tectonic setting and source parameters of the september 19 1985 michoacan mexico earthquake analysis of body waves and long period surface waves from the september 1985 earthquake in coastal michoacan mexico shows that the event was an interplate subduction event with a low dip angle fault plane 9 striking parallel to the mid america trench 288 and a small component of left lateral motion 72 with a point source depth of 17 km and a seismic moment in excess of 1 10 28 dyn cm the earthquake was a multiple event with a second source of identical moment fault geometry and depth occurring approximately 26 s after the first directivity in the body wave time function indicates that the second event occurred roughly 100 km to the southeast of the first this suggests that the earthquake first broke the northern portion of the michoacan gap propagated with low moment release through the rupture zone of the 1981 playa azul earthquake and then broke the remaining asperity in the southern section of the gap the seismic moment determined from rayleigh and love waves is between 1 0 1 7 10 28 dyn cm m w 7 9 8 1 the largest moment determined to date for a mexico subduction earthquake comparison of seismograms at pasadena with records of other large mexico events shows that the michoacan earthquake is basically the same size as the 1932 jalisco mexico earthquake and clearly larger than other significant events in mexico since 1932 the seismic moment and the time since the last large earth quake in michoacan in 1911 fit an empirical relation between moment and recurrence time found for the guerrero oaxaca region of the subduction zone the large aftershock on september 21 m s 7 5 has the same geometry as the mainshock a somewhat larger source depth 22 km a simple time function and a seismic moment between 2 9 4 7 10 27 dyn cm m w 7 6 7 7

application of numerical wave propagation techniques to study local soil effects the case of benevento italy many of the numerical techniques used for seismic zonation studies treat one dimensional structural models and or the incidence of plane polarized body waves these techniques are often not adequate for laterally heterogeneous structures and for sources that are not located beneath the site of interest in such cases a more rigorous treatment of the combined effects of the source the path and the site response is needed this can be accomplished with a hybrid approach combining modal summation and the finite difference technique to demonstrate the differences between these techniques the ground motion in the city of benevento italy is modelled we first compare the results obtained with one and two dimensional structural models for vertical incidence of plane polarized body waves these results are then compared with those obtained with the hybrid approach for two dimensional structural models

microtremor measurement to evaluate site characteristics by horizontal to vertical spectral ratio technique in sikkim northeast himalayas india abstract the measurement of site amplification of microtremors is an important tool for evaluating seismic hazard at local and regional level the h v spectral ratio hvsr method is applied to estimate the amplification of ground motion at resonance frequency the fundamental resonance frequency is estimated at 8 different sites in study region and shows the maximum vulnerability of the site to the earthquakes this frequency ranges between a minimum of 2 8 hz to a maximum of 9 3 hz the thickness of the sediments below the surface of recording sites is calculated using the empirical relationship that comes out to be in a particular range of 9 5 m 33 1 m above the bed rock the sedimentary thickness and the resonance frequency clearly matched with geological setting of the study area the observation shows a slow reduction in the thickness of the sediments and increase in the resonance frequency from south western part to north eastern part of the study region the results show that most of the sites are highly vulnerable to seismic risks with high amplification of seismic waves in the area thus current study provides a deep insight in to the seismic hazard of the sikkim region with a clear emphasis on the site amplification and the sedimentary cover for the region

predictive model for seismic sliding displacement of slopes based on a coupled stick slip rotation approach abstract this paper represents a predictive model for the earthquake induced displacement of slopes using a coupled stick slip rotation approach recently proposed by the authors in a preceding paper a collection of 1363 strong motion records associated with 25 worldwide earthquakes was used to generate the model on the basis of results of sliding block analyses the proposed model predicts sliding displacement in terms of yield acceleration coefficient ratio ky kmax period ratio ts tm and slip length l the regression analysis indicates that dividing the results into the smaller intervals of period ratio can provide a noticeable higher degree of accuracy probable bias of the residuals versus the input variables is examined in detail predictions of the developed equation are compared with some available sliding block equations which similarly assumed a flexible sliding mass the proposed model can be simply used to estimate landslide hazard in seismic prone regions

hydrodynamic control of the supply of reworked terrigenous sediment to coral reefs in the bay of banten nw java indonesia abstract the bay of banten is an example of a shallow water reef environment adjacent to an eroding delta system where corals survive in turbid conditions this study investigated the hydrodynamic controls over residual fluxes of terrigenous sediment in the bay observations of wind waves currents and suspended sediment concentrations in 1998 and 1999 revealed contrasting dynamic turbidity conditions influenced by tides monsoon driven flows and locally generated waves the most sediment rich suspensions originate from the shallow coastal margin of an inactive delta where waves resuspend sediment and small creeks discharge freshwater and sediment because of coupling between monsoonal wind throughflow in the bay and wave height when wave induced resuspension peaks seasonally during the northwest monsoon an eastward throughflow prevents the nearshore reefs in the bay from being directly exposed to turbid water masses generated in the eroding delta in inshore waters tidal asymmetry and the spatial variation of current amplitudes cause residual sediment transport largely depending on the availability of erodible sediment in the center of the bay where there is a patch reef complex the tidal and subtidal currents are weak and therefore here there is a zone where sediment accumulates

deterministic seismic hazard in egypt summary the regional seismic hazard in egypt is assessed using a deterministic approach based on the computation of synthetic seismograms at a set of gridpoints located at distances of 0 2u from each other the main input for this computation are earthquake sources and structural models the earthquake sources are parametrized using focal mechanisms seismogenic areas and regional seismicity a number of deep seismic profiles have been used to define the crustal structures similar sets of gravity profiles have been used to define the density of the layers the peak displacement dmax peak velocity vmax and design ground acceleration dga are chosen and plotted to construct the seismic hazard maps there are similarities between computed and observed amplitudes of ground motion in terms of their values and spatial distributions the results obtained from the deterministic and probabilistic approaches are comparable the areas of high seismic hazard level are of great socio economic importance

coseismic sediment deformation during the 1989 loma prieta earthquake 1 inelastic horizontal sediment deformation from the ms 7 1 17 october 1989 loma prieta earthquake has been estimated to be on the order of 20 cm at a site in gilroy california about 32 km east of the epicenter this estimate was based on combined deterministic stochastic simulations using ground motion data and sediment properties measured from in situ seismic tests and laboratory tests on cored sediment samples of up to 170 m deep the calculated deformation is comparable to measured horizontal coseismic displacements at various stations in the santa cruz network suggesting that previously back figured fault rupture mechanisms may have been influenced by the coseismic sediment deformation

modeling of sh and p sv wave fields and seismic microzonation based on response spectra for talchir basin india abstract the p sv and sh wave field in the talchir basin is simulated along eight profiles four profiles strike across the basin and the other four along the basin the hybrid method which combines two computational techniques modal summation and finite differences is used to produce multiphase synthetic seismograms an m 6 earthquake is considered with hypocenter along the north orissa boundary fault nobf at a depth of 5 km and with the focal mechanism parameters dip 90 strike 160 and rake 180 the peak acceleration a max along each profile is determined considering the maximum acceleration obtained at the horizontal components the response spectra ratio rsr as a function of frequency is computed for the eight profiles and the higher amplification is seen to increase in correspondence with the thicker sedimentary cover especially for the radial component higher site amplification for all the profiles is observed in the frequency range from 0 5 to 1 4 hz to validate the obtained site effects the sources for the profiles across the basin are placed near to the southern end of the profile and the site amplifications are recomputed even if the spatial distribution of a max is mainly controlled by the epicentral distance i e the geometrical spreading prevails on local soil effects the rsr shows a pattern that can be easily correlated with the local site conditions the rsr at the intersection of the profiles is dependent not only upon the local lithology and sediment thickness but also upon the epicentral distance the talchir basin is classified into three zones based on the rsr values low rsr zone 1 6 1 9 intermediate rsr zone 2 0 2 8 and high rsr zone 2 9 5 2 the pga estimated for the bedrock model by bhatia et al 1999 for the study region is around 0 05 to 0 10 g while the indian seismic zonation map estimated it to be in the range from 0 1 to 0 2 g in the present study that considers the effects of lateral variations in the structure the pga is estimated to be as high as 0 55 g along the ba profile

influence of source on 2 d site effects 1 the site response has been theoretically estimated along seven 2 d profiles distributed in the broader urban area of thessaloniki the hybrid method employed allows the simulation of various events located at different distances and azimuths around the city we focus on the results obtained at all points where the profiles intersect the diversity of the site response at each intersection is attributed mainly to the influence of the seismic source suggesting that the ground response does not depend only on local soil characteristics but also on different earthquake scenarios generating the impingent wavefield

two dimensional ground motion at a soft viscoelastic layer hard substratum site in response to sh cylindrical seismic waves radiated by deep and shallow line sources ii numerical results summary we consider using theory and associated synthetic seismograms the seismic response of a site comprising a horizontal homogeneous soft viscoelastic layer of infinite lateral extent overlying and in welded contact with a homogeneous hard elastic substratum of half infinite radial extent we show that for shear horizontal motion 1 coupling to love modes is all the weaker the deeper the source modelled as a line assumed to lie in the substratum is from the lower boundary of the soft layer 2 for a line source close to the lower boundary of the soft layer the ground response is characterized by possible beating phenomena and is of significantly longer duration than for excitation by cylindrical waves radiated by deep sources numerical applications of the theory show for instance that a line source located 40 m below the lower boundary of a 60 m thick soft layer in a hypothetical mexico city like site radiating a sh pulse of 4 s duration produces substantial ground motion during 200 s with marked beating at an epicentral distance of 3 km results from this modelling study are supported by field examples taken from published literature

unravelling the causes of tidal asymmetry in deltas abstract tidal asymmetry in deltas is caused by both the intrinsic asymmetry resulting from the combination of astronomical tides and by nonlinear tidal interactions that occur in shallow water the relative importance of these sources of tidal asymmetry in delta channel networks have remained poorly studied partly due to the limitations of classical harmonic analysis ha in hindcasting nonstationary tides the pearl river delta prd is a multichannel system with rapidly changing bathymetry subject to severe human interventions this work applies a nonstationary harmonic model ns tide to hydrological data from 15 stations in the prd spanning the period 1961 2012 the spatiotemporal variation of multiple sources of tidal asymmetry is quantified by a skewness metric revealing how similar or dissimilar the development of alternative sources of tidal asymmetry develop in the delta subject to study a relative sensitivity coefficient rsc is introduced to decompose the contribution of tidal amplitude variations to multiple tidal asymmetries analytical results show the development of tides becoming gradually more asymmetric as they propagate into delta channel networks and how this depends on the river flow variation in the orientation of tidal asymmetries induced by different combinations of tidal constituents leads to a complex pattern of the overall tidal asymmetry in the prd our results show that tidal asymmetry in deltas can be significantly dependent on the river flow

source characteristics of the 1985 michoacan mexico earthquake at periods of 1 to 30 seconds source characteristics of the sept 19 1985 michoacan mexico earthquake and its aftershock on sept 21 were inferred from broadband and short period teleseismic gdsn records we fourier transformed the p waves corrected for instrument response attenuation geometrical spreading and radiation pattern including the depth phases and then averaged to obtain the teleseismic source spectrum from 1 to 30 s the michoacan source spectrum is enriched at 30 s and depleted at 1 to 10 s relative to an average source spectrum of large interplate subduction events source spectra for the sept 21 aftershock 1981 playa azul 1979 petatlan and 1978 oaxaca events follow a trend similar to that of the 1985 michoacan event this spectral trend may characterize the mexican subduction zone a station by station least squares inversion of the michoacan earthquake records for the source time function yielded three source pulses which we interpreted as events on the fault plane the first two are similar in moment and the third contains only 20 of the moment of the first directivity is evident in the timing at each station we measured the time differences between the pulses and performed a least squares nonlinear estimation of the strike distance and time separation between the events to locate them relative to one another the second event occurred 26 s after the first and 82 km southeast of it indicating southeastward rupture along the trench the third event occurred 21 s after the second and about 40 km seaward of it the two large events are also seen in the near field strong motions the mainshock records spectrum and time functions contain less high frequency radiation than those of the 1985 valparaiso chile earthquake apparently the michoacan earthquake ruptured two relatively smooth strong patches which generated large 30 s waves but small 1 to 10 s waves such behavior contrasts with the valparaiso event which had a more complex rupture process and generated more 1 to 5 s energy this difference is consistent with the higher near field accelerations recorded for the valparaiso event

the main features of the local geological conditions can explain the macroseismic intensity caused in xiji langfu beijing by the ms 7 7 tangshan 1976 earthquake the special geological conditions in the xiji langfu area are the main reason for the anomalous high macroseismic intensity caused by the tangshan 1976 earthquake the area is formed by deep deposits mainly alluvium sands and clays poorly consolidated and with high water content that have been trapped by the xiadian fault from simulated ground motion we have computed quantities commonly used for engineering purposes like the acceleration maximum amplitude amax and the total energy of ground motion w which is related to the arias intensity the thick low velocity deposits are responsible for the large increment of the values of amax and w inside the basin on the two sides of the xiadian fault amax and w can vary by 200 and 700 respectively and these variations are quite stable with varying thickness of the sedimentary deposit used in the models with the existing relationships between acceleration amax and macroseismic intensity i our results can explain the large values of i observed in the xiji langfu area in connection with the tangshan earthquake

comment on a hybrid method for the estimation of ground motion in sedimentary basins quantitative modeling for mexico city by d fah p suhadolc st mueller and g f panza abstract two possible extensions of the commented article are suggested with the aim to more efficiently couple the source and path simulation on one side and the site effect simulation on the other 1 new excitation lines surrounding the sedimentary basin reduce the necessary size of the 2d finite difference model of the site they also better represent the 3d nature of the excitation including the focal mechanism effect 2 new 2 5d approximate equations of motion improve the way the 3d excitation is propagated within the 2d site model the two suggested improvements can help in solving problems when a purely 2d treatment is oversimplified but a true 3d treatment is too expensive

towards a reliable seismic microzonation in tehran iran abstract a hybrid method for the calculation of realistic synthetic seismograms in laterally heterogeneous anelastic media has been used to model the ground motion in tehran city the synthetic records compare reasonably well with the observed ground motion due to the 2004 firozabad kojor earthquake located 60 km north of tehran the ratio between the response spectrum for the signals calculated along a laterally varying structure sa 2d and that for the signals at the bedrock regional reference structure sa 1d shows a high amplification of seismic waves in tehran the procedure can be readily implemented for the entire tehran city which experienced large historical earthquakes in the past simply by extending the analysis made so far in space and to different scenario earthquakes consistent with the local and regional tectonics

on the duration of seismic motion incident onto the valley of mexico for subduction zone earthquakes summary we have used finite difference simulations in 2 d models of the lithosphere to estimate the duration of long period 2 s ground motion incident onto the valley of mexico for subduction zone earthquakes our simulations suggest that two heterogeneous structures extend the duration of the ground motion between the subduction zone and mexico city by more than 1 min 1 the mexican volcanic belt and 2 two low velocity layers in the coastal region the accretionary prism and the water layer the duration generated by a crustal model including these structures is similar to that for earthquake records observed in between the coast and mexico city in the valley of mexico our models including only regional scale heterogeneity reproduce approximately one half of the observed duration the results suggest that both the regional and the local scale low velocity structures must be taken into account in order to explain the observed extended signal duration in the valley of mexico

a hybrid method for the estimation of ground motion in sedimentary basins quantitative modeling for mexico city to estimate the ground motion in two dimensional 2d laterally heterogeneous anelastic media a hybrid technique has been developed that combines modal summation and the finite difference method in the calculation of the local wave field owing to a seismic event both for small and large epicentral distances it is possible to take into account the source path and local soil effects as a practical application we have simulated the ground motion in mexico city caused by the michoacan earthquake of september 19 1985 by studying the one dimensional 1d response of the two sedimentary layers present in mexico city it is possible to explain the difference in amplitudes observed between records for receivers inside and outside the lake bed zone these simple models show that the sedimentary cover produces the concentration of high frequency waves 0 2 to 0 5 hz on the horizontal components of motion the large amplitude coda of ground motion observed inside the lake bed zone and the spectral ratios between signals observed inside and outside the lake bed zone can only be explained by 2d models of the sedimentary basin in such models the ground motion is mainly controlled by the response of the uppermost clay layer the synthetic signals explain the major characteristics relative amplitudes spectral ratios and frequency content of the observed ground motion the large amplitude coda of the ground motion observed in the lake bed zone can be explained as resonance effects and the excitation of local surface waves in the laterally heterogeneous clay layer also for the 1985 michoacan event the energy contributions of the three subevents are important to explain the observed durations

part i theoretical site response estimation for microzoning purposes we estimate the theoretical site response along seven cross sections located in the city of thessaloniki greece for this purpose the 2 d structural models used are based on the known geometry and the dynamic soil properties derived from borehole measurements and other geophysical techniques several double couple sources have been employed to generate the seismic wavefield and a hybrid method that combines the modal summation with finite differences has been deployed to produce synthetic accelerograms to a maximum frequency of 6 hz for all components of motion the ratios between the response spectra of signals derived for the 2 d local model and the corresponding spectra of signals derived for the 1 d bedrock reference model at the same site allow us to estimate the site response due to lateral heterogeneities we interpret the results in terms of both geological and geometrical features of the models and of the characteristics of the wave propagation the cases discussed confirm that the geometry and depth of the rock basement along with the impedance contrast are responsible for ground amplification phenomena such as edge effects and generation and entrapment of local surface waves our analysis also confirms that the peak ground acceleration is not well correlated with damage and that a substantially better estimator for possible damage is the spectral amplification

psv wave propagation in a medium with local heterogeneities a hybrid formulation and its application summary hybrid methods which combine so called numerical and analytical methods are a successful tool for computing synthetic seismograms for media with localized heterogeneous regions each of the two methods is applied in that part of the medium in which it can be employed efficiently this paper deals with a combination of a finite difference algorithm applied in the neighbourhood of the heterogeneity and a frequency wavenumber filter for the psv wave equation applied outside this method is an alternative to the use of green s theorem as a wavefield continuation method e g van den berg 1984 in the hybrid method presented here absorption can be incorporated additionally for different models with first and second order discontinuities the hybrid method was tested successfully against the reflectivity method the hybrid method was applied to study the effects of a heterogeneous lower crust on the wavefield this application has been inspired by recent deep seismic reflection profiling which often reveals a highly reflecting lower crust the scattering models have been divided into three groups horizontal vertical and isotropic scatterers the comparison of the reflection responses of these models shows that thin horizontal or small isotropic scatterers yield high reflected energy coherent over a few kilometres in the time window of lower crustal reflections vertical structures characterized by a small correlation length in horizontal direction have less energy in this time window but they can generate a complex moho reflection with a strong moho coda it is also shown that the acoustic approximation is mostly not sufficient to describe the wave propagation in such complex media

crustal structure of oaxaca mexico from seismic refraction measurements seismic refraction and gravity data have been analyzed to obtain a model of the compressional wave structure of the ocean to continent transition in the state of oaxaca in southwestern mexico crustal thickness on the continent at the latitude 18 n is 45 4 km based on reflected phases from the moho discontinuity the crust has been modeled with three layers with velocities of 4 3 to 4 6 5 0 to 5 7 and 6 85 to 7 0 km sec each with positive velocity gradient the crust thins to 10 km at the coast near pinotepa nacional where precambrian metamorphic rocks are exposed 45 km from the mid america trench offshore the oceanic structure consists of an 8 km thick crust with a normal crustal velocity structure spudich and orcutt 1980 the apparent dip of the subducting plate beneath western mexico is 10 on the oceanic side strong reflections suggest a minimum depth of 35 km for the lithosphere asthenosphere boundary the asthenosphere has a seismic velocity of 7 6 km sec and a thin lid in which the velocity is 8 6 km sec

seismic motion in urban sites consisting of blocks in welded contact with a soft layer overlying a hard half space we address the problem of the response to a seismic wave of an urban site consisting of a large and infinite number n b of identical equispaced blocks overlying a soft layer underlain by a hard substratum the results of the theoretical analysis appealing to a space frequency mode matching mm technique are compared to those obtained by a space time finite element fe method the two methods are shown to give rise to much the same prediction of seismic response for n b 10 the mm technique is also applied to the case n b infty notably to reveal the structure and natural frequencies of the vibration modes of the urban site the mechanism of the interaction between blocks and the ground as well as that of the collective effects of the blocks are studied it is shown that the presence of a large number of blocks modifies the seismic disturbance in a manner which evokes and may partially account for what was observed during many earthquakes in mexico city disturbances at a much smaller level induced by a small number of blocks are studied in the companion paper

comment on 3d site effects a thorough analysis of a high quality dataset by f j chavez garcia j castillo and w r stephenson chavez garcia et al 2002 presented an analysis of 64 weak motion events recorded by a temporary digital seismometer array operating at parkway valley new zealand from 1 august to mid october 1995 the most significant record was obtained on 11 august for a m l 4 9 earthquake at 80 km epicentral distance with a peak ground acceleration of 1 gal and a peak ground velocity of 5 mm sec the main indication of their analysis was that ground motion is dominated by surface waves originating at the northern edge of the valley and propagating southward mainly in the direction of the sloping base of the valley they also gave much emphasis to a supposed contradiction between this result and the finding reported by paolucci et al 2000 that the ground motion in the frequency band around 1 6 hz shows a clear pattern related to the 2d fundamental vibration mode of the valley chavez garcia et al 2002 argued that paolucci et al 2000 were deceived by the simultaneous arrivals of surface waves at the stations along the different alignments considered fig 1 the alignments being roughly perpendicular to the main direction of propagation of surface waves according to the same authors the error of paolucci et al 2000 p 1950 was originated by considering only groups of stations instead of all of them together figure 1 detail of parkway valley with the station numbers and the alignments considered by paolucci et al 2000 we will briefly recall the main considerations that lead us to the previous conclusions including further results to show that the contradiction is only apparent and that the occurrence of a 2d in plane resonance pattern cannot be ruled out at all by the arguments of chavez garcia et al 2002 2d resonance pattern inferred from records the displacement histories at three station alignments across the valley fig

a study on the response of a soft basin for incident s p and rayleigh waves with special reference to the long duration observed in mexico city abstract the responses of two types of soft basins for incident sh sv p and rayleigh waves in a 2 d elastic half space are investigated with special reference to the long duration of strong motions observed in mexico city during the michoacan mexico earthquake of 1985 first the difficulty for simple 1 d models to reproduce the later part of the accelerogram observed in mexico city is shown then the effect of a 2 d deep basin structure of a relatively large scale 10 km wide and 1 km deep and a moderate impedance ratio 2 5 is studied the results show that surface waves generated at the edges of the basin are clearly propagating inside the basin back and forth however the increase in duration by these surface waves is 20 sec at most introducing another much softer layer inside the basin we found that the calculated durations and envelop shapes become very similar to the observed ones because of the slowness of surface wave propagation these theoretical studies suggest that the exceptionally long duration observed in mexico city might be caused by a strong constructive interaction of soft surface layers with a deep basin structure beneath the city

linear amplification of horizontal strong ground motion in zagreb croatia for a realistic range of scaled point sources the linear amplification of the larger horizontal component of strong ground motion along a selected profile in the city of zagreb is estimated by examining the synthetic waveforms corresponding to a suite of 16 realistically chosen scaled point sources the accelerograms computed for the average bedrock model by modal summation are propagated through local laterally heterogeneous anelastic models by the finite difference algorithm the ratio of peak ground acceleration pga and of the response spectra rs obtained by using local and bedrock models define the pga and rs amplification amp pga and amp rs respectively even variations of the order of commonly observed uncertainties of only dip and rake angles of the causative fault show that both amp pga and amp rs vary at some sites by more than a factor of two it follows that especially for strongly laterally heterogeneous structures local effects must be determined for each of the relevant sources considering all associated uncertainties as completely as possible such a conclusion certainly holds for the case of the microzonation of zagreb where the local geology is quite complex and the seismicity is not confined to a single seismic source zone

the nile valley of egypt a major active graben that magnifies seismic waves the nile valley and the nile delta are part of the active rift that is probably connected with the red sea tectonism this zone is characterized by small to moderate size earthquakes that have caused extremely severe damage to recent and historical constructions the most vulnerable area along the nile valley is the one of cairo faiyoum small local and large distant earthquakes could be a source of huge socio economic damage in this area the loose soft alluvial sediments of the nile canyon are the main factor behind this potential damage because they may greatly amplify the ground motion as demonstrated by strong ground motion modelling the largest amplification is generally concentrated along the edges of the graben and occurs at frequencies between 1 hz and 2 hz this may explain the huge damage caused by distant earthquakes during recent and historical times the distribution of intensity values during the events of 1926 and 1992 is well correlated with the modelled spatial distribution of the spectral amplification

seismic effects of a small sedimentary basin in the eastern tibetan plateau based on numerical simulation and ground motion records from aftershocks of the 2008 mw7 9 wenchuan china earthquake abstract in this study the ground motions that can be attributed to the aftershocks of the 2008 mw7 9 wenchuan china earthquake recorded in the wudu basin which is a small basin in the eastern tibetan plateau are analyzed to investigate the seismic effect of a small sedimentary basin in case of the wudu basin the site responses from the basin edge are stronger than those from the basin center the monitoring sites located near the wudu basin edge and the wudu basin center are sensitive to the low frequency 5 hz components of ground motion respectively it indicates that some different seismic phenomena occurred in a small sedimentary basin compared with a large sedimentary basin to further study the ground motion in a small sedimentary basin a simulation of the wudu basin was conducted using the finite element method with a viscous elastic artificial boundary the grid size of the surface layer of the basin is 2 5 2 5 m2 and high frequency up to 10 hz components of a synthetic waveform were obtained the simulation denoted that the surface wave initially appeared in the wudu basin edge and subsequently propagated into its interior the near surface soil layers exhibiting a relatively low wave velocity magnified the amplitude of the seismic wave in the wudu basin furthermore the numerical simulation results are basically consistent with the actual ground motion records especially with the same predominant frequencies of ground motions at the sites located near the wudu basin edge

deterministic earthquake scenario for the basel area simulating strong motions and site effects for basel switzerland 1 the basel earthquake of 18 october 1356 is considered one of the most serious earthquakes in europe in recent centuries i0 ix m 6 5 6 9 in this paper we present ground motion simulations for earthquake scenarios for the city of basel and its vicinity the numerical modeling combines the finite extent pseudodynamic and kinematic source models with complex local structure in a two step hybrid three dimensional 3 d finite difference fd method the synthetic seismograms are accurate in the frequency band 0 2 2 hz the 3 d fd is a linear explicit displacement formulation using an irregular rectangular grid including topography the finite extent rupture model is adjacent to the free surface because the fault has been recognized through trenching on the reinach fault we test two source models reminiscent of past earthquakes the 1999 athens and the 1989 loma prieta earthquake to represent mw 5 9 and mw 6 5 events that occur approximately to the south of basel to compare the effect of the same wave field arriving at the site from other directions we considered the same sources placed east and west of the city the local structural model is determined from the area s recently established p and s wave velocity structure and includes topography the selected earthquake scenarios show strong ground motion amplification with respect to a bedrock site which is in contrast to previous 2 d simulations for the same area in particular we found that the edge effects from the 3 d structural model depend strongly on the position of the earthquake source within the modeling domain

fully coupled inelastic site response analysis for 1986 lotung earthquake two major earthquakes m 6 2 and m 7 with different characteristics took place in the eastern coast of taiwan in 1986 within a 4 month period a test site at lotung was located near the epicenters of the two quakes the site was instrumented with three dimensional 3d surface and downhole accelerometer arrays and pore pressure transducers embedded at depths from 3 to 16 m below the ground surface field investigation of the site including sampling undisturbed soils was carried out before the two events and followed by a laboratory test program aimed at gaining detailed soil properties based on the available information numerical analyses were performed using a fully coupled multidirectional dynamic procedure incorporating a bounding surface hypoplasticity model the calculated responses for the two different events showed equally reasonable agreements with the field records in both 3d acceleration and pore pressure time histories this paper reports the methodology of the analyses and presents

deterministic earthquake scenarios for the city of sofia the city of sofia is exposed to a high seismic risk macroseismic intensities in the range of viii x msk can be expected in the city the earthquakes that can influence the hazard in sofia originate either beneath the city or are caused by seismic sources located within a radius of 40 km the city of sofia is also prone to the remote vrancea seismic zone in romania and particularly vulnerable are the long period elements of the built environment the high seismic risk and the lack of instrumental recordings of the regional seismicity make the use of appropriate credible earthquake scenarios and ground motion modelling approaches for defining the seismic input for the city of sofia necessary complete synthetic seismic signals due to several earthquake scenarios were computed along chosen geological profiles crossing the city applying a hybrid technique which combines the modal summation technique and finite differences the modelling takes into account simultaneously the geotechnical properties of the site the position and geometry of the seismic source and the mechanical properties of the propagation medium acceleration velocity and displacement time histories and related quantities of earthquake engineering interest e g response spectra ground motion amplification along the profiles have been supplied the approach applied in this study allows us to obtain the definition of the seismic input at low cost exploiting large quantities of existing data e g geotechnical geological seismological it may be efficiently used to estimate the ground motion for the purposes of microzonation urban planning retrofitting or insurance of the built environment etc

spectral element modelling of seismic wave propagation in visco elastoplastic media including excess pore pressure development numerical modelling of seismic wave propagation considering soil nonlinearity has become a major topic in seismic hazard studies when strong shaking is involved under particular soil conditions indeed when strong ground motion propagates in saturated soils pore pressure is another important parameter to take into account when successive phases of contractive and dilatant soil behaviour are expected here we model 1 d seismic wave propagation in linear and nonlinear media using the spectral element numerical method the study uses a three component 3c nonlinear rheology and includes pore pressure excess the 1 d 3c model is used to study the 1987 superstition hills earthquake ml 6 6 which was recorded at the wildlife refuge liquefaction array usa the data of this event present strong soil nonlinearity involving pore pressure effects the ground motion is numerically modelled for different assumptions on soil rheology and input motion 1c versus 3c using the recorded borehole signals as input motion the computed acceleration time histories show low frequency amplification and strong high frequency damping due to the development of pore pressure in one of the soil layers furthermore the soil is found to be more nonlinear and more dilatant under triaxial loading compared to the classical 1c analysis and significant differences in surface displacements are observed between the 1c and 3c approaches this study contributes to identify and understand the dominant phenomena occurring in superficial layers depending on local soil properties and input motions conditions relevant for site specific studies

probabilistic and deterministic seismic hazard results and influence of the sedimentary more basin ne atlantic abstract seismic hazard assessments have been conducted for the ormen lange gas field in the norwegian sea on the flank of the more basin the study used logic tree based probabilistic methods combined with semi deterministic methods for hazard contributions from mapped faults and the hazard was computed in terms of peak ground acceleration pga and spectral acceleration the probabilistic seismic hazard results were complemented by deterministic modelling in 1d wave number integration and 2d finite difference crustal models the deterministic modelling first of all elucidated the shaking duration problem indicating that thick offshore sediment structures like the ones in the more basin may significantly extend the shaking duration of an earthquake the presence of sedimentary layers with large velocity contrasts are responsible for this observation and a conventional soil amplification analysis would not have revealed this phenomenon a modelling along similar lines as indicated in the present paper may be recommended in certain vulnerable situations and in geologic provinces with thick sedimentary layers with significant internal velocity contrasts even though large earthquakes most likely have occurred in the region during the postglacial period the study could not resolve if the huge storegga slide which occurred about 8100 yb was triggered by an earthquake

flow asymmetry associated with astronomical tides implications for the residual transport of sediment 1 tidal current asymmetry is usually associated to nonlinear tidal interactions in shallow water generating compound tides and overtides the present paper demonstrates that tidal asymmetry is not only caused by nonlinear tidal interaction but is also generated by astronomical tides in absence of shallow water effects in particular the k1 o1 and m2 constituents give an asymmetrical periodic flow pattern with the largest peak velocities persistently in the same direction a theoretical explanation for this phenomenon is presented and an inventory is made of other subordinate constituents that may contribute to repetitive asymmetric flow patterns tidal current asymmetry may induce residual transport of sediment analytical expressions are derived which quantify the residual transport of sediment due to the k1 o1 and m2 tides as a function of the phases and amplitudes of these constituents and the time lag between variation in suspended sediment transport and flow velocity the residual transport induced by the k1 o1 and m2 tides is compared to the residual transport due to the asymmetry associated with the m2 and m4 tides the former mechanism is particularly relevant in diurnal or mixed mainly diurnal tidal regimes where the k1 and o1 tides are dominant

comment on on the role of diurnal tides in contributing to asymmetries in tidal probability distribution functions in areas of predominantly semi diurnal tide by p l woodworth d l blackman d t pugh and j m vassie estuarine coastal and shelf science 64 2005 235 240 abstract the present paper comments on a recent publication by woodworth et al woodworth p l blackman d l pugh d t vassie j m 2005 on the role of diurnal tides in contributing to asymmetries in tidal probability distribution functions in areas of predominantly semi diurnal tide estuarine coastal and shelf science 64 2 3 235 240 it is shown how tidal asymmetries associated with astronomical tides can be accounted for in an extreme sea level analysis despite the difficulty of deriving probability distribution functions if a large number of tidal constituents are considered the use of the term spring neap cycle in a diurnal tidal regime is discussed

estimation of site effects in beijing city for the realistic modeling of the seismic ground motion in lateral heterogeneous anelastic media the database of 3 d geophysical structures for beijing city has been built up to model the seismic ground motion in the city caused by the 1976 tangshan and the 1998 zhangbei earthquakes the hybrid method which combines the modal summation and the finite difference algorithms is used in the simulation the modeling of the seismic ground motion for both the tangshan and the zhangbei earthquakes shows that the thick quaternary sedimentary cover amplifies the peak values and increases the duration of the seismic ground motion in the northwestern part of the city therefore the thickness of the quaternary sediments in beijing city is the key factor controling the local ground effects four zones are defined on the base of the different thickness of the quaternary sediments the response spectra for each zone are computed indicating that peak spectral values as high as 0 1 g are compatible with past seismicity and can be well exceeded if an event similar to the 1697 sanhe pinggu occurs

site specific microzonation study in delhi metropolitan city by 2 d modelling of sh and p sv waves delhi the capital of india lies on a severe earthquake hazard threat not only from local earthquakes but also from himalayan events just 200 250 km apart the seismic ground motion in a part of delhi city is computed with a hybrid technique based on the modal summation and the finite difference scheme for site specific strong ground motion modelling complete realistic sh and e5 e5 sv wave seismograms are computed along two geological cross sections 1 north south from inter state bus terminal isbt to sewanagar and 2 east west from tilak bridge to punjabi bagh two real earthquake sources of july 15 1720 mmi ix m 7 4 and august 27 1960 m 6 0 have been used in modelling the response spectra ratio rsr i e the response spectra computed from the signals synthesized along the laterally varying section and normalized by the response spectra computed from the corresponding signals synthesized for the bedrock reference regional model have been determined as expected the sedimentary cover causes an increase of the signal amplitude particularly in the radial and transverse components to further check the site effects we reversed the source location to the other side of the cross section and recomputed the site amplifications there are only a few sites where a large amplification is invariant with respect to the two source locations considered the rsr ranges between 5 to 10 in the frequency range from 2 8 to 3 7 hz for the radial and transverse components of motion along the ns cross section along the ew cross section rsr varies between 3 5 to 7 5 in the frequency range from 3 5 to 4 1 hz the amplification of the vertical component is considerable at high frequency 4 hz whereas it is negligible in lower frequency range

microtremor survey in talchir india to ascertain its basin characteristics in terms of predominant frequency by nakamura s ratio technique abstract the talchir basin one of india s oldest basins has been a subject of interest because of its rich coal deposits the maximum thickness of the basin is about 1500 m beyond the basin is the hard metamorphic rocks of precambrian age the ambient noise survey data have been analyzed for the talchir basin using nakamura s technique of horizontal vertical spectral ratio hvsr to ascertain the basin structure in terms of the predominant frequency the predominant frequency varies from 0 25 hz to 7 8 hz but a major portion of the basin comes under the range of 0 3 hz 2 4 hz while on the metamorphic rocks it is as high as 7 8 hz the variation in predominant frequency shows a good correlation with the sediment thickness of the basin the results have been compared with the previous studies by other researchers and it shows consistency with the northerly dip of the basin the present study has also been compared with the results of the synthetic seismogram that was performed for the talchir basin the predominant frequency obtained from hvsr technique complements well with the frequency at which the peak response spectra ratio is observed the present study of the predominant frequency identifies quite well the characteristics of talchir basin and is in good agreement with the synthetic ground motion modeling of the region

extension of the basin rayleigh wave amplification theory to include basin edge effects the presence of sediments near the earth s surface can significantly amplify the strength of shaking during earthquakes such basin or site amplification effects have been well documented in numerous regions yet the complex and often situational dependence of competing reasons for this amplification makes it hard to quantify in a general sense or to determine the most significant contributions simple 1d seismic profiles can be used to estimate the amplitude differences between a basin site and a hard rock reference site but this ignores any reflections or conversions at the basin edge or a resonance effect depending on the basin s geometry in this article we explore an analytic model based on coupling coefficients for surface rayleigh waves to account for the lateral discontinuities at a basin s edge datta 2018 we use this simple tool to explore the relationship between the basin s rayleigh wave amplification spectrum and various parameters such as basin depth edge slope angle and impedance contrast the step by step construction of the model allows us to quantify the contributions from various wave propagation effects with the goal of identifying situations under which various basin edge effects must be considered in addition to purely 1d estimates for the most velocity contrasts less than a factor of 5 the error made by the 1d theory in predicting maximum rayleigh wave basin amplification is under 35 for both the horizontal and the vertical components for simple basins the vertical amplification dominates at larger high frequencies and the horizontal at lower frequencies finally we demonstrate from comparisons with spectral element wavefield simulations that realistic velocity structures can be reduced to a simpler box shape for the semi analytic formulation used here with reasonable results for the purposes of estimating site amplification or microzonation an improved model that accounts for basin edge effects can be implemented without high computational cost

some contributions of the neo deterministic seismic hazard assessment approach to earthquake risk assessment for the city of sofia this paper describes the outcome of the advanced seismic hazard and seismic risk estimates recently performed for the city of sofia based on the state of the art of knowledge for this site some major results of the neo deterministic scenario based seismic hazard assessment approach ndsha to the earthquake hazard assessment for the city of sofia are considered further validations of the recently constructed synthetic strong motion database containing site and seismic source specific ground motion time histories are performed and discussed displacement and acceleration response spectra are considered the elastic displacement response spectra and displacement demand are discussed with regard to earthquake magnitude seismic source to site distance seismic source mechanism and local geological site conditions the elastic response design spectrum from the standard pseudo acceleration versus natural period t n format converted to a capacity diagram in s a s d format is discussed in the perspective of the eurocode 8 provisions a brief overview of the engineering applications of the seismic demand obtained making use of the ndsha is supplied some applications of the outcome of ndsha procedure for engineering purposes are shown the obtained database of ground shaking waveforms and time histories computed for city of sofia is used to 1 extract maximum particle velocities 2 calculate the space distribution of the horizontal strain factor log10 e 3 estimate liquefaction susceptibility in terms of standard penetration test n values and initial over burden stress 4 estimate damage index distribution and 5 map the distribution of the expected pipe breaks and red tagged buildings for given scenario earthquakes etc the theoretically obtained database based on the simultaneous treatment of the data from many disciplines contains data fully suitable for practical use the proper use of this database can lead to a significant seismic vulnerability reduction and thus contributes to earthquake preparedness

microzonation of bucharest state of the art the 1940 mw 7 7 and 1977 m w 7 4 vrancea earthquakes romania inflicted heavy damage and casualties in bucharest and the statistics indicate a recurrence interval of 25 years for m w 7 0 events under these circumstances the seismic microzonation represents important information for detailed urban planning that establishes an appropriate level of preparedness to the earthquake threat this paper reviews the main studies concerning the seismicity of the vrancea region the site conditions of the city the characterization of the building stock and the codes of practice that regulate the antiseismic design the first order microzonation of bucharest was performed starting from the existing database of structural and geotechnical parameters new insights originating from direct instrumental observation and interpretation of the local effects as well as realistic numerical modeling that update and improve the input data necessary for a detailed microzoning map of the city are also discussed

numerical modelling of sh lg waves in and near continental margins summary the effect of transition regions between continental and oceanic structures on the propagation of l waves from continental sources is examined in particular the attenuation due to variations in layer thickness in such transition regions is calculated and explained for a suite of simple models the measured attenuation due tq the geometry of the transition regions between the oceanic and continental structures within a partially oceanic path with source and receiver in a continental structure is at most a factor of four for frequencies from 0 01 to 1 hz this is inadequate to explain the observed extinction of l along such paths this extinction has previously been attributed to the effects of the transition region geometry the method used to calculate the results presented in this study is developed and its validity and accuracy are demonstrated propagator matrix seismograms are coupled into a finite element calculation to produce hybrid teleseismic sh mode sum seismograms these hybrid synthetics can be determined for paths including any regional transition zone or other heterogeneity that exists as part of a longer mostly plane layered path numerical results presented for a suite of transition models show distinct trends in each of the regions through which the wavefield passes the wavefield passes through a continent ocean transition region then a region of oceanic structure and finally through an ocean continent transition region when an l wavefront passes through a continent ocean transition the amplitude and coda duration of the l wave at the surface both increase at the same time much of the modal l energy previously trapped in the continental crust is able to escape from the lower crust into the subcrustal layers as body waves the magnitude of both these effects increases as the length of the transition region increases when the wavefront passes through the region of oceanic structure further energy escapes from the crustal layer and produces a decrease in l amplitude at the surface the rate of amplitude decrease is maximum near the transition region and decreases with distance from it when the wavefield passes through the oceancontinent transition region a rapid decrease in the l amplitude at the surface of the crust results the energy previously trapped in the oceanic crustal layer spreads throughout the thickening crustal layer some of the body wave phases produced when the wavefield passes through the continent ocean transition region are incident on the continental crust in the ocean continent transition region these waves are predominantly transmitted back into the crust the other body wave phases reach depths below the depth of the base of the continental crust before reaching the ocean continent transition and thus escape from the system

geodetic strain observations and return period of the strongest earthquakes of a given seismic source zone we present the basis for a method for estimating the return period of large and medium earthquakes that is independent of current deterministic and probabilistic approaches the two standard techniques of seismic hazard assessment probabilistic seismic hazard assessment psha and deterministic seismic hazard assessment dsha suffer from limited knowledge of seismic prehistory a further weakness of psha is its requirement of homogeneous seismic activity within a seismic zone moreover psha and dsha were developed for seismically active areas and thus cannot reliably be used in areas of medium and low activity in this paper we propose the combined use of geodetic strain rate data and the seismic moment data set determined for past seismic events this combination represents a new and independent approach to estimation of future seismic activity using a modified version of kostrov s phys solid earth 1 23 40 1974 equation and the catalogue of seismic moments the minimum return period of the strongest earthquakes of a source area is estimated

destructive strong ground motion in mexico city source path and site effects during great 1985 michoacan earthquake simultaneous consideration of source path and site effects on ground motion during the michoacan earthquake of 1985 allows us to draw coherent conclusions regarding the roles played for the disaster in mexico city by the rupture process the mode of propagation of the waves between the epicentral zone and mexico city and the local amplification in contrast to the horizontal component which showed dramatic amplification for the 2 to 3 sec motion at lake sediment sites we observe almost identical vertical displacement seismograms containing ripples with 2 to 3 sec period throughout the mexico city valley whether the recording site is on the lake sediments or on hard rock we therefore conclude that the 2 to 3 sec motion responsible for the destruction of mexico city was present in the incident field after performing a phase analysis we interpret the signal as the superposition of long period rayleigh waves and short period lg with a dominant period of about 3 sec the analysis of the teleseismic records indicates that the radiation of this event is enhanced for waves around the 3 sec period except in the case of stations for which an anomalous path effect is suspected the records present ripples appearing a few seconds after the beginning of the signal the characteristics of near fault records show that the rupture process consists of the growth of a smooth crack the numerical simulation indicates that the 3 sec period ripples can be explained by a series of changes of the rupture front velocity we examine two alternative source models associated with different crustal models to explain the characteristics of the vertical displacements recorded in mexico city our preferred model attributes the cause of the enhanced 3 sec motion to the irregularity in the rupture propagation in addition to the effect of the local conditions in mexico city this interpretation leads to a very coherent scenario of what happened from the start of the failure on the fault up to the destruction in mexico city this example illustrates the need to consider simultaneously source path and site effects in order to understand strong ground motions

comment on the origin of neap spring tidal cycles by erik p kvale marine geology 235 2006 5 18 abstract this paper comments on a recent publication by erik p kvale marine geology 235 2006 5 18 who underlines the importance of tropically driven neap spring cycles here it is stressed that tropically driven neap spring cycles feature a systematic asymmetry prevalent in both flow velocity time series and sealevel records which results from the angular frequency relationship between the k 1 o 1 and m 2 tides persisting tidal asymmetry in turn can determine ebb or flood dominance and plays a prominent role in the depositional processes relevant for marine geological records it is further argued that shoreline changes can alter the transitions from semidiurnal to diurnal tidal regimes especially in narrow straits

ground response in lotung total stress analyses and parametric studies previous papers have reported on the performance of a recently developed nonlinear ground response analysis code spec tra with reference to the prediction of the free field response at a large scale seismic test site in lotung taiwan during the m6 5 earthquake of may 20 1986 two more major earthquakes of different characteristics shook this test site later that same year a m6 2 earthquake that occurred on july 30 and a m7 0 earthquake that occurred on november 15 the present article analyzes the free field responses recorded by a downhole array from these latter two events using the code spectra and a widely used equivalent linear analysis code shake the studies focus on the relative accuracy and sensitivity of the two codes with respect to the variations of the input material parameters using time histories acceleration response spectra fourier acceleration amplitude spectra and arias intensities as criteria for the comparison the two codes captured the general wave form of the acceleration histories well but there was a general tendency for both codes particularly shake to underpredict the arias intensities of the earthquakes

an overview on the seismic zonation and microzonation studies in india abstract the present study presents a review on the progressive development of the seismic zonation map of india both from official agencies and also from independent individual studies the zonation map have been modified and updated regularly with the occurrence of major destructive earthquakes over the years in the indian subcontinent with the addition of new data this study discusses the criteria chosen for the progressive zonation and the major earthquakes that were responsible for retrospection of the earlier published maps the seismic zonation maps of india have also been prepared by various independent workers by adopting different approaches to achieve the purpose of the zonation despite the endeavors from various sources to provide a solution for the problem of earthquake hazards in india there were many limitations on the zonation map as it gives the picture at a regional scale mostly on the bedrock level without addressing the local site conditions but nevertheless the seismic zonation map gives basic guidelines for any region to know the hazard scenario and if any city or urban population is under threat from seismic point of view further site specific seismic microzonation may be carried out in the international scenario the global seismic hazard assessment program gshap in 1999 prepared a hazard map for world in terms of peak ground acceleration pga with a 10 probability of exceedance in 50 years but it turned out to be an underestimation of the hazard parameter when compared with the observed pga to tackle the problem of seismic hazards there was a need to have a detail study on the local site conditions in terms of its geological geophysical and geotechnical properties with the advent of better instrumentation and knowledge on the mechanics of earthquakes it was possible to identify zones of hazards at a local level and this gives rise to the study of seismic microzonation seismic microzonation work has been carried out in india in some of the strategic important mega cities and industrial build up that has the potential of being damaged from future earthquakes as has been shown in the past though the microzonation map is not the final output map as it can still be updated at later stage with more input data it does provide a more realistic picture on the site specific seismic hazard