estimation of seismic hazard parameters for the himalayas and its vicinity from complete data files the maximum likelihood estimation of earthquake hazard parameters has been made in the himalayas and its surrounding areas on the basis of a procedure which utilizes data containing complete files of the most recent earthquakes the entire earthquake catalogue used covers the period from 1900 1990 the maximum regional magnitude m max the activity rate of the seismic event the mean return period r of earthquakes with a certain lower magnitude m max m along with their probability of occurrence as well as the parameter b of of gutenberg richter magnitude frequency relationship have been determined for six different seismic zones of the himalayas and its vicinity it is shown that in general the hazard is higher in the zone nei and ban than the other four zones the high difference of the b parameter and the hazard level from zone to zone reflect the high seismotectonic complexity and crustal heterogeneity

ground motion zoning of santiago de cuba an approach by sh waves modelling the expected ground motion in santiago de cuba basin from earthquakes which occurred in the oriente fault zone is studied synthetic sh waves seismograms have been calculated along four profiles in the basin by the hybrid approach modal summation for the path source profile and finite differences for the profile for a maximum frequency of 1 hz the response spectra ratio rsr has been determined in 49 sites distributed along all considered profiles with a spacing of 900 m the corresponding rsr versus frequency curves have been classified using a logical combinatorial algorithm the results of the classification in combination with the uppermost geological setting geotechnical information and geological geometry of the subsoil are used for the seismic zoning of the city three different main zones are identified and a small sector characterized by major resonance effects due to the particular structural conditions each zone is characterized in terms of its expected ground motion parameters for the most probable strong earthquake m s 7 and for the maximum possible m s 8

new relationships between vs thickness of sediments and resonance frequency calculated by the h v ratio of seismic noise for the cologne area germany noise measurements were carried out in the cologne area germany and the resonance frequency of each site was estimated from the main peak in the spectral ratio between the horizontal and vertical component for 32 of these sites the thickness of the sedimentary cover was known from boreholes and a clear correlation between resonance frequency and sediment thickness was observed a formula that correlates cover thickness with frequency of the main peak in the horizontal to vertical spectral ratio was derived in addition a best fitting shear wave velocity distribution with depth vs z as well as a relationship between average shear wave velocity vs and thickness of the sedimentary cover was calculated by using all of the noise measurements and applying the derived relationships we obtained a subsoil classification for the cologne area

site specific modeling of sh and p sv waves for microzonation study of kolkata metropolitan city india kolkata one of the oldest cities of india is situated over the thick alluvium of the bengal basin where it lies at the boundary of the zone iii and zone iv of the seismic zonation map of india an example of the study of site effects of the metropolitan kolkata is presented based on theoretical modeling full synthetic strong motion waveforms have been computed using a hybrid method that combines the modal summation and finite difference techniques the 1964 calcutta earthquake which was located at the southern part of kolkata is taken as the source region with the focal mechanism parameters of dip 32 strike 232 and rake 56 four profiles are considered for the computation of the synthetic seismograms from which the maximum ground acceleration a max is obtained response spectra ratios rsr are then computed using a bedrock reference model to estimate local amplifications effects the a max varies from 0 05 to 0 17 g and the comparison of the a max with the different intensity scales mm msk rf and mcs shows that the expected intensity is in the range from vii to x mcs for an earthquake of magnitude 6 5 at an epicentral distance of about 100 km this theoretical result matches with the empirical historical and recent intensity observations in kolkata the rsr as a function of frequency reaches the largest values largest amplification in the frequency range from 1 0 to 2 0 hz the largest site amplification is observed at the top of loose soil

core complex geometries and regional scale flow in the lower crust a simple flexural model that treats the lithosphere as a thin elastic plate overlying a fluid asthenosphere produces an excellent fit to the domal detachment fault geometries observed in typical core complexes of the basin and range province however this mode of isostatic compensation requires an unacceptably large reduction in local topographic elevation 3 5 km above core complex structures because topographic lows of this magnitude are not observed above core complexes today it requires mountain ranges 3 5 km higher than the surrounding areas to have existed at the site of each future core complex and requires these mountain ranges to have had large crustal roots that were subsequently uplifted to form a flat moho as the core complexes developed an alternate mode of isostatic compensation whereby compensation occurs primarily by regional scale flow of material within the lower crust beneath an elastic midcrust provides an equally good fit to the observed detachment fault geometries while requiring little reduction in local topographic elevation above developing core complex structures and providing an obvious means of maintaining a flat moho beneath these zones of upper crustal doming if this interpretation is correct then the effective elastic plate thickness below the basin and range province probably cannot exceed a maximum of about 4 km with a best guess estimate of about 0 5 to 1 km computation of the temperature structure associated with crustal flow during doming shows that an increase in temperature at the moho of about 100 c follows doming by several million years perhaps explaining the observed coincidence of core complexes with crustally derived igneous rocks subsequent cooling of the mid to lower crust beneath the core complex could result in freezing of the initially ductile lower crust within the core of the dome effectively locking the domal shape into the crust even after the detachment surface is cut by younger faults

seismicity and seismic hazard in alexandria egypt and its surroundings alexandria city has suffered great damage due to earthquakes from near and distant sources both in historical and recent times sometimes the source of such damages is not well known seismogenic zones such as the red sea gulf of aqaba dead sea hellenic arc suez cairo alexandria eastern mediterranean cairo faiyoum and the egyptian costal area are located in the vicinity of this city the egyptian coastal zone has the lowest seismicity and therefore its tectonic setting is not well known

first order seismic microzonation of haldia bengal basin india using a gis platform the seismic microzonation of the bengal basin haldia region india is carried out using the analytical hierarchy process ahp on the geographic information system gis three themes are used for the seismic microzonation namely peak ground acceleration pga predominant frequency and elevation map an analysis of the maximum magnitude mmax and the b value is carried out after preparing the earthquake catalogue from various sources on the basis of the tectonic set up and seismicity of the region five seismic zones are delineated which can be a threat to haldia they are broadly classified as zone 1 arakan yoma zone ayz zone 2 himalayan zone hz zone 3 shillong plateau zone spz zone 4 bay of bengal zone bbz and zone 5 shield zone sz the mmax for zones 1 2 3 4 and 5 are 8 30 0 51 9 09 0 58 9 20 0 51 6 62 0 43 and 6 61 0 43 respectively the pga value is computed for haldia following the attenuation relationship taking the mmax of each source zone the expected pga at haldia varies from 0 09 0 19 g the predominant frequency of haldia is also calculated using the h v ratio with a frequency ranging from 0 1 3 0 hz the elevation map of haldia is also generated using the shuttle radar topography mission strm data a first order seismic microzonation map of haldia is prepared in which four zones of hazard have been broadly classified for haldia as very high seismic hazard zone high seismic hazard zone moderate seismic hazard zone and less seismic hazard zone the very high seismic hazard zone is observed along the southern part of haldia where there are major industrial and port facilities the pga for the four hazard zones are 0 09 0 13 g for low hazard zone 0 13 0 15 g for moderate hazard zone 0 15 0 16 g for high hazard zone and 0 16 0 19 g for very high hazard zone

the detection and interpretation of hydrogen in fault gases hydrogen gas can be released by chemical and mechanical changes in crustal rocks once released it is highly mobile buoyant and almost insoluble in groundwater a fault system may act as a conduit allowing hydrogen to accumulate in soil gases near a surface expression since hydrogen is scarce in ambient air its presence at elevated levels in soil gases may be a tool for fault mapping in order to evaluate this tool we surveyed eleven different faults by measuring the concentration of hydrogen and methane in 2 to 21 soil gas samples that were collected near each of them the sense of motion at four of those faults is normal western united states greece at five it is strike slip or dip slip california colorado japan and at two it is thrusting california at four of these faults hebgen lake yellowstone yamasaki burro mountain maximum concentrations of hydrogen ranged from 80 ppm to 70 and methane from 300 ppm to 5 all other sites showed ambient levels of both gases except for one sample taken at mt borah idaho that was 2 methane from this preliminary study it is not clear whether the presence of hydrogen is correlated uniquely to the location of faults or whether it occurs randomly the conditions required to produced and accumulate hydrogen are also not clear excess hydrogen may well be produced by different mechanisms in different geological regimes for example if ferrous hydroxide is present in local rocks it may react to produce hydrogen detailed and extensive studies are needed to clarify the connection between hydrogen and tectonic faulting

modes of continental lithospheric extension experimental verification of strain localization processes abstract three modes of continental lithospheric extension narrow rift wide rift and core complex were studied by means of analogue experiments the experimental method is based on models which simulate an idealized lithospheric strength profile and are scaled for gravity various styles of lithospheric extension were induced by systematic variation of brittle upper crustal thicknesses narrow rifting occurs during stable lithospheric extension when the resistance of the brittle upper crust dominates the deformation process wide rifting results from unstable lithospheric extension when the brittle upper crust is thin and ductile flow in the lower crust allows expansion of the deformation zone periodic instabilities with two wavelengths dominate wide rifting core complex mode extension is transitional between unstable and stable lithospheric extension it begins as a distributed zone of unstable extension due to thin upper brittle crust but lower crustal flow induced by the gravity force causes a relocalization of strain into narrow zones transitions between the three modes of extension are characterized in terms of competition between the strength of lithosphere and gravity forces as well as between stable and unstable deformation processes

seismic ground motion in napoli for the 1980 irpinia earthquake the seismic ground motion in the urban area of napoli has been computed for the 1980 earthquake m s 6 9 with a hybrid technique based on the mode summation and the finite difference methods the detailed geological setting of each quarter has been reconstructed from several stratigraphies and six geological zones have been recognized shear wave velocity profiles have been assigned based on hole tests and inversion of rayleigh group velocities artificially generated

structural style in a young flexure induced oblique extensional system north western bonaparte basin australia abstract in the north western bonaparte basin north west shelf of australia neogene to recent flexure induced extension superimposed obliquely over the mesozoic rift structures thus the area offers a good opportunity to investigate the dynamics and architecture of oblique extension fault systems analysis of basin scale 2d and 3d seismic data along the vulcan sub basin shows that neogene deformation produced a new set of extensional en echelon faults at places accompanied by the reactivation of the mesozoic faults the pre existing mesozoic structures strongly control the distribution of the neogene recent deformation both at regional and local scales main controls on the neogene recent fault style density and segmentation linkage include 1 the orientation of the underlying mesozoic structures 2 the obliqueness of the younger extension relative to the rift inherited faults and 3 the proximity to the timor trough three types of vertical relationships have been observed between mesozoic and neogene recent faults hard linkages seems to develop when both fault systems trend parallel therefore increasing risks for trap integrity it is suggested that the orientation of maximum horizontal stress s hmax relative to the mesozoic faults forming hydrocarbon traps is critical for their potential seal leak behaviour stratigraphic growth across the faults indicates that main fault activity occurred during the plio pleistocene which corresponds to the timing of tectonic loading on timor island and the development of lithospheric flexure synchronism of normal faulting with flexural bending suggests that extensional deformation on the descending australian margin accompanied the formation of the timor trough

seismic hazard analysis of india using areal sources in view of the major advancement made in understanding the seismicity and seismotectonics of the indian region in recent times an updated probabilistic seismic hazard map of india covering 6 38 degrees n and 68 98 degrees e is prepared this paper presents the results of probabilistic seismic hazard analysis of india done using regional seismic source zones and four well recognized attenuation relations considering varied tectonic provinces in the region the study area was divided into small grids of size 0 1 degrees x 0 1 degrees peak horizontal acceleration pha and spectral accelerations for periods 0 1 s and 1 s have been estimated and contour maps showing the spatial variation of the same are presented in the paper the present study shows that the seismic hazard is moderate in peninsular shield but the hazard in most parts of north and northeast india is high c 2012 elsevier ltd all rights reserved

monitoring of hydrogen along the san andreas and calaveras faults in central california in 1980 1984 hydrogen h2 has been monitored continuously at 1 5 m depth at nine sites along the san andreas and calaveras faults in central california since december 1980 site characteristic small noninstrumental diurnal variations were recorded during quiescent periods at most sites abrupt h2 changes were observed concurrently at two sites on the calaveras fault some of these were correlated with oscillatory fault slips large 1000 4000 ppm h2 increases were recorded at some sites on the san andreas fault between july 1982 and november 1983 which may be correlated with eleven m 5 earthquakes that occurred near coalinga during this period we attribute both the h2 increases and the triggering of the earthquakes to a large scale compressive stress field within the ductile mafic crust near the plate boundary the stress perhaps caused bulging of the base of the brittle upper crust and thus caused dilation of the san andreas fault zone allowing the escape of pent up h2 generated by hydration reaction of the mafic crust at the same time mobile serpentinites may have squeezed into the seismogenic fault beneath the coalinga area triggering the earthquakes

control of the rheological structure of the lithosphere on the inward migration of tectonic activity during continental rifting analogue models are used to analyse the parameters controlling the evolution of extensional deformation in continental rifts models are deformed in a centrifuge and simulate the continental lithosphere floating and extending above a low viscosity asthenosphere model results reproduce the typical evolution of deformation during continental narrow rifting with early activation of large boundary faults and basin subsidence followed by their abandonment and localization of tectonic activity in internal faults near the centre of the rift the experiments document the strong influence exerted by the thickness of both brittle and ductile crustal layers and syn rift sediment accumulation on the evolution of deformation namely on the amount of bulk extension preceding inward fault migration thin upper and or lower crust and absent or low syn rift sedimentation promote a rapid abandonment of boundary faults and a transition to in rift fault development for low amounts of extension conversely thick upper and or lower crust and high syn rift sediment accumulation favour prolonged slip on boundary faults and delayed development of internal faulting the experimental results suggest that the inward migration of faulting during extension of continental lithosphere results from the interplay between the ductile stresses acting at the base of the upper crust and the total resistance of this brittle layer

hydrogen gas of organic origin in shales and metapelites abstract the changes in inorganic and organic gases retained in shales and metapelites with increasing heating temperature are not fully understood the compositional and isotopic changes of residual gases such as h 2 ch 4 and co 2 in marine shales and metapelites during burial diagenesis and metamorphism were investigated in the present study shale rocks and metapelites which experienced paleo temperatures in the range of 100 600 c were collected from the borehole cores in niigata sedimentary basin and outcrops exposed in kochi district japan gases released from shale or metapelite fragments during pulverization in the laboratory were analyzed as the residual gas the major residual gas in shales and metapelites changes from co 2 ch 4 to h 2 in this order with increasing temperature drastic decrease of co 2 derived from decarboxylation of sedimentary organic matter is due to the expulsion of pore fluids with dissolved co 2 the ch 4 concentration in residual gas subsequently increases with organic maturation and reaches the maximum at paleo temperature of ca 250 c the ch 4 concentration decreases during late metagenesis to metamorphism probably due to the formation of h 2 gas and graphite the h 2 starts to increase at paleo temperature of ca 200 c the h 2 gas is the most abundant gas in residual gas of metapelite the 2 value of h 2 in shales and metapelites is quite low to be in the range of ca 850 to 650 the change of major residual gas from ch 4 to h 2 with increasing paleo temperature and the significantly low 2 h values of h 2 suggest that h 2 gas in shales and metapelites is largely derived from liberation of hydrogen in organic matter

crustal structure of the sw moroccan margin from wide angle and reflection seismic data the dakhla experiment part b the tectonic heritage abstract the dakhla 2002 experiment on the northwest african margin obtained deep penetration multichannel reflection mcs and wide angle seismic obs data these results were combined with total magnetic intensity data kinematic reconstructions and geological field studies to decipher the early tectonic and sedimentary history of the south moroccan margin adjacent to the reguibat shield the structural study of this margin shows that the crust thins from about 28 km beneath the un thinned continental domain to less than 10 km over a lateral distance of about 120 km the dakhla margin differs from the structural scheme of the adjacent african margin segments there the moho rise generally observed just above the deepening of the top of the basement is achieved with an offset of around 50 km with respect to the latter in early jurassic time the break up of continental crust in what is now the central atlantic led to the formation of two basins one on either side of the reguibat which correspond to the older parts of segments of the late palaeozoic hercynian orogen the dakhla segment appears as a precambrian cratonic zone squeezed between two orogenic segments which have remained unaffected by break up processes and the lower crust of this particular domain has behaved differently from all other neighbouring appalachian north america and mauritanide domains this observation points to the important role of tectonic inheritance in the structural development of passive continental margins

experimental studies of the mechanisms of seismo geochemical precursors the following aspects of modeling experiments on seismo geochemical precursors are described 1 gas emission during laboratory stress loading and rupture of rocks 2 field measurements with explosion sources 3 aquifer mixing tests in the field 4 experimental studies of physico chemical processes caused by stress events from these studies three conclusions have been drawn 1 long term seismo geochemical anomalies appear to be related to the stage of elastic deformation of rocks under stress loading prior to a seismic event short term anomalies appear to be related to the plastic deformation of rock and spike like anomalies appear to be related to shear displacement before an earthquake 2 anomalous changes in chemical composition of groundwater and the escape of gases from the ground appear to result from rock fracturing which opens up pathways for the upward migration of water from deep confined aquifers and for the upward migration of gases from the deeper crust 3 chemical reactions induced by increasing stress in the epicentral region may result in the anomalous changes in chemical composition of groundwater observed before some large earthquakes

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

origin of hydrogen and carbon dioxide in fault gases and its relation to fault activity gases occluded in fracture zones of active faults are characterized by a high concentration of h 2 and or co 2 a predominant gas species h 2 or co 2 is related to the lithofacies which the fault cuts carbon dioxide concentration in sediments fluctuates with temperature this evidence and sigma 13 c of co 2 about 20 suggests that co 2 originates from organic materials carbon dioxide with sigma 13 c of 5 to 17 in brecciated gneiss containing marble may have been produced by interaction between organically derived co 2 and the marble or alternatively may have been magmatically derived hydrogen usually occurs in sheared silicate rocks and its concentration fluctuates a great deal the concentration of h 2 from active faults associated with historical earthquakes usually amounts to as high as several percent in maximum whereas the concentration of h 2 from quaternary faults not associated with historical earthquakes is at most 1

tectonic and denudational history of the rennick graben north victoria land implications for the evolution of rifting between east and west antarctica 1 the tectonic depression of the rennick graben northern victoria land antarctica is a key element for deciphering the cenozoic separation history between east and west antarctica and evolution of the west antarctic rift system the geometry kinematics and timing of the boundary faults of the rennick graben are presented on the basis of a detailed structural study of the major fault segments combined with apatite fission track data the structural architecture of the rennick graben is controlled by distributed and partitioned right lateral strike slip faulting fission track data indicate that the last significant denudation stage of the rennick graben shoulders started from eocene times with increasing cooling and denudation since 40 50 ma a direct structural connection is then established between cenozoic denudation and the activation of the dextral strike slip regime in north victoria land during the cenozoic in this framework the rennick graben is interpreted as a localized tectonic depression generated as a displacement accommodation area of the regionally sized dextral strike slip shearing the results of this study 1 invalidate the commonly assumed link between mesozoic ross sea rifting and opening of the rennick graben 2 argue against orthogonal rifting models for the cenozoic evolution of the ross sea region and 3 provide constraints to the modalities and timing of the separation between the east antarctic craton and the west antarctica extensional province

b values of two tectonic parts in the circum pacific belt two different data sets have been applied to compute theb parameter of the magnitude frequency relation for two different areas in the circum pacific belt these areas are a south america middle america and mexico b all the remaining island arcs of the circum pacific belt starting from alaska and the aleutian islands and proceeding southeastwards the first data set spreads over 77 years while the second one covers a 90 year period in both cases the results clearly showed that theb values are lower in the first of the above mentioned areas while respectively higher in the second this is due to the tectonic conditions in these areas as estimated during the present work

seismicity and tectonic structures in the site of algiers and its surroundings a step towards microzonation we intend to reappraise the seismogenic potential of the geologic structures in the site of algiers and its surroundings a compilation of a working earthquake catalogue is first made using all events reported in all previous documentation available however for the sake of homogeneity and a certain degree of reliability of the data only revised seismic events with epicenter coordinates magnitude and or intensity are included a tectonic setting of the zone under investigation and available fault plane solutions are presented the results obtained in previous seismological studies of the most recent earthquakes of the area are also discussed the findings highlight the great interest to be taken in the detailed and timely assessment of the seismic hazard of algiers and its surroundings which is made possible by the realistic modelling of the scenario seismic input

modelling the lithospheric rheology control on the cretaceous rifting in west antarctica small scale analogue models were used to investigate the process of cretaceous orthogonal extension in the west antarctic rift system the models considered the transition from the east antarctic craton to a weaker lithosphere and the results support previous hypotheses about the strong control exerted by lateral variations in lithospheric structures on the process of extension strain was mostly accommodated at the boundary between the two types of lithosphere with a relative uplift of the cratonic block which remained essentially undeformed conversely the weaker lithosphere showed wide rifting style geometry locally associated with core complex like structures in agreement with the natural prototype this tectonic scenario led to a long lasting extension without continental break up and to the absence of relevant surface magmatism 2007 blackwell publishing ltd

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

global seismicity of 2003 centroid moment tensor solutions for 1087 earthquakes abstract centroid moment tensor cmt solutions are presented for 1087 earthquakes that occurred during 2003 the solutions are obtained using the method of dziewonski et al dziewonski a m chou t a woodward j h 1981 determination of earthquake source parameters from waveform data for studies of global and regional seismicity j geophys res 86 2825 2852 and applying corrections for aspherical earth structure as represented by the whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging vol 19 plenum press new york pp 785 797 the model of inelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of inelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms the focal mechanisms of the largest or otherwise significant earthquakes of 2003 are reviewed

h2 generation by reaction between h2o and crushed rock an experimental study on h2 degassing from the active fault zone granite and quartz were crushed under moist conditions in the temperature range of 25 270 c in order to obtain the information on the mechanism operative for h2 degassing along active faults it was found that the amounts of h2 gas released by crushing granite and quartz increased with temperature up to around 200 c and then decreased suddenly the results indicate that h2 gas is generated by a chemical reaction between water and such radicals as si and si o formed on the fresh surfaces when the si o si bonds are destroyed by crushing and that the existence of a maximum for amount of h2 gas is due to the decrease of the lifetime of si o radical at the temperature higher than about 200 c the results lend credence to the possibility that h2 gas is generated in the temperature range of 25 270 c along the active fault through the reaction between groundwater and the fresh surfaces of underground rocks formed by the fault movements

radon and helium in soil gases at canadas caldera tenerife canary islands spain abstract the spatial distribution of soil radon was investigated at canadas caldera tenerife in two surveys carried out in the summers of 1992 and 1995 by using particle sensitive cellulose nitrate films track etch and emanometry respectively soil helium was studied at several transects crossing different structural features of the area radon concentration measured by track etch ranged from 1 0 to 1990 pci l while that measured by emanometry ranged from 0 1 to 618 pci l soil helium concentration varied from 5250 to 15 560 ppb with an average value of 6197 ppb the spatial distribution of soil radon correlates quite closely with structural features fractures emission centers etc where the main geothermal manifestations fumaroles steam ground and high subsurface temperature and gas contents also occur areas showing high soil rn concentrations occur at the summit of teide roques de garcia caldera rim and south and east off side of the caldera high soil helium anomalies correlate well spatially with those of radon especially at the summit of teide where relatively high 3 he 4 he isotopic ratios occur suggesting a deep contribution for these emanations data indicate that radon and helium are supplied mostly from a deep source with a minor contribution from u and th rich shallow rocks and soils

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

mantle exhumation at passive margins abstract laboratory models of lithosphere necking have been used to study the modes of passive margin formation and related mantle exhumation at continent ocean boundary four layer models were constructed with sand and silicone putty to represent the brittle and ductile layers respectively of both crust and mantle it is shown that necking of the whole lithosphere model is nearly symmetrical pure shear but that asymmetrical structures simple shear develop internally due to heterogeneous boudinage and or faulting of brittle layers relative movements between brittle layers is accommodated by layer parallel shear in the ductile layers defining a set of conjugate shear zones with increasing stretching lower crust and mantle shear zones become juxtaposed as the lower ductile mantle layer rises up through the separation zone of boudins in the brittle layer the experimental results are used to propose a general model of passive margin formation leading to mantle exhumation they are also compared to the situation observed on the west iberia margin the exhumation of lithosphere mantle is the result of a bulk pure shear at lithospheric scale shearing of exhumed mantle rocks does not correspond to detachment faults cross cutting the whole lithosphere at the onset of rifting but results from heterogeneous stretching and boudinage of the high strength sub moho mantle

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

transition from continental break up to punctiform seafloor spreading how fast symmetric and magmatic 1 we present a comparison between numerical and analogue models focusing on the role of inherited lithospheric structures in influencing the process of continental break up our results highlight that the presence of pre existing anisotropies localizes strain and favors continental break up and formation of a new ocean for a fixed strain rate the pre rift lithosphere configuration influences rift duration melt production and width and symmetry of the continental margin pair model results show a mainly two phase tectonic history from continental extension to oceanization in the first phase extension affects contemporaneously the whole rift structure while in the second phase asthenosphere upwelling occurs into punctiform regularly spaced spots sequentially propagating in an extension orthogonal direction index terms 8109 tectonophysics continental tectonics extensional 0905 8120 tectonophysics dynamics of lithosphere and mantle general 8150 tectonophysics plate boundary general 3040 citation corti g j van wijk m bonini d sokoutis s cloetingh f innocenti and p manetti transition from continental break up to punctiform seafloor spreading how fast symmetric and magmatic geophys res lett 30 12 1604 doi 10 1029 2003gl017374 2003

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

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

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

dynamics of magma emplacement in centrifuge models of continental extension with implications for flank volcanism a set of experimental small scale models of continental extension investigated the emplacement of orthogonal and oblique magma chambers initially underplated at the base of the crust the models are driven by a centrifugal body force which simulates the role of gravity in nature the models represent crustal conditions analogous to relatively mature continental rifts and consider both symmetric and asymmetric extension the experimental results suggest that magma emplacement is controlled by the interactions between tectonics and rheology of the crustal layers in particular extension is mainly accommodated by lateral flow and ductile doming in the viscous layer simulating the lower crust and by listric normal faults in the overlying brittle layer associated with the ductile domal uplift stretching of the continental crust induces a reactive migration of viscous layers into the footwall of major normal faults where magma accumulation at the core of the domes takes place this behavior suggests that widespread magmatism is expected to localize in the footwall of major normal faults a situation that is often observed in core complex structures although the models presented here are intended to simulate magma emplacement during extension of a two layer brittle ductile system lateral flow and migration of magma initially underplated at the base of the crust beneath narrow rifts e g the ethiopian rift may also provide a similar mechanism and a possible explanation for the occurrence of important volcanoes on the plateaus flanking the rift zones in the suggested model such volcanoes are related to large basaltic magma reservoirs located at the base of the crust to accommodate the space vacated by lateral flow and thinning of the ductile crust the similarity in structure of the models with natural examples of continental extension modes such as rift systems and core complexes may suggest a close similarity of dynamic processes

gas geochemistry applied to earthquake prediction an overview terrestrial gases in groundwater and soil air have been extensively studied in recent years in seismically active areas especially in ussr china japan and united states in search of premonitory changes that might be useful for earthquake prediction concentrations of radon helium hydrogen mercury carbon dioxide and several other volatiles have been found generally to be anomalously high along active faults suggesting that the faults may be paths of least resistance for the terrestrial gases generated or stored in the earth to escape to the atmosphere temporal gas concentration changes with durations of a few hours to many months have been observed before many large earthquakes at a relatively small number of favorably situated stations at epicentral distances of up to several hundreds of kilometers these sensitive stations are generally located along active faults especially at intersections or bends of faults or some other structurally weak zones possibly because of tectonic strain concentration at such places however gas concentrations especially those measured at or near the ground surface may also be significantly affected by meteorological hydrological and other nontectonic changes in the environment the nontectonically induced variations must be carefully eliminated or recognized in the search of true earthquake related anomalies

ross sea mylonites and the timing of intracontinental extension within the west antarctic rift system there are few direct constraints on the timing and style of faulting in the ross sea sector of the west antarctic rift system although cretaceous plate reconstructions indicate that ross sea extension between east and west antarctica occurred prior to breakup of the gondwana margin ca 80 ma mylonitic gneisses dredged from the eastern ross sea indicate shear zone deformation considerably earlier at 98 95 ma strain analysis of fab rics indicates 85 100 extension overprinting brittle structures record translation of shear zone gneisses into the upper crust samples yield sensitive high resolution ion microprobe u pb zircon ages of 102 97 ma correlated to byrd coast granite onshore and concordant 40 ar 39 ar biotite and k feldspar ages of 98 95 ma indicating that granites were mylonitized soon after emplacement and cooled rapidly apatite fission track data corroborate this rapid cooling event and reveal a second rapid cooling event ca 80 ma evidence for contemporaneous deformation and a similar thermal evolution at deep sea drilling project site 270 on the ross sea central high and for a migmatite dome on land attests to the regional extent of intracontinental extension extension occurred at a time of complex microplate interactions along the cretaceous active gondwana margin sug gesting that distributed deformation in the overriding antarctic plate may be related to plate boundary dynamics

cenozoic evolution of the yilan yitong graben in ne china an example of graben formation controlled by pre existing structures abstract the ne trending yilan yitong graben yyg occurs along the yilan yitong fault zone in the northern segment of the tan lu fault zone northeastern china it shows an unusually narrow straight shape in map view with a length of ca 600 km and width of

microzonation for earthquake hazards yenisehir settlement bursa turkey abstract detailed geological hydrogeological and geotechnical studies were performed for the assessment of the foundation conditions of the present and future settlement areas of yenisehir yenisehir is located 50 km east of bursa turkey within an east west trending elliptical sedimentary basin the present and future development areas of yenisehir cover 10 km 2 the topography of the settled area is quite smooth and the slopes are generally less than 10 yenisehir is located within a first degree earthquake zone of turkey according to the seismic design code the seismicity of the town is mainly controlled by the geyve iznik and bursa fault zones the study also involves trial pitting drilling in situ testing and laboratory testing borehole logs index properties of soils standard penetration test results and groundwater level measurements were used for activity and liquefaction assessments of the foundation material based on the evaluation of the data two geotechnical zones were distinguished the northern part of the area is characterized by cohesive soils of high expansion behaviour and the southern part by alternation of cohesive and non cohesive soils showing high liquefaction potential

dynamic processes controlling evolution of rifted basins abstract the extension of the lithosphere controlling the development of rifted basins is driven by a combination of plate boundary forces frictional forces exerted on the base of the lithosphere by the convecting asthenosphere and deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system although mantle plumes are not a primary driving force of rifting they play an important secondary role by weakening the lithosphere and by controlling the level of rift related volcanic activity a distinction between active and passive rifting is only conditionally justified the extension of the lithosphere depending on its rate and magnitude and the potential temperature of the asthenosphere can cause by adiabatic decompression partial melting of the lower lithosphere and upper asthenosphere in rift systems the level and timing of volcanic activity is highly variable the lack of volcanic activity implies passive rifting an initial passive rifting stage can be followed by a more active one during which magmatism plays an increasingly important role magmatic destabilization of the moho may account for the frequently observed discrepancy between upper and lower crustal extension factors combined with evidence for thermal thinning of the mantle lithosphere this suggest that the volume of the lithosphere is not necessarily preserved during rifting as advocated by conventional stretching models the structural style of rifts is controlled by the rheological structure of the lithosphere the availability of crustal discontinuities that can be tensionally reactivated the mode orthogonal or oblique and amount of extension and the lithological composition of pre and syn rift sediments simple shear extension prevails in rifts that subparallel the structural grain of the basement pure shear extension is typical for rifts cross cutting the basement grain pre existing crustal and mantle lithospheric discontinuities contribute to the localization of rift systems the duration of the rifting stage of extensional basins is highly variable stress field changes can cause abrupt termination of rifting in major rift systems progressive strain concentration on the zone of future crustal separation entails abandonment of lateral rifts depending on constraints on lateral block movements crustal separation can be achieved after as little as 9 my and as much as 280 my of rifting activity syn rift basin subsidence is controlled by isostatic adjustment of the crust to mechanical stretching of the lithosphere its magmatic inflation and thermal attenuation of the mantle lithosphere post rift basin subsidence is governed by thermal reequilibration of the lithosphere asthenosphere system deep seated thermal anomalies related to syn rift pull up of the asthenosphere lithosphere boundary have decayed after 60 my by about 65 and after 180 my by about 95 the magnitude of post rift subsidence is a function of the rift induced thermal anomaly and crustal density changes the potential temperature of the asthenosphere and initial water depths intraplate stresses can have an overprinting effect on post rift subsidence stretching factors derived from post rift subsidence analyses must be corrected for such effects

asymmetric rifts due to asymmetric mohos an experimental approach large scale asymmetries in structures and in the uplift width and volcanism of pairs of conjugate passive margins have been documented in various parts of the world these asymmetries reflect the dominant mode of extension preceding the break up of the continental lithosphere of the many parameters involved the pre rift crustal structure has been shown to play a fundamental role in controlling the process of continental rifting in this work we have used analogue models to show how initial asymmetric moho configurations are prone to produce asymmetric rifting with prominent asymmetries in the amount of extension accommodated by boundary faults in the patterns of lithospheric thinning asthenospheric upwelling and in the trajectories of magma migration after continental break up these deformative patterns are expected to lead to the development of a pair of asymmetric passive margins with one narrow strongly volcanic margin and a wider less volcanic or with areas of concentrated volcanic activity counterpart

microtremor measurements used to map thickness of soft sediments the observations about the behavior of microtremor spectra presented here show that noise measurements can be used as a powerful tool to determine the thickness of soft cover layers the most suitable method for this determination is nakamura s technique which is the ratio of the horizontal component noise spectrum and that of the vertical component i i v spectrum the frequency of the main peak in these spectral ratios correlates well with the sediment thickness at the site using an extensive database of microtremor measurements carried out in the western lower rhine embayment germany it was possible to show that this correlation is clearly valid for a wide range of thickness namely from tens of meters to more than 1000 m a simple formula was derived that for the sediments to be found in the area investigated directly calculates the cover thickness from the frequency of the main peak in the h v spectrum a comparison with calculated resonant frequencies sug gests the relation derived from the noise measurements depending on the velocity depth function of the shear wave classical spectral ratios are shown to be strongly influenced by the noise level and are therefore less reliable in determining the res onant frequency of the subsoil the practical relevance of the investigation is illus trated by means of cross sections constructed from results of the microtremor anal yses which provide a convincing image of the surficial structure of the areas investigated

first level seismic microzonation map of al madinah province western saudi arabia using the geographic information system approach the identification of natural hazard prone areas for future planning requires an efficient decision support tool to provide the appropriate weights for the various topographical geological and seismological factors responsible for the expected hazards in the present study an analytical hierarchy process ahp with six earthquake hazard parameters ehps was used as a decision support system for the identification of earthquake triggered hazards in the al madinah region of the kingdom of saudi arabia the pairwise comparison matrix and the final weights for all the ehps during the implementation of ahp were calculated with an acceptable limit of consistency ratio a gis based integrated analysis was carried out on all the selected attributes to generate the final hazard and microzonation map from the analysis it was observed that 15 of the region fall under a very high or high hazard category the very high seismic hazard zone is located in the northwestern region of al madinah province while the eastern and southern regions show low to very low hazard the result of the study may be used as a first level hazard and reliability map in selecting the appropriate earthquake resistant sites in designing the forthcoming new buildings against the potential seismic hazard of the province

source parameters of earthquakes and intraplate deformation beneath the shillong plateau and the northern indoburman ranges we determined the fault plane solutions and focal depths of 17 earthquakes beneath the shillong plateau and the northern indoburman ranges by combining results from the inversion of long period p and sh waveforms and amplitudes from polarities of first motions and from the identification of pp and sp phases on short period seismograms fault plane solutions of 15 earthquakes show mixtures of thrust and strike slip faulting but the p axes for these events are nearly horizontal and consistently oriented north northeast south southwest all of these earthquakes occurred at depths greater than 29 km beneath the shillong plateau one event occurred at a depth of 52 km the relatively large depths for earthquakes in an intraplate setting suggest that the indian lithosphere in this area is especially cold earthquakes beneath the northern indoburman ranges define a gently east southeast dipping zone from 30 to 45 km beneath the bengal basin to 40 to 90 km beneath the ranges this zone seems to steepen and connect with the zone of intermediate depth seismicity that dips eastward beneath burma these earthquakes cannot have occurred along the interface between a subducting indian plate and the overriding indoburman lithosphere because the p axes not the nodal planes are parallel to the north south trending seismic zone although a couple of the earthquakes might have occurred within the indoburman lithosphere most of this seismicity seems to have occurred within the indian plate recently and currently being subducted eastward beneath the indoburman ranges the consistent north northeast trend of the p axes implies that the orientation of maximum compressional strain in the indian plate throughout its northeastern pan is nearly perpendicular to that responsible for roughly north south trending folds of the indoburman ranges thus either recently in geologic time since 1 ma the orientation of maximum compression changed dramatically or more likely the deformation in the indoburman ranges is decoupled from that in the underlying indian plate meanwhile the seemingly identical northward displacement of india and the indoburman ranges with respect to south china must be accommodated farther east along the sagaing and other faults

insights from analogue modelling into the deformation mechanism of the vaiont landslide abstract the vaiont landslide southern alps italy represents one of the most catastrophic landslides in the world recorded in the modern history the landslide occurred on 9th october 1963 involved about 3 10 8 m 3 of rock that collapsed in an artificial lake more than 1900 people died as a consequence of the tsunami produced by the sudden fall of the mass in the water despite the importance of this event many aspects of the vaiont rockslide still remain unexplained particularly its fast emplacement in order to obtain a better understanding of the vaiont disaster this paper focuses on the results of analogue models designed to get insights into the internal and surficial deformation patterns that characterized the sliding rock mass plan view reconstructions of surface model displacement reveal that the rock mass is subdivided into compartments with different relative movements and differential rotations believed to have played a significant role in causing the fast collapse the deformation of the analogue models compared with geological cross sections and in situ data suggests that sliding of the rock mass was accomplished by the development of some new or the reactivation of pre existing fractures into the rock mass

earthquake site response study in giumri formerly leninakan armenia using ambient noise observations we have tested whether ambient noise observations reveal useful information regarding site response at sediment sites in giumri formerly leninakan armenia this was done by comparing the noise observations with spectral ratio site response estimates based on aftershock data of the 7 december 1988 earthquake we show that neither the horizontal component noise spectra alone nor spectral ratios taken with respect to a nearby bedrock site reveal useful information regarding site response however spectral ratios of horizontal components taken with respect to vertical components nakamura s method exhibit a prominent peak that corresponds to the fundamental resonant frequency observed in the aftershock data based on this and other recent investigations we conclude that nakamura s method may be a reliable procedure for determining the fundamental resonant frequency of sedimentary deposits from ambient noise observations

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