re estimated effects of deep episodic slip on the occurrence and probability of great earthquakes in cascadia abstract mazzotti and adams 2004 estimated that rapid deep slip during typically two week long episodes beneath northern washington and southern british columbia increases the probability of a great cascadia earthquake by 30 100 times relative to the probability during the 58 weeks between slip events because the corresponding absolute probability remains very low at 0 03 per week their conclusion is that though it is more likely that a great earthquake will occur during a rapid slip event than during other times a great earthquake is unlikely to occur during any particular rapid slip event this previous estimate used a failure model in which great earthquakes initiate instantaneously at a stress threshold we refine the estimate assuming a delayed failure model that is based on laboratory observed earthquake initiation laboratory tests show that failure of intact rock in shear and the onset of rapid slip on pre existing faults do not occur at a threshold stress instead slip onset is gradual and shows a damped response to stress and loading rate changes the characteristic time of failure depends on loading rate and effective normal stress using this model the probability enhancement during the period of rapid slip in cascadia is negligible

complex zoning in apatite from the idaho batholith a record of magma mixing and intracrystalline trace element diffusion apatite crystals in a sample of biotite granodiorite from the idaho batholith display complex chemical zoning characterized by abrupt changes in ree y si content more subtle variations in s na la yb and mn contents and petrographic evidence for multiple episodes of partial resorption the zoning is attributed to changes in melt composition resulting from magma mixing and differentiation although the possibility that some rounded cores may be inherited cannot be disproved high s contents in apatite cores and the presence of an included anhydrite grain indicate crystallization from an oxidized host magma divalent cations that occupy the apatite ca sites sr mn fe show evidence of having been redistributed between zones by intracrystalline diffusion whereas cations that participate in coupled substitutions involving the tetrahedral site si y ree na s were not readily redistributed the main ree substitution in this case is ree super 3 si super 4 ca super 2 p super 5 and ree diffusion is rate limited by slow si diffusion however exchange of lree e g lasm sub 1 on the ca sites does not involve si and proceeds more rapidly resulting in homogenization of la sm between zones within individual crystals relative diffusion rates inferred from zoning profiles in this study are mn sr fe and lasm sub 1 are faster than na s and layb sub 1 which are faster than si these data imply that ree patterns can be decoupled from ree abundances during diffusion and that even apatite zones or cores that appear sharply bounded in backscattered electron images may not retain their original chemical or sr nd isotopic traits

an intensity survey of households affected by the northridge california earthquake of 17 january 1994 following the northridge california earthquake of 17 january 1994 the humboldt earthquake education center heec conducted a telephone survey of approximately 6000 adults from within the felt region to study the earthquake s effects on individual households we tabulate human responses to the earthquake and observations of the earthquake s effects on inanimate objects from the heec survey as a function of independently assigned u s geological survey modified mercalli usgs mm intensity for the same communities human responses and subjective judgments about the severity of shaking when averaged over a large number of samples are useful discriminants of the levels of strong ground motion up to those associated with usgs mm intensity vii notwithstanding that individual human responses and subjective judgments are notoriously unreliable a threshold of strong ground motion corresponds to usgs mm intensity of about vii above which over 40 of respondents described the earthquake as violent and most people reported difficulty standing furniture displaced and some damage to their homes even at intensities viii and ix however relatively few people about 15 described their reaction as panic and only about 12 reported major damage to their homes the heec phone survey data show that in communities of low to moderate shaking usgs mm intensities estimated from a single postal questionnaire are quite robust at usgs mm intensity of v and below 88 of usgs mm intensities determined from postal questionnaires are within one intensity unit of intensities determined from the more numerous heec telephone survey data for the same community we introduce the concept of a community decimal intensity scale cdi based on telephone survey data and calibrated to agree on average with the usgs mm intensities the cdis are more regularly distributed than the usgs mm intensities and show much less scatter when plotted as a function of epicentral distance cdis show promise as a tool for comparing regional attenuation for delineating variations in shaking strength within areas mapped as a single mm zone and for rapid preliminary intensity estimates utilizing electronic media

an 1800 year archeological experiment in remagnetization limestone masonry from monuments dating from 300ad to 1940 remagnetized partly and progressively with age parallel to the present earth s magnetic field the remagnetization was probably due to viscous remanent magnetization vrm neel s theory predicts that natural vrm acquired at low temperature ta over a long time ta disappears at a higher temperature td in a short period td in the laboratory i calibrated td for the postconstruction remagnetization against the ages td of masonry used in well dated historic buildings in eastern england empirically ta m td b relates acquisition age tayears to demagnetization temperature td c lincoln limestone remagnetizes more quickly m 1 298 10 6 and b 3 598 over 1800 years than speeton chalk m 4298 10 6 and b 1 973 over 350 years magnetite with an effective pseudo single domain or small multidomain size carries the remanence

columbia river flood basalts from a centralized crustal magmatic system the columbia river basalt group in the northwestern united states derived from flood basalt eruptions that occurred 16 million years ago exhibits variability in geography and trace element geochemistry that has led to a number of proposed magma origins however the geochemical variability can be explained by a relatively simple model in which magma is derived from a mantle plume that assimilated continental crust in a centralized magma system the columbia river basalt group in the northwestern united states1 comprising about 230 000 cubic kilometres of rock exhibits unusual patterns in lava distribution geochemistry and its apparent relationship to regional tectonics consequently there is little consensus on the origin of its magmas2 3 4 5 6 7 8 9 10 11 12 here we examine the isotopic ratios of sr nd pb and os and trace element abundances in columbia river basalts the results suggest that most of the lava was produced when magma derived from a mantle plume assimilated continental crust in a central magma chamber system located at the boundary between the north american craton and the accreted terranes of idaho and oregon other related basalts are the product of mixing between the mantle plume and different types of regional upper mantle magma was then transported over a wide region by an extensive network of dykes a process that has been identified in other flood basalt provinces as well13 interactions of the plume with surrounding upper mantle and of mantle derived magmas with regional crust provide a relatively simple6 7 9 14 15 model to explain the more unusual features of the main phase columbia river basalts

remagnetization dating of roman and mediaeval masonry abstract the earth s magnetic field may partially remagnetize rocks often by the process of viscous remanent magnetization vrm thus when masonry is turned and placed in a monument it magnetizes parallel to the earth s field partly overprinting any older geological magnetizations the intensity of this new overprint will increase with time if the masonry is undisturbed older magnetizations require higher demagnetization temperatures thus the unblocking temperature tub relates directly to the age of the remanence and therefore the age of stabilization of the masonry for suitable rocks we can calibrate the remagnetization time scale for the rock using historically dated structures the scale then permits us to estimate the age of more enigmatic structures by interpolation or modest extrapolation some samples reveal multiple episodes of remagnetization showing that masonry was recycled acquiring a differently oriented remanence each time that it stabilized in a new architectural configuration masonry from the bishop s palace lincoln u k includes roman c ad 300 mediaeval 1160 1450 post civil war 1650 1720 and victorian phases that have characteristic tub consistent with their ages some mediaeval masonry recycled roman building materials

a comparison and test of various site response estimation techniques including three that are not reference site dependent abstract we compare various site response estimation techniques using after shock data of the 1989 loma prieta earthquake collected in oakland california because of recent interest in comparing results from weak and strong motion to infer any nonlinearity and between direct s and coda waves we pay particular attention to the uncertainties first sediment to bedrock spectral ratio estimates between pairs of sites are compared with those obtained from various generalized inversion approaches where the source and site effects of multiply recorded events are solved for simultaneously we find that the site amplification factors are very similar among these approaches but that the uncertainties can be significantly different depending on how the data are weighted we also examine and test three site response estimation techniques that do not rely on a reference site to estimate source and path effects the first involves a parameterized source and path effects inversion even when the bedrock data are excluded from consideration this approach is found to reveal the frequency dependence of site response at each of the sediment sites the second technique involves taking horizontal to vertical component spectral ratios receiver function type estimates of shear wave aftershock data these are also found to reveal the frequency dependence of site response at the sediment sites and the results for the bedrock site are relatively flat and near unity the third estimate is formed by taking horizontal to vertical component ratios of ambient seismic noise and these are shown to reveal the fundamental resonant frequency of the sediment sites unfortunately discrepancies exist among all of the site response estimates and with one dimensional predictions with respect to a frequency independent scaling factor nevertheless the highly frequency dependent character of site response is well constrained and the fact that non reference site dependent methods are capable of revealing this is promising for site specific hazard assessments in regions that lack adequate reference sites

coastline uplift in oregon and washington and the nature of cascadia subduction zone tectonics coastline deformation resulting from great shallow thrust earthquakes can provide information concerning the paleoseismicity of a subduction zone and thus information on the nature of potential seismicity the cascadia subduction zone is different from most other subduction zones in that it has been quiescent with respect to great earthquakes for at least the past 200 yr the washington oregon coastline also differs from most other coastlines associated with subduction zones in its lack of uplifted holocene shoreline features and low overall rate of late quaternary uplift 0 2 0 6 mm yr the uplift differences suggest that repeated great earthquakes have not occurred along the cascadia subduction zone at least during the late holocene alternatively if the plate interface has generated earthquakes the differences may be explained by longer recurrence intervals for great earthquakes smaller magnitude earthquakes or a mechanism that does not result in uplift of the coastline where expected

viscous magnetization archaeology and bayesian statistics of small samples from israel and england 1 certain limestones remagnetize viscously and noticeably over archaeological time intervals after their reorientation into monuments the laboratory demagnetization temperatures tub for the vrm increase with the installation age with rates of 0 07 c0 year for israel chalk and 0 1c0 year for english chalk the empirical relationship may be used to date enigmatic buildings or geomorphological features e g land slips such correlations also give some insight into the viscous remagnetization process over time intervals 4000 years which are unobtainable in laboratory studies the tub age relationship for the viscous remagnetization appears to follow a power law linearized as log10 b log10 tub different pelagic limestones follow different curves and whereas conventional regression estimates the power law exponent b the small sample size recommends a bayesian statistical approach from sites constructed with pelagic chalk from eastern england precise prior information b 0 761 is compared with less precise information for much more ancient sites in northern israel b 0 873 the collective posterior correlation shows a generalized power law exponent b 0 849 that regression explains 84 9 of the collective variance in age r2 0 849 of course site specific calibration is required for archaeological age determinations

site effects in avcilar west of istanbul turkey from strong and weak motion data approximately 1000 people were killed in the collapse of buildings in istanbul turkey during the 17 august 1999 izmit earthquake whose epicenter was roughly 90 km east of the city most of the fatalities and damage occurred in the suburb of avcilar that is 20 km further west of the epicenter than the city proper to investigate this pattern of damage the u s geological survey in cooperation with the kandilli observatory earthquake research institute koeri deployed portable digital seismographs at seven free field sites in western istanbul to record aftershocks during the period from 24 august to 2 september the primary objective of this deployment was to study the site effects by comparing the aftershock ground motions recorded at sites inside and outside the damaged area and to correlate site effects with the distribution of the damaged buildings in addition to using weak motion data mainshock and aftershock acceleration records from the koeri permanent strong motion array were also used in estimating the site effects site effects were estimated using s waves from both types of records for the weak motion data set 22 events were selected according to the criteria of signal to noise ratio s n ratio and the number of stations recording the same event the magnitudes of these events ranged from 3 0 to 5 2 the acceleration data set consisted of 12 events with magnitudes ranging from 4 3 to 5 8 and included two mainshock events results show that the amplifying frequency band is in general less than 4 hz and the physical properties of the geologic materials are capable of amplifying the motions by a factor of 5 10 in this frequency band there is a good agreement among the spectral ratios obtained from the two mainshocks and their aftershocks the damage pattern for the 17 august izmit earthquake is determined by several factors however our study suggests that the site effects in avcilar played an important role in contributing to the damage manuscript received 30 august 2000

low temperature demagnetization and ice pressure demagnetization in magnetite and haematite summary low temperature demagnetization ltd is confirmed as an effective method of removing soft low coercivity components of remanence in magnetite bearing specimens by passing the magnetite through its low temperature transition 130 k haematite has its low temperature transition at approximately 258 k when some specimens bearing fine grained haematite pigment pass through this transition the directional component which is hardest highest coercivity may be more reduced than the soft components in other samples of the same material the opposite may occur depending on the range of coercivities represented in each directional component thus ltd does not consistently isolate hard directional components of remanence in haematite it is therefore an unsuitable method for routine palaeomagnetic cleaning of natural remanent magnetization carried by haematite specimens that contain moisture for example from recent drilling with watercooled equipment show greater reductions in remanence intensity after ltd this is attributed to ice pressure demagnetization due to the effects of stress as pore ice thaws when the specimens warm to room temperature it is recommended that porous samples are thoroughly dried out before ltd is performed if consistent results are required

active deformation of the pacific northwest continental margin tilted and uplifted marine terraces in southern oregon show progressive landward tilting of the coastal ranges at about 5 16 10 8 rad yr 1 for the last 0 25 m y tide gauges in washington and british columbia and ten resurveyed leveling lines running inland from the coast indicate contemporary landward down to the east tilt rates of about 1 12 10 8 rad yr 1 averaged over periods of from 10 to 50 years the leveling lines traverse and the terraces cut across dipping cenozoic strata pleistocene dips to 3 mio pliocene dips to 30 and eocene dips to 60 southern oregon from cape blanco to the siletz river shows geodetic or terrace tilting in the same direction as the underlying stratal dips hence present day deformation continues past deformation of the coastal ranges and is most likely related to active subduction of the juan de fuca plate the steep stratal dips lack of major active faults and historic earthquakes and presence of very young bedding plane faults suggest that much of the onshore deformation and shortening within the overlying north american plate is taken up by folding rather than thrust faulting present shortening rates across north trending folds near the coast are between 0 02 and 1 9 10 7 yr 1 the rate of shortening decreases rapidly eastwards from the juan de fuca north american plate boundary a total of about 25 mm yr 1 of permanent shortening could be occurring within the north american plate most of it in the westernmost 40 km the landward tilt and shortening rates are similar to those above many other subduction zones that have experienced great thrust earthquakes while a high strain rate measured near seattle washington has been interpreted as elastic strain accumulation before a thrust earthquake the low level of historic seismicity and the similarity of short and long term deformation rates suggest alternatively that the subduction beneath washington is aseismic the issue has considerable implications for seismic hazard evaluation in the pacific northwest and could be resolved by a search for the effects or lack of effects of prehistoric great earthquakes

erosion by rivers and transport pathways in the ocean a provenance tool using 40ar 39ar incremental heating on fine grained sediment measured from 39 ar and 37 ar respectively are consistent with typical values for k and ca bearing minerals calculations show that the bulk mineralogy is reflected in the outgassing k ca spectra and identify plagioclase as the dominant mineral contributing to the plateau defining portion of the age spectra a second model predicts bulk sediment ages from integrated bedrock cooling age area estimates in order to examine whether bulk sediment plateau ages are representative of the average cooling age of rocks from a given river basin calculated and observed ages are notably similar in three river basins when topographic and lithologic effects are accounted for overall this technique shows considerable promise not only in tracking individual terrigenous sources in the marine realm but also for understanding processes such as erosion and sediment transport in terrestrial systems

thermoviscous remagnetization in some appalachian limestones experimental evidence shows that blocking temperature relaxation time theory for single domain magnetite can grossly underestimate laboratory thermal demagnetization temperatures of a present day viscous remanence in devonian limestones of new york state thermoviscous remagnetization at moderately elevated burial temperatures during the late paleozoic cannot therefore be readily excluded for the origin of the stable secondary component in these rocks more generally these results emphasize that single domain thermal activation theory cannot be assumed a priori to correctly predict temperature of thermoviscous remanence acquisition in all magnetite bearing rocks the prob leto

nonlinear and linear site response and basin effects in seattle for the m 6 8 nisqually washington earthquake we used recordings of the m 6 8 nisqually earthquake and its m l 3 4 aftershock to study site response and basin effects for 35 locations in seattle washington we determined site amplification from fourier spectral ratios of the recorded horizontal ground motions referenced to a soft rock site soft soil sites generally national earthquake hazard reduction program nehrp class e on artificial fill and young alluvium have the largest 1 hz amplifications factors of 3 7 for both the mainshock and aftershock these amplifications are correlated with areas of higher damage from the mainshock to major buildings and liquefaction there are several indications of nonlinear response at the soft soil sites for the mainshock ground motions despite relatively modest peak accelerations in the s waves of 15 22 g first the mainshock spectral ratios do not show amplification at 2 8 hz as do the aftershock spectral ratios spectral peaks at frequencies below 2 hz generally occur at lower frequencies for the mainshock spectral ratios than for the aftershock ratios at one soft soil site there is a clear shift of the resonant frequency to a lower frequency for the mainshock compared with the aftershock the frequency of this resonance increases in the coda of the mainshock record indicating that the site response during the weaker motions of the coda is more linear than that of the initial s wave three of the soft soil sites display cusped one sided mainshock accelerograms after the s wave these soft soil sites also show amplification at 10 20 hz in the s wave relative to the rock site that is not observed for the aftershock the cusped waveforms and 10 20 hz amplification are symptomatic of nonlinear response at the soft soil sites these sites had nearby liquefaction the largest amplifications for 0 5 hz occur at soft soil sites on the southern portion of the seattle basin stiff soil sites nehrp classes d and c on pleistocence age glacial deposits display similar spectral amplification for the mainshock and aftershock indicating approximately linear response the stiff soil sites generally have moderate amplification factors of 1 1 2 4 at 0 5 and 1 hz amplifications at 1 and 5 hz for all sites generally increase with decreasing shear wave velocity measured in the top 30 m v s 30 however larger amplifications at 0 5 and 1 hz for sites with similar v s 30 values are observed for sites in the seattle basin illustrating the amplification from the deeper 30 m sediments and the contribution from basin surface waves record sections for the mainshock and aftershock show that basin surface waves produce the peak velocities for many of the sites in the seattle basin and often dominate the amplitude at 1 hz and lower frequencies

mass transfer along the yellowstone hotspot track ii kinematic constraints on the volume of mantle derived magma abstract this paper evaluates the neogene kinematic evolution of the eastern snake river plain esrp to estimate the volume of mafic magma transferred from mantle to crust during passage over the yellowstone hotspot four major kinematic processes affected the esrp including densification due to emplacement of gabbro into the middle crust subsidence and consequent filling of a 6 km deep basin with volcanic and plutonic rocks 20 extension via dike injection or faulting ductile attenuation and lower crustal flow from esrp to the adjacent basin and range two kinematic models involving these processes are proposed overall the two models are viable only if the initial crustal thickness were 43 47 km thick otherwise the lost mass of the esrp is not balanced by the excess mass in the basin and range in the first model densification eruption and extension by dike injection the esrp crust receives mantle derived gabbro equivalent to a 16 km thick layer but would need to lose 10 km of crust via lower crustal flow in the second model densification eruption and extension by faulting and ductile attenuation the esrp crust receives a 9 4 km equivalent thickness of mantle derived gabbro and would need to lose 6 km of crust via lower crustal flow the cumulative amount of mantle derived gabbro in the esrp crust derived by this kinematic analysis equivalent to a 9 4 16 km thick layer is nearly identical to the amount estimated independently using a mass balance petrologic model suggesting it is a robust result

prehistoric earthquake history revealed by lacustrine slump deposits five strong paleoseismic events were recorded in the past 15 k y in a series of slump deposits in the subsurface of lake lucerne central switzerland revealing for the first time the paleoseismic history of one of the most seismically active areas in central europe although many slump deposits in marine and lacustrine environments were previously attributed to historic earthquakes the lack of detailed three dimensional stratigraphic correlation in combination with accurate dating hampered the use of multiple slump deposits as paleoseismic indicators this study investigated the fingerprint of the well described a d 1601 earthquake i vii viii mw 6 2 in the sediments of lake lucerne the earthquake triggered numerous synchronous slumps and megaturbidites within different subbasins of the lake producing a characteristic pattern that can be used to assign a seismic triggering mechanism to prehistoric slump events for each seismic event horizon the slump synchronicity was established by seismic stratigraphic correlation between individual slump deposits through a quasi three dimensional high resolution seismic survey grid four prehistoric events dated by accelerator mass spectrometry 14c measurements and tephrochronology on a series of long gravity cores occurred at 2420 9770 13 910 and 14 560 calendar yr ago these recurrence times are essential factors for assessing seismic hazard in the area the seismic hazard for lakeshore communities is additionally amplified by slump induced tsunami and seiche waves numerical modeling of such tsunami waves revealed wave heights to 3 m indicating tsunami risk in lacustrine environments

magnetic characterization using a three dimensional hysteresis projection illustrated with a study of limestones summary limestones provide an important source of palaeomagnetic information despite their low content of submicroscopic remanence bearing minerals the chief sources of these minerals are thought to be clastic volcanic magnetite and titanomagnetite and organic magnetite the latter mostly from bacterial sources chemically remagnetized limestones carry magnetite or pyrrhotite three hysteresis properties prove useful in identifying and characterizing these mineralogical influences on limestones the ratio of zero field maximum remanence to saturation remanence m r m s in an applied field coercivity of remanence b cr and coercivity b c to a lesser extent k f m s may be useful where k f is the ferrimagnetic susceptibility traditionally these have been plotted on a combination of 2 d graphs that of necessity only preserve two variables day et al 1977 wasilewski 1973 however we found that magnetic discrimination and characterization of the limestones was much easier on a three axis hysteresis projection that preserves the values of b cr b c and m r m s as independent variables using logarithmic scales the regression surfaces through the data become almost planar and distinguish pelagic shallow marine shelf and remagnetized limestones on the basis of the slope and intercept of the associated regression surface clearly there are sensitive sedimentological geochemical or organic influences that dictate the magnetic mineralogy through sedimentary environment moreover the 3 d plot of hysteresis criteria avords easy recognition of remagnetized limestones and may permit the rejection of material unsuitable for palaeomagnetic study the 3 d hysteresis projection may be useful for the characterization of other rocks and magnetic materials

ground motion amplification geology and damage from the 1989 loma prieta earthquake in the city of san francisco main shock and aftershock accelerograms from the loma prieta earthquake sequence are analyzed to study relative ground amplification at sites in the city of san francisco main shock spectra are estimated for those stations that recorded only aftershocks by comparing their records to those from stations that recorded both the ratios of the spectra with respect to a stable bedrock station located at fort mason show distinct spectral shapes that are strongly correlated with the rock type underlying the site earthquake damage is quantified using estimates of the modified mercalli intensity at the recording sites and safety tags issued by the city of san francisco building department these intensities are compared with ground amplification in three frequency bands and with the intensities at the same sites from the 1906 san francisco earthquake there is sufficient correlation to show that site amplification is one of the controlling factors in damage distribution

strontium and oxygen isotopic evidence for strike slip movement of accreted terranes in the idaho batholith abstract the oxygen and strontium isotope compositions of granitic rocks of the idaho batholith provide insight into the magma source assimilation processes and nature of the suture zone between the precambrian craton and accreted arc terranes granitic rocks of the idaho batholith intrude basement rocks of different age triassic jurassic accreted terranes to the west of the salmon river suture zone and the precambrian craton to the east the age difference in the host rocks is reflected in the abrupt increase in the initial 87 sr 86 sr ratios of granitic rocks in the batholith across the previously defined 0 706 line initial 87 sr 86 sr ratios of granitic rocks along slate creek on the western edge of the batholith jump from less than 0 704 to greater than 0 707 along an approximately 700 m transect normal to the salmon river suture initial 87 sr 86 sr ratios along the slate creek transect do not identify a transition zone between accreted arcs and the craton and suggest a unique tectonic history during or after suturing that is not documented along other transects on the west side of the idaho batholith the lack of transition zone along slate creek may be a primary structure due to transcurrent transpressional movement rather than by contractional thrust faulting during suturing or be the result of post imbrication modification

soil response on the fraser delta to the mw 5 1 duvall washington earthquake strong motion recordings of the 3 may 1996 mw 5 1 duvall washington earthquake made in southwestern british columbia provide the best constraints to date on soil response to seismic shaking on the fraser delta just south of vancouver a total of nine strong motion instruments in southern b c triggered during this earthquake seven of which are on or near the fraser delta these recordings were made at epicentral distances of 140 to 180 km a preliminary analysis of these data clearly shows that for low frequencies 3 hz seismic spectral amplification by a factor of 2 to 7 occurs on the fraser delta relative to nearby bedrock or thin firm soil sites however at higher frequencies moderate attenuation is observed at the fraser delta sites the largest peak ground accelerations recorded generally around 2 to 3 hz were not on the thickest delta sediments but nearer the edge of the delta peak amplification is more pronounced in the horizontal component of ground motion than in the vertical the average sh z ratio for peak values at the fraser delta sites is 4 5 0 9 compared to 1 6 0 6 for the bedrock and firm soil sites in addition to the strong motion records we also utilize five three component broadband recordings of this earthquake made in southern b c epicentral distances of 140 to 520 km and 12 short period vertical component recordings epicentral distances of 130 to 380 km to document attenuation of peak acceleration with distance for this earthquake the observed values are slightly lower than those predicted by the ground motion relations proposed for the year 2000 national building code of canada

the accuracy of soil response estimates using soil to rock spectral ratios spectral ratios between soft soil and reference rock sites are often used to predict the sedimentary site response to earthquakes however their relationship with the genuine site specific amplification function is often unclear we compare the soil to rock spectral ratios between the stations that are 3 3 km apart with the genuine response given by the ratios between the surface and 17 and 47 m down hole data from the smart1 array in taiwan are used the weak and strong motion records are addressed separately to allow for nonlinear soil response the soil to rock spectral ratios are nearly identical to the true amplification at the fre quencies from 1 to 10 hz if the finite depth of the borehole is taken into account they correctly capture the strong motion deamplification effect however the soil to rock spectral ratios are roughly 1 4 times more uncertain than surface to 47 m ratios in summary the soil to rock spectral ratios can be considered as the reliable estimates of the real site response

site effects in the city of thessaloniki greece estimated from acceleration data and 1d local soil profiles abstract in this study the site effects on seismic ground motion in the city of thessaloniki greece are estimated by applying experimental methods on acceleration data and theoretical modeling the technique of standard spectral ratio ssr is applied to a reference station located on rock while the horizontal to vertical spectral ratio hvsr technique is applied to earthquake records entire record length including p and s waves as well as on noise recordings in addition the ssr method is also applied to the vertical components the results from all methods are compared in terms of resonant frequencies and amplification levels the fundamental resonant frequency is identified by all methods while the average amplification level is generally underestimated when the hvsr technique is used an attempt is made to correlate the site amplifications computed in this study with the observed macroseismic intensities reported at the same sites for the 20 june 1978 earthquake a relation of the form i b log s s f is derived where i is the intensity increment with respect to the intensity of the reference station and ssr is the mean amplification factor obtained at each station using the ssr technique for a certain frequency band in the numerical approach we construct complete strong motion synthetics using the modal summation method for the p sv waves up to frequencies of 10 hz as input four point sources are used located at different distances and azimuths from the stations ratios of response spectra of the local 1d over the regional 1d synthetic seismograms are calculated the obtained mean spectral amplifications are compared with those derived from experimental data and the two sets are found to be consistent at most stations

site response in victoria british columbia from spectral ratios and 1d modeling this article examines site response in victoria british columbia using weak ground motion recordings 3 5 g of the 2001 m w 6 8 nisqually earthquake in washington state 150 km distant significant variations are observed in acceleration spectra across the city that can be largely attributed to local site conditions thin soil sites 3 m generally have flat amplitude spectra at frequencies less than 10 hz whereas thicker soil sites 5 11 m show peak amplitudes at 2 5 hz standard spectral ratios bedrock reference and horizontal to vertical spectral ratios are computed for sites with varying geology thin soil sites show flat site response like bedrock at frequencies 10 hz whereas the thicker soil sites show peak amplification of up to six times that of bedrock at frequencies of 2 5 hz there is good agreement between these standard spectral ratio site response estimates with the horizontal to vertical spectral ratios at each site and spectral ratios from four other earthquakes between 1996 and 2002 ground motion spectra obtained from numerical 1d modeling indicate that 3 m of soft soil national earthquake hazard reduction program nehrp class e generates a flat response at 10 hz whereas thick layers of either grey victoria clay nehrp class e or pleistocene till nehrp class c produce peak amplitudes at 2 5 hz the correlation of near surface soft soil conditions on crystalline bedrock with observed weak ground motions provides an important baseline toward future seismic hazard studies in the victoria area

simulations of seismic hazard for the pacific northwest of the united states from earthquakes associated with the cascadia subduction zone we investigate the impact of different rupture and attenuation models for the cascadia subduction zone by simulating seismic hazard models for the pacific northwest of the u s at 2 probability of exceedance in 50 years we calculate the sensitivity of hazard probabilistic ground motions to the source parameters and the attenuation relations for both intraslab and interface earthquakes and present these in the framework of the standard usgs hazard model that includes crustal earthquakes our results indicate that allowing the deep intraslab earthquakes to occur anywhere along the subduction zone increases the peak ground acceleration hazard near portland oregon by about 20 alternative attenuation relations for deep earthquakes can result in ground motions that differ by a factor of two the hazard uncertainty for the plate interface and intraslab earthquakes is analyzed through a monte carlo logic tree approach and indicates a seismic hazard exceeding 1 g 0 2 s spectral acceleration consistent with the u s national seismic hazard maps in western washington oregon and california and an overall coefficient of variation that ranges from 0 1 to 0 4 sensitivity studies indicate that the paleoseismic chronology and the magnitude of great plate interface earthquakes contribute significantly to the hazard uncertainty estimates for this region paleoseismic data indicate that the mean earthquake recurrence interval for great earthquakes is about 500 years and that it has been 300 years since the last great earthquake we calculate the probability of such a great earthquake along the cascadia plate interface to be about 14 when considering a time dependent model and about 10 when considering a time independent poisson model during the next 50 year interval

geology geochemistry and isotopic character of the colville igneous complex northeastern washington the colville igneous complex in northeastern washington comprises paleocene orthogneisses and leucocratic granitic rocks and eocene volcanic plutonic suites which were emplaced during early tertiary extension the colville igneous complex is divided into three components 1 65 4 ma orthogneisses of the okanogan dome or metamorphic complex and similar gneisses in the kettle and lincoln complexes 2 61 51 ma leucocratic granitic rocks and 3 53 47 ma intermediate to felsic volcanic plutonic rocks the leucocratic granites and younger volcanic plutonic rocks are divided on the basis of age geochemical and isotopic characteristics and emplacement mechanism the older leucocratic granites are silica rich corundum normative and sr and light rare earth element ree enriched and they form several large discrete compositionally zoned plutons and intrusive suites the younger eocene volcanic plutonic rocks can be divided into two suites an older compositionally restricted 68 72wt sio2 sr enriched medium k suite and a younger intermediate to felsic high k calcalkalic suite sr isotopic measurements of volcanic and plutonic rock in the colville igneous complex yield variable initial 87sr 86sr ratios sri ranging from about 0 704 to values greater than 0 710 in general the volcanic rocks are especially variable with little or no correlation between sri and geographic location the leucocratic granites however show a systematic west to east increase across the area which probably reflects an increased involvement with precambrian crust the variable nature of sri in the colville igneous complex may also be controlled by crustal thickness and or depth of melting within individual volcanic and plutonic suites there is a crude correlation of mean sri with age there is a systematic decrease in sri with increasing age which may reflect either a migration of the site s of melting or a decreased upper crustal residence time possibly related to the onset of extension the leucocratic granites may have formed by small degrees of partial melting in the lower crust perhaps facilitated by thermal blanketing of an initially overthickened crust the ascent of large bodies of leucocratic magmas may have increased the geothermal gradient which allowed for upper more radiogenic crust to be melted

high density macroseismic survey in urban areas part 2 results for the city of rome italy high density macroseismic surveys were carried out in rome following both the 14 october 1997 m w 5 6 i 0 viii mcs and the 26 march 1998 m w 5 3 i 0 vi vii mcs umbria marche central italy earthquakes the aim of the work was to investigate the relationship between intensity and local geology for the modern urban area of rome an issue yet to be examined in contemporary times intensity data for both earthquakes were correlated with near surface geology the results show a statistically significant amplification in holocene alluvial deposits in particular we found one degree of difference in mcs intensity between hard rock and recent alluvium formations furthermore the distribution of the earthquake effects in alluvium filled valleys was studied as a function of the shape ratio h l of the alluvial basins in the tiber river valley higher effects were found to be concentrated within a 150 m wide band along the bedrock alluvium surface contact suggesting the occurrence of an edge effect surprising results were observed in the minor alluvial valleys which displayed the strongest effects in terms of shaking the narrowest valleys width

seismic potential associated with subduction in the northwestern united states despite good evidence of present day convergence of the juan de fuca and north american plates there has been remarkably little historical seismic activity along the shallow part of the juan de fuca subduction zone although we cannot completely rule out the possibility that the plate motion is being accommodated by aseismic creep we find that the juan de fuca subduction zone shares many features with other subduction zones that have experienced great earthquakes

paleoseismicity of the cascadia subduction zone evidence from turbidites off the oregon washington margin cores from cascadia deep sea channel contain sequences of turbidites that can be correlated and dated by the first occurrence of volcanic glass from the mount mazama eruption 6845 50 radiocarbon yrbp turbidity currents from the tributaries appear to have occurred synchronously to form single deposits in the main channel there being only 13 turbidite deposits in the lower main channel since the mazama eruption instead of the twice as many expected if the tributaries had behaved independently in addition to the cascadia channel 13 post mazama turbidites have been deposited in the astoria canyon and at two sites off cape blanco sample locations that span 580 km of the oregon washington margin pelagic intervals deposited between the turbidites suggest that in each place the turbidity currents occurred fairly regularly every 590 170 years on average the best explanation of the spatial and temporal extent of the data is that the turbidity currents were triggered by 13 great earthquakes on the cascadia subduction zone the variability of turbidite timing is similar to that for great earthquake cycles the thickness of the topmost pelagic layer suggests the last event was 300 60 years ago from three places along the margin but this number may be a biased underestimate it is however consistent with the youngest sudden subsidence event on the washington coast the turbidite data demonstrate that the near term hazard of a great earthquake on the cascadia subduction zone is of the order of 2 10 in the next 50 years

an overview of local site effects and the associated building damage in adapazari during the 17 august 1999 izmit earthquake two major earthquakes occurred in turkey along the north anatolian fault in 1999 the first one which occurred on 17 august 1999 had a moment magnitude of 7 4 and ruptured the 140 km segment of the fault in the marmara region adapazari a city with a population of 190 000 which is mostly located on a deep alluvial basin in the near field of the ruptured fault was among the worst affected urban areas in the earthquake affected region the distribution of damage over the city was highly nonuniform indicating the variability of the ground response to the strong motion five to six story buildings located over deep alluvial soils were most adversely affected by the earthquake geotechnical characteristics of the alluvial basin of adapazari are evaluated using the deep and shallow borehole logs and the measured parameters from the field and laboratory this data is used for developing representative one dimensional site response models for various depths of alluvium and for liquefaction assessment in saturated surface soils recorded data from several aftershocks are utilized for model calibration the results of soil response studies are found to be highly correlated with the general trends in the intensity and distribution of building damage based on in situ tests soil liquefaction is determined to have occurred extensively in adapazari which is in conformity with the postearthquake observations of widespread liquefaction induced foundation displacements evidently liquefied soil layers served as passive isolation mechanism for numerous buildings some of which were subjected to excessive foundation displacements of various forms without signs of significant structural damage manuscript received 30 august 2000

source parameters of the 1949 magnitude 7 1 south puget sound washington earthquake as determined from long period body waves and strong ground motions teleseismic p sh and sv first motions and sh to sv amplitude ratios recorded at eight teleseismic receivers from the 1949 magnitude 7 1 olympia washington earthquake in combination with data from three stations at regional distances were utilized in a grid testing routine to constrain focal mechanism identification of the pp phase places the event at 54 km depth distinct pulses assumed to be source effects are observed in the far field waveforms analysis of these pulses for directivity made possible discrimination between the fault and auxiliary planes the plane taken to represent the fault surface strikes east west 15 dips 45 15 to the north and has nearly pure left lateral slip the preferred source model has an eastward propagation of 40 km surface reflections of successive source pulses suggest an upward component of propagation of 5 km bounds on the earthquake location and rupture of the 13 april event were determined using depth and source mechanism constraints from the teleseismic study and characteristics of local strong ground motion recordings the 9 sec s instrument trigger time seen in the seattle acceleration recordings places the event at least 60 km from seattle strong motion velocity at the olympia highway test laboratory is characterized by an impulsive and rectilinear s wave the low amplitude of the vertical component of initial s motion suggests that either the epicenter is within 5 km of the olympia highway test laboratory for a pure incident sv wave or located along an azimuth of n159 if the wave is sh the combined constraint of minimum distance from seattle and the s polarization angle implied by the teleseismic data focal mechanism places the initiation of rupture 5 to 10 km north to north northwest of the olympia highway test laboratory at 47 13 n 122 95 w this is approximately 20 km west of previously determined epicenters the t axis gently dipping to the southeast supports other evidence that the juan de fuca plate dips to the southeast in a zone between segments of the plate north and south of the event s location the fault plane s slip is taken to indicate that subduction is still active beneath washington and that motion of the two segments is probably independent

distribution of ground motion intensity inferred from questionnaire survey earthquake recordings and microtremor measurements a case study in christchurch new zealand during the 1994 arthurs pass earthquake the areal distribution of seismic ground motion intensity in the city of christchurch new zealand during the 1994 arthurs pass earthquake ml 6 6 was evaluated using an intensity questionnaire together with local site amplifications inferred from seismic recordings and microtremors in order to estimate the intensity in parts of the city where no intensity data were available intensity data were compared to relative levels of shaking determined from both weak motion and microtremor recordings weak ground motion amplification factors were determined using ratios of ground accelerations at five sediment sites with respect to a rock site microtremor amplification factors were determined from horizontal to vertical spectral ratios at a 1 km spacing throughout the city a positive correlation between weak motion and microtremor amplification factors allowed extrapolation of microtremor amplification to estimated mm intensity emmi emmi ranged from 3 to 6 and was consistent with the questionnaire intensity and geological conditions and showed detailed information on the areal distribution of ground motion intensity in the city

experimental deformation of two component irm in magnetite bearing limestone a model for the behaviour of nrm during natural deformation abstract experimental room temperature triaxial deformation at 200 mpa 2 kbar and at a controlled strain rate of 10 5 s 1 is performed on three limestones with magnetic behaviour dominated by single domain magnetite permanent deformation is achieved mainly by twinning of calcite isothermal remanent magnetisation irm in the samples is reduced in magnitude especially when parallel to compressive stress the decrease in magnitude correlates slightly better with peak stress than with strain in accord with previous work in uniaxial tests indicating the role of stress in deformational demagnetisation remanences have their vector plots condensed after deformation particularly in the range 0 30 mt a two component irm is used as a simple model of a multi component natural remanent magnetisation nrm the resultant vector is deflected by the action of stress towards whichever components are least reduced by deformation in the case of magnetite bearing rocks this appears to be the most coercive components in the case of a natural deformation it is predicted that the effects of stress at any stage should be to remove progressively any low coercivity components added to an nrm by remagnetisation during tectonism especially those parallel to compressive stress

an assessment of the megathrust earthquake potential of the cascadia subduction zone the active tectonic setting of the southwest coast of canada and the pacific northwest coast of the united states is dominated by the cascadia subduction zone the zone can be divided into four segments where oceanic lithosphere is converging independently with the north american plate the winona and the explorer segments in the north the larger juan de fuca segment that extends into both canada and the united states and the gorda segment in the south the oceanic lithosphere entering the cascadia subduction zone in all segments is extremely young less than 10 ma of the other six zones around the pacific where young 20 ma lithosphere is being subducted five have had major thrust earthquakes megathrust events on the subduction interface in historic time an estimation based on potential area of rupture gives maximum possible earthquake magnitudes along the cascadia subducting margin of 8 2 for the winona segment 8 5 for the explorer segment 9 1 for the juan de fuca segment and 8 3 for the so

site response for urban los angeles using aftershocks of the northridge earthquake ground motion records from aftershocks of the 1994 northridge earthquake are used to estimate site response in the urban los angeles area over 1300 shear wave records from 61 sources and 90 sites are used in a linear inversion for source and site response spectra the methodology makes no assumptions about the shape of the source spectrum to obtain a stable unique inverse a q model and geometrical spreading factor are assumed in addition the site response at a hard rock site is constrained to be approximately 1 0 with a kappa of 0 02 the site response spectra compare favorably with the results of previous and on going investigations in los angeles a couple of first order effects are lower site response in the surrounding mountains dominated by mesozoic and tertiary rocks and higher values in the san fernando and los angeles basins containing surficial pleistocene and holocene alluvial deposits results show good correlation of high site response spectral values with localized areas of severe damage interstate 10 collapse sherman oaks northridge interstate 5 14 collapse however widespread trends in site response across the sedimentary basins are not obvious the data suggest that site responses are lower near the southern margin of the san fernando valley for sources to the north due to north dipping sedimentary structures but the general pattern of site response is characterized by high variability on length scales less than a kilometer variations of a factor of 2 in site response are observed over the length scale of 200 m and for the same surficial geologic unit for some of the alluvial basin sites surface wave generation is a significant contributor to elevated site response at lower frequencies below 2 hz the total damage pattern for the northridge earthquake is influenced by strong source directivity to the north and strong local site effects the correlation of weak motion site response estimates with areas of significant damage demonstrates the value of these field measurements in future urban planning and in the reduction of seismic risk in urban areas

uncertainty of linear earthquake site amplification via bayesian inversion of surface seismic data abstractwe examine uncertainty in predicted linear 1d site amplification due to uncertainty in shear wave velocity vs structure quantified from bayesian probabilistic inversion of microtremor array dispersion data based on a sample of vs profiles drawn from the posterior probability density of the microtremor inversion probability distributions are computed for common predictors of site amplification including vsz traveltime average vs to a depth z and amplification spectra based on seismic impedance variations and full transverse shear wave effects these methods are applicable for any site but the resulting probabilistic site amplification analyses are specific to the two sediment sites studied here with strongly contrasting geology in high population centers of british columbia canada the site amplification probability distributions for the two sites are shown to be more informative than amplification estimated for a single best fit vs profile by characterizing the uncertainty and therefore

magnetic hysteresis of limestones facies control abstract the hysteresis properties of 116 non red marine limestones from 92 localities indicate that remanence is carried by magnetite of pseudo single domain psd and small multidomain md size pelagic limestones have paramagnetic matrices and hysteresis properties compatible with larger psd or md grain sizes of magnetite probably associated with detrital clay minerals introduced by pelagic rain out thus they may be less suitable recorders of stable remanence other limestone facies excepting dolomitized examples have diamagnetic matrices they include shallow subtidal limestones which tend to have smaller psd sizes of magnetite as do backreef lagoonal undifferentiated shelf and reef facies it is believed that the wide geographical and temporal range of samples minimizes effects related to post compaction groundwater flow late diagenesis and that the associations recognized should be tested in future studies

bayesian inversion of microtremor array dispersion data in southwestern british columbia summary this paper applies bayesian inversion with evaluation of data errors and model parametrization to produce the most probable shear wave velocity profile together with quantitative uncertainty estimates from microtremor array dispersion data generally the most important property for characterizing earthquake site response is the shear wave velocity vs profile the microtremor array method determines phase velocity dispersion of rayleigh surface waves from multi instrument recordings of urban noise inversion of dispersion curves for vs structure is a non unique and non linear problem such that meaningful evaluation of confidence intervals is required quantitative uncertainty estimation requires not only a non linear inversion approach that samples models proportional to their probability but also rigorous estimation of the data error statistics and an appropriate model parametrization this paper applies a bayesian formulation that represents the solution of the inverse problem in terms of the posterior probability density ppd of the geophysical model parameters markov chain monte carlo methods are used with an efficient implementation of metropolis hastings sampling to provide an unbiased sample from the ppd to compute parameter uncertainties and inter relationships nonparametric estimation of a data error covariance matrix from residual analysis is applied with rigorous a posteriori statistical tests to validate the covariance estimate and the assumption of a gaussian error distribution the most appropriate model parametrization is determined using the bayesian information criterion which provides the simplest model consistent with the resolving power of the data parametrizations considered vary in the number of layers and include layers with uniform linear and power law gradients parameter uncertainties are found to be underestimated when data error correlations are neglected and when compressional wave velocity and or density nuisance parameters are fixed in the inversion bayesian inversion of microtremor array data is applied at two sites in british columbia the area of highest seismic risk in canada to study the ability to recover an accurate vs profile in relatively deep and shallow geological settings on the fraser river delta in greater vancouver and in victoria respectively a well resolved vs profile to at least 110 m depth is determined at the fraser river delta site for a power law gradient parametrization at the victoria site a layer with low vs and a weak linear gradient is indicated to 15 18 m depth above much higher velocity material invasive vs measurements from seismic cone penetration testing and or surface to downhole methods are used to assess the reliability of the bayesian microtremor inversion results with excellent agreement obtained at both sites

transport and accumulation of river derived sediment on the washington continental shelf usa the combined results of many physical oceanographic geochemical and geological investigations provide a coherent picture of the sedimentology of the washington continental shelf the major source of modern sediment is the columbia river sediment on the shelf is transported by bottom currents resulting from surface wind stress and gravity waves which occur as individual storm or wave events lasting one to several days primarily during the winter months field measurements of the sediment response to wind and wave generated bottom currents suggest that the modern sediment is transported as suspended load and disperses primarily northward parallel to the isobaths and is associated with a well developed mid shelf silt deposit smaller quantities of sediment are transported seaward over the shelf edge and into the numerous submarine canyons that incise the shelf analysis of available wave data suggests that thresholds of sediment motion were exceeded on the order of 22 16 and 1 5 of the time annually on the inner central and outer shelf respectively bottom current measurements suggest that threshold conditions were exceeded 13 and 6 of the time annually on the inner and central shelf respectively measurements of accumulation rates using 210 pb geochronology show that about 67 of the annual sediment discharge from the columbia river is being deposited in the mid shelf silt deposit 6 is being deposited over the shelf edge on the open slope and 11 is accumulating in the four major submarine canyons

accumulation of modern sediment in quinault submarine canyon abstract twenty box cores have been studied from quinault submarine canyon a major pathway between the washington continental shelf and the deep sea for silt and clay originating from the columbia river sediment accumulation rates on a 100 yr time scale are calculated from profiles of excess 210pb and of 137cs accumulation rates decrease with increasing distance downcanyon from 14 10 2 g cm 2 yr 1 in the upper canyon lower head to 3 10 2 g cm 2 yr 1 in the lower canyon in the upper canyon lower head channel floor areas have a higher mean accumulation rate 12 10 2 g cm 2 yr 1 than channel wall areas 5 10 2 g cm 2 yr 1 the difference in accumulation rate between channel floor and channel wall areas indicates preferential accumulation i e focusing in topographic lows the decrease in accumulation rate from high rates in the channel floors of the upper canyon to low rates in the lower canyon may be caused by progressive depletion of a nepheloid layer source and or may be an artifact of sediment focusing in the upper canyon the silty clay and clayey silt accumulating in the canyon show no significant trend in grain size or clay mineralogy with depth in cores or with distance downcanyon the lack of sorting probably results from the transport of sediment in aggregate form with a nearly random distribution of size and mineralogy within aggregates quinault canyon is accumulating approximately 5 5 10 5 mt of sediment yr 1 the lithogenic component 64 accounts for 1 4 of the columbia river discharge similarity of sediment trap deposition rates including storm events and 210pb accumulation rates indicates that the vertical flux is a major input of sediment to quinault canyon and that storms are important in the accumulation of sediment on a 100 yr time scale

validation of the intensity based source inversions of three destructive california earthquakes the objective of our work is to invert the intensities of preinstrumental destructive earthquakes to retrieve their principal source characteristics this is relevant in countries as italy and greece where a large and high quality data bank of earthquake intensities during the past few centuries exists we have previously validated our technique presented in this journal for the m l 5 9 1987 whittier narrows earthquake and here we demonstrate that our algorithm works on three other earthquakes with known sources three more validations of the algorithm are presented here by using the site intensities observed by the u s geological survey for the m 6 4 1983 coalinga the m s 7 1 1989 loma prieta and the m w 6 7 1994 northridge earthquakes our simplified kf formula simulates the body wave radiation from a linear source and 11 source parameters are retrieved the three nucleation coordinates the fault plane solution the seismic moment the rupture velocities the along strike and antistrike rupture lengths and the shear wave velocity in the half space to find the minima on the hypersurface of the residuals in the multiparameter model space we use a genetic process with niching niching genetic algorithm because we have already shown that the problem is bimodal for pure dip slip mechanisms the objective function of the nonlinear inversion is the sum of the squared residuals calculated minus observed intensity at all sites the three tests presented here were successful because the results agreed with the sources already known from instrumental measurements a very accurate solution was found for loma prieta notwithstanding the complexity of its source in the two other cases sources close to the reference ones were retrieved the quality of our source determinations are obviously lower than those of instrumentally based models but would be highly noteworthy for earthquakes without seismological recordings the potential of the kf inversions seems particularly promising for european countries where seismicity rates are not very high and where a lot of information on earthquake damage is available for preinstrumental earthquakes the present series of validations raises our hope that further information on historic seismic events can be obtained from intensities thus increasing the knowledge of seismotectonics and seismic hazard

a comparative ground response study near los angeles using recordings of nevada nuclear tests and the 1971 san fernando earthquake a comparative ground response study at sites in the los angeles region is based on the extensive strong motion data set recorded in the 1971 san fernando earthquake and 159 three component recordings of distant nuclear tests in nevada amplitude spectral ratios computed for the nuclear test data over those frequency bands for which there is an adequate signal to noise ratio provide statistically stable estimates of the local ground response related to the type of local geologic conditions comparison of the strong motion data recorded from the 1971 san fernando earthquake with that recorded at 28 of the same sites for the nuclear tests show that the corresponding amplitude spectral ratios are statistically equivalent for most sites provided reference stations are chosen to minimize effects on the earthquake data of azimuthal source variations and crustal propagation path statistical equivalence of the spectral ratios for the two types of data sources suggests that amplitude spectral ratios computed with respect to the appropriate reference station provide a first order estimate of local ground response

mid cretaceous transtension in the canadian cordillera evidence from the rocky ridge volcanics of the skeena group the age relations geochemistry and sedimentology of the rocky ridge formation of the skeena group are used to test competing tectonic reconstructions for the mid cretaceous canadian cordillera as well as the timing and location of the accretion of the insular superterrane pollen and macrofossil assemblages indicate that these intrabasinal basalts were erupted along the southern margin of the bowser basin in the early albian to early cenomanian single crystal fusion and step heating 40ar 39ar dating of hornblendes in one basalt flow from the uppermost part of the formation yielded middle cenomanian ages of 94 3 0 4 95 6 1 6 and 95 0 1 6 ma vesicular basalt flows interbedded with crystal rich tuff breccias contain evidence for hot emplacement as pyroclastic flows individual eruptive centers are identified by their proximal facies paleoflow indicators within the lava flows paleoflow indicators within interbedded volcaniclastic fluvial deposits geochemical differences and geographic isolation of volcanic deposits major and trace element geochemistry from 20 sampled lava flows indicates an alkali basalt composition for the volcanics the basalts of the northern rocky ridge volcanic center show enrichment of light rare earth and large ion lithophile elements with strong negative nb ta anomalies whereas the basalts of the southern tahtsa lake volcanic center show depletion to slight enrichment of light rare earth elements slight enrichment of large ion lithophile elements with minimal negative nb ta anomalies the geochemistry combined with paleogeographic and regional tectonic reconstruction suggests a continental arc setting with intraarc extension the presence of deeper marine facies to the west and the lack of a western sediment source in the skeena group indicate that the technically active insular superterrane was not west of the study area during mid cretaceous time thus we reconsider the omineca belt as the main axis of a mid cretaceous continental arc placing the intermontane superterrane in the intraarc to forearc position with the rocky ridge volcanics erupted along the forearc side of the omineca arc coeval regional strike slip faulting and reconstructed oblique plate convergence suggest a transtensional setting for rocky ridge intraarc extension an electronic supplement of tables a1 a2 may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type exit to leave the system paper 95tc03496 mid cretaceous transtension in the canadian cordillera evidence from the rocky ridge volcanics of the skeena group kari n bassett and karen l kleinspehn diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

comparing intensity variation of the 2001 nisqually earthquake with geology in victoria british columbia this article compares the variation in observed intensity of the 2001 m w 6 8 nisqually washington earthquake in victoria british columbia 150 km from the epicenter with amplification hazard predictions based on the average shear wave velocity of geologic units modified mercalli intensities were assigned from 750 felt reports collected by online web submission augmented by door to door canvassing in regions of particular interest an intensity map was created based on high resolution sub city block georeferencing with the canadian postal code system site specific comparisons of earthquake intensity and geology indicate significant differences in observed felt effects between high and low shear wave velocity substrates bedrock and glacial till versus soft clay and peat overall the observed intensity map for weak levels of shaking supports the assignment of amplification hazard based on shear wave velocities across greater victoria

87 sr 86 sr and 18 o 16 o isotopic systematics and geochemistry of granitoid plutons across a steeply dipping boundary between contrasting lithospheric blocks in western idaho a spatially abrupt geochemical boundary is preserved within four plutonic complexes along the western margin of the cretaceous idaho batholith near mccall idaho these intrusives ranging in composition from tonalite to granite were emplaced across a regional boundary between accreted oceanic arc terranes and the continental margin and their isotopic major element and trace element geochemistry provide detailed information about this change in crustal characteristics at depth indicating that the boundary is nearly vertical and extends deep into the lithosphere the hazard creek complex emplaced west of the transition in wall rock lithology has initial 87sr 86sr ri less than 0 7045 and 18o greater than 7 5 indicating little or no continental crust in its source region however elevated 18o requires some incorporation of rocks formed or altered at the earth s surface a large shift in ri and 18o is observed across the 5 8 km wide little goose creek complex which was emplaced across the wall rock boundary this is interpreted as mixing between 1 a basaltic or andesitic magma with low k2o and high na2o al2o3 and sr similar to that forming the hazard creek complex and 2 materials similar to precambrian sedimentary sedimentary rocks with low sr high 18o 15 and high ri 0 83 at 100 ma the payette river complex emplaced east of the wall rock boundary exhibits at least one additional component with low 18o 6 moderate ri 0 708 and mafic composition this component is inferred to be old basaltic material in the lower crust or upper mantle similar to that inferred to be a minor part of the peninsular ranges batholith in se california silver et al 1979 hill et al 1986 the easternmost complex in the idaho transect is made up of granites that may contain a component of granitic cratonal basement the entire west to east geochemical transition from oceanic arc magmas to cratonal magmas takes place over a lateral distance of less than 20 km although the zone of transitional protolith dominated by metasedimentary rocks is unusually narrow and may have been in part tectonically removed the striking geochemical similarities between this traverse and several other transects across much broader areas of nevada and california suggest that the craton itself was not rifted apart but that juxtaposition of the accreted oceanic arc terranes occurred along the preexisting craton margin the data confirm that the isotopic geochemistry of granitoid plutons can be used as a probe of deep lithospheric character and that major lateral variations in the lithosphere on the order of one to two kilometers in width can be recognized in favorable circumstances

what is a reference site many methods for estimating site response compare ground motions at sites of interest to a nearby rock site that is considered a reference motion the critical assumption in these methods is that the surface rock site record reference is equivalent to the input motion at the base of the soil layers data collected in this study show that surface rock sites can have a site response of their own which could lead to an underestimation of the seismic hazard when these sites are used as reference sites data were collected from local and regional earthquakes on digital recorders both at the surface and in boreholes at two rock sites and one basin site in the san jacinto mountains southern california the two rock sites keenwild and pinon flat are located on granitic bedrock of the southern california peninsular ranges batholith the basin site garner valley is an ancestral lake bed with watersaturated sediments on top of a section of decomposed granite which overlies the competent bedrock ground motion is recorded simultaneously at the surface and in the bedrock at all three sites when the surface rock sites are used as the reference site i e the surface rock motion is used as the input to the basin the computed amplification underestimates the actual amplification at the basin site for frequencies above 2 to 5 hz this underestimation by a factor of 2 to 4 depending on frequency and site results from the rock sites having a site response of their own above the 2 to 5 hz frequencies the near surface weathering and cracking of the bedrock affects the recorded ground motions at frequencies of engineering interest even at sites that appear to be located on competent crystalline rock the bedrock borehole ground motion can be used as the reference motion but the effect of the downgoing wave field and the resulting destructive interference must be considered this destructive interference may produce pseudo resonances in the spectral amplification estimates if one is careful the bedrock borehole ground motion can be considered a good reference site for seismic hazard analysis even at distances as large as 20 km from the soil site

site effect evaluation using spectral ratios with only one station the spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity the purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station the technique originally proposed by nakamura to analyze rayleigh waves in the microtremor records is presented briefly and it is discussed why it may be applicable to study the intense s wave part in earthquake records results are presented for three different cities in mexico oaxaca oax acapulco gro and mexico city these cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city each time we compare the results of nakamura s technique with standard spectral ratios in all three cases the results are very encouraging we conclude that if site effects are caused by simple geology a first estimate of dominant period and local amplification level can be obtained using records of only one station

site effects and microzonation in the city of thessaloniki greece comparison of different approaches ten seismological stations were installed for 3 months in the city of thessaloniki greece to record earthquakes and ambient noise over areas of different geotechnical characteristics about 40 local earthquakes were recorded with a good signal to noise ratio in more than two stations we analyze the records with three different techniques a the classical spectral ratios to a reference station b the receiver functions and c the horizontal to vertical h v spectral ratios on noise recordings the results are compared in terms of predominant frequencies and amplification levels the three methods are found equally able to reveal the fundamental frequency regarding local site amplification they provide significantly different results with a general trend of the two h v ratio methods b and c to underestimate the amplification levels compared to that inferred from the classical spectral ratio technique a the results are then used in relation with the microzonation of the city of thessaloniki a good correlation is found between the local site amplification and the type and age of the local geological formation as well as with the depth of bedrock finally we compare our observations with the damage distribution in the city which was hit by a magnitude 6 5 earthquake in 1978 the amplification levels from spectral ratios obtained at each site exhibit a good agreement with the map of damage intensity

spatial temporal patterns of seismic tremors in northern cascadia 1 we study in detail the two consecutive episodic tremor and slip ets events that occurred in the northern cascadia subduction zone during 2003 and 2004 for both sequences the newly developed source scanning algorithm ssa is applied to seismic waveform data from a dense regional seismograph array to determine the precise locations and origin times of seismic tremors in map view the majority of the tremors occurred in a limited band bounded approximately by the surface projections of the 30 km and 50 km depth contours of the plate interface the horizontal migration of tremor occurrence is from southeast to northwest with an average speed of 5 km d in cross section tremors in both sequences span a depth range of over 40 km across the interface with the majority occurring in the overriding continental crust in particular 50 55 of them are located within 2 5 km from the strong seismic reflector bands above the plate interface the lack of vertical migration implies that a slow diffusion process in the vertical direction cannot be responsible for tremor occurrences the source spectra of tremors clearly lack high frequency content 5 hz relative to local earthquakes we propose two possible models to explain the relationship between slip and tremors the first one regards ets tremors as the manifestation of hydroseismogenic processes in response to the temporal strain variation associated with the episodic slip along the lower portion of the plate interface downdip from the locked zone in the second model tremors and slip are associated with the same process along the same structure in a distributed deformation zone across the plate interface neither model can be dismissed conclusively at this stage

site amplification in the san fernando valley california variability of site effect estimation using the s wave coda and h v methods during the months that followed the 17 january 1994 m 6 7 northridge california earthquake portable digital seismic stations were deployed in the san fernando basin to record aftershock data and estimate site amplification factors this study analyzes data recorded on 31 three component stations from 38 aftershocks ranging from m 3 0 to m 5 1 and depths from 0 2 to 19 km site responses from the 31 stations are estimated from coda waves s waves and ratios of horizontal to vertical h v recordings for the coda and the s waves site response is estimated using both direct spectral ratios and a generalized inversion scheme results from the inversions indicate that the effect of qs can be significant especially at high frequencies site amplifications estimated from the coda of the vertical and horizontal components can be significantly different from each other depending on the choice of the reference site the difference is reduced when an average of six rock sites is used as a reference site in addition when using this multi reference site the coda amplification from rock sites is usually within a factor of 2 of the amplification determined from the direct spectral ratios and the inversion of the s waves however for nonrock sites the coda amplification can be larger by a factor of 2 or more when compared with the amplification estimated from the direct spectral ratios and the inversion of the s waves the h v method for estimating site response is found to extract the same predominant peaks as the direct spectral ratio and the inversion methods the amplifications determined from the hiv method are however different from the amplifications determined from the other methods finally the stations were grouped into classes based on two different classifications general geology and a more detailed classification using a quaternary geology map for the los angeles and san fernando areas average site response estimates using the site characterization based on the detailed geology show better correlation between amplification and surface geology than the general geology classification

spectral amplification in a sediment filled valley exhibiting clear basin edge induced waves various site response estimates are presented for a linear array deployed in the coachella valley california during the 1992 landers big bear aftershock sequence this systematic comparison is unique in that the response of the site is clearly dominated by basin edge induced waves average sediment to bedrock spectral ratios for long s wave windows which include the basin edge induced waves exhibit amplification factors as high as 18 below 7 hz the deep basin structure which gives rise to the obvious multi dimensional effects produces a fundamental resonant peak that shifts between basin sites from 0 23 to 0 48 hz as the depth to bedrock changes above 0 6 hz where the largest amplifications occur the response is remarkably similar between sites and appears to be dominated by a near surface layer that is relatively uniform across the valley the apparent fundamental resonant frequency of this layer is between 0 8 and 1 hz sediment to bedrock spectral ratios computed using shorter windows that exclude the basin edge induced waves imply that the multi dimensional effects are significant only below 4 hz where they increase amplifications by an approximate factor of 2 spectral ratios computed using coda windows taken at twice the s wave travel time exhibit amplifications that are an average factor of 1 7 greater between 1 and 4 hz than those of the s wave estimates this discrepancy does not improve by taking coda windows later at four times the s wave travel time horizontal to vertical component s wave spectral ratios do not agree with the sediment to bedrock ratios however they do exhibit a clear peak at the fundamental resonant frequency of the deep basin structure sediment to bedrock spectral ratios of ambient seismic noise are also inconsistent with the s wave estimates however horizontal to vertical noise ratios exhibit clear peaks near the fundamental resonant frequencies of both the deep basin structure below 0 6 hz and the suspected near surface layer between 0 8 and 1 hz therefore ambient noise data appear to provide valuable constraints on the basin structure ongoing efforts involve multi dimensional modeling of the observed basin edge induced phases and resonant frequencies

geodetic evidence for active landward tilting of the oregon and washington coastal ranges nine leveling routes that extend inland from near the coast of oregon and washington indicate consistent landward tilting of the 600 km long coastal ranges at about 3 10 8 rad yr 1 analysis of tide gauge observations indicates tilting with roughly the same magnitude and sense as the leveling measurements these short term tilt rates 10 80 yr are comparable with longer term rates 100 000 yr deduced from tilted marine terraces contemporary landward tilting is interpreted to result from continuing subduction of the juan de fuca plate beneath north america the similarity between long and short term deformation suggests that present day subduction is occurring via aseismic creep as hypothesized by ando and balazs 1979 however recent measurements of horizontal deformation in northwest washington which have been interpreted to indicate elastic strain accumulation appear to be incompatible with aseismic subduction additional releveling observations along the oregon routes last observed in 1941 and further studies of late pleistocene deformation along the coastal region of oregon and washington could help determine present day tectonics and assess the risk of large thrust earthquakes in this area

paleothermometry of the sydney basin evidence from overprinting of magnetizations of late permian and mesozoic rocks and from the rank of permian coals and mesozoic phytoclasts coal particles suggests that surface rocks in the sydney basin eastern australia have been raised to temperatures of the order of 200 sup 0 c or higher as vitrinite reflectance an index of coal rank or coalification is postulated to vary predictably with temperature and time estimates of the paleotemperatures in the sydney basin based on observed vitrinite reflectance measurements can be made in conjunction with reasonable assumptions about the tectonic and thermal histories of the basin these estimates give maximum paleotemperatures of present day surface rocks in the range 60 249 sup 0 c depending on factors such as location in the basin the thickness of the sediment eroded and the maximum paleogeothermal gradient higher coal rank and consequently larger eroded thicknesses and paleogeothermal gradients occur along the eastern edge of the basin and may be related to seafloor spreading in the tasman sea on the basin s eastern margin a theory of thermal activation of magnetization entailing the dependence of magnetic viscosity on the size distribution of the magnetic grains is used to obtain an independent estimate of the maximum paleotemperaturesmore in the sydney basin this estimate places the maximum paleotemperature in the range 250 300 sup 0 c along the coastal region both coalification and thermal activation of magnetization models provide strong evidence of elevated paleotemperatures which in places exceed 200 sup 0 c and the loss of sediment thicknesses in excess of 1 km due to erosion less

increased marine sediment suspension and fluxes following an earthquake earthquakes are commonly cited as one possible triggering mechanism for turbidity flows dense sediment water plumes that can transport large volumes of sediment great distances down slope in both marine and lacustrine settings1 2 3 4 5 6 heezen and ewing1 were the first to make such a suggestion attributing breaks in a sea floor telephone cable in the north atlantic ocean to turbidity flows generated by the 1929 grand banks earthquake anumber of workers have consequently used sedimentary turbidite records to reconstruct the earthquake histories of various regions2 7 8 here we present direct observations of a seismically induced turbidity flow measurements of light scattering and sediment fluxes in the cariaco basin indicate that the earthquake that occurred along the coast of northern venezuela on 9 july 1997 resulted in considerable downslope displacement of sediments probably 105 tonnes into the deep part of the basin in such a seismically active region this mechanism of sediment transport may be responsible for a significant component of the long term sediment accumulation in the basin furthermore this process may result in the sequestration in deep sea sediments of large amounts of carbon initially deposited at shallow depths

source characteristics of hypothetical subduction earthquakes in the northwestern united states historic earthquake sequences on subduction zones that are similar to the cascadia subduction zone are used to hypothesize the nature of shallow subduction earthquakes that might occur in the northwestern united states based on systematic comparisons of several physical characteristics including physiography and seismicity subduction zones that are deemed most similar to the cascadia subduction zone are those in southern chile southwestern japan and colombia these zones have all experienced very large earthquake sequences and if the cascadia subduction zone is also capable of storing elastic strain energy along its greater than 1000 km length then earthquakes of very large size m w 8 1 2 must be considered circumstantial evidence is presented that suggests but does not prove that large subduction earthquakes along the cascadia subduction zone may have an average repeat time of 400 to 500 yr

time and size of a giant earthquake in cascadia inferred from japanese tsunami records of january 1700 geological evidence shows that great earthquakes have occurred in the recent prehistoric past in the cascadia subduction zone off the pacific coast of north america the most recent event or series of events is dated at about 300 years ago1 4 but the precise date and magnitude have not been determined geological investigations have not been able to distinguish a single giant earthquake from a series of great earthquakes occurring over a timespan of a decade or two4 although this information is important for the assessment of future hazard5 we have found several tsunami records in japan from ad 1700 with no indication of a local cause historical earthquake records and palaeoseismic evidence indicate the absence of a large earthquake in 1700 in south america alaska or kamchatka leaving cascadia as the most likely source of this tsunami the estimated time of the earthquake is the evening about 21 00 local time of 26 january 1700 the magnitude is estimated as 9 from the tsunami heights in which case the earthquake ruptured the entire length of the cascadia subduction zone2 these estimates are consistent with native american legends that an earthquake occurred on a winter night6

soil amplification with a strong impedance contrast boston massachusetts abstract in this study we evaluate the effect of strong sediment bedrock impedance contrasts on soil amplification in boston massachusetts for typical sites along the charles and mystic rivers these sites can be characterized by artificial fill overlying marine sediments overlying glacial till and bedrock where the depth to bedrock ranges from 20 to 80 m the marine sediments generally consist of organic silts sand and boston blue clay we chose these sites because they represent typical foundation conditions in the city of boston and the soil conditions are similar to other high impedance contrast environments the sediment bedrock interface in this region results in an impedance ratio on the order of ten which in turn results in a significant amplification of the ground motion using stratigraphic information derived from numerous boreholes across the region paired with geologic and geomorphologic constraints we develop a depth to bedrock model for the greater boston region using shear wave velocity profiles from 30 locations we develop average velocity profiles for sites mapped as artificial fill glaciofluvial deposits and bedrock by pairing the depth to bedrock model with the surficial geology and the average shear wave velocity profiles we can predict soil amplification in boston we compare linear and equivalent linear site response predictions for a soil layer of varying thickness over bedrock and assess the effects of varying the bedrock shear wave velocity vsb and quality factor q in a moderate seismicity region like boston many earthquakes will result in ground motions that can be modeled with linear site response methods we also assess the effect of bedrock depth on soil amplification for a generic soil profile in artificial fill using both linear and equivalent linear site response models finally we assess the accuracy of the model results by comparing the predicted linear site response and observed site response at the northeastern university neu vertical seismometer array during the 2011 m 5 8 mineral virginia earthquake site response at the neu vertical array results in amplification on the order of 10 times at a period between 0 7 0 8 s the results from this study provide evidence that the mean short period and mean intermediate period amplification used in design codes i e from the fa and fv site coefficients may underpredict soil amplification in strong impedance contrast environments such as boston

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

radiocarbon dating of pollen by accelerator mass spectrometry radiocarbon dating of bulk sediments has been the standard method for establishing chronologies in the studies of lake sediment cores which have contributed significantly to our knowledge of late quaternary paleo environments these bulk sediment dates are presumed to be direct ageindicators for the speciments e g pollen or macrofossils which are actually being studied however several recent studies have reinforced long standing apprehensions concerning this presumption in this study we demonstrate for the first time the radiocarbon dating of pollen concentrate samples by accelerator mass spectrometry the dates obtained by this method should provide more reliable radiocarbon chronologies for paleo environmental studies than have been obtainable by bulk sediment dating

attempts to date salt making activity in iron age britain using magnetic inclinations briquetage describes all the ceramic equipment used in extracting sea salt in prehistoric and roman europe it includes semi cylindrical desiccating troughs and the stands supports and clips used to stabilize them over hearths in many cases the baked hearth linings or superstructures are included under briquetage upon first inspection archeomagnetic dating seems inappropriate because the briquetage is broken and disoriented material although the ancient magnetic declination cannot be referred to the present north direction the desiccating troughs acted as water level gauges so that a tilt correction permits one to estimate the archaeoinclination the range of inclinations brackets the age of the saltern use within the last two centuries bc this is compatible with ceramic styles and two radiocarbon ages of charcoal from a supposedly contemporaneous hearth the archeodeclination of 7 95 10 from a contemporary in situ hearth confirms this age range thus we attribute the lincolnshire salterns to late iron age activity the paleosecular variation for southern britain over the last two millennia is sufficiently characteristic in many time periods to permit the use of inclinations alone to bracket ages this requires material with some original horizontal reference e g masonry fragments disrupted sedimentary layers or pot bases