simulation of topography effects on rockfall generated seismic signals application to piton de la fournaise volcano first ever simulation of high frequency rockfall seismic waves using the 3d spectral element method ground motion amplification induced by volcano topography found to be dependent on soil properties and rockfall position simulations and observations successfully compared by means of inter station spectral ratios and hertz theory

seismic site amplification induced by topographic irregularity results of a numerical analysis on 2d synthetic models abstract this study concerns the evaluation of seismic site effects and their relation to the local topographical characteristics of a slope the seismic amplification sa on the free surface is calculated by a numerical model using the finite elements fe method synthetic models by utilized in the fe analysis represent a slope with an inclination ranging from 10 to 41 at the crest and valley of the slope the models were considered horizontal and indefinite the site effects were calculated on the free surface in several nodal points the input motion used in the analysis was a sv seismic wave with variable frequency between 0 5 and 32 hz the seismic site analysis confirmed that in absence of sediments ground motion is more amplified at the upper slope break than in other points of the model in regard to seismic amplification vs the frequency we can affirm that seismic amplification reaches its maxima in the band 4 16 hz and with slope angle value computed at the highest degree it is also clear that a nonlinear seismic amplification response in the crest and valley zone while sa would seem to have a linear response in other zones we propose an empirical method to estimate the sa in the regular slope far from the crest and valley zone

very high rate 10 hz gps seismology for moderate magnitude earthquakes the case of themw6 3 l aquila central italy event accepted for publication in journal of geophysical research copyright 2010 american geophysical union

site amplifications observed in the gubbio basin central italy hints for lateral propagation effects abstract in this study we investigate the site amplification effects observed in the gubbio plain central italy the recordings of 140 local earthquakes 1 2 ml 4 7 observed by two linear arrays installed along the longitudinal and perpendicular basin axis are analyzed both in the time and frequency domains to determine the spatial variation of the local site effects in the basin the time series recorded in the gubbio plain are characterized by locally generated surface waves which cause a significant increase in both ground motion duration and amplitude with respect to a nearby reference station on a rock site in the middle of the basin where the sedimentary cover is thickest ca 600 m the peak ground velocity is amplified on average by a factor of 5 with respect to the reference station installed on rock and the duration is increased by a factor of about 2 the analyses in the frequency domain show that the spectral energy of the basin generated waves is mainly distributed over the range 0 4 2 hz and affects both horizontal and vertical components the site responses estimated by applying two reference site methods show that the overall shape of the amplification functions is similar for the sites located inside the basin with a difference in the amplification levels which can reach values as high as 30 in the middle of the valley amplifications up to a factor of 10 affect the vertical component of ground motion over a broad frequency range for nearly all basin sites with the maximum amplifications occurring at around 1 hz finally although the horizontal to vertical spectral ratios were found to provide a reliable estimation of the fundamental resonance frequency of the site they fail to estimate the shape of the site transfer function

a 500 year long record of tephra falls from redoubt volcano and other volcanoes in upper cook inlet alaska abstract volcanic ash layers preserved in glacial lacustrine sediments at skilak lake on the kenai peninsula of southcentral alaska constitute a record of eruptions at redoubt volcano and other alaskan volcanoes which affected the upper cook inlet area during the last 500 years high resolution magnetic susceptibility profiling delineates similar sequences of tephra layers in several 1 m long lake sediment cores electron microprobe analyses of glass shards from the tephras indicate correlation of some ash layers with known reference tephras from the source volcanoes while other ash layers record previously unknown prehistoric eruptions skilak lake cores contain ash from the historic 1912 katmai eruption the 1902 redoubt eruption and the 1883 mount st augustine eruption as well as prehistoric ash layers erupted from crater peak at mt spurr ca 250 350 years ago from redoubt volcano at ca 300 400 years ago and again at ca 350 450 years ago and a 500 year old ash from mount st augustine still older tephras from redoubt volcano and crater peak at mt spurr are found lower in the cores the cores indicate that volcanoes in the cook inlet area have erupted every 10 35 years during the 20th century and ash falls have occurred at skilak lake at least once every 50 100 years for the last 500 years with redoubt spurr and augustine volcanoes being the most important sources of tephra

seismic response of a hill the example of tarzana california the northridge california earthquake that strongly shook the city of los angeles in january 1994 produced one of the highest ground accelerations ever recorded in an earthquake at a site located on top of a small hill in tarzana about 6 km south of the epicenter the subsequent study of aftershock recordings obtained by a dense seismic array deployed on the hill a few days after the earthquake showed the existence of a strong amplification at stations located at the top of the hill relative to stations near the base spudich et al 1996 resonances and polarization rotations were also observed we investigate in this study the role that the topography of the site played on the observed ground motions and accelerations to this aim we perform numerical simulations and study the response of the three dimensional topography of the site to incident shear waves polarized in different directions the method used is a boundary integral equation scheme in which the green s functions are calculated by the discrete wavenumber method the results obtained show that the topography of the site though quite gentle the hill is less than 20 m high strongly affects the ground motions in the frequency range between 2 and 15 hz many of the observed characteristics of the seismic response at tarzana are explained in part by its topography the consistent amplification of ground motion at and near the top of the hill the directional seismic response of the hill that results in a strong amplification of the ground motion transverse to the direction of elongation of the hill the existence of a fundamental transverse oscillatory resonance mode of the hill at 3 to 5 hz the rotation of the polarization of ground motion and the spatial variation of amplification over the hill at the fundamental resonance mode the seismic response of the topography however does not fully explain the amplitude of the effects observed the three dimensional geological structure of the site must in some way amplify the effect of the topography to produce the observed seismic response in spite of not being as strong as the observed effect the topographic effect of the site is considerable the ground motion is amplified by factors ranging from 30 to 100 at some locations in the frequency range from 2 to 15 hz rapid spatial variations of ground shaking intensities can take place over distance scales of a few tens of meters at high frequency finally the results of the simulation indicate that the topography of the site amplified the large east west accelerations recorded there during the northridge mainshock by 30 to 40

an exact solution for effects of topography on free rayleigh waves an exact solution for the effects of topography on rayleigh wave amplification is presented the solution is obtained by incorporating conformal mapping into complex variable stress functions developed for free rayleigh wave propagation in an elastic half space with a flat upper surface results are presented for free rayleigh wave propagation across isolated symmetric ridges and valleys it is found for wavelengths that are comparable to ridge widths that horizontal rayleigh wave amplitudes are amplified at ridge crests and that vertical amplitudes are strongly reduced near ridge crests relative to horizontal and vertical amplitudes of free rayleigh waves in the flat case horizontal amplitudes are strongly deamplified at valley bottoms relative to those for the flat case for rayleigh wavelengths comparable to valley widths wave amplitudes in the symmetric ridges and valleys asymptotically approach those for the flat case with increased wavelengths increased ridge and valley widths and with horizontal distance from and depth below the isolated ridges and valleys also prograde particle motion is predicted near crests of narrow ridges and near the bottoms of narrow valleys finally application of the theory at two sites known for topographic wave amplification gives a predicted surface wave amplification ratio of 3 80 at the ridge center for a frequency of 1 0 hz at robinwood ridge in northern california and a predicted surface wave amplification ratio of 1 67 at the ridge center for the same frequency at the cedar hill nursery site at tarzana in southern california

sediment evacuation and glacial erosion rates at a small alpine glacier 1 glacial erosion is known to be driven by sliding which occurs in brief episodes in the melt season what is not known is how well this sliding history is reflected in the sediment output from a glacier and to what degree temporary sediment storage in the glacier smoothes the history of sediment production we document sediment evacuation rates for three seasons at bench glacier a small temperate alpine glacier in the chugach range of alaska two lines of evidence suggest that subglacial sediment storage is small strong hysteresis in the relationship between sediment and water discharge argues for sediment exhaustion from the subglacial system on seasonal and flood event timescales uplift of the glacier surface during periods of enhanced basal motion reflects intimate contact of the glacier sole with up glacier inclined stoss slopes of bedrock bumps sediment evacuation rates at bench glacier should therefore closely track glacial erosion rates over annual timescales much of the sediment emerges in a major pulse that closely follows the termination of enhanced sliding each year suggesting that the conduits and well connected cavities that allowed removal of englacial water to terminate sliding also promoted efficient transport of sediment this small glacier efficiently modifies the landscape lowering its bed by 1 2 mm yr while sliding only 1 2 m yr our sparse measurements of instantaneous bed load discharge average 41 of concurrent suspended sediment discharge assuming that half of the suspended load derives from abrasion of subglacially quarried clasts roughly two thirds of the sediment evacuated can be attributed to quarrying

comparison of varve and 14c chronologies from steel lake minnesota usa annually laminated sediments varves offer an effective means of acquiring high quality palaeoenvironmental records however the strength of a varve chronology can be compromised by a number of factors such as missing varves ambiguous laminations and human counting error we assess the quality of a varve chronology for the last three millennia from steel lake minnesota through comparisons with nine ams 14c dates on terrestrial plant macrofossils from the same core these comparisons revealed an overall 8 4 discrepancy primarily because of missing uncountable varves within two stratigraphic intervals characterized by low carbonate concentrations and obscure laminations application of appropriate correction factors to these two intervals results in excellent agreement between the varve and 14c chronologies these results together with other varve studies demonstrate that an independent age determination method such as 14c dating is usually necessary to verify and potentially correct varve chr

turbidite stratigraphy in proglacial lakes deciphering trigger mechanisms using a statistical approach turbidites embedded in lacustrine sediment sequences are commonly used to reconstruct regional flood or earthquake histories a critical step for this method to be successful is that turbidites and their trigger mechanisms are determined unambiguously the latter is particularly challenging for prehistoric proglacial lake records in high seismicity settings where both earthquake generated and flood generated turbidites interrupt the background varved sedimentation this calls for a new method to allow efficient and objective identification and classification of turbidites this study examined turbidites in five long 9 to 17 m sediment cores from eklutna lake a proglacial lake in south central alaska using standard core logging and grain size data a novel statistical approach is presented in which varve thickness distributions were first analyzed to objectively identify the thickest turbidites and distinguish them from background sedimentation for each turbidite a selection of variables were then measured including basal grain size thickness magnetic susceptibility and spectrophotometric variables triggering mechanisms were discriminated by a combination of principal component analysis and clustering and by calibration with historical events using this approach a 2250 year long lake wide event stratigraphy was constructed with 94 prehistoric events including 24 earthquake and 70 flood events basal grain size and thickness variables turn out to be the most effective proxies for discrimination this statistical approach is a powerful and new method to identify turbidites and their triggering mechanisms in long prehistoric sediment records it opens up new prospects for palaeoseismological palaeohydrological and palaeoclimate studies in proglacial lakes worldwide

a seismic hazard scenario in the sikkim himalaya from seismotectonics spectral amplification source parameterization and spectral attenuation laws using strong motion seismometry 1 in this paper we present a seismic hazard map of the indian himalayan state of sikkim lying between nepal and bhutan himalaya in terms of horizontal peak ground accelerations with 10 exceedance probability over the next 50 years these figures the first for the region were calculated through a stepwise process based on 1 an estimation of the maximum credible earthquake mce from the seismicity of the region and global seismic hazard assessment program considerations and 2 four seismotectonic parameters abstracted from accelerograms recorded at nine stations of the sikkim strong motion array specifically installed for this study the latter include 1 the frequency dependent power law for the shear wave quality factor qs 2 the site response function at each station using receiver function analysis and generalized inversion 3 source parameterization of various events recorded by the array and application of the resulting relationships between m0 and mw and corner frequency fc and mw to simulate spectral accelerations due to higher magnitude events corresponding to the estimated mce and 4 abstraction of regional as well as site specific local spectral attenuation laws at different geometrically central frequencies in low moderate and high frequency bands

ground motion in the presence of complex topography ii earthquake sources and 3d simulations abstract eight seismic stations were placed in a linear array with a topographic relief of 222 m over mission peak in the east san francisco bay region for a period of one year to study topographic effects seventy two well recorded local earthquakes are used to calculate spectral amplitude ratios relative to a reference site a well defined fundamental resonance peak is observed with individual station amplitudes following the theoretically predicted progression of larger amplitudes in the upslope direction favored directions of vibration are also seen that are related to the trapping of shear waves within the primary ridge dimensions spectral peaks above the fundamental one are also related to topographic effects but follow a more complex pattern theoretical predictions using a 3d velocity model and accurate topography reproduce many of the general frequency and time domain features of the data shifts in spectral frequencies and amplitude differences however are related to deficiencies of the model and point out the importance of contributing factors including the shear wave velocity under the topographic feature near surface velocity gradients and source parameters electronic supplement figures of recorded and simulated acceleration response spectra and earthquake ground motion directional response

seismological geodetic macroseismic and historical context of the 2016 mw 6 7 tamenglong manipur india earthquake abstract the 2016 mw 6 7 tamenglong earthquake in the state of manipur in northeastern india on 4 january 2016 at 04 35 indian standard time 3 january 23 05 utc was the strongest earthquake to strike manipur since 1988 using data from indian stations we constrain the hypocentral depth of the mainshock at 59 3 8 km and determine a strike slip mechanism with a moderate reverse component on a steeply dipping plane though coseismic offsets from gps measurements from four nearby sites were inadequate to provide further constraints on the focal mechanism they were consistent with the magnitude and hypocentral depth of the earthquake the epicentre of the mainshock was located 15 km west of the churachandpur mao fault cmf but it was unrelated to this structure and was instead a typical intra slab earthquake within the indian plate a strong motion instrument at the loktak power station lok 56 km from the epicentre recorded a peak ground acceleration pga of 0 027g while a pga of 0 103g was recorded at shillong shl at an epicentral distance of 111 km we also present macroseismic observations from 461 locations in north eastern india and the adjacent areas for this earthquake the highest intensities 7 ems were observed in the manipur valley and in the hills to the west while shaking was perceptible as far as delhi and jaipur lastly we present a catalogue of 333 felt earthquakes in manipur from 1588 1 ce to 1955 derived from the royal chronicle of the kings of manipur known as the cheitharon kumpapa discuss important historical earthquakes in the region and also estimate intensity magnitudes for the 1852 mi 6 5 0 8 1869 mi 7 1 0 7 1880 mi 6 3 0 7 and 2016 mi 6 8 0 8 earthquakes

new approach to assessing age uncertainties the 2300 year varve chronology from eklutna lake alaska usa abstract developing robust chronological frameworks of lacustrine sediment is central to reconstructing past environmental changes we present varve chronologies from five sites extending back 2300 years from eklutna lake in the chugach mountains of south central alaska the chronologies are built from image analysis of high resolution photographs and ct scans of sediment cores the age uncertainty of each record is tested by three methods we first present varve chronologies from individual sites and reconcile the difference in varve delimitation from two observers the varve chronologies from each site are then compared to each other using a series of marker beds that can be traced across the lake basin finally using a new bayesian probabilistic model we develop age models that incorporate information regarding age uncertainty from the multiple observer method and the age distribution of marker layers from multiple cores to evaluate the accuracy of the bayesian model output we used seven radiocarbon ages from terrestrial macrofossils and four tephra layers traceable across the core sites the major element geochemistry of the tephra layers and their ages are presented here for the first time the bayesian age model offers a new approach to quantifying age uncertainty in inter correlated cores of varved sediment

the 1883 and late prehistoric eruptions of augustine volcano alaska abstract the eruptive history of augustine volcano has been characterized by cycles of growth and destruction of the volcano repeated failure of 5 10 of the edifice has produced mobile debris avalanches that reached the sea on all sides high lava extrusion rates rapidly restore the volcano to its pre failure configuration this equilibrium between constructive and destructive processes has resulted in a relatively low lava dome complex surrounded by an apron of volcaniclastic debris three times the volume of the dome complex the most recent edifice collapse occurred in 1883 producing the 0 3 km3 burr point debris avalanche deposit three major slide blocks extended the shoreline up to 2 km and produced a tsunami that swept across cook inlet hummock morphologies change from a proximal radial orientation to a dominantly transverse alignment reflecting deceleration and compression of the avalanches as they enter the sea the breached crater formed by collapse was then largely filled by a 0 09 km3 lava dome and a 0 04 km3 lava flow travelled down the north flank lithic block and ash flows and pyroclastic surges reached the coast the burr point avalanche deposit partially overlaps the rocky point debris avalanche deposit to the west that was probably emplaced 200 400 years b p a major collapse event at ca 1540 110 a d produced the west island debris avalanche ending a period of expansion of the western side of the island an accompanying lateral blast overtopped the avalanche covering a 40 sector of the west flank the plinian tephra layer b may also have been erupted at the time of the west island eruption today augustine volcano has rebuilt itself to a size similar to that which preceded the last edifice failure in 1883 the frequency of past collapses three in the last 500 years suggests that summit collapse is a possibility during any future eruption the next major collapse is expected to involve 0 1 0 5 km3 of the summit the ensuing debris avalanche would likely reach the coast producing a tsunami that could impact populated areas of the kenai peninsula the largest tsunami would result from collapse in directions other than to the north or west tsunami magnitude is contingent on failure volume direction and timing with respect to tides

variability in nonlinear sediment response during the 1994 northridge california earthquake abstract spectral ratios between sediment sites and rock sites for strong and weak ground motion are compared to infer the extent of nonlinear sediment response in the los angeles area during the 1994 northridge earthquake northridge mainshock records form the strong motion database and aftershock records form the weak motion database the degree of nonlinearity is evaluated at 25 locations in and around the san fernando and los angeles basins based on the ratio of weak to strong spectral amplification factors wsaf values of wsaf vary greatly from site to site and for a given site from one frequency band to another over the range from 0 75 to 20 hz this complexity is attributed to differences in several factors material properties under the sites and the amplitude and frequency content of the input ground motions given these observations it is not possible to assign an acceleration or velocity level at which nonlinearity initiates for all the stiff soil sites analyzed however no nonlinearity is seen below a peak acceleration of about 200 to 300 cm sec 2 or peak velocity of 20 to 30 cm sec nonlinearity is seen at all sites in or near the san fernando valley nonlinearity in the los angeles basin is limited to a few isolated sites for the northridge earthquake even sites with strong nonlinearity still show amplification levels greater than 1 0 relative to rock sites for frequencies below 10 hz

simulations of ground motion in the los angeles basin based upon the spectral element method we use the spectral element method to simulate ground motion generated by two recent and well recorded small earthquakes in the los angeles basin simulations are performed using a new sedimentary basin model that is constrained by hundreds of petroleum industry well logs and more than 20 000 km of seismic reflection profiles the numerical simulations account for 3d variations of seismic wave speeds and density topography and bathymetry and attenuation simulations for the 9 september 2001 m w 4 2 hollywood earthquake and the 3 september 2002 m w 4 2 yorba linda earthquake demonstrate that the combination of a detailed sedimentary basin model and an accurate numerical technique facilitates the simulation of ground motion at periods of 2 sec and longer inside the basin model and 6 sec and longer in the regional model peak ground displacement velocity and acceleration maps illustrate that significant amplification occurs in the basin

postglacial eruption history of redoubt volcano alaska abstract volcaniclastic deposits preserved in valleys on the flanks of redoubt volcano comprise a record of the volcano s postglacial eruption history the oldest and largest deposit is the harriet point debris avalanche emplaced more than 10 500 yr b p this debris avalanche travelled more than 30 km down the redoubt creek valley to cook inlet about 3600 yr b p a massive slope failure of redoubt volcano produced at least two lahars that travelled 30 km down the crescent river valley riehle et al 1981 a series of smaller eruptions between ca 3600 1800 yr b p generated additional lahars and floods that affected the upper crescent river valley a pyroclastic fan on the south flank of redoubt volcano probably also formed during this time interval sometime between 1000 and 300 yr b p hydrothermally altered debris collapsed from the summit edifice and produced a large lahar that travelled more than 30 km down the drift river valley at least 5 6 eruptions in the last 250 300 years have produced lahars and floods large enough to impact the site of the drift river terminal on the lower drift river fan if the eruptive pattern of the last several centuries continues another eruption is likely sometime in the next 25 100 years the holocene eruptions produced calc alkaline high silica andesite and dacite although quenched andesite and basaltic inclusions record the presence of more mafic magmas chemical discontinuities indicate that small chemically discrete batches of magma fed individual eruptions progressive enrichments of highly incompatible trace elements presumably reflect crustal contamination of holocene magmas

source and propagation effects on near field co eruptive ground motion at santiaguito volcano guatemala abstract data from a december 2008 january 2009 seismometer deployment show substantial variation in seismic signal characteristics among different sites and eruptive events at santiaguito volcano a station on one of the inactive domes typically records higher amplitudes and a more peaked spectrum than does another station closer to the vent on lower ground amplitude ratios between the stations and spectral peakedness of the station on the dome vary substantially and depend on vertical signal polarity which is controlled by seismic source mechanism finite difference models considering two likely source mechanisms and several hypothetical subsurfaces show that the topography of the free surface and subsurface units can increase or decrease amplitudes by focusing or obstructing body waves a homogeneous velocity structure is shown not to be a close approximation to the actual shallow subsurface while a subsurface including a dipping reflective layer produces results that fit observations better these models also indicate that path effects act more strongly on waves originating from an implosion than from a downward force possibly due to differences in body and surface wave proportions and differing susceptibilities of body and surface waves to these path effects thus recorded data and models both indicate that the level of wave field distortion associated with propagation effects is controlled by the source mechanism

zircon growth and ages of migmatites in the algoma type bif hosted iron deposits in qianxi group from eastern hebei province china timing of bif deposition and anatexis abstract algoma type bifs and associated volcanic suites of the qianxi group in eastern hebei province have undergone high grade metamorphism and anatexis the anatectic event is genetically related to high grade magnetite ores but the age of the anatectic melting has not been well constrained we present detailed textural relationship and internal structures of zircon grains and their age data from eight samples of migmatitic rocks representing the different algoma type bif hosted iron deposits to constrain the formation age of bif deposition and subsequent anatexis six continuous zircon growth stages are distinguished by a series of low cl and high cl zones outside from center to edge inherited magmatic zircon bright cl resorption domain dark cl recrystallization front dark gray cl diffusion domain light gray cl overgrowth and bright cl resorption edge the overgrowths are interpreted as a solid state diffusion of zr of primary zircon during interaction with anatectic melt which resulted in different stages of chemical re equilibration of primary domains and local re deposition of newly grown domains on the suitable isostructural substrate of residual magmatic zircon shrimp zircon u pb dating of inherited magmatic cores and discrete magmatic grains constrains the peak bif deposition age at 2520 ma which is different from the peak at 2 75 2 70 ga for algoma type bifs elsewhere in the world zircon u pb dating of light gray cl rims and newly grown homogeneous grains indicates that the anatectic event lasted from 2511 to 2485 ma at least immediately following the bif deposition the bif depositional event is consistent with widespread late neoarchean magmatism and the anatectic event is consistent with regional metamorphic events in the eastern part of the north china craton

distal volcanic impacts on peatlands palaeoecological evidence from alaska abstract despite the fact that volcanic ash tephra layers are found preserved in peat deposits around the world comparatively little research has investigated the impacts of distal volcanic emissions on peatlands this study investigates the impacts of several late holocene volcanic eruptions on five peatlands in southern alaska using a palaeoecological approach testate amoebae analysis peat humification analysis and a basic analysis of plant macrofossil components were applied across 11 tephra layers changes in macrofossil and testate amoebae assemblages occur across several of the tephra layers the humification results were considered unreliable because of a methodological problem a finding which may have implications for other studies using this technique redundancy analyses on testate amoebae data show statistically significant changes associated with two tephras the most likely causes of the impacts are volcanic gases acidic precipitation or tephra derived leachates the finding that some tephras are associated with impacts whereas others are not may relate to the season of the eruption or meteorological conditions at the time of ash fall these results suggest the sensitivity of peatlands and peatland microbial communities to distal volcanic products and imply that changes in key palaeoclimatic proxies may be caused by a mechanism independent of climate change implications of the results for peat based palaeoclimatic studies are discussed as are possible directions for future research

site effect analysis around the seismically induced ananevo rockslide kyrgyzstan in 1911 the surface wave magnitude 8 2 kemin earthquake hit northeastern tien shan kyrgyzstan close to the cities of bishkek and almaty the capitals of kyrgyzstan and kazakhstan respectively several hundreds of people were killed by the earthquake some by indirect effects such as landslides and mudflows a particular but nonfatal landslide triggered by the kemin event was a rockslide in the vicinity of ananevo north of lake issyk kul kyrgyzstan rockslide located above the fault zone activated in 1911 in the summer of 1999 a geophysical seismological field trip was organized to study geology and to record seismic ground motions on and around the ananevo rockslide the work was part of project assessing seismogenic landslide hazard in northern kyrgyzstan based on various case studies of slope failures in connection with site specific ground motion dynamics the geophysical investigations consisted of seismic refraction tests processed as 2d seismic tomographies and surface wave inversion which were combined to build a 3d geophysical model of the landslide site ground motions from small earthquakes were analyzed using several techniques to define site effects over the mountain massif both h v and standard spectral ratios indicated lower dominant frequencies with stronger amplification in the crest region with respect to the mountain slope these effects could be partially simulated by 1d 2d and 3d finite element modeling by comparing the numerical results with the experimental data the presence of a surficial low velocity layer of varying thickness appeared to be the key factor controlling the ground motion around the rockslide

unified structural representation of the southern california crust and upper mantle we present a new 3d description of crust and upper mantle velocity structure in southern california implemented as a unified structural representation usr the usr is comprised of detailed basin velocity descriptions that are based on tens of thousands of direct velocity vp vs measurements and incorporates the locations and displacement of major fault zones that influence basin structure these basin descriptions were used to developed tomographic models of crust and upper mantle velocity and density structure which were subsequently iterated and improved using 3d waveform adjoint tomography a geotechnical layer gtl based on vs30 measurements and consistent with the underlying velocity descriptions was also developed as an optional model component the resulting model provides a detailed description of the structure of the southern california crust and upper mantle that reflects the complex tectonic history of the region the crust thickens eastward as moho depth varies from 10 to 40 km reflecting the transition from oceanic to continental crust deep sedimentary basins and underlying areas of thin crust reflect neogene extensional tectonics overprinted by transpressional deformation and rapid sediment deposition since the late pliocene to illustrate the impact of this complex structure on strong ground motion forecasting we simulate rupture of a proposed m 7 9 earthquake source in the western transverse ranges the results show distinct basin amplification and focusing of energy that reflects crustal structure described by the usr that is not captured by simpler velocity descriptions we anticipate that the usr will be useful for a broad range of simulation and modeling efforts including strong ground motion forecasting dynamic rupture simulations and fault system modeling the usr is available through the southern california earthquake center scec website http www scec org

the little red hill seismic experimental study topographic effects on ground motion at a bedrock dominated mountain edifice the kinematic response of a bedrock dominated mountain edifice to seismic shaking near lake coleridge in the southern alps of new zealand was examined a small elongated and bedrock dominated mountain ridge little red hill was equipped with a seismic array seven earss instruments mark l 4 3d seismometers were installed along the ridge crest the flank and at the base of the 210 m high 500 m wide and 800 m long mountain edifice from february to july 2006 seismic records of local and regional earthquakes were used to provide information on amplification and deamplification effects as well as on the frequency response at different parts on the edifice the ground motion records were analyzed using three different methods comparisons of peak ground accelerations power spectral density analysis and standard spectral ratio analysis time and frequency domain analyses show that site amplification is concentrated along the elongated crest of the edifice where amplifications of up to 1100 were measured relative to the motion at the flat base the field experiment also highlighted the extreme variations in amplification with regard to closely located sites but at contrasting topographic locations theoretical calculations and frequency analyses of field data indicate a maximum response along the ridge crest of little red hill for frequencies of about 5 hz which correlate to wavelengths approximately equal to the half width or height of the edifice the consequence of amplification effects on the stability and degradation of rock masses can be seen areas showing high amplification effects overlap with the spatial distribution of seismically generated block fields at little red hill it is concluded that topography geometry and distance to the seismic source play key roles in causing amplification effects of seismic ground motion and supporting dilation and degradation of rock mass across bedrock dominated mountain edifices

ground motion observations at hotel montana during the m 7 0 2010 haiti earthquake topography or soil amplification unusually severe structural damage was reported during the 2010 m 7 0 haiti earthquake in the vicinity of hotel montana located on top of a ridge in the district of petionville prompted by the observations u s geological survey seismic stations were deployed and aftershock recordings indicated ground motion amplification on the top of the hill compared to adjacent stations on reference site conditions the presence of topographic relief has been shown to significantly aggravate the consequences of strong ground motion during past events and topographic effects were brought forward to explain the observations in this paper we test the hypothesis of topographic amplification as the dominant factor that contributed to the damage concentration in the vicinity of hotel montana we initially conduct numerical simulations of the ridge seismic response assuming elastic homogeneous site conditions and show that numerical predictions of topographic amplification disagree with the field data both in amplitude and in frequency conversely while 1d ground response analyses for the site conditions at the hilltop predict amplification in the same frequency range as the field data they significantly underestimate the recorded amplitude we then conduct numerical simulations of the foothill ridge response to seismic motion while accounting for soil layering and qualitatively demonstrate that the recorded amplification is most likely attributed to coupled site topographic amplification effects namely to seismic waves trapped in the soft soil layers of the near surface amplified as a consequence of reverberations and further modified due to diffraction and scattering upon incidence on the irregular ground surface parametric investigations of the topography soil amplification coupling effects are then conducted and our results show that when accounting for a hypothetical soil bedrock interface at 100 m depth predictions are in excellent agreement with the observed motion

topographic site effects a comparison of two nonreference methods abstract we present an experimental study of topographic site effects the data we use come from an experiment carried out during the summer of 1989 in epire northern greece ten digital stations recorded a total of 68 small earthquakes a recent article chavez garcia et al 1996 presented a comparison between site effects determined using horizontal to vertical spectral ratios hvsr for this data set and theoretical modeling in this note we compare the topographic site effects determined using hvsr with another independent experimental estimate a generalized inversion scheme gis neither hvsr nor gis depend on the availability of a reference site we obtain a very good agreement between both estimates of topographic site effects for both horizontal components our results support the use of hvsr to determine topographic site effects

effects of topography on seismic wave propagation an example from northern taiwan topography influences ground motion and in general increases the amplitude of shaking at mountain tops and ridges whereas valleys have reduced ground motions as is observed from data recorded during and after real earthquakes and from numerical simulations however recent publications have focused mainly on the implications for ground motion in the mountainous regions themselves whereas the impact on surrounding low lying areas has received less attention here we develop a new spectral element mesh implementation to accommodate realistic topography as well as the complex shape of the taipei sedimentary basin which is located close to the central mountain range in northern taiwan spectral element numerical simulations indicate that high resolution topography can change peak ground velocity pgv values in mountainous areas by 50 compared to a half space response we further demonstrate that large scale topography can affect the propagation of seismic waves in nearby areas for example if a shallow earthquake occurs in the i lan region of taiwan the central mountain range will significantly scatter the surface waves and will in turn reduce the amplitude of ground motion in the taipei basin however as the hypocenter moves deeper topography scatters body waves which subsequently propagate as surface waves into the basin these waves continue to interact with the basin and the surrounding mountains finally resulting in complex amplification patterns in taipei city with an overall pgv increase of more than 50 for realistic subduction zone earthquake scenarios off the northeast coast of taiwan the effects of topography on ground motion in both the mountains and the taipei basin vary and depend on the rupture process the complex interactions that can occur between mountains and surrounding areas especially sedimentary basins illustrate the fact that topography should be taken into account when assessing seismic hazard

the shakeout earthquake scenario verification of three simulation sets summary this paper presents a verification of three simulations of the shakeout scenario an mw 7 8 earthquake on a portion of the san andreas fault in southern california conducted by three different groups at the southern california earthquake center using the scec community velocity model for this region we conducted two simulations using the finite difference method and one by the finite element method and performed qualitative and quantitative comparisons between the corresponding results the results are in good agreement with each other only small differences occur both in amplitude and phase between the various synthetics at ten observation points located near and away from the fault as far as 150 km away from the fault using an available goodness of fit criterion all the comparisons scored above 8 with most above 9 2 this score would be regarded as excellent if the measurements were between recorded and synthetic seismograms we also report results of comparisons based on time frequency misfit criteria results from these two criteria can be used for calibrating the two methods for comparing seismograms in those cases in which noticeable discrepancies occurred between the seismograms generated by the three groups we found that they were the product of inherent characteristics of the various numerical methods used and their implementations in particular we found that the major source of discrepancy lies in the difference between mesh and grid representations of the same material model overall however even the largest differences in the synthetic seismograms are small thus given the complexity of the simulations used in this verification it appears that the three schemes are consistent reliable and sufficiently accurate and robust for use in future large scale simulations

site effects in parkway basin comparison between observations and 3 d modelling summary this paper is a contribution towards filling the large gap that currently exists between theoretical and observational studies of site effects we present results of numerical modelling of ground motion in parkway valley a small alluvial valley in new zealand we use a 3 d finite difference code and compute ground motion for the vertical incidence of plane waves p and s the results are compared with a thorough analysis of site effects in this basin presented previously based on the records obtained using a dense temporary seismic array the results of the simulations confirm the observation that ground motion in parkway basin is dominated by locally generated surface waves diffracted surface waves are generated mainly towards the south this direction does not depend on the polarization of the incident waves we obtain a very good agreement between observed and predicted transfer functions for the two horizontal components of stations located towards the centre of the valley our model clearly performs less well towards the edges of the basin where the details of the real structure are missing in our model our results suggest that the 3 d shape of the basin may be more important than a detailed knowledge of the subsoil mechanical properties in predicting ground response a correct estimate of the absolute amplification level however requires a correct estimate of the impedance contrast but this also applies to any modelling of site response

paleoseismic potential of sublacustrine landslide records in a high seismicity setting south central alaska abstract sublacustrine landslide stratigraphy is considered useful for quantitative paleoseismology in low seismicity settings however as the recharging of underwater slopes with sediments is one of the factors that governs the recurrence of slope failures it is not clear if landslide deposits can provide continuous paleoseismic records in settings of frequent strong shaking to test this we selected three lakes in south central alaska that experienced a strong historical megathrust earthquake the 1964 m w 9 2 great alaska earthquake and exhibit high sedimentation rates in their main basins 0 2 cm yr 1 1 0 cm yr 1 we present high resolution reflection seismic data 3 5 khz and radionuclide data from sediment cores in order to investigate factors that control the establishment of a reliable landslide record seismic stratigraphy analysis reveals the presence of several landslide deposits in the lacustrine sedimentary infill most of these landslide deposits can be attributed to specific landslide events as multiple landslide deposits sourced from different lacustrine slopes occur on a single stratigraphic horizon we identify numerous events in the lakes eklutna lake proximal basin 14 events eklutna lake distal basin 8 events skilak lake 7 events and kenai lake 7 events the most recent event in each basin corresponds to the historic 1964 megathrust earthquake all events are characterized by multiple landslide deposits which hints at a regional trigger mechanism such as an earthquake the synchronicity criterion this means that the landslide record in each basin represents a record of past seismic events based on extrapolation of sedimentation rates derived from radionuclide dating we roughly estimate a mean recurrence interval in the eklutna lake proximal basin eklutna lake distal basin skilak lake and kenai lake at 250 yrs 450 yrs 900 yrs and 450 yrs respectively this distinct difference in recording can be explained by variations in preconditioning factors like slope angle slope recharging sedimentation rate and the sediment source area faster slope recharging and a predominance of delta and alluvial fan failures increase the sensitivity and lower the intensity threshold for slope instability also the seismotectonic setting of the lakes has to be taken into account this study demonstrates that sublacustrine landslides in several alaskan lakes can be used as reliable recorders of strong earthquake shaking when a multi lake approach is used and can enhance the temporal and spatial resolution of the paleoseismic record of south central alaska

frequency scaled curvature as a proxy for topographic site effect amplification and ground motion variability we introduce a new methodology to predict the topographic site effect amplification ground motions obtained from a large database of 3d earthquake simulations show that the curvature of the earth s surface defined as the second spatial derivative of the elevation map is correlated with the topographic site amplification the highest correlation between the frequency dependent topographic amplification and the topographic curvature is reached when the curvature is smoothed over a characteristic length equal to the s wavelength divided by two i e frequency scaled curvature fsc this implies the amplification is caused by topographic features for which horizontal dimensions are similar to half of the s wavelength the largest ground motion variabilities are found at sites located on slopes and on the largest summits whereas intermediate variabilities occur over narrow ridges and a stable behavior in the bottom valleys the fsc proxy allows the identification of topographic features with similar characteristic dimensions and probabilistic estimates of amplification values accounting on the variability of ground motions due to source site interactions amplification estimates using the fsc proxy are robust and easily computed from digital elevation maps provided that reasonable values of s wave velocities are available in the area of interest

an experimental approach for estimating seismic amplification effects at the top of a ridge and the implication for ground motion predictions the case of narni central italy abstract from march to september 2009 a velocimetric network was installed in narni central italy a village on the top of a limestone ridge the aim was to investigate local site effects due to the 220 m high ridge which is characterized by slopes ranging from 22 to 35 to investigate amplification without and with a reference site three stations were installed at the base of the hill and seven at the crest the network recorded 702 earthquakes many of them from the 2009 l aquila sequence to determine the dependence of amplification on the morphological features the spectra were computed for horizontal components rotated into a range of azimuths both the ratio of the horizontal to vertical component spectra and the ratio of the spectra at the ridge crest with respect to a reference station at the base of the ridge showed amplification by a factor of circa 4 5 for frequencies between 4 hz and 5 hz the highest amplifications were seen for the directions of the ground motion perpendicular to the main elongation of the ridge finally considering events with an epicentral distance less than 30 km empirical ground motion models were calibrated for maximum horizontal peak ground acceleration pga velocity and acceleration response spectra 5 damping up to 1 s to estimate the site corrective coefficients for topographic amplification the data show corrective coefficients between 0 35 and 0 48 log 10 scale amplification 2 2 3 0 for the spectral ordinates between 0 2 s and 0 3 s

distribution and characteristics of loess landslides triggered by the 1920 haiyuan earthquake northwest of china abstract on december 16 1920 an earthquake with a magnitude of 8 5 occurred in haiyuan county ningxia hui autonomous region northwest of china this earthquake triggered several thousand loess landslides which resulted in thousands of deaths and blockages of rivers the distribution and characteristics of the landslides triggered by the haiyuan earthquake in loess areas were studied using satellite images and field investigation a total of about 3700 landslides with a cumulative area of about 177 km2 were interpreted over an area of 21 000 km2 it was found that landslides triggered by the earthquake were concentrated in a western of 40 55 km from the haiyuan fault landslides were concentrated near ridge crests with 65 7 of the landslides originating in the upper quadrant of slopes the aspects of the landslides triggered by the haiyuan earthquake were parallel to the faults and there is no back direction effect in landslides triggered by haiyuan earthquake these landslides have long run out distances travel distance l height different h 0 6 and deposited materials in river channels forming 51 dammed lakes that still exist the relationship between the area a and volume v of the landslides is v 4 170 a1 086 based on the relationship between number and volume of landslide and the magnitude of earthquake 100 000 landslides with a cumulative volume of 0 5 1010 m3 were triggered by the haiyuan earthquake as loess is sensitive to liquefaction during an earthquake and tends to produce landslides with long travel distances hence the loess depth slope and geological stresses are the primary factors responsible for the high density of landslides in this region

a comprehensive assessment of ground motions from two 2016 intra slab earthquakes in myanmar abstract we map the distribution of macroseismic intensities from the mw 6 9 kani and the mw 6 8 chauk intra slab earthquakes in 2016 in myanmar using the 1998 european macroseismic scale ems 98 by interpreting data gathered from field surveys community responses sent via social media to the myanmar earthquake committee mec and digital news reports our macroseismic maps for both events provide better spatial data coverage in myanmar india and bangladesh than community derived macroseismic maps e g u s geological survey s did you feel it in myanmar this was driven by improved telecommunication that has allowed social media such as the burmese language facebook portal of the myanmar earthquake committee mec to reach into rural areas from where reports of shaking effects from earthquakes have been previously unavailable our analysis of both the macroseismic intensities and strong motion observations from india and myanmar suggests the two earthquakes had different source properties the comparison of our intensity data with instrumental strong motion records also suggests the peak ground motion intensity relationship by worden et al 2012 generally performs well for both earthquakes in addition ground motion behaviour within the burma and indian plates can be related to different existing ground motion prediction equations gmpes and intensity prediction equations ipes for subduction zones and for stable continental regions respectively we therefore suggest these effects will need to be considered in future regional seismic hazard models or shake maps for this region when evaluating the impact of the future events

lateral propagation effects observed at parkway new zealand a case history to compare 1d versus 2d site effects abstract the importance of 2d or 3d site effects has been shown by theoretical studies however there is a lack of observational evidence of site effects due to lateral heterogeneities we have evaluated 1d and 2d site effects in the data obtained by a dense seismograph array that operated for more than 2 months in the alluvial basin of parkway new zealand 1d site effects were evaluated using three independent techniques spectral ratios relative to a reference station spectral ratios of horizontal relative to vertical ground motion and a generalized inversion scheme site effects due to lateral heterogeneity were investigated in detail for two events using frequency wavenumber analysis our results show that it is not possible to separate 1d from 2d site effects using frequency domain techniques this explains the scatter obtained from standard 1d data analysis the 1d resonance peaks will be more or less contaminated with laterally propagating waves for different events

insights into the catastrophic xinmo rock avalanche in maoxian county china combined effects of historical earthquakes and landslide amplification abstract a large and catastrophic rock avalanche occurred at the xinmo village in the maoxian county of the sichuan province of china on june 24 2017 the avalanche destroyed 64 houses and killed 10 people and 73 people were reported to be missing in this study we focused on the contributions of six historical earthquakes to the collapse of rocks in the source area and the landslide amplification caused by the entrainment of pre existing deposits on the landslide path the historical earthquakes in this area contributed different levels of damage on the source rocks particularly the 1933 diexi earthquake induced a few initial cracks in rocks at the crest of the steep hillslope under the combined time effects of long term weathering and gravity the rock blocks in the source area were detached from the crest along the intersecting cracks and over dip soft layer namely the sliding surface the avalanche was amplified by the entrainment of colluvium on its path the influence of the colluvium on the movement process of the xinmo landslide was modelled by the gpu based parallel discontinuous deformation analysis dda method and the effect of the impact and entrainment in the debris flow was rigorously analysed the results indicate that the impact and entrainment can continuously increase the volume of debris flow and the thickness of the colluvium was established to be in the range of 25 9 33 9 m based on the analysis of the deposit pattern and movement duration of the avalanche there were numerous unstable rocks induced by historical earthquakes at the crests of steep hill slopes in the earthquake stricken area with long term damage caused by environmental factors and gravity the failure of unstable rocks with high potential energy is likely to cause severe disasters the excess pore water pressure likely to be present in the colluvium or deposits during impact and entrainment can considerably reduce the effective stress and degrade friction resistance along the runout path as a result the landslide can be intensively amplified owing to the effect of impact and entrainment under a lower friction resistance

proglacial sediment trapping in recently formed silt lake upper lillooet valley coast mountains british columbia the sedimentology of proglacial silt lake was assessed by lake sediment coring and monitoring of lacustrine processes during a late summer period of high glacier melt to characterize sediment delivery from the heavily glacierized catchment and investigate the sediment trapping dynamics of this upland lake a complete varve chronology was established for a distal basin of the lake which was exposed by lillooet glacier retreat between 1947 and 1962 the varve record showed decreasing sedimentation rates in the basin while the glacier retreated and as the lake became free of ice contact in the early 1970s although recession has continued over recent decades and glacier proximity to the lake has therefore continued decreasing lacustrine sedimentation rates are now accelerating due to changing basin morphometry caused by delta progradation over shorter time scales lake sedimentation patterns respond to changing runoff conditions including late summer glacier melt intensity intra annual flooding events diumal runoff fluctuations and within lake turbidity currents turbidity currents included quasi regular flows during high diurnal discharges and an episodic flushing of temporarily stored sediment from the sandur or delta at a time of low stage suspended sediment yield to silt lake is estimated to exceed 103 mg km 2 a 1 a magnitude that surpasses previous local and regional yield estimates for the glacierized headwaters of the lillooet river valley since silt lake currently traps a significant prooportion of that upland sediment supply and the trapping efficiency of the basin has been variable at decadal time scales the formation and continued development of lilt lake has likely had a significant influence on downstream sediment delivery lacustrine sediment based proxies of long term hydroclimatic variability being developed in glacially distal settings should include provisions for dynamic sediment trapping effects in upstream water bodies that often form in the active proglacial environment copyright 2008 john wiley sons ltd

short baseline variations in site response and wave propagation effects and their structural causes four examples in and around the santa clara valley california abstract ground motion records of local and regional events from a portable array are used to investigate the structural causes of variations in ground motion over distances of a few hundred meters to a few kilometers in the sedimentary basin environment of the santa clara valley california and its margins arrays of portable seismic stations are used to target four study areas with different ground motion patterns 1 an edge of the alluvial basin extending up onto a marginal ridge blossom hill 2 a cenozoic basin with a nearly flat bottom cupertino basin 3 a long narrow cenozoic basin with a steep v profile evergreen basin and 4 a line perpendicular to the trace of the hayward fault average peak velocities on blossom hill from local earthquakes are a factor of 2 5 times higher than nearby valley sites three dimensional 3d modeling is used to conclude that the majority of the amplification is due to lower shear wave velocities along a local fault zone shannon berrocal site amplification over the cupertino basin in the frequency band 0 5 4 hz is generally low less than 2 0 relative to a mesozoic rock site and spatially uniform this response is attributed to the shallow flat bottomed shape of the basin and the uniform flat laying sedimentary fill in contrast site amplification in the evergreen basin generally exceeds 3 0 and is attributed to the deep v shaped geometry of the basin and younger sedimentary fill 3d waveform modeling shows the elongated shape of the evergreen basin causes more efficient trapping of long period waves for sources along the long axis of the basin a low velocity zone is postulated along the hayward fault with a width between 100 and 200 m based on elevated site response along the fault trace and 4 5 hz fault zone guided waves on the horizontal components of stations near the fault

initial investigation of site and topographic effects at robinwood ridge california abstract following the 1989 loma prieta earthquake a dense array of seven digitally recorded three component seismograph stations was deployed on robinwood ridge 7 3 km northwest of the epicenter the purpose of this array was to investigate the cause of high levels of structural damage and ground cracking observed on the ridge crest aftershocks recorded by the array allow a comparison of ground motion up the slope of the ridge from the base to the crest the data present an extremely complicated pattern of ground motion that demonstrates the importance of the three dimensionality of the problem slowness analysis of p wave trains show initial arrivals propagating away from the source with small angles of incidence and large apparent velocities consistent with direct arrivals after 0 5 sec propagation azimuths become more random and apparent velocities drop indicating nearly horizontal wave propagation and multiply reflected and diffracted phases within the ridge slowness analysis and particle motion diagrams of horizontal components of motion show dramatic variations in ground motion with changes in azimuth of the source and a complicated interaction between body waves and rayleigh and love waves results suggest that the larger amplitude more coherent arrivals at the array stations favor a propagation direction parallel to the ridge axis an amplification factor of from 1 5 to 4 5 is seen for frequencies from 1 0 to 3 0 hz with wavelengths comparable to the base of the ridge part of which may be caused by local site effects and part by topographic amplification in addition amplifications of up to a factor of 5 are seen at higher frequencies and are attributed to local site effects these effects are most notable from 4 to 8 hz on the vertical components and from 6 to 9 hz on the horizontal components the entire robinwood ridge area may also have been situated in a region of heightened mainshock ground motion due to source directivity and radiation pattern effects

spectral element simulations of seismic waves generated by the 2009 l aquila earthquake abstract we adopt a spectral element method sem to perform numerical simulations of the complex wavefield generated by the 6 april 2009 m w 6 3 l aquila earthquake in central italy the mainshock is represented by a finite fault solution obtained by inverting strong motion and global positioning system data testing both 1d and 3d wavespeed models for central italy surface topography attenuation and the moho discontinuity are also accommodated including these complexities is essential to accurately simulate seismic wave propagation three component synthetic waveforms are compared to corresponding velocimeter and strong motion recordings the results show a favorable match between data and synthetics up to 0 5 hz in a 200 km 200 km 60 km model volume capturing features mainly related to topography or low wavespeed basins we construct synthetic peak ground velocity maps that for the 3d model are in good agreement with observations thus providing valuable information for seismic hazard assessment exploiting the sem in combination with an adjoint method we calculate finite frequency kernels for specific seismic arrivals these kernels capture the volumetric sensitivity associated with the selected waveform and highlight prominent effects of topography on seismic wave propagation in central italy online material movie of wave propagation waveform fits and stable of station parameters

varve formation during the past three centuries in three large proglacial lakes in south central alaska the sediments stored in the large deep proglacial lakes of south central alaska are largely unstudied we analyzed sediments in 20 cores up to 160 cm long from eklutna kenai and skilak lakes using a combination of repeated lamination counting radionuclide dating event stratigraphy and tephrochronology we show that the characteristically rhythmic layers were deposited annually most of these glacial varves consist of one coarse grained base and a fine grained top but varves composed of multiple coarse grained turbidite pulses are common too they are likely related to successive episodes of high sediment discharge during flooding and they become more frequent in all three lakes along with increased sedimentation rates during the nineteenth century late phase of the little ice age these flood turbidites were generated by rain events and intense melting of snow and ice other mega turbidites are a result of earthquake triggered slope collapses e g a d 1964 some event layers are present in all three lakes in addition the annual time series of varve thickness normalized annual sedimentation rate are significantly correlated among the three lakes p 0 27 p 0 001 differences between the varve thickness records can be attributed partly to the dam construction at eklutna lake and outbursts from an ice dammed lake at skilak lake geomorphologic differences among the catchments result in further differences in sedimentation patterns in the three lakes

characteristics of sedimentary varve chronologies a review abstract we constructed a varve data base vdb to study the worldwide distribution of varved sediment records and the fidelity of their varve chronologies clusters of lakes with varved sediments exist in central north america in the canadian arctic and in northern and central europe among the 108 sites included in the vdb varved records are typically 200 500 cm long and cover a period of 1000 2000 years their varve chronologies are often based on counting of annual layers from fresh sediment surfaces and photographs or from epoxy embedded sediment blocks and thin sections the vdb indicates that chronological errors associated with counting sedimentary varves fall generally between 1 and 3 but only 57 of published records are providing quantitative error estimations for their chronologies with a careful documentation of varves and by applying radiometric dating methods to surface sediments as well as using historical events as time markers there is the potential of having centennial long varved records with a very precise age depth control however it is unrealistic to expect errors significantly below 1 from several millennia long sections we found no indication that varve chronologies would have been substantially more accurate and precise in some parts of the world than in others or statistically dependent on varve thickness or temporal extension of a varved sequence according to the vdb close to 90 of the published varve chronologies have been cross checked with some independent dating methods

kaguyak dome field and its holocene caldera alaska peninsula abstract kaguyak caldera lies in a remote corner of katmai national park 375 km sw of anchorage alaska the 2 5 by 3 km caldera collapsed 5 8 0 2 ka 14c age during emplacement of a radial apron of poorly pumiceous crystal rich dacitic pyroclastic flows 61 67 sio2 proximal pumice fall deposits are thin and sparsely preserved but an oxidized coignimbrite ash is found as far as the valley of ten thousand smokes 80 km southwest postcaldera events include filling the 150 m deep caldera lake emplacement of two intracaldera domes 61 5 64 5 sio2 and phreatic ejection of lakefloor sediments onto the caldera rim co2 and h2s bubble up through the lake weakly but widely geochemical analyses n 148 including pre and post caldera lavas 53 74 sio2 define one of the lowest k arc suites in alaska the precaldera edifice was not a stratocone but was instead nine contiguous but discrete clusters of lava domes themselves stacks of rhyolite to basalt exogenous lobes and flows four extracaldera clusters are mid to late pleistocene but the other five are younger than 60 ka were truncated by the collapse and now make up the steep inner walls the climactic ignimbrite was preceded by 200 years by radial emplacement of a 100 m thick sheet of block rich glassy lava breccia 62 65 5 sio2 filling the notches between the truncated dome clusters the breccia now makes up three segments of the steep caldera wall which beheads gullies incised into the breccia deposit prior to caldera formation they were probably shed by a large lava dome extruding where the lake is today

varves in lake sediments a review abstract downcore counting of laminations in varved sediments offers a direct and incremental dating technique for high resolution climatic and environmental archives with at least annual and sometimes even seasonal resolution the pioneering definition of varves by de geer 1912 had been restricted to rhythmically deposited proglacial clays one century later the meaning of varve has been expanded to include all annually deposited laminae in terrestrial and marine settings under favourable basin configurations and environmental conditions limnic varves are formed due to seasonality of depositional processes from the lake s water column and or transport from the catchment area subsequent to deposition of topmost laminae the physical preservation of the accumulating varved sequence requires the sustained absence of sediment mixing for example via wave action or macrobenthic bioturbation individual sub laminae in varved lake sediments typically express contrasting colours always differ in terms of their organic chemical and or mineralogical compositions and often also differ with regard to grain size various predominating climatic and depositional conditions may result in clastic biogenic or endogenic incl evaporitic varved sediments and their mixtures to reliably establish a varve chronology the annual character of laminations needs to be determined and verified in a multidisciplinary fashion sources and influences of possible errors in varve chronologies are best determined and constrained by repeated varve counts and by including radioisotopes and correlation with historically documented events a well established varve chronology greatly enhances the scientific value of laminated limnic archives by securely anchoring the wealth of multi proxy palaeoenvironmental information in the form of time series for multidisciplinary investigations applications of varved records are discussed with special reference to advances since the 1980s these span fields like calibrating radiometric dating methods reconstructing past changes of the earth s magnetic field or detecting fluctuations in solar forcing once a varve chronology is established it can be applied to precisely date events like volcanic ash layers earthquakes or human impact as well as short and long term climate temperature precipitation wind hydroclimatic conditions or flooding and environmental changes eutrophication pollution due to their exceptional high temporal resolution and in combination with their robust and accurate internal time scale in calendar years annually laminated sediments can be regarded as one of the most precious environmental archives on the continents these records are necessary to extend temporally limited instrumental records back in time as such they have societal relevance with regard to risk assessments related to natural hazards arising from e g flooding or volcanic eruptions

ground motion amplifications in small size hills case study of gokgang ri south korea during the 2017 ml 5 4 pohang earthquake sequence

topographic fingerprints of bedrock landslides bedrock landslides in mountainous regions may be triggered by either storms or earthquakes the dominant mechanism in a region affects both landscape evolution and landslide hazard we describe a simple observational test to distinguish between storm and earthquake triggers based on a probabilistic measure of hillslope morphology in areas that are dominated by storm triggered landslides steep topographic slopes are concentrated on the lowermost parts of the hillslopes storm triggers act primarily on the hillslope toes and landslides preferentially remove material from those locations giving rise to inner gorges areas where most landslides are earthquake triggered have more uniform spatial distributions of steep topographic slopes because coseismic shaking causes failures at both ridge crests and hillslope toes earthquake triggered landslides lead to planar hillslopes and rare or absent inner gorges

3d site effects a thorough analysis of a high quality dataset this article is a contribution toward filling the large gap that currently exists between theoretical and observational studies of site effects we present a detailed analysis of 10 events recorded by a dense temporary seismograph network that operated in the small roughly 1 3 by 0 4 km alluvial valley of parkway new zealand we computed f k spectra for the three recorded components of those 10 events as a function of frequency and time window along the seismograms our results show that a major part of the energy in the records propagates as surface waves the small size of the basin explains the observation that small phase velocity waves appear shortly after direct p and s wave arrivals both love and rayleigh waves are present it was difficult to isolate individual wavetrains but directions of propagation are dominated by southerly directions especially at lower frequencies and earlier times along the seismograms the inversion of observed phase velocity dispersion is in very good agreement with available information on the subsoil structure for this valley a comparison with a different interpretation of one event from our dataset shows clearly how misleading it can be to analyze partial observations the large variability of ground motion in the time domain contrasts with the very stable results obtained for this dataset in the frequency domain and indicates that we still have a long way to go before we are able to incorporate locally generated surface waves into the frame of modern building codes

a faulting model for the 1992 petrolia earthquake can extreme ground acceleration be a source effect the 1992 petrolia earthquake m 7 0 was quite remarkable in that an accelerometer at cape mendocino cap recorded a high frequency pulse of almost 2 g whereas the nearby roughly 6 km away petrolia station pet recorded a maximum of only 0 6 g in our model for this event we have investigated the possibility that extreme ground acceleration with high spatial variability can be caused by a source effect specifically the rupture of a barrier asperity this type of rupture feature can produce extreme ground acceleration provided that certain geometrical constraints are met in the present study we derive a combined high and low frequency faulting model for the 1992 petrolia earthquake that is consistent with the slip distribution on the fault and that produces the high frequency pulse at cap our model consists of four parts 1 a low frequency 0 1 0 6 hz inversion that determines the slip rupture time and risetime distributions on the fault 2 an interpolation and perturbation of the above distributions that produces synthetic accelerograms between 0 6 and 3 0 hz 3 random phase signal that is scaled to the spectral amplitude level of the data between 3 0 and 12 5 hz and 4 the rupture of a barrier like asperity that produces greatly amplified radiation at cap but not at other stations we find that our model produces a good fit to the near source records of the 1992 petrolia event the results emphasize the interaction between fault geometry and rupture propagation to produce ground motion as well as the hazard associated with locations above the hanging walls of dipping faults where the geometry permits the production of extreme ground acceleration

off fault ground ruptures in the santa cruz mountains california ridge top spreading versus tectonic extension during the 1989 loma prieta earthquake the ms 7 1 loma prieta earthquake of 18 october 1989 produced abundant ground ruptures in an 8 by 4 km area along summit road and skyland ridge in the santa cruz mountains predominantly extensional fissures formed a left stepping crudely en echelon pattern along ridges of the hanging wall block southwest of the san andreas fault about 12 km northwest of the epicenter the fissures are subparallel to the san andreas fault and appear to be controlled by bedding planes faults joints and other weak zones in the underlying tertiary sedimentary strata of the hanging wall block the pattern of extensional fissures is generally consistent with tectonic extension across the crest of the uplifted hanging wall block also many displacements in laurel creek canyon and along the san andreas and sargent faults are consistent with right lateral reverse faulting inferred for the mainshock additional small tensile failures along the axis of the laurel anticline may reflect growth of the fold during deep seated compression however the larger ridge top fissures commonly have displacements that are parallel to the north northeast regional slope directions and appear inconsistent with east northeast extension expected from this earthquake measured cumulative displacements across the ridge crests are at least 35 times larger than that predicted by the geodetically determined surface deformation these fissures also occur in association with ubiquitous landslide complexes that were reactivated by the earthquake to produce the largest concentration of co seismic slope failures in the epicentral region the anomalously large displacements and the apparent slope control of the geometry and displacement of many co seismic surface ruptures lead us to conclude that gravity is an important driving force in the formation of the ridge top fissures shaking induced gravitational spreading of ridges and downslope movement may account for 90 or more of the observed displacements on the linear fissures similar fissures occurred in the same area and elsewhere near the san andreas fault during the predominantly right lateral 1906 san francisco earthquake and suggest that the loma prieta ground ruptures may in large part be independent of fault kinematics

euro seistest strong motion array near thessaloniki northern greece a study of site effects abstract the effects of local geology on the characteristics of strong ground motion have been and continue to be a field of active research despite the considerable efforts made so far there are still several unresolved and controversial issues remaining in particular debates still continue over the limits of applicability of one dimensional 1d wave propagation models there are also unresolved questions related to the implementation and reliability of site response estimation techniques such as the standard spectral ratio ssr and the horizontal to vertical spectral ratio hvsr this study addresses these issues on the basis of data from the euro seistest strong motion array at volvi near thessaloniki greece the data set used consists of accelerograms of 32 earthquakes almost exclusively local covering a magnitude range from m l 2 0 to 6 1 the range of recorded accelerations is 0 001 0 042 g we implement two 1d wave propagation models the haskell thompson matrix method and kennett9s reflectivity coefficient method and the hvsr site response assessment technique we test the applicability of the 1d models in a basin environment we use both fourier amplitude and response spectra to compute hvsr and investigate how hvsr is influenced by the choice of the time window and smoothing procedure we found the hvsr technique and 1d sh wave modeling to perform reasonably well in a sediment valley environment the modeling was performed for a site in the center of the valley

site effects in the city of lourdes france from h v measurements implications for seismic risk evaluation abstract the pilgrimage city of lourdes in the french pyrenees has been heavily damaged by earthquakes in the seventeenth and eighteenth centuries assessments of local seismic hazard have been performed through a seismic microzonation of the city a campaign of urban noise recording has been conducted at about 180 points to determine seismic wave amplification by means of spectral ratios of the horizontal to vertical h v components a comparison of this ratio obtained from ambient noise measurements with spectral ratios obtained from earthquake s wave recording h href reveals that the fundamental resonance frequency is well estimated but that the site amplification is generally underestimated resonance frequencies and amplitudes exhibit coherent patterns that relate to the geological structure bedrock sites are generally characterized by flat spectra whatever the geological nature of bedrock unless topography or karst are present along the river in particular at the pilgrimage site thick sediments induce low resonance frequencies with large amplifications along and across valleys north and east of the city h v spectra show systematic variations according to sediment filling properties finally on the hill flanks east of the city h v spectra rather relate to topography an additional issue with h v spectral ratios based on ambient noise is whether this indicator reflects meaningful geological variations this question is tested on sites where the s wave ground velocity structure is known a first test consists of estimating h v spectral ratios by means of simulation of urban noise through the summation of synthetic seismograms with random properties a second test consists of estimating h href spectral ratios by propagating an earthquake record through a 1d soil profile these two modelings successfully predict most of the observed spectrum characteristics in addition they give some information on the nature of the urban noise which may include a significant amount of shear energy

geometry mass balance and thinning at eklutna glacier alaska an altitude mass balance feedback with implications for water resources we analyzed glacier surface elevations 1957 2010 and 2015 and surface mass balance measurements 2008 2015 on the 30 km 2 eklutna glacier in the chugach mountains of southcentral alaska the geodetic mass balances from 1957 to 2010 and 2010 to 2015 are 0 52 0 46 and 0 74 0 10 m w e a 1 respectively the glaciological mass balance of 0 73 m w e a 1 from 2010 to 2015 is indistinguishable from the geodetic value even after accounting for loss of firn in the accumulation zone we found most of the mass loss over both time periods was from a broad low slope basin that includes much of the accumulation zone of the main branch ice equivalent surface elevation changes in the basin were 1 0 0 8 m a 1 from 1957 to 2010 and 0 6 0 1 m a 1 from 2010 to 2015 shifting the glacier hypsometry downward and resulting in more negative mass balances an altitude mass balance feedback net mass loss from eklutna glacier accounts for 7 1 of the average inflow to eklutna reservoir which is entirely used for water and power by anchorage alaska s largest city if the altitude mass balance feedback continues this deglaciation discharge dividend is likely to increase over the short term before it eventually decreases due to diminishing glacier area

faulting and effects of associated shaking at pisgah crater volcano caused by the 16 october 1999 hector mine earthquake mw 7 1 central mojave desert california a 240 m long zone of left stepping fractures and scarps was mapped on 23 and 24 october 1999 on the east flank of the main cinder cone at pisgah crater volcano about halfway between the north end of the surface rupture as mapped by other investigators and highway i 40 the pisgah crater fractures are faults not slump features although undoubted slumps and shallow slides are present and abundant nearby the free faces of the scarps range from 10 to 80 cm high evidence of strike slip was not observed the scarps are at the base of an erosion scarred 2 m high bench in the cone slope that suggests the cone has been faulted previously indicators of strong motion associated with the hector mine earthquake include shattered earth and tossed ground extensive collapse of oversteepened quarry slopes and slumping of waste dump slopes quarry cuts and gully banks a 1000 kg boulder that rested on a nearly flat surface was displaced 10 cm southward from its original position within its socket extensive sand slips on angle of repose slopes expulsion of dust and silt from compacting cinders local collapse of lava tubes and dislodgment of precariously balanced boulders from quarry faces were also seen taken together our observations suggest that strong motion associated with the hector mine earthquake on pisgah crater was nearly thrice the 0 33 g measured elsewhere by other investigators

dynamic stability analysis of jointed rock slopes using the dda method king herod s palace masada israel abstract a dynamic two dimensional stability analysis of a highly discontinuous rock slope is demonstrated in this paper the studied rock slope is the upper terrace of king herod s palace in masada situated on the western margins of the seismically active dead sea rift the slope consists of sub horizontally bedded and sub vertically jointed stiff dolomite blocks the dynamic deformation of the slope is calculated using a fully dynamic version of dda in which time dependent acceleration is used as input the analytically determined failure modes of critical keyblocks in the jointed rock slope are clearly predicted by dda at the end of the dynamic calculation it is found however that for realistic displacement estimates some amount of energy dissipation must be introduced into the otherwise fully elastic un damped dda formulation comparison of predicted damage with actual slope performance over a historic time span of 2000 years allows us to conclude that introduction of 2 kinetic damping should suffice for realistic damage predictions this conclusion is in agreement with recent results of tsesarsky et al in y h hatzor ed stability of rock structures proceedings of the fifth international conference of analysis of discontinuous deformation balkema publishers lisse 2002 pp 195 203 who compared displacements of a single block on an inclined plane subjected to dynamic loading obtained by dda and by shaking table experiments using dynamic dda it is shown that introduction of a simple rock bolting pattern completely stabilizes the slope

effects of local soil conditions on the topographic aggravation of seismic motion parametric investigation and recorded field evidence from the 1999 athens earthquake during the 1999 athens earthquake the town of adames located on the eastern side of the kifissos river canyon experienced unexpectedly heavy damage despite the particular geometry of the slope that caused significant motion amplification topography effects alone cannot explain the uneven damage distribution within a 300 m zone parallel to the canyon s crest which is characterized by a rather uniform structural quality in this article we illustrate the important role of soil stratigraphy and material heterogeneity on the topographic aggravation of surface ground motion for this purpose we first conduct an extensive time domain parametric study using idealized stratified profiles and gaussian stochastic fields to characterize the spatial distribution of soil properties and using ricker wavelets to describe the seismic input motion the results show that both topography and local soil conditions significantly affect the spatial variability of seismic motion we next perform elastic two dimensional wave propagation analyses based on available local geotechnical and seismological data and validate our results by comparison with aftershock recordings

flocculation a key process in the sediment flux of a large glacier fed lake this study investigates the consequences of flocculation for sediment flux in glacier fed lillooet lake british columbia based on density fractal dimension in situ profiles of sediment concentration and size distribution and settling velocity equations presented in the literature sediment flux attributed to macroflocs during the late spring and summer accounts for a significant portion of sediment flux in the lake equivalent to at least one quarter of the average annual sediment flux fine sediment is reaching the lake floor faster in flocs than occurs if settling as individual grains this flux varies both spatially and temporally over the observation period suggesting a link between deposition via flocculation and the properties of bottom sediments macrofloc flux increased through june reached a peak during july and then declined into august macrofloc flux was greatest in the distal end of the first basin approximately 10 km from the point of inflow relatively high excess densities 0 1 g cm 3 at 500 m for flocs in situ are consistent with a composition dominated by inorganic primary particles microlaminations within lillooet lake varves have been linked by earlier workers to discharge events and the action of turbidity currents emanating from the lillooet river while turbidity currents undoubtedly occur in lillooet lake these results demonstrate flocculation as an adjunct process linking discharge lake level macrofloc flux bulk density and microlaminations in situ measurements of sediment settling velocity in glacier fed lakes are required to better constrain flux rates and permit comparison between flocculation in lacustrine environments with existing studies of estuarine marine and fluvial flocculation copyright 2009 john wiley sons ltd

trinet strong motion data from the m 7 1 hector mine california earthquake of 16 october 1999 the m w 7 1 hector mine earthquake of october 16 1999 was recorded by more than 300 stations of trinet which is administered cooperatively by the california division of mines and geology s california strong motion instrumentation program cdmg csmip california institute of technology and the u s geological survey usgs the earthquake occurred in a remote part of the mojave desert approximately 190 km northeast of downtown los angeles and there were no strong motion stations close to the surface rupture the nearest station hector is about 27 km north of the epicenter it recorded a peak horizontal ground acceleration of 0 33g the two next closest stations amboy and joshua tree are to the east and south both at epicentral distances of about 50 km each recorded peak ground accelerations of about 0 2g the new digital instruments installed for the trinet project recorded a large set of reliable data at epicentral distances up to 275 km these data can significantly improve empirical peak ground motion attenuation relationships which are usually developed for distances only up to 100 km boore et al 1993 1997 because adequate data have not been available at greater distances hector mine peak ground motions demonstrate reasonable agreement with empirical attenuation relationships for acceleration in contrast higher than expected ground velocities and displacements were recorded at epicentral distances of about 150 to 220 km especially in the los angeles sedimentary basin where anomalously high amplitude displacements with periods of 6 to 7 sec were recorded in los angeles long beach and other areas these long period surface or basin generated waves can have significant effects on large structures the m w 7 3 landers earthquake of 1992 similarly produced strong long period waves in the basin the peak ground motions produced by the landers earthquake were on average 1 6 times higher than for the hector mine earthquake in the los angeles area ground motion data recorded by digital instruments were uniformly processed in the frequency band 0 067 to 46 hz 0 022 15 sec the processed data set includes records from 213 ground response stations in an effort to make strong motion data available quickly to the engineering and scientific communities important records from this event were made available by file transfer protocol ftp beginning the day of the earthquake

machine learning classifiers for attributing tephra to source volcanoes an evaluation of methods for alaska tephras glass composition based correlations of volcanic ash tephra traditionally rely on extensive manual plotting many previous statistical methods for testing correlations are limited by using geochemical means masking diagnostic variability we suggest that machine learning classifiers can expedite correlation quickly narrowing the list of likely candidates using well trained models eruptives from alaska s aleutian arc alaska peninsula and wrangell volcanic field were used as a test environment for 11 supervised classification algorithms trained on nearly 2000 electron probe microanalysis measurements of glass major oxides representing 10 volcanic sources artificial neural networks and random forests were consistently among the top performing learners accuracy and kappa 0 96 their combination as an average ensemble effectively improves their performance using this combined model on tephras from eklutna lake south central alaska showed that predictions match traditional methods and can speed correlation although classifiers are useful tools they should aid expert analysis not replace it the eklutna lake tephras are mostly from redoubt volcano besides tephras from known holocene active sources holocene tephra geochemically consistent with pleistocene emmons lake volcanic center dawson tephra but from a yet unknown source is evident these tephras are mostly anchored by a highly resolved varved chronology and represent new important regional stratigraphic markers

directional topographic site response at tarzana observed in aftershocks of the 1994 northridge california earthquake implications for mainshock motions abstract the northridge earthquake caused 1 78 g acceleration in the east west direction at a site in tarzana california located about 6 km south of the mainshock epicenter the accelerograph was located atop a hill about 15 m high 500 m long and 130 m wide striking about n78 e during the aftershock sequence a temporary array of 21 three component geophones was deployed in six radial lines centered on the accelerograph with an average sensor spacing of 35 m station c00 was located about 2 m from the accelerograph we inverted aftershock spectra to obtain average relative site response at each station as a function of direction of ground motion we identified a 3 2 hz resonance that is a transverse oscillation of the hill a directional topographic effect the top base amplification ratio at 3 2 hz is about 4 5 for horizontal ground motions oriented approximately perpendicular to the long axis of the hill and about 2 for motions parallel to the hill this resonance is seen most strongly within 50 m of c00 other resonant frequencies were also observed a strong lateral variation in attenuation probably associated with a fault caused substantially lower motion at frequencies above 6 hz at the east end of the hill there may be some additional scattered waves associated with the fault zone and seen at both the base and top of the hill causing particle motions not spectral ratios at the top of the hill to be rotated about 20 away from the direction transverse to the hill the resonant frequency but not the amplitude of our observed topographic resonance agrees well with theory even for such a low hill comparisons of our observations with theoretical results indicate that the 3d shape of the hill and its internal structure are important factors affecting its response the strong transverse resonance of the hill does not account for the large east west mainshock motions assuming linear soil response mainshock east west motions at the tarzana accelerograph were amplified by a factor of about 2 or less compared with sites at the base of the hill probable variations in surficial shear wave velocity do not account for the observed differences among mainshock acceleration observed at tarzana and at two different sites within 2 km of tarzana