trishear kinematic modeling of extensional fault propagation folding we present a new non linear 2 d numerical trishear model that is capable of modeling both symmetrical and asymmetrical trishear zones and a strain prediction approach based on the velocity field within the trishear zone a simple relationship exists between the shape factor r of the velocity field the hanging wall apical angle and footwall apical angle the implication of this relationship is that when dealing with a real deformed state cross section one can measure the hanging wall and footwall apical angles to determine the r value to specify the velocity field within the trishear zone for either the forward modeling or restoration the new trishear model can accurately reproduce the geometry of two experimental clay models and an extensional fault propagation fold from the gulf of suez predicted strain is greatest directly above the fault tip and decreases with distance from the fault tip as in the experimental models greater strain occurs in the hanging wall because of the greater velocity gradient there whereas the footwall is much less intensely deformed consequently secondary faulting and fracturing if present should be better developed along the fault tip line or in the hanging wall the orientation of fractures or minor faults can be predicted from the strain ellipses calculated from the trishear velocity field

radial upper mantle attenuation structure of inactive back arc basins from differential shear wave measurements we measure differential attenuation between ss s and sscs scs phase pairs to characterize the variation of attenuation with depth in the upper mantle of five inactive back arc basins the kuril basin sea of japan banda sea the celebes and sulu seas and the shikoku basin a spectral ratio technique is used to measure the differential attenuation operator of the transversely polarized waveforms over a frequency band of 10 to 83 mhz two algorithms are employed to compute the vertically averaged attenuation structure a spectral stacking procedure and a least squares inversion in the spectral stacking method the individual spectra are corrected for the elastic structure at the ss or sscs bounce point and the differential attenuation operator is computed by spectral division the attenuation operators are then normalized and stacked by source depth to obtain more stable spectra and an average t for sources within a restricted depth range is obtained from the slope of the log amplitude spectrum a model for the depth dependent q structure is then calculated from the t measurements assuming q is frequency independent alternatively t measurements for individual phase pairs are made using a similar technique and analyzed by ray tracing and a least squares inversion to obtain the q 1 estimates the q results obtained from the stacking and inversion methods are generally in good agreement the q 1 structures for the various back arc regions are similar to each other within the uncertainties of the derived q models in addition to computing q models for each individual region we partitioned the data into three tectonic provinces based upon bounce point locations the resulting average radial q structure for an inactive basin shows a q of 54 in the uppermost mantle 115 at intermediate depths and 173 in the transition zone we also find a low q zone of 36 beneath active island arcs the q values for inactive back arc basins are lower than the global averages derived from normal modes but are generally consistent with previous body and surface wave studies of other young oceanic regions the most striking feature of this study is the observation of very strong attenuation concentrated at shallow depths 160 km in the upper mantle beneath these basins

high precision analysis of an embryonic extensional fault related fold using 3d orthorectified virtual outcrops the viewpoint importance in structural geology abstract image based 3d modeling has recently opened the way to the use of virtual outcrop models in geology an intriguing application of this method involves the production of orthorectified images of outcrops using almost any user defined point of view so that photorealistic cross sections suitable for numerous geological purposes and measurements can be easily generated these purposes include the accurate quantitative analysis of fault fold relationships starting from imperfectly oriented and partly inaccessible real outcrops we applied the method of image based 3d modeling and orthorectification to a case study from the northern apennines italy where an incipient extensional fault affecting well layered limestones is exposed on a 10 m high barely accessible cliff through a few simple steps we constructed a high quality image based 3d model of the outcrop in the model we made a series of measurements including fault and bedding attitudes which allowed us to derive the bedding fault intersection direction we then used this direction as viewpoint to obtain a distortion free photorealistic cross section on which we measured bed dips and thicknesses as well as fault stratigraphic separations these measurements allowed us to identify a slight difference i e only 0 5 between the hangingwall and footwall cutoff angles we show that the hangingwall strain required to compensate the upward decreasing displacement of the fault was accommodated by this 0 5 rotation i e folding and coeval 0 8 thickening of strata in the hangingwall relatively to footwall strata this evidence is consistent with trishear fault propagation folding our results emphasize the viewpoint importance in structural geology and therefore the potential of using orthorectified virtual outcrops

seismic attenuation beneath europe and the north atlantic implications for water in the mantle abstract it is well known that anelasticity has significant effects on the propagation of seismic waves as manifested by physical dispersion and dissipation investigations of anelasticity provide complementary constraints on the physical properties of earth materials but contrary to imaging with elastic waves progress in mapping earth s anelasticity has been relatively slow and there is only limited agreement between different studies or methodologies here within the framework of adjoint tomography we use frequency dependent phase and amplitude anomalies between observed and simulated seismograms to simultaneously constrain upper mantle wavespeeds and attenuation beneath the european continent and the north atlantic ocean in the sea floor spreading environment beneath the north atlantic we find enhanced attenuation in the asthenosphere and within the mantle transition zone mtz in subduction zone settings for example beneath the hellenic arc elevated attenuation is observed along the top of the subducting slab down to the mtz no prominent reductions in wavespeeds are correlated with these distinct attenuation features suggesting that non thermal effects may play an important role in these environments a plausible explanation invokes the transport of water into the deep earth by relatively cold subducting slabs leading to a hydrated mtz as previously suggested by mineral physics and geodynamics studies

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

estimation of thermal structure in the mantle wedge of northeastern japan from seismic attenuation data 1 we estimated thermal structure in the mantle wedge of ne japan by applying the experimental results of olivine dominated rocks to seismic attenuation data obtained temperatures at a 40 km depth are 1000 1130 c and 960 1090 c beneath the volcanic front and the back arc side respectively we cannot obtain the areas with a temperature higher than 1400 c in the mantle wedge which have been inferred from petrological studies this is perhaps due to the localization of such anomalous areas the obtained temperature is higher than that of the wet solidus of peridotite in the greater part of the back arc side which suggests that the addition of aqueous fluids plays an important role in generating melts in the mantle wedge

lithospheric scale structure across the bolivian andes from tomographic images of velocity and attenuation for p and s waves we have developed a three dimensional lithospheric scale model across the bolivian andes at 20 s based on tomographic images of velocity and attenuation for both p and s waves observations of travel time and attenuation for this study are from regional mantle earthquakes in the subducted nazca plate recorded on a portable broadband seismic array broadband andean joint experiment and seismic exploration of the deep andes in bolivia and chile the shallow mantle under the altiplano from 18 s to 21 s is high velocity and moderately high q vp 8 3 vs 4 7 qp 500 and qs 200 suggesting lithospheric mantle high velocity material in the altiplano extends to a depth of 125 150 km the shallow mantle of the western cordillera is characterized by high vp vs 1 83 suggesting a correlation between vp vs and arc volcanism seismic velocity in the western cordillera mantle is on average only slightly reduced from global averages however velocity and attenuation anomalies are locally strong vp 7 8 vs 4 3 qp 200 and qs 100 consistent with partial melt conditions under the los frailes volcanic field in the eastern cordillera shallow mantle velocity and q decrease drastically from the neighboring altiplano vp 7 8 vs 4 3 qp 300 qs 100 however high vp vs is not as pervasive as it is in the western cordillera we believe that slab derived water and perhaps other volatiles strongly influence the western cordillera while the eastern cordillera low velocity region is more affected by partial melt and or compositional changes average velocity and q in the shallow mantle across the bolivian andes where the tomographic images are best resolved are significantly higher than in most mantle wedge environments where corresponding images are available this is likely the result of a compressional back arc setting in the andes this implies that lithospheric shortening and thickening associated with the formation of the andes has profoundly influenced the shallow mantle structure across the range shallow mantle structure is locally influenced by the subduction processes particularly under the western cordillera however the differing volcanism and seismic character under the two cordilleras suggest that the volcanic process in the eastern cordillera may be distinct from arc volcanism tertiary volcanism in the eastern cordillera is located in the region where mantle shortening is suspected to be greatest both the timing and location of volcanism are consistent with upward migration of mantle wedge asthenosphere following the removal of over thickened lithosphere

caspian black sea mediterranean corridors during last 30 ky sea level change and human adaptive strategies proceedings of igcp 521 481 inqua 501 sixth and seventh plenary meetings and field trips

atlas of modern dinoflagellate cyst distributions in the black sea corridor from aegean to aral seas including marmara black azov and caspian seas abstract we present the first comprehensive taxonomic and environmental study of dinoflagellate cysts in 185 surface sediment samples from the black sea corridor bsc which is a series of marine basins extending from the aegean to the aral seas including marmara black azov and caspian seas for decades these low salinity semi enclosed or endorheic basins have experienced large scale changes because of intensive agriculture and industrialisation with consequent eutrophication and increased algal blooms the bsc atlas data provide a baseline for improved understanding of linkages between surface water conditions and dinoflagellate cyst dinocyst distribution diversity and morphological variations by cross reference to dinocyst occurrences in sediment cores with radiocarbon ages covering the past c 11 700 years the history of recent biodiversity changes can be evaluated the seabed cyst samples integrate seasonal and multi year data which are not usually captured by plankton samples and the cyst composition can point to presence of previously unrecorded motile dinoflagellate species in the bsc results show the presence of at least 71 dinocyst taxa of which 36 can be related to motile stages recorded in the plankton comparison with sediment core records shows that five new taxa appear to have entered or re entered the region over the past century statistical analysis of the atlas data reveals the presence of four ecological assemblages which are primarily correlated with seasonal and annual surface water salinity and temperature correlation with phosphate nitrate and silicate nutrients chlorophyll a and bottom water oxygen is less clear but may be important for some taxa biodiversity indices reveal strong west east biogeographical differences among the basins that reflect the different histories of mediterranean versus ponto caspian connections the atlas data provide a standardised taxonomy and regional database for interpreting downcore cyst variations in terms of quantitative oceanographic changes the atlas also provides a baseline for monitoring further changes in the bsc dinocysts that may accompany the accelerating development of the region

mechanical analysis of the geometry of forced folds a mechanical model of forced folding comprised of an anisotropic cover overlying displaced rigid basement blocks is used to investigate the influence of various parameters on theoretical fold form shape and dip of basement fault strength of basement cover contact and degree of anisotropy of the cover we show that the degree of anisotropy in the cover largely influences the geometry of the forelimb of the forced fold folds produced in isotropic cover display forelimbs that taper from large dip angles near the basement cover contact to low dip angles at the ground surface in contrast dips in the forelimbs of folds in anisotropic cover are nearly uniform with depth we show that the basement cover contact and the shape of the basement fault largely influence the geometry of the backlimb backlimb rotation occurs in cover welded to the basement and in cover underlying curved basement faults in addition the kinematic features of the theoretical folds are compared with the fold geometry generated by parallel kink and trishear models folds in isotropic cover overlying straight basement faults closely resemble the fold forms produced by the trishear kinematic model while fold forms in anisotropic cover more closely resemble folds produced by parallel kink geometric constructions

near surface attenuation and site effects from comparison of surface and deep borehole recordings abstract near surface attenuation and site effects are investigated using the seismograms of 17 local earthquakes recorded at depths of 0 0 3 1 5 2 5 and 2 9 km in the cajon pass borehole southern california the borehole penetrates 500 m of miocene sandstone and then crystalline granitic basement rock previous estimates of site response have been limited to shallower holes where the surface reflection interferes with the upgoing direct wave and the deepest sensor is not below the severe near surface effects in bedrock spectral ratios of the direct p and s waves for each earthquake between the different recording levels are well modeled with frequency independent q and amplification at the borehole q p 27 8 and q s 21 7 in the upper 2 9 km increasing from q p 26 and q s 15 in the upper 300 m to q p 133 and q s 47 between 1 5 and 3 km one event was also recorded at a surface granite site less than 1 5 km from the wellhead comparison of the 2 9 km recording with that at this granite site gives q p 50 and q s 23 the similarity of these values with those of previous studies at a wide range of sites suggests that q is very low in the near surface independent of rock type near surface amplification appears considerably more site dependent at the wellhead the amplifications at 1 hz of the direct p and s waves are 12 7 and 13 7 respectively these values include the free surface effect and are in reasonable agreement with the impedance contrast from the borehole logs at the granite site amplification of both p and s waves is less than four direct wave amplification at the wellhead is therefore at least three times that of the granite site the spectra of the direct and coda waves of the one earthquake recorded at both the wellhead and granite sites are compared with the corresponding 2 9 km recording coda wave amplification is in good agreement with the direct wave at the rock site but at the borehole the coda wave amplification factor overestimates the direct wave amplification by a factor of 3

how do horizontal frictional discontinuities affect reverse fault propagation folding abstract the development of new reverse faults and related folds is strongly controlled by the mechanical characteristics of the host rocks in this study we analyze the impact of a specific kind of anisotropy i e thin mechanical and frictional discontinuities in affecting the development of reverse faults and of the associated folds using physical scaled models we perform analog modeling introducing one or two initially horizontal thin discontinuities above an initially blind fault dipping at 30 in one case and 45 in another and then compare the results with those obtained from a fully isotropic model the experimental results show that the occurrence of thin discontinuities affects both the development and the propagation of new faults and the shape of the associated folds new faults 1 accelerate or decelerate their propagation depending on the location of the tips with respect to the discontinuities 2 cross the discontinuities at a characteristic angle 90 and 3 produce folds with different shapes resulting not only from the dip of the new faults but also from their non linear propagation history our results may have direct impact on future kinematic models especially those aimed to reconstruct the tectonic history of faults that developed in layered rocks or in regions affected by pre existing faults

on corner frequencies attenuation and low frequency earthquakes we have recently suggested that the nearly constant duration of low frequency earthquakes lfes and equivalently the band limitation of tectonic tremor manifests a moment duration scaling that is fundamentally different from regular earthquakes and is most easily explained as rupture on asperities of roughly constant dimension in that work we employed qualitative arguments against potential bias by attenuation here we examine the role of attenuation more quantitatively through an analysis that avoids specification of particular source e g brune models and relies on the particle velocity spectral maximum as the definition of apparent corner frequency the analysis leads to the formal definition of a saturation frequency as the limiting value of apparent corner frequency as the true corner frequency tends infinity the saturation frequency a formal equivalent to fmax can be used to set bounds on path averaged quality factor q we apply these relations to deep crustal and intraslab earthquakes beneath vancouver island to estimate bulk crustal attenuation parameters that are subsequently used to correct apparent corner frequency measurements of lfes reported in our earlier work the attenuation bias due to bulk crustal structure is shown to be small with negligible effect on the principal conclusions of that study however a review of laboratory and seismic refraction measurements of attenuation in oceanic basalts and evidence for high p to s lfe corner frequency ratios raises the possibility that strong highly localized near source attenuation accompanying high pore fluid pressures could cause the bandlimited nature of lfes through the depletion of high frequencies

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

frequency dependence of q in earth s upper mantle inferred from continuous spectra of body waves q0 f f0 a and applied a grid search to determine the best fit a and q0 the inferred frequency dependence 0 2 a 0 4 in most regions is consistent with laboratory data on solid olivine but not on partially molten olivine rich rocks except those data for deep events close agreement between seismological and laboratory observations on frequency dependence of q suggests that physical mechanisms of seismic wave attenuation are common and therefore laboratory data can be used to infer the physical state of earth s upper mantle from seismic wave attenuation index terms 5144 physical properties of rocks wave attenuation 7218 seismology lithosphere and upper mantle 8162 tectonophysics rheology mantle citation shito a s karato and j park 2004 frequency dependence of q in earth s upper mantle inferred from continuous spectra of body waves geophys res lett 31 l12603

deep structure of an arc continent collision earthquake relocation and inversion for upper mantle p and s wave velocities beneath papua new guinea we examine mechanisms of lithospheric growth and modes accommodating subcrustal convergence following the cessation of subduction by analyzing the seismicity and upper mantle velocities in the new guinea arc continent collision earthquakes in the papua new guinea png region from 1967 to 1984 have been relocated in a joint inversion with seismic velocities using p and s wave arrival times recorded by seismographs in png a total of 957 well recorded earthquakes were chosen for use in three dimensional velocity inversions from an initial catalog of 12 960 events based on the stability of initial hypocenter relocations constant velocity blocks were defined as irregular polyhedra to give fine detail in heavily sampled areas without introducing a large number of poorly controlled parameters and to exploit a priori knowledge of the geometry of velocity anomalies spherical geometry was used to accurately calculate long ray paths up to 1500 km in length most of the 700 best located hypocenters from the png data set are in the upper mantle beneath the finisterre huon fh ranges the newly accreted island arc terrane beneath the papuan peninsula and in the new britain seismic zone an oceanic subduction system these hypocenters show a well defined seismic zone dipping vertically or steeply to the north beneath the northern fh ranges from 125 to 250 km depth continuous along strike with the new britain seismic zone to the east which shows earthquakes to 600 km depth the steeply dipping intermediate depth seismicity flattens near 100 km depth beneath the fh ranges and forms a subhorizontal seismic zone beneath the fh ranges by contrast seismicity continues upward to the surface beneath new britain where the arc has not yet collided with new guinea the 100 km deep flat zone does not continue south of the fh ranges but appears to be truncated below the eastern and southern boundaries of the island arc terrane and no clear evidence for a south dipping seismic zone could be found the relationship of the flat part of the slab 100 km beneath the fh ranges and surface faulting is difficult to discern the apparent surface suture bounding the south side of the fh ranges is 100 km directly above the southern termination of intermediate depth seismicity nowhere in png could clear evidence for arc polarity reversal be found from seismicity all of the well located subcrustal earthquakes beneath the papuan peninsula lie in a narrow horizontal line between 125 and 175 km depth that follows the center of the peninsula and are distinctly separated from the fh seismic zone to the north these events do not require a southward subducting plate beneath the papuan peninsula an alternate and reasonable explanation for these events is that they are a result of unstable thickening of the lithosphere information on lateral heterogeneity in the mantle is limited because large variations in crustal velocities dominate the observed pattern of travel time residuals allowing for only crustal heterogeneity reduces travel time residual variances by 40 from a simple one dimensional structure while allowing for additional mantle heterogeneity results in 10 further reduction for the various parameterization s attempted here inversions with several different block geometries show low velocities at 35 to 171 km km depth beneath the bismarck sea back arc basin and high velocities just south of the intermediate depth fh seismic zone the pattern of lateral heterogeneity supports the inference from seismicity of north dipping slabs beneath both northeast new guinea and new britain

numerical modeling of trishear fault propagation folding in contrast to kink band migration modeling methods trishear numerical models produce fault propagation folds with smooth profiles and rounded hinges modeled fold hinges tighten and converge downward within a triangular zone of distributed deformation which is focused on the fault tip such features have been reported from field studies and are also seen in analogue models of compressional deformation however apart from its initial application to laramide folds little quantitative work has been undertaken on trishear fault propagation folding in other settings in addition no study has been undertaken into the growth strata which might be associated with such structures this paper uses an equivalent velocity description of the geometric model of trishear together with models of erosion and sedimentation to investigate trishear fault propagation folding of both pregrowth and growth strata the trishear model is generalized to include a variety of fault propagation to slip ratios and fault propagation from a flat decollement the models show continuous rotation of the forelimb with the characteristic development of cumulative wedges within growth strata when total slip on a structure is high the model predicts overturned pregrowth and growth strata during the initial stages of deformation beds in the forelimb thicken but later thin when they become steep or overturned the effect of variations in fault propagation to slip ratios on two dimensional finite strain in the models is assessed by the use of initially circular strain markers high fault propagation to slip p s ratios lead to narrow zones of high finite strain while lower p s ratios lead to more ductile deformation and broader zones of high strain in all cases hanging wall anticlines and footwall synclines originate as early ductile folds which are later cut by the propagating fault modeled structures are compared with natural examples

foreland basement involved structures basement involved structures commonly occur as long irregular chains of uplifts in foreland basins these structures commonly contain significant hydrocarbon accumulations with most major fields located on the broad crests of these structures the search for complex traps in deeper targets and in subthrust structures requires an improved understanding of the geometry and evolution of these structures characteristic features of basement structures include deformation zones within the sedimentary cover that dissipate significant fault slip and gently dipping frontlimbs and backlimbs fault slip in the basement is usually accommodated in the cover by a triangular widening upward deformation zone on the forelimb with the nature of deformation controlled primarily by the mechanical stratigraphy if the cover contains interlayered competent and incompetent units the incompetent units are characterized by significant penetrative deformation whereas the competent units are faulted after a relatively small amount of penetrative deformation depending on the competency contrast between the basement and cover the nature of basement and the physical conditions of deformation the deformation zone may also propagate downward into the basement gently dipping backlimb and frontlimb panels are related to movement of the hanging wall over synclinal and anticlinal bends in the major fault respectively many basement faults are characterized by a number of synclinal fault bends within the basement which result in long and gently dipping backlimbs forelimb panels are related to anticlinal bends that typically occur at the basement cover interface as well as at one or more locations in the sedimentary cover case studies of well constrained examples of structures from the bighorn and uinta basins and the central basin platform demonstrate the development of these characteristic features and their strong dependence on the mechanical stratigraphy these models and case studies will be useful in interpreting foreland basement structures in areas with poor or limited data

seismic attenuation tomography of the tonga fiji region using phase pair methods the anelastic structure of the region surrounding the tonga slab and lau back arc spreading center in the southwest pacific is studied using data from 12 broadband island stations and 30 ocean bottom seismographs two differential attenuation methods determine t over the frequency band 0 1 to 3 5 hz for earthquakes in the tonga slab the s p method measures the difference in spectral decay between p and s waves arriving at the same station the p p method measures the difference in spectral decay for p waves with different paths through the upper mantle eight hundred sixty phase pairs are used to invert for two dimensional 1 q structure using a nonnegative least squares algorithm a grid search method determines the q q ratio most compatible with both the s p and p p differential measurements the highest attenuation q 90 is found within the upper 100 km beneath the active portions of the lau basin extending westward to the lau ridge these regions probably delineate the source region for the back arc spreading center magmas expected to be within the upper 100 km based on petrological considerations the high attenuation regions also correlate well with zones of low p wave velocity determined by regional velocity tomography somewhat lower attenuation is found beneath the fiji plateau than beneath the lau basin the entire back arc is characterized by a gradual decrease in attenuation to a depth of 300 to 400 km the slab is imaged as a region of low attenuation q 900 material a q q ratio of 1 75 provides the best fit between the s p and p p data sets upon inversion spectral stacking shows no frequency dependence within the frequency band analyzed

on the robustness of attenuation measurements on teleseismic p waves insights from micro array analysis of the 2017 north korean nuclear test author s bezada mj byrnes j eilon z abstract summary despite their importance as a fundamental constraint on earth properties regional scale measurements of body wave seismic attenuation are scarce this is partially a result of the difficulty in producing robust estimates of attenuation in this paper we focus on measuring differential attenuation on records of teleseismic p waves we examine a unique data set of five records of the north korean nuclear test of 2017 measured at five broad band seismic stations deployed within a few metres of each other but using different installation procedures given their extreme proximity we expect zero differential intrinsic attenuation between the different records however we find that different attenuation measurement methods and implementation parameters in fact produce significant apparent differential attenuation t frequency domain methods yield a wide range of t estimates between stations depending on measurement bandwidth and nuances of signal processing this measurement instability increases for longer time windows time domain methods are largely insensitive to the frequency band being considered but are sensitive to the time window that is chosen we determine that signal generated noise can affect measurements in both the frequency and time domain in some cases the range of results amounts to a significant fraction of the range of differential attenuation across the conterminous united states as determined by a recent study we suggest some approaches to manage the inherent instability in these measurements and recommend best practices to confidently estimate body wave attenuation

comment on the timing and evolution of the post glacial transgression across the sea of marmara shelf south of istanbul by eris et al marine geology 243 57 76 abstract in their recent paper eris and co authors attempt to refute much of our work on deltaic sediments at the southern exit of the bosphorus strait turkey first their age model is completely inconsistent with the well constrained chronology of our cores mar02 110 and mar02 111 their calypso core md 2750 must have seriously oversampled the holocene section giving an erroneous impression of true thicknesses and ties to seismic data and therefore leading to an incorrect assessment of the timing of deltaic sedimentation second they have ignored evaporative drawdown in the marmara sea from 14 7 11 3 ka lowering of the sea surface by evaporation is a better explanation for a lowstand shoreline at 83 m elevation than their proposal that the dardanelles sill was this deep at the time of reconnection with the global ocean third we contest their conclusion that the uppermost delta in this area was sourced from the kurbagalidere river the sediment flux of this river is too little it cannot account for the strong upward climb of the topset to foreset transition into a rapidly rising ocean and eris et al make no attempt to explain the absence of a precursor shelf edge delta that would be mandatory if this river had the water and sediment discharge that they suggest

low radiation efficiency of the intermediate depth earthquakes in the japan subduction zone robust determination of earthquake source parameters over a continuous depth range is central to inferring rupture mechanisms dominant at different depths we employed a cluster event method to constrain the source parameters as well as along path attenuation for earthquakes over 0 150 km depths and 4 orders of seismic moments in the japan subduction zone we found that corner frequency and stress drop increase with depth whereas the radiated energy scaled by seismic moment declines with depth slightly as a result the radiation efficiency exhibits a notable deficit for events deeper than 60 km together these suggest an increased energy dissipation during faulting in ductile deformation regime consistent with shear heating instability as an important faulting mechanism for intermediate depth earthquakes

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

comparison of seismic body wave and coda wave measures of q measurements of seismic attenuation q 1 can vary considerably when made from different parts of seismograms or using different techniques particularly at high frequencies these discrepancies may be methodological or may reflect earth processes to investigate this problem we compare body wave with coda q 1 results utilizing three common techniques i parametric fit to spectral decay ii coda normalization of s waves and iii coda amplitude decay with lapse time q 1 is measured from both body and coda waves beneath two mountain ranges and one platform from recordings made at seismic arrays in the caucasus and kopet dagh over paths 4 long if q is assumed frequency independent spectral decay fits show q s and q coda near 700 800 for both mountain paths and near 2100 2200 for platform paths similar values are determined with the coda normalization technique however frequency dependent parameterizations fit the data significantly better with q s 1 hz and q coda l hz near 200 300 for mountain paths and near 500 600 for platform paths lapse decay measurements are close to the frequency dependent values showing that both spectral and lapse decay methods can give similar results when q has comparable parameterizations above 6 hz coda measurements suggest some enrichment relative to body waves perhaps due to scattering but intrinsic absorption appears to dominate at lower frequencies all approaches show sharp path differences between the eurasian platform and adjacent mountains and all are capable of resolving spatial variations in q

seismic anisotropy under central alaska from sks splitting observations 1 seismic anisotropy under central alaska is studied using shear wave splitting observations of sks waves recorded on the broadband experiment across the alaska range beaar 1999 2001 splitting results can be divided into two distinct regions separated by the 70 km contour of the subducting pacific plate waves that travel through the thicker mantle wedge show fast directions that are parallel to the strike of the slab these slab parallel directions appear to indicate along strike flow in the mantle wedge and splitting delay times increase with path length in the mantle wedge suggesting anisotropy of 7 9 0 9 the region of along strike flow corresponds to high seismic attenuation and hence high temperatures along strike flow here may be driven by secular shallowing of the slab driven by subduction of buoyant yakutat terrane crust or by toroidal flow around the east end of the aleutian slab waves traveling southeast of the 70 km contour sample the pacific plate and the nose of the mantle wedge they show fast directions that parallel the direction of plate motion these fast directions are most likely due to flow under the subducting pacific plate and or anisotropy within the subducting pacific lithosphere the high splitting delay times 0 8 1 7 s associated with these convergence parallel directions cannot be produced in the mantle wedge which is 10 30 km thick here thus anisotropy shows a sharp 90 change in fabric associated with the onset of high temperature wedge flow

deformation and secondary faulting associated with basement involved compressional and extensional structures experimental clay modeling is used to study the geometry and evolution of deformation zones formed above basement faults the nature of deformation is compared for reverse faults dipping 30 45 and 60 vertical faults and normal faults dipping 60 and 75 basement faulting results in the formation of a sheared triangular deformation zone that widens upward in the cover units most of the deformation is focused within a central zone of secondary faults which propagate upward and eventually break through the entire section basal units exhibit steeper dips and higher fault densities whereas stratigraphically higher units exhibit gentler dips and lower fault densities the width of the deformation zone is generally greater for reverse faults with low dips the anticlinal axial surface typically dips in the same direction as the synclinal axial surface for low to moderate angle reverse faults however the axial surfaces dip in opposite directions for vertical faults and normal faults particle paths suggest a convex upward rotation within the deformation zone suggesting transfer of material across the extension of the master fault reverse faults are associated with secondary faults with reverse and thrust separations vertical faults are associated with mostly vertical and reverse secondary faults whereas normal faults are generally associated with normal separation of most secondary faults therefore the nature of secondary faults varies with structural position possibly within the same layer these results provide some key insights that are useful in the interpretation of macroscopic surface and subsurface basement involved structures

dispersion of regional body waves at 100 150 km depth beneath alaska in situ constraints on metamorphism of subducted crust phase delays at high frequencies are observed in body waves that travel in the alaska slab along its strike at 100 150 km depth the delays between 2 6 hz energy and the direct 0 5 1 hz arrival are 0 5 1 5 s for p waves and 1 5 4 s for s waves such dispersion suggests a waveguide structure that parallels the slab perhaps near its top a channel that is 2 6 km thick and 2 5 5 slower than surrounding mantle can explain the observations the thickness of the layer is comparable to that of subducted oceanic crust or somewhat thinner the layer may be crust that is slow at these depths the required velocity anomaly is too small to be due to a continuous layer of metastable gabbro yet too large to represent an eclogite layer it may indicate a mixture of the two or persistence of hydrated mineral assemblages to depth

the southern tyrrhenian subduction zone deep geometry magmatism and plio pleistocene evolution abstract we report on a high resolution vp vp vs and qp model of the southern tyrrhenian subduction zone obtained by the inversion of p and s wave arrival times and t values from intraslab seismicity the arcuate shape of the southern apennines calabrian arc sicilian maghrebides is perfectly mirrored by two rather continuous low and high vp bands lying beneath the belt system at ca 25 and 100 km respectively between 100 and 300 km two independent high vp slabs lie beneath the neapolitan region and the southern tyrrhenian sea separated by unperturbed mantle we suggest that the ca 150 km wide slab window beneath the southern apennines opened after a tear occurring within a composite subduction system formed by the apulian continental lithosphere and the ionian oceanic slab the abrupt slab rupture induced ultrafast southeastward retreat of the ionian slab and the 19 cm yr spreading of the back arc oceanic marsili basin between ca 2 1 and 1 6 ma ago the 25 km low vp zone beneath the arc denotes continental upper crustal rocks below the chain its striking continuity requires a unique orogenic wedge at 25 km depth below the southern apennines the calabrian arc and the sicilian maghrebides the alternative explanation would imply the ubiquitous occurrence of autochthonous lower plate rocks at 25 km depth i e a puzzling autochthonous continental calabria the ionian slab beneath calabria shows high vp high qp and low vp vs anomalies typical of old oceanic lithosphere intermediate depth seismicity is concentrated within its thin oceanic crust suggesting the occurrence of vigorous metamorphism the slab dehydration promotes the melting of the overlying mantle as testified by high vp vs and low qp anomalies between the slab and the aeolian magmatic arc

reconciling mantle attenuation temperature relationships from seismology petrology and laboratory measurements seismic attenuation measurements provide a powerful tool for sampling mantle properties laboratory experiments provide calibrations at seismic frequencies and mantle temperatures for dry melt free rocks but require 102 103 extrapolations in grain size to mantle conditions also the effects of water and melt are not well understood at the same time body wave attenuation measured from dense broadband arrays provides reliable estimates of shear wave attenuation qs 1 affording an opportunity for calibration we reanalyze seismic data sets that sample arc and back arc mantle in central america the marianas and the lau basin confirming very high attenuation qs 25 80 at 1 hz and depths of 50 100 km at each of these sites independent petrological studies constrain the temperature and water content where basaltic magmas last equilibrated with the mantle 1300 1450 c the qs measurements correlate inversely with the petrologically inferred temperatures as expected however dry attenuation models predict qs too high by a factor of 1 5 5 modifying models to include effects of h2o and rheology dependent grain size shows that the effects of water enhanced dissipation and water enhanced grain growth nearly cancel so h2o effects are modest therefore high h2o in the arc source region cannot explain the low qs nor in the back arc where lavas show modest water content most likely the high attenuation reflects the presence of melt and some models of melt effects come close to reproducing observations overall body wave qs can be reconciled with petrologic and laboratory inferences of mantle conditions if melt has a strong influence beneath arcs and back arcs

geometric and experimental models of extensional fault bend folds the geometric models ranged from simple models of listric normal faults with continuous hanging wall deposition to complex models of normal faults with ramps and flats and footwall deposition and or erosion the inclined shear angle i e the angle between the horizontal and the shear direction was 70 in all models withjack and peterson 1993 describe the modeling technique in the experimental models a 4 cm thick layer of either wet clay or dry sand covered a flat metal base consisting of overlapping plates or precut blocks movement of the plates or blocks produced a listric normal fault in the overlying clay or sand layer we added growth layers after every centimeter of displacement withjack and callaway 2000 describe the properties of the wet clay and dry sand

three dimensional attenuation structure beneath the northeastern japan arc estimated from spectra of small earthquakes abstract a fine scale three dimensional attenuation structure beneath the northeastern japan arc has been obtained using a joint inversion for source parameters site response and q values data used for this study are p wave spectra of microearthquakes occurring in the subducting pacific plate the subducting plate is found to have higher q values than the overlying mantle there is an along arc variation in the distribution of low q zones in the crust and the mantle wedge within the study area for the southern part of the study area low q zones are distributed in the crust beneath the volcanic front they extend into the mantle wedge and become deep toward the west that is toward the backarc region on the other hand the northern part of the study area has low q zones at two depth ranges at shallower depths just beneath the volcanic front and at the deeper part of the mantle wedge beneath the backarc region the region without active volcanoes along the volcanic front has relatively high mantle q values seismic activity in the lower plane of the double planed deep seismic zone is high beneath this relatively high q region of the mantle wedge spatial distribution of low q zones found in the present study is nearly consistent with that of the low velocity zones estimated from studies of travel times tomography partial melting zones in the mantle wedge whose existence has been suggested from the study of seismic velocity structure and laboratory experiments are located in the low q zones obtained in the present study these results suggest that spatial distribution of q values is closely related to heterogeneous distribution of temperature in the mantle wedge

attenuation of broadband p and s waves in tonga observations of frequency dependent q teleseismic broadband recordings of intermediate and deep focus earthquakes are used to quantify both compression q and shear q wave attenuation within the lau backarc basin a spectral ratio method is employed to measure differential attenuation t between the depth phases ss pp and sp and the direct s and p phases over the frequency band 0 05 and 0 5 hz we use a stacking algorithm to combine the spectra of several phase pairs from a single event having similar azimuth and range to obtain more robust t measurements these estimates are then used to compute the average q above the focal depth q and q are measured directly from the ss s and pp p phase pairs respectively however the interpretation of t measured from sp p requires assumptions about the ratio q q we find an empirical ratio of q q 1 93 for this region and use it to compute q and q from the q sp observations

deep structures along the boundary of a collisional belt attenuation tomography of p and s waves in the greater caucasus summary seismic attenuation q 1 o fp and s waves shows a major discontinuity from the russian platform to the tectonically active greater caucasus broadband records show this boundary over paths 4 long as revealed by the decay of amplitude spectra from a digital seismic network flanking the greater caucasus we measure attenuation from individual spectra using a non linear least squares procedure to determine an attenuation parameter t simultaneously with source parameters at frequencies between 1 and 15 hz the t measurements are then inverted for spatial variations of q 1 with parametrizations of varying complexity model variance for heterogeneous structures improves by more than 30 per cent compared with homogeneous parametrizations site corrections also significantly improve the fit in these inversion results mountainous regions exhibit q values 2 3 times lower q s 775 75 than do the adjacent shields q s 2060 315 showing that the discontinuity is large for both regions q p is roughly equal to q s comparison of body wave to coda spectra indicates that intrinsic absorption rather than scattering dominates the q 1 measurements at least beneath the mountains hence q 1 variations may give a reasonable proxy for temperature if so then temperature beneath the mountains exceeds that beneath the shield by 70 400 c these temperature increases may not be high enough to generate widespread partial melting beneath the mountains but could produce regional metamorphism and could contribute substantially to isostatic compensation of the mountains whatever their origin the boundary in seismic attenuation is abrupt and large between stable craton and an adjacent mountain belt demonstrating that q 1 is a sensitive indicator of tectonic process

body wave attenuation in the tonga subduction zone attenuation p and s waves of in the tonga subduction zone is estimated from locally recorded data using a spectral ratio method the data consist of three component digital seismograms of 77 earthquakes recorded at two stations in fiji and one in tonga the stations in the fiji islands lie above the deep earthquakes in the subduction zone while the tonga station is close to the top of the subducted slab variations in the high frequency spectral decay rate define four attenuation provinces paths from earthquakes deeper than 350 km to stations on viti levu fiji and the lau ridge traverse mantle with normal attenuation qp 570 qs 200 400 the subducting tonga slab has very low attenuation qp 2000 qs 1800 relative to the surrounding mantle the wedge of mantle above the slab at depths shallower than 350 km and east of the lau ridge is extremely attenuating for p waves qp 240 several paths from main thrust zone events to the station in tonga show intermediate attenuation qp 300 500 in the forearc region the observed spectra do not require q to be frequency dependent in the 1 0 hz to 7 6 hz band in this region

mantle wedge structure in the miyagi prefecture forearc region central northeastern japan arc and its relation to corner flow pattern and interplate coupling 1 we applied three dimensional 3 d seismic tomography to both active source data and local earthquake data recorded at onshore and offshore seismic stations in the miyagi prefecture forearc region of central northeastern japan to obtain a detailed seismic velocity model of the mantle wedge the velocity model showed a clear boundary that divides the mantle wedge into an oceanward high velocity toe and a landward low velocity region that extends trenchward from beneath currently active arc volcanoes the top of the seaward dipping boundary is about 20 30 km landward from the coastline and its bottom is approximately beneath the coastline we consider that this velocity boundary represents the trenchward limit of corner flow and the high velocity toe represents a stagnant mantle wedge the high spatial resolution of the tomographic image we produced allowed us to identify a spatial correlation between velocity variations in the mantle wedge immediately above the plate boundary and the spatial extent of the rupture areas of the large interplate earthquakes that occur repeatedly in the region our results suggest that variations of the volume fraction of serpentinization in the mantle wedge cause the irregularity of rupture patterns of megathrust earthquake sequences we also identified a swarm of active microseismicity in the mantle wedge well above the seismogenic plate boundary this activity may be related to dehydration of a detached seamount

three dimensional attenuation variations in southern california seismic attenuation 1 q in southern california varies substantially over distances of tens of kilometers these variations are apparent in high frequency spectral decay of body waves we measure the spectral decay from earthquake seismograms at regional distances by estimating a frequency independent decay parameter t for both p and s waves for frequencies of 0 5 25 hz and invert the resulting 1138 t values to show spatial 1 q variations in the crust and upper mantle the p and s results agree closely with each other and both correlate with regional tectonics the upper crust 0 5 14 km depth exhibits high 1000 q 2 0 q 500 in the los angeles basin and transverse ranges compared to low 1000 q 1 0 q 1000 in the mojave desert high 1 q of the los angeles basin probably reflects high porosity in basin sediments the lower crust exhibits areas of high 1 q beneath the salton trough 1000 qp 1 5 and 1000 qs 2 3 or qp 700 and qs 400 and beneath the san gabriel mountains 1000 qp 2 2 and 1000 qs 1 7 values 2 4 times larger than other areas high 1 q beneath the salton trough may reflect elevated temperature or partial melt resulting from active rifting the high 1 q beneath the san gabriel mountains may represent elevated temperature associated with active mountain building as seen in similar tectonic settings elsewhere attenuation varies less in the mantle perhaps because resolution is poorer relatively high qp qs 1 5 beneath the salton trough may similarly indicate high temperatures these measurements show large variation in 1 q across the region relevant to any complete model for ground shaking in southern california

tomographic imaging of the alaska subduction zone the alaska subduction zone is characterized by the pacific plate descending beneath the north american plate causing abundant seismic activity in the crust and along the wadati benioff zone down to a depth of approximately 200 km we have used 142 908 p wave arrival times from 12 237 shallow and intermediate depth earthquakes recorded by the alaska earthquake information center jointly run by the geophysical institute university of alaska fairbanks and u s geological survey in the period from january 1977 to november 1991 to investigate the three dimensional 3 d p wave velocity structure beneath central and southern alaska travel times and ray paths are accurately calculated by using an efficient 3 d ray tracing technique the nonlinear tomographic problem is solved by iteratively conducting linear inversions and the velocity structure and hypocentral locations are simultaneously determined we conducted two types of inversions one is an inversion with a laterally homogeneous starting model the others are what we call slab inversions in which we introduce into the initial model the high velocity subducting pacific plate as a priori information we found that the slab inversions gave a seismologically more plausible result and a final root mean square travel time residual significantly smaller than that of the inversion with the homogeneous starting model detailed p wave tomographic images are obtained for the crust and upper mantle down to a depth of 200 km with spatial resolutions of 30 60 km the tomographic image of the upper crust correlates well with the major surface geological features such as slow sedimentary basins and fast ultramafic bodies prominent low velocity anomalies exist in the crust and upper mantle beneath active volcanoes in the mantle wedge the low velocity anomalies dip toward the continental side and extend to a depth of about 150 km which are considered to be associated with the active volcanism in the alaska subduction zone the results suggest that the subducting pacific plate has a thickness of 45 55 km and a p wave velocity 3 6 higher than that of the surrounding mantle

seismic wave dispersion and attenuation in aheim dunite an experimental study summary a machine has been developed which provides for the study of both shear modulus dispersion and internal friction in geological materials through the observation of forced torsional oscillations of low frequency 10 1000 mhz and strain amplitude 1000 c the eventual goal is an understanding of the dispersion and attenuation of seismic shear waves in the earth s upper mantle measurements have been made on cylindrical specimens of an olivine rich rock from aheim norway which contains in addition to olivine about 10 per cent pyroxene and 5 10 per cent of hydrous silicate phases dominantly clinochlore serpentine and talc in order to separate aspects of the mechanical behaviour associated with the olivine aggregate from those attributable to the hydrous phases and or their dehydration products the specimens were either previously fired under controlled oxygen fugacity at 1200 c for 24 hours in order to effect complete dehydration within the olivine stability field or simply oven dried at 110 c linearity of the mechanical behaviour has been demonstrated by the amplitude independence of the results for the strain amplitude range 10 8 10 6 and by the quantitative consistency between the observed modulus dispersion and that calculated from the measured internal friction through the kramers kronig relations of linear theory both the pressure dependence at room temperature and the temperature dependence at 300 mpa of the shear modulus and internal friction have been investigated much of the variation of the shear modulus is attributed to changes of crack porosity associated with changes in pressure and temperature and with in situ dehydration temporal evolution of q 1 towards a lower asymptotic value over periods of hours of exposure to given conditions of high pressure and temperature is tentatively attributed to the gradual diminution of enhanced anelastic relaxation associated with regions of decaying stress concentration at asperities on cracks and or grain boundaries at the highest pressures and temperatures achieved in this study 300 mpa and 1000 c marked dispersion of the shear modulus amounting to 5 per cent between periods of 3 and 100 s and concomitant strong internal friction varying with oscillation period to approximately as 0 011to1 6 are observed the energy dissipation appears to be concentrated within rather than at the boundaries between the olivine grains these results provide the clearest indication yet that solid state probably intragranular anelastic relaxation in ultramafic rocks gives rise to losses comparable with those observed seismologically in the earth s upper mantle although the mechanistic basis for the observed anelasticity remains to be established

strain variation with progressive deformation in basement involved trishear structures abstract basement involved structures associated with reverse vertical and normal faults commonly involve non parallel shear within a triangular deformation trishear zone located on the front limbs of the structures deformation within the trishear zone is characterized by shear gradients and an associated decrease in the dips of the beds in stratigraphically higher units geometric models suggest that the layer parallel strain within the trishear zone depends on the type of fault normal reverse or vertical the dip and throw of the fault the dip of the anticlinal or synclinal axial surfaces and the distance of any unit above the initial tip of the trishear zone located at the basement sediment contact at any given location reverse faults typically show increasing layer parallel shortening followed by decreasing layer parallel shortening and a transition to extension with increasing throw the transition from contraction to extension occurs at lower values of throw for stratigraphically lower units and also for faults with smaller dips vertical and normal faults exhibit increasing layer parallel extension of all units with increasing throw with larger extension for stratigraphically lower units experimental models suggest that the trishear zone can expand with increasing fault throw the strain within the trishear zones is accommodated largely by secondary faults which are rotated with progressive deformation the strain variations in the experiments closely mimic those predicted by the geometric models for reverse vertical and normal faults

p wave attenuation structure of the lau back arc basin and implications for mantle wedge processes abstract we image 3 d seismic p wave attenuation structure of the tonga subduction zone and the lau back arc basin using local earthquake waveforms recorded by land and ocean bottom seismographs of the 2009 2010 lau spreading center imaging project the amplitude spectra of p waves from local earthquakes are inverted for the path average attenuation operator t with a variety of frequency dependence exponent values analysis shows that the data are best fit by the assumption of a weak frequency dependence 0 3 consistent with laboratory results modeled as the effects of grain boundary sliding the t measurements are inverted for a 3 d tomographic q p 1 model the results show high p wave attenuation within the upper 100 km of the back arc mantle with a sharp boundary at the tofua arc between high attenuation sub arc mantle and the low attenuation fore arc perhaps the highest p wave attenuation q p 1 0 036 or q p 28 known in the mantle occurs at 20 60 km depth beneath the back arc spreading centers high attenuation anomalies form an inclined zone dipping from the spreading centers to the west away from the slab indicating abnormally high temperature and the existence of hydrous partial melt these observations suggest that hot materials supplied from the australian mantle upwell along with the mantle wedge flow pattern triggering extensive decompression melting near the back arc spreading centers the along strike variation of p wave attenuation is different from that of sv velocity possibly implying the different effects of partial melt on seismic attenuation and velocity

three dimensional attenuation model of the shallow hikurangi subduction zone in the raukumara peninsula new zealand 1 the material properties of the shallow subduction zone are imaged with data from a passive seismic deployment in the raukumara peninsula attenuation images are obtained using t values measured from 2848 spectra of p wave arrivals the t values are inverted for frequency independent three dimensional 3 d qp using a 3 d velocity model linked nodes in a preliminary 2 d inversion are used to obtain the most reliable initial model for 3 d inversions the results show the benefits of obtaining 3 d q in addition to 3 d vp and vp vs q is related to localized permeability and heterogeneity and thus 3 d q is an important tool for interpreting active tectonic regions qp in the shallow overlying plate generally corresponds to the mapped geology two high qp features 600 represent subducted seamounts or cretaceous volcanics within the overlying plate the gradient above the subducting plate is the strongest feature in the qp model with the slab having high qp 600 900 below 20 km depth and above the plate interface there is a zone of 50 decrease in qp and high vp vs about 10 km thick which represents actively subducting sediment and has distributed microearthquake activity associated with active underplating

a review of deformation pattern templates in foreland basin systems and fold and thrust belts implications for the state of stress in the frontal regions of thrust wedges aesthetically appealing thrust systems and related large scale anticlines in both active and fossil foreland fold and thrust belts and the economic potential associated with the m have captured the interest of structural geologists for many decades as a consequence a large amount of data on sub seismic deformation patterns from thrust related an ticlines is available in the literature we provide a review of deformation pattern templates from fi eld data in foreland fold and thrust belts and show that the most frequent tre nds of sub seismic syn orogenic deformation structures hosted in km scale thrust related folds frequently and pa radoxically indicate a syn th rusting strike slip stress fi eld con fi guration with a near vertical 2 and a sub horizontal 3 rather than a contractional one where the latter is expected to be the vertical principal axis of the stress ellipsoid this a pparent inconsistency between sub seismic syn orogenic deformation structures and stress fi eld orientation is here named the 2 paradox field data support a possible expla nation of the paradox provided by the major role played by i nherited early orogenic extensional deformation struc tures on thrust fault nucleation nucleation of major thru sts and their propagation is facilitated and driven by the positive inversion and linkage of the early orogenic sub s eismic extensional inheritance developed in the foreland basin this process eventually leads to the development of l argereversefaultzonesandcanoccurbothincontractional and strike slip stress fi eld con fi gurations

northern california seismic attenuation 3d qp and qs models the geological complexity of northern california and its accreted terranes produces pronounced regional variations in the attenuation 1 q of earthquake waves using local earthquakes 3d q p and q s models have been obtained for this region that includes the san andreas fault system the great valley the sierra nevada batholith and the gorda subduction volcanic system path attenuation t values were determined from p and s spectra of 959 spatially distributed earthquakes magnitude 2 5 6 0 using 1254 stations from northern california earthquake data center networks and mendocino and sierra nevada temporary arrays the t data were used in q inversions using existing 3d velocity models and basic 10 km node spacing uneven data coverage was accommodated with linking nodes into larger areas for useful q images across the 3d volume results at shallow depth show very low q in the sacramento delta the eureka area and parts of the san francisco bay area in the brittle crust low q tends to be associated with regions of fault zones and microearthquakes in the ductile lower crust low q is observed below fault zones with large cumulative displacement and inferred grain size reduction with apparent broad ductile shear zones across the fault system in the coast ranges underlying active arc volcanoes low q features are apparent below 20 km depth under the long valley caldera two distinct partial melt features at 3 and 15 km depth are inferred moderately high q is associated with sierra nevada and salinian igneous rocks whereas the franciscan subduction complex shows moderately low q prominent high q relates to the great valley ophiolite the pattern of path specific attenuation rate from 3d q is generally similar to the pattern of psuedospectral acceleration residuals for the south napa earthquake indicating that it may be beneficial to incorporate 3d q models into future ground motion prediction equations for northern california online material figures of q p and q s resolution and station delays for t and table of q p v p q s and v s

defect microdynamics in minerals and solid state mechanisms of seismic wave attenuation and velocity dispersion in the mantle the propagation of seismic waves in the earth s mantle can be significantly affected by relaxation processes causing attenuation and velocity dispersion reduction this paper reviews the solid state mechanisms of relaxation processes based on the theory of defect microdynamics in solids together with some experimental observations on defects in minerals particularly in olivine for a given mechanism to have a significant effect on seismic wave propagation both the density and the mobility of the defects must be in an appropriate range the examination of the densities and geometry and mobilities of defects in olivine shows that dislocation and or grain boundary mechanisms can have a significant effect on seismic wave propagation although wide distributions of geometrical factors such as spacing of pinning points and of mobilities are required to explain all available data point defect mechanisms however are unlikely to be important because their densities are too small and or their mobilities are too large since the dislocation density and or grain size are determined in most cases by the long term tectonic stress seismic wave attenuation and velocity dispersion reduction involving these defects are likely to depend on the magnitude of the tectonic stress as well as the temperature theoretical considerations suggest a wide range of dependence of seismic wave attentuation and velocity dispersion on the long term tectonic stress this is particularly the case for dislocation mechanisms and warrants careful experimental investigation dislocations and or grain boundaries cause anelastic behavior relaxation peaks when they are pinned or blocked at some points pinning or blocking becomes ineffective at high temperatures and or low frequencies causing a transition to viscoelastic behavior both laboratory and seismological observations of internal friction are dominated by the high temperature background where internal friction increases monotonically with temperature which can be interpreted as a gradual transition to viscoelastic behavior or to a wide distribution of relaxation times however in most experimental studies to date the dislocation densities or the grain sizes were not well controlled making it difficult to identify the attenuation mechanisms and preventing any quantitative applications to earth the need for better characterization of defect microstructures in experimental specimens is emphasized

attenuation structure beneath the volcanic front in northeastern japan from broad band seismograms abstract anelastic structure in the asthenosphere beneath the volcanic front in northeastern japan arc is estimated by using the spectral amplitude ratio data of p and s waves from about 100 events which occurred in the subducting pacific slab below japan these earthquakes occurred within a 90 km radius centered about the station sawauchi swu with focal depths ranging from 60 to 200 km waveforms were recorded by the carnegie broad band three component seismograph and were corrected for instrument responses crustal reverberations corner frequencies and superimposed noise ray paths and travel times of p and s waves are calculated using a three dimensional velocity model zhao d hasegawa a horiuchi s 1992 j geophys res 97 19909 19928 we find a low q region qs 70 extending down to 55 km depth from the lower crust beneath the volcanic front using q temperature laboratory results sato h sacks i s murase t muncill g fukushima h 1989 j geophys res 94 10647 10661 this implies a temperature of about 130 c higher than the eastern forearc region and about 30 c higher than the western backarc region in good agreement with the tomographic results of zhao et al zhao d hasegawa a horiuchi s 1992 j geophys res 97 19909 19928 this suggests that low velocities in the crust and uppermost mantle beneath swu may be explained by a subsolidus temperature increase without partial melting

seismic attenuation and mantle wedge temperatures in the alaska subduction zone 1 anelastic loss of seismic wave energy or seismic attenuation 1 q provides a proxy for temperature under certain conditions the q structure of the upper mantle beneath central alaska is imaged here at high resolution an active subduction zone where arc volcanism is absent to investigate mantle thermal structure the recent broadband experiment across the alaska range beaar provides the first dense broadband seismic coverage of this region the spectra of p and sh waves for regional earthquakes are inverted for path averaged attenuation operators between 0 5 and 20 hz along with earthquake source parameters these measurements fit waveforms significantly better when the frequency dependence of q is taken into account and in the mantle frequency dependence lies close to laboratory values inverting these measurements for spatial variations in q reveals a highly attenuating wedge with q 500 assuming frequency dependence comparison with p results shows that attenuation in bulk modulus is negligible within the low q wedge as expected for thermally activated attenuation mechanisms bulk attenuation is significant in the overlying crust and subducting plate indicating that q must be controlled by other processes the shallowest part of the wedge shows little attenuation as expected for a cold viscous nose that is not involved in wedge corner flow overall the spatial pattern of q beneath alaska is qualitatively similar to other subduction zones although the highest wedge attenuation is about a factor of 2 lower the q values imply that temperatures exceed 1200 c in the wedge on the basis of recent laboratory based calibrations for dry peridotite these temperatures are 100 150 c colder than we infer beneath japan or the andes possibly explaining the absence of arc volcanism in central alaska

attenuation tomography in the western central andes a detailed insight into the structure of a magmatic arc high quality data from 1498 local earthquakes recorded by the pisco 94 proyecto de investigation sismologica de la cordillera occidental 1994 and ancorp 96 andean continental research project 1996 temporary seismological networks allowed the detailed determination of the three dimensional 3 d attenuation structure qp 1 beneath the recent magmatic arc in the western central andes 20 to 24 s assuming a frequency independent qp 1 in a frequency band between 1 and 30 hz whole path attenuation t was estimated from the amplitude spectra of the p waves using spectral ratios and a spectral inversion technique the damped least squares inversion tomography of the data reveals a complex attenuation structure crust and mantle of the forearc and subducting slab are generally characterized by low attenuation qp 1000 crust and mantle beneath the magmatic arc show elevated attenuation the strongest anomaly of extremely low qp is found in the crust between 22 and 23 s beneath the recent volcanic arc qp 100 n s variations can be observed the western flank of the crustal attenuation anomaly follows the curved course of the volcanic front north of 21 s the attenuation is less developed in the northern part of the study area the low qp zone penetrates in the forearc mantle down to the subducting slab in the south a deeper zone of high attenuation is resolved between 23 and 24 s directly above the subducting slab low qp in the mantle correlates with earthquake clusters the strong crustal attenuation is confined to the distribution of young ignimbrites and silicic volcanism and is interpreted as a thermally weakened zone with partial melts the attenuation pattern in the upper mantle might reflect the variable extent of the asthenosphere and maps variations of subduction related hydration processes in the mantle wedge from slab derived fluids

seismic evidence for fluids in fault zones on top of the subducting cocos plate beneath costa rica summary in the 2005 ticocava explosion seismology study in costa rica we observed crustal turning waves with a dominant frequency of 10 hz on a linear array of short period seismometers from the pacific ocean to the caribbean sea on one of the shot records from shot 21 in the backarc of the cordillera central we also observed two seismic phases with an unusually high dominant frequency 20 hz these two phases were recorded in the forearc region of central costa rica and arrived 7 s apart and 30 40 s after the detonation of shot 21 we considered the possibility that these secondary arrivals were produced by a local earthquake that may have happened during the active source seismic experiment such high frequency phases following shot 21 were not recorded after shots 22 23 and 24 all in the backarc of costa rica which might suggest that they were produced by some other source however earthquake dislocation models cannot produce seismic waves of such high frequency with significant amplitude in addition we would have expected to see more arrivals from such an earthquake on other seismic stations in central costa rica we therefore investigate whether the high frequency arrivals may be the result of a deep seismic reflection from the subducting cocos plate the timing of these phases is consistent with a shear wave from shot 21 that was reflected as a compressional s p and a shear s s wave at the top of the subducting cocos slab between 35 and 55 km depth the shift in dominant frequency from 10 hz in the downgoing seismic wave to 20 hz in the reflected waves requires a particular seismic structure at the interface between the subducting slab and the forearc mantle to produce a substantial increase in reflection coefficients with frequency the spectral amplitude characteristics of the s p and s s phases from shot 21 are consistent with a very high v p v s ratio of 6 in 5m thick slab parallel layers this result suggests that a system of thin shear zones near the plate interface beneath the forearc is occupied by hydrous fluids under near lithostatic conditions the overpressured shear zone probably takes up fluids from the downgoing slab and it may control the lower limit of the seismogenic zone

qp melting temperature relation in peridotite at high pressure and temperature attenuation mechanism and implications for the mechanical properties of the upper mantle the anelastic properties of compressional waves in a peridotite have been determined in the laboratory at sufficiently high temperatures to 1280 c and pressures to 0 73 gpa to warrant comparison with seismic measurements of the earth a substantial decrease of qp is observed at temperatures well below the onset of partial melting qp systematically increases with increasing pressure over the entire temperature range of major significance is the finding that qp is dependent on the ratio of the temperatures to the melting solidus temperature i e qp depends on the homologous temperature the pressure dependence of qp appears through the pressure dependence of the solidus of the peridotite within the uncertainties of measurement of both qp and the phase diagram it appears that melting and high temperature anelastic properties have a common origin in peridotite the homologous temperature dependence of qp suggests that we may estimate the temperature and pressure dependence of qp for peridotites of different compositions and possibly even for hydrous peridotites if solidus temperatures are known as a function of pressure a far easier measurement than elastic and anelastic properties the activation volume of qp is greatly reduced at high pressure since the slope of solidus versus pressure rapidly decreases with increasing pressure pressure dependence of seismic velocity and melt fraction in peridotite also appears to be related to the homologous temperature the qp homologous temperature relation suggests a connection between qp and the properties of the grain boundaries that is the major loss of seismic energy occurs at the grain boundaries grain boundary relaxation or high temperature background attenuation is a possible mechanism for the grain boundary damping no frequency dependence of qp is resolved 0 0 2 in qp f over the pressure temperature and frequency ranges of the measurement the present results and the model of grain boundary relaxation suggest that an appropriate choice of grain size may give an ultrasonic q that is applicable to the earth experimentally determined anelastic properties of a peridotite are critical for modeling mechanical properties of the upper mantle implications of the results are as follows 1 seismic data commonly interpreted as indicating a partially molten asthenosphere may instead reflect a hot solid asthenosphere at 90 100 of the solidus temperature 2 partial melting may not produce any abrupt change of seismic velocity and q rather elastic and anelastic properties of the upper mantle will change gradually at the boundary where the geotherm crosses the solidus 3 there may be no sharp mechanical boundary between the lithosphere and the asthenosphere

transient rheology of the upper mantle beneath central alaska inferred from the crustal velocity field following the 2002 denali earthquake the m7 9 2002 denali earthquake alaska is one of the largest strike slip earthquakes ever recorded the postseismic gps velocity field around the 300 km long rupture is characterized by very rapid horizontal velocity up to 300 mm yr for the first 0 1 years and slower but still elevated horizontal velocity up to 100 mm yr for the succeeding 1 5 years i find that the spatial and temporal pattern of the displacement field may be explained by a transient mantle rheology representing the regional upper mantle as a burghers body 1 infer steady state and transient viscosities of 1 2 8 x 10 18 pa s and 2 1 0 x 10 17 pa s respectively corresponding to material relaxation times of 1 3 and 0 05 years the lower crustal viscosity is poorly constrained by the considered horizontal velocity field and the quoted mantle viscosities assume a steady state lower crust viscosity that is 7 1 systematic bias in predicted versus observed velocity vectors with respect to a fixed north america during the first 3 6 months following the earthquake is reduced when all velocity vectors are referred to a fixed site this suggests that the post denali gps time series for the first 1 63 years are shaped by a combination of a common mode noise source during the first 3 6 months plus viscoelastic relaxation controlled by a transient mantle rheology

fault patterns associated with extensional fault propagation folding abstract extensional fault propagation drape folds are a common type of structure in rift basins and a number of oil and gas fields produce from these structures the detailed geometry and trap volumes are dependent on the relationship between the basement faults and the overlying folds and associated secondary faults in the sedimentary cover experimental models were used to study the 3 d geometry and secondary fault patterns of drape folds associated with single faults and two or more intersecting faults two layer clay models consisting of stiff and soft clay were used to model the deformation zones in the basement and sedimentary cover respectively extension on single basement faults normal to the direction of extension results in the development of a deformation zone with expanding width in which the fault density initially increases and then remains approximately constant extension on terminating faults results in conical drape folds with faults oblique to the fold axis along the propagating tip basement faults oblique to the direction of extension are characterized by oblique secondary faults along the boundaries of the deformation zone which curve into a direction normal to the extension direction in the center trapdoor fault geometries associated with two or more intersecting faults result in a triangular uplift with maximum relief at the apex the difference in relief between the flanks and the apex is greatest in the case of propagating basement faults en echelon secondary faults initiate on the flanks and extend into the apex area curving into orientations that are closer to normal to the regional direction of extension the width of the fault zone and the total fault length increase with increasing extension the fault density initially increases and then remains approximately constant with increasing extension

inverse modeling for possible rather than unique solutions abstract despite the implementation of several kinematic and mechanical models for fault related folding and the incorporation of structural uncertainty in geological models structural modeling is still too deterministic the current focus is on forward modeling of a unique fit we show the application of trishear inverse modeling global optimization and markov chain monte carlo mcmc methods to a clay model of basement involved compressional faulting from which we know both total and incremental deformation global optimization and mcmc methods provide a range of possible models rather than a unique fit total inversions give an average of the model s deformation while incremental inversions are more physically related to the model s evolution global optimization identifies the full range of possible models while mcmc characterizes expected parameter values and their uncertainties structural inversions without sound geology are meaningless a robust stratigraphy geomorphic markers mesoscopic structures analogue and mechanical modeling can all greatly improve the inversions

experimental models of extensional forced folds we have used single layer and multilayer clay models to study the development of forced folds above normal faults our modeling results show that the deformation patterns associated with extensional forced folding depend on the dip of the underlying normal fault and the presence of layer parallel detachments in single layer clay models extensional forced folds are upward widening monoclines anticlinal axial surfaces dip in the same direction as underlying master normal faults and synclinal axial surfaces dip in the opposite direction of master normal faults most secondary faults are upward steepening normal faults if master normal faults are steeply dipping however many secondary normal faults become high angle reverse faults at shallow depths the propagation and linkage of secondary faults into through going normal faults terminates the development of extensional forced folds more folding occurs prior to fault linkage if the master normal fault is steeply dipping rather than gently dipping most dipping beds and secondary faults are preserved in the hanging walls of the through oing normal faults in multilayer clay models with layer parallel detachments extensional forced folds are also upward widening monoclines slip on the lowest detachment laterally transfers extension induced by normal faulting and forced folding from the master normal fault to the detachment edge slip on overlying detachments accommodates minor thickness changes associated with upward widening of the fold secondary faults include low angle normal faults near the anticlinal axial surface minor thrust faults near the synclinal axial surface and high angle normal faults above the detachment edge the model predicted deformation patterns are similar to those of extensional forced folds from the gulf of suez and offshore norway this similarity suggests that our modeling results apply to extensional forced folds and can provide guidelines for interpreting field well and seismic data

grain size sensitive seismic wave attenuation in polycrystalline olivine 1 in order to investigate the processes responsible for the attenuation of seismic shear waves in the earth s upper mantle four olivine polycrystals ranging in mean grain size d from 3 to 23 m have been fabricated characterized and mechanically tested in torsion at high temperatures and seismic frequencies both the shear modulus which governs the shear wave speed vs and the dissipation of shear strain energy q 1 have been measured as functions of oscillation period to temperature t and for the first time grain size at sufficiently high t all four specimens display similar absorption band viscoelastic behavior adequately represented for 1000 t 1200 or 1300 c and 1 to 100 s by the expression q 1 a tod 1 exp e rt with a 7 5 102 s m 0 26 and e 424 kj mol 1 this mildly grain size sensitive viscoelastic behavior of melt free polycrystalline olivine is attributed to a combination of elastically and diffusionally accommodated grain boundary sliding the latter becoming progressively more important with increasing t and or to extrapolation to the larger mm cm grain sizes expected in the earth s upper mantle yields levels of dissipation comparable with those observed seismologically implying that the same grain size sensitive processes might be responsible for much of the observed seismic wave attenuation the temperature sensitivity of vs is increased substantially by the viscoelastic relaxation allowing the lateral variability of wave speeds to be associated with relatively small temperature perturbations

grain size distribution in the mantle wedge of subduction zones 1 mineral grain size plays an important role in controlling many processes in the mantle wedge of subduction zones including mantle flow and fluid migration to investigate the grain size distribution in the mantle wedge we coupled a two dimensional 2 d steady state finite element thermal and mantle flow model with a laboratory derived grain size evolution model in our coupled model the mantle wedge has a composite olivine rheology that incorporates grain size dependent diffusion creep and grain size independent dislocation creep our results show that all subduction settings lead to a characteristic grain size distribution in which grain size increases from 10 to 100 m at the most trenchward part of the creeping region to a few centimeters in the subarc mantle despite the large variation in grain size its effect on the mantle rheology and flow is very small as 90 of the deformation in the flowing part of the creeping region is accommodated by grain size independent dislocation creep the predicted grain size distribution leads to a downdip increase in permeability by 5 orders of magnitude this increase is likely to promote greater upward migration of aqueous fluids and melts where the slab reaches 100 km depth compared with shallower depths potentially providing an explanation for the relatively uniform subarc slab depth seismic attenuation derived from the predicted grain size distribution and thermal field is consistent with the observed seismic structure in the mantle wedge at many subduction zones without requiring a significant contribution by the presence of melt

complex patterns of fluid and melt transport in the central andean subduction zone revealed by attenuation tomography abstract we present a high resolution 3 d model of p wave attenuation q p 1 for the central andean subduction zone data from 1500 mostly intermediate depth 60 250 km earthquakes recorded at three temporary seismic networks covering the forearc arc and backarc around 23 s were used for tomographic inversion the forearc is characterised by uniformly high q p values indicating low temperature rocks in accordance with low surface heat flow values prominent low q p anomalies are found beneath the magmatic arc and the backarc in the crust and mantle continuous regions of low q p connect earthquake clusters at 100 km and 200 km depth with zones of active volcanism in the arc and backarc fluids fluxed from the subducted oceanic lithosphere into the overlying mantle wedge where they induce melting explain our observations we propose that low q p regions indicate source and ascent pathways of metamorphic fluids and partial melts ascent of fluids and melts as imaged by seismic q p are not vertical as is often implicitely assumed instead sources of fluids are located at different depth levels and ascent paths are complex and exhibit significant variation within the study area the largest quaternary backarc volcano cerro tuzgle is fed by mantle melts which are imaged as a plume of low q p material that reaches to the strong earthquake cluster at 200 km depth

high frequency borehole seismograms recorded in the san jcinto fault zone southern california part 2 attenuation and site effects we examine surface and downhole p and s wave spectra from local earthquakes recorded at two borehole seismometer arrays knw bh and pfo bh installed in the southern california batholith region of the san jacinto fault zone by the u s geological survey to assess the influence of the weathered layer on the spectral content of high frequency 2 to 200 hz seismic signals earthquake signals recorded downhole at both sites show significantly improved seismic bandwidth due to both a reduction in ambient noise levels and especially to dramatically increased levels of high frequency signal significant seismic signal is observed up to approximately 190 hz for p waves at knw bh stacked spectral ratios from these signals indicate that the highly weathered near surface between 0 and 150 m at knw bh and pfo bh exerts a much larger influence on seismic signals than deeper between 150 and 300 m material modeling of uphole downhole spectral ratio data suggests q 6 5 and q 9 between 0 and 150 m increasing to q 27 and q 26 between 150 and 300 m an outcrop mounted anza network station deployed approximately 0 4 km from knw bh displays roughly similar high frequency content to the knw bh downhole sensors but it exhibits spectra that are significantly colored by directional resonances low q and low velocity near surface material forms a lossy boundary layer at these borehole sites that is advantageous to the high frequency downhole environment not only are noise levels reduced but reflections from the surface and near surface are greatly attenuated as a result high frequency recordings from below the weathered zone more nearly resemble those recorded in a whole space than would otherwise be expected