dynamic triggering stress modeling and a case study 1 changes in the static stress can trigger nearby earthquakes that occur within a few fault lengths from the causative event transient stresses caused by passage of surface waves commonly trigger events at remote distances yet little is documented or understood about the processes and stresses necessary for remote triggering to understand the causative stresses and environments behind remote or dynamic triggering we must decipher the stresses caused by the passage of the surface waves in relation to the local stress field and fault conditions where the triggered events occur in this study we model the change in the stress field that the passing of rayleigh and love waves causes on a fault plane of arbitrary orientation relative to the direction of propagation of the waves and we apply a coulomb failure criterion to calculate the potential of these stress changes to trigger reverse normal or strike slip failure we compare these model results with data from dynamically triggered earthquakes in the australian bowen basin an area with low seismicity and mapped regional stress and that is at the margin of a stable continental craton our data analysis shows that for this region surface waves arriving at 45 from the average strike direction are the most likely to trigger local seismicity this agrees with our observations

long runout rockslide on glacier at tsar mountain canadian rocky mountains potential triggers seismic and glaciological implications a rhomboidal shaped rockslide with a length of 2 2 km and an area of 1 35 km2 covers 30 of a small clemenceau icefield group cirque glacier by means of remote sensing airborne photography climate and seismic data analysis the extent timing possible trigger mechanisms and rockslide effects on the glacier are discussed an ml 2 0 seismic event on 14 september 2000 represents the rockslide and has a spindle shaped waveform and high energy in the low frequencies based on a strong signal duration of 56 108 seconds the rockslide had an average runout velocity of 22 45 m s 1 stress fatigue and a combination of rain and snow followed by rapid melt and night time freezing could have co triggered the slide additional seismic events with epicentres 40 km from the cirque were recorded 26 times since 1985 and range between ml 0 9 3 3 but none were caused by or triggered large mass movement with a rock source volume of 1 6 106 m3 and a deposited volume of 2 4 106 m3 the sum of bulking and entrainment is between 25 and 150 five melt seasons post event levees 20 30 m wide tower 30 m over the surrounding glacier rockslide characteristics and its fahrboschung of 15 height length h l 0 28 indicate that this rockslide is quite typical for long runout rockslides on glaciers however the basal friction coefficient was higher than found on other glaciers and could relate to the presence of medial moraines transverse to the flowline and to pre slide debris cover the difference between the coefficient of friction in the main flowline 0 11 0 14 and that in a lobe confined between two medial moraines 0 065 suggests that confinement increases mobility by 70 115 apart from reduced ablation under the rock debris effects of the rockslide on the glacier were minimal copyright 2010 john wiley sons ltd

alternative rupture scaling relationships for subduction interface and other offshore environments abstract alternative fault rupture scaling relationships are developed for m w 7 1 9 5 subduction interface earthquakes using a new database of consistently derived finite fault rupture models from teleseismic inversion scaling relationships are derived for rupture area rupture length rupture width maximum slip and average slip these relationships apply width saturation for large magnitude interface earthquakes approximately m w 8 6 for which the physical characteristics of subduction zones limit the depth extent of seismogenic rupture and consequently the down dip limit of strong ground motion generation on average the down dip rupture width for interface earthquakes saturates near 200 km 196 km on average accordingly the reinterpretation of rupture area scaling for subduction interface earthquakes through the use of a bilinear scaling model suggests that rupture asperity area is less well correlated with magnitude for earthquakes m w 8 6 consequently the size of great magnitude earthquakes appears to be more strongly controlled by the average slip across asperities the sensitivity of the interface scaling relationships is evaluated against geographic region or subduction zone and average dip along the rupture interface to assess the need for correction factors although regional perturbations in fault rupture scaling could be identified statistical significance analyses suggest there is little rationale for implementing regional correction factors based on the limited number of interface rupture models available for each region fault rupture scaling relationships are also developed for intraslab within the subducting slab extensional outer rise and offshore strike slip environments for these environments the rupture width and area scaling properties yield smaller dimensions than interface ruptures for the corresponding magnitude however average and maximum slip metrics yield larger values than interface events these observations reflect both the narrower fault widths and higher stress drops in these faulting environments although expressing significantly different rupture scaling properties from earthquakes in subduction environments the characteristics of offshore strike slip earthquake ruptures compare similarly to commonly used rupture scaling relationships for onshore strike slip earthquakes electronic supplement table of rupture parameters

stress sensitivity of fault seismicity a comparison between limited offset oblique and major strike slip faults we present a new three dimensional inventory of the southern san francisco bay area faults and use it to calculate stress applied principally by the 1989 m 7 1 loma prieta earthquake and to compare fault seismicity rates before and after 1989 the major high angle right lateral faults exhibit a different response to the stress change than do minor oblique right lateral thrust faults seismicity on oblique slip faults in the southern santa clara valley thrust belt increased where the faults were unclamped the strong dependence of seismicity change on normal stress change implies a high coefficient of static friction in contrast we observe that faults with significant offset 50 100 km behave differently microseismicity on the hayward fault diminished where right lateral shear stress was reduced and where it was unclamped by the loma prieta earthquake we observe a similar response on the san andreas fault zone in southern california after the landers earthquake sequence additionally the offshore san gregorio fault shows a seismicity rate increase where right lateral oblique shear stress was increased by the loma prieta earthquake despite also being clamped by it these responses are consistent with either a low coefficient of static friction or high pore fluid pressures within the fault zones we can explain the different behavior of the two styles of faults if those with large cumulative offset become impermeable through gouge buildup coseismically pressurized pore fluids could be trapped and negate imposed normal stress changes whereas in more limited offset faults fluids could rapidly escape the difference in behavior between minor and major faults may explain why frictional failure criteria that apply intermediate coefficients of static friction can be effective in describing the broad distributions of aftershocks that follow large earthquakes since many of these events occur both inside and outside major fault zones

static stress transfer during the 2002 nenana mountain denali fault alaska earthquake sequence 1 on 23 october 2002 the mw 6 7 nenana mountain earthquake occurred in central alaska it was followed on 3 november 2002 by the mw 7 9 denali fault mainshock the largest strike slip earthquake to occur in north america during the past 150 years we have modeled static coulomb stress transfer effects during this sequence we find that the nenana mountain foreshock transferred 30 50 kpa of coulomb stress to the hypocentral region of the denali fault mainshock encouraging its occurrence we also find that the two main earthquakes together transferred more than 400 kpa of coulomb stress to the cross creek segment of the totschunda fault system and to the denali fault southeast of the mainshock rupture and up to 80 kpa to the denali fault west of the nenana mountain rupture other major faults in the region experienced much smaller static coulomb stress changes

earthquake induced snow avalanches i historical case studies strong ground motions caused by earthquakes can induce catastrophic avalanches massive snow avalanching has also been observed on slopes near quarries and underground mines where ground motions are produced by explosives to address a lack of information regarding seismogenic snow avalanches we have compiled an inventory to document case histories for the period 1899 2010 22 cases are identified worldwide related to natural or artificial seismicity with magnitudes of 1 9 mw 9 2 and source to site distances of 0 2 640 km in the extreme case many thousands of simultaneously released large scale avalanches have been reported the obtained distribution and variety of parameters are discussed and compared with earthquake induced landslides and ice avalanches the results are similar among these three types of failure events although all data derived from statistical analyses i e non witnessed cases represent outliers suggesting a significant reduction in the threshold magnitudes proposed for landslides this proposal could be verified by the collection of additional data

the 2002 denali fault earthquake alaska a large magnitude slip partitioned event the mw moment magnitude 7 9 denali fault earthquake on 3 november 2002 was associated with 340 kilometers of surface rupture and was the largest strike slip earthquake in north america in almost 150 years it illuminates earthquake mechanics and hazards of large strike slip faults it began with thrusting on the previously unrecognized susitna glacier fault continued with right slip on the denali fault then took a right step and continued with right slip on the totschunda fault there is good correlation between geologically observed and geophysically inferred moment release the earthquake produced unusually strong distal effects in the rupture propagation direction including triggered seismicity

the postseismic response to the 2002 m 7 9 denali fault earthquake constraints from insar 2003 2005 summary insar is particularly sensitive to vertical displacements which can be important in distinguishing between mechanisms responsible for the postseismic response to large earthquakes afterslip viscoelastic relaxation we produce maps of the surface displacements resulting from the postseismic response to the 2002 denali fault earthquake using data from the canadian radarsat 1 satellite from the periods summer 2003 summer 2004 and summer 2005 a peak to trough signal of amplitude 4 cm in the satellite line of sight was observed between summer 2003 and summer 2004 by the period between summer 2004 and summer 2005 the displacement rate had dropped below the threshold required for observation with insar over a single year the insar observations show that the principal postseismic relaxation process acted at a depth of 50 km equivalent to the top of the mantle however the observations are still incapable of distinguishing between distributed viscoelastic relaxation and localized afterslip deformation the imposed coseismic stresses are highest in the lower crust and assuming a maxwell rheology a viscosity ratio of at least 5 between lower crust and upper mantle is required to explain the contrast in behaviour the lowest misfits are produced by mixed models of viscoelastic relaxation in the mantle and shallow afterslip in the upper crust profiles perpendicular to the fault show significant asymmetry which is consistent with differences in rheological structure across the fault

inversion migration tomography seismic inversion broadly enough defined is equivalent to doing migration and reflection tomography simultaneously diffraction tomography and inversion work best when sources and receivers surround the region of interest as in medical imaging applications theoretical studies have shown that high vertical wavenumber velocity perturbations are resolved by inverting surface seismic reflection data but the low vertical wavenumbers must be obtained using a separate step such as velocity analysis or reflection tomography i propose that a nonlinear iterative inversion that updates a varying background velocity obtains all wavenumbers that are resolvable separately by migration and tomography the background velocity must contain reflectors to provide data on both upward and downward transmission paths through the earth and hence the low wavenumbers by considering the downward transmission paths to be between surface sources and buried image geophones and the upward transmission paths to be between surfa

sutton alaska earthquake of 1984 evidence for activity on the talkeetna segment of the castle mountain fault system a magnitude 5 7 mb 5 2 ms earthquake occurred on 14 august 1984 14 km north of sutton in the vicinity of the mapped trace of the talkeetna segment of the castle mountain fault system the focal mechanism of the earthquake and the spatial distribution of well controlled aftershock hypocenters indicate that the shock involved dextral slip at 13 to 20 km depth on the talkeetna fault segment the depth of the shocks is consistent with the lack of observed surface breakage the sutton earthquake sequence plus recent small shocks recorded by the southern alaska seismograph network provide definitive evidence that the talkeetna segment of the fault system is active

static stress transfer and earthquake triggering no lower threshold in sight the main objective of this study is to see if a lower threshold for earthquake triggering exists resolving this issue is important for the understanding of earthquake mechanics and for the purpose of hazard analysis we compute the cumulative static stress changes imposed on 63 m 4 5 earthquakes in central california between 1969 and 1998 by adding the stress changes imposed by all previous m 4 5 earthquakes as a function of time prior to the events we find that 85 of the cumulative stress changes at the time of rupture are positive for stress change magnitudes of 10 kpa 0 1 bar and 70 are positive for stress changes of 10 kpa 0 1 bar as well as 1 kpa 0 01 bar a comparison between these results and those obtained for synthetic catalogs in which the timing or focal mechanisms of the earthquakes were randomized shows that this degree of triggering is very unlikely to be found in a random catalog thus we conclude that no lower threshold for earthquake triggering in central california has been found we show that the temporal distribution of stress changes that discourage failure is consistent with the theoretical prediction that the time delay increases with the magnitude of the stress change

denali fault slip rates and holocene late pleistocene kinematics of central alaska the denali fault is the principal intracontinental strike slip fault accommodating deformation of interior alaska associated with the yakutat plate convergence we obtained the first quantitative late pleistocene holocene slip rates on the denali fault system from dating offset geomorphic features analysis of cosmogenic 10be concentrations in boulders n 27 and sediment n 13 collected at seven sites offset 25 170 m by the denali and totschunda faults gives average ages that range from 2 4 0 3 ka to 17 0 1 8 ka these offsets and ages yield late pleistocene holocene average slip rates of 9 4 1 6 12 1 1 7 and 8 4 2 2 mm yr 1 along the western central and eastern denali fault respectively and 6 0 1 2 mm yr 1 along the totschunda fault our results suggest a westward decrease in the mean pleistocene holocene slip rate this westward decrease likely results from partitioning of slip from the denali fault system to thrust faults to the north and west

statistical analysis of the 2002 mw 7 9 denali earthquake aftershock sequence we study the scaling properties of the aftershock sequence of the 2002 m w 7 9 denali earthquake the sequence exhibits nontrivial scaling behavior in magnitude aftershock decay rates and aftershock inter occurrence times in particular we observe a marked variability in the gutenberg richter gr exponent the b value in space between early and late times after the mainshock and over different magnitude ranges we find strong indications that certain aspects of this variability might be ascribed to the occurrence of some of the aftershocks on and around a supershear rupture associated with this event particularly we observe a statistically higher b value for the aftershocks that occurred in the zone surrounding the supershear rupture we further outline a method to obtain an average b value consistent with the theory and statistical properties of the data we find a significant difference between the magnitude of the largest aftershock and the mainshock this is analyzed and discussed using the modified bath s law it is observed that the aftershock decay rate can be approximated by the modified omori law the distribution of inter occurrence times is studied and we show that it can be explained in terms of a nonhomogeneous poisson process through time we further observe that the rescaled inter occurrence time distributions for various magnitude thresholds collapse into a universal functional form which indicates that the aftershock sequence exhibits self similarity in both magnitude and time in particular the statistical features of the aftershock sequence show that the rupture process or the preconditions that lead to it may influence aftershock statistics

tectonic drivers of the wrangell block insights on fore arc sliver processes from 3 d geodynamic models of alaska intracontinental shear zones can play a key role in understanding how plate convergence is manifested in the upper plate in regions of oblique subduction however the relative role of the driving forces from the subducting plate and the resisting force from within intracontinental shear zones is not well understood results from high resolution geographically referenced instantaneous 3d geodynamic models of flat slab subduction at the oblique convergent margin of alaska are presented these models investigate how viscosity and length of the denali fault intracontinental shear zone as well as coupling along the plate boundary interface modulate motion of the wrangell block forearc sliver and slip across the denali fault models with a weak denali fault 1017 pa s and strong plate coupling 1021 pa s were found to produce the fastest motions of the wrangell block 10 mm yr the 3d models predict along strike variation in offs et along the denali fault changing from dextral strike slip motion in the eastern segment to oblique convergence towards the fault apex models further show that the flat slab drives oblique motion of the wrangell block and contributes to 20 models with a short fault and 28 models with a long fault of the observed quaternary slip rates along the denali fault the 3d models provide insight into the general processes of forearc sliver mechanics and also offer a 3d framework for interpreting hazards in regions of flat slab subduction

earthquake rupture through a step over fault system an exploratory numerical study of the leech river fault southern vancouver island the leech river fault lrf zone located on southern vancouver island is a major regional seismic source we investigate potential interactions between earthquake ruptures on the lrf and the neighb

modified frequency wavenumber algorithm for regional seismograms using filon s quadrature modelling of lg waves in eastern north america summary the main focus of this study is to develop an efficient frequency wavenumber code to synthesize high frequency say 10 hz regional seismograms up to a distance of more than 1000 km in a medium consisting of a large number of crustal layers and investigate effects of regional waveguides on lg waves in this newly developed code the frequency wavenumber response is evaluated by using the filon s quadrature at high frequency and the polynomial approximation of bessei s functions implementing trapezoidal integration at low frequency this has reduced the computation time by several folds compared to the time needed for the trapezoidal integration using this algorithm both broad band seismograms at harvard and short period ectn eastern canadian telemetered network seismograms from 1988 november 25 saguenay earthquake were successfully modelled a moment magnitude of 5 9 was used initially an average waveguide was calibrated to successfully excite the regional pnl and snl waves at hrv its near surface structure constrained by matching the recorded frequency content the crust mantle transition zone was constrained by modelling the strength of the broad band snl waves consisting of sn ssmsnsmssms and ssmssms phases relative to the initial pnl waves the model was modified to consist of thin layers with an alternating high and low velocity distribution to match the high frequency ectn lg waves observed from 300 to 600 km away in addition the effect of a near surface irregular receiver structure on the duration of lg waves was also investigated by convolving its response with the regional lg seismograms initial study suggests this method as viable for modelling the entire lg waves including the coda numerical studies suggest that the shapes and peak amplitudes on lg seismograms depend more strongly on the source depth anelasticity and crustal waveguide than do the pnl seismograms

complex geometry and segmentation of the surface rupture associated with the 14 november 2001 great kunlun earthquake northern tibet china abstract the 14 november 2001 kunlun china earthquake with a moment magnitude m w 7 8 occurred along the kusai lake kunlun pass fault of the kunlun fault system we document the spatial distribution and geometry of surface rupture zone produced by this earthquake based on high resolution satellite landsat etm aster spot and ikonos images combined with field measurements our results show that the surface rupture zone can be divided into five segments according to the geometry of surface rupture including the sun lake buka daban hongshui river kusai lake hubei peak and kunlun pass segments from west to east these segments each 55 to 130 km long are separated by step overs the sun lake segment extends about 65 km with a strike of n45 75 w between 90 05 e 90 50 e along the previously unrecognized west sun lake fault a gap of about 30 km long exists between the sun lake and buka daban peak where no obvious surface ruptures can be observed either from the satellite images or field observations the buka daban hongshui river kusai lake hubei peak and kunlun pass segments run about 365 km striking n75 85 w along the southern slope of the kunlun mountains between 91 07 e 94 58 e this segmentation of the surface rupture is well correlated with the pattern of slip distribution measured in the field detailed mapping suggest that these five first order segments can be further separated into over 20 second order segments with a length of 10 30 km linked by smaller scale step overs or bends our result also shows that the total coseismic surface rupture length produced by the 2001 kunlun earthquake is about 430 km excluding the 30 km long gap which is the longest coseismic surface rupture for an intracontinental earthquake ever recorded finally we suggest a multiple bilateral rupture propagation model that shows the rupture process of the 2001 m w 7 8 earthquake is complex it consists of westward and eastward rupture propagations and interaction of these bilateral rupture processes

the 14 november 2001 kokoxili kunlunshan tibet earthquake rupture transfer through a large extensional step over the 14 november 2001 kokoxili tibet earthquake m w 7 8 ruptured 400 km of the western kunlun fault in northern tibet we apply two inversion methods to p and sh waves recorded by the global seismographic network to recover the spatial and temporal history of the rupture process the observed surface rupture consists of two strike slip segments offset by an extensional step over little surface rupture was observed in the graben system in this step over which is approximately 45 km long and over 10 km wide our results imply that the rupture did not jump this large gap but that the rupture was continuous through the graben the earthquake began with a small strike slip subevent presumably along the westernmost of the two segments this was followed 5 sec later by a subevent of about the same magnitude but having an oblique mechanism with a large normal faulting component the likely location for this subevent is within the graben this oblique slip event probably enabled transfer of the rupture onto the main kunlun fault the main moment release began 18 sec after rupture initiation and propagated over 350 km eastward along the kunlun fault slip on this segment was very heterogeneous averaging 2 m for the first 200 km followed by a sharp increase to a maximum of 7 5 m within the next 50 km and then a rapid decline the average rupture velocity along the main segment was high 3 6 km sec 1 and probably exceeded the local shear wave velocity the m w 7 8 kokoxili earthquake had a longer surface rupture and faster average rupture velocity radiated more energy and probably had a lower average fracture energy than the november 2002 m w 7 9 denali fault alaska earthquake evidence suggests that the velocity of the rupture front dropped significantly after passing the point of maximum slip implying a large difference in frictional strength between the two ends of the fault online material waveform fits to teleseismic body waves

evidence of instantaneous dynamic triggering during the seismic sequence of year 2000 in south iceland 1 we analyze the coseismic stress perturbation during the 17 june 2000 south iceland seismic sequence the main shock ms 6 6 was followed by three large events within a few tens of seconds 8 26 and 30 s located within 80 km the aim of this paper is to investigate short term fault interaction and instantaneous triggering this happens when a fault perturbed by a stress change fails before the end of the transient stress perturbation we compute the shear normal and coulomb stress changes as functions of time in a stratified elastic half space by using discrete wave number and reflectivity methods we calculate dynamic stresses caused by the main shock at the hypocenters of these three subsequent events our numerical results show that the onset of the last two events is slightly delayed with respect to the arrival time of the second positive peak of coulomb stress variation while the first event occurred after the first positive stress peak we have also analyzed the response of a spring slider system representing a fault governed by a rate and state dependent friction law perturbed by shear and normal stress variations caused by the main shock the fault response to the computed stress perturbations is always clock advanced we have found suitable constitutive parameters of the modeled fault that allow the instantaneous dynamic triggering of these three earthquakes if the initial sliding velocity is comparable with the tectonic loading velocity we obtained failure times close to the observed origin times for low values of the initial effective normal stress

source model for the mw 6 7 23 october 2002 nenana mountain earthquake alaska from insar 1 the 23 october 2002 nenana mountain earthquake mw 6 7 occurred on the denali fault alaska to the west of the mw 7 9 denali earthquake that ruptured the same fault 11 days later we used 6 interferograms constructed using radar images from the canadian radarsat 1 and european ers 2 satellites to determine the coseismic surface deformation and a source model data were acquired on ascending and descending satellite passes with incidence angles between 23 and 45 degrees and time intervals of 72 days or less modeling the event as dislocations in an elastic half space suggests that there was nearly 0 9 m of right lateral strike slip motion at depth on a near vertical fault and that the maximum slip in the top 4 km of crust was less than 0 2 m the nenana mountain earthquake increased the coulomb stress at the future hypocenter of the 3 november 2002 denali earthquake by 30 60 kpa

geophysical data reveal the crustal structure of the alaska range orogen within the aftershock zone of the mw 7 9 denali fault earthquake geophysical information including deep crustal seismic reflection magnetotelluric mt gravity and magnetic data cross the aftershock zone of the 3 november 2002 mw 7 9 denali fault earthquake these data and aftershock seis micity jointly interpreted reveal the crustal structure of the right lateral slip denali fault and the eastern alaska range orogen as well as the relationship between this structure and seismicity north of the denali fault strong seismic reflections from within the alaska range orogen show features that dip as steeply as 25 north and extend downward to depths between 20 and 25 km these reflections reveal crustal structures probably ductile shear zones that most likely formed during the late cretaceous but these structures appear to be inactive having produced little seis micity during the past 20 years furthermore seismic reflections mainly dip north whereas alignments in aftershock hypocenters dip south the denali fault is nonre flective but modeling of mt gravity and magnetic data suggests that the denali fault dips steeply to vertically however in an alternative structural model the denali fault is defined by one of the reflection bands that dips to the north and flattens into the middle crust of the alaska range orogen modeling of mt data indicates a rock body having low electrical resistivity 10 xm that lies mainly at depths greater than 10 km directly beneath aftershocks of the denali fault earthquake the maxi mum depth of aftershocks along the denali fault is 10 km this shallow depth may arise from a higher than normal geothermal gradient alternatively the low electrical resistivity of deep rocks along the denali fault may be associated with fluids that have weakened the lower crust and helped determine the depth extent of the after shock zone

stratigraphic evidence for seven meters of dextral slip on the san andreas fault during the 1857 earthquake in the carrizo plain the smallest geomorphic offsets along a 35 km section of the san andreas fault in the carrizo plain vary from 7 to 10 m our three dimensional excavation of alluvial deposits a few km southeast of wallace creek confirms that at least 6 6 to 6 9 m of dextral slip occurred there during the latest large earthquake in 1857 dates on detrital charcoal suggest that the last event prior to the 1857 earthquake occurred before a date within the range a d 1305 to 1623 the 3 m range in smallest offsets along this portion of the fault may reflect either a 3 m variation in slip along the san andreas in 1857 or 2 to 3 m of slip during an event prior to 1857 observations made after the recent landers earthquake are compatible with the hypothesis of large local variations in slip during a single earthquake but do not explain the cause of such variations off fault dextral rotations would be one plausible explanation however paleoseismic data in the carrizo plain are too sparse to allow rejection of the alternative hypothesis that slip in the event prior to 1857 was only 2 to 3 m an amount of slip which would be several times too small to fit a time predictable model

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

aftershock sequence parameters in new zealand abstract regional generic models describing the temporal and magnitude distribution of aftershocks are routinely used in california to assess aftershock hazard this note applies the reasenberg and jones 1989 formulation of aftershock parameters to 17 new zealand earthquake sequences of m 5 5 from 1987 through 1995 the median values of the aftershock parameters are similar to those obtained for california

fault kinematic and geomorphic observations along the north tehran thrust and mosha fasham fault alborz mountains iran implications for fault system evolution and interaction in a changing tectonic regime summary neighbouring faults can interact potentially link up and grow and consequently increase the seismic and related natural hazards in their vicinity despite evidence of quaternary faulting the kinematic relationships between the neighbouring mosha fasham fault mff and the north tehran thrust ntt and their temporal evolution in the alborz mountains are not well understood the ene striking ntt is a frontal thrust that delimits the alborz mountains to the south with a 2000 m topographic front with respect to the proximal tehran plain however no large instrumentally recorded earthquakes have been attributed to that fault in contrast the sigmoidally shaped mff is a major strike slip fault located within the alborz mountains sinistral motion along the eastern part of the mff is corroborated by microseismicity and fault kinematic analysis which documents recent transtensional deformation associated with nne ssw oriented shortening to better understand the activity of these faults on different timescales we combined fault kinematic analysis and geomorphic observations to infer the kinematic history of these structures our fault kinematic study reveals an early dextral shear for the ntt and the central mff responsible for dextral strike slip and oblique reverse faulting during nw oriented shortening this deformation regime was superseded by ne oriented shortening associated with sinistral oblique thrusting along the ntt and the central western mff sinistral strike slip motion along subsidiary faults in the central mff segment and folding and tilting of eocene to miocene units in the mff footwall continued thrusting along the ntt took place during the quaternary however folding in the hanging wall and sinistral stream offsets indicate a left oblique component and quaternary strike slip reactivation of the eastern ntt segment close to its termination this complex history of faulting under different stress directions has resulted in a composite landscape with inherited topographic signatures our study shows that the topography of the hanging wall of the ntt reflects a segmentation into sectors with semi independent uplift histories areas of high topographic residuals and apparent high uplift underscore the fault kinematics combined our data suggest an early mechanical linkage of the ntt and mff fault systems during a former dextral transpressional stage caused by nw compression during ne oriented shortening the ntt and mff were reactivated and incorporated into a nascent transpressional duplex the youngest manifestation of motion in this system is sinistral transtension however this deformation is not observed everywhere and has not yet resulted in topographic inversion

resolution of fault slip along the 470 km long rupture of the great 1906 san francisco earthquake and its implications data from all available triangulation networks affected by the 1906 earthquake have been combined to assess the trade off between slip resolution and its uncertainty and to construct a conservative image of coseismic slip along the rupture because of varying network aperture and station density slip resolution is very uneven although slip is determined within uncertainties of 1 0 m along 60 of the fault constraints are poor on the remaining mostly offshore portions of the rupture slip decreases from maxima of 8 6 and 7 5 m at shelter cove and tomales bay to 4 5 m near mount tamalpais and 2 7 m at loma prieta the geodetically derived slip distribution is in poor agreement with estimates based on analysis of s wave seismograms probably because these waves register only 20 30 of the total seismic moment obtained from longer period surface waves consideration of a range of fault geometries for 1906 slip near loma prieta indicates right lateral motions lie between 2 3 and 3 1 m these values are considerably greater than the 1 5 m of measured surface slip on which several assessments of high earthquake hazard for this fault segment were based this factor along with the absence of 1989 slippage where 1906 surface slip was used to make the forecasts casts doubt on some claims of success in predicting the 1989 m 6 9 loma prieta earthquake

infrasound associated with the 2002 denali fault earthquake alaska 1 infrasonic waves associated with the november 3 2002 magnitude 7 9 earthquake in alaska were detected by the microphone array i53us in fairbanks alaska the epicenter of the earthquake lay some 150 km south of the fairbanks array both seismic and acoustic signals were recorded successively by the microphone array the fault rupture of the earthquake moved east southeast along the denali totschunda system fault for approximately 294 km the northern side of the fault moved to the east and vertically upward relative to the southern side displacements up to 8 8 meters were measured at various points along the fault eberhart phillps et al 2003 the seismic p wave signal arrived at the array approximately 27 seconds after initiation of the rupture with a trace velocity of 5 km sec this was followed some 12 minutes later by an infrasonic wavetrain that had an average trace velocity of 0 34 km sec and lasted about ten minutes the azimuth of arrival of the infrasonic waves steadily moved eastward throughout the wave train apparently following the rupture s leading edge along the fault the largest infrasonic signals reaching over 12 pa came from the azimuth of the regions of largest ground motion along the fault the source of the infrasound is taken to be the sudden local motion of the mountains in the alaska range along the denali fault as they responded to the eastward propagating fault rupture

identifying the unique ground motion signatures of supershear earthquakes theory and experiments the near field ground motion signatures associated with sub rayleigh and supershear ruptures are investigated using the laboratory earthquake experiment originally developed by rosakis and co workers xia et al 2004 2005a lu et al 2007 rosakis et al 2007 heterodyne laser interferometers enable continuous high bandwidth measurements of fault normal fn fault parallel fp and vertical v particle velocity ground motion records at discrete locations on the surface of a homalite 100 test specimen as a sub rayleigh or a supershear rupture sweeps along the frictional fault photoelastic interference fringes acquired using high speed digital photography provide a synchronized spatially resolved whole field view of the advancing rupture tip and surrounding maximum shear stress field the first phase of experimental investigations examine and verify the ground motion signatures of supershear ruptures experimental results demonstrate that a shear mach front produced by a stable supershear rupture is characterized by a dominant fp velocity component the situation is shown to reverse in the sub rayleigh rupture speed regime whereby the fn particle velocity component dominates the ground motion record additional distinguishing particle velocity signatures consistent with theoretical and numerical predictions and repeatedly observed in experimental records are 1 a pronounced peak in the fp velocity record induced by the leading dilatational field which sweeps the measurement station in advance of the shear mach front and 2 a pronounced velocity swing in the fn record associated with the arrival of a trailing rayleigh sub rayleigh secondary rupture which follows the arrival of the shear mach front analysis of the particle velocity records also confirms 2d steady state theoretical predictions pertaining to the separation attenuation and radiation partitioning of the shear and dilatational portions of the rupture velocity field components the second phase of our experimental investigations re examine the 2002 mw7 9 denali fault earthquake and the remarkable set of near source ground motion records obtained at ps10 located approximately 85 km east of the epicenter and just 3 km north of the fault along the alaska pipeline motivated by the analysis and interpretation of these records by ellsworth et al 2004 dunham and archuleta 2004 2005 we attempt to mimic the denali strike slip rupture scenario and replicate the ps10 ground motion signatures using a laboratory earthquake experiment the experiments feature a left to right west to east propagating right lateral rupture within a homalite 100 test specimen with particle velocity data collected at a near field station situated just above north of the fault both sub rayleigh and supershear laboratory earthquake experiments are conducted using the denali ps10 configuration in order to compare and contrast the resulting particle velocity signatures supershear laboratory records capture all of the prominent features displayed within the ps10 ground motion records noted velocity signatures are correlated to the location of the rupture fronts and their noted arrival times in the synchronized photoelastic image sequence scaling relationships are also presented which transform the laboratory records through six orders of magnitude in time to match the scale of the ps10 ground motion records the strong correlation between the scaled experimental records and the actual ps10 ground motion records support the hypothesis that the denali strike slip fault exhibited a supershear burst finally we present a 2d steady state stress velocity formulation that relates the fp and fn particle velocity records measured close to the fault to the evolution of the stress tensor at the same location a locally steady state condition is assumed within a restricted time interval in order to invoke these relationships and estimate the dynamic stresses xx t and t at the near fault station dynamic stress measurements enable a new class of friction investigations using the laboratory earthquake configuration experimental findings are presented which capture the temporal and spatial distributions of xx and evolution of the dynamic friction coefficient and velocity weakening behavior of a supershear slip pulse

the aftershock signature of supershear earthquakes recent studies show that earthquake faults may rupture at speeds exceeding the shear wave velocity of rocks this supershear rupture produces in the ground a seismic shock wave similar to the sonic boom produced by a supersonic airplane this shock wave may increase the destruction caused by the earthquake we report that supershear earthquakes are characterized by a specific pattern of aftershocks the fault plane itself is remarkably quiet whereas aftershocks cluster off the fault on secondary structures that are activated by the supershear rupture the post earthquake quiescence of the fault shows that friction is relatively uniform over supershear segments whereas the activation of off fault structures is explained by the shock wave radiation which produces high stresses over a wide zone surrounding the fault

temporal and spatial history of the 1999 2000 endeavour segment seismic series juan de fuca ridge 1 two large clusters of earthquake activity in june of 1999 and january of 2000 have dominated recent seismicity along the endeavour segment of the juan de fuca ridge the impacts of the june 1999 sequence on the hydrologic system which include changes in vent temperature and chemistry within the main endeavour vent field have been well documented previously analysis of seismic and hydroacoustic data indicates that both sequences exhibit a swarm like behavior characterized by the absence of a dominant main shock event the epicentral locations of events within the two swarms overlap spatially with centroid positions near 47 49 and 47 46 n latitude during the june 1999 swarm the initial activity spans the along axis region where a shallow axial magma chamber reflector was later imaged the epicenters then migrate 12 km to the south at a rate of 0 3 m s consistent with lateral dike propagation a distinct subcluster of events also occurred in the vicinity of surveyor volcano on the overlapping portion of the cobb segment given its distance from the main swarm this activity may represent a triggered response to dynamic shaking the january 2000 swarm has a more limited along axis extent relative to the june 1999 swarm with no indication of lateral migration much of this activity is concentrated in a region predicted to have undergone extension due to dike propagation in 1999 although it contains fewer total events and is of shorter duration relative to the june 1999 swarm the january 2000 activity exhibits a higher peak rate of seismicity and greater mean event magnitude as in situ temperature monitoring was not in place during january 2000 and vent fluids were not sampled until june 2000 the impacts of this swarm on the hydrothermal system are unknown the southernmost tip of the endeavour segment also is found to be a region of repeating swarm activity although morphologic evidence indicates the cobb segment has been propagating northward recently this seismic activity suggests that the western limb of the endeavour cobb overlap zone remains active

shaking table modeling of seismically induced deformations in slopes physical model experiments were performed on a 1 g shaking table with the principal goals of 1 investigating the mechanisms of seismically induced permanent deformations in slopes and 2 assessing the accuracy and applicability of the newmark sliding block procedure for estimating seismically induced deformations in slopes each of the clayey slope models deformed in response to strong shaking with the principal mode of deformation being deep rotational translational sliding displacement deformations were principally focused along one or more highly localized shear surfaces though a significant amount of additional deformation was also distributed over a relatively wide region of the models the newmark analyses generally provided moderately accurate although somewhat unconservative estimates of deformations displacements computed using the rigid sliding block analysis ranged from 27 to 225 of maximum measured displacements and averaged about 75 of measured displacements for the test series the newmark type analyses were most reliable for those model tests that experienced large deformations where the sliding resistance was controlled principally by postpeak to residual strengths

coseismic and postseismic fault slip for the 17 august 1999 m 7 5 izmit turkey earthquake we use global positioning system gps observations and elastic half space models to estimate the distribution of coseismic and postseismic slip along the izmit earthquake rupture our results indicate that large coseismic slip reaching 5 7 meters is confined to the upper 10 kilometers of the crust correlates with structurally distinct fault segments and is relatively low near the hypocenter continued surface deformation during the first 75 days after the earthquake indicates an aseismic fault slip of as much as 0 43 meters on and below the coseismic rupture these observations are consistent with a transition from unstable episodic large earthquakes to stable fault creep sliding at the base of the seismogenic zone

probability of multifault rupture abstract earthquake hazard modelers often assume that earthquake ruptures will be confined to individual faults and that earthquakes magnitudes will not exceed values related to the mapped fault length however earthquakes have been observed to jump from one fault to another producing a rupture longer than the originating fault the magnitudes of these earthquakes can exceed the value based on the originating fault length we estimated the probability of jumping as a function of interfault distance based on retrospective observations from past earthquakes a simple model consistent with the few available observations suggests that an earthquake on one strike slip fault may jump to another with a probability that decreases exponentially with separation the scale distance is about 3 km the model implies a nonnegligible probability of jumping as much as 10 km many california faults are within 10 km of one another we identified those and wrote a simple program to calculate the interfault distance and thus the jump probabilities we also formulated a simple way to estimate the magnitude frequency distribution for a pair of nearby faults as a function of their independent magnitude distributions and their separation distance allowing for multifault rupture increases the estimated upper magnitude limits for faults relative to a model in which faults are independent if the magnitude frequency distribution is constrained to be consistent with a fixed moment rate from fault slip rates for example then increasing the upper magnitude limits will reduce the rate of intermediate and small events

beryllium 10 surface exposure dating of glacial successions in the central alaska range glacial landforms and outwash terraces in the nenana river valley reindeer hills and monahan flat in the central alaska range were dated with 60 10 be exposure ages to determine the timing of late pleistocene glaciation in the nenana river valley glaciation occurred at 104 180 ka lignite creek glaciation ca 55 ka healy glaciation and ca 16 ka carlo creek phase glaciers retreated in the reindeer hills and monahan flat by ca 14 ka and ca 13 ka respectively the carlo creek moraine is similar in age to at least six other moraines in the alaska range ahklun mountains and brooks range the new data suggest that post depositional geological processes limit the usefulness of 10 be methods to the latter part 60 ka of the late quaternary in central alaska ages on healy and younger landforms cluster well with the exception of riley creek moraines and monahan flat west sites where boulders were likely affected by post depositional processes copy right 2010 john wiley sons ltd supporting information may be found in the online version of this article

seismic velocity structure and seismotectonics of the eastern san francisco bay region california the hayward fault system is considered the most likely fault system in the san francisco bay area california to produce a major earthquake in the next 30 years to better understand this fault system we use microseismicity to study its structure and kinematics we present a new 3d seismic velocity model for the eastern san francisco bay region using microseismicity and controlled sources which reveals a 10 velocity contrast across the hayward fault in the upper 10 km with higher velocity in the franciscan complex to the west relative to the great valley sequence to the east this contrast is imaged more sharply in our localized model than in previous regional scale models thick cenozoic sedimentary basins such as the livermore basin which may experience particularly strong shaking during an earthquake are imaged in the model the accurate earthquake locations and focal mechanisms obtained by using the 3d model allow us to study fault complexity and its implications for seismic hazard the relocated hypocenters along the hayward fault in general are consistent with a near vertical or steeply east dipping fault zone the southern hayward fault merges smoothly with the calaveras fault at depth suggesting that large earthquakes may rupture across both faults the use of the 3d velocity model reveals that most earthquakes along the hayward fault have near vertical strike slip focal mechanisms consistent with the large scale orientation and sense of slip of the fault with no evidence for zones of complex fracturing acting as barriers to earthquake rupture online material velocity model validation experiments and additional seismicity plots

triggered seismic events along the eastern denali fault in northwest canada following the 2012 mw 7 8 haida gwaii 2013 mw 7 5 craig and two mw 8 5 teleseismic earthquakes we conduct a systematic search for remotely triggered seismic activity along the eastern denali fault edf in northwest canada an intraplate strike slip region we examine 19 distant earthquakes recorded by nine broadband stations in the canadian national seismograph network and find that the 2012 m w 7 8 haida gwaii and 2013 m w 7 5 craig alaska earthquakes triggered long duration 10 s emergent tremor like signals near the southeastern portion of the edf in both cases tremor coincides with the peak transverse velocities consistent with love wave triggering on right lateral strike slip faults the 2011 m w 9 0 tohoku oki and 2012 m w 8 6 indian ocean earthquakes possibly triggered tremor signals although we were unable to locate those sources in addition we also identify many short duration 5 s bursts that were repeatedly triggered by the rayleigh waves of the 2012 m w 7 8 haida gwaii earthquake although we were unable to precisely locate the short duration 5 s events they appear to be radiating from the direction of the klutlan glacier and from a belt of shallow historical seismicity at the eastern flank of the wrangell st elias mountain range the fact that these events were triggered solely by the rayleigh waves suggests a different source mechanism as compared with triggered tremor observed along the edf and other plate boundary regions online material description of rayleigh wave polarization detection figures of spectograms s wave amplitudes polarization analysis and static stress changes tables of earthquake catalogs and velocity model and animations of tremors and bursts

illuminating the near sonic rupture velocities of the intracontinental kokoxili mw 7 8 and denali fault mw 7 9 strike slip earthquakes with global p wave back projection imaging 1 the denali and kokoxili strike slip earthquakes are two of the longest recent intracontinental ruptures previous studies report a range of rupture velocities here we image these earthquakes by reverse time migration of the intermediate frequency p wave train recorded by global broadband seismometers this technique permits a relatively direct measure of rupture velocity speed and direction as constrained by the radiated seismic energy free from restrictive assumptions or rupture speed bounds placed on the solution we compare our results with published seismic gps displacement and surface slip inversion results both ruptures were initially subshear and transitioned over a distance no longer than 40 km to supershear speeds close to the p wave speed of 5 6 km s we investigate the accuracy of our results with synthetic data and experiment with using different imaging parameters and seismic subnetworks these tests allow us to rule out the possibility of subshear speeds along the supershear segments although we cannot exclude supershear speeds of 4 5 6 5 km s our most reliable rupture velocities of 5 6 km s are close to the local p wave speeds we hypothesize that these intracontinental faults have weak shear strengths or high breakdown slips or crustal rigidities and experience at least moderate slip or slip rate weakening our observations and previous published results lead us to speculate that very long surface extending faults with general homogeneity in prestress and fault strength together with smaller adjacent fault segments to provide triggering may be necessary ingredients for the sub rayleigh to supershear rupture speed transition in strike slip earthquakes

subsalt imaging improvement possibilities through a combination of fwi and reflection fwi abstract despite continuous improvements in seismic acquisition and processing technology imaging under salt remains challenging specifically because of the difficulty in updating complex salt geometries and subsalt velocity synthetic studies show that when certain conditions are met full waveform inversion fwi can recover very complex velocity models including the geometry of the salt and the subsalt velocity unfortunately currently available seismic field data fall short of meeting the requirements needed to replicate what can be achieved on synthetic data we first use a wide azimuth data set from the mexican side of the gulf of mexico gom to show how fwi can improve imaging in the subsalt in addition to utilizing the diving wave energy to derive a reliable model in the shallow sediment overburden we use reflection fwi rfwi to update the velocity model in the deep area rfwi utilizes the low wavenumber components of the fwi gradient associated with waves reflected in the model which mak

3d angle gathers from reverse time migration reverse time migration rtm based on directly solving the two way wave equation provides a natural way to deal with large lateral velocity variations and imposes no dip limitations on the seismic images it has become a standard migration tool for subsalt imaging in the gulf of mexico in addition the adoption of wide azimuth waz data acquisition provides better subsurface illumination and more azimuthal information which significantly aids imaging beneath complex overburdens because waz data are richer in the propagation directions of the waves recorded rtm and waz acquisition go hand in hand

generic precursors to coastal earthquakes inferences from denali fault earthquake recent research has shown evidence of strong coupling between the atmosphere and lithosphere in coastal regions associating abnormal atmospheric phenomena to the occurrence of strong earthquakes surface latent heat flux slhf total column water vapor cwv relative humidity rh and total ozone column toc analyzed over the epicentral region of the denali fault earthquake of november 3 2002 exhibit anomalous behavior that could be related to the earthquake preparatory process and its occurrence the complementary nature of the parameters provides strong support that the anomalous values were driven by lithospheric processes rather than other atmospheric phenomena due to the wide availability of remote sensing observations of atmospheric parameters the detection of anomalies can be used to mitigate the earthquake risks

stress transfer to the denali and other regional faults from the m 9 2 alaska earthquake of 1964 stress transfer from the great 1964 prince william sound earthquake is modeled on the denali fault including the denali totschunda fault segments that ruptured in 2002 and on other regional fault systems where m 7 5 and larger earth quakes have occurred since 1900 the results indicate that analysis of coulomb stress transfer from the dominant earthquake in a region is a potentially powerful tool in assessing time varying earthquake hazard modeled coulomb stress increases on the northern denali and totschunda faults from the great 1964 earthquake coincide with zones that ruptured in the 2002 denali fault earthquake although stress on the susitna glacier thrust plane where the 2002 event initiated was decreased a southeasterly trending coulomb stress transect along the right lateral totschunda fairweather queen charlotte trend shows stress transfer from the 1964 event advancing slip on the totschunda fairweather and queen charlotte segments including the southern fairweather segment that ruptured in 1972 stress transfer retarding right lateral strike slip was observed from the southern part of the totschunda fault to the northern end of the fairweather fault 1958 rupture this region encompasses a gap with shallow thrust faulting but with little evidence of strike slip faulting connecting the segments to the northwest and southeast stress transfer toward failure was computed on the north south trending right lateral strike slip faults in the gulf of alaska that ruptured in 1987 and 1988 with inhibitory stress changes at the northern end of the northernmost 1987 rupture the northern denali and totschunda faults including the zones that ruptured in the 2002 earthquakes follow very closely within 3 for about 90 an arc of a circle of radius 375 km the center of this circle is within a few kilometers of the intersection at depth of the patton bay fault with the alaskan megathrust this inferred asperity edge may be the pole of counterclockwise rotation of the block south of the denali fault these observations suggest that the asperity and its recurrent rupture in great earthquakes as in 1964 may have influenced the tectonics of the region during the later stages of evolution of the denali strike slip fault system

evidence for a supershear transient during the 2002 denali fault earthquake elastodynamic considerations suggest that the acceleration of ruptures to supershear velocities is accompanied by the release of rayleigh waves along the fault from the stress breakdown zone these waves generate a secondary slip pulse trailing the rupture front but manifest almost entirely in ground motion perpendicular to the fault in the near source region we construct a spontaneously propagating rupture model exhibiting these features and use it to explain ground motions recorded during the 2002 denali fault earthquake at pump station 10 located 3 km from the fault we show that the initial pulses on both the fault normal and fault parallel components are due to the supershear stress release on the fault whereas the later arriving fault normal pulses result from the trailing subshear slip pulse on the fault online material mpeg movies of rupture history and ground motion

kinematic behavior of southern alaska constrained by westward decreasing postglacial slip rates on the denali fault alaska long term slip rates for the denali fault in southern alaska are derived using 10 be cosmogenic radionuclide crn dating of offset glacial moraines at two sites correction of 10 be crn model ages for the effect of snow shielding uses historical regional snow cover data scaled to the site altitudes to integrate the time variation of snow cover we included the relative changes in effective wetness over the last 11 ka derived from lake level records and 18 o variations from alaskan lakes the moraine crn model ages are normally distributed around an average of 12 1 1 0 ka n 22 1 the slip rate decreases westward from 13 mm a at 144 49 w to about 7 mm a at 149 26 w the data are consistent with a kinematic model in which southern alaska translates northwestward at a rate of 14 mm a relative to a stable northern alaska with no rotation this suggests progressive slip partitioning between the denali fault and the active fold and thrust belt at the northern front of the alaska range with convergence rates increasing westward from 4 mm a to 11 mm a between 149 w and 145 w as the two moraines sampled for this study were emplaced synchronously our suggestion of a westward decrease in the slip rate of the denali fault relies largely upon the measured offsets at both sites regardless of any potential systematic uncertainty in the crn model ages

what controls selenium release during shale weathering this study demonstrates that only a combination of a chromous chloride reduction with dual sequential extraction schemes can clearly separate the proportions of se present in the sulphide versus the organic pools in shales the data reveals that even small amounts of pyrite outcompete the organic matter for the available se and pyrite oxidation will control the release of selenium during shale weathering

the garden banks model experience to better understand deepwater imaging challenges in the gulf of mexico we constructed a large 3d model based on the complex salt geology of the garden banks protraction area we simulated a regional wide azimuth waz streamer survey with offsets of 8 km inline and 4 km crossline over this model using the true velocity model reverse time migration of this data set produced a usable subsalt image nearly everywhere the same synthetic seismic data set was passed to interpreters and geophysicists to process and image as if it were real field data they did not get to see the true velocity model instead they performed conventional migrate pick and flood top down velocity model building followed by final imaging through their interpreted velocity model where the salt was relatively simple we found that the interpreted velocity model was reasonably accurate reverse time migration of the seismic data through these parts of the velocity model produced an image that was imperfect but still usable for exploration scale structural interpretation where the salt structure was complex however it was sometimes grossly misinterpreted the ensuing large scale errors in the interpreted velocity model resulted in an unusable shattered subsalt image we next simulated a low frequency ocean bottom node obn acquisition with offsets up to 30 km in all azimuths we started with the imperfect model produced by the interpreters and investigated what it would take for full waveform inversion fwi to successfully find and fix the gross interpretation errors initial results suggest this interpretation followed by fwi methodology could produce a velocity model capable of generating an adequate subsalt image but it may require ultrawide offsets 30 km ultralow frequencies below 2 hz and improved fwi algorithms to do so