strong ground motion and damage in the taipei basin from the moho reflected seismic waves during the march 31 2002 hualien taiwan earthquake 1 the march 31 2002 hualien offshore earthquake ml6 8 mw7 0 caused minor damage near its epicenter but significant damage in taipei about 110 km from the epicenter the recorded pga values around the taipei basin vary in a factor of 5 the high pga values in the southeastern part of the basin correspond to the most significant damage area during the earthquake strong ground motion recordings from this event recorded at stations around the taipei basin exhibit several distinct large amplitude seismic arrivals that can be interpreted as the pmp smp and sms phases the largest amplitude of the critically reflected s wave from the moho sms and the amplification of soft shallow sediments unique for each site are responsible for the maximum peak ground motion and the significant damage in the taipei basin during the hualien offshore earthquake

site amplification in the los angeles basin from three dimensional modeling of ground motion it is well established that sedimentary basins can significantly amplify earthquake ground motion however the amplification at any given site can vary with earthquake location to account for basin response in probabilistic seismic hazard analysis therefore we need to know the average amplification and intrinsic variability standard deviation at each site given all earthquakes of concern in the region due to a dearth of empirical ground motion observations theoretical simu lations constitute our best hope of addressing this issue here 0 0 5 hz finite difference finite fault simulations are used to estimate the three dimensional 3d response of the los angeles basin to nine different earthquake scenarios amplifi cation is quantified as the peak velocity obtained from the 3d simulation divided by that predicted using a regional one dimensional 1d crustal model average ampli fication factors are up to a factor of 4 with the values from individual scenarios typically differing by as much as a factor of 2 5 the average amplification correlates with basin depth with values near unity at sites above sediments with thickness less than 2 km and up to factors near 6 above the deepest 9 km and steepest dipping parts of the basin there is also some indication that amplification factors are greater for events located farther from the basin edge if the 3d amplification factors are divided by the 1d vertical sh wave amplification below each site they are lowered by up to a factor of 1 7 the duration of shaking in the 3d model is found to be longer by up to more than 60 seconds relative to the 1d basin response the simu lation of the 1994 northridge earthquake reproduces recorded 0 0 5 hz particle velocities relatively well in particular at near source stations the synthetic and observed peak velocities agree within a factor of two and the log standard deviation of the residuals is 0 36 this is a reduction of 54 and 51 compared to the values obtained for the regional 1d model and a 1d model defined by the velocity and density profile below a site in the middle of the basin dow respectively this result suggests that long period ground motion estimation can be improved consid erably by including the 3d basin structure however there are uncertainties con cerning accuracy of the basin model model resolution the omission of material with shear velocities lower than 1 km s and the fact that only nine scenarios have been considered therefore the amplification factors reported here should be used with caution until they can be further tested against observations however the results do serve as a guide to what should be expected particularly with respect to increased amplification factors at sites located above the deeper parts of the basin

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

three dimensional finite difference waveform modeling of strong motions observed in the sendai basin japan we perform three dimensional 3d finite difference fd waveform modeling of strong motions in the frequency range 0 2 to 1 67 hz observed in the sendai basin japan during the japan meteorological agency magnitude m j 5 0 1998 miyagiken nanbu earthquake in a previous we estimated s wave velocity structures above the pre tertiary bedrock at six sites in the sendai basin based on array records of microtremors to interpolate these velocity structures in space we conduct single station microtremor measurements at a total of 61 locations and estimate the s wave velocity structure at each site by modeling the horizontal to vertical spectral ratio of fundamental mode rayleigh waves an initial 3d model of the basin is constructed using the velocity structures estimated from both array and single station microtremor measurements along with other information such as surface geology this model encompasses a region 33 km long 30 km wide and 19 km deep the final model is obtained through a trial and error process by fitting 3d fd synthetic waveforms to the bandpass filtered 0 2 hz to 1 67 hz displacement records 12 stations for the 1998 miyagiken nanbu earthquake we compute the synthetics using a fourth order staggered grid 3d fd method with variable grid spacing as the 3d model is modified the source parameters strike dip rake and seismic moment are estimated by a grid search method using 1d site specific models derived from the modified 3d model the observed waveforms are reproduced well at most stations by the final 3d basin model this agreement suggests the validity of the final 3d basin model for theoretical strong motion prediction of large earthquakes in the frequency range from 0 2 to 1 67 hz manuscript received 7 june 2000

hypsometry of titan cassini radar topography data are used to evaluate titan s hypsometric profile and to make comparisons with other planetary bodies titan s hypsogram is unimodal and strikingly narrow compared with the terrestrial planets to investigate topographic extremes a novel variant on the classic hypsogram is introduced with a logarithmic abscissa to highlight mountainous terrain in such a plot the top of the terrestrial hypsogram is quite distinct from those of mars and venus due to the glacial buzz saw that clips terrestrial topography above the snowline in contrast to the positive skew seen in other hypsograms with a long tail of positive relief due to mountains there is an indication weak given the limited data for titan so far that the titan hypsogram appears slightly negatively skewed suggesting a significant population of unfilled depressions limited data permit only a simplistic comparison of titan topography with other icy satellites but we find that the standard deviation of terrain height albeit at different scales is similar to those of ganymede and europa

seismic attenuation in faroe islands basalts we analysed vertical seismic profiling vsp data from two boreholes at glyvursnes and vestmanna on the island of streymoy faroe islands to determine the magnitude and causes of seismic attenuation in sequences of basalt flows the work is part of seifaba a major project integrating data from vertical and offset vsp surface seismic surveys core samples and wireline log data from the two boreholes values of effective seismic quality factor q obtained at glyvursnes and vestmanna are sufficiently low to significantly degrade the quality of a surface reflection seismic image this observation is consistent with results from other vsp experiments in the north atlantic region we demonstrate that the most likely cause of the low values of effective q at glyvursnes and vestmanna is a combination of 1d scattering and intrinsic attenuation due to seismic wave induced fluid flow within pores and microcracks tests involving 3d elastic wave numerical modelling with a hypothetical basalt model based on field observations indicate that little scattering attenuation is caused by lateral variations in basalt structure

the composition and structure of volcanic rifted continental margins in the north atlantic further insight from shear waves abstract imaging challenges caused by highly attenuative flood basalt sequences have resulted in the understanding of volcanic rifted continental margins lagging behind that of non volcanic rifted and convergent margins massive volcanism occurred during break up at 70 of the passive margins bordering the atlantic ocean the causes and dynamics of which are still debated this paper shows results from traveltime tomography of compressional and converted shear wave arrivals recorded on 170 four component ocean bottom seismometers along two north atlantic continental margin profiles this traveltime tomography was performed using two different approaches the first a flexible layer based parameterisation enables the quality control of traveltime picks and investigation of the crustal structure the second with a regularised grid based parameterisation requires correction of converted shear wave traveltimes to effective symmetric raypaths and allows exploration of the model space via monte carlo analyses the velocity models indicate high lower crustal velocities and sharp transitions in both velocity and vp vs ratios across the continent ocean transition the velocities are consistent with established mixing trends between felsic continental crust and high magnesium mafic rock on both margins interpretation of the high quality seismic reflection profile on the faroes margin confirms that this mixing is through crustal intrusion converted shear wave data also provide constraints on the sub basalt lithology on the faroes margin which is interpreted as a pre break up mesozoic to paleocene sedimentary system intruded by sills

amplification of seismic ground motion in the tunis basin numerical bem simulations vs experimental evidences this paper aims at the analysis of seismic wave amplification in a deep alluvial basin in the city of tunis in tunisia this sedimentary basin is 3000m wide and 350m deep since the seismic hazard is significant in this area the depth of the basin and the strong impedance ratio raise the need for an accurate estimation of seismic motion amplification various experimental investigations were performed in previous studies to characterize site effects the boundary element method is considered herein to assess the parameter sensitivity of the amplification process and analyse the prevailing phenomena the various frequencies of maximum amplification are correctly estimated by the bem simulations the maximum amplification level observed in the field is also well retrieved by the numerical simulations but due to the sensitivity of the location of maximum amplification in space the overall maximum amplification has to be considered the influence of the wave field incidence and material damping is also discussed

attenuation tomography of the western united states from ambient seismic noise 1 we show that the spatial coherency of the ambient seismic field can be used for attenuation tomography in the western united states we evaluate the real portion of the spatial coherency with an elastic geometric spreading term a bessel function and a distance dependent decay an attenuation coefficient in order to invert the spatial coherency a weight stack inversion technique is applied we recover phase velocity and attenuation coefficient maps at periods of 8 32s which correspond to the elastic and anelastic structure at crustal and upper mantle depths the phase velocity maps obtained by this method are of similar resolution to more standard two station methods the attenuation results provide an important complement to the information extracted from earthquake based tomography several geological features are easily identifiable in the attenuation coefficient maps such as the highly attenuating sedimentary basins along the west coast of the united states and the highly attenuating yellowstone region and the boundaries of the snake river plains

multiwell study of seismic attenuation at the co2crc otway project geosequestration site comparison of amplitude decay centroid frequency shift and 1d waveform inversion methods

simulations of strong ground motion and 3d amplification effect in the taipei basin by using a composite grid finite difference method we perform full elastic wave field simulations within the taipei basin by using a three dimensional 3d discontinuous finite difference method the 3d taipei basin model is determined from a seismic reflection study two major subsurfaces the songshan formation surface soil layer and the basin basement are constituted in the model a parallel based composite grid technique a containing scalene grid and a discontinuous grid is developed in this study to deal with the possible numerical prob lem of thin depth and low velocity of the songshan formation taking advantage of the composite grid the resolution of the subsurface structure can be reached to 20 m and a higher frequency up to 3 hz of the synthetic waveform can be achieved in our strong ground motion simulations we assume a constant velocity in each subsurface three different types of models are considered in the study the songshan formation with a basement structure model a basin basement model and a layered half space model results indicate that only the model with both the songshan formation and the basement structure can produce the apparent basin amplification effects first the surface wave generated after the primary s wave is trapped at the shallow part of the basin then when the wave propagates through the deepest part of the basin most of the energy is reflected from the boundary and focused back into the basin in addi tion part of the seismic wavefront turns and follows the shallow basin edge resulting in further amplification our study indicates that the complex taipei basin geometry and fairly low velocity of the songshan formation dominate the amplification and wave propagation behavior that result in extraordinary strong shaking patterns in the taipei metropolitan region

ground motion amplification in the santa monica area effects of shallow basin edge structure abstract the 1994 northridge earthquake produced ground motions in the northwest portion of the los angeles basin that were significantly larger than rock site motions observed at locations just north of the basin the santa monica area was hit particularly hard with numerous structures being damaged or destroyed by the strong ground shaking in this region the basin edge geology is controlled by the active strand of the east west striking santa monica fault and virtually all of the structural damage occurred at or south of the fault location we have used 2d finite difference ground motion simulations to investigate the effect of the basin edge structure in amplifying ground response constraints on the basin edge structure come from geologic cross sections geophysical data and seismological observations our simulations indicate that the shallow basin edge structure 1 km deep formed by the active strand of the santa monica fault creates a large amplification in motions immediately south of the fault scarp in very good agreement with mainshock damage patterns recorded ground motions and locations of elevated site response this large amplification results from constructive interference of direct waves with the basin edge generated surface waves and is quite similar to the basin edge effect associated with the 1995 kobe earthquake in addition we find that focusing effects created by the deeper basin structure 3 to 4 km deep cannot explain the large motions observed immediately south of the fault scarp this strongly suggests that the deep basin focusing models proposed by gao et al 1996 and alex and olsen 1998 are not likely explanations of the observed pattern of ground motion amplification in the santa monica area

seismic attenuation of atlantic margin basalts observations and modeling paleogene basalts are present over much of the northeastern atlantic european margin in regions containing significant thicknesses of layered basalt flows conducting seismic imaging within and beneath the volcanic section has proven difficult largely because the basalts severely attenuate and scatter seismic energy we use data from a vertical seismic profile vsp from well 164 07 1 that penetrated 1 2 km of basalt in the northern rockall trough west of britain to measure the seismic attenuation caused by the in situ basalts the effective quality factor qeff of the basalt layer is found from the vsp to be 15 35 which is considerably lower more attenuative than the intrinsic attenuation measured on basalt samples in the laboratory we then run synthetic seismogram models to investigate the likely cause of the attenuation full waveform 1d modeling of stacked sequences of lava flows based on rock properties from the same well indicates that much of the seismic attenuation observed from the vsp can b

seeing below the basalt offshore faroes exploration in the basalt covered areas of the faroes offshore has always suffered from poor seismic imaging below the basalt long offset 2d and 3d seismic data were acquired and a significant improvement in the seismic image below top basalt has been achieved deep towing of the source and receiver cables helped by extending the seismic bandwidth towards lower frequencies bubble tuned rather than conventional peak tuned source arrays gave little if any incremental benefit the improvement in the imaging comes primarily from the approach to processing the data high frequencies dominantly noise are filtered out of the data early in the processing to concentrate on the low frequency data careful multiple removal is important with several passes of demultiple being applied to the data using both surface related multiple elimination srme and radon techniques velocity analysis is performed as an iterative process taking into account the geological model reprocessing legacy 2d surveys acquired with wide ranging parameters using these processing techniques improved these datasets significantly indicating that sub basalt imaging seems to be more sensitive to processing than to the choice of acquisition parameters

modelling and analysis of attenuation anisotropy in multi azimuth vsp data from the clair field anisotropic variations in attenuation are of interest since they can give information on the fracture system and may be more amenable to measurement than absolute attenuation values we examine methods for detecting changes in relative attenuation with azimuth from vsp data and validate the techniques on synthetic data analysis of a multi azimuth walkaway vsp data set from a fractured hydrocarbon reservoir indicates that such azimuthal variations in p wave attenuation are observable the effects are localized in the reservoir and analysis allows the prediction of a fracture strike direction which agrees with geological information the observed effects can be modelled under reasonable assumptions which suggests the validity of the link between the anisotropic attenuation and the fracturing

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

strong ground motion from the michoacan mexico earthquake the network of strong motion accelerographs in mexico includes instruments that were installed under an international cooperative research program in sites selected for the high potenial of a large earthquake the 19 september 1985 earthquake magnitude 8 1 occurred in a seismic gap where an earthquake was expected as a result there is an excellent descripton of the ground motions that caused the disaster

nonlinear analysis on seismic site response of fuzhou basin china based on the parallel computing cluster platform of the abaqus software a large scale 2d finite element refined nonlinear modeling approach was used to study seismic site effects in the fuzhou basin such as peak ground acceleration pga spectral acceleration duration and acceleration transfer functions a 1d equivalent linear wave propagation analysis was conducted also with proshake for supplementation and calibration the simulation results demonstrated the following 1 pga amplification factors exhibited spatial variation characteristics that varied both laterally and with depth and exhibited a nonmonotonic decreasing characteristic with soil depth from the 2d results a greater motion amplification and focusing effect for some shallow soil layers was observed where there was significant fluctuation of the underlying bedrock interface the moderate and long period ground motion components were obviously amplified but were was less pronounced in the 1d result 2 for low moderate and high level earthquakes the surface pga amplification factors were 1 4 2 5 1 3 2 0 and 1 1 2 0 respectively and the predominant periods of the basin were 0 35 0 65 s 0 40 0 75 s and 0 50 1 05 s respectively 3 ground motion durations were prolonged to different degrees which were closely related to the characteristics of seismic bedrock motions 4 the sensitive frequency band of the seismic site response was from 0 5 to 2 hz 5 ground motion amplification in the downtown section of the city of fuzhou was generally larger to a certain extent the 2d results reflect the influences of the surface topography relief the fluctuation of the underlying bedrock interface and lateral heterogeneity of soils on seismic wave propagation

interface scattering versus body scattering in subbasalt imaging and application of prestack wave equation datuming the presence of high velocity highly heterogeneous layers such as basalt have a detrimental effect on imaging below those structures internal characteristics of the basalt itself can also degrade the subbasalt image quality in many cases the boundary surfaces of a basalt sequence are not smooth but contain some roughness at a scale similar to the seismic wavelength interface scattering resulting from interface roughness can be a serious problem in this paper body and interface scattering problems are addressed through acoustic finite difference modeling interface scattering seems to have the most detrimental effect on imaging at depth a wave equation prestack datuming procedure is applied to synthetic acoustic data to remove the effects of rough interfaces this computational process transforms seismic data to a new datum plane in the subsurface eliminating propagation effects between the surface and the new datum plane the technique leads to a much improved image of below the basalt with the g

inversion of strain dependent nonlinear characteristics of soils using weak and strong motions observed by borehole sites in japan during the 1995 hyogo ken nanbu earthquake strong motions with horizontal peak ground accelerations of 507 cm sec 2 or more 187 cm sec 2 and 126 cm sec 2 were observed at surface stations of borehole sites at amagasaki takasago and nanko in japan respectively we showed qualitative evidence of nonlinear soil response during strong motions at amgasaki and takasago but not at nanko using cross correlation and spectral ratio analyses of weak and strong motions we evaluated soil nonlinearity by inversion for s wave velocities and frequency dependent damping factors the strain dependence of shear modulus ratios inverted for gravel is larger than that for clay which is consistent with laboratory test results in the shear strain range from about 10 4 to 10 3 the strain dependence of shear modulus ratios inverted for clay and gravel at amagasaki and takasago is consistent with empirical relations based on laboratory test results for clay and gravel respectively these results support using laboratory estimates of shear modulus ratios to simulate strong motions at clay and gravel sites the damping factors for gravel inverted from the mainshock at amagasaki are the largest among the others but the strain dependence of damping factors are not as significant as that of shear modulus ratios the reason why the strain dependence of damping factors is not so significant may be because scattering attenuation is relatively dominated in the low strain range

the use of vertical seismic profiles in seismic investigations of the earth during the past 8 years the u s geological survey has conducted an extensive investigation on the use of vertical seismic profiles vsp in a variety of seismic exploration applications seismic sources used were surface air guns vibrators explosives marine air guns and downhole air guns source offsets have ranged from 100 to 7800 ft well depths have been from 1200 to over 10 000 ft we have found three specific ways in which vsps can be applied to seismic exploration first seismic events observed at the surface of the ground can be traced level by level to their point of origin within the earth thus one can tie a surface profile to a well log with an extraordinarily high degree of confidence second one can establish the detectability of a target horizon such as a porous zone one can determine either before or after surface profiling whether or not a given horizon or layered sequence returns a detectable reflection to the surface the amplitude and character of the reflection can also

geophysical response of flood basalts from analysis of wire line logs ocean drilling program site 642 voring volcanic margin analysis of wire line logs at ocean drilling program site 642 the deepest scientific hole yet drilled in an offshore large igneous province lip reveals the main features of the extrusive complex constructed during formation of a volcanic margin a characteristic cyclic log response images tholeiitic lavas and thin tuffs corresponding to the seaward dipping reflectors in the seismic record flows are 0 6 18 5 m thick while most sediments are 2000 m focused resistivity kicks the large flow scale variations in physical properties show that representative core measurements must be densely sampled both on flow and sequence scales site 642 log responses appears typical for the north atlantic volcanic province and other lips but differs from logs in deep ocean crustal holes principal differences in log responses reflect mode of crustal emplacement and alteration hence site 642 forms a reference hole for extrusive constructions on oceanic lips

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

borehole study of compressional and shear attenuation of basalt flows penetrated by the brugdan and william wells on the faroes shelf we investigated the seismic attenuation of compressional p and converted shear s waves through stacked basalt flows using short offset vertical seismic profile vsp recordings from the brugdan 6104 21 1 and william 6005 13 1a wells in the faroe shetland trough the seismic quality factors q were evaluated with the classical spectral ratio method and a root mean square time domain amplitude technique we found the latter method showed more robust results when analysing signals within the basalt sequence for the brugdan well we calculated effective q estimates of 22 26 and 13 17 for p and s waves respectively and 25 33 for p waves in the william well an effective qs qp ratio of 0 50 0 77 was found from a depth interval in the basalt flow sequence where we expect fully saturated rocks p wave quality factor estimates are consistent with results from other vsp experiments in the north atlantic margin while the s wave quality factor is one of the first estimates from a stacked basalt formation using vsp data synthetic modelling demonstrates that seismic attenuation for p and s waves in the stacked basalt flow sequence is mainly caused by one dimensional scattering while intrinsic absorption is small

sub surface geology and velocity structure of the krafla high temperature geothermal field iceland integrated ditch cuttings wireline and zero offset vertical seismic profile analysis abstract the krafla geothermal area in northern iceland comprises one of the best studied examples of a high temperature geothermal field associated with an active volcanic rift zone of key importance to improved resource exploration and development in volcanic areas such as krafla is the interpretation and understanding of the subsurface geology within this study we present results from an integrated analysis of the downhole volcanic stratigraphy from the k 18 borehole within the krafla caldera based on combined wireline ditch cuttings and zero offset vsp vertical seismic profile analyses this study presents the first published sonic log velocity data from a high temperature geothermal borehole in iceland and clearly demonstrates the importance of borehole velocity data for improving volcanic facies interpretations the shallow subsurface geology of the k 18 site from c 0 380 m comprises an inter layered sequence of sub aerial basaltic lavas hyaloclastites and tuffaceous lithologies of both felsic and basic composition which are progressively replaced by basaltic sheet intrusions with increasing depth an interval of variably basic to more evolved mixed tuffaceous facies is identified based on cuttings analysis gamma and sonic velocities between c 790 1120 m depth discrete high sonic vp units cut the lower c 100 m of this interval and are interpreted as either sheet intrusions or lava interiors at c 1800 m a sharp increase in p wave velocity from c 4 5 to c 5 5 km s represents the transition from a mixed lava and sheet intrusion dominated sequence into a dense basic intrusion forming the local basement that persists to the bottom of the borehole at c 2215 m reduced travel time analysis of processed zero offset vsp results reveal good correspondence with the major stratigraphic boundaries in the borehole supporting the potential for vsp studies to robustly characterize complex volcanic stratigraphy in high temperature geothermal fields finally the application of percentage based ditch cuttings analyses methods for volcanic facies analysis in geothermal boreholes is tested and assessed to have future potential

three dimensional simulations of seismic wave propagation in the taipei basin with realistic topography based upon the spectral element method we use the spectral element method to simulate strong ground motion throughout the taipei metropolitan area mesh generation for the taipei basin poses two main challenges 1 the basin is surrounded by steep mountains and 2 the city is located on top of a shallow low wave speed sedimentary basin to accommodate the steep and rapidly varying topography we introduce a thin high resolution mesh layer near the surface the mesh for the shallow sedimentary basin is adjusted to honor its complex geometry and sharp lateral wave speed contrasts variations in moho thickness beneath northern taiwan are also incorporated in the mesh spectral element simulations show that ground motion in the taipei metropolitan region is strongly affected by the geometry of the basin and the surrounding mountains the amplification of ground motion is mainly controlled by basin depth and shallow shear wave speeds although surface topography also serves to amplify and prolong seismic shaking

modelling basin effects on earthquake ground motion in the santiago de chile basin by a spectral element code summary simulations of strong ground motion within the santiago de chile metropolitan area were carried out by means of 3 d deterministic wave propagation tool based on the spectral element method the simulated events take into account the pronounced interface between the low velocity sedimentary basin and the bedrock as well as topography of the area to verify our model we simulated a regional earthquake recorded by a dense network installed in the city of santiago for recording aftershock activity after the 2010 february 27 maule main shock the results proof the alluvial basin amplification effects and show a strong dependence of spectral amplification in the basin on the local site conditions moreover we studied the seismic response due to a hypothetical mw 6 0 event occurring along the active san ramon fault which is crossing the eastern edge of the city the scenario earthquakes exhibit that an unfavourable interaction between fault rupture radiation mechanism and complex geological and topographic conditions in the near field region may give rise to large values of peak ground velocity in the basin finally 3 d numerical predictions of ground motion are compared with the one computed according to ground motion prediction equations selected among the next generation attenuation relationships in terms of ground motion peak values and spectral acceleration the comparison underlines that the 3 d scenario simulations predict a significantly higher level of ground motion in the santiago basin especially over deep alluvial deposits moreover also the location of the rupture nucleation largely influences the observed shaking pattern

unexpected values of qs in the unconsolidated sediments of the mississippi embayment we studied the attenuation of shear waves at three sites in the mississippi embayment using data recorded in boreholes drilled to depths of up to 60 m the source was a highly repeatable compressed air driven hammer to estimate attenuation we used a spectral ratio technique for fixed depth and variable frequency the best fit line for each depth z gives a measure of the cumulative attenuation indicated by z then we fit a straight line to z for a range of values of z the slope of this line gives an estimate of the average attenuation per distance and was used to determine an average q s for one of the sites newport northeastern arkansas q s ranges between 34 1 5 m z 44 2 m and 44 1 5 m z 51 8 m these values are significantly higher than the more typical value of about 10 determined for unconsolidated sediments by other authors in addition these high values correspond to sediments with low average shear wave velocity about 300 m sec in contrast average q s and velocity for sediments in shelby forest near memphis tennessee are 22 and 348 m sec 22 6 m z 60 1 m respectively therefore these results go against the conventional wisdom that low velocity implies low q for the third site marked tree northeastern arkansas average q s and velocity are 18 and 251 m sec 9 8 m z 33 6 m respectively this site is about 75 km from newport and the differences in attenuation appear related to differences in lithology manuscript received 5 april 2001

pacing early mars river activity embedded craters in the aeolis dorsa region imply river activity spanned 1 20 myr we find net sedimentation rate 13 200 m yr in the aeolis dorsa region mars using the frequency of crater river interactions this sets a lower bound of 1 20 myr on the total interval spanned by fluvial activity which we correlate to the noachian hesperian transition the main uncertainty is the impact flux at the time of deposition this result rules out basin filling by a single catastrophic episode such as a single impact induced water vapor greenhouse

p wave attenuation anisotropy in fractured media a seismic physical modelling study we used a laboratory scale model to study the effects aligned fractures might have on seismic wave propagation at a larger scale in real earth imaging our main objective was to investigate the effect of aligned fractures on seismic p wave amplitude through the estimation of the induced attenuation the physical model was constructed from a mixture of epoxy resin and silicon rubber with inclusions designed to simulate two sets of inclined fractures at an angle of 29 2 with each other two dimensional reflection data were acquired using the pulse and transmission method in three principal directions relative to the fracture strike azimuth with the model submerged in a water tank we used the quality versus offset qvo method an extension of the classical spectral ratio method for determining attenuation to estimate the induced attenuation inverse of the seismic quality factor from the common mid point cmp pre processed gathers the results of our analysis show that the induced p wave attenuation is anisotropic with elliptical cos2 variations with respect to the survey azimuth angle the minor axis of the q ellipse corresponds to the fracture normal in this direction i e across the material grain the attenuation is a maximum the major axis corresponds to the fracture strike direction parallel to the material grain where minimum attenuation occurs these attenuation results show consistency with the azimuthal anisotropy observed in the stacking velocities in the fractured layer and are all consistent with the physical model and thus provide a physical basis for using attenuation anisotropy to derive fracture properties from seismic data

numerical modelling of ground motion in the taipei basin basin and source effects summary the taipei basin in northern taiwan is located in a high seismicity region and was affected by several earthquakes in the past ml 7 3 on 1909 april 15 ml 6 8 on 1986 november 15 the chi chi ml 7 3 earthquake on 1999 september 21 and ml 6 8 on 2002 march 31 the main characteristic of the taipei basin is its complex shape with a deep western and shallow eastern part the uppermost sungshan formation with its low shear wave velocities 90 200 m s 1 is also a distinct feature of the basin based on the large data base of earthquake records obtained from the taiwan strong motion instrumentation program network many studies on ground motion within the taipei basin exist however the influence of the various subsurface structures on the observed ground motions as well as the variability of ground motion with respect to earthquake location is not fully understood we apply a 3 d finite difference method to simulate wave propagation up to 1 hz for a small earthquake close to the basin in order to resolve these open questions by varying source and structural parameters we explore the variability of ground motion our study includes a subsurface model that is based on recent studies on the basin structure and on the crustal structure of taiwan from our simulations we find a good fit between simulated and observed waveforms and peak ground accelerations for the considered small earthquake near the basin we also explore the influence of fault plane orientation hypocentre location deep basin structure and soft soil surface layers of the sungshan formation by varying the subsurface structure and earthquake position our studies reveal that the basin structure produces an amplification factor of about 4 compared to hard rock conditions additionally the soft soil sungshan formation produce amplification of a factor of 2 this results in a maximum amplification of the basin structure of about 8 which is in good comparison with amplification values larger than 5 found from the analysis of observed earthquakes these values clearly exceed the amplification values of about 2 3 obtained when applying standard 1 d site effect analysis our simulations for different earthquake positions show that ground motion depends strongly on earthquake location and fault orientation therefore the application of average values of spectral amplification obtained from the analysis of recorded data from distant earthquakes with different azimuths and fault planes may significantly underestimate future ground motions of possible earthquakes on known faults close to the taipei basin the simulation of a small earthquake near the taipei basin presented in this study will help to set up adequate simulation parameters for a possible large earthquake close to the taipei basin such a simulation of a scenario earthquake close to the taipei basin would allow to significantly improve hazard assessment as no observations of strong earthquakes in the vicinity of the basin exist

coseismic reverse and oblique slip surface faulting generated by the 2008 mw 7 9 wenchuan earthquake china the mw 7 9 wenchuan china earthquake ruptured two large thrust faults along the long menshan thrust belt at the eastern margin of the tibetan plateau this earthquake generated a 240 km long surface rupture zone along the beichuan fault and an additional 72 km long surface rupture zone along the pengguan fault maximum vertical and horizontal offsets of 6 5 m and 4 9 m respectively were measured along the beichuan fault a maximum vertical offset of 3 5 m was measured along the pengguan fault coseismic surface ruptures integrated with aftershocks and industry seismic profiles show that two imbricate structures have ruptured simultaneously resulting in the largest continental thrust event ever documented large oblique thrusting observed during this earthquake indicates that crustal shortening is an important process responsible for the high topography in the region as everywhere along the edge of tibetan plateau

causes of low frequency ground motion amplification in the salt lake basin the case of the vertically incident p wave summary we use simulations of 1 d 2 d and 3 d wave propagation to identify the major causes of low frequency 0 2 1 2 hz seismic amplification in the salt lake basin for a simple two layer basin model and a vertically incident p wave we examine how amplification is influenced by mode conversion surface wave generation impedance effects at the sediment bedrock boundary resonance and 2 d and 3 d focusing and scattering results show the following 1 approximately 30 per cent of the total cumulative kinetic energy at the salt lake valley floor consists of shear wave energy generated by p to s converted waves and surface waves the surface waves appear to be generated primarily along the edges of the basin and the instantaneous sip energy ratio in the sedimentary layer is as large as 3 2 the largest peak particle velocity at the free surface is due to the direct p wave the value is roughly predicted by the transmission coefficient of 1 46 at the sediment bedrock interface i e a normally incident p wave in the stiff bedrock will be magnified in amplitude by 1 46 times as it enters the softer sediments 3 the low frequency elastic response of the two layer salt lake basin model is characterized by surface wave propagation and resonance from vertically interfering waves 4 the peak particle velocities cumulative kinetic energies and mean spectral magnitudes computed from the 2 d 1 d synthetics underestimate the values computed from the 3 d synthetics by up to 40 per cent 48 per cent along a profile above the deepest part of the basin model the 2 d and 1 d signal duration times underestimate the 3 d values by up to 59 and 94 per cent respectively our results suggest that 2 d basin modelling may yield good approximations to the 3 d ground motion amplification above the deepest part of the salt lake basin our results show that several mechanisms contribute significantly to lowfrequency seismic amplification in the semi consolidated sediments of the salt lake basin p to s wave conversion surface wave generation impedance effects at the sediment bedrock boundary and resonance future attempts to estimate ground motion amplification in the salt lake basin should therefore account for the amplification effects of all these mechanisms

attenuation anisotropy and the relative frequency content of split shear waves summary the variation of frequency dependent seismic wave attenuation with direction attenuation anisotropy contains additional information to that contained in velocity anisotropy in particular it has the potential to distinguish between different mechanisms that can cause velocity anisotropy for example aligned fracturing might be expected to cause measurable velocity and attenuation anisotropy while preferred crystal orientation leads to significant velocity anisotropy but may cause only small amounts of attenuation attenuation anisotropy may also contain useful information about pore fluid content and properties we present a methodology for analysis of attenuation anisotropy and apply it to a microseismic data set previously analysed for shear wave splitting by teanby et al 2004 attenuation anisotropy values obtained show a temporal variation which appears to correlate with the temporal variation in the velocity anisotropy the comparison of the relative frequency content of fast s1 and slow s2 split shear waves is a convenient method for examining seismic attenuation anisotropy provided that s1 and s2 initially have the same spectral colouring that no spectral distortion is introduced by the differences between receiver responses of geophone components and that spectral distortion due to background noise can be ignored or corrected for we can attribute any differences in their frequency content to attenuation anisotropy attenuation anisotropy where present should be detected by the different approximately orthogonal polarizations of s1 and s2 as they pass through the anisotropic medium in the presence of attenuation anisotropy s1 and s2 should experience different levels of frequency dependent attenuation we quantify the differential attenuation of s1 and s2 using a scheme based on a spectral ratio method we present results from a microseismic data set acquired in an abandoned oil well at valhall a north sea oil field the results are surprising in that sometimes the slower arrival s2 is richer in high frequencies than the faster s1 this appears to be contrary to results predicted by theoretical crack models for attenuation anisotropy e g hudson 1981 the mechanism responsible for these observations is not clear our differential attenuation attribute correlates with the angle between the strike of the inferred initial shear wave source polarization and the fast shear wave polarization which suggests that the split shear wave with the larger amplitude is preferentially attenuated our attribute also correlates with the event backazimuth and the minimum percentage anisotropy

seismic response and construction of seaward dipping wedges of flood basalts voring volcanic margin geological and geophysical data from the 900 m of volcanic basement drilled at ocean drilling program site 642 provide the framework for studying seismic properties of huge extrusive constructions on volcanic margins the main part of the drilled section corresponding to a prominent seaward dipping reflector sequence consists of subaerially emplaced tholeiitic basalt flows and thin interbedded sediments the basalts exhibit a characteristic velocity and density lava flow distribution reflecting changing porosity pore aspect ratio distribution and alteration stacks of laterally continuous basalt flows appear to have thin layer transverse isotropic properties for typical wavelengths in multichannel seismic data vertical seismic profiling and average sonic log velocities are similar 3 77 km s and 3 88 km s respectively while comparable refraction velocities are 10 20 higher synthetic seismogram modeling based on downhole logs shows that basement reflectors originate from interference and tuning effects of numerous basalt flow and interbedded sediment interfaces though the most continuous reflectors are related to thick flows seismic models based on the characteristic velocity and density basalt flow distributions and site 642 stratigraphy show that reflector truncation and onlap may be caused by seismic interference phenomena in a sequence of landward thinning flows the base of the dipping reflector sequence reflector k correlates with flows in the lower part of upper series basalts while the transition from basaltic to underlying dacitic andesitic lavas correlates with a locally defined reflector a model for the breakup related volcanism includes 1 prebreakup dacitic andesitic volcanism 2 early breakup basaltic volcanism infilling the prebreakup relief 3 main breakup stage with intense focused volcanism large subsidence and lava pounding and 4 late breakup volcanism during a period of decreased subsidence and local off axis activity

multiscale seismic attributes a wavelet based method and its application to high resolution seismic and ground truth data we propose a wavelet based method to characterize acoustic impedance discontinuities from a multiscale analysis of seismic reflected waves our approach relies on the analysis of ridge functions which contain most of the information of the wavelet transform in a sparse support this method falls in the framework of the wavelet response wr introduced by le gonidec et al which analyses the impedance multiscale behaviour by propagating dilated wavelets into the medium we further extend the wr by considering its application to broad band seismic data we take into account the bandpass filter effect related to the limited frequency range of the seismic source we apply the method to a deep water seismic experiment performed in 2008 during the erig3d cruise to demonstrate the potential of ridge functions as multiscale seismic attributes in conjunction to the analysis of seismic data acquired by the deep towed sysif system 200 2200 hz we use ground truth data to characterize the fine scale structure of superficial sediments by using the continuous wavelet transform cwt the availability of in situ measurements allows to validate the relationship between cwt andwr and to estimate the attenuation of seismic waves into the sediments once validated the method is applied on a whole seismic profile and wr ridge functions are computed for two particular reflectors the reflector thicknesses fall below the resolution limit of the seismic experiment making the wr seismic attributes a super resolution method

exploration beneath volcanics snake river plain idaho coincident gravity magnetotelluric mt and seismic reflection refraction surveys were conducted along a line traversing the boundary between the volcanic covered eastern snake river plain idaho and the sediment covered western overthrust belt one dimensional mt and seismic refraction analysis away from the immediate boundary between sediments and volcanics successfully maps the depths to units of igneous and sedimentary or metasedimentary rock substantially different models of the volcanic covered terrain and of the sediment covered terrain are linked by a gravity anomaly and by an elongation and rotation of mt anisotropy ellipses which indicate a fault fault dip depth extent and motion are constrained by marked changes in the first arrival apparent velocities and by an electrical marker layer the analysis shows that metasediments extend laterally at least 16 km beneath the volcanic cover the two terrains are connected by a boundary zone which is a major normal fault

determination of shallow shear wave attenuation in the mississippi embayment using vertical seismic profiling data abstract we used vertical seismic profiling vsp data collected in four shallow boreholes about 40 to 60 m deep to study the shear wave attenuation in the mississippi embayment in southwestern tennessee the source was an air powered hammer that produces repeatable sh waves that were recorded by monitor geophones deployed on the surface very close to the source the spectral ratio method was used to estimate the shear wave quality factor q s the method assumes that the amplitudes of the seismic waves decay exponentially in the frequency domain the spectral ratio was computed using a vsp trace at a certain depth and the corresponding monitor trace using the source monitor trace as reference eliminates possible artifacts that may be introduced by changes in the source ground coupling the slope of a least square line fitted to the logarithm of the spectral ratio versus frequency gives the attenuation coefficient z for that depth then a straight line is fitted to z as a function of z and the slope of this line is used to estimate an average value of q s for the four sites shelby farms covington brownsville and jackson the q s values are 25 3 2 6 18 6 3 4 18 4 7 6 and 16 4 2 6 respectively to assess the reliability of these results synthetic vsp data were generated from the first cycles of the monitor traces recorded in the four sites and these q s values except for brownsville good matches with correlation coefficients equal to 96 99 were obtained between the synthetic vsps and the actual vsps indicating that the q s values we obtained are reliable in addition these values are also consistent with recent results obtained by others using seismic data generated by small earthquakes recorded by the japanese strong motion network kiban kyoshin kik net

azimuthal variation in p wave signatures due to fluid flow the favored dominant mechanism for attenuation in the upper crust at seismic frequencies is intracrack fluid flow in cracked media the azimuthal attenuation of the p wave amplitudes arising from such flow is predicted to be quite substantial the consequence of this variation in azimuth is a modification in the amplitude behavior of the base event from a cracked reservoir due to transmission through the attenuative layer indeed the effect is of sufficient strength to exacerbate diminish or reverse variations that arise solely due to the reflectivity coefficient thus although this attenuation is always greatest perpendicular to the crack strike the direction of the dimming or brightening of the base reservoir event will depend upon the exact attenuation law and the crack properties the combination of these factors contributes to a wave behavior that can provide a more adequate discrimination between conditions of brine and oil fill than an interpretation assuming the reflection coefficient alone

rupture history of the 2008 mw 7 9 wenchuan china earthquake evaluation of separate and joint inversions of geodetic teleseismic and strong motion data an extensive data set of teleseismic and strong motion waveforms and geodetic offsets is used to study the rupture history of the 2008 wenchuan china earthquake a linear multiple time window approach is used to parameterize the rupture because of the complexity of the wenchuan faulting three separate planes are used to represent the rupturing surfaces this earthquake clearly demonstrates the strengths and limitations of geodetic teleseismic and strong motion data sets geodetic data static offsets are valuable for determining the distribution of shallower slip but are insensitive to deeper faulting and reveal nothing about the timing of slip teleseismic data in the distance range 30 90 generally involve no modeling difficulties because of simple ray paths and can distinguish shallow from deep slip teleseismic data however cannot distinguish between different slip scenarios when multiple fault planes are involved because steep takeoff angles lead to ambiguity in timing local strong motion data on the other hand are ideal for determining the direction of rupture from directivity but can easily be over modeled with inaccurate green s functions leading to misinterpretation of the slip distribution we show that all three data sets are required to give an accurate description of the wenchuan rupture the moment is estimated to be approximately graphic 1 with the slip characterized by multiple large patches with slips up to 10 m rupture initiates on the southern end of the pengguan fault and proceeds unilaterally to the northeast upon reaching the cross cutting xiaoyudong fault rupture of the adjacent beichuan fault starts at this juncture and proceeds bilaterally to the northeast and southwest 1 embed inline graphic 1 gif

compressional wave q estimation from full waveform sonic data there is significant evidence that the anelastic loss of seismic energy is linked to petrophysical properties such as porosity permeability and clay content thus reliable estimation of anelastic attenuation from seismic data can lead to improved methods for the prediction of petrophysical properties this paper is concerned with methods for the estimation of attenuation at sonic frequencies 5 30 khz from in situ data two independent methods have been developed and tested for estimating compressional wave attenuation from full waveform sonic data a well established technique the logarithm spectral ratio lsr method is compared with a new technique the instantaneous frequency if method the lsr method uses the whole spectrum of the seismic pulse whilst the if method uses a carefully estimated value of instantaneous frequency which is representative of the centre frequency of the pulse in the former case attenuation estimation is based on the relative variation of amplitudes at different frequencies whilst in the latter case it is based on the shift of the centre frequency of the pulse to lower values during anelastic wave propagation the if method does not assume frequency independence of q which is a necessary assumption for the lsr method and it provides a stable frequency log the peak instantaneous frequency pif log which may be used as an indicator for attenuation under certain limitations the development and implementation of the two methods is aimed at minimizing the effect of secondary arrivals such as leaky modes and involved a series of parameter tests testing of the two methods using full waveform sonic data of variable quality obtained from a gas bearing sandstone reservoir showed that the if method is in general more stable and suitable for full waveform sonic data compared with the lsr method this was evident especially in data sets with high background noise levels and wave interference effects for good quality data the two methods gave results that showed good agreement whilst comparison with other log types further increased confidence in the results obtained a significant decrease approximately 5 khz in the pif values was observed in the transition from an evaporite shale sequence to the gas bearing sandstone average q values of 54 and 51 were obtained using good quality data from a test region within the gas saturated sandstone reservoir using the lsr and if methods respectively

climatic control of bedrock river incision bedrock river incision drives the development of much of earth s surface topography and thereby shapes the structure of mountain belts and modulates earth s habitability through its effects on soil erosion nutrient fluxes and global climate although it has long been expected that river incision rates should depend strongly on precipitation rates quantifying the effects of precipitation rates on bedrock river incision rates has proved difficult partly because river incision rates are difficult to measure and partly because non climatic factors can obscure climatic effects at sites where river incision rates have been measured here we present measurements of river incision rates across one of earth s steepest rainfall gradients which show that precipitation rates do indeed influence long term bedrock river incision rates we apply a widely used empirical law for bedrock river incision to a series of rivers on the hawaiian island of kaua i where mean annual precipitation ranges from 0 5 metres to 9 5 metres ref 12 over 70 per cent of the global range and river incision rates averaged over millions of years can be inferred from the depth of river canyons and the age of the volcanic bedrock both a time averaged analysis and numerical modelling of transient river incision reveal that the long term efficiency of bedrock river incision across kaua i is positively correlated with upstream averaged mean annual precipitation rates we provide theoretical context for this result by demonstrating that our measurements are consistent with a linear dependence of river incision rates on stream power the rate of energy expenditure by the flow on the riverbed these observations provide rare empirical evidence for the long proposed coupling between climate and river incision suggesting that previously proposed feedbacks among topography climate and tectonics may occur

compressional wave attenuation in oceanic basalts to understand better the seismic attenuation in the upper volcanic regions of the oceanic crust compressional wave attenuations of oceanic basalts have been measured as a function of confining pressure using an ultrasonic pulse echo spectral ratio technique capable of measuring attenuations to pressures of 500 mpa seven basalts five from deep sea drilling project cores and two from dredge samples have wide ranges of densities porosities and alterations making possible an analysis of the parameters influencing basalt attenuation attenuation increases with the volume of secondary minerals present and with increasing porosity thus vesicularity and compositional changes associated with basalt alteration will produce variations in attenuation with the application of hydrostatic pressure cracks close thereby reducing attenuations this pressure dependence should be manifested in oceanic layer 2 by decreasing attenuation with depth an inverse relationship between velocity and attenuation is observed at high hydrostatic pressures water saturation increases attenuation at pressures below 200 mpa and enhances the sensitivity of attenuation to pressure thus making the state of saturation important in the 40 to 100 mpa range generally found in layer 2 these results provide a framework for interpreting marine attenuation data

interpretation of a vertical seismic profile conducted in the columbia plateau basalts seismic reflection data are often of poor quality when recorded in areas where volcanic rocks are present at or near the surface in order to investigate this phenomenon a vertical seismic profiling vsp experiment was conducted in the columbia plateau basalts so that the behavior of seismic energy in subsurface volcanic rocks could be observed directly thus giving insight into data acquisition in volcanic terrains the lithologic section at the vsp site consists of low velocity 400 m s to 900 m s alluvium in the uppermost 50 m beneath which are layers of high velocity about 5800 m s high density basalts interbedded with clay layers with much lower velocities about 1700 m s and densities these large velocity and density contrasts dramatically influence wave generation and propagation in spite of the small source borehole offset 61 m large amplitude s waves are generated by the downgoing p waves when they reach a shallow 250 m clay basalt boundary these s waves in turn generate strong

seismic wave attenuation in methane hydrate bearing sediments vertical seismic profiling data from the nankai trough exploratory well offshore tokai central japan 1 data from two vertical seismic profiles vsps from the nankai trough exploratory well offshore tokai central japan are used to estimate compressional attenuation in methane hydrate mh bearing sediments at seismic frequencies of 30 110 hz we compare spectral ratio and centroid frequency shift methods for measuring attenuation to isolate intrinsic attenuation from total attenuation attenuation is computed from multiples using one dimensional synthetic vsp data from sonic and density logs the use of two different measurement methods and two vsps recorded at just 100 m separation provides an opportunity to validate the attenuation measurements no significant compressional attenuation was observed in mh bearing sediments at seismic frequencies macroscopically the peaks of highest attenuation in the seismic frequency range correspond to low saturation gas zones in contrast high compressional attenuation zones in the sonic frequency range 10 20 khz are affected by the presence of methane hydrates in the same well locations thus this study demonstrated the frequency dependence of attenuation in mh bearing sediments mh bearing sediments cause attenuation in the sonic frequency range rather than the seismic frequency range

global drainage patterns and the origins of topographic relief on earth mars and titan rivers have eroded the topography of mars titan and earth creating diverse landscapes however the dominant processes that generated topography on titan and to some extent on early mars are not well known we analyzed drainage patterns on all three bodies and found that large drainages which record interactions between deformation and erosional modification conform much better to long wavelength topography on titan and mars than on earth we use a numerical landscape evolution model to demonstrate that short wavelength deformation causes drainage directions to diverge from long wavelength topography as observed on earth we attribute the observed differences to ancient long wavelength topography on mars recent or ongoing generation of long wavelength relief on titan and the creation of short wavelength relief by plate tectonics on earth

three dimensional simulation of earthquakes on the los angeles fault system we have used a 3d finite difference method to simulate ground motion from elastodynamic propagating ruptures with constant slip on faults in the metropolitan area of los angeles california simulations are carried out for hypothetical m 6 75 earthquakes on the palos verdes and elysian park faults and for comparison an approximation to the 17 january 1994 m 6 7 northridge earthquake the dominant subsurface features of this area are the deep sedimentary los angeles basin and the smaller and shallower san fernando basin simulated ground motions are restricted to the frequency range 0 0 to 0 4 hz ground motion time histories show that in general sites associated with the largest particle velocities and cumulative kinetic energies are located 1 in the epicentral area 2 above the deepest parts of the basins and 3 near the steepest edges of the los angeles basin we find maximum particle velocities for the palos verdes elysian park and northridge simulations of 0 44 0 67 and 0 58 m sec respectively in each case both the directivity of the rupture and the lower impedance of the basins significantly amplify the ground motion although the gross radiation pattern from these ruptures is observable the 3d basin structure distorts the wave field and becomes a source for edge generated waves signal durations at some basin sites last beyond 90 sec due to love waves and refracted s waves that propagate into the sediments from the basin edges compared with the palos verdes event the durations are generally smaller for the elysian park earthquake due to a smaller amount of love waves generated at the basin edges a simple approximation to the northridge earthquake reproduces the overall spatial pattern of the long period particle velocities successfully predicts the timing of late arriving waves and matches the peak velocities with discrepancies generally less than a factor of 2 however for localized areas immediately north and south of the santa monica mountains the computed ground motion underpredicts the observed horizontal peak velocities but matches the vertical ones the pattern of simulated total cumulative kinetic energies is similar to that for the damage intensities observed near the epicenter of the northridge event while the northridge earthquake caused damage in the los angeles area the 3d simulations show that earthquakes with the same magnitude on the palos verdes or elysian park faults produce more severe ground shaking in the los angeles basin

identification and inversion of converted shear waves case studies from the european north atlantic continental margins summary wide angle shear wave arrivals converted from compressional to shear waves at crustal interfaces enable crustal vp vs ratios to be determined which provide valuable constraint on geological interpretations analysis of the converted shear wave phases represents the next logical step in characterizing the crustal structure and composition following multichannel seismic structural imaging and tomographic inversion of the wide angle compressional wave phases in this offshore study across two passive margins extending from stretched continental to fully oceanic crust the high data density 2 10 km ocean bottom seismometer obs spacing and a consistent efficient conversion interface produced shear wave data sets suitable for traveltime inversion the shear waves were recorded by three orthogonal geophones in each obs arrival phases visible to 180 km offset were identified using their arrival times moveout velocities and particle motions across the north atlantic volcanic rifted continental margins studied breakup was accompanied by the eruption of large volumes of basalts of the north atlantic igneous province the interface between post volcanic sediments and the top of the basalts provides the dominant conversion boundary across the oceanic crust and the continent ocean transition however the shear wave data quality was significantly diminished at the continental ends of the profiles where the thick basalt flows and hence this conversion interface feathers out and crustal attenuation increases initial modelling of the converted shear wave phases was carried out using a layer based approach with arrivals converted on the way up used to constrain the vp vs ratio of the post volcanic sedimentary sequence beneath each obs to produce a model with continuous crustal s wave velocities the compressional wave velocities beneath the sediment top basalt interface were transformed into starting shear wave velocities using a constant value of vp vs and the inversion carried out by specifying the appropriate ray path once the data set had been fully interpreted correction of the traveltimes to effective symmetric ray paths enabled us to apply a regularized grid inversion such inversions are less subjective than the layer based approach and yield more robust minimum structure results with quantifiable errors except in the vicinity of a known subbasalt low velocity zone encountered on the faroes margin monte carlo analyses were performed for this approach the average model from multiple inversions using randomized starting models and traveltimes shows the structure required by the traveltimes and the model standard deviation gives an estimate of uncertainty model and inversion parametrizations were fully tested and optimum parameters chosen for compressional and shear wave inversions this allows after appropriate model smoothing an estimate to be made of the spatial variation of the vp vs ratio within the crust there are marked gradients in vp vs and vp vs ratio across the continent ocean transition which may result from intrusion of high magnesium mafic igneous material into the crystalline continental crust the vp vs ratio used in conjunction with vp also provides constraints on the subbasalt lithologies forming the low velocity zone we conclude from such an analysis that this zone is unlikely to be composed entirely of igneous hyaloclastite material some proportion of clastic sedimentary rocks is likely to be present the vp vs and vp properties of the units underlying the low velocity zone are inconsistent with crystalline

q estimation from vertical seismic profile data and anomalous variations in the central north sea four different methods of estimating q from vertical seismic profile vsp data based on measurements of spectral ratios pulse amplitude pulse width and zeroth lag autocorrelation of the attenuated impulse are described the last procedure is referred to as the pulse power method practical problems concerning nonlinearity in the estimating procedures uncertainties in the gain setting of the recording equipment and the influence of structure are considered in detail vsp data recorded in a well in the central north sea were processed to obtain estimates of seismic attenuation these data revealed a zone of high attenuation from approximately 4 900 ft to 5600 ft with a value of 25 3 results of the spectral ratio analysis show that the data conform to a linear constant q model in addition since the pulse width measurement is dependent upon the dispersive model adopted it is shown that a nondispersive model cannot possibly provide a match to the real data no unambiguous evidence is presented that e

geodynamics of the shanxi rift system china the pliocene quaternary shanxi rift system of northern china transsects the domal axis of the shanxi highlands and is defined by an s shaped string of asymmetric basins extending from huailai yanqing in the north via taiyuan to yuncheng in the south this rift system has a length of about 1200 km and a width of 20 80 km it is characterized by strong earthquakes its central nne trending transtensional segment forms the main element of the shanxi rift system basin subsidence commenced during the early pliocene along nne oriented master faults characterized by large strike slip rates 5 68 7 mm yr crustal extension amounts to some 1 4 km basins are separated by push up blocks destructive earthquakes m 7 8 are unevenly distributed the ene trending northern and southern branches of the shanxi rift system are characterized by orthogonal crustal extension along ene striking normal faults amounting to about 8 km these areas are characterized by a basin and range type structural style and weak seismic activity the shanxi rift system developed on a some 40 km thick thermally cool precambrian crustal segment that was overprinted during mesozoic diastrophic events there is only minor rift related volcanic activity the moho is pulled up by a few kilometers only under the axial rift zone sub moho compressional velocities are in the 8 0 8 1 km s range the shanxi rift system evolved in response to the build up of regional stress fields related to the collision of india and eurasia its localization involved reactivation of pre existing fracture systems

the seismic response of the los angeles basin california using strong motion data recorded in the los angeles region from the 1992 mw 7 3 landers earthquake we have tested the accuracy of existing three dimensional 3d velocity models on the simulation of long period 2 sec ground motions in the los angeles basin and surrounding san fernando and san gabriel valleys first the overall pattern and degree of long period excitation of the basins were identified in the observations within the los angeles basin the recorded amplitudes are about three to four times larger than at sites outside the basins amplitudes within the san fernando and san gabriel valleys are nearly a factor of 3 greater than surrounding bedrock sites then using a 3d finite difference numerical modeling approach we analyzed how variations in 3d earth structure affect simulated waveforms amplitudes and the fit to the observed patterns of amplification significant differences exist in the 3d velocity models of southern california that we tested magistrale et al 1996 graves 1996a hauksson and haase 1997 major differences in the models include the velocity of the assumed background models the depth of the los angeles basin and the depth location and geometry of smaller basins the largest disparities in the response of the models are seen for the san fernando valley and the deepest portion of the los angeles basin these arise in large part from variations in the structure of the basins particularly the effective depth extent which is mainly due to alternative assumptions about the nature of the basin sediment fill the general ground motion characteristics are matched by the 3d model simulations validating the use of 3d modeling with geologically based velocity structure models however significant shortcomings exist in the overall patterns of amplification and the duration of the long period response the successes and limitations of the models for reproducing the recorded ground motions as discussed provide the basis and direction for necessary improvements to earth structure models whether geologically or tomographically derived the differences in the response of the earth models tested also translate to variable success in the ability to successfully model the data and add uncertainty to estimates of the basin response given input scenario earthquake source models

seismic wave attenuation in volcanic rocks from vsp experiments seismic wave attenuation in the columbia plateau basalts and snake river plain volcanics was analyzed using vertical seismic profiling vsp data the computation of attenuation coefficients is based on fitting a straight line to the logarithm of amplitude ratios computed for fixed values of frequency and variable depth this approach does not require any assumptions on the dependence of q on frequency for the columbia plateau basalts the attenuation coefficients obtained from the field data are smaller than those computed from the synthetic vsp generated using the sonic and density logs indicating that the observed attenuation is related to scattering effects and is substantially larger than the intrinsic attenuation of basalt therefore it is concluded that only a lower bound for q can be established in agreement with recent findings by other authors the effective attenuation of seismic energy in basalts about 1 1 10 4dbs m for the peak frequency is comparable to the effective attenuation observ

seismic imaging through the volcanic rocks of the snake river plain insights from project hotspot hotspot the snake river geothermal drilling project was undertaken to better understand geothermal systems across the snake river plain volcanic province a series of surface and borehole seismic profiles were obtained to provide insights into volcanic stratigraphy and test the capabilities of engineering scale seismic imaging in such terranes the kimberly site drilled through 1 9 km of mostly rhyolite with thin sedimentary interbeds in the upper part of the section the kimama site drilled through 1 9 km of mostly basalt with sedimentary interbeds at 200 m depth and 1700 m depth the mountain home site contained numerous sediment and volcanic rock layers downhole and surface vibroseis seismic results suggest sedimentary interbeds at depth correspond with low velocity high temperature zones that relate to reflections on seismic profiles our results suggest that eruption flow volumes can be estimated and flow boundaries can be imaged with surface seismic methods using relatively high fold and wide angle coverage high frequency attenuation is observed at all sites and this deficit may be countered by acquisition design and a focus on signal processing steps separation of surface and body waves was obtained by muting and the potential for large static effects was identified and addressed in processing an accurate velocity model and lithology contacts derived from borehole information improved the confidence of our seismic interpretations

the validity of q estimates from borehole data using spectral ratios the measurement from borehole sonic data of q the acoustic attenuation coefficient of an earth section can be achieved in three ways forward modeling chuen and toksoez 1981 spectral ratios gladwin and stacey 1974 and inversion cheng et al 1986 the spectral ratio technique has been applied to real data goldberg et al 1985 but is unstable and not very reliable experiments have shown that the spectral ratio technique applied to waveforms gives q estimates which are lower than those measured from cores in the laboratory goldberg and zinszner 1989 we investigate this phenomenon using synthetic and real data

attenuation differences in layer 2a in intermediate and slow spreading oceanic crust in situ seismic attenuationq 1logs are derived from borehole velocity profiles and reveal sharp boundaries between morphologies of the extrusive volcanic layers in intermediate and slow spreading oceanic crust q 1logs are calculated from the scattering attenuation associated with vertical velocity heterogeneity in ocean drilling program holes 504b and 896a and in hole 395a located in 5 9 7 3 ma crust on the pacific and atlantic plates respectively our results strongly tie crustal properties to seismic measurables and observed geological structures we find that the scattering attenuation can be used to identify the extrusive volcanic sequence because it is closely related to changes in the degree of vertical heterogeneity we interpret a distinct decrease in the q 1log at the transition below the extrusive volcanic layer to correspond with the seismic layer 2a 2b boundary the boundary is located at 465 m depth below the sea floor in both hole 395a and 504b although this is likely to be a coincidence of the sediment thickness at these sites layer 2a is estimated to be approximately 150 m thick in hole 504b and 300 m thick in hole 395a cyclic sequences of high porosity pillows and low porosity massive units in the uppermost 100 m of volcanics in hole 395a result in large velocity heterogeneities which cause 5 times more attenuation in this layer than in hole 504b in hole 896a by contrast fewer pillows more massive flows and a greater volume of carbonate veins decrease the velocity heterogeneity and attenuation significantly over only 1 km distance from hole 504b we conclude that the attenuation in the extrusive volcanics of the ocean crust is largely controlled by variation in local heterogeneity and morphology as well as by subsequent hydrothermal alteration the observed differences inq 1profiles and layer 2a thickness at these sites may be attributed to variations in the volume and duration of volcanic activity at mid ocean spreading centers for these pacific and atlantic ridge segments

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

three dimensional simulation of the near fault ground motion for the 1995 hyogo ken nanbu kobe japan earthquake abstract the 17 january 1995 hyogo ken nanbu earthquake is a typical example showing that the ground motions along basin edge faults can be very destructive in this study we simulate the near fault ground motion from this earthquake based on a kinematic fault model and a simplified 3d velocity structure of the kobe area the kinematic earthquake rupture and the wave propagation are modeled using a 3d finite difference method fdm our simulation identifies the basin edge effect as an important factor that influenced the ground motion amplification pattern in the kobe area we found that the coupling of the source directivity and basin edge effects causes impulsive ground motions with extremely high amplitude at periods greater than 1 sec and in a narrow zone offset less than 1 km from the basin edge the combination of these effects acted to create a fairly continuous band of amplification that extends about 30 km in an elongated zone parallel to the basin edge boundary in some areas localized site effects might have been as important as the abovementioned effects but they cannot explain the continuity of the extended east west zone of damage

in situ investigation of seismic body wave attenuation in heterogeneous media field experiments have been carried out to study the nature and magnitude of seismic wave attenuation for a variety of lithologies in each survey two three component sets of geophones with wall clamping mechanisms were lowered down boreholes and signals originating from surface compressional and shear wave sources were recorded the data collected were corrected for spherical divergence and analyzed to determine intrinsic attenuation for situations of anomalous wavefront expansion and in cases where multiple reflection losses may be significant corrections were supplied by a synthetic seismogram programme to improve the estimates of intrinsic attenuation values of attenuation were obtained for pure sandstone sandstone marl sequences and fissured unfissured chalk sequences these formations were all near surface and relatively porous significant differences in the relative values of compressional and shear wave attenuation in the various lithologies were noted in particular compressional absorption in the fissured zones of chalk was twice the absorption associated with the seismic velocities and the absorption of shear waves fluctuated much less a large contrast in p wave attenuation was also observed between pure bunter sandstone and the sandstone marl sequence absorption was over three times as small in the former a smaller contrast was noted for shear attenuation the results obtained suggest that for the relatively homogeneous formations such as pure sandstone and unfissured chalk shear absorption was dominant over bulk absorption in contrast bulk absorption was larger than shear absorption for other formations e g the fissured chalk sequences and a partially saturated chalk section attenuation was found to be approximately proportional to frequency in all experiments

oblique high angle listric reverse faulting and associated development of strain the wenchuan earthquake of may 12 2008 sichuan china the 2008 wenchuan earthquake occurred on imbricate oblique steeply dipping slowly slipping listric reverse faults measurements of coseismic slip the distribution of aftershocks and fault plane solution of the mainshock all confirm this style of deformation and indicate cascading earthquake rupture of multiple segments each with coseismic slip occurring in the shallow crust above a depth range of 10 to 12 km interactions among three geological units eastern tibet the longmen shan and the sichuan basin caused slow strain accumulation in the longmen shan so that measurable preearthquake slip was minor coseismic deformation however took place mostly within the interseismically locked longmen shan fault zone the earthquake may have initiated from slip on a fault plane dipping 30 40 northwest in a depth range from 15 to 20 km and triggered oblique slip on the high angle faults at depths shallower than 15 km to form the great wenchuan earthquake

measurements of attenuation from vertical seismic profiles values of attenuation have been extracted from five detailed velocity surveys significant amounts of attenuation are observed in all five wells measured values of attenuation vary by a factor of 10 ranging from less than 0 1 to 0 9 db wavelength correlation of attenuation with lithology is good considering the resolution limits of the surveys one of the surveys was performed in west texas and the other four were carried out in the gulf coast area the total number of recording depths in each survey varied from 31 to 208 with downhole recordings taken every 10 or 20 ft over key stratigraphic zones in all five surveys a monitor geophone was placed near the well to check for source consistency our procedure for measuring attenuation involved constructing the spectral ratio between each downhole pulse and one particular reference pulse a value of cumulative attenuation ca was then extracted from each spectral ratio and plotted as a function of geophone depth this method allowed us to use many m

seismic wave attenuation in metamorphic rocks from vsp data recorded in germany s continental super deep borehole vertical seismic profiling vsp data recorded in the german continental deep borehole ktb between 3 and 6 km have been used to study the attenuation of p waves a vibrator source was used to generate the data in this depth range the lithology is dominated by a metabasite unit amphibolite and metagabbro with various degrees of alteration intercalated with paragneisses the method used to determine attenuation is based on the fit of a straight line to the logarithm of amplitude ratios for variable depth and fixed frequency inspection of the corresponding attenuation curves showed sharp discontinuities which correlate with changes in the seismic source mostly related to changes in location as recorded by a nearby monitor geophone to avoid the uncertainties introduced by these changes the analysis was restricted to a depth interval 3576 4538 m for which the source was not moved even in this case however the monitor traces showed significant variations in their frequency content although not much variation in their peak time domain amplitudes to account for these variations the attenuation coefficients obtained for the actual data were corrected for source variations by subtraction of the attenuation coefficients determined from the analysis of synthetic vsp data computed using source wavelets extracted from the monitor traces after these corrections the values of q for frequencies between 7 8 and 46 9 hz are between 14 and 32 these values are quite low and may be related to the presence of fluids known to exist in the depth range under consideration although scattering processes may also contribute to the high attenuation the variation of q with frequency may be the result of processing artifacts

neotectonics of the sevier desert basin utah as seen through the lens of multi scale geophysical investigations abstract geophysical surveys conducted in the clear lake fault zone utah constrain the interpretation of neotectonics and volcanism along a portion of the colorado plateau basin and range transition zone the fault zone lies within the sevier desert a region marked by numerous quaternary fault scarps and bimodal volcanism lavas as young as 660 a b p are usually cut by faults and many scarps have significant offsets implying the potential for m 7 earthquakes the range of scarp heights and uncertainty in scarp magnitude regressions suggest variations on the order of 0 75 moment magnitude units in order to characterize the range of deformation styles in the clear lake fault zone three fault scarps were investigated for their patterns of shallow