anatomy of strong ground motion near source records and three dimensional physics based numerical simulations of the mw 6 0 2012 may 29 po plain earthquake italy

half graben versus large offset low angle normal fault importance of keeping cool during normal faulting 1 we study the effect of temperature in the crust on the style of faulting during the extension of a model lithosphere two distinct fault patterns are seen depending on whether the brittle layer thickness hl is greater or less than a critical value hc for a thin layer hl hc a rift develops with multiple faults bounding an evolving set of grabens numerical results show that the value of hc depends on how the thermal structure and therefore the thickness distribution of the lithosphere evolve during extension in the region where the displacement occurs along the fault the brittle lithosphere thins and we show that this promotes development of multiple faults in models with heat transfer only by rock motion and conduction the advective thinning effect can greatly reduce hc with rift velocities greater than 1 cm yr 1 hc is reduced by a factor of 5 to unreasonably small values however inclusion of simulated hydrothermal cooling increases hc this allows large offsets to develop in model lithospheres with brittle layers of order 10 km thick extension of layers thicker than 10 km tends to produce a rift with multiple graben structures finally we compare the result of a simplified analytic model of extension to data we find that the style of faulting seen in a variety of continental rifts is broadly consistent with our model predictions

tomographic determination of velocity and depth in laterally varying media estimation of reflector depth and seismic velocity from seismic reflection data can be formulated as a general inverse problem the method used to solve this problem is similar to tomographic techniques in medical diagnosis and we refer to it as seismic reflection tomography seismic tomography is formulated as an iterative gauss newton algorithm that produces a velocity depth model which minimizes the difference between traveltimes generated by tracing rays through the model and traveltimes measured from the data the input to the process consists of traveltimes measured from selected events on unstacked seismic data and a first guess velocity depth model usually this first guess model has velocities which are laterally constant and is usually based on nearby well information and or an analysis of the stacked section the final model generated by the tomographic method yields traveltimes from ray tracing which differ from the measured values in recorded data by approximately 5 ms root mean square the i

weak faults rotten cores earthquakes are triggered when crustal deformation produces displacements along fault zones the rock in these zones is found to be weaker than adjacent material but what are the mechanisms of this loss of strength in his perspective holdsworth 1 discusses how recent studies of exposed ancient fault zones combined with laboratory analyses are revealing that rock properties at the grain scale can determine the large scale behavior of crustal deformation 1 http www sciencemag org cgi content full 303 5655 181

bayesian rupture imaging in a complex medium the 29 may 2012 emilia northern italy earthquake we develop a new approach to image earthquake rupture from strong motion data we use a large data set of aftershock waveforms interpolated over the seismic fault to obtain green s function approximations next we deploy a bayesian inversion method to characterize the slip distribution the rupture velocity the slip duration and their uncertainties induced by errors in the green s functions the method is applied to the 29 may 2012 mw 6 emilia earthquake which ruptured a fault buried below the po plain sediments northern italy despite the particularly complex wave propagation the near field strong motion observations are well reproduced with 15 rupture parameters the rupture and slip velocities were notably slow 0 5 vs and 0 5 m s respectively implying that the fault was difficult to break this method opens some perspectives for earthquake rupture studies in areas where numerical simulations suffer from imprecise knowledge of the velocity structure

dynamic development of fault rocks in a crustal scale detachment an example from western norway 1 the nordfjord sogn detachment nsd zone of western norway juxtaposes eclogites and gneisses of lower crustal affinity with sedimentary deposits suggesting that the zone experienced substantial displacement during devonian extensional denudation of the caledonides renewed activation occurred in permian and jurassic cretaceous times the detachment zone consists of a succession of fault related rocks reflecting various crustal positions and deformation mechanisms during activation and unroofing in more detail the lower 1 2 km thick section of the nsd zone consists of mylonites with various protoliths showing a general upward decrease in metamorphic grade the mylonitic section is truncated by the nsd fault defining the boundary toward hanging wall nappe rocks that are topped by sedimentary basins in an attempt to provide precise descriptions of the observed fault rocks we classify these rocks into 1 noncohesive breccias 2 cemented and indurated breccias of secondary cohesion and 3 cataclasites phyllonites and mylonites formed with primary cohesion along and across strike sections of the fault reveal the spatial and temporal relationships of the nsd fault the fault zone consists of a lower section of phyllonites and cataclasites reaching a total thickness of 50 70 m significant volumes of pseudotachylyte were injected into these fault rocks and were later reworked reactivation of the fault is suggested by overprinting carbonate cemented breccias that are cut by a discrete fault itself associated with breccias and gouge by comparing the various fault rocks and their formation mechanisms some constraints can be applied to the unroofing history the nsd fault developed in the ductile brittle transition zone of the crust where it experienced an initial shift from mainly frictional to plastic flow caused by reaction softening before hardening caused a return to frictional flow at the same time repeated pulses of pseudotachylyte were generated possibly lubricating the fault zone and contributing to strain localization these pseudotachylyte pulses also show that the fault was affected by seismic slip events before returning to a creep regime within a wider section than that ruptured by earthquakes younger cemented breccias and noncohesive breccias and gouge reflect earthquake rupturing and frictional flow within the seismogenic crust

fluid record of rock exhumation across the brittle ductile transition during formation of a metamorphic core complex naxos island cyclades greece fluid inclusions trapped in quartz veins hosted by a leucogneiss from the southern part of the naxos metamorphic core complex attic cycladic massif greece were studied to determine the evolution of the fluid record of metamorphic rocks during their exhumation across the ductile brittle transition three sets of quartz veins v m2 v bd v b are distinguished the v m2 and v bd are totally or respectively partially transposed into the foliation of the leucogneiss they formed by hydrofracturing alternating with ductile deformation accommodated by crystal plastic deformation the v b is discordant to the foliation and formed by fracturing during exhumation without subsequent ductile transposition fluids trapped during crystalplastic deformation comprise two very distinct fluid types namely a co2 rich fluid and a high salinity brine that are interpreted to represent immiscible fluids generated from metamorphic reactions and the crystallization of magmas respectively they were initially trapped at approximate to 625 degrees c and 400mpa and then remobilized during subsequent ductile deformation resulting in various degrees of mixing of the two end members with later trapping conditions of approximate to 350 degrees c and 140mpa in contrast brittle microcracks contain aqueous fluids trapped at 250 degrees c and 80mpa all veins display a similar 13c pointing to carbon that was trapped at depth and then preserved in the fluid inclusions throughout the exhumation history in contrast the d signature is marked by a drastic difference between i v m2 and v bd veins that are dominated by carbonic aqueous carbonic and high salinity fluids of metamorphic and magmatic origin characterized by d between 56 parts per thousand and 66 parts per thousand and ii v b veins that are dominated by aqueous fluids of meteoric origin characterized by d between 40 parts per thousand and 46 parts per thousand the retrograde pt pathway implies that the brittle ductile transition separates two structurally chemically and thermally distinct fluid reservoirs namely i the ductile crust into which fluids originating from crystallizing magmas and fluids in equilibrium with metamorphic rocks circulate through a geothermal gradient of 30 degrees c km1 at lithostatic pressure and ii the brittle upper crust through which meteoric fluids percolate through a high geothermal gradient of 55 degrees c km1 at hydrostatic pressure

development and testing of a 3d seismic velocity model of the po plain sedimentary basin italy abstract we built a 3d seismic model of the po plain and neighboring regions of northern italy covering altogether an area about 600 km by 300 km with an approximately 1 km spaced grid we started by collecting an extensive and diverse set of geological and geophysical data including seismic reflection and refraction profiles borehole logs and available geological information major geological boundaries and discontinuities have thus been identified and mapped into the model we used kriging to interpolate the geographically sparse information into continuous surfaces delimiting geological bodies with laterally varying thickness seismic wave properties have been assigned to each unit using a rule based system and v p v s and derived from other studies sedimentary strata although with varying levels of compaction and hence material properties may locally reach a thickness of 15 km and give rise to significant effects in seismic wave propagation we have used our new model to compute the seismic response for two recent earthquakes to test its performance results show that the 3d model reproduces the large amplitude and the long duration of shaking seen in the observed waveforms recorded on sediments whereas paths outside the basin may be well fit by more homogeneous 1d hard rock structure we conclude that the new model is suited for simulation of wave propagation mostly for t 3 s and may serve well as a constraint for earthquake location and further improvements via body or surface wave inversion

velocity analysis by iterative profile migration in conventional seismic processing velocity analysis is performed by using the normal moveout nmo equation which is based on the assumption of flat horizontal reflectors imaging by migration either before or after stack is done normally in a subsequent step using these velocities in this paper velocity analysis and imaging are combined in one step and migration itself is used as a velocity indicator because unlike nmo migration can be formulated for any velocity function migration based velocity analysis methods are capable of handling arbitrary structures i e those with lateral velocity variations in the proposed scheme each shot gather profile is migrated with an initial depth velocity model profile migration is implemented in the x domain but the actual implementation of profile migration is not critical as long as it is not done in a spatial wavenumber domain which would preclude handling of lateral velocity variations after migration with an initial velocity model the

maximum slip in earthquake fault zones apparent stress and stick slip friction the maximum slip observed or inferred for a small patch within the larger fault zone of an earthquake is a remarkably well constrained function of the seismic moment a large set of maximum slips mostly derived from slip models of major earthquakes indicate that this parameter increases according to the cube root of the seismic moment consistent with this finding neither the average slip rate for the patches of maximum slip nor the apparent stresses of earthquakes show any systematic dependence on seismic moment maximum average slip rates are several meters per second independent of moment and for earthquakes in continental crustal settings the apparent stress is limited to about 10 mpa results from stick slip friction experiments in the laboratory combined with information about the state of stress in the crust can be used to predict quite closely the maximum slips and maximum average slip rates within the fault zones of major earthquakes as well as their apparent stresses these findings suggest that stick slip friction events observed in the laboratory and earthquakes in continental settings even with large magnitudes have similar rupture mechanisms manuscript received 24 february 2003

migration velocity analysis from locally coherent events in 2 d laterally heterogeneous media part i theoretical aspects we present a new method based on migration velocity analysis mva to estimate 2 d velocity models from seismic reflection data with no assumption on reflector geometry or the background velocity field classical approaches using picking on common image gathers cigs must consider continuous events over the whole panel this interpretive step may be difficult particularly for applications on real data sets we propose to overcome the limiting factor by considering locally coherent events a locally coherent event can be defined whenever the imaged reflectivity locally shows lateral coherency at some location in the image cube in the prestack depth migrated volume obtained for an a priori velocity model locally coherent events are picked automatically without interpretation and are characterized by their positions and slopes tangent to the event even a single locally coherent event has information on the unknown velocity model carried by the value of the slope measured in the cig the velocity is e

trans dimensional finite fault inversion summary this paper develops a probabilistic bayesian approach to the problem of inferring the spatiotemporal evolution of earthquake rupture on a fault surface from seismic data with rigorous uncertainty estimation to date uncertainties of rupture parameters are poorly understood and the effect of choices such as fault discretization on uncertainties has not been studied we show that model choice is fundamentally linked to uncertainty estimation and can have profound effects on results the approach developed here is based on a trans dimensional selfparametrizationofthefault avoidsregularizationconstraintsandprovidesrigorousuncertainty estimationthataccountsformodel selectionambiguityassociatedwiththefaultdiscretization in particular the fault is parametrized using self adapting irregular grids which intrinsically match the local resolving power of the data and provide parsimonious solutions requiring few parameters to capture complex rupture characteristics rupture causality is ensured by parametrizing rupture onset time by a rupture velocity field and obtaining first rupture times from the eikonal equation the bayesian sampling of the parameter space is implemented on a computer cluster with a highly efficient parallel tempering algorithm the inversion is applied to simulated and observed w phase waveforms from the 2010 maule chile earthquake simulation results show that our approach avoids both over and underparametrization to ensure unbiased inversion results with uncertainty estimates that are consistent with data information the simulation results also show the ability of w phase data to resolve the spatial variability of slip magnitude and rake angles in addition sensitivity to spatially dependent rupture velocities exists for kinematic slip models application to the observed data indicates that residual errors are highly correlated and likely dominated by theory error necessitating the iterative estimation of a non stationary data covariance matrix the moment magnitude for the maule earthquake is estimated to be 8 9 with slip concentrated in two zones updip of and north and south of the hypocentre respectively while this aspect of the slip distribution is similar to previous studies we show that the slip maximum in the southern zone is poorly resolved compared to the northern zone both slip maxima are higher than reported in previous studies which we speculate may be due to the lack of bias caused by the regularization used in other studies

north south extension within the convergent himalayan region recent work by burg et al 1984 indicates the presence of east west striking gently north dipping normal faults in the higher himalayas and southern tibet that formed during postcollisional convergence of india and tibet these faults extend for at least 800 km along strike we interpret these normal faults as probable late miocene extensional features with perhaps several tens of kilometres of down to the north displacement a simple elastic model suggests that these normal faults may have formed during gravitational collapse of the miocene topographic front between india and tibet in this interpretation gravitational collapse occurred by southward motion relative to india and tibet of a wedge of crustal rocks bounded above by gently north dipping normal faults and below by thrust faults that probably dip north north south extension produced in this way is probably confined to upper crustal levels only and does not reflect regional extension of the entire lithosphere

correlation of earthquake source parameters inferred from dynamic rupture simulations 1 we analyzed 315 dynamic strike slip rupture models computed up to 5 0 hz to get a quantitative understanding of the correlation and amplitude distributions of parameters describing the earthquake source such as slip and rupture velocity to account for the epistemic uncertainty of the problem we constructed a database of dynamic ruptures computed by ourselves and other authors this database contains ruptures computed using different models of initial stress peak stress and critical slip weakening distance using the set of computed ruptures we constructed probability density functions pdfs for the amplitude distributions of the source parameters and for the correlation between the source parameters we tried to extract parameter pairs that showed a small variability in the spatial correlation given the large epistemic uncertainty in the input we only analyzed the areas on the fault with subshear propagation speed the principal findings are as follows 1 final slip amplitude does not show correlation with the local rupture velocity 2 final slip amplitude correlates well with risetime 3 rupture velocity correlates well with peak slip rate and the duration of the impulsive part of the slip rate function 4 the pdf of rupture velocity risetime and peak slip rate depends on the distance from the nucleation zone 5 fracture energy is not the single controlling factor for the rupture velocity the slope of the linear slip weakening curve has a significant effect on the rupture velocity 6 the crack length length that is slipping at a given time decreases with the distance from the nucleation zone

variability of seismic source spectra estimated stress drop and radiated energy derived from cohesive zone models of symmetrical and asymmetrical circular and elliptical ruptures large variability of earthquake stress drops and scaled energy has been commonly reported in the literature but it is difficult to assess how much of this variability is caused by underlying physical source processes rather than simply observational uncertainties here we examine a variety of dynamically realistic rupture scenarios for circular and elliptical faults and investigate to what extent the variability in seismically estimated stress drops and scaled energy comes from differences in source geometry rupture directivity and rupture speeds we numerically simulate earthquake source scenarios using a cohesive zone model with the small scale yielding limit where the solution approaches a singular crack model with spontaneous healing of slip compared to symmetrical circular source models asymmetrical models result in larger variability of estimated corner frequencies and scaled energy over the focal sphere the general behavior of the spherical averages of corner frequencies and scaled energy in the subshear regime extends to the supershear regime although shear mach waves generated by the propagation of supershear rupture lead to much higher corner frequency and scaled energy estimates locally our results suggest that at least a factor of 2 difference in the spherical average of corner frequencies is expected in observational studies simply from variability in source characteristics almost independent of the actual stress drops translating into a factor of 8 difference in estimated stress drops furthermore radiation efficiency estimates derived from observed seismic spectra should not be directly interpreted as describing rupture properties unless there are independent constraints on rupture speed and geometry

effects of three dimensional crustal structure and smoothing constraint on earthquake slip inversions case study of the mw6 3 2009 l aquila earthquake earthquake slip inversions aiming to retrieve kinematic rupture characteristics typically assume 1 d velocity models and a flat earth surface however heterogeneous nature of the crust and presence of rough topography lead to seismic scattering and other wave propagation phenomena introducing complex 3 d effects on ground motions here we investigate how the use of imprecise green s functions achieved by including 3 d velocity perturbations and topography affect slip inversion results we create sets of synthetic seismograms including 3 d heterogeneous earth structure and topography and then invert these synthetics using green s functions computed for a horizontally layered 1 d earth model we apply a linear inversion regularized by smoothing and positivity constraint and examine in detail how smoothing effects perturb the solution among others our tests and resolution analyses demonstrate how imprecise green s functions introduce artificial slip rate multiples especially at shallow depths and that the timing of the peak slip rate is hardly affected by the chosen smoothing the investigation is extended to recordings of the 2009 mw6 3 l aquila earthquake considering both strong motion and high rate gps stations we interpret the inversion results taking into account the lessons learned from the synthetic tests the retrieved slip model resembles previously published solutions using geodetic data showing a large slip asperity southeast of the hypocenter in agreement with other studies we find evidence for fast but subshear rupture propagation in updip direction followed by a delayed propagation along strike we conjecture that rupture was partially inhibited by a deep localized velocity strengthening patch that subsequently experienced afterslip

exhuming norwegian ultrahigh pressure rocks overprinting extensional structures and the role of the nordfjord sogn detachment zone 1 the nordfjord sogn detachment zone nsdz is widely cited as one of the primary structures responsible for the exhumation of norwegian ultra high pressure uhp rocks here we review data from the considerable volume of research describing this shear zone and compile a strikeparallel cross section along the nsdz from the solund basin in the south to the soroyane uhp domain in the north this cross section highlights several previously unrecognized patterns revealing a shear zone with top to the west asymmetric fabrics that 1 initiated at amphibolite facies 2 overprints metamorphic breaks and tectonostratigraphic contacts and 3 has a gradational continuum of muscovite cooling ages these patterns constrain the kinematic evolution of the nsdz and suggest a new three step model for the exhumation of norwegian u hp rocks the initial stages of exhumation were characterized by the rise of crustal rocks from u hp depths to the base of the crust by buoyancydriven mechanisms not specified in this paper mantle exhumation was followed by top to thewest normal sense displacement within a broad noncoaxial ductile shear zone near the base of the crust that overprinted tectonostratigraphic contacts formed previously during mantle exhumation in the final stages of crustal exhumation top w brittleductile detachments soled into and partially excised this ductile shear zone dropping the devonian basins into contact with rocks of varying tectonostratigraphic levels this new interpretation of the nsdz is significant as it accounts for the extreme crustal excision observed in western norway using three sequentially overprinting structures active at different stages of uhp rock exhumation citation johnston s m b r hacker and t b andersen 2007 exhuming norwegian ultrahigh pressure rocks overprinting extensional structures and the role of the nordfjord sogn detachment zone tectonics 26 tc5001

shear zone evolution during core complex exhumation implications for continental detachments abstract the formation of low angle detachments involves exhumation of previously ductile material and fault zone weakening to better understand this relationship we studied a deeply eroded metamorphic core complex which formed in the core of the bergen arcs w norway during caledonian post orogenic collapse multi scale structural mapping in the oygarden complex constrains three structural levels characterized by localized shear upper unit distributed deformation middle unit and a migmatite double dome lower unit all levels show retrogressive e w stretching accompanied by extension parallel recumbent folding albeit with opposing shear senses at upper and middle lower levels the systematic comparison of 23 shear zones constrains the ductile to brittle structural evolution initially high temperatures and partial melting controlled pervasive deep crustal flow and ductile doming during retrogressive shearing lithological heterogeneity controlled strain localization and channelized fluid flow causing retrograde phyllosilicate growth this established a feedback loop of fluid flow fabric weakening and progressive shear localization the interconnection of inherited and newly formed weak phyllosilicate rich layers promoted the formation of bivergent detachments that rapidly exhumed a dome of previously ductile crust retrogressive weakening in a kilometer wide ductile to brittle processing zone may be essential for the formation of continental detachments

source modelling of the m5 6 emilia romagna italy earthquakes 2012 may 20 29 on 2012 may 20 and 29 two damaging earthquakes with magnitudes mw 6 1 and 5 9 respectively struck the emilia romagna region in the sedimentary po plain northern italy causing 26 fatalities significant damage to historical buildings and substantial impact to the economy of the region the earthquake sequence included four more aftershocks with mw 5 0 all at shallow depths about 7 9 km with similar wnw ese striking reverse mechanism the timeline of the sequence suggests significant static stress interaction between the largest events we perform here a detailed source inversion first adopting a point source approximation and considering pure double couple and full moment tensor source models we compare different extended source inversion approaches for the two largest events and find that the rupture occurred in both cases along a subhorizontal plane dipping towards ssw directivity is well detected for the may 20 main shock indicating that the rupture propagated unilaterally towards se based on the focal mechanism solution we further estimate the co seismic static stress change induced by the may 20 event by using the rate and state model and a poissonian earthquake occurrence we infer that the second largest event of may 29 was induced with a probability in the range 0 2 0 4 this suggests that the segment of fault was already prone to rupture finally we estimate peak ground accelerations for the two main events as occurred separately or simultaneously for the scenario involving hypothetical rupture areas of both main events we estimate mw 6 3 and an increase of ground acceleration by 50 per cent the approach we propose may help to quantify rapidly which regions are invested by a significant increase of the hazard bearing the potential for large aftershocks or even a second main shock

new insights into the 2012 emilia italy seismic sequence through advanced numerical modeling of ground deformation insar measurements 1 we provide new insights into the two main seismic events that occurred in 2012 in the emilia region italy we extend the results from previous studies based on analytical inversion modeling of gps and radarsat 1 insar measurements by exploiting radarsat 2 data moreover we benefit from the available large amount of geological and geophysical information through finite element method fem modeling implemented in a structural mechanical context to investigate the impact of known buried structures on the modulation of the ground deformation field we find that the displacement pattern associated with the 20 may event is consistent with the activation of a single fault segment of the inner ferrara thrust in good agreement with the analytical solution in contrast the interpretation of the 29 may episode requires the activation of three different fault segments and a block roto translation of the mirandola anticline the proposed fem based methodology is applicable to other seismic areas where the complexity of buried structures is known and plays a fundamental role in the modulation of the associated surface deformation pattern

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

uncertainty in earthquake source imaging due to variations in source time function and earth structure abstract one way to improve the accuracy and reliability of kinematic earthquake source imaging is to investigate the origin of uncertainty and to minimize their effects the difficulties in kinematic source inversion arise from the nonlinearity of the problem nonunique choices in the parameterization and observational errors we analyze particularly the uncertainty related to the choice of the source time function stf and the variability in earth structure we consider a synthetic data set generated from a spontaneous dynamic rupture calculation using bayesian inference we map the solution space of peak slip rate rupture time and rise time to characterize the kinematic rupture in terms of posterior density functions our test to investigate the effect of the choice of stf reveals that all three tested stfs isosceles triangle regularized yoffe with acceleration time of 0 1 and 0 3 s retrieve the patch of high slip and slip rate around the hypocenter however the use of an isosceles triangle as stf artificially accelerates the rupture to propagate faster than the target solution it additionally generates an artificial linear correlation between rupture onset time and rise time these appear to compensate for the dynamic source effects that are not included in the symmetric triangular stf the exact rise time for the tested stfs is difficult to resolve due to the small amount of radiated seismic moment in the tail of stf to highlight the effect of earth structure variability we perform inversions including the uncertainty in the wavespeed only and variability in both wavespeed and layer depth we find that little difference is noticeable between the resulting rupture model uncertainties from these two parameterizations both significantly broaden the posterior densities and cause faster rupture propagation particularly near the hypocenter due to the major velocity change at the depth where the fault is located online material figures of inverted rupture models trade off curve and posterior probability density function

residual stereotomographic inversion depth migration requires highly accurate knowledge of the subsurface velocity field different traveltime tomographic methods are used for this purpose stereotomography is a tomographic method that uses local dip estimates in addition to traveltimes for velocity model estimation we present a new methodology for velocity model updating it combines poststack stereotomography and residual moveout velocity inversion the former is used for initial model construction and the latter for updating the velocity model residual inversion is a kind of stereotomographic inversion applied to common reflection point crp gathers after model based moveout correction velocity analysis can be made more efficient by preselecting the traces that contribute to a series of crp gathers and using only these traces for inversion the algorithm is defined in a two step procedure first ray tracing from the reflection point for nonzero reflection offsets defines the source and receiver locations of the data traces in the crs gather then these traces are moveout corrected according to the calculated traveltimes and residual moveout is estimated the interval velocity model is updated by fitting the velocity that minimizes estimated residuals application of the proposed technique demonstrates its robustness and reliability for fast and automatic velocity model estimation

simulation of the basin effects in the po plain during the emilia romagna seismic sequence 2012 using empirical green s functions the two main earthquakes that occurred in 2012 may 20 and 29 in the reggio emiliano region northern italy were relatively small mw 6 1 and mw 5 9 but they generated unexpected damages in a large area around the epicenter on some stations the observed seismic levels exceeded design levels recommended by the ec8 seismic code for buildings and civil engineering works the ground motions generated by the two mainshocks have specific characteristics the waveforms are mainly controlled by surface waves generated by the deep sedimentary po plain by local site effects and also on some stations by non linear behaviors in this particular context we test the ability of an empirical green s function egf simulation approach to reproduce the recorded seismograms in a large frequency band without any knowledge of the underground medium we focus on the possibility to reproduce the strong surface waves generated by the basin at distances between 25 and 90 km we choose to work on the second mainshock of the sequence mw 5 9 which occurred on may 29 2012 because it is better recorded by the seismological networks than the may 20th first mainshock we use a k 2 kinematic source model to generate a set of 100 slip distributions on the fault plane and choose the recordings of a close by mw 3 9 event as egf we then generate a set of broad band seismograms from 0 2 to 35 hz and compare them to the mainshock signals at 15 stations seismograms fourier spectra pga pgv duration stockwell transforms at epicentral distances from 5 to 160 km we find that the main specific features of the signals are very well reproduced for all the stations within and beyond the basin nevertheless at nearby stations the pga values are over evaluated which could be explained by the fact that non linear effects are not taken into account in the simulation process a better fit was found for a position of the nucleation point to the bottom west of the fault that suggest a directivity effect of the rupture process of the may 29th event towards the north east

the combined inversion of seismic and geodetic data for the source process of the 16 october 1999 mw 7 1 hector mine california earthquake we investigate the source process of the m w 7 1 hector mine earthquake by inverting broadband regional and local seismic displacement waveforms com bined with global positioning system gps and synthetic aperture radar interfer ometry insar geodetic measurements we find that the three data sets individually produce remarkably similar slip distributions over a multisegment fault a simulta neous inversion of the three data sets is presented and the sensitivity of the combined inversion to the weighting of the three independent data sets is examined the results indicate that the overall length of the fault that slipped is 42 km with a peak slip of 5 50 m and total scalar seismic moment of 6 8 10 19 n m the majority of slip is located on the western branch of the lavic lake fault to the northwest of the hypo center although the overall rupture is bilateral with appreciable slip on the bullion fault to the southeast some slip is located on an eastern branch of the lavic lake fault an apparent bifurcation which is also evident from aftershock locations the average slip and stress drops are 2 70 1 62 1 60 m and 78 36 and 55 bars for the western lavic lake the eastern lavic lake and bullion faults respectively the results also indicate that the overall rupture process is relatively slow which is char acterized by a several second delay before the onset of significant slip a 1 8 km sec rupture velocity of the primary asperity and long spatially variable dislocation rise times

stereotomography of seismic data acquired on undulant topography stereotomography is a robust method for building velocity models from seismic reflection data and has been applied to offshore seismic data but there is almost no stereotomographic study with rugged topographic conditions we study the topographic effects on the slopes of locally coherent events of seismic data and propose an approach to calculating the slopes on an undulant observation surface using the horizontal and vertical components of slowness vectors estimated then we present an extended stereotomography with undulant observation surface based on the conventional one tests on synthetic data validate the extended stereotomography application to the field seismic data in a foothill belt in xinjiang of the west china shows that the extended stereotomography is an effective tool to build velocity models for prestack depth migration of seismic data acquired on rugged topography

source characterization for broadband ground motion simulation kinematic heterogeneous source model and strong motion generation area we estimate strong motion generation areas that reproduce near source ground motions in a broadband frequency range 0 2 10 hz using the empirical green s function technique the strong motion generation areas are defined as extended areas with relatively large slip velocities within a total rupture area four m 6 class the 1997 kagoshima on march and may 1997 yamaguchi and 1998 iwate and several moderate size earthquakes in japan were analyzed we examine the relationship between the strong motion generation area and the area of asperities which is characterized based on heterogeneous slip distributions estimated from low frequency 1 hz waveform inversions somerville et al 1999 we performed waveform fitting in acceleration velocity and displacement then obtained the strong motion generation area occupying about a quarter of the total rupture area the size and position of the strong motion generation area coincide with those of characterized asperities we find self similar scaling of seismic moment to both the size of the strong motion generation area and the rise time for a magnitude range of analyzed earthquakes based on our results we propose a characterized source model for the broadband ground motion simulation which consists of strong motion generation areas with large slip velocities and a background slip area with a small slip velocity waveform modeling of the characterized source model suggests that the strong motion generation areas play important roles in simulating broadband ground motions and have the potential to be an about 10 mpa stress release area on the fault manuscript received 22 august 2002

opposing shear senses in a subdetachment mylonite zone implications for core complex mechanics 1 global studies of metamorphic core complexes and low angle detachment faults have highlighted a fundamental problem since detachments excise crustal section the relationship between the mylonitic rocks in their footwalls and the brittle deformation in their hanging walls is commonly unclear mylonites could either reflect ductile deformation related to exhumation along the detachment fault or they could be a more general feature of the extending middle crust that has been captured by the detachment in the first case we would expect the kinematics of the mylonite zone to mirror the sense of movement on the detachment in the second case both the direction and sense of shear in the mylonites could be different the northern snake range decollement nsrd is a classic basin and range detachment fault with a well documented top east of displacement we present structural paleomagnetic geochronological and geothermometric evidence to suggest that the mylonite zone below the nsrd locally experienced phases of both east and west directed shear inconsistent with movement along a single detachment fault we therefore propose that the footwall mylonites represent a predetachment discontinuity in the middle crust that separated localized deformation above from distributed crustal flow below localized distributed transition ldt the mylonites were subsequently captured by a moderately dipping brittle detachment that soled down to the middle crust and exhumed them around a rolling hinge into a subhorizontal orientation at the surface producing the present day nsrd in this interpretation the brittle hanging wall represents a series of rotated upper crustal normal faults whereas the mylonitic footwall represents one or more exhumed middle crustal discontinuities ldts

smooth velocity models in reflection tomography for imaging complex geological structures summary seismic imaging of geological structures with severe lateral velocity variations requires pre stack depth migration of the seismic data such processing requires itself an accurate determination of the distribution of the propagation velocities reflection tomography turns out to be quite attractive for this purpose furthermore migration velocity analysis can complete this technique whenever complexity of wave propagation makes the picking of reflection traveltimes very cumbersome if not impossible two different subsurface representations can be used to perform these methods the blocky model representation and the smooth model representation in reflection tomography using blocky models with finite velocity jumps can create shadow zones and the possible non definition of the forward problem smooth models on the other hand are created such that they do not have such shadow zones but require specific techniques to integrate a priori geological information also use of blocky models for migration brings in general artificial dicontinuities to migrated seismic events thus making almost impossible the interpretation of these events which is the basis of migration velocity analysis should we use smooth models such an interpretation becomes possible thus in spite of some inherent limitations smooth models are well adapted to run reflection tomography coupled with migration velocity analysis for the imaging of complex geological structures

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

imaging the 2016 mw 7 8 kaikoura new zealand earthquake with teleseismic p waves a cascading rupture across multiple faults the 13 november 2016 mw 7 8 kaikoura new zealand earthquake was investigated using teleseismic p waves backprojection of high frequency p waves from two regional arrays shows unilateral rupture of at least two southwest northeast striking faults with an average rupture speed of 1 4 1 6 km s and total duration of 100 s guided by these backprojection results 33 globally distributed low frequency p waves were inverted for a finite fault model ffm of slip the ffm showed evidence of several subevents however it lacked significant moment release near the epicenter where a large burst of high frequency energy was observed a local strong motion network recorded strong shaking near the epicenter hence for this earthquake the distribution of backprojection energy is superior to the ffm as a guide of strong shaking for future large earthquakes that occur in regions without strong motion networks initial shaking estimates could benefit from backprojection constraints

u pb dates and trace element geochemistry of zircon from migmatite western gneiss region norway significance for history of partial melting in continental subduction article i nfo thewesterngneissregion wgr norway isdominatedbymigmatiticgneissthatcontainsinclusionsofeclogite some of which contain evidence for ultrahigh pressure metamorphism to evaluate geochemical and age relation ships between host migmatite and eclogite we obtained la icp ms u pb dates and trace element analyses for zircon from a variety of textural types of leucosome from layer parallel to crosscutting zircon textures euhedral oscillatory and sector zone grains indicate a likely magmatic origin of the leucosomes caledonian u pb zircon dates from zircon rim and near rim regions are as old as 410 406 ma coeval with previously determined ages of high and ultrahigh pressure metamorphismof wgr eclogite trace elementanalysesobtained simultaneously with u pb dates indicate crystallization of zircon under garnet present conditions in the majority of leucosomes other zircons including those from crosscutting pegmatite yield younger ages as young as 385 ma coinciding with dates determined for amphibolite facies retrogression of eclogite trace element analyses suggest that these zircons grew under plagioclase present garnet absent conditions combined age and trace element data for leucosome zircons record the transition from high pressure garnet present plagioclase absent crys tallization to lower pressure plagioclase present crystallization if the euhedral zircons that yield ages coeval with peak or near peak uhp metamorphism represent crystallization from anatectic leucosomes these results combined with field and petrographic observations of eclogite migmatite relationships are consistent with the presence of partially molten crust in at least part of the wgr during continental subduction the decreased viscosity and increased buoyancy and strain weakening associated with partial melting may have assisted the rapid ascent of rocks from mantle to crustal depths

flow of partially molten crust and the internal dynamics of a migmatite dome naxos greece 1 migmatite domes are common in metamorphic core complexes dome migmatites deform in the partially molten or magmatic state and commonly record complex form surfaces folds and fabrics while units mantling the dome display a simpler geometry typically formed by transposition during crustal extension we use field observations and magnetic fabrics in the naxos dome greece to quantify the complex flow of anatectic crust beneath an extensional detachment system the internal structure of the naxos dome is characterized by second order domes subdomes pinched synforms and curved lineation trajectories which suggest that buoyancy driven flow participated in dome evolution subdomes broadly occur within two compartments that are separated by a steep n s oriented high strain zone this pattern has been recognized in domes formed by polydiapirism and in models of isostasy dominated flow the preferred model involves a combination of buoyancy and isostasy driven processes the naxos dome may have been generated by regional n s extension that triggered convergent flow of partially molten crust at depth and the upwelling of anatectic migmatites within the dome this pattern is complicated by gravitational instabilities and or overturning of the high melt fraction crust leading to the growth of subdomes as the migmatites within the naxos dome reached a higher structural level they were affected by regional top to the nne kinematics of the detachment system dome formation therefore occurred by a combination of coeval and coupled processes upper crustal extension deep crust contraction during convergent flow of anatectic crust diapirism and or density driven crustal convection forming subdomes and north directed detachment kinematics

scardec a new technique for the rapid determination of seismic moment magnitude focal mechanism and source time functions for large earthquakes using body wave deconvolution accurate and fast magnitude determination for large shallow earthquakes is of key importance for post seismic response and tsumami alert purposes when no local real time data are available which is today the case for most subduction earthquakes the first information comes from teleseismic body waves standard body wave methods give accurate magnitudes for earthquakes up to mw 7 7 5 for larger earthquakes the analysis is more complex because of the non validity of the point source approximation and of the interaction between direct and surface reflected phases the latter effect acts as a strong high pass filter which complicates the magnitude determination we here propose an automated deconvolutive approach which does not impose any simplifying assumptions about the rupture process thus being well adapted to large earthquakes we first determine the source duration based on the length of the high frequency 1 3 hz signal content the deconvolution of synthetic double couple point source signals depending on the four earthquake parameters strike dip rake and depth from the windowed real data body wave signals including p pcp pp sh and scs waves gives the apparent source time function stf we search the optimal combination of these four parameters that respects the physical features of any stf causality positivity and stability of the seismic moment at all stations once this combination is retrieved the integration of the stfs gives directly the moment magnitude we apply this new approach referred as the scardec method to most of the major subduction earthquakes in the period 1990 2010 magnitude differences between the global centroid moment tensor cmt and the scardec method may reach 0 2 but values are found consistent if we take into account that the global cmt solutions for large shallow earthquakes suffer from a known trade off between dip and seismic moment we show by modelling long period surface waves of these events that the source parameters retrieved using the scardec method explain the observed surface waves as well as the global cmt parameters thus confirming the existing trade off for some well instrumented earthquakes our results are also supported by independent studies based on local geodetic or strong motion data this study is mainly focused on moment determination however the scardec method also informs us about the focal mechanism and source depth and can be a starting point to study systematically the complexity of the stf

slip rates of blind thrusts in slow deforming areas examples from the po plain italy abstract we calculate plio pleistocene slip rates on the blind thrusts of the outer northern apennines fronts that are the potential sources of highly damaging earthquakes as shown by the m w 6 1 6 0 2012 emilia romagna seismic sequence slip rates are a key parameter for understanding the seismogenic potential of active fault systems and assessing the seismic hazard they pose however they are difficult to calculate in slow deforming areas like the po plain where faulting and folding is mostly blind to overcome this we developed a workflow which included the preparation of a homogeneous regional dataset of geological and geophysical subsurface information rich in plio pleistocene data we then constructed 3d geological models around selected individual structures to decompact the clastic units and restore the slip on the fault planes the back stripping of the differential compaction eliminates unwanted overestimation of the slip rates due to compaction induced differential subsidence finally to restore the displacement we used different methods according to the deformation style i e fault parallel flow for faulted horizons trishear and elastic dislocation modeling for fault propagation folds the result of our study is the compilation of a slip rate database integrating former published values with 28 new values covering a time interval from the pliocene to the present it contains data on 14 individual blind thrusts including the mirandola thrust seismogenic source of the 29 may 2012 m w 6 0 earthquake our study highlights that the investigated thrusts were active with rates ranging between 0 1 and 1 0 mm yr during the last 1 81 myr the mirandola thrust slipped at 0 86 0 38 mm yr during the last 0 4 myr these rates calculated with a homogeneous methodology through the entire po plain can be charged entirely to the thrust activity and not to secondary effects like the differential compaction of sediments across the structures

are stress drop and rupture velocity of earthquakes independent insight from observed ground motion variability we demonstrate that the variability of the peak ground acceleration pga generated by earthquakes can be simply related to the variability of stress drop rupture velocity vr and their correlation by compiling recent observations of variability of and vr we show that the hypothesis of independence between and vr leads to an overestimation of the pga variability we suggest that and vr must be anticorrelated so as to match recent observations of pga variability

seismic stereometry reveals preparatory behavior and source kinematics of intermediate size earthquakes although moderate size earthquakes are poorly studied by lack of near fault observations they can provide key information about larger damaging earthquakes here we propose a new approach inspired by double difference relocation that uses high coherency waveforms recorded at neighboring sensors to study the preparation phase and dynamics of moderate size earthquakes we validate this technique by analyzing the 2016 m w 5 2 borrego springs earthquake in southern california and find consistent rupture velocities of 2 km s highlighting two main rupture asperities the analysis of the 2019 ml5 2 le teil earthquake in france reveals slow nucleation at depth that migrates to the surface and propagates northward with a velocity of 2 8 km s highlighting two main rupture events also imaged by insar by providing unprecedented resolution in our observation of the rupture dynamics this approach will be useful in better understanding the preparation phase and rupture of both tectonic and induced earthquakes plain language summary small and moderate size earthquakes are much more numerous yet studied in much less detail than large and damaging earthquakes this is because to study small earthquakes precisely one needs seismometers very close to the rupture which is rarely the case it is still unclear if small and large earthquakes start the same way thus studying more systematically small earthquakes could help to answer this question here we show that we can use two close by seismometers as we would do with 3 d glasses to observe with a stereoscopic effect the evolution of intermediate size earthquakes when they rupture along a fault we can retrieve the direction of rupture the speed at which the fault breaks and the length of the rupture important parameters that help to characterize the earthquakes using this new method we can sometimes also observe the behavior of the fault before the main rupture which will be useful to better understand how earthquakes start

new insights into fault activation and stress transfer between en echelon thrusts the 2012 emilia northern italy earthquake sequence here we present the results of the inversion of a new geodetic data set covering the 2012 emilia seismic sequence and the following 1 year of postseismic deformation modeling of the geodetic data together with the use of a catalog of 3 d relocated aftershocks allows us to constrain the rupture geometries and the coseismic and postseismic slip distributions for the two main events mw 6 1 and 6 0 of the sequence and to explore how these thrust events have interacted with each other dislocation modeling reveals that the first event ruptured a slip patch located in the center of the middle ferrara thrust with up to 1 m of reverse slip the modeling of the second event located about 15 km to the southwest indicates a main patch with up to 60 cm of slip initiated in the deeper and flatter portion of the mirandola thrust and progressively propagated postseismically toward the top section of the rupture plane where most of the aftershocks and afterslip occurred our results also indicate that between the two main events a third thrust segment was activated releasing a pulse of aseismic slip equivalent to a mw 5 8 event coulomb stress changes suggest that the aseismic event was likely triggered by the preceding main shock and that the aseismic slip event probably brought the second fault closer to failure our findings show significant correlations between static stress changes and seismicity and suggest that stress interaction between earthquakes plays a significant role among continental en echelon thrusts