radar interferometric mapping of deformation in the year after the landers earthquake although the 1992 landers california earthquake sequence occurred in an area well sampled by geodetic networks1 3 the postseismic deformation in the months following the earthquake has been measured at only 15 geodetic stations4 another shortcoming in the geodetic coverage occurs west of the primary rupture where the existing geodetic observations suggest but cannot resolve sympathetic slip on secondary faults1 such measurements which are needed to place the landers earthquake sequence in the context of a recurring seismic cycle in california can be obtained with the dense spatial coverage provided by satellite radar interferometry5 9 here we present radar maps of the surface deformation field which reveal features that would otherwise have been poorly sampled particularly if the earthquake had occurred in a less accessible area we see triggered slip at the level of several centimetres as far as 100 km from the primary rupture and can resolve the geodetic signal of at least one small magnitude 5 aftershock the amount of surface slip following the main shock is less than a decimetre and is consistent with an exponential decay time of several months for the postseismic deformation

small scale deformations associated with the 1992 landers california earthquake mapped by synthetic aperture radar interferometry phase gradients the landers earthquake mw 7 3 occurred on june 28 1992 and ruptured nearly 100 km of previously mapped and unmapped faults in the mojave desert we use synthetic aperture radar interferometry insar to examine the cumulative surface deformation between april 24 and august 7 1992 in a 100 100 km region surrounding the northern portion of the earthquake rupture also we introduce a technique for manipulating sar interferograms to extract short wavelength displacement information this technique involves computation and subsequent combination of interferometric phase gradient maps the insar results show significant deformation signatures associated with faults fractures dry lake beds and mountainous regions within 75 100 km of the main rupture using the phase gradient method we are able to extract small scale deformation patterns near the main rupture many of the preexisting mapped faults within 50 km of the main rupture experienced triggered slip these include the old woman lenwood johnson valley west calico and calico faults the insar results also indicate right lateral offsets along secondary fractures trending n ne within the left lateral zone of shear between the main rupture and the johnson valley fault additionally there are interesting interferogram fringe signatures surrounding troy dry lake and coyote dry lake that are related to deformation of dry lake beds

near real time radar interferometry of the mw 7 1 hector mine earthquake the hector mine earthquake mw 7 1 16 oc tober 1999 ruptured 45 km of previously mapped and un mapped faults in the mojave desert the ers 2 satellite imagedthemojavedeserton15septemberandagain on20 october just 4 days after the earthquake using a newly developed ground station we acquired both passes and were able to form an interferogram within 20 hours of the second overflight estimates of slip along the main rupture are 1 2 meters greater than slip derived from geological mapping the gradient of the interferometric phase reveals an inter esting pattern of triggered slip on adjacent faults as well as a 30 mm deep sink hole along interstate 40

high resolution 3 d crustal shear wave velocity model reveals structural and seismicity segmentation of the central southern tanlu fault zone eastern china abstract the early mesozoic collision between the north and south china cratons resulted in different tectonic and geologic structures including the tanlu fault zone one way to understand the geodynamic processes beneath these structures is by studying the velocity structures and spatial distribution of earthquakes in the region we performed ambient noise tomography for the region around the central southern tanlu fault zone using the vertical component of continuous ambient noise data obtained in central east china empirical green s functions were retrieved from ambient noise cross correlation functions from which we extracted the rayleigh wave phase velocity dispersion curves and performed quality control on the dispersion data the direct surface wave tomography method was used to invert all phase velocity dispersion data for the 3 d shear wave velocity model in the crust and uppermost mantle our results show velocity segmentations with high velocity structures existing beneath orogenic belts and uplifts within the first 10 km depths which correspond to the high pressure ultra high pressure metamorphic rocks in the area the existence of high velocity structures beneath orogenic belts at shallow depths implies that the exhumation of eclogites is confined to the uppermost crust generally fault zones in this area are characterized by a low velocity from 0 to 5 km and relatively high velocity in the lower part of the upper crust and the middle crust the spatial distribution of earthquakes along tanlu fault reveals two seismicity zones the southern segment and the suqian tancheng segment with a low velocity transitional zone at suqian which suggests that the two segments respond differently to stresses regions of dense earthquake distribution correspond to the transition zones of high to low shear wave velocities which could be as a result of instability in the upper mantle and variation in compositions of crustal materials

inelastic response of compliant fault zones to nearby earthquakes 1 using dynamic rupture models we examine the response of compliant fault zones that surround pre existing faults to nearby earthquakes we find that some portions of a compliant fault zone can experience inelastic deformation due to dynamic stress perturbations while the remaining portions deform elastically inelastic response of the fault zone results in sympathetic fault parallel motion i e consistent with long term geologic slip across the fault while elastic response causes retrograde motion i e opposite to long term geologic slip in the static displacement field inelastic deformation signals along fault zones detected geodetically may be used to constrain the stress state in the crust because inelastic response occurs only when the prestress level is close to material strength which can be measured in the laboratory

development of the eastern california shear zone walker lane belt the effects of microplate motion and pre existing weakness in the basin and range abstract the role that the motion of microplates has played in the development of the eastern california shear zone in western north america is unclear it was previously proposed that shear related to baja california motion has propagated from the gulf of california northward into nevada however there is evidence that the formation of the eastern california shear zone predates the inception of baja california motion thus either baja california began to move northwestward prior to 6 ma or the eastern california shear zone formed by shear strain resulting from different microplate motion than baja california the role of sierra nevada motion on the development of an adjacent shear zone remains untested we present a numerical modeling study that examines the deformational response of western north america to baja california and or sierra nevada microplate motion in particular we study if and under what condition of microplate motion shear strain can localize in the northern and southern part of the eastern california shear zone separated by the garlock fault we find that given the pre existing weakness from miocene basin and range extension a lithospheric strength contrast or normal faults shear strain from either the baja california or sierra nevada microplates can lead to the formation of the eastern california shear zone furthermore the presence of a pre existing weakness explains the earlier initiation of strike slip faulting north of the garlock fault our models suggest that today baja california microplate motion is the major player for present day deformation rates along the eastern california shear zone and was in the past 6 myrs also a major driver of strain localization in southern eastern california shear zone within the mojave block

coseismic displacements from the hector mine california earthquake results from survey mode global positioning system measurements we describe the collection and processing of global positioning system gps data from 77 locations around the hector mine earthquake which we use to estimate coseismic displacements related to this shock the existence of pre event gps data some collected to monitor postseismic displacements from the 1992 landers earthquake and some to establish survey control in the meizoseismal area provided a relatively dense coverage close to the rupture zone the data available were collected mostly within the 2 years prior to the 1999 earthquake we reobserved many points within a few days after the shock and all within 6 months after we include corrections for interseismic motion to provide the best value possible for coseismic motion caused by this earthquake the displacements in general display the pattern expected for a strike slip fault though a few show significant vertical motion the maximum horizontal displacement observed was 2 m one station between fault ruptures showed little horizontal motion but significant uplift

seismic evidence for the absence of deeply subducted continental slabs in the lower lithosphere beneath the central orogenic belt of china abstract a study of teleseismic p wave tomography was carried out along the central orogenic belt of china cobc consisting of the qinling tongbai hong an dabie and sulu orogens that were created by northward subduction of the south china block beneath the north china block to subarc depths in the paleozoic to mesozoic the results show the presence of high velocity anomaly underneath the cobc and its adjacent cratonic regions but the absence of high velocity anomaly in the lower lithosphere beneath the cobc the high velocity anomaly is deep underneath the cobc possibly representing the relic of the subducted paleo tethyan oceanic slab predating the continental deep subduction of the south china block the high velocity anomaly is also deep underneath the southeastern part of the north china block possibly being a relic of the subducted paleo pacific slab however no relic of the deeply subducted continental slab is seismically detected in the lower lithosphere beneath the dabie and sulu orogens though the occurrence of ultrahigh pressure metamorphic rocks in the two orogens has clearly demonstrated continental deep subduction to subarc depths in the triassic instead there is only the relatively flat and uniform moho boundary beneath the cobc region indicating that the subduction thickened continental lithosphere along the cobc has lost its root it is inferred that the orogenic root beneath the cobc region has been foundered into the asthenospheric mantle at the postcollisional stage the foundering would have taken place in the early cretaceous as indicated by the extensive occurrence of magmatic and migmatitic rocks along the cobc as a consequence the seismic tomography cannot detect the deeply subducted continental slab remnant from the triassic period it is possible that the tomographic visibility of continental subduction in the lower lithosphere is limited to the past 100 myr

diamond from the dabie shan metamorphic rocks and its implication for tectonic setting diamond occurs in ultrahigh pressure metamorphic rocks from dabie shan anhui province eastern china diamond bearing rocks include eclogite gamet pyroxenite and jadeitite diamond occurs in a mineral assemblage with coesite and jadeite the diamonds and diamondiferous rocks of dabie shan are interpreted to be the products of ultrahigh pressure metamorphism in the underthrust basement of the yangtze continental plate during the early mesozoic at greater than 4 0 gigapascals and 900 c this interpretation is based on the distribution of rock units the stability field of diamond and isotopic data indicating a crustal origin for the rocks most diamonds occur as euhedral inclusions in garnets and are 10 to 60 micrometers across although some are up to 700 micrometers across

surface deformation and coherence measurements of kilauea volcano hawaii from sir c radar interferometry the shuttle imaging radar c x synthetic aperture radar sir c x sar radar on board the space shuttle endeavor imaged kilauea volcano hawaii in april and october 1994 for the purpose of measuring active surface deformation by the methods of repeat pass differential radar interferometry observations at 24 cm l band and 5 6 cm c band wavelengths were reduced to interferograms showing apparent surface deformation over the 6 month interval and over a succession of 1 day intervals in october a statistically significant local phase signature in the 6 month interferogram is coincident with the pu u o o lava vent interpreted as deformation the signal implies centimeter scale deflation in an area several kilometers wide surrounding the vent peak deflation is roughly 14 cm if the deformation is purely vertical centered southward of the pu u o o caldera delays in the radar signal phase induced by atmospheric refractivity anomalies introduce spurious apparent deformation signatures at the level of 12 cm peak to peak in the radar line of sight direction though the phase observations are suggestive of the wide area deformation measured by global positioning system gps methods the atmospheric effects are large enough to limit the interpretation of the result it is difficult to characterize centimeter scale deformations spatially distributed over tens of kilometers using differential interferometry without supporting simultaneous spatially distributed measurements of refractivity along the radar line of sight studies of the interferometric correlation of images acquired at different times show that l band is far superior to c band in the vegetated areas even when the observations are separated by only 1 day these results imply longer wavelength instruments are more appropriate for studying surfaces by repeat pass observations

high resolution rayleigh wave group velocity tomography in north china from ambient seismic noise abstract this study presents the results of the rayleigh wave group velocity tomography in north china performed using ambient seismic noise observed at 190 broadband and 10 very broadband stations of the north china seismic array all available vertical component time series for the 14 months span between january 2007 and february 2008 are cross correlated to obtain empirical rayleigh wave green functions that are subsequently processed with the multiple filter method to isolate the group velocity dispersion curves of the fundamental mode of rayleigh wave tomographic maps with a grid spacing of 0 25o 0 25o are computed at the periods of 4 5s 12s 20s 28s the maps at short periods reveal an evident lateral heterogeneity in the curst of north china quite well in agreement with known geological and tectonic features the north china basin is imaged as a broad low velocity area while the taihangshan and yanshan uplifts and ordos block are imaged as high velocity zones and the quaternary intermountain basins show up as small low velocity anomalies the group velocity contours at 4 5s 12s and 20s are consistent with the bouguer gravity anomalies measured in the area of the taihangshan fault that cuts through the lower crust at least most of the historical strong earthquakes m 6 0 are located where the tomographic maps show zones with moderate velocity gradient

crustal structure and exhumation of the dabie shan ultrahigh pressure orogen eastern china from seismic reflection profiling crustal penetrating seismic reflection data across the ultrahigh pressure uhp dabie shan orogen show that the yangtze craton was subducted beneath the sino korean craton forming a bivergent orogenic fabric strikingly similar to normal non uhp collision belts hence preservation of uhp minerals coesite and diamond may be unrelated to differences between collisional histories but may be due to opportunities for subsequent intracrustal uplift of material that is routinely returned from mantle depths into the lower crust in most collisional orogens only a narrow channel 5 km now exists from the mantle into the crust through which uhp material was returned to lower crustal depths as thin slabs we image the dabie shan as a crustal scale dome formed during postcollisional intracrustal uplift by core complex type exhumation of the lower crust tectonically unrelated to the earlier exhumation from 100 km to 35 40 km

timing of collision of the sino korean and yangtse cratons u pb zircon dating of coesite bearing eclogites the suture zone between the sino korean and yangtse cratons in central china is marked by a series of fault bounded belts composed of crustal protoliths in the dabie mountains some of these blocks contain coesite and diamond indicating subduction to minimum depths of 120 km as a result of continental collision the blocks range from the structurally lowest ultrahigh pressure metamorphic belt and decrease in metamorphic grade upsection to the structurally highest low greenschist facies belt furthermore the faults mark large contrasts in metamorphic grade these features form a structure that is similar to metamorphic core complexes indicating extension as part of the exhumation process timing of the continental collision has previously been inferred as late triassic from regional geologic relations or caledonian from 40 ar 39 ar dating of the adjacent and possibly related qinling metamorphic belt u pb dating of zircon from ultra high pressure eclogites yields a metamorphic age of 209 2 ma this age coincides with later stages of collision and is therefore a minimum estimate of the time of collision

slab like high velocity anomaly in the uppermost mantle beneath the dabie sulu orogen seismic tomography is used to determine three dimensional velocity structure of the dabie sulu orogen in eastern china the high resolution image of the p waves velocity structure is obtained for the uppermost mantle to a depth of at least 150 km along the latitudes of 30 38 n and longitudes of 114 122 e results of this inversion reveal a slab like high velocity anomaly under this orogen in the depth from moho discontinuity to at least 110 km it may represent a remnant of the subducted yangtze block during the period of triassic continent continent collision

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

three dimensional s wave velocity model of the bohemian massif from bayesian ambient noise tomography abstract we perform two step surface wave tomography of phase velocity dispersion curves obtained by ambient noise cross correlations in the bohemian massif in the first step the inter station dispersion curves were inverted for each period ranging between 4 and 20 s separately into phase velocity maps using 2d adjoint method in the second step we perform bayesian inversion of the set of the phase velocity maps into an s wave velocity model to sample the posterior probability density function the parallel tempering algorithm is employed providing over 1 million models from the model samples not only mean model but also its uncertainty is determined to appraise the reliable features the model is correlated with known main geologic structures of the bohemian massif the uppermost low velocity anomalies are in agreement with thick sedimentary basins in deeper parts 4 20 km the s wave velocity anomalies correspond in general to main tectonic domains of the bohemian massif the exception is a stable low velocity body in the middle of the high velocity moldanubian domain and high velocity body resembling a promontory of the moldanubian into the tepla barrandian domain the most pronounced high velocity anomaly is located beneath the eger rift that is a part of a tertiary rift system across europe

crustal and uppermost mantle structure across the lower yangtze region and its implications for the late mesozoic magmatism and metallogenesis eastern south china abstract we present here high resolution seismic sections of crustal and uppermost mantle structure along two dense linear arrays across the lower yangtze region in the eastern south china block scb our seismic images reveal two low velocity anomalies lvas in the uppermost mantle which we interpreted as relic still cooling mantle magma chambers ponding and underplating beneath the base of the crust in the areas of the dexing porphyry copper deposits and the cretaceous south anhui granites the moho and lab discontinuities imaged also exhibit deformation directly above the two mantle lvas which probably indicate local mantle lithosphere destruction by asthenospheric upwelling in the mesozoic this local asthenospheric upwelling may have triggered melting of the mantle lithosphere and generated the observed mantle magma chamber system through interactions with lower crustal materials low vs bodies revealed in the middle upper crust at depth of 10 km may indicate the corresponding solidified intrusive granitoids these observations provide unambiguous seismological evidence connecting deep magmatism with surface geological features combined with previous petrologic and geochemical studies the findings presented here outline a mantle magma chamber based magmatic system that was underplated beneath the base of the crust and kept supplying heat and materials in forming the voluminous yanshanian igneous rocks and associated metallogenesis in the lower yangtze region

postseismic rebound in fault step overs caused by pore fluid flow near field strain induced by large crustal earthquakes results in changes in pore fluid pressure that dissipate with time and produce surface deformation synthetic aperture radar sar interferometry revealed several centimeters of postseismic uplift in pull apart structures and subsidence in a compressive jog along the landers california 1992 earthquake surface rupture with a relaxation time of 270 45 days such a postseismic rebound may be explained by the transition of the poisson s ratio of the deformed volumes of rock from undrained to drained conditions as pore fluid flow allows pore pressure to return to hydrostatic equilibrium

coesite bearing eclogite from the dabie mountains in central china coesite and coesite pseudomorphs are recognized in eclogite from the dabie mountains a collision zone between the sino korean and yangtze cratons in central china this third known occurrence of coesite in deep crustal rocks is within an archean gneiss terrane and is the first locality where coesite has been identified as an inclusion in both omphacite and garnet crystals at the same location coesite bearing eclogite is estimated to form at pressures of 28 kbar and temperatures from 600 to 710 c the dabie mountains eclogite underwent retrograde metamorphism to amphibolite facies after its formation the preservation of coesite in eclogite is found to be strongly controlled by the pressure temperature time path that coesite bearing eclogite followed during its uplift and retrograde metamorphism

crustal structure beneath the dabie orogenic belt from ambient noise tomography abstract the qinling dabie sulu orogenic belt in east central china is the largest high and ultrahigh pressure hp and uhp metamorphic zone in the world the dabie mountains are the central segment of this orogenic belt between the north china and yangtze cratons this work studies the nature of the crustal structure beneath the dabie orogenic belt to better understand the orogeny to do that we apply ambient noise tomography to the dabie orogenic belt using ambient noise data from 40 stations of the china national seismic network cnsn between january 2008 and december 2009 we retrieve high signal noise ratio snr rayleigh waves by cross correlating ambient noise data between most of the station pairs and then extract phase velocity dispersion measurements from those cross correlations using a spectral method taking those dispersion measurements we obtain high resolution phase velocity maps at 8 35 second periods by inverting rayleigh wave phase velocity maps we construct a high resolution 3d shear velocity model of the crust in the dabie orogenic belt the resulting 3d model reveals interesting crustal features related to the orogeny high shear wave velocities are imaged beneath the hp uhp metaphoric zones at depths shallower than 9 km suggesting that hp uhp metaphoric rocks are primarily concentrated in the upper crust underlying the high velocity hp uhp metamorphic zones low shear velocities are observed in the middle crust probably representing ductile shear zones and or brittle fracture zones developed during the exhumation of the hp uhp metamorphic rocks strong high velocities are present beneath the northern dabie complex unit in the middle crust possibly related to cooling and crystallization of intrusive igneous rocks in the middle crust resulting from the post collisional lithosphere delamination and subsequent magmatism a north dipping moho is revealed in the eastern dabie with the deepest moho appearing beneath the northern dabie complex unit consistent with the model of triassic northward subduction of the yangtze craton beneath the north china craton

high temperature geochronology constraints on the tectonic history and architecture of the ultrahigh pressure dabie sulu orogen 1 new u pb zircon and th pb monazite ages are presented from the giant sulu ultrahigh pressure uhp terrane combined with sm nd ages rb sr ages inclusion relationships and geologic relationships they help define the timing of peak recrystallization the timing of subsequent amphibolite facies metamorphism and the architecture of the dabie sulu suture zone between the collided sino korean and yangtze cratons the data indicate a 15 myr record of uhp recrystallization the first clearly documented for a giant uhp terrane this requires that continental subduction in the dabie sulu orogen involved multiple uhp tectonic or recrystallization events a 244 236 ma precursor uhp event seen only in the dabie shan was followed by a second 230 220 ma main uhp event which was itself terminated by a 220 205 ma amphibolite facies overprint older eclogite facies events seen in the qinling segment of this orogenic belt raise the possibility that these rocks have undergone u hp metamorphism three or four times but at present there is no geochronological evidence in the dabie sulu area to support this the subduction of the lower yangtze plate did not proceed in a simple fashion the ages of inherited zircon cores demonstrate that a ribbon continent of yangtze affinity escaped subduction and became wedged against the sino korean plate hanging wall

some thoughts on measuring earthquake deformation using optical imagery optical imagery has been proven to be an effective tool for measuring earthquake deformation in continental regions since its first application in the 1999 izmit earthquake in this article we compile and analyze all the earthquakes that have been investigated with optical image matching by 2019 based on which we comment on various issues regarding measuring earthquake deformation with optical imagery new generations of very high resolution vhr data are effective for earthquake studies but orthorectification of the vhr images is the major source of error which is often ignored we found that the displacements derived from the worldview images strongly correlate with the errors in the shuttle radar topography mission srtm digital elevation model dem that was used in orthorectification based on the observed correlation between displacements and topography we propose a new dem based method using the advanced land observing satellite alos world 3 d dem to reduce the orthorectification errors combining the published optical data of earthquake deformation we re analyze the coseismic slip distribution and shallow slip deficit ssd the ssd model states that the coseismic slip in many strike slip earthquakes decreases in magnitude toward the surface but this model remains arguable because the interferometric synthetic aperture radar insar derived slip is usually not well constrained at shallow depths due to decorrelation because optical matching directly measures the surface slip we re examine the slip distribution of 11 strike slip earthquakes and find that the ssd model may primarily be artifacts in the insar measurements it is therefore of great importance to include the optical data in earthquake studies to constrain coseismic slip inversions

contrasting plate tectonic styles of the qinling dabie sulu and franciscan metamorphic belts the dabie mountains are part of the 2000 km long qinling dabie sulu suture zone juxtaposing the sino korean and yangtze cratons an eastern extension apparently crosses korea and lies along the japan sea side of honshu as the imjingang and sangun terranes respectively a northeastern segment may be present in sikhote alin russian far east this orogenic belt records late paleozoic ocean floor consumption and the triassic collision of two precambrian continental massifs in east central china coesite and microdiamond inclusions in strong refractory minerals of eclogite facies ultrahigh pressure uhp metamorphic rocks in the dabie sulu area attest to profound subduction of a leading salient of the old cold yangtze craton now recovered through tectonic exhumation and erosion northward increase in intensity of subsolidus recrystallization of the suture complex is analogous to the internal progression in grade of high pressure hp and uhp metamorphism documented in the western alps in both regions subduction of narrow prongs of continental material uhp metamorphism and return toward midcrustal levels of relatively lower density buoyant microcontinental blocks resulted from delamination of these rocks from the descending higher density oceanic crust capped lithospheric plate such salients of continental crust represent an integral structural part of the downgoing slab remain intact and may be dragged to great depths before disengaging and rising differentially as coherent blocks uhp parageneses include trace mineralogic relics requiring peak metamorphic conditions of 700 900 c and 28 35 kbar or more in contrast pacific type hp metamorphic belts as represented by the franciscan complex of western california recrystallized under physical conditions up to 200 500 c 10 3 kbar in this setting voluminous quartzo feldspathic and graywacke debris was carried downward on oceanic crust capped lithosphere choking the subduction zone with incompetent material sited between both plates and strongly adhering to neither this buoyant largely sedimentary complex decoupled at 25 30 km depth and ascended toward the surface in both alpine type intracontinental collision and pacific type underflow light sialic material displaced dense mantle thus the return to midcrustal levels was propelled dominantly by body forces

radar interferometry and its application to changes in the earth s surface geophysical applications of radar interferometry to measure changes in the earth s surface have exploded in the early 1990s this new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times the resulting interferogram is a contour map of the change in distance between the ground and the radar instrument these maps provide an unsurpassed spatial sampling density 100 pixels km 2 a competitive precision 1 cm and a useful observation cadence 1 pass month 1 they record movements in the crust perturbations in the atmosphere dielectric modifications in the soil and relief in the topography they are also sensitive to technical effects such as relative variations in the radar s trajectory or variations in its frequency standard we describe how all these phenomena contribute to an interferogram then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments including the four satellites currently in orbit ers 1 ers 2 jers 1 and radarsat the next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement respecting the limits of the technique assessing its uncertainty recognizing artifacts and discriminating different types of signal we then review the geophysical applications published to date most of which study deformation related to earthquakes volcanoes and glaciers using ers 1 data we also show examples of monitoring natural hazards and environmental alterations related to landslides subsidence and agriculture in addition we consider subtler geophysical signals such as postseismic relaxation tidal loading of coastal areas and interseismic strain accumulation we conclude with our perspectives on the future of radar interferometry the objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it

role of partial melting in the evolution of the sulu eastern china ultrahigh pressure terrane strongly deformed potassium feldspar rich dikes are widely distributed in the northern part of the sulu ultrahigh pressure uhp metamorphic terrane eastern china the fact that the crystallization ages of these dikes overlap with the age of peak uhp metamorphic conditions implies the presence of melt during metamorphism sr isotopic ratios of the dikes are compatible with their origin as partial melts of the dominant felsic sulu gneiss partial melting may be the key to solving several unusual features of the sulu and other uhp terranes such as the almost complete lack of mineralogical evidence for uhp conditions and the limited growth of zircon during uhp conditions in the dominant felsic gneiss in addition because partial melting will cause a drastic reduction in the strength of the uhp gneisses the most likely exhumation mechanism is diapiric rise of a low viscosity partially molten mass containing entrained blocks of eclogite and not a thin sheet as usually proposed

new insight into cainozoic sedimentary basins and palaeozoic suture zones in southeast australia from ambient noise surface wave tomography 1 detailed images of rayleigh wave group velocity are derived from ambient seismic noise recorded by wombat a large rolling seismic array project in southeast australia group velocity maps sensitive to crustal structure exhibit low velocity anomalies in the presence of sedimentary basins and recent hot spot volcanism and high velocities in regions of out cropping metamorphic and igneous rocks distinct and well constrained patches of low velocity within the murray basin provide new insight into the spatial extent and possible composition of pre tertiary infra basins in a broader tectonic context our results show little evidence for the palaeozoic building blocks of the southeast australian continent that have been inferred from geological mapping and potential field data this may mean that apparent changes in basement terrane near the surface are not associated with major changes in composition at depth

ambient noise love wave tomography in the eastern margin of the tibetan plateau abstract we collected continuous waveform data from june to december 2007 recorded by 49 broadband seismic stations in western sichuan and eastern tibet and applied an ambient noise technique to obtain a high resolution tomography model of the crust beneath the eastern margin of the tibetan plateau cross correlations of ambient noise data are calculated in one hour segments and stacked over 7 months then love wave group dispersion curves along approximately 700 station pairs were determined using the multiple filter analysis method the study region was divided into a grid of 0 2 0 2 and group velocity distribution maps between 8 and 40 s were obtained the love wave group velocity maps show good correlations with surface features from the group velocity maps we inverted a 3 d model for sh wave velocity the inferred sh velocity heterogeneities generally agree with variations in sv derived from rayleigh wave dispersion discrepancies between them are examined in view of non uniqueness of the models and radial anisotropy both the rayleigh and love wave inversions show the significant difference of the crustal structure and reveal a prominent low velocity zone within the mid to lower crust beneath the eastern margin of the tibetan plateau

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

high pressure blueschists and eclogites in hong an a framework for addressing the evolution of high and ultrahigh pressure rocks in central china the hong an region in the qinling dabie collisional zone in eastern china hosts a series of metamorphic rocks exposing a south to north distribution from blueschist blueschist greenschist amphibolite eclogite kyanite free and kyanite eclogite to coesite eclogite facies rocks that represent progressively deeper levels of the mesozoic subduction collision complex the hong an area is interesting for three reasons 1 it escaped the thermal and structural overprint imparted on much of the dabie mountains during early cretaceous intrusion of voluminous granites and granodiorites 2 the high pressure hp hong an eclogites are widely distributed often preserve prograde crystallization histories and can be directly linked in time and space to the blueschist blueschist greenschist rocks exposed to the south 3 the blueschist blueschist greenschist facies rocks are generally better exposed than their equivalents in the southeastern dabie mountains and offer some opportunity for simultaneous structural and metamorphic analysis the hong an area hp rocks offer perhaps the closest approximation to a preserved snapshot of mesozoic pressure temperature p t conditions attending early subduction exhumation in the region and are thus essential to generating a coherent picture of the dynamics attending both metamorphism and exposure of the coeval ultrahigh pressure uhp rocks the purpose of this contribution is twofold 1 to document previously unpublished metamorphic and structural data characterizing these hp sequences and their relative continuity in hong an 2 to incorporate these data with recent geochronologic structural and paleomagnetic information in the context of protracted late paleozoic through mesozoic subduction collision and exhumation metamorphism and exhumation of some of the southern hong an hp sequences appear to have occurred concomitant with oceanic subduction immediately to the west and thus may have preceded widespread continental subduction collision moreover all of the hp uhp sequences in the region were exhumed before the end of collision between the sino korean and yangtze cratons at ca 160 ma exhumation of hp uhp rocks both before and during continental plate collision is neither novel for central china nor for other hp uhp zones but is important to take into account when reconstructing the evolution of such orogens

crustal structure of the dabie orogenic belt eastern china inferred from gravity and magnetic data abstract in order to better characterize the crustal structure of the dabie orogen and its tectonic history we present a crustal structure along a 500 km long profile across the dabie orogenic belt using various data processing and interpretation of the gravity and magnetic data source depth estimations from the spectral analysis by continuous wavelet transform cwt provide better constraints for constructing the initial density model the calculated gravity effects from the initial model show great discrepancy with the observed data especially at the center of the profile more practical factors are then incorporated into the gravity modeling first we add a high density body right beneath the high pressure metamorphic hpm and ultrahigh pressure metamorphic uhpm belt considering the exposed hpm and uhpm rocks in the mid of our profile then the anomalous bodies a b and c inferred from the cwt based spectral analysis results are fixed in the model geometry in the final crustal density structure two anomalous bodies b and c with high density and low magnetization could possibly be attributed to metasomatised mantle materials by sio2 rich melt derived from the foundering subducted mafic lower crust under the extensional environment in the early cretaceous the upwelling metasomatised mantle was partially melted to produce the parental magma of the post collisional mafic ultramafic intrusive rocks as for the low density body a with strong magnetization located in the lower crust right beneath the hp and uhp metamorphic belt it is more likely to be composed of serpentinized mantle peridotite smp this serpentinized mantle peridotite body smpb represents the emplacement of mantle derived peridotites in the crust accompanying the exhumation of the uhp metamorphic rocks

potential misidentification of love wave phase velocity based on three component ambient seismic noise people have calculated rayleigh wave phase velocities from vertical component of ambient seismic noise for several years recently researchers started to extract love waves from transverse component recordings of ambient noise where transverse is defined as the direction perpendicular to a great circle path or a line in small scale through observation sensors most researches assumed rayleigh waves could be negligible but rayleigh waves can exist in the transverse component when rayleigh waves propagate in other directions besides radial direction in study of data acquired in western junggar basin near karamay city china after processing the transverse component recordings of ambient noise we obtain two energy trends which are distinguished with rayleigh wave and love wave phase velocities in the frequency velocity domain using multichannel analysis of surface waves masw rayleigh waves could be also extracted from the transverse component data because rayleigh wave and love wave phase velocities are close in high frequencies 0 1 hz two kinds of surface waves might be merged in the frequency velocity domain rayleigh wave phase velocities may be misidentified as love wave phase velocities to get accurate surface wave phase velocities from the transverse component data using seismic interferometry in investigating the shallow geology our results suggest using masw to calculate real love wave phase velocities

rayleigh wave phase velocity maps of tibet and the surrounding regions from ambient seismic noise tomography ambient noise tomography is applied to the significant data resources now available across tibet and surrounding regions to produce rayleigh wave phase speed maps at periods between 6 and 50 s data resources include the permanent federation of digital seismographic networks five temporary u s program for array seismic studies of the continental lithosphere passcal experiments in and around tibet and chinese provincial networks surrounding tibet from 2003 to 2009 totaling 600 stations and 150 000 interstation paths with such a heterogeneous data set data quality control is of utmost importance we apply conservative data quality control criteria to accept between 5000 and 45 000 measurements as a function of period which produce a lateral resolution between 100 and 200 km across most of the tibetan plateau and adjacent regions to the east misfits to the accepted measurements among passcal stations and among chinese stations are similar with a standard deviation of 1 7 s which indicates that the final dispersion measurements from chinese and passcal stations are of similar quality phase velocities across the tibetan plateau are lower on average than those in the surrounding nonbasin regions phase velocities in northern tibet are lower than those in southern tibet perhaps implying different spatial and temporal variations in the way the high elevations of the plateau are created and maintained at short periods 20 s very high velocities are imaged in the tarim basin the ordos block and the sichuan basin these phase velocity dispersion maps provide information needed to construct a 3 d shear velocity model of the crust across the tibetan plateau and surrounding regions

crustal structure of the eastern qinling orogenic belt and implication for reactivation since the cretaceous a high resolution crustal model of the eastern qinling belt and central north china craton central ncc is obtained along a n s trending profile corridor by joint inversion of surface wave and receiver function the ncc is one of the oldest cratons on earth and the qinling belt is the suture zone between the ncc and south china block scb the qinling belt is characterized by low crustal velocity 1 8 the forward gravity modeling supports the presence of a high density layer 3 05 g cm3 at the base of the crust beneath the central ncc we propose that the high velocity in the lowermost crust beneath the central ncc is most likely due to the repeated mafic underplating which also results in high crustal vp vs ratio and is responsible for the rapid crustal uplift during the late mesozoic

lithospheric structure of hubei province central china from rayleigh wave tomography insight into the spatial contact relationship between the yangtze plate and the eastern qinling dabie orogenic belt

moho imaging based on receiver function analysis with teleseismic wavefield reconstruction application to south china abstract a detailed and reliable moho structure can improve our understanding of the tectonic evolution of crust and mantle most researchers directly interpolate the imaging results of receiver functions rfs from the sparse stations to obtain a continuous moho image however the interpolation process is usually not robust because of the sparse and irregular geometry of seismic networks in light of the approximate plane wave feature of the teleseismic wavefront we introduce the radial basis function rbf technique a high precision interpolator with strong adaptability into teleseismic wavefield reconstruction then we use the reconstructed wavefield to image the moho structure beneath south china with rf analysis compared to the conventional h stacking methods the moho that is obtained through this reconstructed wavefield exhibits more details and shows greater consistency to the tectonic provinces the moho depths beneath south china gradually shallow from 50 km at the yangtze block yb in the northwest to 25 km to the southwest of the cathaysia block cb the vp vs ratio at the yb is 1 80 decreasing to 1 57 at the jiangnan orogen and then increasing to 1 70 at the cb obviously varying moho depths and vp vs ratios in both the ganjiang fault gf and tancheng lujiang fault tlf regions is observed which indicates a great similarity in the deep tectonic environment of the gf and tlf the mantle corner flow under south china is suspected to invade into the interior of the yangtze craton teleseismic wavefield reconstruction as a pre processing technique can effectively improve the imaging quality of rf analysis

geochemical and sr nd pb isotopic compositions of cretaceous granitoids constraints on tectonic framework and crustal structure of the dabieshan ultrahigh pressure metamorphic belt china abstract the dabie orogenic belt can be divided into four tectonic and lithological units they are from north to south the north huaiyang nhy unit the northern dabie complex ndc unit the ultrahigh pressure uhp metamorphic unit and high pressure hp metamorphic unit cretaceous granitoids from the four tectonic units irrespective of tectonic unit and lithology show surprisingly similar major and trace element and particularly sr nd pb isotopic compositions indicating a similar crustal source for their magma genesis they have initial 87 sr 86 sr t values of 0 7068 0 7091 and nd depleted mantle model ages of 1 6 2 4 ga and e nd t values at the time of their emplacement 120 ma ranging from 13 to 26 their present day pb isotopic compositions are 206 pb 204 pb 15 62 17 06 207 pb 204 pb 15 21 15 44 and 208 pb 204 pb 36 59 37 81 with comparison to the sr nd pb isotopic compositions of the basement rocks in the dabie orogenic belt the isotopic compositions of the cretaceous granitoids indicate a source that is similar to the northern dabie complex but distinct from the ultrahigh pressure metamorphic unit this strongly suggests that the exposed northern dabie complex extends in the deep crust southward beneath the uhp hp metamorphic units and northward beneath the north huaiyang unit the northern dabie complex is best interpreted as the core of a dome within the dabie orogenic belt the uhp hp metamorphic unit is only a thin skinned slab confined in shallower crustal levels over the northern dabie complex present tectonic framework for the uhp hp terrain was formed by extensional tectonics and post the uhp hp metamorphism the northern dabie complex has an affinity to the yangtze craton the similar source for the cretaceous granitoids also suggests that the suture between the north china and the yangtze cratons is marked by the xiaotian mozitang fault separating the north huaiyang unit and the northern dabie complex rather than the previously thought wuhe shuiko fault which separates the northern dabie complex and the uhp unit

velocity and anisotropy structure of the crust in the dabieshan orogenic belt from wide angle seismic data abstract in order to investigate the crust and upper mantle structure of velocity and anisotropy for dabieshan orogenic belt a wide angle reflection refraction survey from anyi jiangxi province to zhuangmu anhui province pr china was undertaken in 1994 we reconstructed initial images of p and s wave velocities and two anisotropy factors with anderson s notation by using multi parameter velocity analysis technique in 2d anisotropic media and fitted the observed traveltimes for p and s reflecting waves to that calculated by forward modelling and produced the final models of p and s wave velocity and two anderson s anisotropy factors the structures of two anisotropy factors are very different from the structures of p and s wave velocities the structures of p and s wave velocities show the characteristic of layering and blocking and the structures of anderson s anisotropy factors displays the characteristics of chimney structure the thickness of the crust in the studied area varies in the 34 41 km range with a mountain root beneath the dabieshan orogenic belt the average p wave and s wave velocity in the upper middle and lower crust are 5 6 6 0 km s about 3 4 km s 6 2 6 3 km s about 3 6 km s and 6 4 6 8 km s about 4 0 km s respectively the poisson ratio varies from 0 24 to 0 29 with the polarization analysis to the phase s g we find that the fast polarization directions for the yangtze block dabie block and northern china block are about n77 e n18 w and n53 e respectively the seismic anisotropy factors are up to about 5 the zone with strong anisotropy shows the chimney structure which indicates force direction endured by materials flowed upward we inferred that the subduction of the yangtze plate and the mantle flow of materials have played important role in exhuming the ultra high pressure metamorphic rocks of the dabieshan orogenic belt

interactions between the landers and hector mine california earthquakes from space geodesy boundary element modeling and time dependent friction the m w 7 1 hector mine earthquake happened 7 years after the 1992 m w 7 3 landers earthquake within a system of right lateral strike slip faults comprising the eastern california shear zone because estimates of recurrence intervals of m 7 earthquakes on these faults range anywhere from 1500 to 50 000 years the close temporal spacing of these two earthquakes suggests that there is some interaction between the two current models of simple coulomb static stress interactions between the earthquake ruptures do not predict an obvious cause and effect relationship the interaction between the computed normal and right lateral shear stress reductions induced by the landers earthquake at the hector mine hypocenter is unclear we use a combination of space geodesy boundary element modeling and computer modeling of time dependent fault friction to investigate the interaction between the two earthquakes we compare stress changes on the hector mine rupture plane induced by the landers earthquake with the detailed slip distribution inferred using a combination of gps and insar data the slip distributions of both earthquakes are also used to infer the magnitude of the shear stress drop on each earthquake rupture and the orientation of the remote background stress consistent with these two recent events for each earthquake the azimuth of the remote maximum compressive stress was approximately 17 6 and the magnitude of the shear stress drop was 8 1 mpa on the landers rupture and 10 2 mpa on the hector mine rupture using a simple spring and slider model as a proxy for the rate and state frictional response of the hector mine faults to landers earthquake imposed stress steps we find that while a decrease in normal stress at the hector mine hypocenter would by itself have caused the hector mine earthquake to nucleate immediately the simultaneous decrease in shear stress may have caused a delay in the peak shear loading consideration of an acceptable range of rate and state friction parameters secular strain rates and crustal stiffnesses leads us to conclude that this delay could have been 0 to 40 years

measuring near field coseismic displacements from sar images application to the landers earthquake we describe a procedure to compute sar interferograms based on the compensation of the images mis registrations due to the ground deformation and on a specific adaptive filtering to improve the snr in the measurement where displacement gradients are large applied to the landers earthquake case the registration reduces the phase noise by 20 rms near the fault and the interferogram reveals fringes that would not show out otherwise the interferogram is validated by comparison in the far field with a gps edm based model the inferred displacement field shows discontinuities that follow the fault within few hundred meters close to the fault the measured displacements differ significantly from that predicted by elastic modeling of the far field data interferometry and measurements derived from the images amplitude offsets appear to be complementary techniques providing original measurements that may help to reconcile seismological and geodetic models of coseismic deformation with measurements of fault slip at the surface

surface wave array tomography in se tibet from ambient seismic noise and two station analysis ii crustal and upper mantle structure summary we determine the 3 d shear wave speed variations in the crust and upper mantle in the southeastern borderland of the tibetan plateau sw china with data from 25 temporary broad band stations and one permanent station interstation rayleigh wave phase velocity dispersion curves were obtained at periods from 10 to 50 s from empirical green s function egf derived from ambient noise interferometry and from 20 to 150 s from traditional two station ts analysis here we use these measurements to construct phase velocity maps from 10 to 150 s using the average interstation dispersion from the egf and ts methods between 20 and 50 s and estimate from them with the neighbourhood algorithm the 3 d wave speed variations and their uncertainty the crust structure parametrized in three layers can be well resolved with a horizontal resolution about of 100 km or less because of the possible effect of mechanically weak layers on regional deformation of particular interest is the existence and geometry of low shear velocity layers lvls in some regions prominent lvls occur in the middle crust in others they may appear in the lower crust in some cases the lateral transition of shear wave speed coincides with major fault zones the spatial variation in strength and depth of crustal lvls suggests that the 3 d geometry of weak layers is complex and that unhindered crustal flow over large regions may not occur consideration of such complexity may be the key to a better understanding of relative block motion and patterns of seismicity

on the derivation of coseismic displacement fields using differential radar interferometry the landers earthquake we present a map of the coseismic displacement field resulting from the landers california june 28 1992 earthquake derived using data acquired from an orbiting high resolution radar system we achieve results more accurate than previous space studies and similar in accuracy to those obtained by conventional field survey techniques data from the ers 1 synthetic aperture radar instrument acquired in april july and august 1992 are used to generate a high resolution wide area map of the displacements the data represent the motion in the direction of the radar line of sight to centimeter level precision of each 30 m resolution element in a 113 km by 90 km image our coseismic displacement contour map gives a lobed pattern consistent with theoretical models of the displacement field from the earthquake fine structure observed as displacement tiling in regions several kilometers from the fault appears to be the result of local surface fracturing comparison of these data with global positioning system and electronic distance measurement survey data yield a correlation of 0 96 thus the radar measurements are a means to extend the point measurements acquired by traditional techniques to an area map format the technique we use is 1 more automatic 2 more precise and 3 better validated than previous similar applications of differential radar interferometry since we require only remotely sensed satellite data with no additional requirements for ancillary information the technique is well suited for global seismic monitoring and analysis

continental dynamics of eastern china insights from tectonic history and receiver function analysis east asia records a complex sequence of tectonic processes with the mosaic of cratonic blocks and orogenic belts in china preserving evidence for multiple episodes of amalgamation and reworking from the archean to cenozoic the prolonged subduction of the pacific plate from the east has been invoked to explain the volcanic activities in the ne china region and in the songliao basin as well as the extensive destruction of the sub continental lithospheric mantle of the north china craton ncc the collision between the ncc and the yangtze craton involved deep subduction and exhumation of ultrahigh pressure metamorphic orogen in the south china craton the yangtze and cathaysia blocks collided along the shaoxing jiangshan pingxiang suture here we present an overview of the results from multidisciplinary studies on the major tectonic events in the eastern china region and evaluate the geodynamics of these in the light of our recent work based on receiver function analysis the compression induced by the westward subduction of the pacific plate in the ncc and south china appears to have triggered lower crustal and lithospheric delamination we also identify mantle upwelling as a dominant trigger for the major tectonic process in this region

heterogeneity and anisotropy of the lithosphere of se tibet from surface wave array tomography 1 understanding the geotectonic evolution of the southeastern tibetan plateau requires knowledge about the structure of the lithosphere using data from 77 broadband stations in sw china we invert rayleigh wave phase velocity dispersion curves from ambient noise interferometry t 1 0 40 s and teleseismic surface waves t 2 0 150 s for 3 d heterogeneity and azimuthal anisotropy in the lithosphere to 150 km depth our surface wave array tomography reveals 1 deep crustal zones of anomalously low shear wave speed and 2 substantial variations with depth of the pattern of azimuthal anisotropy upper crustal azimuthal anisotropy reveals a curvilinear pattern around the eastern himalayan syntaxis with fast directions generally parallel to the main strike slip faults the mantle pattern of azimuthal anisotropy is different from that in the crust and varies from north to south the tomographically inferred 3 d variation in azimuthal anisotropy helps constrain the source region of shear wave splitting south of 26 n off the high plateau most of the observed splitting can be accounted for by upper mantle anisotropy but for stations on the plateau proper with thick crust crustal anisotropy cannot be ignored on long wavelengths the pattern of azimuthal anisotropy in the crust differs from that in the mantle this is easiest explained if deformation varies with depth the deep crustal zones of low shear wave speed and presumably mechanical strength may represent loci of ductile deformation but their lateral variation suggests that in se tibet localized crustal channel flow and motion along the major strike slip faults are both important

p wave velocities anisotropy and hysteresis in ultrahigh pressure metamorphic rocks as a function of confining pressure 1 the chinese continental drilling project ccsd has drilled to a depth of 5100 m at maobei n34 40 e118 67 donghai county jiangsu province in the eastern segment of the dabie sulu ultrahigh pressure uhp metamorphic terrane the borehole which penetrated through all of the high velocity layers and seismic reflectors observed within the uppermost crust on seismic refraction and reflection profiles reveals the main lithologies to be coesite bearing felsic gneisses metabasic rocks i e amphibolite retrogressed and non retrogressed eclogites and ultramafic rocks i e garnet peridotite and serpentinite p wave velocities anisotropy and hysteresis of 31 typical ccsd core samples and 35 representative surface samples collected from the sulu uhp belt were measured at hydrostatic confining pressures up to 800 mpa the velocity pressure curves can be well described by a four parameter exponential equation derived from theory v p v0 dp b0 exp kp where v0 is the projected velocity at zero pressure if pores cracks were absent d is the intrinsic pressure derivative of velocity in the linear elastic regime b0 is the initial velocity drop caused by the presence of pores cracks at zero pressure and k is the decay constant of the velocity drop in the nonlinear poro elastic regime the seismic hysteresis is caused by irreversible changes in grain contact increases in microcrack aspect ratios and reduction of void space during the pressurization depressurization cycle the statistical properties of p wave velocities in the uhp rocks provide an important set of basic information for the interpretation of field seismic data from the root zones of continental convergent orogenic belts and modern and ancient subduction zones

crustal thicknesses and poisson s ratios in china by joint analysis of teleseismic receiver functions and rayleigh wave dispersion 1 a new grid search scheme which extends the stacking h algorithm to multi layered crustal models and fits observed dispersion of surface wave group velocity simultaneously is proposed to estimate the thickness poisson s ratio and average p wave speed of the crust we first apply it to a synthetic data of a 2 layered crustal model then we show the results analyzing records from 45 permanent broadband seismic stations in china the estimates at six stations agree well with results from deep seismic sounding profiles the crustal thicknesses agree in general with the crust 2 0 model we find that the poisson s ratio in the yangtze platform is rather low compared with the other two platforms the stations along the southeast coast of china have higher poisson s ratios the poisson s ratio of the whole region tends to increase as the average p wave velocity

crustal and uppermost mantle velocity structure and its relationship with the formation of ore districts in the middle lower yangtze river region abstract in this study we conduct ambient noise tomography and teleseismic two plane wave tomography to probe the crustal and uppermost mantle structures in the middle lower yangtze river region the data used include 14 months from july 2012 to august 2013 of continuous vertical component ambient noise data and 219 teleseismic earthquakes recorded at 138 broadband seismic stations from chinese provincial networks and 19 temporary seismic stations deployed by china university of geosciences beijing first we apply ambient noise tomography to the collected ambient noise data to generate rayleigh wave group and phase velocity maps at 5 42 s periods and two plane wave tomography method to earthquake data to generate intermediate to long period phase velocity maps at 20 143 s periods we then combine the short to intermediate period velocity maps from ambient noise and the intermediate to long period phase velocity maps from earthquake data to generate broadband phase velocity maps at periods from 5 to 143 s by inverting these 5 143 s rayleigh wave velocity maps we construct a 3 d shear wave velocity model from the surface to 250 km depth in the middle lower yangtze river region the 3 d model shows that in the upper crust the basin regions including the jianghan hehuai subei hefei and nanyang basins are all featured with low velocities and the mountain regions with high velocities in the uppermost mantle a low velocity zone at 100 200 km depth is observed beneath the middle lower yangtze river metallogenic belt moreover our tomographic results show that the ningwu and ningzhen ore districts are clearly characterized by the strongest low velocity anomaly in the uppermost mantle at 70 200 km depth the depth extent of the low velocity zone becomes shallower and the amplitude of low velocity anomaly becomes larger from the southwest jiurui ore district to northeast ningwu ore districts the change pattern of the low velocity zone in the depth extent and the amplitude is consistent with the fact that peak ages of magmatic events along the middle lower yangtze river metallogenic belt progressively become younger and younger from 148 ma in the southwest to 125 ma in the northeast the observed low velocity zone may represent the cooling hot upper mantle which was partially molten in the past resulting from partial melting of the paleo pacific plate or of an enriched mantle source induced by the westward subduction of the paleo pacific plate the upwelling of the mantle derived magmas may result in the formation of these granitic rocks and coeval ores deposits along the middle lower yangtze river metallogenic belt

flake tectonics in the sulu orogen in eastern china as revealed by seismic tomography 1 seismic tomographic image reveals a crocodile like p waves velocity structure beneath the sulu orogenic belt which marks the subduction collision zone between the sino korean block sk and yangtze block yz in eastern china it may imply that the upper crust of the yz was detached from its lower crust and thrust over the sk for a maximum of 400 km in the sulu region whereas the remnant of the subducted yangtze lithosphere was lay beneath the sk this crustal detached structure flake tectonics might have occurred after the triassic subduction collision

ambient noise rayleigh wave tomography in western sichuan and eastern tibet abstract we perform rayleigh wave tomography in western sichuan and eastern tibet by applying the ambient noise method to broadband data recorded at 49 stations from the sichuan digital seismic network cross correlations of vertical component ambient noise data are computed in one hour segments and stacked over 7 months from june to december 2007 then rayleigh wave group dispersion curves from 6 to 48 s were measured using the multiple filter analysis method group velocity maps at periods from 8 to 44 s were inverted the resulting group velocity maps generally show good correlations with tectonic features the sichuan basin is clearly resolved with lower group velocities at the short periods 8 to 20 s due to thick sedimentary layers and a prominent low velocity zone exhibits in the middle crust beneath the eastern margin of the tibetan plateau the longmen shan thrust belt marks not only the rapid lateral velocity variation between the topographically high tibetan plateau and low elevation sichuan basin but also the transition from the thick crust beneath the tibetan plateau to the normal continental crust beneath the sichuan basin

crustal structure and continental dynamics of central china a receiver function study and implications for ultrahigh pressure metamorphism abstract the qinling tongbai hong an dabie sulu orogenic belt records the tectonic history of paleozoic convergence between the south china and north china blocks in this study the distribution of crustal thickness and p and s wave velocity ratio vp vs is obtained by using the h k stacking technique from the dabie sulu belt in central china our results show marked differences in the crustal structure between the dabie and sulu segments of the ultrahigh pressure uhp orogen the lower crust in the dabie orogenic belt is dominantly of felsic intermediate composition whereas the crust beneath the sulu segment is largely intermediate mafic the crust of the dabie orogenic belt is thicker by ca 3 5 km as compared to that of the surrounding region with the presence of an orogenic root the crustal thickness is nearly uniform in the dabie orogenic belt with a generally smooth crust mantle boundary a symmetrically thickened crust in the absence of any deep structural features similar to that of the yangtze block suggests no supportive evidence for the proposed northward subduction of the yangtze continental block beneath the north china block we propose that the collision between the yangtze and north china blocks and extrusion caused crustal shortening and thickening as well as delamination of the lower crust resulting in asthenospheric upwelling and lower crustal uhp metamorphism along the dabie orogen our results also reveal the presence of a se to nw dipping moho in the north china block beneath the tran north china orogen and eastern block suggesting the fossil architecture of the northwestward subduction of the kula plate

what brought them up exhumation of the dabie shan ultrahigh pressure rocks metamorphic coesite and diamond in the dabie shan eastern china testify to subduction of continental crust to 100 km depth exhumation of these ultrahigh pressure rocks through the crust encompassed two stages 1 south dipping foliation southeast plunging stretching lineation lineation parallel isoclinal folds and boudins indicate extreme subhorizontal shortening and subvertical extension during top to northwest shearing at 200 180 ma syntectonic recrystallization occurred at eclogite and amphibolite facies temperatures and at pressures below coesite stability 2 northwest southeast subhorizontal extension from 133 to 122 ma was concentrated within an asymmetric structural dome in a magmatic complex that forms the northern half of the dabie shan pluton cores at deep structural levels have weak hypersolidus fabrics and pluton carapaces are mylonitic gneisses formed at upper amphibolite facies conditions deformation is concentrated in greenschist facies mylonites and ultramylonites along the xiaotian mozitang detachment fault at the northern topographic limit of the dabie shan our preferred exhumation model involves two stages triassic indentation vertical extrusion and erosion followed by cretaceous plate margin transtension

carboniferous and triassic eclogites in the western dabie mountains east central china evidence for protracted convergence of the north and south china blocks shrimp u pb dating and laser ablation icp ms trace element analyses of zircon from four eclogite samples from the north western dabie mountains central china provide evidence for two eclogite facies metamorphic events three samples from the huwan shear zone yield indistinguishable late carboniferous metamorphic ages of 312 5 307 4 and 311 17 ma with a mean age of 309 3 ma one sample from the hong an group 1 km south of the shear zone yields a late triassic age of 232 10 ma similar to the age of ultra high pressure uhp metamorphism in the east qinling dabie orogenic belt ree and other trace element compositions of the zircon from two of the huwan samples indicate metamorphic zircon growth in the presence of garnet but not plagioclase namely in the eclogite facies an interpretation supported by the presence of garnet omphacite and phengite inclusions zircon also grew during later retrogression zircon cores from the huwan shear zone have ordovician to devonian 440 350 ma ages flat to steep heavy ree patterns negative eu anomalies and in some cases plagioclase inclusions indicative of derivation from north china block igneous and low pressure metamorphic source rocks cores from hong an group zircon are neoproterozoic 780 610 ma consistent with derivation from the south china block in the western dabie mountains the first stage of the collision between the north and south china blocks took place in the carboniferous along a suture north of the huwan shear zone the major triassic continent continent collision occurred along a suture at the southern boundary of the shear zone the first collision produced local eclogite facies metamorphism in the huwan shear zone the second produced widespread eclogite facies metamorphism throughout the dabie mountains sulu terrane and a lower grade overprint in the shear zone

into the forbidden zone very low temperatures at high pressures have long been believed to constitute a forbidden zone not realized in earth however recent studies of ultrahigh pressure uhp terranes indicate that these rocks have experienced such forbidden zone conditions liou et al discuss the implications of these observations for plate tectonics

crustal radial anisotropy beneath the dabie orogenic belt from ambient noise tomography summary in this study we continue our previous work of imaging isotropic shear velocity to study the crustal radial anisotropy beneath the dabie orogen and surrounding regions by jointly analysing rayleigh wave and love wave dispersion curves in addition to processing the vertical component data to retrieve rayleigh waves we collect horizontal component continuous ambient noise data and retrieve love waves from cross correlations of horizontal component noise data between station pairs then we measure love phase velocity dispersion curves at periods from 8 to 35 s using a spectral method and perform surface wave tomography to obtain high resolution phase velocity maps finally we determine crustal radial anisotropy by inverting the local phase velocity dispersion curves of rayleigh and love waves our model of crustal radial anisotropy reveals complex anisotropic patterns associated with the dynamic processes of continent continent collisions and post collision reworking between the north china craton and the yangtze craton in the huabei basin the radial anisotropy is positive throughout the entire crust corresponding to areas with extensional tectonics developed since the middle mesozoic in the jianghan basin strong positive radial anisotropy in the middle and lower crust is observed most likely resulting from subhorizontal alignment of seismic anisotropic materials under the crustal extensional deformation in the eastern dabie orogenic belt the radial anisotropy beneath northern dabie complex ndc appears positive in the upper and lower crust and negative in the middle crust the positive radial anisotropy in the upper crust is probably because of the presence of igneous rocks with anisotropic minerals aligned subhorizontally under the action of the extensional tectonics during igneous extrusion and emplacement whereas the positive radial anisotropy in the lower crust is probably because that subhorizontal alignment of anisotropic materials induced by magmatic underplating formed after the delamination of the orogeny in the middle crust finite strains associated with the vertical intrusion of deep magma might cause crystalline anisotropic minerals aligned vertically resulting in observed negative radial anisotropy in the western dabie orogenic belt positive radial anisotropy is present in the whole crust except beneath the hong an ultrahigh pressure uhp area where radial anisotropy is negative in the middle crust similar to ndc the hong an uhp probably experienced similar thermal geodynamic processes as the eastern dabie and the negative radial anisotropy might be also the result of vertical alignment of anisotropic minerals caused by the vertical intrusion of deep magma strong localized negative radial anisotropy in the middle crust beneath the xinyang area is imaged most likely caused by the vertical alignment of anisotropic minerals crystallized from the vertically intruding mafic magma originated from the upper mantle during the volcanism

crustal structure determined from ambient noise tomography near the magmatic centers of the coso region southeastern california we apply seismic ambient noise tomography to image and investigate the shallow shear velocity structure beneath the coso geothermal field and surrounding areas data from a passcal experiment operated within the coso geothermal field between 1998 and 2000 and surrounding broadband stations from the southern california seismic network are acquired and processed daily cross correlations of ambient noise between all pairs of stations that overlapped in time of deployment were calculated and then stacked over the duration of deployment phase velocities of rayleigh waves between 3 and 10 s periods are measured from the resulting cross correlations depending on the period between about 300 and 600 reliable phase velocity measurements are inverted for phase velocity maps from 3 to 10 s periods which in turn are inverted for a 3 d shear velocity model beneath the region the resulting 3 d model reveals features throughout the region that correlate with surface geology beneath the coso geothermal area shear velocities are generally depressed a prominent low velocity anomaly is resolved clearly within the top 2 km no significant anomaly is seen below about 14 km depth and a weakly resolved anomaly is observed between 6 and 12 km depth the anomaly in the top 2 km probably results from geothermal alteration in the shallow subsurface no magmatic body is imaged beneath 14 km depth but the shear velocity anomaly between 6 and 12 km may be attributable to partial melt the thickness and amplitude of the magma body trade off in the inversion and are ill determined low velocities in the regions surrounding coso at depths near 7 km underlie areas with miocene to recent volcanism suggesting that some magmatic processing of the crust could be focused near this depth

exhumation of high pressure rocks a review of concepts and processes the exhumation of high pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures or the transport of the metamorphic rocks through the overburden exhumation cannot be achieved simply by thrusting or strike slip faulting it may be caused by erosion of shortened and thickened crust but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km one or more of the following additional mechanisms may be involved 1 corner flow of low viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock and may explain some occurrences of high pressure tectonic blocks in melange this process does not however appear to be adequate to explain the exhumation of regional high pressure terrains 2 buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings this is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle but cannot explain the emplacement of coherent tracts of high density metamorphic rock into shallow crustal levels some high pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low density mud or serpentinite 3 extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high pressure terrains extension may occur in the upper part of an accretionary wedge thickened by underplating or it may affect the whole lithosphere in a region of intracontinental convergence if surface elevation has been increased by the removal of a lithospheric root in the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the metamorphic terrain

anisotropy of complex magnetic susceptibility as an indicator of strain and petrofabric in rocks bearing sulphides abstract a new method anisotropy of complex magnetic susceptibility acms for determining the petrofabric of specimens with conductive minerals is developed the method uses the same induction coil equipment and techniques that can be used for the measurement of the anisotropy of magnetic susceptibility ams however a higher 100 khz operating frequency emphasizes the electrical conductivity response and thus yields a measure of the anisotropy of electrical conductivity of the specimen the method was tested on variably deformed plasticine samples containing aluminium fabric markers and on synthetic aggregates of pyrrhotite and talc pyrrhotite mixtures deformed triaxially at a confining pressure of 200 mpa 2 kbar by up to 35 homogeneous shortening acms successfully defines the petrofabric and permits prediction of the principal directions of finite strain the intensity of ams and to a lesser extent of acms correlate with the strain ratio in these simple coaxial flattening plane strain experimental deformations on selected materials

a crustal model of the ultrahigh pressure dabie shan orogenic belt china derived from deep seismic refraction profiling we present a new crustal cross section through the east west trending ultrahigh pressure uhp dabie shan orogenic belt east central china based on a 400 km long seismic refraction profile data from our profile reveal that the cratonal blocks north and south of the orogen are composed of 35 km thick crust consisting of three layers upper middle and lower crust with average seismic velocities of 6 0 6 0 2 km s 6 5 6 0 1 km s and 6 8 6 0 1 km s the crust reaches a maximum thickness of 41 5 km beneath the northern margin of the orogen and thus the present day root beneath the orogen is only 6 5 km thick the upper mantle velocity is 8 0 6 0 1 km s modeling of shear wave data indicate that poisson s ratio increases from 0 24 6 0 02 in the upper crust to 0 27 6 0 03 in the lower crust this result is consistent with a dominantly felsic upper crustal composition and a mafic lower crustal composition within the amphibolite or granulite metamorphic facies our seismic model indicates that eclogite which is abundant in surface exposures within the orogen is not a volumetrically significant component in the middle or lower crust much of the triassic structure associated with the formation of the uhp rocks of the dabie shan has been obscured by post triassic igneous activity extension and large offset strike slip faulting nevertheless we can identify a high velocity 6 3 km s zone in the upper 5 km depth crustal core of the orogen which we interpret as a zone of ultrahigh pressure rocks a north dipping suture and an apparent moho offset that marks a likely active strike slip fault

moho mapping in the dabie ultrahigh pressure collisional orogen central china eight wide angle reflection refraction seismic profiles with a total length of 1700 km and near vertical reflection seismic profiles with a total length of 340 km across the dabie orogen eastern china have been completed in recent years and allow the moho depth and uppermost mantle velocity to be mapped across 40 000 km 2 these data reveal the detailed structure of the crust and upper mantle of this orogen that resulted from collision of the north china craton ncc with the yangtze craton yc the dabie orogen is an asymmetric orogen with a thin crustal root 6 km preserved in its northern part highlighted by a north dipping moho compared to the nearly seismically transparent lower crust the moho crust mantle transition zone under the dabie orogen is a prominent north dipping strongly layered reflection which is inferred to reflect the remnants of subduction of yc under the edge of the ncc or post collisional exhumation of ultrahigh pressure uhp rocks and indicates the northward polarity of subduction of the yc the moho of the yc and ncc meet beneath the northern part of the dabie mountains and the ncc moho north is uplifted by 4 to 5 km offset 1 over the yc moho south marking the ncc yc collision zone along the southern margin of the dabie mountains the moho below the yangtze foreland is underthrust beneath the moho of the dabie mountains forming another moho overlap offset 2 with a depth difference of 5 to 6 km the two moho overlaps offsets at both flanks of the dabie mountains formed two crustal scale boundaries at depth between the ncc and the dabie orogen and the dabie orogen and the yc respectively offset 1 is considered to be the triassic suture between the yc and ncc as supported by the metamorphic ages of uhp rocks this displays a wedge shaped offset zone opening towards the east that acted as a channel for exhumation of uhp rocks offset 2 under the southern margin of the dabie orogen is connected to the xiangfan guangji fault that gave rise to a large scale thrust detachment that propagated towards the foreland of the dabie orogen during the jurassic thus our moho mapping confirms that there are structural remnants of the triassic deep continental subduction preserved despite the superimposed jurassic deformation