be used to obtain site response functions the observations of empirical green s functions are used as a basis for developing the theory for using empirical green s functions in deconvolution for source pulses and synthesis of seismograms of larger earthquakes

background baseline normalization and contamination of heavy metals in the liao river watershed sediments of china abstract the quantitative assessment of heavy metal contamination in the sediments is a challenge due to the lacking of geochemical background or baseline levels and sediment heterogeneity in this study a procedure is suggested to elucidate the average background levels and geochemical baseline levels gbls of cr cu ni pb and zn in the liao river water sediments and to develop their geochemical baseline functions gbfs the average background levels of cr cu ni pb and zn were 32 6 11 1 13 1 16 3 and 37 8 mg kg respectively while their gbls the upper limit of background level were 60 21 27 23 and 96 mg kg the linear correlation of heavy metals cr cu ni pb and zn with particle size proxy elements normalizers sc fe and al was statistically significant at p

the effects of attenuation and site response on the spectra of microearthquakes in the northeastern caribbean abstract the spectra of microearthquakes recorded by a seismic network in the northeastern caribbean were analyzed to determine the effects of attenuation and site response on these spectra the ratios of the spectral amplitudes at 5 and 20 hz were measured for several earthquakes at different distances from a fixed receiver to estimate q for p and s waves in the crust and upper mantle the average q p determined from three stations was 380 for epicentral distances between 40 and 200 km the average q s determined from two stations was estimated at 400 spectra of earthquakes closer than 40 km to one station indicate that a high q path q 800 exists for these short distances in the island arc platform the near equivalence of q p and q s observed in this study of the upper lithosphere contrasts with estimates of anderson et al 1965 that q p 9 4 q s in the asthenosphere this finding that q p is approximately equal to q s suggests that the attenuation mechanism in the upper lithosphere differs from that in the asthenosphere the spectra of nearby microearthquakes unaffected by crustal attenuation display corner frequencies which are uniform despite large differences in the seismic moments of the events the corner frequencies of these spectra appear to be characteristic of the receiver site and insensitive to the location and moment of the earthquakes at one station the s wave corner frequency of a nearby blast was identical to the corner frequency of a magnitude 4 8 earthquake derived from the record of a strong motion accelerograph at the same site

secondary grain size effects on li and cs concentrations and appropriate normalization procedures for coastal sediments the sediment grain size effect gse a fundamental factor relevant to the interpretation of elemental concentrations and isotopic compositions has been normalized using conservative elements such as aluminum al cesium cs and lithium li c al c cs c li which serve as proxies for the natural metal controlling variables of grain size mineralogy and organic matter however a secondary gse reportedly remains even after compensation by the al normalization procedure particularly for the concentrations of transition metals c t m this secondary effect also occurred in the c li c cs c al ratios of the korean coastal sediments examined in this study the primary and secondary gses on cs and li concentrations can be explained by the quartz dilution effect and the cs and li incorporation effect of phyllosilicate minerals respectively based on a model involving three component end members a cs and li free sand dominated sediment component consisting mostly of quartz and feldspar a cs and li bearing silt dominated component of mica and a cs and li enriched clay dominated component of illite although the primary and secondary gses on the concentrations of transition metals particularly cu and ni in coastal sediments might be normalized by dividing the metal concentrations by the square of the al concentration c t m c al 2 the gses can also be normalized by dividing the concentrations by the exact cs or li concentration c t m c cs c 2016 elsevier ltd all rights reserved

source processes of three aftershocks of the 1983 goodnow new york earthquake high resolution images of small symmetric ruptures broadband large dynamic range geos data from four aftershocks m l 2 to 3 of the 1983 goodnow new york earthquake recorded at hard rock sites 2 to 7 km away from the epicentral area are used to study rupture processes of three larger events with an m l 1 6 event as the green s function event we analyze the spectra and spectral ratios of ground velocity at frequencies up to 100 hz and conclude that 1 there are resolvable p wave f max 51 and 57 hz at two sites 2 there is abundant information on sources of larger events up to frequencies of 50 to 60 hz and 3 there is an unstable nonlinear instrument resonance at about 90 hz we analyze the artifacts of low pass filters in the deconvolved rupture process including the limited time resolution and biases in the rise time measurement some extensions of the empirical green s function egf method are proposed to reduce these artifacts and to precisely estimate the relative locations of events that are close both in time and in space applying the egf method to three aftershocks we find that these events have ruptures that are simple crack like characterized by small fault radii 70 to 120 m and static stress drops that vary depending on the size of the events between about 5 to 16 bars we also find that two of the events with origin times differing by 0 60 sec are separated by 190 110 meters assuming a causal relationship between the two would result in a slow propagation velocity 0 05 0 03 time of the local shear wave velocity we therefore interpret the corresponding ruptures as being distinct the area between the rupturing patches having a characteristic length much smaller than those of the rupturing patches comparison of the results of this study with those obtained for the goodnow main shock and microearthquakes in california and hawaii suggests that the stress drops of the goodnow aftershocks decrease considerably by up to a factor of 25 or more from those estimated for the main shock even after the estimated large uncertainty in the latter estimates is considered this decrease is similar to those reported for the nahanni earthquakes m b 5 0 to 6 5 in northwest territories and for the north palm springs earthquake m l 5 9 sequence in california the stress drops of the simple crack like microearthquakes are significantly variable by factors between 3 and 27 within the single source areas the median of stress drops of the intraplate goodnow aftershocks is lower by factors of 2 to 4 than the medians calculated for the other interplate microearthquake sequences

rupture histories of eastern north american earthquakes abstract digital worldwide records of p and sh waves are used to invert for rupture histories of the recent larger eastern north american earthquakes the data include a broad bandwidth to facilitate recovery of both source details and total moment the following events are studied 9 january 1982 new brunswick 5 october and 23 december 1985 nahanni 25 november 1988 saguenay and 25 december 1989 ungava earthquakes we employ a finite fault waveform inversion scheme that discretizes the slip history as a function of position on the fault this formulation allows estimation of rise time and slip velocity in addition to the spatial distribution of slip static stress drops averaged over the entire rupture surface range from a few tens of bars to just over 100 bars and are similar to values estimated for western united states earthquakes estimates of stress drop for spatially limited asperities are in the range of a few hundred bars with the value for the saguenay earthquake asperity being the largest approaching 1 kbar the variation in stress drop is considerable but no evidence is seen for a scaling relation in which stress drop increases with moment maximum slip velocities on the fault also have a wide range from 50 cm sec to perhaps greater then 200 cm sec with the saguenay and 5 october nahanni earthquakes lying at the upper end of this range of the events studied the saguenay earthquake is unique in terms of its greater depth spatially concentrated source and large asperity stress drop

direct observation of rupture propagation during the 1979 imperial valley earthquake using a short baseline accelerometer array abstract the 1979 imperial valley california earthquake m s 6 9 was recorded on the el centro differential array a 213 m long linear array of 5 three component digital accelerometers 5 6 km from the nearest tectonic surface rupture although absolute time was not recorded on the array elements a relative time base was established using the main shock hypocentral p wave and the p and s waves from a later aftershock a cross correlation technique was used to measure the difference in arrival times of individual seismic waves in a moving 0 6 to 1 2 sec window at each array element which would then be converted into the wave9s slowness 1 velocity along the array when applied to the main shock vertical and horizontal accelerograms results from both components of motion indicated that the early arriving energy came from a source to the south of the array and the source of the energy moved rapidly to the north of the array during the strong shaking the ground motions at the array elements were well correlated for about the first 11 sec of motion these observations suggest that we have observed the initiation of rupture south of the array and its subsequent propagation along the fault to a position north of the array in about 10 sec and that the energy was radiated from a fairly compact region around the rupture front if the observed vertical and horizontal ground motions are assumed to be caused by p and s waves respectively then the observed slownesses show irregularities which can be interpreted as implying that the observed high frequency ground motions originated at irregularly distributed regions on the fault surface or that the rupture velocity was variable or both one possible interpretation of the data suggests that the rupture proceeded at near p wave velocity over a 7 km long section of fault average rupture velocities of about 2 7 to 3 2 km sec at 8 km depth are consistent with the data and 2 8 km sec is weakly preferred under the assumption that rupture propagates at a fixed fraction of the shear velocity the large vertical pulse which had a peak acceleration of 1 7 g at e06 was emitted from the portion of the fault extending 25 to 30 km northwest of the hypocenter near meloland overpass and not from the point on the fault closest to the differential array nothing can be said about fault behavior southeast of the hypocenter

inversion for p and s wave attenuation structure long valley caldera california p and s wave amplitude data from digital three component seismograms of local earthquakes recorded on a temporary seismic array have been used to tomographically invert for the three dimensional attenuation structure in the upper crust of long valley caldera california differential attenuation q 1 values are obtained through the use of a spectral ratio technique that minimizes the site effect on the spectral ratios the spectral ratios are inverted for q 1 using the lsqr algorithm zones of high positive p wave q 1 greater p wave attenuation are observed at a depth of 4 5 km beneath the east flank of mammoth mountain and at 6 8 km beneath the southwestern edge of the resurgent dome a region of positive s wave q 1 is seen at 7 8 km beneath the southern edge of the resurgent dome whereas at 6 7 km the s wave results are near average the region of positive s wave q 1 at 7 8 km beneath the resurgent dome may indicate the roof of a magmatic system the positive p wave q 1 at 4 5 km beneath mammoth mountain and 6 8 km beneath the resurgent dome may be due to the presence of a compressible fluid such as supercritical water these zones may represent some of the source regions for the long valley geothermal system

finite difference simulations of seismic scattering implications for the propagation of short period seismic waves in the crust and models of crustal heterogeneity synthetic seismograms produced by the finite difference method are used to study the scattering of elastic and acoustic waves in two dimensional media with random spatial variations in seismic velocity the results of this study provide important insights about the propagation of short period 5 the self similar medium is characterized by a scattering q that is constant with frequency whereas theory predicts that the apparent q in an exponential medium is proportional to frequency these alternative models of crustal heterogeneity can thus be tested by improved measurements of the frequency dependence of crustal q at frequencies greater than about 1 hz assuming that scattering is responsible for most of the attenuation at these frequencies measurements of the time decay of the synthetic coda waves clearly show that the single scattering model of coda decay is not appropriate in the presence of moderate amounts of scattering attenuation scattering q 200 in these cases q values derived from the coda decay rate using the single scattering theory do not correspond to the transmission q of the medium the cross correlation of synthetic waveforms observed for an array of receivers along the free surface is observed to be dependent on the correlation distance of the medium the self similar random medium proposed here for the crust produces waveform variations at high frequencies 15 30 hz similar to those reported for actual small scale seismic arrays with apertures of hundreds of meters

the 1982 enola arkansas swarm and scaling of ground motion in the eastern united states abstract the north central arkansas swarm which began in january of 1982 and was still active as of december 1983 has produced over 30 000 events three of these events had duration magnitudes greater than 4 0 fifty three locatable events in the magnitude range 3 8 and below were recorded during the 2 1 2 weeks our 10 digital seismographs were in place the hypocentral locations are confined to a tight cluster with a radius of approximately 1 km depths range between 4 and 7 km focal mechanisms determined for 10 of the events show a combination of strike slip and normal faulting source parameters seismic moment source radius and stress drop were calculated for 48 of the events the seismic moments range from 10 18 to 10 21 dyne cm while the stress drops range from 0 2 to 60 bars acceleration spectra are band limited at the high end at 30 hz the stress drops increase with seismic moment up to 10 20 dyne cm but appear to be constant at greater moment values the arkansas source parameters are similar to other body wave source parameters determined from near source investigations of earthquakes in eastern and central north america e g new brunswick and south carolina and in california e g mammoth lakes oroville and anza but differ substantially from lg wave source parameters estimated for earthquakes in the eastern and central united states

source parameters of loma prieta aftershocks and wave propagation characteristics along the san francisco peninsula from a joint inversion of digital seismograms abstract aftershock recordings from 10 digital seismographs deployed along the axis of the san francisco peninsula from the epicenter of the 18 october 1989 loma prieta earthquake to san francisco provide the data for a joint inversion for source wave propagation and site effects the inversion procedure is a least squares method using the singular value decomposition algorithm and is done in two parts the first solves only for the source and attenuation terms for all events and the second projects the residuals from the first inversion onto the site terms the coefficient of geometrical spreading is solved for as part of the model of attenuation residuals plotted versus distance and frequency provide a check on the appropriateness of the attenuation model the earthquakes are all located near the san andreas fault mostly in the aftershock zone of the loma prieta mainshock but some area near daly city on the peninsula the data set provided by geos recorders consists of 148 digital seismograms for 33 events from 10 sites that form a linear profile from the epicentral region to the city of san francisco a distance of approximately 100 km strong motion accelerograms are also available for the larger events body wave spectra are fit surprisingly well by our model especially at distances beyond about 20 km where differences due to radiation pattern effects and changes in angle of incidence become less important results from the inversion show that estimates of moment are only 1 higher for the p waves compared to the s waves apparently there are no major biases in the estimates as each is determined independently of the other p wave corner frequencies are 1 5 times higher than s wave corner frequencies on average stress drops with an average of 176 bars for events that range in magnitude from 1 7 to 4 2 are higher than those found in previous studies where site and path were not explicitly taken into account the exponents of geometrical spreading are very close to one 1 019 for p waves and 1 017 for s waves for this data set which extends to about 100 km the whole path q assumed to be frequency independent was about 800 for both p and s waves specifically 790 for p waves and 830 for s waves the average p wave attenuation at all sites is quantified by a t of 0 020 sec which compares to 0 03 sec for s waves t determined for each site range from a low of 0 008 sec at san bruno mountain a hard rock site to a high of 0 065 sec at corralitos in the epicentral area residuals of the model fits which are distance dependent show larger amplitudes near the epicenter but fall off with a minimum at about 30 km where amplitudes are about 30 to 60 lower than average at distances farther than 30 km amplitudes rise out to the limit of the data at about 105 km where amplitudes are about average at frequencies less than 10 hz but are slightly above average for higher frequencies the location of this low in amplitude can be explained as the boundary between the amplitude decay of direct arrivals and the emergence of wide angle reflections from the lower crust and moho which increase in amplitude beyond 30 km these amplitudes correlate with damage patterns from the mainshock as less damage was observed along the peninsula but appeared to increase towards san francisco even when damage in the marina and china basin districts of san francisco are not included in the damage census

modeling ground motion attenuation in eastern north america abstract in this study we have utilized our understanding of the physics of elastic wave propagation to simulate ground motions within about 200 km from earthquakes in eastern north america detailed crustal velocity structure models were developed for sources located in the grenville and appalachian provinces the former consists of a single gradient in the crust while the latter contains a mid crustal discontinuity and a deep moho semi empirical synthetic seismograms were computed by convolving the generalized ray response of the structures with an empirical source function obtained from a recording close to the source peak ground motions derived from the synthetic seismograms adequately interpolate the sparse empirical data while providing information on the wave propagation phenomena that define ground motion attenuation they suggest that peak ground motion amplitudes are controlled by in order of increasing range the upgoing direct s wave the diving s wave post critical reflections from the mid crustal or moho discontinuities and finally l g

observations of mine seismicity in the eastern wasatch plateau utah u s a a possible case of implosional failure in the summer of 1984 a three dimensional high resolution microearthquake network was operated in the vicinity of two coal mines beneath gentry mountain in the eastern wasatch plateau utah during a six week period approximately 3 000 seismic events were observed of which the majority were impulsive higher frequency 10 hz short duration 2 3 sec events probably associated with the caving of the roof from a longwall operation in contrast 234 of the largest located events appeared to occur predominantly beneath the mines to a depth of 2 to 3 km consistent with previous studies the magnitudes of these events ranged from less than m c 0 to 1 6 in addition to the unusual depths of these latter events an anomalous aspect displayed by the events was an apparent dilatational focal mechanism suggesting a non double couple possibly implosional source implosional events have been observed in other studies of mine seismicity however the generally inadequate instrumental coverage of the focal sphere has cast some doubt on the validity of such mechanisms previously suggested source mechanisms for such implosional events have included tensional failure through strata collapse and a shear implosional displacement mechanism shear failure must be involved in the failure process of the gentry mountain implosional events as evidenced by well defined shear waves in the observed seismograms simultaneous monitoring in the east mountain coal mining area to the south by the university of utah revealed typical shear failure events mixed with implosional events the observed double couple reverse focal mechanisms at east mountain were similar to mechanisms determined in previous studies and a composite focal mechanism determined in this study for a sequence outside the mining areas this suggested that the shear events within the mining areas are being influenced by the regional tectonic stress field thus in addition to the seismic events associated with caving of the roof from the longwall operation there appear to be at least two other types of mining induced seismic events occurring in the eastern wasatch plateau both submine in origin 1 events characterized by apparent non double couple possibly implosional focal mechanisms and well defined shear waves and 2 shear events which are indistinguishable from tectonic earthquakes and may be considered mining triggered earthquakes the small mining induced stress changes that occur beyond a few hundred meters from the mine workings suggest both types of seismic events are occurring on critically stressed pre existing zones of weakness topography overburden method of mining and mine configuration also appear to be significant factors influencing the occurrence of the implosional submine events

spatial gradient analysis for linear seismic arrays i incorporate the spatial gradient of the wave field recorded from one dimensional arrays into a processing method that yields the horizontal wave slowness and the change of geometrical spreading with distance in general the model for seismic wave propagation is enough to be appropriate for body and surface waves propagating from nearby seismic sources but can be simplified into a plane wave model although computation of the spatial gradient requires that array elements be closer than 10 of the horizontal wavelength seismic array apertures in the usual sense may extend over many horizontal wavelengths and illuminate changes within the wave field array images of horizontal slowness and the relative geometrical spreading changes of seismic waves are derived using filter theory and used to interpret observed array wave fields errors in computing finite difference spatial gradients from array nodes are explicitly considered to avoid spatial aliasing in the estimates i apply the method to interpret waves in strong ground motion and small scale refraction data sets use of the wave spatial gradient accentuates spatial differences in the wave field that can be theoretically exploited in fine scale tomographic studies of structure and is complementary to frequency wavenumber or beam forming array processing techniques

spectral analysis and earthquake scaling of the petatlan earthquake m s 7 6 aftershocks recorded at stations along the pacific coast and between the coast and mexico city spectral parameters have been estimated for 214 petatlan aftershocks recorded at stations between petatlan and mexico city and between petatlan and acapulco the spectral parameters were used to obtain empirical relations for the estimation of seismic moment from coda length and fromm l stress drops using brune s model were calculated for these aftershocks six events with large stress drop are located within a previously suggested asperity and seven more suggest a boundary zone at the intersection of the petatlan and zihuatanejo aftershock rupture volumes stress drops increase with increasing seismic moment up to 1020 dyne cm but appear to be constant at greater moment values the peak horizontal velocity times distance of aftershocks recorded near the coast and between the coast and mexico city 30 to 270 km away scales linearly with seismic moment and predicts well the peak horizontal values of large m s 7 0 coastal thrust events recorded on rock sites at mexico city peak horizontal velocity is a straightforward measurement thus this relation allows us to evaluate expected ground motion between the pacific coast and mexico city from the seismic moment of subduction related earthquakes along the coast

earthquake source parameters and the frequency dependence of attenuation at coalinga mammoth lakes and the santa cruz mountains california least squares best fits were calculated to the fourier amplitude spectra of p and s waves of locally recorded earthquakes attenuation amplification and earthquake source parameters were calculated from parameters of the fits approximately 8200 spectra were fit at 39 sites at coalinga mammoth lakes and the santa cruz mountains california typically the spectra were fit from 2 to 45 hz for p waves and 2 to 20 hz for s waves the source spectral falloff of p waves was limited to be no greater than f 2 5 f is frequency by low attenuation sites in the sierra nevada attenuation was measured through t the travel time divided by q attenuation was considered to be frequency dependent according to t to f which is equivalent to q qof negative values of were found to minimize the sum of squared residuals at most of the sites studied attenuation and amplification varied from site to site systematically with site geology source parameters were determined for individual earthquakes by averaging fit parameters from between four and 18 spectra depending on the earthquake seismic moments ranged from roughly 5 1012 to 1015 nm at coalinga and mammoth lakes moments ranged from 2 1011 to 3 1014 nm in the santa cruz mountains when the fits were determined using negative values of a the seismic moments trended approximately as fc 3 fc is the corner frequency for 0 5 stress drops varied from roughly 0 2 to 50 mpa at coalinga and mammoth lakes stress drops were lower in the santa cruz mountains ranging from approximately 0 05 to 8 mpa

source spectra for the 1988 saguenay quebec earthquakes abstract source spectra are obtained for the 1988 saguenay quebec earthquake m n 6 5 its foreshock m n 4 8 and largest aftershock m n 4 1 using recordings from analog and digital seismographs on rock sites at epicentral distances from 40 to 700 km the source spectra of the foreshock and the aftershock are well matched by a single corner frequency 2 model with seismic moments of 2 2 10 22 and 2 2 10 21 dyne cm respectively and a stress parameter of 65 bars for both events by contrast the spectrum of the mainshock differs dramatically from this simple shape a stress parameter of 500 bars is required to match the observed high frequency amplitudes using the seismic moment determined from teleseismic observations as a constraint this single corner frequency model however overestimates amplitudes at frequencies near 1 hz by a factor of about 2 the relative radiation of short and long period energy for the mainshock is inconsistent with that from other intraplate earthquakes the fore and aftershocks appear typical in this regard the extraction of source spectra from the regional data required a careful examination of attenuation azimuthal variations were observed with the attenuation being most severe to the southeast normal to the st lawrence valley and the dominant structural grain of the region the st lawrence river coincides in part with the boundary between the grenville and appalachian tectonic provinces and the difference in attenuation may be related to the difference in tectonic province the distribution of data however makes it difficult to obtain good estimates of the attenuation in each province lumping the data from both provinces and the three earthquakes together results in an anelastic attenuation factor given by q 755 f 0 5 for frequencies f from 0 6 to 18 hz using data at distances r beyond 100 km from the sources and assuming 1 r geometrical spreading this attenuation is similar to that obtained in a number of other studies in the general area three component recordings were available at a few stations and from these the following frequency dependent ratio of horizontal to vertical motion was obtained hiv 1 14 0 118 f 0 00638 f 2 for frequencies from 0 2 to 15 hz different methods of correcting observations for attenuation in order to derive source spectra were examined source spectra derived by simple regression analyses of observed data assuming a uniform medium are very similar to those based on a more complicated synthetic seismogram correction which accounts for wave propagation in a layered earth

source pulse enhancement by deconvolution of an empirical green s function observations of the earthquake source time function are enhanced if path recording site and instrument complexities can be removed from seismograms assuming that a small earthquake has a simple source its seismogram can be treated as an empirical green s function and deconvolved from the seismogram of a larger and or more complex earthquake by spectral division when the deconvolution is well posed the quotient spectrum represents the apparent source time function of the larger event this study shows that with high quality locally recorded earthquake data it is feasible to fourier transform the quotient and obtain a useful result in the time domain in practice the deconvolution can be stabilized by one of several simple techniques in this paper the method is implemented and tested on high quality digital recordings of aftershocks of the jan 9 1982 miramichi new brunswick earthquake in particular seismograms from a jan 17 aftershock 017 13 33 gmt local mag 3 5 exhibit path or site effects which complicate the determination of source parameters after deconvolution the apparent far field source of this event is a simple pulse in displacement with duration 0 07 second for both p and s

crosshole seismology and seismic imaging in crystalline rocks a borehole to borehole audiofrequency seismic system using piezoelectric transducers as active elements has been developed and used to investigate crystalline rocks in canada high quality seismograms have been recorded for transmitter receiver distances of up to 230 meters it has been found that both travel times and signal amplitudes provide diagnostic information about rock quality two dimensional images of seismic velocity and transparency distributions between two boreholes derived from observed arrival times and amplitudes by simple back projection tomography reflect lithology and geological structure the results indicate the potential usefulness of crosshole seismic imaging as a tool for rock mass characterization

distribution of attenuation in the kaoiki hawaii source volume estimated by inversion of p wave spectra a new method to simultaneously invert for q structure and source parameters was used on a set of 635 microearthquakes 0 9 m 2 0 in the kaoiki area of southern hawaii approximately 2800 signals were analyzed which had been recorded by 6 short period vertical seismographs at epicentral distances of a few to 10 km the hypocentral depths ranged from o to 14 km with the bulk of the sources in the 7 5 10 5 km range the hypothesis to be tested was that the source volume of the m 6 6 kaoiki main shock of november 16 1983 may be heterogeneous in attenuation distribution we assumed that the observed p wave displacement spectra could be modelled by a source spectrum with an 2 high frequency decay a single layer resonance filler to account for local site resonances and whole path attenuation along the ray path in a next step the attenuation factor q was constrained by tomographically reconstructing the three dimensional q structure for the source region and using it as starting model for a nonlinear inversion of the corner frequency the seismic moment m0 and a new q value this process was iterated until the results changed less than 0 1 and were accepted as final the average q was approximately constant and very low 105 q 115 between o and 7 km depth it increased to approximately 160 between 9 and 11 km in the depth ranges were the spatial coverage was good 3 9 km the q values in the nw part of the 1983 aftershock volume were larger by approximately 10 15 compared to those in the se part this 12 contrast correlates with other evidence for heterogeneity the nw region shows high coda q no surface faulting medium seismicity rate and medium precursory quiescence while the se region shows low coda q pervasive faulting high seismicity rate strong precursory quiescence and possibly low b values we conclude that the kaoiki source volume is strongly heterogeneous with the contrasting density of cracks controlling the difference in crustal parameters the new simultaneous inversion technique is well suited to derive detailed q structure and source parameter information from microeaithquake spectra recorded at close epicentral distances

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

attenuation of short period p waves at mount st helens an increase of seismicity occurred at mount st helens between may and july 1998 with more than 900 events md 2 2 recorded by the pacific north west seismograph network this article describes an attempt to estimate the temporal and spatial variation in seismic attenuation using 200 microearthquakes that occurred before january 1995 april 1998 during and after august december 1998 the period of higher seismicity and recorded on three different one component seismic stations epicentral distances of the studied events ranged between 0 5 and 15 km we performed the analysis distinguishing the deep depth 5 5 km from shallow depth 5 5 km events we used the frequency decay method to estimate the quality factor q and station site correction s for p waves in the frequency bands 2 7 and 18 30 hz the results show that the attenuation varies from site to site systematically and decreases with depth lower qp values are obtained for focal depths less than 5 5 km moreover the spatial variations of qp show minimum values 30 in the crater area that are interpreted as due to a low density mass distribution under the crater we find that qp was 30 higher before the period of high seismicity than after this change may be attributed to an increase of pressure in the magma chamber producing new cracks and or reopening of pre existing cracks which are the most viable mechanisms for increasing attenuation

the 25 november 1988 saguenay quebec earthquake source parameters and the attenuation of strong ground motion the saguenay earthquake of 25 november 1988 occurred close to the southern margin of the saguenay graben in southern quebec it was caused by almost purely dip slip faulting centered at a depth of 26 km with a p axis oriented northeast southwest this faulting mechanism is similar to those of the larger historical earthquakes in eastern north america but the focal depth is substantially greater than all but one of these events the seismic moment estimated from regional pni waves and teleseismic long period body waves is 5 10 24 dyne cm corresponding to a moment magnitude of 5 8 the source duration of the earthquake is estimated to be 1 8 sec corresponding to a stress drop of 160 bars which is not significantly higher than the average stress drop of 120 bars estimated from previous large earthquakes in eastern north america in order to simultaneously match the recorded ground motion amplitudes of strong motion acceleration strong motion velocity and teleseismic short period and long period body waves it is necessary to use a source function having a complex shape that implies the presence of asperities and larger local stress drops the large set of strong motion recordings of the saguenay earthquake has been used to validate a procedure for estimating strong ground motion attenuation based on a simple wave propagation model the most important feature of the recorded strong motions is that their peak amplitudes do not decay significantly with distance inside 120 km but then decay abruptly beyond 120 km profiles of recorded accelerograms with absolute times indicate that at distances beyond 64 km the peak ground motions are due to strong postcritical reflections from velocity gradients in the lower crust the principal shear wave arrivals and the variation of their peak amplitudes with distance were reproduced in synthetic seismograms generated using a regional crustal structure model the critical distances for the postcritical reflections were short because of the deep focal depth of the event causing the elevation of ground motion amplitudes out to 120 km similar studies of earthquakes in other regions of eastern north america indicate that the strength of the postcritical reflections and the distance ranges over which they are dominant are controlled by the focal depth and crustal structure regional variations in crustal structure thus give rise to predictable regional variations in strong ground motion attenuation

seismic source spectrum of microearthquakes the seismic source spectra of microearthquakes having seismic moments between 1014 and 1018 dyne cm were investigated by using local recordings from an excellent hard rock site the p wave velocity near the site was estimated as about 6 km sec even immediately below the ground surface the effect of anelastic attenuation was thought to be very small since predominant frequencies of greater than 100 hz were detected in seismograms recorded at focal distances greater 10 km many seismograms with s p times of less than 0 6 sec were observed the first cycle of the p wave velocity seismogram was used in this study the waveforms after the first cycle are likely formed near the site since their periods are exactly the same for earthquakes that have different source processes in the high frequency portion of the estimated displacement source spectra the slopes of the fall off have values much greater than 2 the source process of microearthquakes is assumed to be very slow and smooth

high frequency spectral scaling of a main shock aftershock sequence near the norwegian coast a high frequency seismic element was recently added to the noress regional array in norway this system can monitor seismic signals at frequencies up to 50 hz in february 1986 the high frequency seismic element recorded an mblg 4 7 main shock and several aftershocks which occurred 420 km northwest of noress off norway s western coast these events produced high frequency signals which were well above the background noise at the station p wave spectra of these events scale in a manner consistent with the square constant stress drop source model the data do not require any change in this scaling to magnitudes mblg below 2 in contrast to previous reports that constant stress drop scaling breaks down at smaller magnitudes

rupture characteristics and tomographic source imaging of ml 3 earthquakes near anza southern california the rupture characteristics of several ml 3 earthquakes near anza california are determined from time domain analysis of path corrected displacement pulses these pulses are corrected for propagation effects apparent attenuation scattering site resonance using the waveforms of adjacent small events ml 2 1 as empirical green s functions the earthquakes studied occurred during two swarm sequences near cahuilla in an area characterized by swarm activity at shallow depth 5 km the data consist of seismograms recorded by the anza seismic network a high dynamic range local array with digital telemetry the waveforms of adjacent small events ml 2 1 are deconvolved from those of the ml 3 events to yield the source time functions of the larger earthquakes the ml 3 earthquakes display a variety of rupture modes similar to those reported for large shocks but over much shorter time scales and distances events with single and multiple ruptures are observed relative locations of the subevents are obtained from azimuthal differences in the time separation of pulses in the deconvolved displacement waveforms some events as small as ml 2 4 display unilateral rupture propagation as manifested by azimuthal variations in the pulse widths of the deconvolved displacement pulses a tomographic back projection technique is applied to the deconvolved displacement pulses to image the slip velocity on the fault as a function of time after nucleation and distance along the fault using a one dimensional fault model the tomographic inversion for one of the events ml 2 4 reveals a unilateral rupture with rupture velocity about equal to the shear wave velocity vs and fault length of 300 m a similar inversion for an ml 3 7 event resolves two subevents separated by about 200 m and yields an average rupture velocity of 0 8vs these rupture velocities are similar to those reported for large earthquakes indicating that rupture velocity is independent of seismic moment down to 3 1 1019 dyn cm the smallest event studied there are clear variations in pulse width for neighboring events with similar seismic moments implying significant differences in static stress drops factor of five variations in stress drop 11 61 bars are calculated for events within 200 m of each other thus the stress and or strength along this fault zone varies considerably over distances of hundreds of meters

the anza array a high dynamic range broadband digitally radiotelemetered seismic array a small aperture seismic array has been deployed along a 30 km stretch of the san jacinto fault in the vicinity of the town of anza california the array was installed to study specifically the scaling laws of body wave spectra the character of high frequency ground motion the physical interpretation of seismic stress drops and the interaction of earthquakes this region was chosen for these studies due to its high rate of seismic activity in the 2 m 4 5 range the likelihood of a m 6 event in the next decade and the existence of the southern california batholith on either side of the fault reducing problems associated with attenuation and large scale anisotropy these studies employ an instrument package with a frequency response of 100 hz a dynamic range of 138 db a sampling rate of 250 times per second per component and a 16 bit a d converter the array consists of 10 three component stations telemetered via digital vhf radio to a nearby mountain peak and thence via a microwave link to la jolla california a minicomputer system monitors the array s performance detects events and records data upon demand initial results demonstrate the feasibility of digital transmission with an inherent increase in data quality over analog systems

high frequency observations and source parameters of microearthquakes recorded at hard rock sites we have estimated the source parameters of 53 microearthquakes recorded in july 1983 which were aftershocks of the miramichi new brunswick earthquake that occurred on 9 january 1982 these events were recorded by local three component digital seismographs at 400 sps component from 2 hz velocity transducers sited directly on glacially scoured crystalline basement outcrop hypocentral distances are typically less than 5 km and the hypocenters and the seven digital seismograph stations established all lie essentially within the boundaries of a granitic pluton that encompasses the faults that ruptured during the main shock and major aftershocks the p wave velocity is typically 5 km sec at the surface and at least 6 km sec at depths greater than about 1 km the events have s wave corner frequencies in the band 10 to 40 hz and the calculated brune model seismic moments range from 1015 to 1018 dyne cm the corresponding stress drops are generally less than 1 0 bars but there is considerable evidence that the seismic source signals have been modified by propagation and or site effects the data indicate a there is a velocity discontinuity at 0 5 km depth b the top layer has strong scattering attenuating properties c some source receiver paths differentiate the propagated signal d there is a hard rock site p wave f max between 50 and 100 hz and e some hard rock sites are characterized by p wave resonance frequencies in the range 50 to 100 hz comparison of this dataset with the january 1982 new brunswick digital seismograms which were recorded at sites underlain by several meters of low velocity surface sediments suggests that some of the hard rock site phenomena listed above can be explained in terms of a layer over a half space model for microearthquakes this result implies that spectrally determined source dimension scales with site dimension thickness of the layer more generally it emphasizes that it is very difficult to accurately observe the details of seismogenic processes from the earth s surface

high frequency 1 100 hz noise and signal recorded at different depths in a mine northwest adirondacks ny seismograms of noise recorded simultaneously at the surface and at two subsurface stations 335m and 945m below surface level show that high frequency 1 100 hz background noise is reduced at the subsurface stations seismometers at all three stations are well coupled to hard crystalline bedrock most of the noise reduction occurs between the surface and 335m depth between 1 and 3 hz seismic noise correlates well with wind speed at all levels above 3 hz wind speed up to 8 m sec does not influence high frequency noise levels at 335m or 945m depths at the surface however high frequency noise is associated with wind speeds in excess of 2 m s a site resonance is characteristic of the surface spectra but is not characteristic of the subsurface sites spectral signal to noise s n ratios measured for s waves from a regional earthquake delta 530 km m sub b 4 1 are roughly equal from 1 10 hz at all depths above 10 hz however s n is greater at the subsurface stations with s n greater than 1 up to 30 hz for the surface station approx 50 hz for the 335m station and approx 70 hz for the 945m station results indicate the advantage of employingmore high frequency sensors sufficiently below the surface to reduce the level of noise and to improve the s n ratio in the high frequency range such an advantage could be critically important for nuclear test detection and discrimination less

aftershock sequences of the 1982 miramichi new brunswick earthquakes the mb 5 7 miramichi new brunswick earthquake of 9 january 1982 was located by comparison to the aftershock distribution in central new brunswick canada at 47 00 n 66 60 w with a focal depth of 7 km and an uncertainty of 3 km on each of the spatial coordinates the main shock was followed by a long and complex aftershock sequence with four events m 4 5 and more than 800 events m 1 0 until 30 june 1982 the aftershocks were studied by three temporary field networks set up in the epicentral areas from 10 to 20 january 2 to 7 april and 17 to 23 june 1982 and by the permanent canadian seismograph networks the aftershock activity was concentrated in a volume approximately 6 km ns 6 km ew 8 km deep and arranged in a north trending conjugate v pattern the miramichi earthquakes were predominatly thrust earthquakes occurring on north trending mid to high angle faults in the upper 8 km of the crust in the presence of an east west compressive horizontal regional stress field detailed field surveys have not yet been able to associate the earthquakes with any known preexisting faults the main shock had a moment of 2 2 0 7 1024 dyne cm and a stress drop of 35 to 70 bars the rupture started at 7 km depth on a plane striking 195 dipping 50 down to the west and propagated up to the east with a rake angle of 120 aftershocks deeper than 3 5 km had composite mechanisms very similar to the main shock s but shallower events took place on more steeply dipping planes up to 78 dip the rupture planes of the main shock and its principal aftershocks may have been similarly curved the magnitude frequency relationship b 0 8 of the aftershocks was comparable to the regional one the aftershock activity decayed as t 0 8 and had the highest rate of activity following the principal aftershock on 11 january that aftershock mb 5 4 appears to have ruptured the east dipping plane conjugate to the main shock s plane two other principal aftershocks mb 5 1 on 9 january and mb 5 0 on 31 march were associated with the main shock rupture plane while the fourth large event mb 4 7 on 16 june occurred 30 km west of the other activity and was seemingly unrelated however all the earthquakes were apparently associated with the same granitic terrain the miramichi earthquakes did not produce any significant surface faulting one small 25 mm surface displacement was found but it was identified as a secondary stress induced movement along a preexisting joint

metal fixation by bacterial cell walls all biomass contains a significant quantity of metallic constituents and mineralization in living and dead biodebris may contribute to element transport from the hydrosphere into sediments the anionic cell walls of bacteria are remarkable in their ability to fix metals and provide sites for nucleation and growth of minerals results presented show the types of cell wall polymers that are responsible for metal binding in walls of gram positive and gram negative bacteria

seismic source parameters for microearthquakes of the granada basin southern spain abstract ninety five microearthquakes of the granada basin southern spain with duration magnitudes ranging from 1 3 to 3 5 moment magnitude from 0 9 to 2 5 have been spectrally analyzed with digital recordings from ten stations of the andalusian seismic network the coda q quality factor qc assumed to be frequency dependent was used instead of q for the path correction and the q adopted was equal to 9 4 qc the k parameter for site attenuation correction had values in the range of 0 02 0 05 fourier displacement spectra were calculated for p and s waves and analyzed with respect to the source model of brune 1970 1971 spectral parameters were automatically determined by the method of snoke 1987 the seismic moment ranged from 1017 to 1020 dyne cm with average m0 p to m0 s ratio of 1 02 and the source radii spanned from 0 14 to 0 40 km with average r p to r s ratio of 1 3 the seismic energy values ranged from 1 103 to 9 107 j with p to s energy ratio from 1 to 10 for about 85 of the events whereas the static stress drop varied from 0 02 to 2 6 bar the scaling relation between the seismic moment and the stress drop indicates a decrease in stress drop with decreasing seismic moment apparent stress is linearly correlated with stress drop and have on average similar values and this points out to a partial stress drop

application of waveform modeling to determine focal mechanisms of four 1982 miramichi aftershocks the objective of this study is to determine the focal mechanisms of small earthquakes at very near epicentral distances and use them to predict the observed waveforms to achieve our objectives the following steps were adopted before attempting to match the entire waveform a obtain an appropriate velocity model b calculate the green s functions and predict ground motions due to an earthquake specified by dip slip and strike of a fault c select all mechanisms which satisfy the first motion polarity at all stations d select a subset of focal mechanisms from those obtained in step c which produce p and s amplitudes and p sv and sv sh amplitude ratios correctly and e use focal mechanisms of step d to match waveforms as an alternative approach a least squares inversion for the moment tensor elements was performed and decomposition of moment tensor matrix to two double couples major and minor was performed green s functions were computed using the cagniard de hoop theory helmberger and harkrider 1978 we applied the above approaches to four aftershocks mblg 3 5 of the new brunswick earthquake of 9 january 1982 and succeeded in obtaining focal mechanisms and producing synthetic waveforms very similar to the observed waveforms two groups of focal mechanisms are found two of the earthquakes are found to have reverse fault geometry similar to that of the main event of 9 january 1982 mb 5 7 while the other two have significant components of strike slip motion on a dipping plane the results obtained from the least squares analysis support the results of the search method the fault geometries determined by the search method correspond well to the results of the major double couple of the least square inversion for completeness of the source characteristics investigation spectral analysis of the seismograms was performed to determine the source parameters corner frequencies fc seismic moments source dimensions and stress drops

site response modelling by non linear waveform inversion microearthquake waveforms and spectra are well known to be strongly influenced by the shallow subsurface conditions at the recording site we make use of this fact to determine optimum site models from sh wave microearthquake seismograms using a non linear waveform inversion technique based on simulated annealing site models are optimized in terms of thicknesses s wave velocities and densities of the uppermost layers 100 m for 1d plane layer models in addition the source parameters in terms of brune model source time functions are optimized simultaneously the synthetic seismograms are calculated using a modification of haskell s plane sh wave algorithm using aftershock recordings of the loma prieta earthquake a 1d plane layer model has been obtained for a selected site in central california which has been occupied during the aftershock experiment for this dataset cross correlation coefficients between optimized synthetics and observed records reach values above 0 8 the site model at the selected station for varying sources is fairly stable especially for the uppermost layers we observe systematic variations of layer parameters with back azimuth which would be in agreement with slightly dipping layer interfaces

how geology can influence scaling relations abstract this study presents an attempt to determine the influence of the environment through lithology and mechanical properties on source parameters and subsequently scaling relations this aim is pursued using data collected from a gas field during a 3 year long period the induced seismicity is recorded by a local permanent network allowing the precise location of 149 earthquakes with local magnitudes ranging from 1 0 to 4 2 moreover geology of the site is defined by 70 bore holes up to 5 km deep such information allows a geological correlation of seismic events then a spectral analysis is performed to compute the source parameters of earthquakes using a dynamic circular fault model seismic moments source radii and post rupture stress drops are evaluated taking into account source propagation and site effects however it is shown from our results that relative uncertainties remain especially for seismic moments and stress drops the diagram of seismic moment versus source radius for the whole data set indicates relatively constant stress drops around 10 bar confirming the self similarity assumption even for microearthquakes in contradiction with this result scaling relations in each geological unit do not verify self similarity this feature implies that second order factors as the mechanical properties of the rock influence source characteristics and bring new complications in scaling relations however even in this case of a very differentiated medium these parameters cannot explain a global breakdown in scaling laws

experimental and numerical investigation of the saint adelphe landslide after the 1988 saguenay earthquake on 25 november 1988 after the saguenay earthquake a landslide occurred in the municipality of saint adelphe the soil profile indicated that the deposit was composed of a stiff clay crustal layer

garner valley downhole array of accelerometers instrumentation and preliminary data analysis the garner valley downhole array gvda in southern california 33 41 60 n 116 40 20 w is a five element array of three component dual gain force balance accelerometers that are capable of measuring accelerations from 3 10 6 to 2 0 g over a frequency range from 0 0 to 100 hz the accelerometers are placed at depths of 0 6 15 22 and 220 m the lithostratigraphy is 19 m of soil overlying a 24 m layer of weathered granite below which is granite tonalite the array only 7 km from the san jacinto fault is located at the northern end of the anza seismic gap on the san jacinto fault where an m 6 5 or greater earthquake can be expected it is only 35 km from the indio segment of the san andreas fault which last ruptured with an m 8 earthquake around 1700 a d from its installation in july 1989 through july 1991 gvda has recorded 280 earthquakes with magnitudes ranging from 1 2 to 4 7 and epicentral distances ranging from from 0 to 110 km the maximum acceleration recorded was 89 cm sec 2 from an m l 4 2 earthquake 15 8 km hypocentral distance from gvda the average amplification of the apparent seismic moment between 220 m depth and the surface is about 13 for over five orders of magnitude in the size of the recorded earthquakes the spectral ratio 0 220 of horizontal acceleration amplitude spectrum shows a mean amplification of about 10 for the frequency range of 2 0 to 30 hz for 17 events resonance peaks exist at about 1 7 3 0 and 12 0 hz where the spectral ratio 0 220 is nearly 40 analysis of the acceleration spectra of two specific earthquakes that have nearly the same hypocenter but with different magnitudes m 4 2 and 2 5 shows that the weathered granite zone beneath the soil strongly attenuates the spectral amplitudes for frequencies greater than 40 hz the impedance of the soil relative to the weathered granite amplifies all frequencies by about a factor of 3 leading to spectral levels that are greater at the surface than at 22 m depth near the top of the weathered granite the acceleration spectra at each depth show resonant peaks at the same frequencies the spectra at each depth are well correlated for both earthquakes the acceleration spectrum at 220 m is nearly constant for frequencies less than 60 hz which implies that there is little or no attenuation

the dependence of peak horizontal acceleration on magnitude distance and site effects for small magnitude earthquakes in california and eastern north america abstract one hundred and ninety free field accelerograms recorded on deep soil 10 m deep were used to study the near source scaling characteristics of peak horizontal acceleration for 91 earthquakes 2 5 m l 5 0 located primarily in california of the six attenuation relationships developed in this study the one considered most reliable is given by the expression ln p h a 2 5 0 1 0 6 2 3 m l 1 0 ln r 7 2 8 where pha is the mean of the two horizontal components of peak acceleration in g m l is local magnitude r is epicentral distance in kilometers and is a random error term with mean of zero and standard deviation of 0 506 an analysis of residuals based on an additional 171 near source accelerograms from 75 earthquakes indicated that accelerograms recorded in building basements sited on deep soil have 30 per cent lower accelerations and that free field accelerograms recorded on shallow soil 10 m deep have 82 per cent higher accelerations than free field accelerograms recorded on deep soil accelerations recorded on rock were found to be similar in amplitude to those recorded on deep soil a separate analysis of site effects for the imperial valley and oroville regions of california indicated that peak accelerations from individual sites can depart significantly from predictions based on broad site classifications an analysis of residuals based on 27 selected strong motion recordings from 19 earthquakes in eastern north america indicated that near source accelerations associated with frequencies less than about 25 hz are consistent with predictions based on attenuation relationships derived for california once site effects and differences in regional magnitude scales are taken into account

strong motion seismology strong motion seismology is concerned with earthquake ground motion in the amplitude range that poses the threat of human injury or property damage because the occurrence of strong motion cannot be predicted in advance and because the time between significant events at any one place may range from tens to thousands of years strong motion data is recorded on triggered instruments that typically must be maintained in readiness for years between periods of significant recording as a consequence the strong motion data set is sparse because of the engineering need for estimates of future ground motion the scope of the field of strong motion seismology encompasses seismic source theory and any other aspect of seismology that can provide insights helpful in making the best possible estimates given the limited data this relationship with the rest of seismology is a reciprocal one in that strong motion data gives perhaps the best information available on earthquake source processes

metal uptake and fe ti oxide biomineralization by acidophilic microorganisms in mine waste environments elliot lake canada acidic effluent containing enhanced concentrations of toxic heavy metals discharges from a cumulative total of 104 ha of mine tailings waste in canada communities of acidophilic microorganisms specifically the unicellular alga euglena sp and bacteria thrive in many of the hostile low ph effluent environments which are otherwise devoid of life the micro organisms concentrate aqueous dissolved metals onto cell walls and at intracellular sites during the life cycle and strongly bind metals during early diagenesis a sequence is observed in which amorphous fe and ti concentrated at cell walls are progressively transformed to microcrystalline aggregates of goethite ferrihydrite maghemite magnetite haematite lepidocrocite and ilmenite the bioprecipitated ti and fe oxides and oxyhydroxides act as scavengers for heavy metals such as cu pb zn ni cd and th acidophilic microorganisms play a central role in the toxic metal budget of mine tailings waste by efficiently sequestering aqueous metals

the abandoned pb zn mine of ingurtosu sardinia italy abstract the ingurtosu pb zn mine situated in the southwestern part of sardinia has been in production from the beginning of the last century up to 1968 the orebody consists of galena sphalerite barite siderite veins in ordovician arenaceous and phyllitic sediments near the contact with a hercynian batholith abundant tailings were collected in a pond from which they were discharged during the winter months into the sea via the rio naracauli stream today this area of outstanding scenic beauty is degraded by tailings and waste rock scattered all along the stream material derived from mining activities was studied for grain size mineralogical and geochemical composition the rio naracauli was sampled over a length of ten kilometers at regular intervals the results can be summarized as follows a tailings contain a varying but often quite high percentage of pb lower percentages were found for zn and cd b a sharp increase in dissolved zn cd and pb was observed in the rio naracauli where it leached the tailings and c tailings and waste rocks should be recycled or revegetated

the 1982 cocrust seismic experiment across the ottawa bonnechere graben and grenville front in ontario and quebec summary during the summer of 1982 the canadian consortium for crustal reconnaissance using seismic techniques cocrust conducted a major long range seismic refraction and wide angle reflection experiment across the grenville province of the canadian shield three seismic lines each approximately 300 km in length were located i along the ottawa bonnechere graben ii perpendicular to the graben and iii perpendicular to the crenville front geological evidence indicates that the graben may have originated from a failed arm of the st lawrence rift system and the grenville front marks the boundary between the grenville province and the much older superior province other geological features of the grenville province that were traversed by the profiles were the central metasedimentary belt and the central gneiss belt analysis of the data involved conventional traveltime procedures coupled with the use of synthetic seismogram analysis using programs that were written to handle laterally heterogeneous structures results from the survey indicate a variation in near surface seismic velocity

new evidence for the existence and internal structure of a thin layer of magma at mid crustal depths near socorro new mexico the characteristics of a strong mid crustal reflector in the rio grande rift southwest of socorro new mexico were studied using high quality digital seismograms of microearthquakes the data are from a tight cluster of hypocenters located almost directly beneath the recording station 2 km cross correlation of the direct and reflected microearthquake s phases yields coefficients which are positive and large in absolute value average 0 79 because these two phases leave the focal region 180 out of phase for this swarm reflection must occur at a discontinuity where a 180 phase shift occurs waveforms for the p wave reflections are not identical from event to event within the swarm the character of the p reflection indicates a magma body with rapid lateral changes in internal structure the spectral characteristics of the reflected p phase are suggestive of constructive interference the near normal incidence geometry of both the reflected and direct p phase implies an essentially common path through the upper crust and near surface phanerozoic rocks for these two phases the earthquakes examined in this study are quite small ml 0 hence the initial portion of the direct p phase may be used as the response function for the path through the upper crust during modeling of the reflected p phase synthetic seismograms which include attenuation effects and interbed multiples were calculated and compared to the observed waveforms the results of modeling the stacked spectra of the pzp phase indicate a thin 70 m layer of nonrigid low velocity material underlain by a second thin 60 m layer of slightly higher velocity material this second layer may be an earlier partially solidified intrusion or a crystalline mush at the base of a single magma chamber the total thickness of the magma body is estimated to be 150 m

source parameters of microearthquakes at mount st helens usa summary we estimate the source parameters for a selection of microearthquakes that occurred at mount st helens in the period 1995 1998 excluding the activity of 2004 september this time period includes the most intense episode of earthquake activity since the last dome building eruption in 1986 october 200 seismograms were processed to obtain seismic moments source radii stress drops and average fault slip the source parameters were determined from the spectral analysis of p waves after correction for attenuation and site effects in particular p wave quality qp and site s factors have been previously calculated in the frequency ranges 2 7 hz and 18 30 hz because it was impossible to perform corrections for qp and s over the whole spectrum we applied a new approach based on the notion of holed spectrum to estimate spectral parameters the term holed spectrum indicates a spectrum lacking corrected spectral amplitude values at certain frequencies we carried out a statistical study to verify that dealing with the holed spectrum does not lead to significant differences in the estimates of spectral parameters we also investigated the dependence of spectral parameters low frequency level corner frequency and high frequency decay on the bandwidth of spectral hole and defined the threshold values for three different spectral models displacement holed spectra corrected by attenuation and site response are then used to determine spectral parameters in order to calculate seismic source parameters seismic moments range from 1017 to 1019 dyne cm source dimensions from 100 to 350 m and average fault slip from 0 003 to 0 1 cm self similarity seems to break down in that stress drops are very low 0 1 1 bars we postulate that seismicity is associated with a brittle shear failure mechanism occurring in a highly heterogeneous material under a relatively low stress regime

microearthquake spectra from the anza california seismic network site response and source scaling abstract we analyzed spectra of local microearthquakes recorded by the anza california seismic network to isolate the effects of site response and to investigate the scaling of source parameters for small earthquakes spectra of microearthquakes m m o 19 dyne cm at anza have shapes characteristic of the receiver sites and are generally independent of the source region thus the site response is a major conditioner of the observed spectral shape to remove the effects of site response from the spectra of a m 3 event and isolate its source spectrum we divided by the spectra of an adjacent aftershock used as an empirical green9s function event the spectral ratios indicate that the apparent corner frequencies of small earthquakes m o 19 dyne cm observed at even the high f max stations on hard rock are much lower than the source corner frequencies the spectral ratios are consistent with stress drop remaining constant with decreasing seismic moment for events with moments as small as 10 18 dyne cm the spectral ratios display remarkable agreement between sites which showed vast differences in their original spectra indicating that the spectral division effectively removed the site response the source spectrum of the m 3 event has a high frequency spectral fall off of about 2 an apparent dependence of high frequency fall off with seismic moment in the original spectra can also be explained by the effects of site response the difference between the p and s wave corner frequencies and high frequency roll offs in the observed spectra for these events is the result of the site response and is not a source property the shapes of the spectra of microearthquakes at anza can largely be explained by attenuation at shallow depth with a frequency independent q for some sites near surface resonances are also apparent in the spectra of microearthquakes it is indicated by t values determined for each site that q p q s for the shallow low q layer further evidence of low near surface q is observed in the anomalous spectra of an unusually shallow earthquake source depth 1 km in the network the spectra from this shallow event are depleted in high frequency energy at most stations relative to those of deeper events this observation can be explained by a low q surficial zone for stations of the network situated on alluvium this low q layer has a maximum thickness of about 3 km and maximum p and s wave q values of 30 to 50

source attenuation and site parameters of the 1997 umbria marche seismic sequence from the inversion of p wave spectra a comparison between constant qp and frequency dependent qp models 1 the attenuation of p waves the site responses and the source parameters seismic moment corner frequency source dimension of 490 seismic events that occurred during the 1997 colfiorito umbria marche seismic sequence have been inferred from the inversion of p wave velocity spectra the boatwright source model has been assumed to model the source spectra a global nonlinear inversion scheme was developed to avoid any a priori selection of the initial qp and the corner frequency to establish if a frequency dependent qp model fits the data better than a constant qp model two inversion results have been compared application of the akaike information criterion indicates that the constant qp model represents the best compromise between model simplicity and data misfit the station qp values are small in the range of 50 to 200 a one dimensional qp model is obtained by back projecting the inverted t our results indicate both well defined near site attenuation effects at some sites and heterogeneity in the inelastic properties of the crust with the exception of the amplification response at five seismic stations most of the recording sites did not show amplification peaks at particular frequencies the stress drop clearly increases as a function of the seismic moment which indicates a deviation from self similarity whereas it does not show an increase with depth probably owing to the effects of fluid pressurization in the crust a stress drop of about 39 mpa is inferred the relationship between the seismic moment and the local magnitude for p waves has been calibrated

an investigation into earthquake ground motion characteristics in eastern north america abstract a random vibration model of the hanks mcguire type is used to predict peak ground motions at rock sites in eastern north america the assumed geometric decay and distance dependent duration approximate the propagation of direct body waves at short distances and lg waves at regional distances the model predicts peak acceleration and velocities as well as response spectra and magnitude for a given seismic moment and corner frequency to predict ground motions for a given lg magnitude m lg the model is first used to calculate the seismic moment corresponding to that magnitude assuming a source scaling law then knowing the moment and corner frequency the model is used to calculate peak ground motions available data from strong motion recordings and from the ectn and lrsm networks modified to estimate horizontal ground motions on rock where appropriate are used to verify the model9s assumption and predictions modified mercalli intensity data are also used ground motions predicted by the model with a stress drop of 50 to 200 bars agree with the ground motion data but the m lg values computed by the model for given seismic moments do not agree with nuttli9s 1983 moment versus m lg data for large earthquakes resolution of the latter disagreement awaits the collection of instrumental data from large events in eastern north america

source parameters and effects of bandwidth and local geology on high frequency ground motions observed for aftershocks of the northeastern ohio earthquake of 31 january 1986 abstract a 10 station array geos yielded recordings of exceptional bandwidth 400 sps and resolution up to 96 db for the aftershocks of the moderate m b 4 9 earthquake that occurred on 31 january 1986 near painesville ohio nine aftershocks were recorded with seismic moments ranging between 9 10 16 and 3 10 19 dyne cm m w 0 6 to 2 3 the two largest aftershocks depth 5 3 5 6 km oblique right slip rake 30 strike n25 e yielded seismic signals above background noise at frequencies as high as 130 hz at epicentral distances up to 17 km the aftershock recordings at a site underlain by 8 m of lakeshore sediments show significant levels of high frequency soil amplification of vertical motion at frequencies near 8 20 and 70 hz viscoelastic models for p and sv waves incident at the base of the sediments yield estimates of vertical p wave response consistent with the observed high frequency site resonances but suggest additional detailed shear wave logs are needed to account for observed s wave response peak acceleration values obtained from the broadband recordings are about two and four times as large as those that would be recorded on strong motion recorders or short period networks with upper bandwidth limits of 30 and 15 hz respectively attenuation corrected acceleration spectra are used to reduce the influence of high frequency up to 100 hz local site effects on corner frequency estimates the moment versus source radius trend inferred for events with moments as small as 9 10 16 dyne cm based on the brune source model extends previous relations inferred for the central united states shows little evidence for a minimum source radius and suggests that stress drops for the smaller events m 0 19 dyne cm decrease with decreasing moment

anatase nanoparticles on supergene platinum palladium aggregates from brazil titanium mobility in natural waters abstract supergene aggregates of platinum palladium pt pd intermetallic compounds from the corrego bom sucesso alluvial deposit minas gerais brazil are coated with abundant poorly crystalline nanoparticles of anatase tio 2 the anatase coating is widespread suggesting that the surface of the pt pd grains catalytically destabilised ti which was likely dissolved by organic ligands in the ground waters association of tio 2 nanocrystallites with organic matter further suggests that biogenic processes could have mediated their formation these anatase coated pt pd grains demonstrate an unexpected ti mobility in supergene environments

high frequency borehole seismograms recorded in the san jcinto fault zone southern california part 2 attenuation and site effects we examine surface and downhole p and s wave spectra from local earthquakes recorded at two borehole seismometer arrays knw bh and pfo bh installed in the southern california batholith region of the san jacinto fault zone by the u s geological survey to assess the influence of the weathered layer on the spectral content of high frequency 2 to 200 hz seismic signals earthquake signals recorded downhole at both sites show significantly improved seismic bandwidth due to both a reduction in ambient noise levels and especially to dramatically increased levels of high frequency signal significant seismic signal is observed up to approximately 190 hz for p waves at knw bh stacked spectral ratios from these signals indicate that the highly weathered near surface between 0 and 150 m at knw bh and pfo bh exerts a much larger influence on seismic signals than deeper between 150 and 300 m material modeling of uphole downhole spectral ratio data suggests q 6 5 and q 9 between 0 and 150 m increasing to q 27 and q 26 between 150 and 300 m an outcrop mounted anza network station deployed approximately 0 4 km from knw bh displays roughly similar high frequency content to the knw bh downhole sensors but it exhibits spectra that are significantly colored by directional resonances low q and low velocity near surface material forms a lossy boundary layer at these borehole sites that is advantageous to the high frequency downhole environment not only are noise levels reduced but reflections from the surface and near surface are greatly attenuated as a result high frequency recordings from below the weathered zone more nearly resemble those recorded in a whole space than would otherwise be expected