hillslope infiltration planar slopes the solution of the full nonlinear unsaturated flow equation is given for a problem of infiltration and associated subsurface flows into a planar hillslope of a homogeneous isotropic soil with uniform initial moisture content the solution uses the assumption that at some distance below the slope crest a spatial equilibrium is approached with the moisture content and other properties independent of downslope coordinate x and dependent only on the normal coordinate z and time t the analysis is found to be generally applicable beyond a small distance from the slope crest or from a point of slope change for slope angles less than 30 infiltration normal to the slope differs relatively little from infiltration from a horizontal surface interesting aspects of the solution include a time independent total horizontal flow into the slope and a time dependent downslope total flow component which behaves as t1 2 at small t and as t at large t previously hillslope flows in these directions have been discussed in terms of soil anisotropy and layering but these flows in a homogeneous isotropic soil are simple physical consequences of capillarity and gravity the analysis applies with minor modification to two simple types of hillslope anisotropy 1 anisotropy parallel to the slope and 2 horizontal anisotropy type 1 yields a complicated time dependence of the horizontal flow and type 2 affects downslope flow similarly these flow directions will commonly reverse during the course of the infiltration process

deterministic approach for the seismic microzonation of bucharest the mapping of the seismic ground motion in bucharest due to the strong vrancea earthquakes is carried out using a complex hybrid waveform modeling method which combines the modal summation technique valid for laterally homogeneous anelastic media with finite differences technique and optimizes the advantages of both methods for recent earthquakes it is possible to validate the modeling by comparing the synthetic seismograms with the records we consider for our computations the frequency range from 0 05 to 1 0 hz and control the synthetic signals against the accelerograms of the magurele station low pass filtered with a cut off frequency of 1 0 hz of the 3 last major strong m w 6 vrancea earthquakes using the hybrid method with a double couple seismic source approximation scaled for the source dimensions and relatively simple regional bedrock and local structure models we succeeded in reproducing the recorded ground motion in bucharest at a satisfactory level for seismic engineering extending the modeling to the entire territory of the bucharest area we construct a new seismic microzonation map where five different zones are identified by their characteristic response spectra

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

realistic modeling of seismic input in urban areas a unesco iugs igcp project the estimation of realistic seismic input can be obtained from the computation of a wide set of time histories and spectral information corresponding to possible seismotectonic scenarios for different source and structural models such a data set can be very constructively used by civil engineers in the design of new seismo resistant structures and in the reinforcement of the existing built environment therefore supplying a particularly powerful tool to the prevention efforts of civil defense the availability of realistic numerical simulations enables us to estimate the amplification effects in complex geological structures exploiting the available geotechnical lithological geophysical parameters topography of the medium tectonic historical paleoseismological data and seismotectonic models the realistic modeling of the ground motion is a very important source of knowledge for the preparation of groundshaking scenarios which represent a valid and economical tool in seismic microzonation

sea beam deep tow investigation of an active oceanic propagating rift system galapagos 95 5 w we have tested and corroborated the propagating rift hypothesis with high resolution sea beam and deep tow data collected over the galapagos 95 5 w propagating rift system the propagating rift is continuously breaking through the cocos plate at a velocity of about 50 km m y with an azimuth of about 273 away from the galapagos hotspot this process transfers cocos lithosphere to the nazca plate including the preexisting spreading center which fails as it is gradually preempted by the propagating rift the spreading center azimuth is being changed by about 8 clockwise by this rift propagation the active propagating and failing rift axes overlap by about 15 km and are joined by a broad and anomalously deep zone of nonrigid plate deformation rather than by a transform fault although rift propagation is continuous on a scale of a few kilometers 50 000 years and lithospheric transferral from one plate to the other occurs mostly continuously as the preexisting rift fails it breaks into discrete segments the geometry of seafloor fabric and tectonic elements such as active and failed rifts the v shaped pattern of pseudofaults and the oblique tectonic fabric in the sheared zone of transferred lithosphere are observed as predicted this quantitative verification provides strong support for the propagating rift hypothesis

infiltration and downslope unsaturated flows in concave and convex topographies the solution of the nonlinear unsaturated flow equation is given for a problem of infiltration and associated subsurface flows into concave and convex topographies made up of homogeneous isotropic soil with uniform initial moisture content the analysis embraces concave and convex surfaces which are parts of the surfaces of circular cylinders and spheres we thus model concave and convex slopes of both ridges and isolated hills valley bottoms and hollows and ridgecrests and hillcrests the major geometrical influence on the flow processes is the slope angle only when 1 surface total curvature is less than about 10 times the characteristic infiltration length lgrav or 10 times the sorptive length does the perturbation due to surface curvature need to be taken into account accordingly the earlier analysis of infiltration on planar hillslopes has wide applicability to slopes with surface curvature

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

analysis of spectral ratios for estimating ground motion in deep basins abstract use of nakamura9s spectral ratio horizontal versus vertical components is investigated theoretically for deep sedimentary basins by considering semi circular and semi spherical valleys the ratio is evaluated from the steady state surface response for different incident waves based on this ratio both the resonant frequencies and ground motion amplification are determined the results based on nakamura9s ratio are compared with those based on the sediment to bedrock spectral ratios kagami9s ratio the results show that for both two and three dimensional models nakamura9s technique predicts well the fundamental resonant frequency but it could not determine higher resonant frequencies of the basins the error in nakamura9s estimate of the fundamental resonant frequency increases for stations near the valley center for alluvial valleys considered in this article nakamura9s ratio failed to predict accurately surface ground motion amplification

investigation of a vine matthews magnetic lineation from a submersible the source and character of marine magnetic anomalies we report here the first attempt to map directly the boundary of a vine matthews magnetic stripe on the seafloor our objectives are to study the processes of oceanic crustal accretion as recorded in the reversal transition zone and to investigate the formation of the magnetic source of vine matthews magnetic anomalies our deep tow and alvin based magnetic studies focus on the matuyama brunhes reversal transition on the flanks of the east pacific rise near 21 n while the sea level magnetic anomalies are less than average in clarity for the east pacific rise a three dimensional inversion of deep tow data reveals a sharp strike linear polarity transition less than 1 8 km wide macdonald et al 1980a these measurements have been augmented by mounting a vertical magnetic gradiometer on alvin and making 280 reliable polarity determinations along and across the polarity transition zone even on long traverses across both sides of the boundary we find that nearly every magnetic target has the correct polarity i e the same polarity as the regional magnetic lineation this homogeneity in polarity of the magnetic lineations is surprising the magnetic polarity transition in the outcropping volcanic section is sharp and linear along strike delineated in some cases by a clear geologic contact of opposing flow fronts of different ages several weakly magnetized outcrops mapped within the transition zone may have erupted during the time in which the geomagnetic field was reversing the reversal boundary mapped on the seafloor from alvin is displaced 250 m to 500 m nw away from the spreading axis relative to the position of the average boundary as derived from inversion of the deep tow and sea level magnetic data this offset provides a means for estimating the spillover of lava flows away from the spreading axis during the time the crust was formed the combination of deep tow and alvin measurements suggests that circa 0 7 m y ago the crustal accretion zone magnetized volcanic intrusive and plutonic rocks was 2000 2800 m wide while the zone of recent volcanism alone was only 1000 2000 m wide the determination for the most recent reversal agrees well with submersible observations at the present spreading center where the zone of recent volcanism neovolcanic zone varies between 600 and 2000 m in width this very orderly picture for the formation of magnetic lineations and crustal accretion processes appears to conflict with complex deep sea drilling project dsdp magnetic results from the atlantic we suggest that the crustal generating processes and resulting magnetic structure vary significantly with spreading rate on the slow spreading mid atlantic ridge major episodes of volcanism are likely to be infrequent 104 years the magma chamber may be non steady state and the neovolcanic zone shifts or varies in width considerably this sporadic start and stop spreading process will contribute to a highly heterogeneous and complex crustal and magnetic structure as seen in dsdp holes in addition significant faulting and tilting may disrupt slow spreading crust for intermediate to fast spreading centers more frequent volcanism 50 600 years a nearly steady state magma chamber and a narrow stable neovolcanic zone will create a less complex magnetic and crustal structure both as seen from alvin and as inferred from clear sea level magnetic anomalies in the pacific

vrancea source influence on local seismic response in bucharest the mapping of the seismic ground motion in bucharest due to the strong vrancea earthquakes is carried out using a complex hybrid waveform modeling method that allows easy parametric tests starting from the actually available strong motion database we can make realistic predictions for the possible ground motion the basic information necessary for the modeling consists of a the representative mechanisms for the strong subcrustal events b the average regional structural model and c the local structure for bucharest two scenario earthquakes are considered and the source influence on the local response is analyzed in order to define generally valid ground motion parameters to be used in the seismic hazard estimations the source has its own detectable contribution on the ground motion and its effects on the local response in bucharest are quite stable on the transversal component t while the radial r and vertical v components are sensitive to the scenario earthquake although the strongest local effects affect the t component both observed and synthetic a complete determination of the seismic input for the built environment requires the knowledge of all three components of motion r v t the damage observed in bucharest for the march 4 1977 vrancea event the strongest earthquake to strike the city in modern times is in agreement with the synthetic signals and local response

regional differences in attenuation modelling for eastern china abstract this paper describes the development of seismological models for three sub regions within eastern china an important feature of the modelling is that two main types of local data were used to determine parameters for input into the seismological model shear wave velocity data was used in step one of the procedure for deriving the upper crustal factors which are part of the seismological model two further steps were involved in incorporating the historical intensity mmi data into the modelling in step two the simulated peak ground velocity pgv values were converted to mmi values and site factor was calculated by dividing the inferred pgv value by the respective simulated pgv value for each given short distance earthquake scenario in step three the quality q factor of the seismological model for each sub region was calibrated in accordance with the criterion that site factors inferred from records of long distance earthquakes in the database match with the median site factor obtained in step two for short distance earthquakes importantly the q values obtained by this calibration method were highly consistent with coda q values obtained for each sub region from a previous study by jin and aki based on analysing records of local earth tremors the calibrated q values in combination with the developed crustal factors and geometrical attenuation factor constitute the regional seismological model for eastern china the seismological model so developed takes into account intra regional differences and has been used to simulate strong ground motions by the stochastic method for assessing the potential seismic hazards in the region

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

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

hundreds of small volcanoes on the median valley floor of the mid atlantic ridge at 24 30 n we have identified 481 seamounts from 6 000 km2 of sea beam swaths of the median valley floor of the mid atlantic ridge mar between 24 and 30 n we find that seamount abundances are an order of magnitude larger on average 80 per 1 000 km2 with relief above 50 m than estimated in previous studies along mid ocean ridges in the pacific1 and south atlantic2 suggesting that at this section of the mar seamount volcanism plays an important part in the formation of new oceanic lithosphere the neovolcanic ridge often observed on the inner valley floor3 appears to be constructed totally of individual coalesced seamounts so that our counts represent a minimum estimate the frequency distribution of summit heights of the mar seamounts is consistent with the exponential model describing the heights of off axis seamounts in the eastern pacific4 6 but with different parameters such a distribution of heights may be a fundamental aspect of seamount volcanism related to lithospheric properties and or magmatic plumbing seamount dominated axial volcanism must create a crustal structure very different from classic fissure fed models

simulation of the seismic response of a 2d sedimentary basin a comparison between the indirect boundary element method and a hybrid technique abstract the seismic response of a two dimensional sedimentary basin is studied with the indirect boundary element method ibem and compared with the results of a hybrid technique that combines modal summation and the finite difference technique to perform this numerical experiment we used the observed ground motion at the edge of the basin computed independently with the hybrid technique this ground motion is used to estimate the apparent incoming wave field the estimation is based on a simplified polarization analysis that led us to select time windows for various incident plane wave types the numerical simulations with ibem gave results in the time and frequency domain that compare well with those of the hybrid approach it suggests that a realistic simulation of strong ground motion is possible using two dimensional wave propagation modeling together with an estimate of the incident wavefield this estimate can be obtained with a polarization analysis of observed ground motion at a station located on bedrock as long as the different wave types can be separated in time and frequency

single plume model for asynchronous formation of the lamont seamounts and adjacent eeast pacific rise terrains sonar reflectance is used to quantify the relative ages of young volcanic terrains on a seamount chain and a nearby spreading center in the north equatorial pacific the reflectance is a measure both of the burial of lava by pelagic sedimentation and of the microrelief of the lava the extent of sediment cover and the lava type distribution are calibrated with thousands of bottom photographs the relative ages indicate that the locus of volcanic eruptions has migrated toward the east pacific rise axis zero age activity lies just to the west of the east pacific rise south of the clipperton transform and is probably the cause of an anomalously shallow neovolcanic zone the evidence fits a scenario in which eruptive centers appear evolve and become extinct in succession with little or no overlap in time the eruptive centers are fed in sequence through conduits from buoyant tightly focused magma plumes the near identical heights of many of the centers at the time of their latest eruptions suggest that the seamounts tap the same mantle depth range broad summit plateaus with calderas are formed if the plume volume is such that the hydraulic head is reached and magma is trapped within the volcano in ephemeral magma chambers or conduits if the plume volume is small and the hydraulic head is not reached the seamount remains small with only a small crater the plumes ascend asynchronously from a common region of nucleation in the asthenosphere plumes that follow in close succession build a composite seamount with a string of summit calderas plumes that rise less often result in a line of discrete circular volcanoes

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 i theory summary we consider using theory herein and associated synthetic seismograms in a companion paper 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 stronger the closer in the vertical direction the source modelled as a line assumed to lie in the substratum is to the lower boundary of the soft layer 2 all anomalous features such as long duration of the seismic wavefield including those for regional earthquakes are primarily the result of strong excitation of love modes 3 1 d body wave type of response is non resonant obtained for deep sources and usually characterized by relatively short durations 4 for shallow sources and hypocentral distances that are not very large the response results from a complex interplay of love mode and body wave contributions which requires a numerical description furnished in the companion paper

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

hillslope infiltration divergent and convergent slopes this perturbation analysis of divergence convergence effects on hillslope infiltration and downslope unsaturated flow indicates that in general these effects are unimportant for usual hillslope topography only where the radius of the contour is less than about 10 times the characteristic infiltration length lgrav or 10 times the sorptive length need the perturbation be taken into account this result opens up a considerable extension of applicability of the analysis of infiltration on planar hillslopes to embrace slopes with curved contours such as ridge noses and hollows

geotechnical characterization of the upper pleistocene holocene alluvial deposits of roma italy by means of multivariate geostatistics cross validation results abstract we are presenting an attempt to evaluate the spatial variability of geotechnical parameters in the upper pleistocene holocene alluvial deposits of roma italy by means of multivariate geostatistics the upper pleistocene holocene alluvial deposits of roma are sensitive to high levels of geohazard they occupy a sizable and significant part of the city being the foundation for many monuments historical neighborhoods and archaeological areas and the main host of the present and future subway lines we have stored information from more than 2000 geotechnical boreholes crossing the alluvial deposits into a relational database for the present study only the boreholes with lithologic textural interpretation and geotechnical information were selected the set includes 283 boreholes and 719 samples which have a set of geotechnical information comprising physical properties and mechanical parameters techniques of multivariate statistics and geostatistics were combined and compared to evaluate the estimation methods of the mechanical parameters with special reference to the drained friction angle from direct shear test principal component analysis was applied to the dataset to highlight the relationships between the geotechnical parameters through cross validation analysis multiple linear regression kriging and cokriging were tested as estimators of cross validation demonstrates that the cokriging with granulometries as auxiliary variables is the most suitable method to estimate in addition to proving that cokriging is a good estimator of cross validation demonstrates that input data are coherent and this allows us to use them for estimation of geotechnical parameters although they come from different laboratories and different vintages nevertheless to get the same good results of cross validation in estimation it is necessary for granulometries to be available at grid points since this information being not available at all grid points it is expected that in the future textural information can be derived in an indirect way i e from lithologic textural spatial reconstructions

characterization of seismogenic zones of romania although the time and magnitude range covered by available seismological data is limited several significant regional trends are outlined in the seismogenic zones of romania vrancea region which is by far the most seismically active area has a persistent rate of occurrence of intermediate depth earthquakes clustered in a very confined focal volume and a clear compressive stress regime the deformation field as deduced from the available fault plane solutions is drastically reduced in the crust where the maximum magnitude is below 6 5 except shabla zone in bulgaria the system of major faults developed in a nw se direction in the carpathians foredeep area is certainly linked to the subduction process in vrancea although they seem not to play a significantly active role as could be expected for an active subduction process the existing data indicate an extensional deformation regime over the foredeep area and southern carpathians while a predominant compressive regime is outlined at the contact between the eastern margin of the pannonian depression and carpathians orogen in agreement with the bending tendency of the maximum horizontal compression orientation of the crustal stress field from ne sw in western and central europe to e w in the intra carpathian region grunthal and strohmeyer 1992

marine magnetic data processing in equatorial regions off ghana summary total field magnetic values recorded during a survey by rrs charles darwin off ghana yielded large track crossover errors of up to 120 nt rms value of 58 7 nt which masked the weak magnetic anomalies in this equatorial region the heading effect of the ship s magnetic field and strong diurnal variation in the earth s field are likely causes of the errors a heading effect experiment shows differences of up to 30 nt for charles darwin on different headings which have been corrected for the diurnal variation has been calculated by using the magnetic field observations themselves because observatories are either too distant or were inoperative at the time of the survey a method that uses the anomalies corrected for heading effect and differences at track crossovers was found to produce an acceptable curve with an amplitude of 120nt and a shape similar to that of equatorial observatories fully corrected anomalies have crossover errors of up to only 40 nt with an rms value of 17 5 nt these anomalies reveal a linear magnetic anomaly low along the continental slope off ghana

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

no evidence from multichannel reflection data for a crustal magma chamber in the mark area on the mid atlantic ridge the role of crustal magma chambers in the construction of oceanic crust along the slowly spreading mid atlantic ridge mar is still highly disputed1 some investigators have argued for small short lived crustal magma bodies2 whereas others have postulated the presence of permanent reservoirs centred between ridge offsets which expand and contract in response to a fluctuating magma supply3 thermal modelling4 5 detailed seismic refraction experiments at several different locations along the mar6 9 and micro earthquake10 11 and teleseismic source mechanism studies12 preclude the existence of large steady state magma chambers under the entire mar rift valley however smaller localized crustal magma bodies could be present at least intermittently here we use multichannel seismic reflection profiles to look for evidence of a crustal magma chamber along the mar south of the kane fracture zone in one of the most magmatically robust and hydro thermally active areas presently known along the mar although some subbasement reflectors are imaged we do not see a shallow large amplitude intracrustal reflector that might be associated with a crustal magma body if a crustal magma chamber was associated with the most recent volcanic episode along this part of the mar our results suggest that it was extremely short lived

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

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

ridge jumps and propagations in the south atlantic ocean the normal pattern of mid ocean ridge divergent plate boundaries comprises straight spreading segments with narrow zones of crustal accretion bounded by transform faults where these segments are offset normally the configuration of spreading segments and transform faults is stable for long periods but in places on fast and medium rate spreading ridges the transform offsets have propagated along the ridge axis as some spreading segments have grown at the expense of adjacent ones1 7 although such behaviour has hitherto not been well documented on slow spreading ridges we have mapped multiple ridge jumps and propagating rifts in two areas of the slow spreading 18 mm yr 1 half rate south atlantic ridge crest we attribute this anomalous behaviour in the south atlantic to the presence of hotspots near our study areas causing elevated asthenospheric mantle temperatures and lateral mantle flow with consequent excess volcanism and disruption of the normally well focused melt delivery processes at the ridge crest

stress in the descending relic slab beneath the vrancea region romania we examine the effects of viscous flow phase transition and dehydration on the stress field of a relic slab to explain the intermediate depth seismic activity in the vrancea region a 2 d finite element model of a slab gravitationally sinking in the mantle predicts 1 downward extension in the slab as inferred from the stress axes of earthquakes 2 the maximum stress occurring in the depth range of 70 km to 160 km and 3 a very narrow area of the maximum stress the depth distribution of the annual average seismic energy released in earthquakes has a shape similar to that of the depth distribution of the stress in the slab estimations of the cumulative annual seismic moment observed and associated with the volume change due to the basalt eclogite phase changes in the oceanic slab indicate that a pure phase transition model cannot solely explain the intermediate depth earthquakes in the region we consider that one of the realistic mechanisms for triggering these events in the vrancea slab can be the dehydration of rocks which makes fluid assisted faulting possible

estimation of site effects in bucharest caused by the may 30 31 1990 vrancea seismic events the vrancea region seismicity characterized by focal depths larger than 60 km and major events with magnitudes m w 6 9 is responsible for the most destructive effects experienced in the romanian territory and may seriously affect high risk construction located on a wide area from central to eastern europe this seismogenic volume must be taken into account both for seismic hazard analysis at the regional level southeastern europe and national level romania and bulgaria as well as for microzonation studies of the highly populated cities located in the range of influence of this source since about four destructive earthquakes occur every century in vrancea the microzonation of bucharest the main city exposed to the potential damages due to these strong intermediate depth shocks represents an essential step towards the mitigation of the local seismic risk two main approaches can be considered for the evaluation of the local seismic hazard a collection and extended use for engineering purposes of the recorded strong motion data and b advanced modelling techniques that allow us the computation of a realistic seismic input which can compensate for the lack of strong motion records actually available only for a few events that occurred in the last 20 30 years

a linearized solution of the slope crest infiltration problem it was found recently that the long slope ponded infiltration solution applies also to a wide range of nonplanar topographies the long slope solution neglects any slope crest effect and a careful analysis of this is needed the present work reassesses the previous primitive estimate of the crest effect we solve the problem of linearized infiltration into a symmetrical ridge with 45 slope angles the integral matching of flow behavior gives results of ample accuracy for our purpose the 45 slope is very steep in nature but yields a simple product solution we use this to calibrate the previous long slope criterion for arbitrary slope angle the primary slope crest effect is increase of moisture content and decrease of capillary potential gradients near the crest the affected region propagates downslope but its influence on infiltration dynamics tends to dissipate because the relative importance of capillarity diminishes as time increases we find that the previous criterion for applicability of long slope infiltration dynamics was too conservative by a factor ranging from 2 at very small infiltration times to 100 at large times the solution gives details of both downslope and inslope unsaturated flows the ponded infiltration rate is least at the crest and increases downslope this result is independent of linearization or slope angle

geodynamics and intermediate depth seismicity in vrancea the south eastern carpathians current state of the art abstract the vrancea region of the south eastern carpathians is a remarkable site of intra continental intermediate depth seismicity a large set of geological geophysical and geodetic observations has been accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath vrancea the crustal and mantle dynamics and the linkage between deep and surface processes in the region in this article we review geology and tectonics of the vrancea region including post collisional to recent deformations syn to post collisional magmatism and orogenic exhumation along the east and south carpathians the regional seismicity is analysed and the recent seismic studies including reflection refraction body and surface wave tomography are reviewed we discuss new geodetic measurements of horizontal and vertical movements in the region geoelectric studies density gravity and thermal modelling qualitative and quantitative including retrospective geodynamic models developed for vrancea are analysed the knowledge of regional tectonics geodynamics seismicity lithospheric deformation and stress regime in the vrancea earthquake prone region assists in an assessment of strong ground motion seismic hazard and risk the earthquake simulation seismic hazard and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface finally we discuss unresolved problems in vrancea in order to improve our understanding of the regional evolution present tectonics mantle dynamics intermediate depth seismicity and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the vrancea region the problems to be solved include i the origin of the high velocity body revealed by seismic tomography studies oceanic versus continental ii the lithospheric scale mechanism driving the miocene subsidence of the transylvania basin iii sub crustal structure between 40 and 70 km iv contemporary regional horizontal and vertical movements and v a comprehensive seismic hazard assessment in the region

realistic modeling of seismic wave ground motion in beijing city algorithms for the calculation of synthetic seismograms in laterally heterogeneous anelastic media have been applied to model the ground motion in beijing city the synthetic signals are compared with the few available seismic recordings 1998 zhangbei earthquake and with the distribution of observed macroseismic intensity 1976 tangshan earthquake the synthetic three component seismograms have been computed for the xiji area and beijing city the numerical results show that the thick tertiary and quaternary sediments are responsible for the severe amplification of the seismic ground motion such a result is well correlated with the abnormally high macroseismic intensity zone in the xiji area associated with the 1976 tangshan earthquake as well as with the ground motion recorded in beijing city in the wake of the 1998 zhangbei earthquake