the 11 25 88 m 6 saguenay earthquake near chicoutimi quebec evidence for anisotropic wave propagation in northeastern north america on november 25 1988 a magnitude 6 earthquake occurred in the province of quebec canada this earthquake triggered nine digital strong motion instruments in new york and maine at epicentral distances of 200 to 820 km which were installed as part of an effort by the national center for earthquake engineering research nceer to study ground motions and wave propagation in eastern north america we calculate q f at discrete frequencies from 0 6 to 26 hz assuming that geometrical spreading causes a l r0 5 decay in spectral amplitudes of the nine stations four are in the adirondack mountains in new york and three are in eastern maine if we calculate q f for these two clusters of stations separately we obtain higher values for the adirondack stations the quebec adirondack path is along the strike of the predominant structural trends in northeastern north america in the grenville province crust while the quebec maine path is at high angle to the structural grain and crosses the boundary between the grenville and the appalachian provinces we thus have instrumental data in support of earlier observations based on contours of intensity from historic earthquakes seismic wave propagation in northeastern north america is more efficient along the predominantly ne sw striking geological trends we address possible biases due to site effects

peak ground motions and site response at anza and imperial valley california power spectra of shear waves for eighteen earthquakes from the anza imperial valley region were inverted for source mid path q site attenuation and site response the motivation was whether differences in site attenuation parameterized as t r cq where r is distance along ray path near the site c is shear velocity and q is the quality factor that parameterizes attenuation and site response could be correlated with residuals in peak values of velocity or acceleration after removing the affect of distance dependent attenuation we decomposed spectra of s waves from horizontal components of 18 earthquakes from 2010 to 2018 into a common source for each event with 2 spectral fall off at high frequencies and then projected the residuals onto path and site terms following the methodology of boatwright et al bull seismol soc am 81 1754 1782 1991 the site terms were constrained to have an amplification at a particular frequency governed by vs30 at two of the sites which had downhole shear wave logs the 18 events 3 m 4 had moments between approximately 1020 and 1022 dyne cm and stress drops between 1 and 100 bars average mid crust attenuation had a q of 844 reflecting the average path through the crystalline rock of the san jacinto mountains t for each station corresponded to the geologic environment such that stations on hard rock had low t e g stations knw pfo and rdm a station in the san jacinto fault zone station snd had a moderate t of 0 035 s and stations in the imperial valley usually had higher t s generally t correlated with average amplification suggesting that sites characterized by low surface velocities and higher attenuation also have more amplification in the 1 6 hz band residuals of peak values were determined by subtracting the prediction of boore and atkinson 2008 there is a correlation between average amplification and peak velocity but not peak acceleration interestingly there is less scatter at high values of amplification although there is also less data scatter in values of peak velocity and peak acceleration are higher at shorter compared to longer durations when using a frequency dependent form for q variances are higher sometimes much higher the dataset does not support frequency dependent q which is not similar to results from the imperial valley and northeastern north america

comparison of synthetic pseudoabsolute response spectral acceleration psa for four crustal regions within central and eastern north america cena abstract this study contributes to the development of a new ground motion model for central and eastern north america cena we evaluate the impact of the seismic velocity structure for different crustal regions on ground motion measures we present an overview of the regionalization of the crustal structure of cena the physical parameters used for the simulation codes and the statistical method applied for the comparison of pseudoabsolute response spectral accelerations psas of four crustal regions defined within cena the four crustal regions are 1 the atlantic coastal plain acp 2 the appalachians app 3 central north america cna and 4 the mississippi embayment gulf coast mem for each region and its statistically representative velocity structure psa matrices were computed covering response oscillator frequencies from 0 5 to 20 hz and hypocentral distances up to 500 km psa matrices for earthquakes at four different focal depths 5 10 20 and 30 km were calculated the developed method of the normed mean differences gives a meaningful measure for inter regional differences of ground motions in comparison with intra regional variability in this study we compare the ln psa of the app acp and mem region with the reference region cna respectively the percentage of ln psa mean difference values that are smaller than the ln psa standard deviation of the reference region cna lies between 73 and 91 for the app region dependent on the focal depth for the acp region it is about 70 for all focal depths except for the 20 km source depth which was excluded because a layer boundary at 20 5 km causes unrealistically strong reflections the percentage for the mem region is less than 50 for each of the focal depths this analysis demonstrates that there are two distinct ground motion groups for cena group 1 cna app and acp group 2 mem electronic supplement figures of crustal velocity structures table of q studies and q studies illustrated for one region

near surface deformation in the new madrid seismic zone as imaged by high resolution sh wave seismic methods over 1 5 kilometers of high resolution sh wave refraction and reflection profiles have been performed in the madrid bend area of northwestern tennessee approximately 8 km north of tiptonville tennessee to establish the existence of neo tectonic near surface deformation the specific area was chosen because of the access it provided to the tiptonville dome a holocene flexure and the trend of contemporary seismicity within the new madrid seismic zone nmsz we believed the highest likelihood of near surface deformation to be over these features partially reversed refraction reflection walk away tests and common depth point cdp seismic profiling using the non traditional sh wave method have traced antiformal flexure and numerous faults into the late eocene and holocene sediments of the tiptonville dome province of the lake county uplift lcu vertical displacements exhibited across the faults range from approximately 3 to 30 m these structures have been interpreted to be neo tectonic features associated with tensional stresses across the tiptonville dome

earthquake faulting related deformation in soil evidenced in s wave shallow reflection data field results from portugal abstract expressions of ductile soft sediment deformations induced by ground movements due to past earthquakes are difficult to recognize in near surface soils we have carried out shallow s wave reflection studies in a seismically active area located northeast of metropolitan lisbon portugal identifying shallow disturbed zones and hidden fault segments in this area is important but quite difficult because of small vertical slips due to earthquakes the holocene alluvial cover hiding the fault segments and a high rate of surficial sedimentation we have performed s wave reflection profiling at two sites vila franca xira and castanheira de ribatejo we detected different but interrelated evidence of soft sediment deformation in the seismic data this evidence includes sharp lateral changes in the s wave velocity field changes in the reflection horizons in stacked sections aligned diffractions in unmigrated sections discontinuities in common offset gathers and discontinuities backscattered and d

acceleration source spectra anticipated for large earthquakes in northeastern north america a set of 16 large intraplate earthquakes are considered on the basis of their tectonic settings compressive focal mechanisms and shallow focal depths as possible analogs for large earthquakes that may be anticipated to occur in northeastern north america the earthquakes range in seismic moment from 5 1023 to 3 1026 dyne cm and include the mainshocks and largest aftershocks of the 1982 miramichi canada the 1985 to 1988 nahanni canada and the 1988 tennant creek australia earthquake sequences the teleseismic recordings of these earthquakes are spectrally analyzed by correcting the logarithmically averaged acceleration spectra for the frequency dependent effects of attenuation and interference of the depth and direct phases the resulting acceleration source spectra are generally flat at high frequencies the mainshock spectra exhibit intermediate spectral falloffs that is u where 1 over frequencies that characteristically extend from 0 1 to 0 5 hz in contrast the largest aftershocks of the three sequences named above exhibit 2 spectral shapes the high frequency source spectral levels increase with seismic moment approximately as ru m 1 3 the 1988 saguenay canada earthquake which occurred significantly deeper than the other earthquakes exhibits an anomalous spectral shape combining the teleseismic data with strong motion recordings indicates that the intermediate spectral falloff for this earthquake extends from 0 2 to 3 hz the spectral amplitude at 3 hz is a factor of 3 higher than the amplitude anticipated for an earthquake of this size from the other 15 earthquakes

late quaternary earthquake related soft sediment deformation along the belgian portion of the feldbiss fault lower rhine graben system abstract trench investigations along the bree fault scarp in belgium in the framework of a first paleoseismological experience in the area of the lower rhine graben system have not only demonstrated the existence of seismogenic faults almost extending to the present ground surface but also exposed several types of soft sediment deformation affecting sandy sediments and soils of inferred late weichselian to holocene age the observed features include asymmetric folding small scale normal faulting possible sand intrusions and small water escape or load structures establishing a seismic origin for the individual features is not always possible based on their sedimentary characteristics only particularly due to the potential confusion with periglacial phenomena but their abundance the close association of different deformational styles and their vicinity to a known active fault all seem to be compatible with an earthquake induced scenario the features are to some extent comparable to those generated during the recent ms 5 3 roermond earthquake at the opposite side of the roer valley graben stratigraphical and mutual geometrical relationships suggest the occurrence of at least three distinct deformational events since probably 30 000 years and one event before that time since nothing is yet known about their regional distribution however estimating the associated paleomagnitudes from these soft sediment deformations is premature

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

finite difference modeling experiments for seismic interferometry in passive seismic interferometry new reflection data can be retrieved by crosscorrelating recorded noise data the quality of the retrieved reflection data is among others dependent on the duration and number of passive sources present during the recording time the source distribution and the source strength to investigate these relations we set up several numerical modeling studies to carry out the modeling in a feasible time we design a finite difference algorithm for the simulation of long duration passive seismic measurements of band limited noise signatures in the subsurface novel features of the algorithm include the modeling of thousands of randomly placed sources during one modeling run the modeling experiments explore the dependency relation between the retrieved reflections and source signature length source positions number of sources and source amplitude variations from these experiments we observed that the positions of the passive sources and the length of the source signals are of direct influence on the quality of the retrieved reflections random amplitude variations among source signals do not seem to have a big impact on the retrieved reflections

seismic wave attenuation determined from tectonic tremor in multiple subduction zones abstract tectonic tremor provides a new source of observations that can be used to constrain the seismic attenuation parameter for ground motion prediction and hazard mapping traditionally recorded earthquakes of magnitude 3 8 are used to develop ground motion prediction equations however typical earthquake records may be sparse in areas of high hazard in this study we constrain the distance decay of seismic waves using measurements of the amplitude decay of tectonic tremor which is plentiful in some regions tectonic tremor occurs in the frequency band of interest for ground motion prediction i e 2 8 hz and is located on the subducting plate interface at the lower boundary of where future large earthquakes are expected we empirically fit the distance decay of peak ground velocity from tremor to determine the attenuation parameter in four subduction zones nankai japan cascadia united states canada jalisco mexico and southern chile with the large amount of data available from tremor we show that in the upper plate the lower crust is less attenuating than the upper crust we apply the same analysis to intraslab events in nankai and show the possibility that waves traveling from deeper intraslab events experience more attenuation than those from the shallower tremor due to ray paths that pass through the subducting and highly attenuating oceanic crust this suggests that high pore fluid pressure is present in the tremor source region these differences imply that the attenuation parameter determined from intraslab earthquakes may underestimate ground motion for future large earthquakes on the plate interface

average qlg qsn and observation of lg blockage in the continental margin of nova scotia the term lg blockage refers to the sudden disappearance of the lg phase along a particular propagation path which is commonly seen at continental oceanic transition zones in this paper we present observational evidence of lg blockage across the continental margin of nova scotia in eastern canada regional lg and sn spectra from 91 events with epicentral distances between 100 and 1200 km and magnitudes between 2 5 and 4 7 are inverted simultaneously for the source spectrum site amplification and average attenuation the vertical displacement spectra were estimated between 0 9 and 10 75 hz the assumptions include a fixed frequency independent geometric spreading rate for lg and a frequency dependent spreading model for the sn estimates for the apparent regional attenuations are qlg f 615 25 f0 35 0 04 and qsn f 404 23 f0 45 0 03 results from this study provide an accurate parameterization of observed amplitude spectra and are valuable for representing wave propagation in the region based on the observation of a strong trade off between sn and lg amplitudes which have different attenuation characteristics we conclude any attenuation study based on measuring amplitude of a package of several different phases without taking into consideration the propagation characteristics of individual waveforms at the region of study may bias the estimation of average regional q

site amplifications for generic rock sites seismic shear wave velocity as a function of depth for generic rock sites has been estimated from borehole data and studies of crustal velocities and these velocities have been used to compute frequency dependent amplifications for zero attenuation for use in simulations of strong ground motion we define a genetic rock site as one whose velocity at shallow depths equals the average of those from the rock sites sampled by the borehole data most of the boreholes are in populated areas for that reason the rock sites sampled are of particular engineering significance we consider two genetic rock sites rock corresponding to the bulk of the borehole data and very hard rock such as is found in glaciated regions in large areas of eastern north america or in portions of western north america the amplifications on rock sites can be in excess of 3 5 at high frequencies in contrast to the amplifications of less than 1 2 on very hard rock sites the consideration of unattenuated amplification alone is computationally convenient but what matters for ground motion estimation is the combined effect of amplification and attenuation for reasonable values of the attenuation parameter k 0 the combined effect of attenuation and amplification for rock sites peaks between about 2 and 5 hz with a maximum level of less than 1 8 the combined effect is about a factor of 1 5 at 1 hz and is less than unity for frequencies in the range of 10 to 20 hz depending on t using these amplifications we find provisional values of about ao 70 bars and k 0 0 035 sec for rock sites in western north america by fitting our empirically determined response spectra for an m 6 5 event to simulated values the borehole data yield shear velocities 033o of 618 and 306 rrdsec for rock and soil sites respectively when averaged over the upper 30 m from this we recommend that v30 equals 620 and 310 m sec for applications requiring the average velocity for rock and soil sites in western north america by combining the amplifications for rock sites and the site factors obtained from our analysis of strong motion data we derive amplifications for sites with 17 3o 520 m sec nehrp class c corresponding to a mix of rock and soil sites and v3o 310 and 255 m sec average soil and nehrp class d sites respectively for the average soil site the combined effect of amplification and attenuation exceeds a factor of 2 0 for frequencies between 0 4 and about 4 hz with a peak site effect of 2 4 the peak of the nehrp class d site effect is 2 7

the 2002 m5 au sable forks ny earthquake sequence source scaling relationships and energy budget 1 we find invariant high stress drops and radiated energies for a sequence of intraplate earthquakes we estimate source parameters of the au sable forks ny earthquake m5 2002 and aftershocks this intraplate earthquake was the largest to occur in eastern north america since 1988 and the largest to be recorded by regional broadband networks we use the empirical green s function egf method and define a set of qualitative and quantitative rules for the selection of egf earthquake pairs and for the quality verification of the obtained egf spectral ratio we use a multitaper code that performs the complex spectral division with minimum frequency leakage and allows transformation back to the time domain to check the validity of the egf event we estimate source parameters for 22 earthquakes m1 m5 in the sequence the median stress drop of 104 mpa using madariaga source model and 19 mpa for a brune model is significantly larger than estimates for interplate earthquakes the lower crustal strain rates and longer fault healing times in intraplate environments may be responsible for this high average value we find constant stress drop between m2 and m5 up to the bandwidth resolution limit 80 hz of the study and no evidence of stress drop breakdown for m2 to m1 earthquakes we find consistently high radiated seismic energy and apparent stress and a median radiated energy to seismic moment ratio of 9 10 5 this is significantly larger than estimates for interplate earthquakes 2 10 5 and consistent with higher stress drops and stronger faults

the structural and sedimentary evolution of the arruda and lower tagus sub basins portugal abstract the study discusses the jurassic structural and sedimentary evolution of the arruda and lower tagus sub basins located in the central and southern part of the lusitanian basin of portugal in the last five decades thousands of kilometres of 2d seismic reflection lines were acquired for oil exploration reprocessing and reinterpretation of over 700 km from the study area was carried out after the seismic to well ties based on well logs vsp analysis synthetic seismograms revised petrological analysis and stratigraphic reinterpretation of the wells nine key seismic geologic horizons were mapped and depth converted reinterpretation of the seismic profiles was carried out using outcrop data and reprocessed aeromagnetic and gravimetric data of the study area that was integrated in a gis environment several aspects of the tectonic and sedimentary evolution of the study area were enlightened from the triassic until the late jurassic two rift phases were recognised in agreement with data from other parts of the lusitanian basin the initial rifting phase in the triassic continued until the callovian with three prominent tectonic pulses a first in the late triassic a second in the hettangian and a third from the sinemurian onwards the latter episode lasted until the callovian in the arruda sub basin and at least until the bathonian in the lower tagus sub basin during the middle jurassic the arruda sub basin evolved to a nw deepening carbonate ramp the lower tagus sub basin constituted a platform since the early jurassic limited in the east by the setubal pinhal novo fault and in the west by the cadafais fault the third rifting episode occurred in the late oxfordian early kimmeridgian producing a major n s fault system already recognised by several authors and another important nw se and ne sw fault systems post dating the former

imaging p and s attenuation in the sacramento san joaquin delta region northern california we obtain 3d q p and q s models for the delta region of the sacramento and san joaquin rivers a large fluvial agricultural portion of the great valley located between the sierra nevada batholith and the san francisco bay coast ranges region of active faulting path attenuation t values have been obtained for p and s data from 124 distributed earthquakes with a longer variable window for s based on the energy integral we use frequency dependence with an exponent of 0 5 consistent with other studies and weakly favored by the t s data a regional initial model was obtained by solving for q as a function of seismic velocity in the final model the great valley basin has low q with very low q 50 for the shallowest portion of the delta there is an underlying strong q contrast to the ophiolite basement which is thickest with highest q under the sacramento basin and a change in structure is apparent across the suisun bay as a transition to thinner ophiolite moderately low q is found in the upper crust west of the delta region along the faults in the eastern north bay area whereas moderately high q is found south of the delta implying potentially stronger ground motion for earthquake sources to the south very low q values in the shallow crust along parts of the major fault zones may relate to sediment and abundant microfractures in the lower crust below the san andreas and calaveras hayward rodgers creek fault zones the observed low q is consistent with grain size reduction in ductile shear zones and is lowest under the san andreas which has large cumulative strain similarly moderately low q in the ductile lower crust of the bay area block between the major fault zones implies a broad distributed shear zone online material distribution of earthquake magnitude figures of t values 3d initial regional velocity and q models station terms and q p inversion with 1d initial q p model

estimation of moment magnitude from ground motions at regional distances abstract we present a simple and robust approach to estimate moment magnitude m for events of m m can be estimated from 1 hz response spectral amplitudes for events in north america with an uncertainty standard deviation of residuals of m across regions and that it provides relationships that are consistent with the predictions of a stochastic point source model for typical regional attenuation models online material table of events for which the moment magnitude was estimated

frequency dependent lg q within the continental united states frequency dependent crustal attenuation 1 q is determined for seven distinct physiographic tectonic regions of the continental united states using high quality lg waveforms recorded on broadband stations in the frequency band 0 5 to 16 hz lg attenuation is determined from time domain amplitude measurements in one octave frequency bands centered on the frequencies 0 75 1 0 3 0 6 0 and 12 0 hz modeling errors are determined using a delete j jackknife resampling technique the frequency dependent quality factor is modeled in the form of q q 0 f regions were initially selected based on tectonic provinces but were eventually limited and adjusted to maximize ray path coverage in each area earthquake data was recorded on several different networks and constrained to events occurring within the crust m b 3 5 in size a singular value decomposition inversion technique was applied to the data to simultaneously solve for source and receiver terms along with q for each region at specific frequencies the lowest crustal q was observed in northern and southern california where q is described by the functions q 152 37 f 0 72 0 16 and q 105 26 f 0 67 0 16 respectively the basin and range province pacific northwest and rocky mountain states also display lower q and a strong frequency dependence characterized by the functions q 200 40 f 0 68 0 12 q 152 49 f 0 76 0 18 and q 166 37 f 0 61 0 14 respectively in contrast in the central and northeast united states q functions are q 640 225 f 0 344 0 22 and q 650 143 f 0 36 0 14 respectively show a high crustal q and a weaker frequency dependence these results improve upon previous lg modeling by subdividing the united states into smaller distinct tectonic regions and using significantly more data that provide improved constraints on frequency dependent attenuation and errors a detailed attenuation map of the continental united states can provide significant input into hazard map mitigation both scattering and intrinsic attenuation mechanisms are likely to play a comparable role in the frequency range considered in the study

seismic reflection imaging of tertiary faulting and related post eocene deformation 20 km north of memphis tennessee abstract other than the crittenden county fault zone ccfz little is known about the seismic hazard from earthquake faults within 50 km of memphis tennessee a city that contains a large inventory of older buildings that are vulnerable to moderate and strong earthquake ground shaking to address this lack of knowledge about faulting near memphis we acquired a 4 5 km long mini sosie seismic reflection profile across the boundary between the loess covered bluffs and modern mississippi river flood plain in meeman shelby forest state park north of memphis we imaged a previously unknown reverse thrust fault that displaces paleozoic and cretaceous rocks and upwarps tertiary deposits on the floodplain portion of the profile about 25 km north of downtown memphis the paleozoic and cretaceous rocks are vertically faulted about 70 and 40 m respectively in an up to the west sense of displacement the fault displacement apparently terminates in the basal portion of the paleocene section and causes only an upwarping of the overlying deposits the overlying paleocene and eocene deposits which are probably the youngest deposits imaged are upwarped about 50 60 m with the same sense of displacement as the underlying older units the sense of displacement amplitude and appearance of the fault in the seismic data are very similar to that observed in the seismic reflection images of the ccfz 15 km west of this profile although we have imaged this new fault in only one location its proximity to memphis and similarities to the ccfz leads us to speculate that it may be a parallel structure to the ccfz and thus warrants further study

structure and evolution of the seismically active ostler fault zone new zealand based on interpretations of multiple high resolution seismic reflection profiles abstract to improve our understanding of active faulting away from the main plate boundary on new zealand s south island we have acquired high resolution seismic data across the ostler fault zone twelve 1 2 km long lines perpendicular to fault strike and a 1 6 km long crossline were collected in a region of the mackenzie basin where surface mapping delineates significant complexity in the form of two non overlapping reverse fault strands separated by a transfer zone characterised by multiple smaller strands and increased folding interpretation of the resultant images includes a 45 55 west dipping principal fault and two 25 30 west dipping subsidiary faults one in the hanging wall and one in the footwall of the principal fault the geologically mapped complexities are shown to be caused by shallow variations in the structure of the principal fault which breaks the surface in the north and south but not within the transfer zone where it forms a triangle zone with associated backthrusting and minor faulting these complexities only extend to 300 m depth structures below this level are markedly simpler and much more 2d in nature with the principal fault strand extending over a much longer distance than the individual strands observed at the surface since longer faults are susceptible to larger earthquakes than shorter ones seismic hazard at the study site may be higher than previously thought multiple surface fault strands that give way to a single more major stand at relatively shallow depths may be a common feature of segmented fault systems the deepest layered reflections at our site are consistent with the presence of a late cretaceous tertiary basin underlying the present day mackenzie basin structural restoration of the seismic images back to the base of quaternary fluvioglacial terraces and back to the top of a late pliocene pleistocene fluviolacustrine unit indicate that compression was initiated prior to the late pliocene and that it has continued at a comparatively steady rate of about a millimetre per year to the present day the fluviolacustrine unit has experienced 440 800 m of along fault vertical offset and 870 1080 m of horizontal shortening since that time our study demonstrates that structural reconstructions based on high resolution seismic reflection data provide critical displacement information that can be used to estimate slip rates

the eastern lower tagus valley fault zone in central portugal active faulting in a low deformation region within a major river environment abstract active faulting in the lower tagus valley central portugal poses a significant seismic hazard that is not well understood although the area has been affected by damaging earthquakes during historical times only recently has definitive evidence of quaternary surface faulting been found along the western side of the tagus river the location geometry and kinematics of active faults along the eastern side of the tagus valley have not been previously studied we present the first results of mapping and paleoseismic analysis of the eastern strand of the lower tagus valley fault zone ltvfz geomorphological paleoseismological and seismic reflection studies indicate that the eastern ltvfz is a left lateral strike slip fault the detailed mapping of geomorphic features and studies in two paleoseismic trenches show that surface fault rupture has occurred at least six times during the past 10 ka the river offsets indicate a minimum slip rate on the order of 0 14 0 24 mm yr for the fault zone fault trace mapping geomorphic analysis and paleoseismic studies suggest a maximum magnitude for the eastern ltvfz of m w 7 3 with a recurrence interval for surface ruptures 1 7 ka at least two events occurred after 1175 95 cal yr bp single event displacements are unlikely to be resolved in the paleoseismic trenches thus our observations most probably represent the minimum number of events identified in the trenches

soft sediment deformation within seismogenic slumps of the dead sea basin abstract the late pleistocene lisan formation preserved next to the dead sea provides exceptional 3 d exposures of folds and faults generated during soft sediment slumping and deformation it is possible to generate a range of four different scenarios associated with overprinting in a single slump event the progressive evolution of slump systems may be broadly categorised into initiation translation cessation relaxation and compaction phases thrust packages typically define piggyback sequences during slump translation with back steepening of imbricate faults leading to collapse of folds back up the regional palaeoslope detailed evaluation of slumped horizons may also permit structures to be traced across apparently separate and distinct slumped units the recognition that slumps may be reworked by younger seismically triggered events suggests that in some cases the seismic recurrence interval may be shorter than previously anticipated

modelling rates of sedimentation from icebergs abstract icebergs transport debris from ice masses into the glacimarine environment but iceberg production debris content and sedimentation rate will vary with glacier dynamics and the nature of marine waters a model incorporating glaciological and oceanographic parameters calculates the flux of debris calved in icebergs iceberg melt rates and sedimentation rates with distance from calving tidewater ice fronts the flux of basal debris calved through a 1 m width of tidewater margin is h d c 100 v c where h d and c are basal debris rich ice thickness and sediment content and v c is iceberg calving rate iceberg basal melting for any horizontal interval d x away from the calving glacier is dy m b d x v b where m b is iceberg melt rate and v b is horizontal iceberg velocity sediment release for any x increment depends on iceberg debris concentration and previous berg melt history model parameters vary with the nature of climatic conditions on a continuum from cold polar environments e g high canadian arctic antarctic peninsula through sub polar environments e g baffin island svalbard to more temperate environments e g se alaska these parameters include glacier flow velocity glacier thermal regime basal debris rich ice thickness and marine water temperature model results suggest that iceberg sedimentation rates are lowest for high polar settings and most rapid in warm maritime and some sub polar areas however icebergs in cold waters transport debris to significantly greater distances from the parent glacier the model provides calculations of order of magnitude rates of iceberg sedimentation in varying glacimarine settings

crustal seismic structure beneath portugal and southern galicia western iberia and the role of variscan inheritance abstract the crustal structure in western iberia is the result of a complex geodynamic history most of the surface is covered by rocks dating to the variscan orogeny the coastal ranges dominated by mesozoic structures and mesocenozoic basins covering partially the mainland in this study we present the results of a local earthquake tomographic study performed to image in depth this complex crustal structure down to 24 km depth the obtained tomograms present a good correlation with the surface geology in general with higher vp velocities in the north and lower vp velocities in the south the heterogeneity observed on the surface geology of the galicia tras os montes zone is well marked being a relatively thin layer over the smoother structure of the centro iberia zone ciz the ciz crustal block confined between the porto tomar ferreira do alentejo and the manteigas braganca faults having higher vp values enhancing the contrast to the lusitanian basin to the west the ossa morena zone corresponds to the unit presenting the greater heterogeneity in both vp and vp vs models showing also with a complex transition to the south portuguese zone and a relatively smooth transition to the centro iberian zone unexpectedly the south portuguese zone present an east west velocity variation with no apparent correspondence with the surface geology the transition to the coastal mesocenozoic basins is clearly marked the lower tagus valley corresponding to a 4 km thick low velocity region the relocation inland recorded seismicity in the period 2000 2014 allows cleansing some of the alignments and establish their correlation with some of the active structures in portugal the model features and seismicity pattern reveal the strong role played by the variscan heritage

integrating s wave seismic reflection data and cone penetration test data using a multiangle multiscale approach a cone penetration test cpt is the most common geotechnical testing method used to estimate in situ the strength properties of soil although cpt provides valuable information this information is restricted to the location of the measurement we propose a new concept to integrate shallow s wave reflection seismic data with cpt data in order to obtain laterally continuous subsoil information in this vein a valid quantitative means to relate seismic reflections to cpt data is a primary requirement the approach proposed here is based on the characterization of the scaling behavior of the local fine scale s wave velocity information extracted from the seismic reflection data and the same behavior of the cpt cone resistance the local velocity contrast information is extracted by linearized zoeppritz inversion of the amplitude preserved prestack reflection data we have formulated a multiscale analysis approach employing the continuous wavelet transform in order to quantitatively characterize the nature

the attenuation of fourier amplitudes for rock sites in eastern north america we develop an empirical model of the decay of fourier amplitudes for earthquakes of m 3 6 recorded on rock sites in eastern north america and discuss its implications for source parameters attenuation at distances from 10 to 500 km may be adequately described using a bilinear model with a geometric spreading of 1 r 1 3 to a transition distance of 50 km with a geometric spreading of 1 r 0 5 at greater distances for low frequencies and distances less than 50 km the effective geometric spreading given by the model is perturbed using a frequency and hypocentral depth dependent factor defined in such a way as to increase amplitudes at lower frequencies near the epicenter but leave the 1 km source amplitudes unchanged the associated anelastic attenuation is determined for each event with an average value being given by a regional quality factor of q 525f 0 45 this model provides a match on aver age between the known seismic moment of events and the inferred low frequency spectral amplitudes at r 1 km obtained by correcting for the attenuation model the inferred brune stress parameters from the high frequency source terms are about 600 bars 60 mpa on average for events of m 4 5

analyzing shallow faulting at a site in the wasatch fault zone utah usa by integrating seismic gravity magnetic and trench data abstract gravity magnetic and seismic surveys were conducted across the wasatch fault zone east of springville utah near the mouth of hobble creek canyon the geophysical data were acquired processed and interpreted to determine possible locations of larger total offset greater than 6 ft 1 8 m shallow normal faults within the fault zone interpretations of the individual data sets were integrated to help eliminate spurious readings and to strengthen the interpretations visual methods of integration along with computer modeling were chosen for this study furthermore the geophysical data were correlated and integrated with available trench data and surface data in addition to verifying locations of known faults the geophysical surveys detected numerous possible additional faults not previously mapped of particular interest is a newly discovered graben structure near the southern end of the site where building of new homes has recently been proposed new structural information about fault densities and styles was also determined from the surveys the fault concentration for this site is 1 3 faults 100 ft 30 5 m or one fault per 77 ft 23 5 m interpreted antithetic faults at the hobble creek site account for 65 of the total while synthetic faults account for 35 with respect to the main fault strand information derived from this study should be useful during planning and development of areas within the wasatch fault zone the characteristics of subsurface deformation can be used to gain a better understanding of the potential for surface rupture at a given site this is also useful in planning appropriate site development and remedial measures to help mitigate hazards associated with large magnitude earthquakes

adjusting central and eastern north america ground motion intensity measures between sites with different reference rock site conditions abstract adjustment factors are provided for converting ground motion intensity measures between central and eastern north america cena sites with different reference rock site conditions v s 30 760 2000 and 3000 m s for moment magnitudes ranging from 2 to 8 rupture distances ranging from 2 to 1200 km fourier amplitude spectra fas for frequencies ranging from 0 01 to 100 hz response spectra for periods ranging from 0 01 to 10 0 s peak ground acceleration and peak ground velocity the adjustment factors are given for a wide range of the site diminution parameters 0 for sites with v s 30 760 m s and for a 0 of 0 006 s for two harder rock sites fourteen cena velocity profiles with v s 30 values within a factor of 1 1 of 760 m s were used to derive average fas amplification factors as a function of frequency which were then used in simulations of peak ground motion parameters and response spectra to derive the adjustment factors the amplification function differs from that used in western north america e g campbell and boore 2016 in having a peak near 9 hz due to the resonance of motions in the relatively thin low velocity material over hard rock that characterizes many cena sites with v s 30 near 760 m s we call these b c sites because this velocity marks the boundary between national earthquake hazards reduction program site classes b and c building seismic safety council 2004 the adjustments for short period motions are sensitive to the value of 0 but there are very few if any determinations of 0 for cena b c sites for this reason we determined 0 from multiple recordings at pinyon flat observatory pfo california which has a velocity depth profile similar to those of cena b c sites the pfo and other results from the literature suggest that appropriate values of 0 for cena b c sites are expected to lie between 0 01 and 0 03 s electronic supplement zip files with parameters used by stochastic method simulation smsim and ratios of the ground motion intensity measures between hard rock sites and national earthquake hazards reduction program nehrp b c sites

syn sedimentary gravity slides growth faults in the coal measures of south wales growth faults are an important class of syn sedimentary fault which have been widely recognized in sub surface studies of hydrocarbon bearing clastic basin successions1 4 they are listric normal faults which are active for a limited period during sediment deposition and therefore affect a discrete sedimentary interval whilst active the faults substantially influence sedimentation and a thicker generally sand dominated succession accumulates on the downthrown side which is consistently towards the basin the faults are not directly related to basement tectonics and instead are thought to originate principally by gravity sliding within the sediment pile5 over pressured undercompacted conditions in buried muds aid development of the faults by reducing the slope required to initiate sliding5 and in some cases associated mud diapirism also contributes by creating steeper slopes6 despite their widespread recognition in sub surface studies relatively few examples have been described from exposed successions7 10 and none from the economically important upper carboniferous coal measures of europe here we describe examples of growth faults recently discovered in an opencast site of the coal measures in south wales and comment on their possible significance

evidence for fault weakness and fluid flow within an active low angle normal fault determining the composition and physical properties of shallow dipping active normal faults dips 35 with respect to the horizontal is important for understanding how such faults slip under low resolved shear stress and accommodate significant extension of the crust and lithosphere seismic reflection images1 and earthquake source parameters2 show that a magnitude 6 2 earthquake occurred at about 5 km depth on or close to a normal fault with a dip of 25 30 located ahead of a propagating spreading centre in the woodlark basin here we present results from a genetic algorithm inversion of seismic reflection data which shows that the fault at 4 5 km depth contains a 33 m thick layer with seismic velocities of about 4 3 km s 1 which we interpret to be composed of serpentinite fault gouge isolated zones exhibit velocities as low as 1 7 km s 1 with high porosities which we suggest are maintained by high fluid pressures we propose that hydrothermal fluid flow possibly driven by a deep magmatic heat source and high extensional stresses ahead of the ridge tip have created conditions for fault weakness and strain localization on the low angle normal fault

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

attenuation of lg waves in the new madrid seismic zone of the central united states using the coda normalization method abstract unique properties of coda waves are employed to evaluate the frequency dependent quality factor of lg waves using the coda normalization method in the new madrid seismic zone of the central united states instrument and site responses are eliminated and source functions are isolated to construct the inversion problem for this purpose we used 121 seismograms from 37 events with moment magnitudes m ranging from 2 5 to 5 2 and hypocentral distances from 120 to 440 km recorded by 11 broadband stations a singular value decomposition svd algorithm is used to extract q values from the data while the geometric spreading exponent is assumed to be a constant inversion results are then fitted with a power law equation from 3 to 12 hz to derive the frequency dependent quality factor function the final results of the analysis are q v lg f 410 38 f 0 49 0 05 for the vertical component and q h lg f 390 26 f 0 56 0 04 for the horizontal component where the term after sign represents one standard error for stations within the mississippi embayment with an average sediment depth of 1 km around the memphis metropolitan area estimation of quality factor using the coda normalization method is not well constrained at low frequencies f

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

soft sediment deformation in a tectonically active area the plio pleistocene zarzal formation in the cauca valley western colombia abstract the plio pleistocene zarzal formation corresponds to fluvio lacustrine sediments deposited in an intramontane depression within the colombian andes associated with the cauca romeral fault system it crops out mainly in the cauca valley where numerous field sections have permitted the mapping of the vertical and lateral lithological variations lacustrine deposits of sands silts clays and diatomites are interbedded with fluvial sand and gravel beds and fluvio volcanic mass flows derived from the volcanic central cordillera numerous soft sediment deformation structures are encountered in this formation particularly in fine to medium grained sands silts and clays load structures load casts flame structures pseudonodules water escape structures water escape cusps dish and pillar and pocket and pillar structures soft sediment intrusions clastic sills and dykes disturbed laminites convolute laminations slumps and synsedimentary faulting deformation mechanisms and driving forces are related essentially to gravitational instabilities dewatering liquidization and brittle deformations field and regional geological data show that most of these deformations are related to seismicity and can be interpreted as seismites this area has a geological and recent seismic history and outcrops show both syn and post depositional faulting related to the transpressional regime of this part of the colombian andes which generates strike slip faults and associated local normal faults the drainage pattern within the zarzal formation shows the signature of neotectonics moreover the fine to coarse grained sands of the zarzal formation are lithologies prone to liquefaction when affected by seismic waves the intercalation of the deformed intervals within undisturbed strata confirms the catastrophic nature of the events finally the large areal extent of the deformations and the type of structures are compatible with seismites consequently the existence of seismites in the zarzal formation represents corroboration of tectonic activity in this area during the pleistocene earthquakes with a magnitude higher than 5 can be postulated based upon the proximity of active faults and the types of deformations

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

evaluation of ground motion models for usgs seismic hazard forecasts induced and tectonic earthquakes in the central and eastern united statesevaluation of gmms for usgs seismic hazard forecasts

glacigenic and associated marine sediments in the weddell sea fjords of spitsbergen and the barents sea a review abstract studies of glacigenic and associated marine sediments in the weddell sea fjords of spitsbergen and barents sea show that during periods of limited glacial coverage interstadials large amounts of material may be brought into the sea mainly by meltwater the major load is deposited relatively close to the icefront 1 at times of maximum glacial extent grounded ice extends onto the shelf with the shelf edge as the outer limit and land and inner shelf areas are eroded main glacial depositional sites are then the outer shelf and shelf edge the sedimentary environment outside an ice shelf is characterized by low clastic supply mainly deposited from icebergs due to low turbidity and a supply of nutrient rich water biogenic matter accumulates leading to a glaciomarine sequence rich in bioclastics sea level lowering results in grounding and seaward expansion of the ice shelf subsequent eustatic rise causes the grounded ice to float deglaciation and sea level rise reduces clastic input to the shelves glacial sediments are reworked and carbonates may accumulate forming tillite carbonate sequence e g late precambrian break up of marine ice sheets such as the barents sea ice sheet seems to have taken place stepwise in response to eustatic rise and climatic changes

biogenic facies in the antarctic glacimarine environment basis for a polar glacimarine summary abstract the association of glacial deposits diamicts or tillites with biogenic and or chemically derived sedimentary rocks in the ancient record is one which continues to challenge interpretation an analogous association can be found on portions of the east antarctic continental shelf where relict glacial and glacimarine diamictons are overlain by a varied and complex suite of modern biogenic deposits carbonate bioclastic material can be found in two distinct zones and its deposition may have been contemporaneous with partial glacial expansion onto the shelf a nearshore carbonate facies consists of in situ and partially reworked barnacles bryozoans ostracods pelycepods gastropods planktonic and benthonic foraminifera a siliceous biogenic component is intermixed within the shallow water 500 m siliceous facies of pelagic hemipelagic and sediment gravity flow origin is found within inner shelf depressions and consists predominantly of diatom frustules and radiolaria these accumulations of siliceous ooze and mud clearly post date glacial recession from the shelf and contain laminated cross laminated and massive interbeds which are accumulating at rates of 0 3 cm yr the extreme polar climate inhibits meltwater production and terrigenous influx into marine basins this allows for the accumulation of biogenic rich material which is also favored by the high seasonal productivity inherent in the south polar oceans ancient analogs to these modern deposits exist and their association with glacimarine strata could be used to infer polar climatic settings and glacial retreat that is related to eustatic sea level rather than regional warming

signature of fault zone deformation in near surface soil visible in shear wave seismic reflections small throw seismogenic fault segments hidden in the holocene sediments are crucial but difficult targets in seismic exploration we report here the detection of the deformation pattern and a concealed fault segment in the unconsolidated sediments at vila franca xira portugal through identification in shear wave reflection data of multiple signatures of ductile deformation associated with faulting we find step like changes in the stacking velocity along a shallow subsoil layer boundary indicating synsedimentary faulting we also recognize a consistent distortion in the moveout of the reflection events in the raw shear wave data synthetic modeling of seismic data helps in interpreting these observations and identifying backscattered energy from a steeply dipping shallow fault zone prior to this finding there was no evidence for holocene activity of this fault although the fault is considered to be the most probable source for the disastrous 1531 earthquake

evidence for holocene palaeoseismicity along the basel reinach active normal fault switzerland a seismic source for the 1356 earthquake in the upper rhine graben summary we conducted a palaeoseismic study with geomorphologic mapping geophysical prospecting and trenching along an 8 km long nne ssw trending fault scarp south of basel the city as well as 40 castles within a 20 km radius were destroyed or heavily damaged by the earthquake of 1356 october 18 io ix x the largest historical seismic event in central europe active river incisions as well as late quaternary alluvial terraces are uplifted along the linear basel reinach br fault scarp the active normal fault is comprised of at least two main branches reaching the surface as evident by resistivity profiles reflection seismic data and direct observations in six trenches in trenches the normal fault rupture affects three colluvial wedge deposits up to the base of the modern soil radiocarbon as well as thermoluminescence tl age determinations from other trenches helped to reconstruct the holocene event chronology we identified three seismic events with an average coseismic movement of 0 5 0 8 m and a total vertical displacement of 1 8 m in the last 7800 yr and five events in the last 13 200 yr the most recent event occurred in the interval ad 500 1450 2 and may correspond to the 1356 earthquake furthermore the morphology suggests both a southern and northern fault extensions that may reach 20 km across the jura mountains and across the rhine valley taking this fault length and a 10 km thick seismogenic layer suggests a mw 6 5 or greater event as a possible scenario for the seismic hazard assessment of the basel region

near surface fault detection using high resolution shear wave reflection seismics at the co2crc otway project site australia high resolution near surface shear wave reflection seismic measurements were carried out in november 2013 at the co2crc otway project site victoria australia with the aim to determine and if so where deeper faults reach the near subsurface from a previous p wave 3 d reflection seismic data set that was concentrated on a reservoir at 2 km depth we can only interpret faults up to 400 m below sea level for the future monitoring in the overburden of the co2 reservoir it is important to know whether and how the faults continue in the subsurface we prove that two regional fault zones do in fact reach the surface instead of dying out at depth individual first break signatures in the shot gathers along the profiles support this interpretation however this finding does not imply perforce communication between the reservoir and the surface in the framework of co2 injection the shear wave seismic sections image with high resolution better than 3 m vertically and complementary to existing p wave volumes different tectonic structures similar structures also outcrop on the southern coast of the otway basin both the seismic and the outcrops evidence the complex youngest structural history of the area

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

debris in icebergs and rates of glaci marine sedimentation observations from spitsbergen and a simple model debris distribution and content in spitsbergen icebergs varies but basal debris rich layers often 1 m thick are the most important sources of iceberg rafted material angular iceberg rafted clasts in the glaci marine record imply the presence of nunataks or valley walls rather than unbroken ice sheet surfaces indicating paleo ice mass configuration calculated iceberg melt rates imply that most iceberg rafted debris is released within spitsbergen fjords sedimentation from icebergs is calculated as 1 mm a 1 for inner mollerfjorden and 8 mm a 1 for inner kongsfjorden an order of magnitude lower than total sediment inputs turbid subglacial meltwater is a more important debris source a simple model is proposed to calculate the flux of basal debris in icebergs and iceberg sedimentation rates

the sizes frequencies and freeboards of east greenland icebergs observed using ship radar and sextant the scoresby sund fjord system east greenland contains the most productive fast flowing outlet glaciers draining east from the greenland ice sheet calving 18 km3 a 1 of icebergs the sizes frequencies and freeboards of 1900 icebergs were measured from f s polarstern using ship x band radar and sextant radar beam spreading exaggerates iceberg width by 60 m per nautical mile of range beyond the first mile data sets on iceberg size e g that collated for antarctic icebergs collected using ship radars which do not take this effect into account will overestimate iceberg dimensions significantly the location and concentration of icebergs within the fjord complex can be explained by 1 the locations of the principal source glaciers and 2 fjord topography and bathymetry iceberg concentration maximum 0 6 icebergs km 2 declines with distance from the major iceberg sources we found that 69 of icebergs within the fjord system are 1 km in length the largest is 2 7 km long icebergs become spread more evenly over the range of size classes in the outer fjord and shelf modal iceberg keel depth calculated from freeboard measurements is 4 500 m in the inner fjords shifting to lower values in the outer fjords reflecting shallower bathymetry radar measurements of iceberg width cannot be used to infer keel depths accurately because width and keel depth are only weakly correlated comparison between freeboards and keel depths for icebergs from east greenland and the barents sea indicates that the iceberg source i e floating or grounded exerts a fundamental control on iceberg dimensions the drift pattern of icebergs is from the head to the mouth of the fjord system although fjord bifurcations bathymetry and currents provide additional complications the trends in observed iceberg size and frequency and in inferred keel depth in the scoresby sund region are likely to be applicable to other fjords and shelves around greenland

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

shallow sh wave seismic investigation of the mt angel fault northwest oregon usa abstract the mt angel fault is likely one of the most active faults near the portland metropolitan area and was probably associated with the 1993 scotts mills earthquake sh wave seismic techniques used to image the mt angel fault suggest that the fault offsets late pleistocene gravel 22 to 34 ka at several locations within the study area displacement of the late pleistocene gravel along the strike of the mt angel fault increases from no obvious displacement on the northwest to approximately 18 m on the southeast this trend of increasing offset along the strike of the fault is paralleled by topographic and geomorphic trends a reconnaissance geologic investigation at an anomalous bend in the pudding river near the projected trace of the mt angel fault revealed potential tectonic deformation in sediments younger than the late pleistocene gravel imaged by sh wave data the results of this study have contributed to the paleoseismic record of the mt angel fault laid the groundwork for future geologic investigations along the pudding river and determined potential sites for future paleoseismic trenching investigations

ice ocean interaction on ronne ice shelf antarctica detailed glaciological studies have been completed at 28 sites lying on an approximate flow line extending 760 km across ronne ice shelf parameters measured at each location include ice velocity thickness principal strain rates surface elevation temperature and accumulation rate the data have been used in a steady state model to derive the basal mass flux and the temperature profile with depth at each site from the principles of mass and energy conservation these calculations indicate basal melting in excess of 1 m yr 1 over the first 100 km of the flow line downstream of the grounding line where the ice shelf is between 1200 m and 1600 m thick the maximum melt rates in this region occur near the inland margin and exceed 4 m yr 1 melting continues at a lesser rate over the next 200 km before freezing commences freezing then dominates up to the final 100 km before the ice front resulting in the accumulation of a layer of basal sea ice up to 50 m thick this is rapidly removed as melt rates increase to over 6 m yr 1 at the ice front the cumulative effect of this pattern of basal accumulation and ablation is the wastage by melting of 85 of the mass discharged across the grounding line before it reaches the ice front supporting evidence for a layer of saline ice underlying the ice shelf is provided by the strength of basal radar reflections observed during radio echo sounding of ice thickness in the region where mass balance calculations suggest an accretion of basal sea ice reflection coefficients are consistently low ranging from 6 db to 38 db most of these weak reflections are believed to originate from the true base of the ice shelf the additional energy loss being the result of increased attenuation of the radar signal within the saline layer the derived pattern of basal melting and freezing is consistent with a simple model of sub ice shelf oceanic circulation involving a deep thermohaline convection cell dense saline water which is formed over the continental shelf during winter when the sea surface freezes drains into the deepest parts of the sub ice shelf cavity at the inland margin where this water mass comes into contact with the ice shelf its temperature is 1 c above the local pressure freezing point melting of ice results producing a buoyant outflow of cold relatively fresh water along the ice shelf base basal freezing occurs towards the ice front where the ascending water becomes supercooled this circulation has important implications for the production of antarctic bottom water and for the response of the ice shelf to driving stresses through the temperature dependent viscosity of ice

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

aspects of the structural evolution of the lusitanian basin in portugal and the shelf and slope area offshore portugal abstract the study provides a regional seismic interpretation and mapping of the mesozoic and cenozoic succession of the lusitanian basin and the shelf and slope area off portugal the seismic study is compared with previous studies of the lusitanian basin from the late triassic to the cretaceous the study area experienced four rift phases and intermittent periods of tectonic quiescence the triassic rifting was concentrated in the central part of the lusitanian basin and in the southernmost part of the study area both as symmetrical grabens and half grabens the evolution of half grabens was particularly prominent in the south the triassic fault controlled subsidence ceased during the latest late triassic and was succeeded by regional subsidence during the early early jurassic hettangian when deposition of evaporites took place a second rift phase was initiated in the early jurassic most likely during the sinemurian pliensbachian this resulted in minor salt movements along the most prominent faults the second phase was concentrated to the area south of the nazare fault zone and resulted here in the accumulation of a thick sinemurian callovian succession following a major hiatus probably as a result of the opening of the central atlantic resumed deposition occurred during the late jurassic evidence for late jurassic fault controlled subsidence is widespread over the whole basin the pattern of late jurassic subsidence appears to change across the nazare fault zone north of the nazare fault fault controlled subsidence occurred mainly along nnw sse trending faults and to the south of this fault zone a nne ssw fault pattern seems to dominate the oxfordian rift phase is testified in onlapping of the oxfordian succession on salt pillows which formed in association with fault activity the fourth and final rift phase was in the latest late jurassic or earliest early cretaceous the jurassic extensional tectonism resulted in triggering of salt movement and the development of salt structures along fault zones however only salt pillow development can be demonstrated the extensional tectonics ceased during the early cretaceous during most of the cretaceous regional subsidence occurred resulting in the deposition of a uniform lower and upper cretaceous succession marked inversion of former normal faults particularly along ne sw trending faults and development of salt diapirs occurred during the middle miocene probably followed by tectonic pulses during the late miocene to present the inversion was most prominent in the central and southern parts of the study area in between these two areas affected by structural inversion fault controlled subsidence resulted in the formation of the cenozoic lower tagus basin northwest of the nazare fault zone the effect of the compressional tectonic regime quickly dies out and extensional tectonic environment seems to have prevailed the miocene compressional stress was mainly oriented nw se shifting to more n s in the southern part

evaluation of functional forms for the attenuation of small to moderate earthquake response spectral amplitudes in north america abstract we studied several attenuation forms to evaluate their ability to describe the decay of response spectral amplitudes in eastern canada northeastern united states central united states pacific northwest british columbia northern california and southern california linear bilinear and trilinear regression forms with different combinations of geometric spreading coefficients were tested to assess their ability to describe spectral amplitude decay from 0 33 to 10 hz in the distance range from 10 to 400 km the residual trends and the shapes of the attenuation forms do not show significant differences in goodness of fit between these trial forms making it difficult to see a meaningful distinction between them furthermore statistical measures such as the akaike information criterion are not particularly helpful in drawing such distinctions a simple linear model as well as more complex forms can fit the data in almost every region however this linear model has steeper slope in the west 1 3 than in the east 1 and may not extend well over large distances the linear model effectively smoothes through complications in functional form such as the moho bounce or the transition to surface wave spreading at regional distances a trilinear model has the best statistical fit in most cases but the added complications in shape and parameterization do not appear warranted by the marginal improvement in residuals the bilinear form offers a good compromise between simplicity and the ability to model amplitude decay appropriately at both near and regional distances

determination of stress parameters for eight well recorded earthquakes in eastern north america we determined the stress parameter for the eight earthquakes stud ied by atkinson and boore 2006 using an updated dataset and a revised point source stochastic model that captures the effect of a finite fault we consider four geometrical spreading functions ranging from 1 r at all distances to two or three part functions the values are sensitive to the rate of geometrical spreading at close distances with 1 r 1 3 spreading implying much higher than models with 1 r spreading the important difference in ground motions of most engineering con cern however arises not from whether the geometrical spreading is 1 r 1 3 or 1 r at close distances but from whether a region of flat or increasing geometrical spreading at intermediate distances is present as long as is constrained by data that are largely at distances of 100 km 800 km the simple 1 r model fits the sparse data for the eight events as well as do more complex models determined from larger datasets where the larger datasets were used in our previous ground motion predic tion equations this suggests that uncertainty in attenuation rates is an important com ponent of epistemic uncertainty in ground motion modeling for the attenuation model used by atkinson and boore 2006 the average value of from the point source model ranges from 180 bars to 250 bars depending on whether or not the stress parameter from the 1988 saguenay earthquake is included in the average we also find that for a given earthquake is sensitive to its moment magnitude m with a change of 0 1 magnitude units producing a factor of 1 3 change in the derived

a generalization of the stochastic summation scheme of small earthquakes to simulate strong ground motions a generalization of the stochastic summation scheme of small earthquakes following a general form of the source spectrum n model is developed to estimate the proper probability density functions for rupture propagation over the fault and to simulate site specific strong ground motions in two independent stages the probability density functions for rupture propagation are first developed for a single corner frequency source model and then extended to multiplicative and additive double corner frequency source models to partially account for the effects of finite fault rupture such as fault geometry rise time and rupture time on ground motions and to better match observed fourier amplitude spectra fas the generalized two stage stochastic summation scheme developed in this study can be used to simulate realistic strong ground motion time histories from small events represented as empirical green s functions egfs by specifying only two source parameters of the seismic moment and stress drop for a given site the proposed two stage stochastic summation schemes are tested using numerical examples following the theoretical source models as well as observed ground motions of the 2011 mw 9 0 tohoku earthquake in japan and the 1994 mw 6 7 northridge earthquake in california to verify the applicability of the approach comparisons between the observed and simulated time histories for these two earthquakes their response spectra and fas show satisfactory performance of the proposed approach for engineering purposes the results of these comparisons indicate that the proposed stochastic summation of small events as egfs can adequately replicate observed ground motions and evaluate uncertainties in ground motions with the generation of many time history realizations corresponding to a multitude of possible rupture processes the proposed approach can also be used to generate multiple realistic acceleration time histories matched on average to the target response spectra for use in earthquake performance design and to develop ground motion models for low seismicity regions where there is a lack of recording of strong ground motions

geophysical characterization of the ota vila franca de xira lisbon sesimbra fault zone portugal summary this paper focuses on the reprocessing of seismic reflection profiles aeromagnetic and seismicity data to locate and characterize the ota vila franca de xira lisbon sesimbra fault zone the studied structure is sited in the lower tagus valley an area with over 2 million inhabitants that has experienced historical earthquakes causing many casualties serious damage and economical losses e g 1531 january 26 and 1909 april 23 earthquakes whose tectonic sources are mostly unknown the fault zone trends nne ssw to n s is located near the eastern border of the mesozoic lusitanian basin and partially delimits the lower tagus cenozoic basin at the west mostly hidden under the cenozoic sedimentary fill according to the data presented here the normal structures that compose the fault zone were reactivated in cenozoic times with positive inversion and the development of splays towards the east the fault zone shows three distinct segments with different behaviour in conformity with their various orientations relative to the nw se maximum compressive stress the northern segment splays into a series of nne ssw oriented east verging imbricate thrusts which merge to the west into a major reverse fault that resulted from the tectonic inversion of the former normal fault bordering the

regional spectral analysis of three moderate earthquakes in northeastern north america abstract we analyze fourier spectra obtained from the horizontal components of broadband and accelerogram data from the 1997 cap rouge the 2002 ausable forks and the 2005 riviere du loup earthquakes recorded by canadian and american stations sited on rock at hypocentral distances from 23 to 602 km we check the recorded spectra closely for anomalies that might result from site resonance or source effects we use beresnev and atkinson s 1997 near surface velocity structures and boore and joyner s 1997 quarter wave method to estimate site response at hard and soft rock sites we revise the street et al 1975 model for geometrical spreading adopting a crossover distance of r o 50 km instead of 100 km we obtain an average attenuation of q 410 25 f 0 50 0 03 for s l g surface waves with ray paths in the appalachian and southeastern grenville provinces we correct the recorded spectra for attenuation and site response to estimate source spectral shape and radiated energy for these three earthquakes and the 1988 m 5 8 saguenay earthquake the brune stress drops range from 130 to 419 bars and the apparent stresses range from 39 to 63 bars the corrected source spectral shapes of these earthquakes are somewhat variable for frequencies from 0 2 to 2 hz falling slightly below the fitted brune spectra

variability of crustal attenuation in the northeastern united states from lg waves high quality digital seismograms from eight pairs of collocated earthquakes in the northeastern united states were analyzed to determine accurate source spectrum corner frequencies this was accomplished by applying the empirical green s function method to regional pg and lg or sg phases recorded by vertical component seismographs of the u s national seismographic network usnsn and the lamont doherty cooperative seismographic network lcsn stations the frequency band used was 0 5 16 hz for usnsn and 1 30 hz for lcsn records the source spectrum corner frequencies for the eight larger earthquakes of the event pairs magnitudes between mb lg 2 5 4 1 range from about 4 3 to 16 3 hz based on the comer frequencies obtained independently from the empirical green s function analysis sg or lg wave displacement amplitude spectra up to 30 hz were used to determine the crustal average q factors along 87 event station paths these paths crossed diverse tectonic features in the northeastern united states and were in the epicentral distance range of 41 to 1394 km we found that within the northeastern united states the crustal average qlg we obtained was frequency dependent and showed spatial variability which correlated fairly well with the major tectonic features in the region our attenuation measurements indicated low lg attenuation in the adirondack mountains with exposed precambrian grenville basement with qlg 905 f0 40 high lg attenuation in the central appalachian province with qlg 561 586 f0 46 0 47 and an intermediate lg attenuation in northern new england appalachians with q 705 f0 41

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

geophysical methods applied to fault characterization and earthquake potential assessment in the lower tagus valley portugal abstract the study region is located in the lower tagus valley central portugal and includes a large portion of the densely populated area of lisbon it is characterized by a moderate seismicity with a diffuse pattern with historical earthquakes causing many casualties serious damage and economic losses occurrence of earthquakes in the area indicates the presence of seismogenic structures at depth that are deficiently known due to a thick cenozoic sedimentary cover the hidden character of many of the faults in the lower tagus valley requires the use of indirect methodologies for their study this paper focuses on the application of high resolution seismic reflection method for the detection of near surface faulting on two major tectonic structures that are hidden under the recent alluvial cover of the tagus valley and that have been recognized on deep oil industry seismic reflection profiles and or inferred from the surface geology these are a wnw ese trending fault zone located within the lower tagus cenozoic basin across the tagus river estuary porto alto fault and a nne ssw trending reverse fault zone that borders the cenozoic basin at the w vila franca de xira lisbon fault vertical electrical soundings were also acquired over the seismic profiles and the refraction interpretation of the reflection data was carried out according to the interpretation of the collected data a complex fault pattern disrupts the near surface first 400 m at porto alto affecting the upper neogene and at least for one fault the quaternary with a normal offset component the consistency with the previous oil industry profiles interpretation supports the location and geometry of this fault zone concerning the second structure two major faults were detected north of vila franca de xira supporting the extension of the vila franca de xira lisbon fault zone northwards one of these faults presents a reverse geometry apparently displacing holocene alluvium vertical offsets of the holocene sediments detected in the studied geophysical data of porto alto and vila franca de xira lisbon faults imply minimum slip rates of 0 15 0 30 mm year three times larger than previously inferred for active faults in the lower tagus valley and maximum estimates of average return periods of 2000 5000 years for m 6 5 7 co seismic ruptures