tomography study of the upper mantle around the tesz based on passeq experiment data abstract we present a detailed velocity perturbation model of the earth s upper mantle in the area around the trans european suture zone tesz imaged by the teleseismic tomography the model is based on 12473 p wave arrival times measured on recordings of 273 stations of the passive seismic experiment passeq which was active during 2006 and 2008 station and teleseismic event distribution is sufficient to resolve the structure below the passeq array down to a depth of 350 km the velocity perturbation model clearly shows a 250 km thick uniform layer of positive velocity perturbations north east of the teisseyre tornquist zone ttz and 150 km thick layer south west of the ttz characterized by relatively lower velocity perturbations the former we associate with the precambrian mantle lithosphere of the european plate while the latter represents the much younger phanerozoic lithosphere in the uppermost layer of the model 40 km the boundary between the two regions closely follows the crustal trace of the ttz in deeper layers the boundary shifts south westward at a depth of approximately 120 km the region with positive perturbations reaches the northern part of the bohemian massif bm the shift suggests that the phanerozoic part of the european plate thrusts over the precambrian lithosphere the upper mantle below a depth of 250 km lacks the pronounced division between the two regions around the tesz which allows us to associate these depths with asthenospheric part of the upper mantle

lithospheric structure beneath the zagros collision zone resolved by non linear teleseismic tomography the upper mantle structure across the zagros collision zone in southwest iran is investigated using a non linear weighted damped least squares teleseismic tomography approach the resolution of the structures transitions in the upper mantle is enhanced significantly by correcting the teleseismic relative arrival time residuals for an a priori crustal velocity model and then performing the inversion with fixed crustal blocks to investigate whether or not the lithospheric blocks and major transitions in the resulting model are required by the data or are artefacts of the inversion the data were inverted using two different inverse methods singular value decomposition and a quadratic programming method new high quality seismic velocity models show apparent correlation between surface geological features and seismic velocity structures at lithospheric depth across the zagros collision zone the image shows a sharp lithospheric boundary at the main zagros thrust between 100 km and 250 km depth with p wave velocity about 3 per cent faster within the arabian shield to the south a step like increase in lithospheric thickness across the zagros collision zone is assumed to separate two different mantle structures namely the arabian to the south and the eurasian to the north domains the most striking feature resolved is a north dipping slab like positive velocity anomaly

simulated annealing inversion of teleseismic p wave slowness and azimuth for crustal velocity structure at long valley caldera simulated annealing a non linear global search algorithm is used to invert teleseismic p wave slowness and azimuth data for crustal velocity structure synthetic tests show that simulated annealing is able to locate low p wave velocity zones with reasonable accuracy in space and recovers almost 70 of the target velocity perturbations testing suggests that significant results can be obtained with as few as two stations inversion of ray direction data from long valley caldera finds an asymmetrical low velocity zone beneath the resurgent dome at 8km depth having a perturbation of 25 from the background this zone extends to the east and south to depths of at least 24km with a perturbation of about 10 these features generally agree with previous results from teleseismic travel time inversion and forward modeling of ray direction and are probably associated with the residual long valley caldera magma chamber

reanalysis of s to p amplitude ratios for gross attenuation structure long valley caldera california because of the strong interest in the magmatism and volcanism at long valley caldera eastern california and because of recent significant improvements in our knowledge of the caldera velocity structure and earthquake locations i have reanalyzed the local earthquake s to p amplitude ratio data of sanders 1984 for the gross three dimensional attenuation structure of the upper 10 km of long valley caldera the primary goals of the analysis are to provide more accurate constraints on the depths of the attenuation anomalies using improved knowledge of the ray locations and an objective inversion procedure the new image of the high s wave attenuation anomaly in the west central caldera suggests that the top of the principal anomaly is at 7 km depth which is 2 km deeper than previously determined because of poor resolution in much of the region some of the data remain unsatisfied by the final attenuation model this unmodeled data may imply unresolved attenuation anomalies perhaps small anomalies in the kilometer or two just above the central caldera anomaly and perhaps a larger anomaly at about 7 km depth in the northwest caldera or somewhere beneath the mono craters the central caldera s wave attenuation anomaly has a location similar to mapped regions of low teleseismic p wave velocity crustal inflation reduced density and aseismicity strongly suggesting magmatic association

imaging a crustal low velocity layer using reflected seismic waves from the 2014 earthquake swarm at long valley caldera california the magmatic system roof

teleseismic tomography of the southern tyrrhenian subduction zone new results from seafloor and land recordings 1 teleseismic traveltime data recorded by temporary ocean bottom seismographs deployed in tyrrhenian sea around the aeolian islands tyrrhenian deep sea experiment tyde have been used for the first time in italy to refine the 3 d model for the deep p wave velocity structure of the southern tyrrhenian subduction zone the arrival times of 35 teleseisms have been combined with those recorded by the italian national network in order to obtain a more complete azimuthal coverage of teleseismic rays 80 events recorded by land stations from 1990 to 2002 have been included in the data set in total 2904 p and 314 pkpdf phases 1300 recorded by ocean bottom instruments have been collected the upper mantle structure is reconstructed down to 500 km by a nonlinear inversion of the relative residuals computed with respect to the reference 1 d velocity model ak135 the obtained tomographic model has a higher resolution than those previously published thanks to the recordings of tyde seafloor stations tomographic results confirm the presence of the tyrrhenian slab imaged as a high velocity body extending from the uppermost mantle down to the bottom velocity model with dip 70 75 nw the model better defines the geometry of the seismogenic part of the slab its lateral extension is about 200 km in the depth interval 150 300 km where most of the deep seismicity is concentrated at uppermost mantle depths the fast structure has smaller lateral dimensions about 100 km the inversion also points out a wide well resolved low velocity zone completely surrounding the steeply dipping fast structure from the lower crust down to about 300 km this feature suggests the presence of a three dimensional circulation of asthenospheric flow around the ionian slab caused by retreat and roll back of the slab our results are in agreement with recent laboratory experiments mantle anisotropy studies geochemical and isotopic analyses and modeling based on residual topography

finite difference calculation of traveltimes in three dimensions the traveltimes of first arriving seismic rays through most velocity structures can be computed rapidly on a three dimensional numerical grid by finite difference extrapolation head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 11 percent are found between the results of this technique and ray tracing for a complex but smooth model this scheme has proven useful for earthquake location and shows promise as an inexpensive well behaved substitute for ray tracing in forward modeling and kirchhoff inversion applications

the geophysics of a restless caldera long valley california at 9 33 pdt on the morning of may 25 1980 a strong earthquake of local magnitude ml 6 1 heralded the onset of an earthquake sequence that focused worldwide attention on the major geologic and tectonic fea ture nearest its epicenter the long valley caldera of eastern california this sequence included two additional ml 6 events on may 25 and a fourth ml 6 event on may 27 accompanied by more than 300 ml 3 aftershocks over the next several weeks all of which were located either within or to the south of the caldera uhrhammer ferguson 1980 cramer toppozada 1980 these were not the first major events to occur regionally within the last decade the october 4 1978 bishop event m l 5 7 located some 20 km to the southeast of long valley initiated a sequence of swarm like activity that migrated generally toward the caldera over the next two years ryall ryall 1980 van wormer ryall 1980 in fact van wormer ryall 1980 in a manuscript written prior to the may 1980 earthquakes identified this sequence of events as a

origin of the deccan trap flows at mahabaleshwar inferred from nd and sr isotopic and chemical evidence abstract the deccan flows at mahabaleshwar are divisible into a lower and an upper group based on nd and sr isotopic ratios which define two correlated trends this distinction is supported by incompatible element ratios and bulk compositions the data reflect contamination in a dynamic system of magmas from an lil depleted e juv 8 mantle by two different negative e juv endmembers one undoubtedly continental crust the other either continental crust or enriched mantle the depleted mantle source anomalously high in 87 sr 86 sr may have been in the subcontinental lithosphere or a region of rising indian ocean morb mantle

novel anisotropic teleseismic body wave tomography code anitomo to illuminate heterogeneous anisotropic upper mantle part ii application to data of passive seismic experiment lapnet in northern fennoscandia seismic anisotropy provides a unique constraint on the past and present dynamics of the lithosphere and sublithospheric mantle to contribute to studies of large scale tectonic fabric we have developed code anitomo for regional anisotropic tomography anitomo allows us to invert simultaneously relative traveltime residuals of teleseismic p waves for 3 d distribution of isotropic velocity perturbations and velocity anisotropy in the upper mantle weak hexagonal anisotropy with the symmetry axis oriented generally in 3 d is considered the first application of novel code anitomo to data from passive seismic experiment lapnet results in a model of anisotropic velocities of the upper mantle beneath northern fennoscandia we have opted for northern fennoscandia for the first application because it is a tectonically stable precambrian region with a thick anisotropic mantle lithosphere without significant thermal heterogeneities we carefully analyse the distribution of the rays to limit the fully anisotropic inversion only to the volume with the sufficient directional ray coverage capability of the given inversion setup to reveal large scale anisotropic structures in the upper mantle is documented by a series of synthetic tests the strongest anisotropy and the largest velocity perturbations concentrate at depths corresponding to the mantle lithosphere while in deeper parts of the tomographic model the lateral variations are insignificant we delimit regions of laterally and vertically consistent anisotropy in the mantle lithospheric part of the model we attribute the retrieved domain like anisotropic structure of the mantle lithosphere in northern fennoscandia to preserved fossil fabrics of the archean microplates accreted during the precambrian orogenic processes

shrimp u pb zircon geochronology of the fuping complex implications for formation and assembly of the north china craton abstract the fuping complex located within the central zone of the north china craton is composed of amphibolite to granulite facies orthogneisses interleaved with minor supracrustal rocks at similar metamorphic grade the oldest components recognised are hornblende gneiss enclaves within the predominant biotite orthogneiss which have a shrimp u pb zircon age of 2708 8 ma we consider these enclaves to represent fragments of 2 7 ga continental materials incorporated in the biotite gneiss the biotite gneiss has a shrimp u pb zircon age of 2513 12 ma interpreted to be time of magmatic crystallisation of the igneous precursor based on the igneous characteristics of the zircons this indicates a major magmatic episode at 2 52 ga in the fuping complex identical to the age of felsic volcanism within the low grade wutai complex which crops out immediately to the west a gneissic granite that intrudes the biotite gneisses has a poorly defined 207pb 206pb age of 2045 64 ma this is within error of the age of 2097 46 ma obtained from a fine grained gneiss interlayered with amphibolite of the wanzi supracrustal suite wss interpreted to be volcanic in origin zircons from both these samples have strong oscillatory zoning and provide the first indication of a palaeoproterozoic magmatic event in the area again similar in age to magmatic events recently recognised in the adjacent wutai complex these data indicate a comparable history for the fuping and wutai complexes and support geochemical evidence that they had a common origin and formed part of a late archaean arc affected by later palaeoproterozoic re activation low uranium zircons without oscillatory zoning separated from a sample of biotite gneiss yield data clustered at 1817 26 ma which is interpreted to reflect a period of new zircon growth during a major metamorphic event these data support the recently proposed tectonic model that amalgamation of the north china craton occurred due to collision of the eastern and western blocks along the central zone at 1 8 ga ago

high resolution teleseismic body wave tomography beneath se romania ii imaging of a slab detachment scenario summary non linear teleseismic bodywave tomography with data of the 1999 calixto field experiment carpathian arc lithosphere x tomography in romania provides high resolution imaging of the upper mantle structure in this paper we present the relative p wave velocity distribution of the lithosphere asthenosphere system smearing from strong crustal velocity anomalies into the upper mantle is successfully suppressed by traveltime corrections with an a priori 3 d regional crustal velocity model see martin et al 2005 herein referenced as paper 1 our high resolution image shows a high velocity body beneath vrancea and the moesian platform with a ne sw orientation between 70 and 200 km depth beneath 200 km a change in the orientation from ne sw to n s can be observed the body reaches a maximum depth of about 350 370 km the velocity perturbation is maximal between 110 and 150 km depth 5 2 5 8 per cent and almost constant for depths beneath 200 km 3 2 3 8 per cent as most authors of previous studies agree on miocene subduction along the arc followed by soft continental collision we interpret the high velocity body as the subducted yet not fully detached slab the ne part of the slab appears to be mechanically coupled to the moesian lithosphere and hosts the intermediate depth seismicity in contrast the aseismic sw part is interpreted as decoupled from the overlying lithosphere and torn off from the underlying lithospheric material beneath 200 km depth low velocity anomalies nw of the slab above 110 km depth are interpreted as a shallow asthenospheric upwelling further low velocity anomalies are in agreement with a lithosphere asthenosphere boundary at 110 150 km depth below the moesian platform and deeper than 200 km under the east european platform eep the tomographic images support models proposing slab rollback during subduction collision followed by slab steepening and lithospheric delamination the different degrees of mechanical coupling of the slab to the overlying lithosphere allow to understand the loci of seismicity as volumes of stress concentration independent on the specifics of data interpretation our high resolution image is a novel contribution to understand the process of ongoing lithospheric detachment associated with strong intermediate depth seismicity in se romania

upper crustal structure of the yellowstone caldera from seismic delay time analyses and gravity correlations the 1978 yellowstone snake river plain seismic experiment provided detailed refraction data that were recorded across a two dimensional array of seismographs in yellowstone national park a delay time analysis was applied to 173 crystalline basement pg arrivals from these data to determine the three dimensional distribution of velocities and the layer configuration of the upper crust beneath the yellowstone caldera the p wave velocity structure of the caldera is characterized by a surface layer of combined sediments and rhyolite flows averaging 2 8 km s that range in thickness from 1 5 to 2 0 km adjacent to the caldera the crystalline upper crustal layer has a velocity of 6 05 0 01 km s but this layer decreases by 6 to 5 70 km s beneath the caldera and extends northeast 15 km beyond the caldera smaller zones of very low p velocity 4 0 km s a 30 velocity reduction compared to the 6 05 km s layer occur in the upper crust beneath the northeastern caldera rim and beneath the southwest caldera in the vicinity of the upper and midway geyser basins a three dimensional gravity interpretation based upon densities derived from the seismic model suggests that the regional gravity low of 60 mgal over the caldera correlates directly with 1 the surface layer of combined sediments and rhyolite flows 2 the low velocity 5 7 km s upper crustal layer and 3 the 4 0 km s low velocity zone beneath the northeastern caldera rim an interpretation of the seismic velocities and densities based on experimental data and theoretical models suggests that the 6 05 km s 2 70 g cm3 regional pg velocity is characteristic of crystalline basement rocks such as the precambrian granitic gneisses that are exposed north and south of the yellowstone caldera the 5 7 km s velocity layer 2 65 g cm3 is interpreted to be a 10 km thick hot body of granitic composition the 4 0 km s low velocity body 2 40 g cm3 beneath the northeastern caldera rim is associated with a local 20 mgal gravity anomaly with a range of interpretations from a large steam dominated system to a felsic body of 10 to 50 partial melt the postulated 4 0 km s low velocity layer beneath the southwestern caldera does not have a corresponding gravity signature and may reflect a zone of high seismic attenuation attributed to a saturated fracture zone this seismic velocity model of the yellowstone caldera suggests that the source of the quaternary silicic volcanic rocks corresponds to the 5 7 km s layer in the upper crust that appears to contribute the principal source of heat to the yellowstone hydrothermal systems the anomalous low velocity body in the northeastern caldera rim area may be a cupola of partial melt with an overlying vapor dominated carapace and may represent the waning stages of the third cycle of quaternary volcanism or the beginning of a new cycle of volcanism that will continue the northeastward progression of the silicic volcanism of the yellowstone snake river plain propagating system

non linear body wave teleseismic tomography along the tor array summary the tor project investigates the lithosphere asthenosphere structure under the tornquist zone between denmark and sweden around 150 seismic stations 108 short period 28 broadband and 14 other permanent stations were employed in a rectangular array along a 900 km long by 100 km wide strip across the tornquist zone from july 1996 to august 1997 the results obtained based on a non linear teleseismic tomography algorithm reveal significant p velocity variations up to 5 per cent along the tor array from northern germany to southern sweden distinct lithospheric blocks are also recognized in the inversion results two inverse methods singular value decomposition and a quadratic programming method were implemented in order to investigate whether or not the lithospheric blocks and major boundaries in the inversion are required by the data or are artefacts of the inversion according to the results the lithosphere under northern germany is thin but reaches to intermediate thicknesses of about 120 km in the tornquist zone area farther north in the baltic shield more than 200 km of continental lithosphere is recognized in the model abrupt lateral p velocity changes maximum 5 per cent are seen at both the southern and northern sides of the tornquist zone

shallow velocity structure and seismic site effects at arenal volcano costa rica abstract we use the spatial autocorrelation spac method with improved inversion algorithms to estimate the love and rayleigh dispersion curves at two sites at the west and northeast flanks of arenal volcano costa rica at the west flank site the rayleigh waves phase velocities vary from 765 m s 1 at 1 hz to 300 m s 1 at 12 hz and those of love waves between 780 and 295 m s 1 in the same frequency band at the northeast flank site the rayleigh wave velocities range from 1386 to 300 m s 1 and those of love from 1983 to 315 m s 1 from dispersion curves we derive shallow strong variations in amplitude of the spectral peaks are observed for the seismic events along two radial arrays these site effects are analysed using the h v spectral ratio method and s wave theoretical transfer functions results show that the wave amplifications are related to resonance effects of shallow structure when a resonance of the shallow layers occurs the correlation coefficients between close stations increase at the corresponding frequency the site effects may thus produce spurious results with the spac method the h v spectral ratio used in complement of the spac method can help detecting the site effects and testing the plane layer hypothesis furthermore the theoretical transfer functions calculated for the estimated velocity models is also useful to validate the models

temporal and three dimensional spatial analyses of the frequency magnitude distribution near long valley caldera california summary the 3 d distribution of the b value of the frequency magnitude distribution is analysed in the seismically active parts of the crust near long valley caldera california the seismicity is sampled in spherical volumes containing n 150 earthquakes and centred at nodes of a grid separated by 0 3 km significant variations in the b value are detected with b ranging from b 0 6 to b 2 0 high b value volumes are located near the resurgent dome and at depths below 5 km at mammoth mountain b values are found to be much lower south of the long valley caldera we interpret this to indicate that an active magma body has advanced from depths below 8 km to depths of 4 to 5 km beneath mammoth mountain in 1989 and that anomalous crust either highly fractured or containing unusually high pore pressure such as is the case in the vicinity of active magma bodies exists north of the seismically active area beneath the resurgent dome at all depths we also investigate the spatial distribution of temporal variations of the frequency magnitude distribution by introducing diverential b value maps b values increased from b 0 8 to b 1 5 underneath mammoth mountain at the onset of the 1989 earthquake swarm and remained high thereafter this suggests that an intrusion permanently altered the average distribution of cracks at 5 10 km depth or that the pore pressure permanently increased we propose that high b values are a necessary but not suycient condition near a magmatic body and therefore spatial b value mapping can be used to aid in the identification of active magma bodies

nonlinear teleseismic tomography at long valley caldera using three dimensional minimum travel time ray tracing the authors explore the impact of three dimensional minimum travel time ray tracing on nonlinear teleseismic inversion this problem has particular significance when trying to image strongly contrasting low velocity bodies such as magma chambers because strongly refracted and or diffracted rays may precede the direct p wave arrival traditionally used in straight ray seismic tomography they use a simplex based ray tracer to compute the three dimensional minimum travel time ray paths and employ an interative technique to cope with nonlinearity results from synthetic data show that their algorithm results in better model reconstructions compared with traditional straight ray inversions the authors reexamine the teleseismic data collected at long valley caldera by the u s geological survey the most prominent feature of their result is a 25 30 low velocity zone centered at 11 5 km depth beneath the northwestern quandrant of the caldera beneath this at a depth of 24 5 km is a more diffuse 15 low velocity zone in general the low velocities tend to deepen to the south and east the authors interpret the shallow feature to be the residual long valley caldera magma chamber while the deeper feature may represent basaltic magmas ponded in the midcrust the deeper position of the prominent low velocity region in comparison to earliermore tomographic images is a result of using three dimensional rays rather than straight rays in the ray tracing the magnitude of the low velocity anomaly is a factor of approximately 3 times larger than earlier models from linear arrival time inversions and is consistent with models based on observations of ray bending at sites within the caldera these results imply the presence of anywhere from 7 to 100 partial melt beneath the caldera 40 refs 1 fig 1 tab less

p wave deep velocity structure of the southern tyrrhenian subduction zone from nonlinear teleseismic traveltime tomography a new 3 d model for the p wave velocity structure of the southern tyrrhenian subduction zone stsz is determined from nonlinear inversion of relative arrival times of teleseismic events the data used in the imaging are the travel time residuals of both direct p and pk p df and secondary pp sp pcp pkp bc phases computed with respect to the global 1 d velocity model ak135 2308 teleseismic waveforms were collected for this study from 109 events recorded by the italian national seismic network rsnc during 1988 1998 the velocity perturbation field is reconstructed gradually by means an iterative sequence of linearized inversions incorporating a 3 d minimum travel time ray tracing the tomographic images reveal a broad high velocity zone dominating the pattern of lateral variations beneath the southern tyrrhenian sea and calabria this fast structure extends laterally for a maximum of 350 km from northern sicily to southern campania and vertically for at least 400 km from the uppermost mantle down to 500 km depth below 350 km the geometry of the depicted slab is characterized by horizontal deflection of the subducting lithosphere towards the central tyrrhenian basin

constraints on continued episodic inflation at long valley caldera based on seismic and geodetic observations 1 long valley caldera a large and potentially explosive silicic system has experienced highly anomalous continued inflation since late 1970s we characterize an episode of rapid episodic uplift occurring between 2002 and 2003 following similar episodes of 1979 1980 1983 1989 1990 and 1997 1998 this most recent episode was the first to be observed by a dense array of 13 continuous global positioning system gps stations similar to previously observed episodes of deformation uplift is quasi radially symmetric and is mostly explained by a compact pressure source located 3 km west of the resurgent dome the maximum uplift during the 2002 2003 episode is 35 8 mm about 1 3 the magnitude but with a similar time dependent behavior as the 1997 1998 episode the horizontal source location is well constrained at 118 930 37 678 for a small spherical source and indistinguishable from the location of a vertically dipping prolate spheroidal source a trade off between depth and volume change is observed for both spherical and prolate models with depth between 7 5 and 13 5 km and a volume change of 0 01 0 03 km3 at 95 confidence for prolate spheroidal models depth and volume change are additionally affected by the source axis ratio b a which is greater than 0 55 though the background seismicity remained low during the 2002 2003 episode we identified a significant spike in activity during the maximum rate of uplift similar to observations in both the much larger episodes in 1989 1990 and 1997 1998 more interestingly we additionally find that all three episodes begin immediately after a short period of seismic quiescence with background seismicity falling to levels below background levels following the prior uplift event with the dense gps coverage we also identify increased opening of the mono inyo volcanic chain after the 2002 2003 episode suggesting potential interaction of magmatic fluids between the two systems

velocity structure of the long valley caldera from the inversion of local earthquake p and s travel times a high resolution tomographic study of the long valley region began in 1989 with the installation of a special fan array of eight three component borehole 80 160 m depths receivers on the northwestern rim of the caldera to provide the data necessary for a joint inversion for hypocenters and the three dimensional p and s wave velocity structure in and below the caldera the experiment specifically targeted the subsurface location of the previously inferred magma chamber beneath the resurgent dome additional coverage was provided by existing u s geological survey and university of nevada reno seismographic networks we employed the progressive inversion scheme of thurber 1983 with cubic spline interpolation after michelini and mcevilly 1991 the final model is based on data from 280 well distributed local earthquakes some 6900 arrival times were used including about 700 s wave times from the three component stations the resulting velocity structure reflects the known geology defining the low velocity caldera fill to 2 km depth contrasting markedly with the surrounding higher velocity sierran block and highland terrane no isolated distinct low velocity anomalies are revealed beneath the caldera floor although a diffuse zone of reduced velocity persists to a depth of about 8 km these lower velocities may be related to hydrothermal alteration and or extensive fractures the vp vs structure contains significant lateral variation within and beneath the caldera to about 8 km depth and these variations can be related to accepted models of the active geothermal system the lack of a significant s wave velocity anomaly along with the normal or low values of the vp vs ratio argues against the presence of a sizable and distinct magma body at shallow to midcrustal depth beneath long valley caldera although a very low percentage of partial melt cannot be precluded

tomographic image of the southern california mantle p wave teleseismic travel time delays recorded by the southern california array are inverted by the method of backprojection tomography to obtain images of variations in the p wave velocity structure to a depth of 750 km two major upper mantle features arc resolved one beneath the transverse ranges region and another beneath the salton trough region the transverse ranges feature appears as a curtainlike east trending high velocity anomaly this feature is 60 km thick extends most deeply on its eastern end to 250 km and attains a maximum velocity 3 greater than average southern california mantle of the same depth the salton trough feature which is not as well resolved as the transverse ranges feature is composed of low velocities in the upper 70 100 km these p wave velocities arc depressed 3 4 compared to average southern california mantle tests of the inversion indicate the major aspects of the imaged structure are authentic

seismic tomography of the upper mantle beneath the north eastern bohemian massif central europe abstract we present a 3 d velocity model of the upper mantle beneath the northern and eastern parts of the bohemian massif bm based on data from passive seismic experiment bohema ii may 2004 june 2005 consisted of 35 temporary stations complemented by data of permanent observatories the resulting tomographic model with a variance reduction of 84 shows relatively small velocity variations both in size and in amplitude a small size high velocity perturbation in the eastern part of the model can be related to the complex structure beneath the sudetes moravo silesian unit contact similarly to results from the bohema i experiment in the western bm the presented model from bohema ii data confirms the north southward thickening of the lithosphere though in the upper mantle the low perturbations prevail some inconsistencies among the isotropic velocity perturbation model sp receiver function inferences and anisotropic models of the mantle lithosphere domains indicate that both the topography of the lithosphere asthenosphere boundary and internal velocity structure of the upper mantle beneath the bm can be complex we tested two regularization techniques truncated singular value decomposition and damped least square method results of which lead us to prefer the damped least square method the truncated singular value decomposition seems to be more sensitive to uneven ray geometry

crustal and upper mantle structure beneath the corinth rift greece from a teleseismic tomography study we report here the results of a tomographic lithospheric study in the area of the corinth and evvia rifts greece designed to constrain the mechanism of continental extension sixty seismological stations were deployed in the area for a period of 6 months and 177 teleseismic events were recorded by more than five stations and gave more than 2000 travel time residuals p and pkp phases which were inverted to image the velocity structure down to 200 km depth we use both a linear and a nonlinear method to invert the data set the main result is a long wavelength positive velocity anomaly located in the upper mantle which is interpreted as the subducted african lithosphere the subducted lithosphere is well defined from 7o km depth down to 200 km from synthetic tests as well as from the amplitude of the anomaly more than 7 we conclude that the subduction continues below 200 km in addition a second positive velocity anomaly of about 4 from the surface down to 40 km depth located north of the gulf of corinth has been found this is interpreted as the result of a crustal thinning of several kilometers 5 km shifted to the north from the gulf of corinth and trending obliquily nw se we suggest that this crustal thinning is mainly related to the miocene widespread extension in the aegean and that the quaternary corinth rift initiated where the crust was already thinned the different styles of deformation of the eastern and western part of the rift are consistent with this interpretation no clear velocity anomaly can be related to the evvia rift

constraints on the upper crustal structure of the long valley mono craters volcanic complex eastern california from seismic refraction measurements during the summers of 1982 and 1983 field work was completed on 10 new seismic refraction profiles in the long valley mono craters region located within the technically active zone between the eastern sierra nevada and the basin and range province the four profiles presented here sample the upper 7 10 km of the crust within the western half of long valley cladera the mono craters ring fracture system and the normal crust north and northeast of long valley the entire area shares a common crystalline basement consisting primarily of mesozoic granitic rocks at a depth of 2 km beneath the topographic surface the p wave velocity is uniformly 5 6 km s beneath which the velocity increases with a gradient of about 0 1 s 1 clear secondary arrivals observed on a profile crossing the west part of the caldera support evidence from 1972 seismic refraction profiles for a reflecting boundary at a depth of 7 8 km beneath the west margin of the resurgent dome which may represent the top of a magma chamber structural details resolved in the upper 2 km of the crust lead to the following conclusions 1 p wave velocities in the crystalline basement at depths shallower than 2 km vary from 3 6 to 5 0 km s this variation reflects differences in the degree of fracturing of the upper portion of the basement 2 an apparently homogeneous basement in the upper 7 10 km beneath the mono craters ring fracture system indicates that any extensive magma chamber must be at least 10 km deep there 3 the downdropped crystalline basement beneath the western half of long valley caldera dips genty 5 10 to the northeast apparent offsets along steeply dipping caldera bounding faults are 1 0 1 7 km along the northern western and southern sides of the caldera with largest offsets in the north 4 rocks forming the caldera fill fall into essentially three p wave velocity groups from the surface downward these velocity groups are 100 400 of 1 2 1 8 km s material corresponding to unconsolidated fluvial or lacustrine deposits or highly fractured rhyolite flows 200 400 m of 2 8 3 1 km s material corresponding to sparsely jointed postcaldera rhyolite rhyodacite and basalt flows and approximately 1000 m of 3 9 4 4 km s material corresponding to deposits of bishop tuff

tectonic geomorphology in the shanxi graben system northern china abstract the shanxi graben system is composed of a series of normal fault controlled basins which are arranged in an s shaped curve over a distance of about 1200 km active faults mainly trending nne ssw ne sw or ene wsw caused blocks to become rotated and tilted and river courses and terraces to become deformed volcanoes in the datong basin indicate that the formation of the shanxi graben system has a relationship to upper mantle activity and that the tectonic activity was intense during the middle pleistocene arrangement and movement of the faults indicates there has been right lateral shear in this area which may have resulted from the northward push of the qinghai tibet plateau

velocity variations in the uppermost mantle beneath the southern sierra nevada and walker lane we model pn waveforms from two earthquakes in the southwestern united states mammoth lakes california and western nevada to determine a velocity model of the crustal and mantle structure beneath the southern sierra nevada and walker lane we derive a one dimensional velocity model that includes a smooth crust mantle transition east of death valley and extending south into the eastern mojave desert west of death valley and toward the sierra nevada a low velocity mantle v p 7 6 km s directly below the crust indicates the lithosphere is absent at the base of this low velocity structure at 75 100 km depth the p wave velocity jumps discontinuously to v p 8 0 km s the area of low velocity is bounded by the garlock fault to the south and the sierra nevada to the west but we cannot resolve its northern extent however on the basis of teleseismic travel times we postulate that the anomaly terminates at about 38 n the presence of a low velocity upper mantle anomaly in this area agrees with geochemical research on xenoliths from the southern sierras and recent studies of receiver functions refraction profiles tomography and gravity however the velocity discontinuity at 75 100 km is a new discovery and may represent the top of the once present now unaccounted for and possibly sunken sierra nevada lithosphere

a method to allow temporal variation of velocity in travel time tomography using microearthquakes induced during hydraulic fracturing abstract hydraulic injections produce fluid filled fractures that reduce the seismic velocity of the rock compared to intact rock the travel times of microearthquakes induced by the injections may be used to discern changes in the rock velocities as well as locating the microearthquakes determining the volumes of rock where the velocities have changed provides indirect evidence for the location of the injected fluid and the character of the changes produced in the fractured rock available data are generally insufficient to resolve both the spatial and temporal changes within the rock to extract information about temporal changes and to obtain an improved image of the velocity structure we chose a parameterization scheme in which the velocities of each block are allowed to change from the background velocity only after a threshold number of microearthquakes have occurred in the block regularizing by constraining the velocity of all the altered blocks to be similar helps stabilize the inversion the regularization can be relaxed somewhat to allow the velocity of an altered block to be different from other altered blocks if the travel time data are compelling the parameterization scheme is justified since observations show that the volume of the seismically stimulated rock increases linearly with the volume of the injected fluid we applied the method to data collected in a region of precambrian crystalline rock that was injected with 21 600 m 3 of water we use travel times from a total of 3886 microearthquakes that were induced by the injection the mean rms travel time residual decreases about 7 the velocity structure contains a low velocity zone located near the injection region other distinct low velocity zones are identified the pattern of microearthquake locations found using our method appears to contain more structure than the pattern found in locations determined using a homogeneous velocity structure two clear low velocity regions found near the point where water was injected into the rock are separated by a region whose velocity did not change the region of unaltered velocity had a large number of microearthquakes

regional three dimensional seismic velocity model of the crust and uppermost mantle of northern california 1 we present a three dimensional 3d tomographic model of the p wave velocity vp structure of northern california we employed a regional scale double difference tomography algorithm that incorporates a finite difference travel time calculator and spatial smoothing constraints arrival times from earthquakes and travel times from controlled source explosions recorded at network and or temporary stations were inverted for vp on a 3d grid with horizontal node spacing of 10 to 20 km and vertical node spacing of 3 to 8 km our model provides an unprecedented comprehensive view of the regional scale structure of northern california putting many previously identified features into a broader regional context and improving the resolution of a number of them and revealing a number of new features especially in the middle and lower crust that have never before been reported examples of the former include the complex subducting gorda slab a steep deeply penetrating fault beneath the sacramento river delta crustal low velocity zones beneath geysers clear lake and long valley and the high velocity ophiolite body underlying the great valley examples of the latter include mid crustal low velocity zones beneath mount shasta and north of lake tahoe

three dimensional gravity modeling of the geologic structure of long valley caldera a 48 mgal gravity low coincides with long valley caldera and is mainly attributed to low density caldera fill gravity measurements by unocal geothermal have been integrated with u s geological survey data vastly improving gravity station coverage throughout the caldera a strong regional gravity trend is mainly attributed to isostasy a best fitting based on regional control of basement densities airy heiskanen isostatic model was used for the regional correction a three dimensional multiple unit gravity modeling program with iterative capabilities was developed to model the residual gravity the density structure of long valley caldera and vicinity was modeled with 22 discrete density units most of which were based on geologic units information from drill hole lithologies surface geology and structural geology interpretations constrain the model some important points revealed by the three dimensional gravity modeling are that 1 the volume of ejected magma associated with the bishop tuff eruption is greater than previously thought 2 the caldera structure is strongly influenced by precaldera topography and the extensions of major active faults 3 the main west ring fracture is coincident with the inyo domes mono craters fracture system 4 a relatively low density region probably underlies the caldera and 5 a silicic magma chamber may underlie devils postpile

tectonothermal history of the basement rocks in the western zone of the north china craton and its tectonic implications the basement of the north china craton can be divided into the eastern central and western zones based on lithological structural metamorphic and geochronological data the western zone comprises two different petrotectonic units archaean tonalitic trondhjemitic granodioritic ttg grey gneisses and metamorphic mafic rocks and palaeoproterozoic khondalite series the former is characterized by isobaric cooling ibc type anticlockwise p t paths in the north northwestern part of the zone and near isothermal decompression itd type clockwise p t paths in the eastern part adjacent to the central zone on the other hand the tectonothermal evolution of palaeoproterozoic khondalite series rocks is characterized exclusively by nearly isothermal decompression following the peak of metamorphism and then cooling defining clockwise p t paths the archaean ttg gneisses and associated mafic rocks with anticlockwise metamorphic p t paths reflects an origin related to underplating and intrusion of mantle derived magmas which may be derived from mantle plumes they represent a late archaean continental block in the western part of the north china craton the palaeoproterozoic khondalite series rocks represent passive continental margin deposits they were metamorphosed and deformed in the late palaeoproterozoic during the amalgamation of the western continental block with another continental block in the east part of the north china craton the itd type clockwise p t t paths of the palaeoproterozoic khondalite series rocks record the tectonothermal histories of the collision of the western and eastern continental blocks which resulted in the final assembly of the north china craton at c 1800 ma

p to s converted wave observations at long valley caldera we report observations of p to s converted teleseismic body waves recorded with seismic stations located on the resurgent dome of long valley caldera we observe strong conversions occurring at boundaries that could be the tops of small magma bodies at depths of 4 9 kilometers beneath the resurgent dome this technique could prove to be an extremely powerful tool in the search for magma bodies for geothermal energy development our results from a two month deployment of triggered digital teleseismic recorders are discussed

the p wave velocity structure of deception island antarctica from two dimensional seismic tomography abstract deception island is a volcanic island with a flooded caldera that has a complex geological setting in bransfield strait antarctica we use p wave arrivals recorded on land and seafloor seismometers from airgun shots within the caldera and around the island to invert for the p wave velocity structure along two orthogonal profiles the results show that there is a sharp increase in velocity to the north of the caldera which coincides with a regional normal fault that defines the northwestern boundary of the bransfield strait backarc basin there is a low velocity region beneath the caldera extending from the seafloor to 4 km depth with a maximum negative anomaly of 1 km s refracted arrivals are consistent with a 1 2 km thick layer of low velocity sediments and pyroclastites infilling the caldera synthetic inversions show that this layer accounts for only a small portion of the velocity anomaly implying that there is a significant region of low velocities at greater depths further synthetic inversions and melt fraction calculations are consistent with but do not require the presence of an extensive magma chamber beneath the caldera that extends downwards from 2 km depth

high pressure granulites in the sanggan area north china craton metamorphic evolution p t paths and geotectonic significance high pressure basic granulites are widely distributed as enclaves and sheet like blocks in the huaian ttg gneiss terrane in the sanggan area of the central zone of the north china craton four stages of the metamorphic history have been recognised in mineral assemblages based on inclusion exsolution and reaction textures integrated with garnet zonation patterns as revealed by compositional maps and compositional profiles the p t conditions for each metamorphic stage were obtained using thermodynamically and experimentally calibrated geothermobarometers the low ca core of growth zoned garnet along with inclusion minerals defines a prograde assemblage m1 of garnet clinopyroxene plagioclase quartz yielding 700 c and 10 kbar the peak of metamorphism at about 750 870 c and 11 14 5 kbar m2 is defined by high ca domains in garnet interiors and inclusion minerals of clinopyroxene plagioclase and quartz kelyphites or coronas of orthopyroxene plagioclase magnetite around garnet porphyroblasts indicate garnet breakdown reactions m3 at conditions around 770 830 c and 8 5 10 5 kbar garnet exsolution lamellae in clinopyroxene and kelyphites of amphibole plagioclase around garnet formed during the cooling process at about 500 650 c and 5 5 8 kbar m4 these results help define a sequential p t path containing prograde near isothermal decompression itd and near isobaric cooling ibc stages the clockwise hybrid itd and ibc p t paths of the hp granulites in the sanggan area imply a model of thickening followed by extension in a collisional environment furthermore the relatively high pressures 6 14 5 kbar of the four metamorphic stages and the geometry of the p t paths suggest that the hp granulites together with their host huaian ttg gneisses represent the lower plate in a crust thickened during collision the corresponding upper plate might be the tectonically overlying khondalite series which was subjected to medium to low pressure mp lp 7 4 kbar granulite facies metamorphism with a clockwise p t path including an itd segment both the hp and the mp lp granulite facies events occurred contemporaneously at c 1 90 1 85 ga in a collisional environment created by the assembly process of the north china craton

crustal structure beneath long valley caldera from modeling of teleseismic p wave polarizations and ps converted waves in this study the authors present new constraints on the nature of the low velocity zone beneath long valley caldera based on the measured propagation directions of teleseismic p waves and on modeling of p to s converted waves the low velocity body is a large asymmetrical volume which deepens to the east extending from depths of 7 to 30 km it contains lower velocities than originally proposed by earlier teleseismic studies in particular there is a tabular feature between 7 and 11 km depth that has a reduction in velocity of about 30 these low velocities imply a much greater percentage of melt in the crust beneath long valley caldera than previously estimated array analysis of large delayed arrivals identifies them to be ps converted waves from the shoulders and roof of this tabular zone these conversions bound the depth to the magma chamber roof to be within about 10 km of the surface these results are consistent with elements from several other studies and the authors present an integrated and improved model of crustal structure at long valley the concordance of the deeper low velocity zones with regional structural trends implies that the shallow low velocity feature is a cupola on topmore of an asymmetric diapiric ridge rising up from the migmatized lower crust of the basin and range the authors present two contrasting interpretations of the geometry of low velocity zones in the crust one implies a time invariant magma chamber and conduit system for long valley caldera the other implies an evolution of that system from a simple vertical regime to its current asymmetrical geometry 37 refs 19 figs 1 tab less

high resolution teleseismic body wave tomography beneath se romania i implications for three dimensional versus one dimensional crustal correction strategies with a new crustal velocity model summary the calixto carpathian arc lithosphere x tomography experiment offers a dense high quality data set to study the lithospheric asthenospheric system underneath se romania an earthquake prone region in se europe to increase the image resolution of structures in the uppermost mantle the application of crustal traveltime corrections by a priori information before the teleseismic traveltime inversion has become a well accepted procedure for such a correction we present a regional 3 d crustal seismic velocity model that serves as the basis for a high resolution teleseismic tomography forthcoming paper by martin et al our 3 d crustal model is based on recent research in the region we collect new results from two long range seismic refraction lines 3 d refraction tomography and teleseismic ps conversions adding previously published models of the sediment distribution conrad and moho depths as well as crustal seismic p wave velocities we compile a 3 d crustal model for se romania this 3 d model does not contain shallow small scale heterogeneities 10 km but it reflects the large scale structures such as variations in sediment thickness average seismic velocities and 3 d moho depth it is well suited for the correction of teleseismic traveltime residuals a prerequisite for a high resolution teleseismic tomography study for example traveltime delays of up to 1 3 s are caused by the almost 20 km thick layer of sediments in the focsani basin such delays are comparable to or larger in size than the expected upper mantle traveltime residuals we study the significance of 3 d crustal traveltime corrections relative to 1 d station corrections and show that the complex basin structures in se romania require a 3 d approach to reduce the smearing of crustal anomalies into the mantle by modelling synthetic mantle structures with a slab as it is expected for se romania we also investigate how to adapt the inversion strategy if crustal corrections are applied significant improvements are found by including the already corrected crustal layers in the inversion procedure thereby enabling the inversion algorithm to project still remaining uncertainties in the less resolved upper crustal layers however the fixing of the upper layers during the inversion due to the a priori knowledge of the crustal velocity anomalies clearly leads to smearing of uncorrected anomalies that are possibly located close to the crust mantle boundary

lithospheric structure of the tornquist zone resolved by nonlinear p and s teleseismic tomography along the tor array lithospheric structure of the tornquist zone resolved by nonlinear p and s teleseismic tompgraphy along the tor array

magmatic plumbing of a large permian caldera exposed to a depth of 25 km we report evidence for a 13 km diameter permian caldera associated with a renowned section through the continental crust comprising the ivrea verbano zone and serie dei laghi of northwest italy correlation of ages of volcanic and middle to deep crustal plutonic rocks suggests that they constitute an unprecedented exposure of a subcaldera magmatic plumbing system to a depth of 25 km and points to a cause and effect link between intrusion of mantle derived basalt in the deep crust and large scale silicic volcanism

influence of deccan volcanism synrift magmatism on the crust mantle structure and its implications for the seismogenesis of earthquakes occurring in the kachchh rift zone

p t t paths and tectonic history of an early precambrian granulite facies terrane jining district south east inner mongolia china abstract the widespread khondalite series of south east inner mongolia consists largely of biotite sillimanite garnet gneiss and quartzo feldspathic gneiss with some marble and mafic granulite layers it has experienced two metamorphic events at c 2500 and 1900 2000 ma a pre peak stage of the first metamorphism at t 600 700 c and p 6 7 kbar is recognized by the relict amphibolite facies assemblage ky grt bt pl qtz and protected inclusions of biotite hornblende sodic plagioclase and quartz in garnet or orthopyroxene the peak stage with t c 800 50 c and p 8 10 kbar is characterized by the widespread granulite facies assemblages sil grt bt kfs pl qtz in gneiss and opx cpx pl hbl grt in granulite the p t t path suggests that the supracrustal sequence was buried in the lower crust by tectonic thickening during d1 d2 the beginning of the second metamorphism is characterized by further temperature rise to 700 c or more at lower pressure this stage is manifested by the appearance of cordierite after garnet fibrolite sil2 after biotite in gneiss and transformation of hbl1 into opx2 and cpx2 in granulite coronas of symplectitic opx2 pl2 surrounding grt1 and cpx1 in mafic granulite are interpreted as products of near isothermal decompression the p t t path may be related tectonically to waning extension of the crust by the end of the early proterozoic

crust and upper mantle structure beneath western china from p wave travel time tomography 1 three dimensional velocity images of the crust and upper mantle beneath western china are obtained through seismic tomography by using p wave arrival times of local regional and teleseismic events recorded in chinese and kyrgyzstan seismic networks at shallow depths most mountain belts and tectonically elevated areas are imaged as higher velocities relative to adjacent sediment filled basins and foreland depressions with lower velocities at mid lower crust depths the kyrgyz tian shan is underlain by lower velocity material and a distinct low velocity zone in the south north direction is observed between the eastern and western parts of the chinese tian shan the moho of the southern tarim basin has a greater depth over 50 km in front of the western kun lun compared to the northern and western tarim basin lateral heterogeneity within the upper mantle is apparent at depths from 71 to 571 km the uppermost mantle beneath the kyrgyz tian shan altay qi lian and eastern kun lun is characterized by low velocity material that is probably related to the upwelling of hot mantle the lithospheric thickness varies from 120 to 170 km beneath the chinese tian shan and northern tibetan plateau to 200 250 km beneath the tarim basin deep coupling pattern of the chinese tian shan with adjacent provinces can be classified into the embedding detaching and sinking and underthrusting of lithospheric roots in addition the lithosphere of the northern edge of the tibetan plateau seems to be thickened in contrast to the central part of the northern plateau north dipping low velocities exist in the upper mantle between the tibetan plateau and provinces to its north which might indicate mantle flow from the tibetan plateau toward surrounding areas but it has been blocked by the thick tarim lithosphere

seismic velocity structure and earthquake relocation for the magmatic system beneath long valley caldera eastern california abstract a new three dimensional 3 d seismic velocity model and high precision location catalog for earthquakes between 1984 and 2014 are presented for long valley caldera and its adjacent fault zones in eastern california the simul2000 tomography algorithm is applied to derive the 3 d vp and vp vs models using first arrivals of 1004 composite earthquakes obtained from the original seismic data at the northern california earthquake data center the resulting vp model reflects geological structures and agrees with previous local tomographic studies the simultaneously resolved vp vs model is a major contribution of this study providing an important complement to the vp model for the interpretation of structural heterogeneities and physical properties in the study area the caldera is dominated by low vp anomalies at shallow depths due to postcaldera fill high vp and low vp vs values are resolved from the surface to 3 4 km depth beneath the center of the caldera corresponding to the structural uplift of the resurgent dome an aseismic body with low vp and high vp vs anomalies at 4 2 6 2 km depth below the surface is consistent with the location of partial melt suggested by previous studies based on vp models only and the inflation source locations based on geodetic modeling the sierran crystalline rocks outside the caldera are generally characterized with high vp and low vp vs values the newly resolved velocity model improves absolute location accuracy for the seismicity in the study area and ultimately provides the basis for a high precision earthquake catalog based on similar event cluster analysis and waveform cross correlation data the fine scale velocity structure and precise earthquake relocations are useful for investigating magma sources seismicity and stress interaction and other seismological studies in long valley

three dimensional velocity structure of the upper mantle beneath costa rica from a teleseismic tomography study summary a tomographic study has been carried out in costa rica utilizing teleseismic events recorded by the national seismic network ovsicori una the data consist of 130 earthquakes which occurred at epicentral distances of 23d 100d p phases and 110d 180d pkp phases 1378 iasp91 traveltime residuals were computed and inverted using an iterative linearized inversion procedure which incorporates 3 d minimum traveltime ray tracing the 3 d velocity structure of the upper mantle as derived from teleseismic tomography shows a northeastward dipping high velocity body beneath northern costa rica interpreted as the subducting cocos plate although less evident a similar pattern of lateral heterogeneities characterizes the deep structure of central costa rica there is no evidence for deep high velocity bodies beneath southern costa rica the 3 d reconstruction of the subducting cocos plate shows a steeply dipping slab subvertical beneath northern costa rica here the oceanic lithosphere is older and denser than in central costa rica where the slab dips at about 60d southern costa rica does not show a dipping slab this is in accordance with the subduction collision of the thick and buoyant cocos ridge the geometry of the slab the maximum velocity anomalies and the sudden change in the local seismicity depth pattern suggest the existence of a tear in the subducted plate located between the northern and central costa rican subduction zones the strain field in the overriding plate indicates a strong structural control induced by the along trench variations in subduction northern costa rica shows slight tensile deformation while southern costa rica displays moderate to strong compressive deformation the maximum horizontal gradient of the strain field is located in central costa rica where a sinistral transcurrent fault system crosses the country from the pacific to the atlantic coast this system is likely to be generated by the along trench variations in subduction

constraints on time dependent volcanic source models at long valley caldera from 1996 to 2009 using insar and geodetic measurements summary continuous monitoring of long valley caldera since the late 1970s including data from seismic and geodetic networks has shown renewed episodic unrest with accelerated uplift separated by reduced uplift no activity or slow deflation we examine the time dependent behaviour at long valley caldera from 1996 to 2009 by integrating insar and continuous gps cgps measurements the ers 1 2 radar data between 1996 and 2008 and reprocessed three component cgps data from the long valley gps network from 1996 to 2009 were combined to invert for source geometry and volume change for the following deformation episodes 1997 1998 uplift 2002 2003 uplift 2004 2007 slow subsidence and 2007 2009 slow uplift we employed non linear monte carlo random search approaches random cost and simulated annealing in our inversion and examined models including spherical and finite sources dipping prolate spheroid our results show that the sources of all post 2000 events i e 2002 2003 2007 2009 uplift and 2004 2007 subsidence locate at shallow depths of 6 8 km and have nearly identical surface locations suggesting that these events may be caused by the same source in the mid crust possibly a mixture of hydrothermal and partial melt magma all three events 2002 2003 2004 2007 2007 2009 are characterized by the low total volume change 0 01 0 003 0 006 km3 respectively with corresponding volume change rates of 0 007 0 001 0 002 km3 yr 1 the 1997 1998 inflationary event has a steeper source geometry and much greater volume change rate 0 03 km3 yr 1 than the other events in agreement with previous studies this suggests it is possibly driven by magma intrusion beneath the resurgent dome from a deeper source if we regard post 2000 events as proxies for future eruption hazard the inferred source dynamics e g mid crustal location and subdued volume change and accompanied decrease in earthquake activity from these post 2000 events suggest that the probability for near term eruption is low our study demonstrates that cgps along with insar provide a valuable tool for monitoring time dependent source processes at active volcanic regions

the tornquist zone a north east inclining lithospheric transition at the south western margin of the baltic shield revealed through a nonlinear teleseismic tomographic inversion from july 1996 to august 1997 the tor project operated 130 seismographs in north germany denmark and south sweden with the aim of collecting signals from local regional and teleseismic earthquakes this data set is particularly interesting since the seismic antenna crosses the most significant geological boundary in europe the tornquist zone which in the northern part is the border between the baltic shield and the younger european lithosphere previous studies have shown significant physical changes in the crust and upper mantle across this transition zone including two independent teleseismic tomographic studies of the tor data set but these two studies disagree on the orientation of the slope of the transition both studies used an iterative linearized inversion method we will in this work preprint submitted to elsevier science 27 july 2005 present an inversion based on bayesian statistics where the solution space is examined in order to study a very large number of tomographic solutions and to examine the solution uniqueness and uncertainty the method is applied to measurements of 3345 relative teleseismic p phase travel times from 48 teleseismic earthquakes with good azimuthal coverage with respect to the great circle arc of the tor array we find the lithospheric transition to be a north east inclination of around 30 to 45 off vertical

crust and upper mantle p wave velocity structure beneath valles caldera new mexico results from the jemez teleseismic tomography experiment new results are presented from the teleseismic component of the jemez tomography experiment conducted across valles caldera in northern new mexico we invert 4872 relative ital p wave arrival times recorded on 50 portable stations to determine velocity structure to depths of 40 km the three principle features of our model for valles caldera are 1 near surface low velocities of minus 17 percent beneath the toledo embayment and the valle grande 2 midcrustal low velocities of minus 23 percent in an ellipsoidal volume underneath the northwest quadrant of the caldera and 3 a broad zone of low velocities minus 15 percent in the lower crust or upper mantle crust shallower than 20 km is generally fast to the northwest of the caldera and slow to the southeast near surface low velocities are interpreted as thick deposits of bandelier tuff and postcaldera volcaniclastic rocks lateral variation in the thickness of these deposits supports increased caldera collapse to the southeast beneath the valle grande we interpret the midcrustal low velocity zone to contain a minimum melt fraction of 10 percent while we cannot rule out the possibility that this zone is the remnant 1 2 ma bandelier magma chamber the eruption history and geochemistry of the volcanic rocks erupted in valles calderamore following the bandelier tuff make it more likely that magma results from a new pulse of intrusion indicating that melt flux into the upper crust beneath valles caldera continues the low velocity zone near the crust mantle boundary is consistent with either partial melt in the lower crust or mafic rocks without partial melt in the upper mantle in either case this low velocity anomaly indicates that underplating by mantle derived melts has occurred copyright 1998 american geophysical union less

the petrology of two distinct granulite types in the hengshan mts china and tectonic implications abstract the archean to proterozoic hengshan complex north china craton comprises tonalitic and granodioritic gneisses with subordinate mafic lenses pegmatites and granites amphibolite facies assemblages predominate although granulite facies relics are widespread and greenschist facies retrogression occurs in km wide shear zones mafic lenses locally abundant occur as strongly deformed amphibolite hornblende plagioclase boudins or sheets in contrast to previously published models we find two series of mafic rocks with distinctly different granulite facies evolutions in the north of the complex relict high pressure mafic granulites are garnet clinopyroxene bearing rocks with a secondary development of orthopyroxene around both garnet kelyphites and clinopyroxene coronas south of the newly defined central e w trending zhujiafang shear zone numerous mafic boudins and less deformed dykes exhibit a macroscopically visible magmatic texture with coronitic growth of metamorphic garnet full of quartz inclusions between the magmatic plagioclase and pyroxene domains additional orthopyroxene after magmatic augite and sodic rims to magmatic plagioclase clearly indicate medium pressure granulite facies metamorphism these findings suggest tectonic juxtaposition in this area of three different structural levels of the same proterozoic imprinted crust high pressure granulite grade in the northern hengshan medium pressure granulite grade in the southern hengshan and amphibolite to greenschist facies grade in the wutaishan to the se

distribution of magma beneath the toba caldera complex north sumatra indonesia constrained by three dimensional p wave velocities seismicity and gravity data 1 we estimate the one and three dimensional p wave velocity structure beneath the toba caldera complex a 30 100 km topographic depression in north sumatra using arrival time data of local earthquakes recorded by a 40 station seismic network that operated for 4 months inversions reveal the presence of p velocities up to 37 below normal that likely map the distribution of magma within this subduction related volcanic system considered the world s largest in the upper 10 km of crust the largest low velocity region underlies the southern two thirds of the depression and coincides with a gravity low centered over the resurgent dome a smaller volume of low velocities is observed in the upper crust under the north end of the depression separating the two regions is a zone of locally high velocities indicating that the shallow subcaldera magma system is composed of two separate reservoirs not a single one that extends the entire length of the caldera complex above each low velocity region is a postcollapse volcano that erupted mostly mafic lavas after the last major caldera collapse 74 kyr ago a low velocity column below one of these volcanoes can be traced into the uppermost mantle and corresponds with a planar distribution of low frequency earthquakes in the 20 to 40 km depth range the low frequency earthquakes apparently record the migration of melt in the mafic roots of this large volume crustal magma system

high resolution teleseismic tomography of upper mantle structure using an a priori three dimensional crustal model summary the effect of an a priori known 3 d crustal model in teleseismic tomography of upper mantle structure is investigated we developed a 3 d crustal p wave velocity model for the greater alpine region encompassing the central and western alps and the northern apennines to estimate the crustal contribution to teleseismic traveltimes the model is constructed by comparative use of published information from active and passive seismic surveys the model components are chosen to represent the present large scale alpine crustal structure and for their significant effect on the propagation of seismic wavefields they are first order structures such as the crust mantle boundary sedimentary basins and the high velocity ivrea body teleseismic traveltime residuals are calculated for a realistic distribution of azimuths and distances by coupling a finite difference technique to the iasp91 traveltime tables residuals are produced for a synthetic upper mantle model featuring two slab structures and the 3 d crustal model on top of it the crustal model produces traveltime residuals in the range between 0 7 and 1 5 s that vary strongly as a function of backazimuth and epicentral distance we find that the non linear inversion of the synthetic residuals without correcting for the 3 d crustal structure erroneously maps the crustal anomalies into the upper mantle correction of the residuals for crustal structure before inversion properly recovers the synthetic slab structures placed in the upper mantle we conclude that with the increasing amount of high quality seismic traveltime data correction for near surface structure is essential for increasing resolution in tomographic images of upper mantle structure

evidence for the contemporary magmatic system beneath long valley caldera from local earthquake tomography and receiver function analysis 1 we present a new p wave and s wave velocity model for the upper crust beneath long valley caldera obtained using local earthquake tomography and receiver function analysis we computed the tomographic model using both a graded inversion scheme and a traditional approach we complement the tomographic vp model with a teleseismic receiver function model based on data from broadband seismic stations mlac and mkv located on the se and sw margins of the resurgent dome inside the caldera the inversions resolve 1 a shallow high velocity p wave anomaly associated with the structural uplift of a resurgent dome 2 an elongated wnw striking low velocity anomaly 8 10 reduction in vp at a depth of 6 km 4 km below mean sea level beneath the southern section of the resurgent dome and 3 a broad low velocity volume 5 reduction in vp and as much as 40 reduction in vs in the depth interval 8 14 km 6 12 km below mean sea level beneath the central section of the caldera the two low velocity volumes partially overlap the geodetically inferred inflation sources that drove uplift of the resurgent dome associated with caldera unrest between 1980 and 2000 and they likely reflect the ascent path for magma or magmatic fluids into the upper crust beneath the caldera

petrochemistry and sr pb and nd isotopic geochemistry of early precambrian rocks wutaishan and taihangshan areas china abstract in the wutaishan and taihangshan region china the lowermost high grade metamorphic complex of grey gneiss and amphibolite the fuping complex gives a 2 2 0 2 ga pb pb isochron age with a first stage growth 7 73 and a 2 37 0 07 ga sm nd isochron age with 143nd 144nd 0 0 50963 0 00005 or nd t 1 50 nd depleted mantle model dates tdm of amhibolites 2 48 to 2 60 ga those of gneisses are 2 43 to 2 46 ga the unconformably overlying medium to low grade metavolcanic complex the wutai complex gives a 2 0 0 1 ga rb sr isochron age with 87 86sr 0 0 7025 2 a 2 27 0 02 ga pb pb isochron date with afirst stage growth 7 73 and a 2 26 0 06 ga sm nd isochron first stage 143nd 144nd 0 0 5097 2 or nd t 1 08 individual sample nd depleted mantle model date are 2 5 ga metavolcanic samples from low grade metasedimentary rocks of the hutuo group all lie close to a 2 3 ga reference line on a rb sr isochron plot have nd tdm 2 32 2 34 and 2 62 ga from previous geological work published u pb zircon dating and ourisotopic and geochemical results we infer that the fuping rocks formed 2 6 ga ago in an environment like a modern island arc the wutai complex formed by 2 5 ga ago mostly formed in a tectonic setting similar to that of the fuping complex with the exception that one volcanic cycle formed in an environment like a modern mor and one unit formed in an environment transitional between modern within plate and plate margin settings the hutuo group formed 2 4 ga ago in a within plate tectonic environment there is no evidence for continental crust before 2 6 ga in the wutaishan and taihangshan region this contradicts previous assignment of the fuping complex to 2 8 ga ol older the fuping complex is not an early nucleus of the sino korean craton the new data also confirm that the wutai complex is older than its original assignment as early proterozoic the sm nd systems for metabasaltic rocks in the region either in amphibolite facies or in greenschist facies are all significantly disturbed in contrast with the undisturbed sm nd reported in previous studies of the sino korea craton this study provides further evidence that the archean igneous rocks in china formed at different times from heterogeneous and depleted mantle sources

teleseismic p wave image of crust and upper mantle structure beneath the valles caldera new mexico initial results from the 1993 jtex passive array teleseismic p wave relative arrival time data collected from a temporary array during the 1993 jemez tomography experiment jtex have been inverted to image velocity anomalies beneath the valles caldera in northern new mexico instruments were deployed in two 30 km long profiles one of 8 and one of 9 stations these profiles crossed the caldera trending at azimuths of n46 w and n60 e respectively two dimensional teleseismic relative arrival time inversion of the 1993 data set supplemented with data from an overlapping 1987 profile confirms the existence of a mid crustal low velocity region 30 beneath the valles caldera in the depth range of 8 to 13 km below sea level with about a 6 km horizontal extent this feature is interpreted to be the seismic expression of the remnant magma chamber a shallow low velocity anomaly beneath san antonio mountain coincides with the region of highest thermal gradient values in the caldera a lower crust upper mantle low velocity anomaly is imaged but is not as well constrained due to the limited length of the profile we tentatively correlate this anomaly with the thermal effects of basaltic magmas ponded at the crust mantle boundary

improving depth resolution of teleseismic tomography by simultaneous inversion of teleseismic and global p wave traveltime data application to the vrancea region in southeastern europe summary over the years teleseismic tomography has developed to be a sophisticated method to study the earth s upper mantle on a regional scale using data from tomographic experiments with temporary station networks one faces some inherent problems which include limited resolution at depth and artefacts due to a plane wave approximation at the bottom of the model volume simultaneous inversion of dense regionally recorded teleseismic and global p wave traveltime data provides an opportunity to overcome these specific problems the calculation of the entire ray path using a 3 d ray tracing algorithm and a non linear iterative inversion scheme allow to localize heterogeneities in the earth s mantle and to improve resolution at depth application of a variable parametrization scheme provides not only a regional high resolution model but additionally allows to include a priori constrained structures such as a crustal model derived from independent studies we investigated the effect of different inversion strategies for a priori constrained model parameters and found that for upper mantle studies one must allow further perturbation of the known velocity structure during inversion to avoid artefacts down to the mantle transition zone we apply this approach to the romanian vrancea region in southeastern europe the results show a near vertical narrow high velocity body underneath that region extending down to 280 km depth approximately outlining the narrowly spaced seismogenic volume and a deeper differently oriented positive anomaly coupled to the shallower segment at the latter s southwestern edge at north northwest and west of the vrancea region we find an extended region of decreased seismic p wave velocity down to 200 km depth being interpreted as a shallow lithosphere asthenosphere boundary and asthenospheric mantle flow due to lateral migration of the high velocity body from synthetic reconstruction tests we found that inversion of the combined data set of regionally recorded teleseismic and global traveltime data enhances resolution up to depths greater than could be resolved by the teleseismic data alone

granitoid evolution in the late archean wutai complex north china craton abstract two temporally discrete episodes of granite magmatism have been identified in the wutai complex of the north china craton based on shrimp u pb zircon dating of all major granitoid bodies in the area the older period is latest archean and ranges in age from 2560 to 2515 ma whereas the younger episode is paleoproterozoic with magmatism at 2170 and 2120 ma archean magmatism can be further separated into two pulses based on geochemistry and the association of the younger plutons with extensive coeval volcanic activity in the wutai complex the early phase of archean activity is represented by the lanzhishan ekou and portions of the chechang betai granites with ages ranging from 2560 to 2540 ma the lanzhishan granite is the only one at wutaishan that contains inherited zircon with a number of cores and individual grains giving ages in excess of 2700 ma these are relatively evolved granitoids interpreted to be derived from older basement of the eastern block of the north china craton the shifo guangmingshi the main grey phase of the wangjiahui granite and the major components of the chechang betai granite have ages of 2540 2515 ma and are coeval with felsic volcanism in the wutai complex which is a consequence of subduction and related arc magmatism the dawaliang granite and pink phase of the wangjiahui granite are considerably younger with paleoproterozoic ages of 2170 and 2120 ma respectively these are also evolved granitoids most likely derived by partial melting of the older basement although we have found no evidence of inheritance the petrogenesis of the granitoids reflects the precambrian amalgamation history of the north china craton indicating derivation along the western edge of the eastern block during development and amalgamation of the wutai arc and prior to collision with the western block of the craton 1 8 ga ago

novel anisotropic teleseismic body wave tomography code anitomo to illuminate heterogeneous anisotropic upper mantle part i theory and inversion tuning with realistic synthetic data

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

single chamber silicic magma system inferred from shear wave discontinuities of the crust and uppermost mantle coso geothermal area california 1 analysis of seismograms from teleseismic rays traversing the coso geothermal area near ridgecrest california suggests the geothermal system lies over a single shallow magma reservoir 5 km below the surface that also plays a crucial role in the local change in deformation style from areas to the north and west the character of the magma reservoir and the absence of a lower crustal magma reservoir is inferred from three crustal p to s conversions observed using receiver function analysis 1 a high amplitude shallow negative arrival ps p time of 0 7 0 9 s 3 5 km below sea level bsl 2 a moderate amplitude positive conversion ps p time of 2 1 2 5 s 14 17 km bsl and 3 the moho conversion ps p time of 4 0 4 2 s 30 32 km bsl observations of moho converted arrivals indicate that the interface is mostly flat and uncomplicated throughout the study area while the midcrustal conversion is laterally variable in amplitude and depth the absence of the large negative amplitude conversion on waveforms recorded at stations outside the geothermal area strongly suggests that the feature lies only underneath the modern geothermal area in addition rays sampling the shallow converter also contain later arrivals with retrograde moveout consistent with an origin as reverberations above the conversion receiver functions calculated from synthetic data using a single isotropic layer over a half space indicates that the shear velocity decreases by 30 across the interface vs1 2 6 km s vs2 1 8 km s layer one thickness 4 9 km further supporting the presence of shallow magma

spatio temporal evolution of frequency magnitude distribution and seismogenic index during initiation of induced seismicity at guy greenbrier arkansas abstract in this study we carry out detailed analyses of the spatio temporal variations of seismic b value during the onset of the potentially induced earthquake sequence between guy and greenbrier arkansas to investigate correlations with pore pressure change the range of b values suggests that the seismicity in the guy greenbrier area is mostly a result of the activation of pre existing faults the spatial distribution of b value correlates with modeled pore pressure changes in the northern segment of the fault b value increases with depth due to large pore pressure changes and opening of new fractures in the deeper part and stress relaxation in the shallower parts whereas in the southern segment the shallower part shows higher b values due to higher pore pressure fluctuations but the deeper part in the crystalline basement has low b value due to higher confining stress the correlation between the temporal variation of b value and hypocentral depth explains a previously observed temporal drop of b value this suggests that temporal variations should be interpreted along with the spatial variations estimation of the seismogenic indices for the guy greenbrier fault is provided our analysis suggests that monitoring changes in b value and seismogenic indices during an injection period might be used to avoid the occurrence of significant events if injection volume is reduced at critical times

upper mantle structure of the baltic shield below the swedish national seismological network snsn resolved by teleseismic tomography summary upper mantle structure under the baltic shield is studied using non linear high resolution teleseismic p phase tomography observed relative arrival time residuals from 52 teleseismic earthquakes recorded by the swedish national seismological network snsn are inverted to delineate the structure of the upper mantle the network consists of 47 currently working three component broad band stations located in an area about 450 km wide and 1450 km long in order to reduce complications due to possible significant three dimensionality of earth structure events chosen for this study lay close to in line with the long axis of the array 30 results indicate p wave velocity perturbations of 3 per cent down to at least 470 km below the network the size of the array allows inversion for structures even at greater depths and lateral variations of velocity at depths of up to 680 km appear to be resolved below the central part of the array 60 64 n where ray coverage is best the data reveals a large region of relatively low velocity at depths of over about 300 km at depths less than about 250 300 km the models include a number of features including an apparent slab like structure dipping gently towards the north

seismological studies at parkfield i simultaneous inversion for velocity structure and hypocenters using cubic b splines parameterization a model for the 3d p and s wave velocity structure at parkfield has been developed by the systematic inversion of arrival times for microearthquakes and surface vibroseis sources recorded by nearby calnet stations and by the local borehole installed 10 station high resolution seismic network there a modification of the linear b splines model parameterization method of thurber 1983 to a cubic b splines formulation through tests inverting synthetic data sets for the parkfield configuration is found to produce smooth velocity distributions that still retain some small scale features application of the method to 953 p wave and 288 s wave arrivals from 111 microearthquakes and 8 vibroseis locations throughout the study area yields a velocity structure having variable resolution a low velocity zone appears to coincide with the creeping segment of the san andreas fault zone northwest of the 1966 parkfield earthquake epicenter an increase of about 15 per cent in seismic velocities is seen from the northeast to southwest across this segment of the fault zone the higher velocities to the southwest apparently correspond to the granitic basement the contrast across the fault is subdued to the southeast along the 1966 rupture zone a high vp vs ratio of 1 9 is seen in a 2 km wide volume near the location of the 1966 main shock hypocenter presumably the nucleation zone for the expected m 6 parkfield earthquake