the vallo di diano fault system new evidence for an active range bounding fault in southern italy using shallow high resolution seismic profiling range bounding normal faults can presentsignificant challenges for seis mic exploration this is the case of the fault system bounding the vallo di diano the largest intermountain basin in the southern apennines seismic belt industry reflection profiles define the large scale structure of the basin but barely image the shallow fault system due to unfavorable topographic and near surface conditions along the foothills of the eastern range we present two high resolution hr wide aperture profiles recorded attheeastern marginof thebasin acrossunreported scarpsthat affect middle late pleistocene alluvial fans and slope debris the survey is aimed at identifying possible recent faulting across these challenging terrains and at understanding the re lationship between shallow structures and the master range bounding fault at depth common depth point processing of wide aperture reflection data and first arrival tra vel time tomography provide detailed images of the upper 200 300 m and sounding evidence of recent activity along previously unknown splays of the fault system these splays dissect the mesozoic limestone bedrock and alluvial fan sequences affecting theirdepositionalpattern veryhighresolutionvpandreflectivityimagesalsogivehints ofpossiblecoseismicsurfacefaultinginholocenecolluvia theseresultshaverelevant implicationsfortheevaluationoftheseismogenicpotentialoftherange boundingfault systemandforseismichazardassessmentofthedenselyurbanizedvallodidianobasin online material table of acquisition and data processing parameters and figures showing schematic stratigraphy of the vallo di diano basin restoration of fault dis placement along the hr profile and resolution of the p velocity tomographic images for the vhr profile

holocene paleoseismicity temporal clustering and probabilities of future large m 7 earthquakes on the wasatch fault zone utah the chronology of m 7 paleoearthquakes on the central five segments of the wasatch fault zone wfz is one of the best dated in the world and contains 16 earthquakes in the past 5600 years with an average repeat time of 350 years repeat times for individual segments vary by a factor of 2 and range from about 1200 to 2600 years four of the central five segments ruptured between 620 30 and 1230 60 calendar years b p the remaining segment brigham city segment has not ruptured in the past 2120 100 years comparison of the wfz space time diagram of paleoearthquakes with synthetic paleoseismic histories indicates that the observed temporal clusters and gaps have about an equal probability depending on model assumptions of reflecting random coincidence as opposed to intersegment contagion regional seismicity suggests that for exposure times of 50 and 100 years the probability for an earthquake of m 7 anywhere within the wasatch front region based on a poisson model is 0 16 and 0 30 respectively a fault specific wfz model predicts 50 and 100 year probabilities for an m 7 earthquake on the wfz itself based on a poisson model as 0 13 and 0 25 respectively in contrast segment specific earthquake probabilities that assume quasi periodic recurrence behavior on the weber provo and nephi segments are less 0 01 0 07 in 100 years than the regional or fault specific estimates 0 25 0 30 in 100 years due to the short elapsed times compared to average recurrence intervals on those segments the brigham city and salt lake city segments however have time dependent probabilities that approach or exceed the regional and fault specific probabilities for the salt lake city segment these elevated probabilities are due to the elapsed time being approximately equal to the average late holocene recurrence time for the brigham city segment the elapsed time is significantly longer than the segment specific late holocene recurrence time

investigating the architecture of the paganica fault 2009 mw 6 1 earthquake central italy by integrating high resolution multiscale refraction tomography and detailed geological mapping this article has been accepted for publication in geophysical journal internationa 2017 published by oxford university press on behalf of the royal astronomical society all rights reserved

evidence for active folding and faulting at the northern apennines mountain front near bologna italy from high resolution seismic reflection profiling 1 we have acquired and processed an 2 km long high resolution seismic reflection profile across a segment of the northern apennine mountain front italy west of the city of bologna the profile constrained by several wells targets a long postulated shallow blind or emergent thrust called the pede apenninic thrust fault despite decades of reflection seismology in this part of the apennines a shallow or emergent structure consistent with the surface geology has yet to be definitively identified a problem likely caused by the topography of the apennine front and the traditional focus on deep hydrocarbon targets where the first 0 5 km of strata is poorly imaged our seismic data show an 300 m deep high resolution picture of the po foreland as it meets the apennine mountain front all imaged reflectors are continuous at the mountain front and are foreland dipping showing clear growth relationships higher angle reflectors are interpreted as faults our interpretation includes a possible hinterland dipping blind thrust and surface normal faults which offset late pleistocene holocene deposits as much as 60 m long term slip rates of 0 1 0 25 mm yr that disrupt but do not conceal the growth strata relationships vp tomographic imaging also suggests coseismic surface faulting in holocene colluvium these results have implications relevant for the effective data collection and processing techniques for these kinds of shallow active structures as well as a re evaluation of the seismogenic potential of densely populated cities like bologna along the apennine mountain front

imaging the structural style of an active normal fault through multidisciplinary geophysical investigation a case study from the mw 6 1 2009 l aquila earthquake region central italy firb abruzzo high resolution analyses for assessing the seismic hazard and risk of the areas affected by the 2009 april 6 earthquake no rbap10zc8k 005

tomographic imaging of late quaternary faulting oquirrh mountains utah 1 seismic tomography can be used to image colluvial material in the subsurface by inverting first arrival travel times for velocity colluvial material deposited at the base of a fault scarp free face often appears as a low velocity zone lvz on a tomogram because it is generally less compacted and cemented than the surrounding alluvium a tomogram generated from a forward model of a synthetic velocity structure successfully images two lvzs stacked in the hanging wall of a normal fault the mercur fan oquirrh mountains utah provides an opportunity to look for stacked lvzs in a distributed fault zone three tomographic images across fault scarps on an intermediate age alluvial fan can be used to identify two stacked low velocity zones interpretation of a fourth tomogram is less conclusive these two low velocity zones are interpreted as colluvial packages separated by higher velocity alluvial material and suggest that tectonic activity is interspersed with pulses of fan building

a high resolution seismic reflection and gravity survey of quaternary deformation across the wasatch fault utah high resolution reflection seismic and detailed gravity data were acquired across an exposure of the wasatch fault utah near a trench excavated for dating of quaternary fault displacement the seismic data across the quaternary wasatch fault are interpreted to show three subparallel surfaces dipping from 70 w at the surface to an estimated 45 w at 40 m displaced unconsolidated sediments and colluvial material abutting the main fault detailed gravity data were of assistance in mapping the sediment bedrock interface from the rangefront across the wasatch fault zone a combined high resolution seismic and gravity interpretation reveals that bedrock is 80 m deeper in the hanging wall than in the footwall suggesting that displacement has occurred on several en echelon blocks in the near surface of the wasatch fault movement on the most recent wasatch fault trace began prior to deposition of pleistocene lacustrine sediments the twelvefold high resolution reflection seismic data were recorded and processed to achieve vertical resolution of approximately 1 m and horizontal resolution fresnel zone radii of as good as 5 m on the deepest reflecting interfaces at 40 m reasonably high frequencies and good bandwidth about 80 300 hz in the stacked seismic data permitted a direct comparison to the trenched cross section good correlation between the trench stratigraphy and structure and the seismic data suggests high resolution seismic data can be a valuable tool for analyzing near surface faulting in unconsolidated sediment and for locating potential trench sites

transient electromagnetic investigations in a tectonic domain of the kachchh intraplate region western india a morphotectonic study of the kachchh mainland fault

simple tests of a semi implicit semi lagrangian model on 2d mountain wave problems abstract the fully compressible 3d nonhydrostatic semi implicit semi lagrangian mc2 mesoscale compressible community model described by tanguay et al has been modified in order to incorporate orography through the gal chen and somerville transformation of the vertical coordinate by denis in this study a 2d version of the model is tested against classical solutions covering various mountain wave regimes for continuously stratified flows a close inspection of the propagation of the vertical momentum flux is performed to asses the accuracy and stability of the numerical method the study emphasizes also the fact that a correct representation of forced hydrostatic gravity waves is reliable for courant numbers less than 0 5 this limitation may be less severe as the flow becomes more nonhydrostatic furthermore the sensitivity of the isothermal reference state for flows with realistic static stability and over steep slope mountain is explored

detecting young slow slipping active faults by geologic and multidisciplinary high resolution geophysical investigations a case study from the apennine seismic belt italy 1 the southern apennines range of italy presents significant challenges for active fault detection due to the complex structural setting inherited from previous contractional tectonics coupled to very recent middle pleistocene onset and slow slip rates of active normal faults as shown by the irpinia fault source of a m6 9 earthquake in 1980 major faults might have small cumulative deformation and subtle geomorphic expression a multidisciplinary study including morphological tectonic paleoseismological and geophysical investigations has been carried out across the extensional monte aquila fault a poorly known structure that similarly to the irpinia fault runs across a ridge and is weakly expressed at the surface by small scarps warps the joint application of shallow reflection profiling seismic and electrical resistivity tomography and physical logging of cored sediments has proved crucial for proper fault detection because performance of each technique was markedly different and very dependent on local geologic conditions geophysical data clearly 1 image a fault zone beneath suspected warps 2 constrain the cumulative vertical slip to only 25 30 m 3 delineate colluvial packages suggesting coseismic surface faulting episodes paleoseismological investigations document at least three deformation events during the very late pleistocene 20 ka and holocene the clue to surface rupturing episodes together with the fault dimension inferred by geological mapping and microseismicity distribution suggest a seismogenic potential of m6 3 our study provides the second documentation of a major active fault in southern italy that as the irpinia fault does not bound a large intermontane basin but it is nested within the mountain range weakly modifying the landscape this demonstrates that standard geomorphological approaches are insufficient to define a proper framework of active faults in this region more in general our applications have wide methodological implications for shallow imaging in complex terrains because they clearly illustrate the benefits of combining electrical resistivity and seismic techniques the proposed multidisciplinary methodology can be effective in regions characterized by young and or slow slipping active faults

colluvial wedge imaging using traveltime and waveform tomography along the wasatch fault near mapleton utah summary four high resolution seismic surveys were conducted across the wasatch fault zone near mapleton utah the objective was twofold 1 to use velocity tomograms and reflection images to delineate fault structures and colluvial wedges to more than twice the depth of the mapleton megatrench excavated by urs personnel 2 to assess the strengths and limitations of traveltime and waveform tomography by synthetic studies and comparison of the tomogram to the ground truth seen in the megatrench log four out of the five faults within the trench area are accurately identified in the migrated image and in the tomograms and the main fault s dip angle is estimated to be between 71 and 80 two additional faults are interpreted outside the trench the faults can be delineated down to 30 m below the surface which is 20 m deeper than the excavated trench five out of six colluvial wedges found in the trench log were seen as low velocity zones lvzs in the tomogram however the biggest colluvial wedge could not be identified by either tomography method waveform tomography prevailed over ray based traveltime tomography by more clearly recovering the faults and lvzs a newly discovered lvz at a depth of 18 21 m below the surface possibly represents a colluvial wedge and is estimated to be less than 21 000 years old if this lvz is a colluvial wedge the earthquake history obtained by trenching can be extended from 13 500 to 21 000 yr with seismic tomography our results further demonstrate the capability of tomography in identifying faults and show that waveform tomography more accurately resolves colluvial wedges compared to traveltime tomography however despite the successful recovery of most faults and some but not all colluvial wedges both tomography methods show many more lvzs besides the wedges so that an unambiguous interpretation cannot be made a major part of the ambiguity in the tomograms is due to the many major faults which result in an uneven raypath coverage as our synthetic studies show hence seismic trenching will be more successful at simple fault geometries however even under optimal conditions there will be some ambiguity in the interpretation so that detected lvzs should be drilled cored and dated to determine the history of the ancient earthquakes

cosmogenic 14c in carbonate rocks abstract the rate of in situ production of cosmogenic 14 co in limestone is 18 3 atom g caco3 year corrected to high latitude and sea level based on measurements of 14 co in limestone associated with the bonneville provo shoreline complex in utah in situ cosmogenic 14 co was separated cryogenically from co2 using 14 c dead co as a carrier for in situ cosmogenic 14 co this rate of production was used to estimate an age of 4360 1220 cal year b p for the last movement on the south oquirrh mountain fault zone in northern utah and an age of at least 10 600 900 years for the penultimate event of the pleasant valley fault in northern nevada

resolution limits for crosswell migration and traveltime tomography summary equations are derived for the point scatterer response of the crosswell migration and traveltime tomography operators these formulas are used to estimate the limits of spatial resolution in reflection migration images and traveltime tomograms in particular for a crosswell geometry with borehole length l well offset 2x0 source wavelength and a centred point scatterer i show the following 1 the vertical resolution zmig of the reflection migration image is equal to 2 x0 l under the far field approximation under the fresnel approximation zmig 2 x0 l 2 2 l which says that images become better resolved with an increase in aperture and a decrease in wavelength and well offset 2 the horizontal resolution zmig of the migration image is equal to 16 x02 l2 the lateral resolution of the migrated image is worse than the vertical resolution by a factor of 8x0 l where x0 l 1 under the far field approximation 3 the vertical resolution ztomo of the traveltime velocity tomogram is proportional to x0 this estimate agrees with that of a previous study however the tomographic image of the slowness perturbation behaves as a non local cosine function along the depth axis whereas the migration image behaves as a localized squared sine function in the depth coordinate this is consistent with the empirical observation that interface boundaries are more sharply resolved by migration than by traveltime tomography 4 the horizontal resolution of the slowness image in a traveltime tomogram is equal to 4x0 l 3x0 4 a factor more than 4x0 l worse than the vertical resolution 5 for ns sources and ng geophones the dynamic range of the migrated image is proportional to nsng the dynamic range of the slowness tomogram is proportional to ngns many of the estimates for the resolution limits have simple geometrical interpretations for example the minimum vertical horizontal resolution in a migrated reflectivity section corresponds to the minimum vertical horizontal stretch that a migrated wavelet undergoes in going from the time domain to the depth domain in addition the minimum vertical horizontal resolution in a traveltime tomogram corresponds to the minimum vertical horizontal width of the wavepath at the scatterer location

geometry and kinematics of active normal faults south oquirrh mountains utah implication for fault growth the nnw striking south oquirrh mountains normal fault zone consists of four individual faults the individual faults are arranged in a right stepping pattern in the north and a left stepping pattern in the south forming a convex shaped fault zone in map view with the apex towards the hanging wall late quaternary fault activity is characterized by 2 0 4 5 m high discontinuous fault scarps developed in both late quaternary alluvium and bedrock the fault scarps in bedrock contain evidence of two large rupture events the last large earthquake occurred prior to the highstand of the bonneville lake cycle 15 ka based on cross cutting relationship between the bonneville shoreline and the fault scarp and on comparisons of fault scarp morphology cumulative displacement patterns inferred from range crest elevations bouguer gravity data in the adjacent basin and rotation of the subsidiary faults adjacent to the west mercur fault are similar to the pattern of displacements measured across late quaternary fault scarps that is the maximum displacement is near the apex of the convex shaped fault zone where the west mercur fault is located and then tapers off towards both ends of the fault zone fault traces that range from a few meters to tens of kilometers long are characterized by two dominant orientations strike n11 w and n43 w the two orientations are separated from each other by a statistically constant angle of 33 3 slip directions concentrate on a trend of s70 w for both groups of faults perpendicular to the average strike of the fault zone these data indicate that the geometry of the fault surfaces is non cylindrical and may be composed of self similar structural ridges and troughs of variable wavelength and amplitude that are elongated parallel to slip direction the relationships between fault geometry displacement and geomorphology in the south oquirrh mountains fault zone suggests a growth model of normal faults in which apex points on the convex shaped fault sections mark the nucleation points of primary faults secondary faults developed at the ends of the primary fault step into the footwall block as the fault zone grows laterally intersecting regions between two laterally growing fault zones are concave shaped in map view

seismic attribute inversion for velocity and attenuation structure using data from the glimpce lake superior experiment a simultaneous inversion for velocity and attenuation structure using multiple seismic attributes has been applied to refraction data from the 1986 glimpce lake superior experiment the seismic attributes considered include envelope amplitude instantaneous frequency and travel time of first arrival data instantaneous frequency is converted to t using a matching procedure which approximately removes the effects of the source spectra the derived seismic attributes are then used in an iterative inversion procedure referred to as aft inversion for amplitude instantaneous frequency and time uncertainties and resolution of the velocity and attenuation models are estimated using covariance calculations and checkerboard resolution maps a simultaneous inversion of seismic attributes from the glimpce data results in a velocity model similar to that of previous studies across lake superior a central rift basin and a northern basin are the most prominent features with an increase in velocity near the isle royale fault although there is an indication of the central and northern basins in the attenuation model for depths greater than 4 km the separation is not evident for shallower depths this may result from microfractures masking compositional variations in the attenuation model for shallower depths attenuation q values range from approximately 60 near the surface to near 500 at 10 km depth a relationship between inverse q and velocity of q 0 0210 0 0028 v was found with a correlation coefficient of 0 96 this suggests a nearly linear inverse relationship between q l and velocity beneath lake superior which supports previous laboratory results the inverted velocity and attenuation models provide important constraints on the lithology and physical properties of the midcontinent rift beneath lake superior

seismic imaging of upper crustal structure using travel times from the passcal ouachita experiment a first arrival travel time inversion applied to the 1986 passcal ouachita experiment has been used to image upper crustal structure twenty one shot points every 10 km were recorded along two 100 km long segments with 400 seismographs on each segment a splined velocity model parameterization allowed for the inversion of laterally inhomogeneous models but not velocity discontinuities over 800 travel times were used in the inversion with a variable data covariance weighting the multiple source nature of the experiment design allowed the use of reciprocity relationships among 21 shot points to enhance data correlation a succession of models with velocities specified at 30 90 171 and 221 nodes were inverted for whose horizontal node spacing decreased from 100 to 12 5 km in the final 221 node model vertical node spacings of 3 0 and 1 5 km were used the results of the inversions indicate changes in depth of isovelocity lines which are interpreted as triassic fault structure based on nearby well data the final rms travel time residual is 0 045 s resolution using first arrivals deteriorates rapidly below 9 km depth three distinct velocity gradients can be correlated with geologic units surface exposed cretaceous and jurassic sediments with velocities from 3 0 tomore 3 5 km s extend to 1 5 km depth triassic rift fill sediments which do not outcrop have inverted velocities ranging from 3 5 to 4 75 km s between depths of 1 5 3 0 km paleozoic sediments are imaged by a decreased velocity gradient below a depth of 3 0 km lack of resolution at depths greater than 9 km necessitates detailed modeling of wide angle reflected phases to further constrain deeper crustal structure less

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

shallow high resolution geophysical investigation along the western segment of the victoria lines fault island of malta abstract the victoria lines fault island of malta is a 15 km long and n260 striking segmented normal fault system which is probably inactive since the late pliocene in the westernmost part the fomm ir rih segment displays comparable geologic throw and escarpment height 150 170 m moreover its hangingwall hosts thin patches of middle pleistocene clastic continental deposits red beds which are poorly preserved elsewhere we acquired two seismic transects by collecting ambient vibration recordings processed by using horizontal to vertical spectral ratios complemented by one high resolution 2 d refraction tomography survey crossing this fault where it is locally covered by red beds and recent colluvial deposits we found a resonance peak at 1 0 hz in the hangingwall block whereas clear peaks in the range 5 0 10 0 hz appear when approaching the subsurface fault and we relate them to the fractured bedrock within the fault zone the best fit tomographic model shows a relatively high vp shallow body vp 2200 2400 m s that we relate to the weathered top of the miocene upper coralline limestone fm bounded on both sides by low vp regions 230 m s above the weathered top bedrock our results depict a clear seismic signature of the victoria lines fault characterized by low seismic velocity and high amplification of ground motion we hypothesize that during the middle pleistocene faulting may have affected the basal part of the red beds so that this part of the investigated complex fault system may be considered inactive since 0 6 myr ago

palaeoseismicity of the oquirrh fault utah from shallow seismic tomography the magnitude and frequency of normal fault palaeoearthquakes are usually determined by trenching studies that ascertain the size and number of colluvial wedges along the fault such information can be invaluable in predicting the seismic hazard and potential for a future earthquake in that region digging trenches across normal faults however is environmentally intrusive expensive and limited in the penetration depth to overcome these problems we propose the use of 3 d seismic tomography as a means to identify the shapes and sizes of colluvial wedges along normal faults as an example 2 d and 3 d seismic surveys were conducted across the oquirrh fault utah with the purpose of imaging the normal fault structure to a depth of about 10 m results show that the 3 d tomogram clearly delineates the fault zone and a colluvial wedge both of which correlate extremely well with the geological cross section interpreted from an adjacent trench the thickness of the colluvial wedge image is used in conjunction with a seismic section to compute an estimate of a 6 8 moment magnitude earthquake for the most recent event on this fault which is in close agreement with the 7 0 estimate based on a nearby trenching study these tomographic results demonstrate for the first time that seismic imaging methods can be used in some cases to estimate unambiguously the shapes of colluvial wedges and the sizes of prehistoric earthquakes thus seismic tomography has the possibility of providing cheaper deeper and wider but less resolved images of fault systems than the intrusive excavation of trenches across faults

shallow subsurface imaging of the piano di pezza active normal fault central italy by high resolution refraction and electrical resistivity tomography coupled with time domain electromagnetic data

integrated geophysical techniques for subsurface imaging of active deformation across the himalayan frontal thrust in singhauli kala amb india abstract non invasive geophysical techniques employed across the himalayan frontal thrust hft at singhauli in the north western frontal himalaya to understand shallow subsurface geological structures and their nature in the context of active tectonics the combination of high resolution ground penetrating radar gpr electrical resistivity tomography ert and multi channel analysis of surface waves masw techniques with the different acquisition parameters found to be beneficial in gaining high resolution images of shallow subsurface geological structures the contact zone of resistivity obtained between 134 m suggests the juxtaposition of dissimilar lithological units explained as two faults dipping to the northwest related to the hft the average separation between fault 0 and fault i is 12m which in general agreement with the trench excavation survey the gpr radargram over a length of 45m show offset reflectors at a horizontal distance of 12 15m close to the active deformation zone the horizontal reflectors abruptly truncate across two northerly dipping planes the 2d vs section masw1 2 exhibited dipping attitude of the litho units with different velocity zones in the northeast direction which are also consistent with the local geological setting prominent liquefaction feature identified in the ert section specifically with the 1 and 1 5m electrode spacing show explicit expression of its existence due to contrasting resistivity ranging between 100 and 450 m a strong correlation has been established between the field based geological observations carried out earlier in this area through a trench excavation survey with the present work using geophysical techniques the integrated approach found to be highly beneficial in those areas where contrasting sub lithological units exist in terms of their physical properties this study argues for judicious use of the ert gpr and masw techniques to delineate shallow subsurface geology across various active faults in the himalayan terrain to comprehend the active deformation related to large magnitude paleoearthquakes and earthquake hazard assessment

non subduction origin for 3 2 ga high pressure metamorphic rocks in the barberton granitoid greenstone terrane south africa the occurrence of high pressure hp garnet bearing metamorphic rocks in the southern barberton granitoid greenstone terrane bggt south africa has been proposed as a key indicator of the onset of modern plate tectonics at ca 3 2 ga here we report new zircon titanite u pb ages of garnet bearing hp metamorphic rocks and associated granitoids in the bggt that argue against such an interpretation the results show that hp metamorphism occurred synchronously with granitoid magmatism in the stolzburg domain the supposed subducted plate during two episodes at 3 4 and 3 2 ga and that these two episodes of magmatism occurred on both sides of the assumed suture zone a feature that cannot easily be explained by the subduction model in contrast the coupled magmatism and metamorphism probably resulted from partial convective overturn pco another viable mechanism for production and differentiation of continental crust during early archean

2 d seismic trenching of colluvial wedges and faults abstract images of the depth and shape of colluvial wedges by 3 d travel time tomography can be valuable in estimating the past history of ancient earthquakes and assessing the earthquake hazard of a fault unfortunately 3 d seismic surveys can be both costly and time consuming in this paper we report our first successful results of detecting the shapes and depths of colluvial wedges with 2 d travel time tomography the locations of the colluvial wedges are along the oquirrh fault and the salt lake city segment of the wasatch fault we also report that the tomogram from one of our 2 d surveys suggests the possibility of detecting multiple colluvial wedges at depth using both reflection and tomographic images at another site clearly reveals the presence of a known shallow fault and the contact between native soil and recent fill our results suggest the synergistic use of both seismic tomography and reflection imaging we denote as seismic trenching as a means of detecting shallow colluvial wedges and faults seismic trenching has the potential to significantly expand the lateral extent and depth of investigation of paleoseismology

early arrival waveform tomography on near surface refraction data we develop a waveform tomography method for estimating the velocity distribution that minimizes the waveform misfit between the predicted and observed early arrivals in space time seismograms by fitting the waveforms of early arrivals early arrival waveform tomographyewt naturally takes into account more general wave propagation effects compared to the high frequency method of traveltime tomography meaning that ewt can estimate a wider range of slowness wavenumbers another benefit of ewt is more reliable convergence compared to full waveform tomography because an early arrival misfit function contains fewer local minima synthetic test results verify that the waveform tomogram is much more accurate than the traveltime tomogram and that this algorithm has good convergence properties for marine data from the gulf of mexico the statics problem caused by shallow gassy muds was attacked by using ewt to obtain a more accurate velocity model using the waveform tomogram to correct for statics the stacked section was significantly improved compared to using the normal moveout nmo velocity and moderately improved compared to using the traveltime tomogram inverting high resolution land data from mapleton utah showed an ewt velocity tomogram that was more consistent with the ground truth trench log than the traveltime tomogram our results suggest that ewt can provide supplemental shorter wavelength information compared to the traveltime tomogram for both shallow and moderately deep seismic data