tectonothermal evolution of the mayuan assemblage in the cathaysia block implications for neoproterozoic collision related assembly of the south china craton the mayuan assemblage in the cathaysia block southeast china consists of felsic paragneiss pelitic schist greenschist amphibolite marble calcsilicate and quartzite that underwent three episodes of deformation d1 d3 and four episodes of metamorphism m1 m4 in the early neoproterozoic the m1 assemblage consists of mineral inclusions defining an early foliation s1 within porphyroblasts represented by chlorite muscovite biotite plagioclase quartz in pelitic schist and actinolite chlorite epidote albite quartz enclosed in amphibolite m2 coincides with the development of the regional schistosity s2 and represents the formation of the porphyroblasts and growth of matrix minerals resulting in development of prograde metamorphic zones chlorite biotite garnet staurolite and kyanite zones m3 is simultaneous with the third phase of deformation d3 and produced sillimanite bearing mineral assemblages in pelitic schist and hornblende bearing assemblages in amphibo lite the last metamorphic episode m4 gave rise to the retrogressive assemblage chlorite muscovite in pelitic rock and actinolite chlorite epidote in amphibolite the sequence of mineral assemblages and history of metamorphic reactions built from the petrogenetic grid of pelites suggest a near isothermal decompression clockwise p t path for the mayuan pelitic schists using the tweequ software program the garnet biotite thermometer and garnet muscovite biotite plagioclase barometer yield p t conditions for m1 of 5 5 to 6 0 kb and 450 to 500 c and conditions for the garnet staurolite and kyanite zones of m2 of 6 0 to 7 0 kb and 550 to 600 c 6 0 to 7 5 kb and 600 c and 11 0 to 11 5 kb and 600 c the p t conditions of m3 were estimated at 570 to 625 c and 4 0 to 4 5 kb using the muscovite biotite thermometer and hornblende plagioclase geothermo barometer the garnet chlorite thermometer yields temperatures of 300 to 400 c for m4 but the pressures of m4 cannot be quantitatively estimated because of the lack of a suitable geobarometer these p t estimates also define an near isothermal decompression clockwise p t path which is involved in initial crustal thickening followed by rapid exhumation and final cooling and is related to amalgamation of the cathaysia and yangtze blocks to form the south china craton

effects of prestress state and rupture velocity on dynamic fault branching 1 we consider a mode ii rupture which propagates along a planar main fault and encounters an intersection with a branching fault using an elastodynamic boundary integral equation formulation allowing the failure path to be dynamically self chosen we study the following questions does the rupture initiate along the branch does it continue is the extensional or compressional side most favored for branching does rupture continue on the main fault too failure is described by a slip weakening law for which the strength at any amount of slip is proportional to normal stress our results show that dynamic stresses around the rupture tip which increase with rupture velocity at locations off the main fault plane relative to those on it could initiate rupture on a branching fault as suggested by prior work whether branched rupture can be continued to a larger scale depends on principal stress directions in the prestress state and on rupture velocity the most favored side for branching rupture switches from the extensional to the compressional side as we consider progressively shallower angles of the direction of maximum compressive prestress with the main fault simultaneous rupturing on both faults can be activated when the branching angle is wide but is usually difficult for a narrow branching angle due to strong stress interactions between faults however it can be also be activated by enhanced dynamic stressing when the rupture velocity is very near the rayleigh velocity natural examples seem consistent with the simulations that we present

discontinuity structure of the mantle transition zone beneath the north china craton from receiver function migration 1 a better understanding of the significant phanerozoic tectonic reactivation and destruction of the north china craton ncc demands a detailed knowledge of the deep structural features of the region we applied the wave equation based poststack migration technique to a combined receiver function data set from more than 250 broadband seismic stations to construct the structural image of the mantle transition zone beneath the ncc our imaging results reveal a relatively simple and flat 410 km discontinuity but a structurally complicated 660 km discontinuity beneath the region double discontinuities and a 30 km depression of the 660 km discontinuity are observed locally in the southern part of the eastern ncc in contrast to the smoothly varying structure to the north and in the central and western parts of the craton distinctly rapid variations in both the 660 km discontinuity structure and mantle transition zone thickness were found across the northsouth gravity lineament nsgl near the boundary between the eastern and central ncc which probably reflects different thermal and probably chemical properties on the two sides of the nsgl these differences are possibly associated with the pacific slab which is imaged tomographically as a flat lying structure in the mantle transition zone under the region east of the nsgl the structural variation in the deep upper mantle appears to coincide with the sudden changes in surface topography gravity field and crustal and lithospheric structures as well indicating that the two domains may have tectonically deformed differently throughout the whole upper mantle during the phanerozoic cratonic destruction the mantle transition zone on the eastern side of the nsgl is up to 30 40 km thicker than the global average this thickness and the complex structure of the 660 km discontinuity in this region may reflect the strong influence that the deep subduction and stagnancy of the pacific slab and its possible sporadic penetration into the lower mantle have had on mantle dynamics and lithospheric reactivation in the eastern ncc since the mesozoic time on the other hand the less variable structure and normal to thin mantle transition zone imaged beneath the central and western ncc may indicate that the indiaeurasia collision has had a relatively weak effect on the cenozoic tectonics of these regions

lithospheric thickness beneath the dabie shan central eastern china from s receiver functions summary p and s receiver functions obtained from a portable array of 34 broad band stations in east central china provide a detailed image of the crust mantle and lithosphere asthenosphere boundaries lab in the dabie shan and its adjacent areas clear s to p converted waves produced at the lab show a thin lithosphere beneath the whole study area based on our results the thickest lithosphere of 72 km is observed beneath the southern part of the area within the yangtze craton whereas beneath the north china platform the lithosphere is only 60 km thick s receiver functions also reveal in good agreement with p receiver functions a maximum depth of the moho beneath the dabie shan orogen at approximately 40 km furthermore we interpret the structural difference at 32 latitude as the probable location of

small intermediate fault segments can either aid or hinder rupture propagation at stepovers 1 large scale geometrical complexities along faults are known to be likely endpoints for coseismic rupture as suggested by analysis of historic ruptures and corroborated by models of rupture on bent or discontinuous faults however natural faults also include smaller scale complexities we use the 3d finite element method to model dynamic ruptures on strike slip fault stepovers with a smaller intermediate fault between the main strands we find that such small faults can have a controlling effect on rupture behavior and ground motion intensity and distribution in particular the intermediate fault can either aid or prevent rupture propagation across the stepover depending on its length and basal depth the results have important implications for hazard assessment of faults with large and small scale geometrical complexities and also suggest that more site specific modeling studies may be necessary to develop realistic rupture scenarios for individual complex fault systems

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

hypocenter locations in finite source rupture models we use a database of more than 80 finite source rupture models for more than 50 earthquakes m w 4 1 8 1 with different faulting styles occurring in both tectonic and subduction environments to analyze the location of the hypocenter within the fault and to consider the correlation between hypocenter location and regions of large slip rupture in strike slip and crustal dip slip earthquakes tends to nucleate in the deeper sections of the fault subduction earthquakes do not show this tendency ratios of the hypocentral slip to either the average or the maximum slip show that rupture can nucleate at locations with any level of relative displacement rupture nucleates in regions of very large slip d 2 3 d max in only 16 of the events in regions of large slip 1 3 d max d d max in 35 of the events and in regions of low slip d 1 3 d max in 48 of the events these percentages significantly exceed the percentages of fault area with very large 7 and large 28 slip ruptures that nucleate in regions of low slip however tend to nucleate close to regions of large slip and encounter a zone of very large slip within half the total rupture length applying several statistical tests we conclude that hypocenters are not randomly located on a fault but are located either within or close to regions of large slip

the effects of double fault bends on rupture propagation a geometrical parameter study we use the 2d finite element method to determine how geometrical parameters determine whether rupture will propagate across a linked stepover in a strike slip fault the end segments of the fault system are aligned in the direction of maximum shear and the length and angle of the linking segment are allowed to vary we observe that ruptures propagate through extensional stepovers with steeper angles and longer linking segments than otherwise equivalent compressional step overs these different rupture behaviors form distinct regions in angle stepover length parameter space the boundary between these regions takes the shape of an asymptotic curve in both the extensional and compressional cases models in which the size of the entire fault system was made larger or smaller revealed that the location of the bound aries between regions of different rupture behavior do not scale linearly with the system size it was easier to rupture steeper and relatively longer stepovers in fault systems that were larger overall a separate set of models in which the stress field is rotated so that the parallel end segments were optimally aligned for rupture significantly altered the rupture behavior curves in this stress field it was easier to rupture compressional stepovers with steeper angles and longer linking segments than it was to rupture equivalent extensional stepovers in both the case in which the end segments are aligned with the direction of maximum shear and the case in which the end segments are optimally oriented for rupture the angles at which rupture could no longer propagate through the entire fault corresponded with peaks in the fault s s value

scales of stress heterogeneity near active faults in the santa barbara channel southern california the santa barbara channel represents the offshore portion of the ventura basin in southern california ongoing transpression related to a regional left step in the san andreas fault has led to the formation of e w trending en echelon fault systems that accommodate localized shortening across the basin recent studies have suggested that faults within the channel could be capable of a multisegment rupture and producing a m w 7 7 8 1 tsunamigenic earthquake however dynamic rupture models producing these results do not account for stress heterogeneity with only sparse information available on the stress field in this region further borehole derived stress constraints are essential for obtaining a more comprehensive understanding of the hazards related to the complex fault systems we used caliper logs from 19 wells obtained from industry to identify stress induced borehole breakouts beneath the holly and gail oil platforms in the channel our newly developed forward modeling technique provides constraints on the orientations and relative magnitudes of the three principal stresses at gail we determine a reverse faulting stress regime s hmax 1 7 s hmin 1 6 sv 1 0 and an s hmax azimuth of n45 e our results are consistent with local structures which reflect deeper regional scale trends and with similar studies onshore nearby at holly an s hmax rotation from n36 w to n57 e occurs across 100 m depth in a single well and differs from nearby results indicating that short length scale 10 km laterally and 1 km in depth stress heterogeneity is associated with complex changes in fault geometry

contrasts of seismic velocity density and strength across the moho abstract we provide an overview of contrast of elastomechanical parameters across the moho basically contrasts in seismic wave velocities density and yield strength these can be regarded as dynamic and quasi static endmembers of elastomechanical parameters of the crust mantle transition with respect to practical applications they are closely related because seismic investigations play the role of exploring the earth structure and physical state forming the boundary conditions for determining density and rheological models we address both average global moho models and petrophysical and structural factors that cause deviations from the global averages such as variations in moho depth temperature and rock composition fabric anisotropy and macro scale heterogeneity besides principle considerations these factors are put in a regional context in order to demonstrate how they are related to past and present tectonic processes seismic velocity and density contrasts are found between 0 and 25 whereas strength or viscosity contrasts may be orders of magnitude higher but may vanish as well or show a discontinuity of higher order only especially oceanic and old cratonic crust and near moho mantle may appear as a rheological unit although they are seismically well distinguishable in terms of seismic velocities the moho may vanish mainly under the influence of serpentinization or eclogitization originally defined as a first order discontinuity in seismic velocity the moho has turned out to be an interface across which other seismic properties such as seismic velocity gradients anisotropy and heterogeneity scale parameters can change strongly too however knowledge of these parameters as well as their relation to the rheology of the crust mantle transition is still restricted to local or regional examples so no global conclusions can be drawn

a 21 event 4 000 year history of surface ruptures in the anza seismic gap san jacinto fault and implications for long term earthquake production on a major plate boundary fault paleoseismic work completed at hog lake on the san jacinto fault sjf near anza california indicates that at least 21 surface ruptures have occurred in the anza seismic gap over the past 4 000 years the ages of the ruptures are constrained by 111 radiocarbon dates 97 of which fall in stratigraphic order the average recurrence interval for all ruptures for this period is about 185 105 years although some ruptures such as occurred in the april 1918 earthquake caused only minor displacement we rate the expression of each interpreted event in each of the twelve developed field exposures presented in this work by assigning numeric values for the presence of different criteria that indicate rupture to a paleo ground surface weakly expressed ruptures for example the deformation we interpret to be the result of the historical 1918 earthquake received low scores and are interpreted as smaller earthquakes from this analysis we infer that at least fifteen of the identified ruptures are indicative of large earthquakes similar to the penultimate earthquake inferred to be the m w 7 3 22 november 1800 earthquake the adjusted recurrence interval for large earthquakes lengthens to approximately 254 years comparison with the rupture history at the mystic lake paleoseismic site on the claremont strand indicates that it is plausible that several of the large ruptures identified at hog lake could have jumped the hemet step over at mystic lake and continued on the claremont strand or vice versa but most of the event ages do not match between the two sites indicating that most ruptures do not jump the step finally comparison with san andreas fault ruptures both to the north and south of its juncture with the sjf suggest that some northern sjf ruptures identified at mystic lake may correlate with events identified at wrightwood but that these northern ruptures have no match at hog lake and can not indicate rupture of the entire sjf onto the saf

a grid doubling finite element technique for calculating dynamic three dimensional spontaneous rupture on an earthquake fault summary we present a new finite element technique for calculating dynamic 3 d spontaneous rupture on an earthquake fault which can reduce the required computational resources by a factor of six or more without loss of accuracy the grid doubling technique employs small cells in a thin layer surrounding the fault the remainder of the modelling volume is filled with larger cells typically two or four times as large as the small cells in the resulting non conforming mesh an interpolation method is used to join the thin layer of smaller cells to the volume of larger cells grid doubling is effective because spontaneous rupture calculations typically require higher spatial resolution on and near the fault than elsewhere in the model volume the technique can be applied to non planar faults by morphing or smoothly distorting the entire mesh to produce the desired 3 d fault geometry using our faultmod finite element software we have tested grid doubling with both slip weakening and rate and state friction laws by running the scec usgs 3 d dynamic rupture benchmark problems we have also applied it to a model of the hayward fault northern california which uses realistic fault geometry and rock properties faultmod implements fault slip using common nodes which represent motion common to both sides of the fault and differential nodes which represent motion of one side of the fault relative to the other side we describe how to modify the traction at split nodes method to work with common and differential nodes using an implicit time stepping algorithm

the effects of fault stepovers on ground motion abstract using 3d dynamic models we investigate the effect of fault stepovers on near source ground motion we use the finite element method to model the rupture slip and ground motion of two parallel strike slip faults with an unlinked overlapping stepover of variable width we model this system as both an extensional and a compressional stepover and compare the results to those of single planar faults we find that overall the presence of a stepover along the fault trace reduces the maximum ground motion when compared to the long planar fault whether the compressional or extensional stepover exhibits higher ground motion overall depends on the width of the separation between the faults there is a region of reduced ground motion at the end of the first fault segment when the faults are embedded in a homogeneous material we also experiment with stress fields leading to supershear and subshear rupture velocities and with different stress drops within those conditions we find that subshear rupture produces stronger motions than supershear rupture but supershear ruptures produce that maximum over a larger area than subshear areas even though the overall area that experiences any shaking at all is not drastically different between the two cases lastly we experiment with placing realistic materials along and around the faults such as a sedimentary basin in an extensional stepover a damage zone around the fault and a soft rock layer on top of bedrock through the entire model area these configurations alter the pattern of ground motion from the homogeneous case the peaks in ground motion for the bimaterial cases depend on the materials in question the results may have implications for ground motion prediction in future earthquakes on geometrically complex faults online material mpeg 4 movies of models of dynamic rupture of fault stepovers embedded in heterogeneous material settings

new evidence from seismic imaging for subduction during assembly of the north china craton comment the frozen in information in the crust plays an important role in improving our understanding of cratonic formation and evolution and plate tectonics in the precambrian the trans north china orogen is a continent continent collision belt generated by the assembly of the north china craton the mechanism and modality of the collision are disputed here we present a seismic image of the western block and the trans north china orogen of the north china craton derived using receiver function analysis of the teleseismic records from a dense array a low velocity zone extending from the middle crust to the moho is interpreted as a remnant of upper middle crustal material associated with westward dipping subduction beneath the western block of the north china craton crustal uplift and magmatic underplating resulting from subsequent tectonic events were responsible for modifying the remaining subduction architecture the western boundary of the trans north china orogen is located west of the boundary earlier identified by surface investigation the results combined with previous seismic imaging in the eastern north china craton provide insight into the amalgamation of the eastern and western blocks and the subsequent tectonic deformation of the north china craton

3d simulations of multi segment thrust fault rupture thrust faults such as those that underlie the los angeles basin are typically segmented by tear faults that offset the thrust fault segments we perform 3d finite difference simulations of earthquake rupture to evaluate the effectiveness of these offsets in retarding rupture the simulations include orthogonal intersecting faults to model the interaction of the thrust fault segments with the tear fault for reasonable assumptions for fault segment length strength and stress drop rupture can jump offsets of up to 2 km if a tear fault is present consistent with observations of well studied thrust earthquakes absent a tear fault the maximum offset that can be breached is an order of magnitude smaller

delineation of intrabasin structure in a dilational jog of the san jacinto fault zone southern california three high resolution seismic reflection lines were acquired in the northern part of the san jacinto graben the graben a pull apart basin formed by a dilational right step of the san jacinto fault zone has been previously interpreted as a simple rhombochasm the reflection survey located at least one significant and previously unidentified intrabasin fault referred to here as the farm road strand this fault lies approximately halfway between the claremont and casa loma strands of the san jacinto fault zone at the north end of the basin the southwestern boundary of the graben is interpreted to be the newly identified farm road strand and not the casa loma strand as was previously thought the identification of this intrabasin fault allows us to infer that the san jacinto basin comprises coalescing subbasins and is not a simple pull apart basin with an unusually large length width ratio the distances between the en echelon casa loma farm road and claremont strands are between 1 and 2 km this close spacing would likely permit an earthquake rupture to jump between strands and thus propagate through the san jacinto basin

topographic response to mantle lithosphere removal in the southern sierra nevada region california geological studies of mantle xenoliths entrained in late neogene quaternary lavas from the southern sierra nevada region and regional geophysical studies suggest that the highdensity mantle lithosphere that formed beneath the sierra nevada batholith in conjunction with arc magmatism is being convectively removed as a drip structure this structure as imaged seismically is roughly cylindrical in shape with a diameter of 100 km and extends to 225 km depth centered above this structure is a region 120 km in diameter that is undergoing active subsidence relative to adjacent regions such subsidence is seen in the active fluvial alluvial sediment flooding of mountainous topography of the southwestern sierra and in the development of the adjacent tulare lake basin of the san joaquin valley dynamic modeling of such upper mantle drip structures predicts a phase of overlying surface subsidence during the most vigorous phase of drip formation the southern sierra upper mantle drip and the overlying crust appear to be in this phase of their dynamically coupled evolution

on the trigger of el nino southern oscillation by the forcing of early el chichon volcanic aerosols after the volcanic eruption of el chichon in 1982 the distribution of volcanic aerosols in the upper atmosphere was zonally very inhomogeneous for about a month or more and was located in a fairly uniform zonal band around the earth in the northern subtropical region for the ensuing several months the impact of those aerosols absorbing radiation on the atmospheric motion is discussed in the model of gill 1980 it is shown that the mean westerly wind induced near the central pacific equatorial region would be able to trigger or amplify the el nino southern oscillation several observed results related to the simulation are discussed in some detail the location of the initial center of most aerosols relative to the central pacific is important in the model and the impact of the forcing at the agung event of 1963 is estimated to be smaller than that of the present event which seems to agree with observed results

crustal structure across the yanshan belt at the northern margin of the north china craton abstract we applied an integrated receiver function imaging technique to the teleseismic data from 54 ncisp iii broadband seismic stations to study the fine scale crustal structure beneath the eastern yanshan belt ysb and adjacent areas at the northern margin of the north china craton ncc the robustness and reliability of the resultant crustal image were noticeably improved by achieving imaging consistency between common conversion point stacking and waveform inversion of the receiver functions our imaging result revealed substantial lateral heterogeneities in the crust of the study region as displayed by the undulating intra crustal interfaces highly varying upper middle and lower crust thicknesses and interlayers of low and high velocities the crustal structure of the ysb is characterized by significant structural variations together with a sharp moho a thin to normal crust and a lower crust with lower velocity and normal thickness it differs markedly from the bohai bay basin and the taihang mountains within the interior of the ncc the distinct features and structural complexity of the ysb might be attributed to the complex tectonic history of the region especially the multiple phases of contraction and possible occurrence of crustal delamination which is in large contrast to other subregions of the ncc where tectonic extension likely dominated the crustal deformation since the late mesozoic

where is the north china south china block boundary in eastern china the qinling dabieshan belt results from the collision of the north china and south china blocks the eastern extension of the belt the sulu area consists of several stacked units from top to bottom these are 1 a weakly metamorphosed slate sandstone unit of neoproterozoic paleozoic age 2 a gneiss quartzite unit metamorphosed under high pressure p conditions 3 a marble amphibolite unit 4 an ultrahigh p unit that was very deeply subducted and then exhumed and 5 a migmatitic dome resulting from the melting of ultrahigh p rocks all these units underwent the same deformation which was characterized by a top to the northwest extensional ductile shearing during their exhumation granulite facies restites in the migmatite are not significantly different from granulitized eclogites derived from the ultrahigh p rocks the migmatite exhibits the same structural and petrologic evolution as that determined for the other units the resemblance of petrologic and structural features and the lack of ocean basin rock shows that the boundary between the north china block and south china block must be placed north of the sulu area

segmentation of the northern san jacinto fault zone southern california accurate forecasting of large earthquakes in the san jacinto fault zone depends on the correct determination of fault segmentation we have searched for discontinuities in the fault zone using as data geological maps of the fault traces relocated earthquake hypocenters focal mechanisms slip rates and historic large earthquake rupture zones we identify nine principal discontinuities in the northern san jacinto fault zone these are characterized as structural discontinuities bends steps branches intersections geodetic discontinuities slip rate and lithologic discontinuities most of the discontinuities have more than one defining characteristic we also analyzed the local strain field orientation along the fault zone significant lateral discontinuities in the strain field orientation are coincident with many of the structural and geodetic discontinuities we identify segment lengths defined from the data vary from about 7 to 35 km this range of segment lengths is consistent with the lengths of large historical earthquake ruptures however evidence from small earthquake hypocenter patterns suggests the possibility that in some areas large earthquakes may rupture multiple adjacent segments in these cases maximum magnitudes may be larger than those observed historically because of the short historic record and the sparse paleoseismic record probabilistic estimates of earthquake recurrence for this fault zone have depended heavily on assumed characteristic lengths of individual rupture segments ours and previous delineations of segment lengths have varied considerably indicating that assumed segment length is a major source of uncertainty in the recurrence calculations this source of uncertainty should be taken into account in calculations of the reliability of the probabilistic hazard estimates

rupture termination and jump on parallel offset faults proper evaluation of seismic hazard depends on accurate estimates of potential earthquake size in areas with complex multisegment fault systems such an estimate in turn depends on an ability to predict the circumstances under which rupture may jump between fault segments many observational and numerical studies have analyzed the phenomenon of jumping rupture but none has focused on how the process of rupture termination on the primary nucleating fault segment affects the ability of rupture to jump to a secondary fault segment in the current study i model the dynamics of a simple 2d strike slip fault system with two parallel segments arranged with either a compressional or extensional stepover i vary the suddenness with which the initial shear stress tapers to zero on the primary section if the initial shear stress goes to zero over a very small 100 m distance rupture readily jumps both compressional and extensional stepovers of 1 km if the initial shear stress tapers to zero over 1 km rupture can jump the compressional stepover but not the extensional stepover if the initial shear stress tapers to zero over 2 5 km rupture cannot jump either the compressional or the extensional stepover the results illustrate the importance of the slip gradient and the resultant static stress field and the acceleration of the rupture front and the resultant generation of stopping phases in determining the probability of jumping rupture

laboratory measurements of p wave and s wave velocities across a surface analog of the continental crust mantle boundary cabo ortegal spain the paleozoic cabo ortegal complex of nw spain provides an exposed analog of the continental crust mantle transition it is composed of an overturned section that at its base begins with felsic gneisses followed upward by eclogites intermediate and mafic granulties and ultramafic rocks peak metamorphic conditions reached c 800 c and 1 7 gpa in the middle to late devonian fourteen samples were analysed for p wave and s wave velocities as well as density at the high pressure lab at dalhousie university canada seismic velocities were measured at pressures of 10 to 600 mpa at a temperature of 20 c when possible measurements were made parallel and perpendicular to banding and parallel to the lineation the major element composition of each sample was measured by xrf at the university of barcelona spain samples display a broad range of p wave and s wave velocities 6 2 to 8 2 km s and 3 2 to 4 6 km s at 600 mpa respectively that generally increase with density 2 7 to 3 4 g cm3 and reflect an overall increase from middle to lower crustal velocities in the felsic gneisses and intermediate to mafic granulites to mantle velocities in the eclogites and ultramafic rocks the seismic moho p wave velocity 7 6 km s is reached at the mappable contact between the gneisses and the eclogite whereas the compositional moho or crust mantle transition occurs at the transitional contact between the mafic granulites and peridotites between 200 and 600 mpa p wave anisotropy ranges from between 2 and 8 whereas s wave anisotropy ranges from 1 to around 8 according to rock type poisson s ratios calculated from the laboratory measurements are within the range of those determined from field experiments elsewhere p wave reflection coefficients between the various lithologies range from 0 21 to 0 08 these laboratory data provide a calibration for the physical properties and the nature of reflectivity of the in situ lower continental crust and upper mantle transition

fault geometry rupture dynamics and ground motion from potential earthquakes on the north anatolian fault under the sea of marmara summary using the 3 d finite element method we develop dynamic spontaneous rupture models of earthquakes on the north anatolian fault system in the sea of marmara turkey considering the geometrical complexity of the fault system in this region we find that the earthquake size rupture propagation pattern and ground motion all strongly depend on the interplay between the initial static regional pre stress field and the dynamic stress field radiated by the propagating rupture by testing several nucleation locations we observe that those far from an oblique normal fault stepover segment near istanbul lead to large through going rupture on the entire fault system whereas nucleation locations closer to the stepover segment tend to produce ruptures that die out in the stepover however this pattern can change drastically with only a 10 rotation of the regional stress field our simulations also reveal that while dynamic unclamping near fault bends can produce a new mode of supershear rupture propagation this unclamping has a much smaller effect on the speed of the peak in slip velocity along the fault finally we find that the complex fault geometry leads to a very complex and asymmetric pattern of near fault ground motion including greatly amplified ground motion on the insides of fault bends the ground motion pattern can change significantly with different hypocentres even beyond the typical effects of directivity the results of this study may have implications for seismic hazard in this region for the dynamics and ground motion of geometrically complex faults and for the interpretation of kinematic inverse rupture models

mantle heterogeneities and the scec reference three dimensional seismic velocity model version 3 we determine upper mantle seismic velocity heterogeneities below southern california from the inversion of teleseismic travel time residuals teleseismic p wave arrival times are obtained from three temporary passive experiments and southern california seismic network scsn stations producing good raypath coverage the inversion is performed using a damped least squares conjugate gradient method lsqr the inversion model element spacing is 20 km before the inversion the effects of crustal velocity heterogeneities represented by the southern california earthquake center scec seismic velocity model version 2 are removed from the teleseismic travel times the p wave inversion produces a variance reduction of 43 s wave velocities are determined from laboratory vp vs ratios the most prominent features imaged in the results are high p wave velocities 3 in the uppermost mantle beneath the northern los angeles basin and the previously reported tabular high velocity anomaly 3 to depths of 200 km beneath the transverse ranges crosscutting the san andreas fault we incorporate the upper mantle seismic velocity heterogeneities into the scec southern california reference seismic velocity model the prior accounting for the crustal velocity heterogeneity demonstrates the utility of the top down method of the scec seismic velocity model development

applying a three dimensional velocity model waveform cross correlation and cluster analysis to locate southern california seismicity from 1981 to 2005 we compute high precision earthquake locations using southern california pick and waveform data from 1981 to 2005 our latest results are significantly improved compared to our previous catalog by the following 1 we locate events with respect to a new crustal p and s velocity model using three dimensional ray tracing 2 we examine six more years of waveform data and compute cross correlation results for many more pairs than our last analysis and 3 we compute locations within similar event clusters using a new method that applies a robust fitting method to obtain the best locations satisfying all the differential time constraints from the waveform cross correlation these results build on the relocated catalogs of hauksson and shearer 2005 and shearer et al 2005 and provide additional insight regarding the fine scale fault structure in southern california and the relationship between the san andreas fault saf and nearby seismicity in particular we present results for two regions in which the seismicity near the southern saf seems to align on dipping faults

distinct upper mantle deformation of cratons in response to subduction constraints from sks wave splitting measurements in eastern china abstract interaction between the subducting slab the overriding continental lithosphere and mantle flow are fundamental geodynamic processes of subduction systems eastern china is an ideal natural laboratory to investigate the behavior and evolution of cratonic blocks within a subduction system in this study we investigate deformation of the upper mantle beneath eastern china we present seismic shear wave splitting measurements from three networks consisting of over 483 broadband stations with 157 stations giving a total of 516 results the splitting parameters exhibit complex regional patterns but are relatively coherent within individual tectonic units tectonic blocks exhibited distinctive fast directions relative to regional features the dominant attitude of fast directions for the north china craton was subparallel to the direction of subduction whereas fast directions for southeastern china were perpendicular to the direction of subduction the shear wave splitting measurements were interpreted according to a high resolution tomographic body wave velocity model combining these two datasets showed that the predominant geodynamic models for the region mantle plume mantle wedge and flat slab subduction models are incompatible with the observations presented here we suggest that the north china craton yangtze craton and the cathaysia block have undergone different deformational events due to differing mantle flow patterns and distinct spatial and temporal subduction histories of the pacific and philippine sea plates

straightening of the northern san jacinto fault california as seen in the fault structure evolution of the san jacinto valley stepover abstract we investigate a releasing stepover between the casa loma and claremont strands of the northern san jacinto fault zone to evaluate the late quaternary structural evolution of the fault zone and to assess the likelihood of a rupture jumping across the stepover our new cone penetration test cpt and trench observations along the claremont fault at mystic lake indicate that the main strand of the claremont fault has jumped nearly a half kilometer westward into the san jacinto releasing stepover during the late quaternary multiple faults are inferred from the cpt data within a small sag at the northeast side of the stepover that cuts through younger stratigraphy to the west of the basin bounding fault near mystic lake previous seismic reflection data also suggest the presence of a young fault that cuts basin strata beneath the middle of mystic lake farther west of our study area numerous tectono geomorphic features observed in satellite and light detection and ranging digital elevation model lidar dem imagery are interpreted to delineate the location of the currently active faults including a zone of faults that cut across the basin from the northern end of the casa loma fault to the claremont fault seismicity observations suggest the presence of many faults within the stepover zone finally new paleoseismic data from the mystic lake site suggest that some late holocene earthquakes may have jumped the stepover all of these observations suggest that the san jacinto stepover which has been used as the primary basis for segmenting the northern san jacinto fault zone is being bypassed and that the fault zone may now be capable of larger earthquakes than previously expected

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

lithosphere asthenosphere interaction beneath the western united states from the joint inversion of body wave traveltimes and surface wave phase velocities summary the relation between the complex geological history of the western margin of the north american plate and the processes in the mantle is still not fully documented and understood several pre usarray local seismic studies showed how the characteristics of key geological features such as the colorado plateau and the yellowstone snake river plains are linked to their deep mantle structure recent body wave models based on the deployment of the high density large aperture usarray have provided far more details on the mantle structure while surface wave tomography ballistic waves and noise correlations informs us on the shallow structure here we combine constraints from these two data sets to image and study the link between the geology of the western united states the shallow structure of the earth and the convective processes in mantle our multiphase dna10 s model provides new constraints on the extent of the archean lithosphere imaged as a large deeply rooted fast body that encompasses the stable great plains and a large portion of the northern and central rocky mountains widespread slow anomalies are found in the lower crust and upper mantle suggesting that low density rocks isostatically sustain part of the high topography of the western united states the yellowstone anomaly is imaged as a large slow body rising from the lower mantle intruding the overlying lithosphere and controlling locally the seismicity and the topography the large e w extent of the usarray used in this study allows imaging the slab graveyard a sequence of farallon fragments aligned with the currently subducting juan de fuca slab north of the mendocino triple junction the lithospheric root of the colorado plateau has apparently been weakened and partly removed through dripping the distribution of the slower regions around the colorado plateau and other rigid blocks follows closely the trend of cenozoic volcanic fields and ancient lithospheric sutures suggesting that the later exert a control on the locus of magmato tectonic activity today the dna velocity models are available for download and slicing at http dna berkeley edu

earthquakes quaternary faults and seismic hazard in california data describing the locations slip rates and lengths of quaternary faults are the primary basis in this work for constructing maps that characterize seismic hazard in california the expected seismic moment m0e and the strength of ground shaking resulting from the entire rupture of each mapped fault or fault segment are estimated using empirical relations between seismic moment m0 rupture length source to site distance and strong ground motions assuming a fault model whereby the repeat time t of earthquakes on each fault equals m0e m0g where the moment rate m0g is proportional to fault slip rate it is observed that the moment frequency distribution of earthquakes predicted from the geologic data agrees well with the distribution determined from a 150 year historical record the agreement is consistent with the argument that the geologic record of quaternary fault offsets contains information sufficient to predict the average spatial and size distribution of earthquakes through time in california the estimates of t for each fault are the foundation for constructing maps that depict the average return period of 0 1g peak horizontal ground accelerations and the horizontal components of peak acceleration peak velocity and the pseudovelocity response at 1 period and 5 damping expected to occur at the level of 0 1 probability during a 50 year period of time a map is also formulated to show the probability that 0 1g horizontal ground accelerations will occur during the next 50 years the maps serve to illustrate the potential value of quaternary fault studies for assessing seismic hazard interpretation of available slip rates indicates that the largest and most frequent occurrence of potentially destructive strong ground motions are associated principally with the san andreas san jacinto calaveras hayward and ventura basin fault zones other regions of similarly high hazard may yet remain unrecognized this inadequacy results primarily from an incomplete data set numerous faults for example are mapped along the coastal region of northern california and within the modoc plateau but relatively few studies relating to fault slip rate are reported a similar problem exists for other stretches of coastal california where marine reflection studies provide evidence of active faulting offshore yet yield little or no information of fault slip rate geological and geophysical field studies can work to remove these deficiencies a concerted effort to locate and define rates of activity on all faults in california is the most promising means to further quantify present levels of seismic hazard in california

high resolution body wave tomography models of the upper mantle beneath eastern china and the adjacent areas 1 we present new 3 d tomographic models of vp vs and vp vsratio anomalies in the upper mantle beneath ec and adjacent areas this data was collected and interpreted with the goal of clarifying geodynamic processes that caused spatially variable event histories throughout eastern china ec during mesozoic to cenozoic time the tomographic images were constructed by inverting body wave travel times recorded at 1300 stations within the upgraded china national seismic network and 9 temporary arrays resolution tests for different depths and the featured velocity anomalies verify that the tomographic images capture the velocity heterogeneities in the upper mantle to depths of 700 km the salient features of vp vs and vp vsratio anomalies can be clearly identified these include strong multiscale heterogeneities occupying the upper mantle beneath ec and differences in the spatial scale of anomalies found beneath northern and southern areas of ec these features demonstrate a degree of spatial variability in the geodynamic evolution of ec we propose two mechanisms to explain these patterns first the western front of the subducted slab may have imparted greater horizontal compressional stress in areas where it impinged further eastward into ec these areas would experience stronger convection and an altered stress regime in the upper mantle creating significant thermal anomalies beneath the south china block scb relative to the eastern north china craton ncc second differing thermal states and viscosities for the eastern ncc and the cathaysia block cab resulted in differing responses to regional deformation the archean hinterland of the eastern ncc specifically has a colder thermal state and higher viscosity and therefore exhibits only small scale heterogeneities due to the effect of shear localization the neoproterozoic cab has a relatively warm thermal state with lower viscosity and thus deformed more continuously

formation and tectonic evolution of southeastern china and taiwan isotopic and geochemical constraints abstract the southern part of china consists of the proterozoic yangtze craton and the phanerozoic south china foldbelts including the himalayan foldbelt of taiwan models for continental growth have been many and controversial isotopic and geochemical data from mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of southeastern china and to evaluate whether the young phanerozoic foldbelts are representative of old rejuvenated landmass whether they characterize crustal accretion through successive subduction processes hence suggesting a net growth of continental mass or whether they represent some intermediate situation available sm nd isotopic data for phanerozoic granitoids and metasediments from the south china foldbelts and taiwan invariably show proterozoic model ages t dm ranging from 1 to 2 5 ga with a mean of 1 54 0 30 1 ga all rocks have negative nd t values 2 to 15 suggesting variable but important contributions of old continental materials to the sources of the phanerozoic rocks obviously they do not represent wholesale growth of continental mass the granitoids of the south china foldbelts have multiple origins as viewed from their chemical and isotopic characteristics secular geochemical variation has been established for inland granitoids of proterozoic to mesozoic age their high i sr values 0 710 0 737 suggest that most granitoids are essentially anatectic products of ancient continental crust this is compatible with remelting via microcontinental collision or terrane accretion repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization mesozoic granitoids excluding a type alkaline granites in the coastal region and taiwan show relatively low i sr 0 705 0 710 and high nd values implying that greater amounts of mantle components have been added to ancient continental material in the generation of these rocks this means that mesozoic magmatism in the coastal region resulted from subduction of a paleo pacific plate kula beneath the asian continent the overall geochemical evidence seems to be consistent with a model of serial collisions between microcontinental blocks for the bulk of the south china foldbelts the latest arc continent collision began about 4 ma ago in eastern taiwan

lithospheric structure in the cathaysia block south china and its implication for the late mesozoic magmatism abstract mesozoic granitoids are widely distributed in south china but the mechanism for generating the felsic magmas is still in debate to understand the possible origin of the granitoids we use joint inversion methods and forward modelling of receiver functions to reveal the lithospheric structure in the cathaysia block the joint inversion of receiver functions and surface wave dispersion with p velocity constraints is applied to a dense array in the cathaysia block and the specific crustal vp vs ratios obtained from a generalized h stacking method are introduced to the traditional joint inversion for passive seismic stations the detailed structures provide valuable knowledge of the geological processes 1 the present day lithosphere is 60 70 km thick which has been thinned since the late mesozoic with reference to geochemical data 2 there is a lack of high vp and vs in the lower crust in this region the results may have limited resolution on the localized magmatic underplating but they do not support the extensive magmatic underplating at the late mesozoic other factors could be the mechanism for the granitoid formation in this region

the dynamics of strike slip step overs with linking dip slip faults fault step overs with linking dip slip faults are common features on long strike slip fault systems worldwide it has been noted by various researchers that under some circumstances earthquakes can jump across fault step overs to cascade into large events while under other circumstances rupture is arrested at step overs there is also evidence that fault step overs may be preferential locations for earthquake nucleation the present work uses the 3d finite element method to model the dynamics of strike slip fault systems with step overs and linking dip slip faults i find that the presence of a linking normal or thrust fault greatly increases the ability of earthquake rupture to propagate across the step over leading to a larger event additionally dilational step overs with linking normal faults are more prone to through going rupture than compressional step overs with linking thrust faults this difference is due to the sign of the normal stress increment on the dip slip fault caused by slip on the strike slip segments slip on the strike slip segments causes a negative unclamping normal stress increment on the linking normal fault in a dilational step over whereas the opposite effect occurs on the linking thrust fault in a compressional step over even in cases for which both dilational and compressional step overs can experience through going rupture dilational step overs typically experience higher slip particularly on the linking normal fault in the compressional case rupture nucleation on the linking thrust fault may increase the likelihood of through going rupture compared to nucleation on one of the strike slip segments near the intersections between the fault segments the stress interaction between the fault segments also causes a significant rotation of rake away from that which would be inferred from the regional stress field the results help to emphasize the importance of two way interactions between nearby fault segments during the earthquake rupture process the results also may have implications for the probability of large earthquakes along geometrically complex strike slip fault systems and may help explain why step overs sometimes act as barriers and other times as nucleation locations for large earthquakes

seismic evidence for significant lateral variations in lithospheric thickness beneath the central and western north china craton abstract we have migrated teleseismic s receiver functions to construct detailed lithospheric structure images that cover the three constituent parts of the north china craton ncc our images show that in contrast to the eastern ncc where significantly thinned lithosphere 60 100 km is widespread the central and western ncc are characterized by the coexistence of both preserved thick and dramatically thinned lithosphere the thick lithosphere 200 km is present beneath the stable ordos plateau and the thinned lithosphere up to 80 km is found in the late cenozoic yinchuan hetao and shaanxi shanxi rift areas with sharp changes occurring over a lateral distance of

community fault model cfm for southern california we present a new three dimensional model of the major fault systems in southern california the model describes the san andreas fault and associated strike slip fault systems in the eastern california shear zone and peninsular ranges as well as active blind thrust and reverse faults in the los angeles basin and transverse ranges the model consists of triangulated surface representations t surfs of more than 140 active faults that are defined based on surfaces traces seismicity seismic reflection profiles wells and geologic cross sections and models the majority of earthquakes and more than 95 of the regional seismic moment release occur along faults represented in the model this suggests that the model describes a comprehen sive set of major earthquake sources in the region the model serves the southern california earthquake center scec as a unified resource for physics based fault systems modeling strong ground motion prediction and probabilistic seismic hazards assessment

fault steps and the dynamic rupture process 2 d numerical simulations of a spontaneously propagating shear fracture fault steps may have controlled the sizes of the 1966 parkfield 1968 borrego mountain 1979 imperial valley 1979 coyote lake and the 1987 superstition hills earthquakes this project investigates the effect of fault steps of various geometries on the dynamic rupture process we have used a finite difference code to simulate spontaneous rupture propagation in two dimensions we employ a slip weakening fracture criterion as the condition for rupture propagation and examine how rupture on one plane initiates rupture on parallel fault planes the geometry of the two parallel fault planes allows for stepover widths of 0 5 to 10 0 km and overlaps of 5 to 5 km our results demonstrate that the spontaneous rupture on the first fault segment continues to propagate onto the second fault segment for a range of geometries for both compressional and dilational fault steps a major difference between the compressional and dilational cases is that a dilational step requires a longer time delay between the rupture front reaching the end of the first fault segment and initiating rupture on the second segment therefore our dynamic study implies that a compressional step will be jumped quickly whereas a dilational step will cause a time delay leading to a lower apparent rupture velocity we also find that the rupture is capable of jumping a wider dilational step than compressional step

the effects of d0 on rupture propagation on fault stepovers abstract according to the slip weakening friction law andrews 1976a fault friction drops from a static value to a sliding value over some slip weakening distance d 0 laboratory studies of fault friction confirm this weakening but do not settle on a single value for d 0 however this parameter is a critical input in dynamic earthquake models as it affects rupture nucleation and propagation we use the 2d finite element method to test how the specific value of d 0 affects rupture behavior we consider the ability of rupture to jump from segment to segment of a disconnected stepover or to propagate through the double bends of a connected stepover as a way to gauge rupture energy and behavior we find the stepover width or bend angle through which rupture can propagate is affected by the choice of d 0 but it is not a linear relationship this is true regardless of whether the stepover is connected or disconnected compressional or extensional or whether the initial rupture velocity is supershear or subshear we do find however that scaling the intensity of the regional stress field up or down does linearly correspond to scaling d 0 down or up we interpret the nonlinearity of the d 0 scaling results to be related to the area of the secondary fault that intersects the lobe of failure level coulomb stress change induced by rupture of the first fault segment because 1 the d 0 controlled critical patch size for renucleation must be exceeded on the second segment and 2 the area of this overlap also does not change linearly with distance from the first fault

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

zircon u pb geochronology and hf isotopic compositions of the mesozoic granites in southern anhui province china abstract mesozoic magmatism is extensively developed in eastern china along the eastern asian continental margin but the geochronological framework is not well understood for each area in this study seventy eight samples were collected from the mesozoic igneous rocks in south anhui province east central china in order to precisely constrain their formation ages and contributions to crustal growth zircon u pb age determination using ion probe and laser ablation techniques indicate that magmatism in the area can be divided into two separate stages at 150 136 and 136 120 ma respectively the first stage of granitic rocks not documented in other areas of eastern china is mostly composed of hornblende bearing i type granodiorite and monzogranite and is considered to be formed by slab tearing during pacific subduction the second stage of magmatism coeval to that in other areas of eastern china is characterized by the occurrence of a type granite and syenite and their volcanic counterparts although i type granitic rocks are also developed locally these rocks are mostly distributed around and within the fault controlled volcanic basins and some are closely related to detachment shearing indicating their formation in an extensional setting zircon hf isotopic analyses indicate that archean material might be present in the area but that the main episode of crustal growth took place during the mesoproterozoic with very little juvenile material in the mesozoic

intralithospheric mantle structures recorded continental subduction 1 we investigated the intralithospheric mantle ilm structures beneath the north china craton ncc by the seismic imaging with over 16 000 high quality receiver functions from 255 broadband stations these images were created for six profiles spanning different tectonic units in the ncc initially we inferred the crustal velocity model using an integrated receiver function imaging technique subsequently we performed a series of synthetic tests of common conversion point ccp stacking images to distinguish between the multiple waves generated by the crustal structure and the velocity discontinuities in the ilm the ilm structures were constructed by waveform inversion on the basis of these analyses our imaging results reveal 1 a homogenous lithospheric mantle in the western ncc 2 intermittent and juxtaposed velocity interfaces in the ilm beneath the southern ncc and 3 local high velocity and lower velocity volumes in the ilm beneath the eastern ncc in addition the lower crust beneath the southern ncc is thin and the moho dips northward which present evidence of the yangtze craton subduction beneath the ncc the imaged high velocity volumes in the ilm beneath the southern ncc were interpreted as a subduction remnant in the uppermost mantle which reveal a flat subduction channel resulting from the continent continent collision between the ncc and the yangtze craton the homogeneous ilm beneath a paleoproterozoic amalgamation zone in the ncc implies that the remnants of the lithosphere that were subducted before 1 8 ga might have sunk into the deeper mantle

lidar and field observations of slip distribution for the most recent surface ruptures along the central san jacinto fault we measured offsets on tectonically displaced geomorphic features along 80 km of the clark strand of the san jacinto fault sjf to estimate slip per event for the past several surface ruptures we identify 168 offset features from which we make over 490 measurements using b4 light detection and ranging lidar imagery and field observations our results suggest that lidar technology is an exemplary supplement to traditional field methods in slip per event studies displacement estimates indicate that the most recent surface rupturing event mre produced an average of 2 5 2 9 m of right lateral slip with maximum slip of nearly 4 m at anza a m w 7 2 7 5 earthquake average multiple event offsets for the same 80 kms are 5 5 m with maximum values of 3 m at anza for the penultimate event cumulative displacements of 9 10 m through anza suggest the third event was also similar in size paleoseismic work at hog lake dates the most recent surface rupture event at ca 1790 a poorly located large earthquake occurred in southern california on 22 november 1800 we relocate this event to the clark fault based on the mre at hog lake we also recognize the occurrence of a younger rupture along 15 20 km of the fault in blackburn canyon with 1 25 m of average displacement we attribute these offsets to the 21 april 1918 m w 6 9 event these data argue that much or all of the clark fault and possibly also the casa loma fault fail together in large earthquakes but that shorter sections may fail in smaller events online material topographic contour maps and hillshades generated from b4 lidar data corresponding field photographs and data tables comparing lidar based and field based slip measurements for individual geomorphic features along the clark fault

crustal stress field in southern california and its implications for fault mechanics we present a new high spatial resolution image of stress orientation in southern california based on the inversion of earthquake focal mechanisms we use this image to study the mechanics of faulting in the plate boundary region the stress field contains significant spatial heterogeneity which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause temporal changes in the stress field are also observed primarily related to major earthquakes the observed 15 10 rotation of the stress axes due to the 1992 m7 3 landers mainshock implies that the deviatoric stress magnitude in the crust is low of the order of 10 mpa this suggests that active faults in southern california are weak the maximum principal stress axis near the san andreas fault is often at 50 to the fault strike indicating that the shear stress on the fault is comparable to the deviatoric stress the san andreas in southern california may therefore be a weak fault in a low strength crust

crustal structure across the san andreas fault southern california from teleseismic converted waves crustal structure along a 140 km long profile across the san andreas fault saf in southern california was imaged by stacking teleseismic p s converted phases recorded by a dense short period seismic array the crust mantle discontinuity moho is visible as a continuous feature at a depth around 30 km but is offset 6 to 8 km beneath the saf a small moho disruption can also be seen under the eastern california shear zone ecsz these results suggest that the saf and ecsz extend through the entire crust the moho upwarp under the san gabriel mountains indicates that the mountain ranges were lifted en masse as a result of crustal buckling under horizontal compression

nonuniform prestress from prior earthquakes and the effect on dynamics of branched fault systems 1 to examine the effects of branched fault geometry on the dynamics of fault systems in the long term we perform multicycle simulations on generic faulting models an explicit finite element algorithm is used to simulate spontaneous dynamic rupture of earthquakes the fault stress during the interseismic period is evaluated by an analytical viscoelastic model we find that the fault prestress field becomes highly nonuniform near the branch point and on the two branch segments over multiple earthquake cycles owing to the branched fault geometry and stress interaction between the two segments the principal prestress on faults rotates over multiple earthquake cycles and departs from the regional stress field significantly near the branch point after a number of earthquake cycles the branched fault systems evolve to a steady state in which several patterns of the fault prestress and earthquake rupture repeat the nonuniform prestress developed from previous earthquakes has large effects on the rupture and slip patterns several different rupture scenarios can occur on a given branched fault system in addition backward branching can occur in the nonuniform prestress field either driven by slip on the stem of the fault system or through a triggering mechanism these modeling results may have important implications for understanding fault branching behavior observed in the 1992 landers the 1999 hector mine and the 2002 denali fault earthquakes and for seismic hazard analysis in the areas where branched fault systems exist

the scec southern california reference three dimensional seismic velocity model version 2 we describe version 2 of the three dimensional 3d seismic velocity model of southern california developed by the southern california earthquake center and designed to serve as a reference model for multidisciplinary research activities in the area the model consists of detailed rule based representations of the major southern california basins los angeles basin ventura basin san gabriel valley san fernando valley chino basin san bernardino valley and the salton trough embedded in a 3d crust over a variable depth moho outside of the basins the model crust is based on regional tomographic results the model moho is represented by a surface with the depths determined by the receiver function technique shallow basin sediment velocities are constrained by geotechnical data the model is implemented in a computer code that generates any specified 3d mesh of seismic velocity and density values this parameterization is convenient to store transfer and update as new information and verification results become available

rupture and ground motion models on the northern san jacinto fault incorporating realistic complexity we use the 3d finite element method to conduct dynamic models of rupture and resulting ground motion on the claremont casa loma stepover of the northern san jacinto fault we incorporate complex fault geometry from the u s geological survey usgs quaternary faults database see data and resources 1 a realistic velocity structure the southern california earthquake center community velocity model s a realistic regional stress field with an orientation taken from seismicity relocation literature and several stochastic self similar shear stress distributions as we incorporate more types of complexity the specific effects of any individual factor become less apparent within the overall rupture behavior we also find that the distribution of high and low shear stress that arises from combining regional and stochastic stress fields has the strongest control over where the rupture terminates using a regional stress field alone as well as with the combined regional and stochastic stress realization we find that the stepover presents a significant barrier to rupture regardless of our choice of initial nucleation point and that it is difficult for rupture to propagate the full length of either fault segment greater heterogeneity of stresses tends to produce shorter ruptures within this result we find that the claremont strand is more favorable for long ruptures than the casa loma clark strand low frequency ground motion intensity and distribution are controlled largely by the velocity structure rather than by stress heterogeneity the strongest motions produced in these models are in the san bernardino basin although directivity effects do contribute to the low frequency ground motion distribution particularly in the near field they are secondary to the effects of the velocity structure online material figures of ground motions from models used to calibrate the stress conditions for dynamic rupture propagation 1 sec 18

distinct lateral variation of lithospheric thickness in the northeastern north china craton abstract a detailed knowledge of the thickness of the lithosphere in the northeastern north china craton ncc is important for understanding the significant tectonic reactivation of the craton in the mesozoic and cenozoic time we achieve this goal by applying the newly proposed wave equation based migration technique to the s receiver functions recently collected in the region distinct negative signals are identified below the moho in all the s receiver function migrated images and stacks which we interpret as representing the s to p conversions from the lithosphere asthenosphere boundary lab the imaged lab is as shallow as 60 70 km in the southeast basin and coastal areas and deepens to no more than 140 km in the northwest mountain ranges and continental interior these observations indicate widespread lithospheric thinning in the study region in comparison with the 180 km lithospheric thicknesses typical of most cratonic regions the revealed topography of the lab generally agrees with the lateral variation in upper mantle seismic anisotropy previously measured through sks splitting analysis in particular a sharp lab step of 40 km is detected at the triple junction of the basin and mountains at almost the same place where an abrupt change from nw se to ne sw in fast polarization direction of shear waves was found these findings suggest a close correlation between the seismic anisotropy and hence deformation of the upper mantle the lithospheric thickness and the surface tectonics of the northeastern ncc while the thinned lithosphere and the nw se fast shear wave polarizations in the east areas probably are related to the dominant nw se tectonic extension in the late mesozoic cenozoic time the thicker lithosphere and the ne sw fast polarization direction in the west mountain ranges may reflect earlier contractional deformations of the region synthetic tests indicate that the lab beneath the northeastern ncc is a well defined zone 10 20 km thick combined with seismic tomography results and geochemical and petrological data this suggests that complex modification of the lithosphere probably accompanied significant lithospheric thinning during the tectonic reactivation of the old craton

the effective elastic thickness of the india plate from receiver function imaging gravity anomalies and thermomechanical modelling summary the range and the meaning of the effective elastic thickness eet in continental areas have been subject to controversy over the last two decades here we take advantage of the new data set from the hi climb seismological experiment to re estimate the eet of the india plate along a south north profile extending from the ganges basin to central tibet receiver functions give a high resolution image of the base of the foreland basin at 5 km depth and constrain the crustal thickness which increases northwards from 35 km beneath the indo gangetic plain to 70 km in southern tibet together with available data sets including seismic profiles seismological images from both indepth and himnt experiments deep well measurements and bouguer anomaly profiles we interpret this new image with 2 d thermomechanical modelling solutions using different type of crustal and mantle rheologies we find that 1 the eet of the india plate decreases northwards from 60 80 to 20 30 km as it is flexed down beneath himalaya and tibet due to thermal and flexural weakening 2 the only resistant layer of the india plate beneath southern tibet is the upper mantle which serves as a support for the topographic load and 3 the most abrupt drop in the eet located around 200 km south of the mft is associated with a gradual decoupling between the crust and the mantle we show that our geometrical constraints do not allow to determine if the upper and lower crust are coupled or not our results clearly reveal that a rheology with a weak mantle is unable to explain the geometry of the lithosphere in this region and they are in favour of a rheology in which the mantle is strong

large earthquake hazard of the san jacinto fault zone ca from long record of simulated seismicity assimilating the available instrumental and paleoseismic data we investigate spatio temporal properties of earthquake patterns in the san jacinto fault zone sjfz california between cajon pass and the superstition hill fault using a long record of simulated seismicity constrained by available seismological and geological data the model provides an effective realization of a large segmented strike slip fault zone in a 3d elastic half space with heterogeneous distribution of static friction chosen to represent several clear step overs at the surface the simulated synthetic catalog reproduces well the basic statistical features of the instrumental seismicity recorded at the sjfz area since 1981 the model also produces events larger than those included in the short instrumental record consistent with paleo earthquakes documented at sites along the sjfz for the last 1 400 years the general agreement between the synthetic and observed data allows us to address with the long simulated seismicity questions related to large earthquakes and expected seismic hazard the interaction between m 7 events on different sections of the sjfz is found to be close to random the hazard associated with m 7 events on the sjfz increases significantly if the long record of simulated seismicity is taken into account the model simulations indicate that the recent increased number of observed intermediate sjfz earthquakes is a robust statistical feature heralding the occurrence of m 7 earthquakes the hypocenters of the m 5 events in the simulation results move progressively towards the hypocenter of the upcoming m 7 earthquake

continental subduction and exhumation of uhp rocks structural and geochronological insights from the dabieshan east china in the dabieshan the available models for exhumation of ultrahigh pressure uhp rocks are poorly constrained by structural data a comprehensive structural and kinematic map and a general cross section of the dabieshan including its foreland fold belt and the northern dabieshan domain foziling and luzenguang groups are presented here south dabieshan consists from bottom to top of stacked allochtons 1 an amphibolite facies gneissic unit devoid of uhp rocks interpreted here as the relative autochton 2 an uhp allochton 3 a hp rock unit susong group mostly retrogressed into greenschist facies micaschists 4 a weakly metamorphosed proterozoic slate and sandstone unit and 5 an unmetamorphosed cambrian to early triassic sedimentary sequence unconformably covered by jurassic sandstone all these units exhibit a polyphase ductile deformation characterized by i a nw se lineation with a top to the nw shearing and ii a southward refolding of early ductile fabrics the central dabieshan is a 100 km scale migmatitic dome newly discovered eclogite xenoliths in a cretaceous granitoid dated at 102 ma by the u pb method on titanite demonstrate that migmatization post dates hp uhp metamorphism ductile faults formed in the subsolidus state coeval to migmatization allow us to characterize the structural pattern of doming along the dome margins migmatite is gneissified under post solidus conditions and mylonitic ultramylonitic fabrics commonly develop the north and west boundaries of the central dabieshan metamorphics i e the xiaotian mozitan and macheng faults are ductile normal faults formed before late jurassic early cretaceous a cretaceous reworking is recorded by synkinematic plutons north of the xiaotian mozitan fault the north dabieshan domain consists of metasediments and orthogneiss foziling and luzenguang groups metamorphosed under greenschist to amphibolite facies which never experienced uhp metamorphism a rare n s trending lineation with top to the south shearing is dated at 260 ma by the 40ar 39ar method on muscovite this early structure related to compressional tectonics is reworked by top to the north extensional shear bands the main deformation of the dabieshan consists of a nw se stretching lineation which wraps around the migmatitic dome but exhibits a consistently top to the nw sense of shear the central dabieshan is interpreted as an extensional migmatitic dome bounded by an arched top to the nw detachment fault this structure may account for a part of the uhp rock exhumation however the abundance of amphibolite restites in the central dabieshan migmatites and the scarcity of eclogites found only in a few places argue for an early stage of exhumation and retrogression of uhp rocks before migmatization this event is coeval to the n s extensional structures described in the north dabieshan domain recent radiometric dates suggest that early exhumation and subsequent migmatization occurred in triassic liassic times the main foliation is deformed by north verging recumbent folds coeval to the south verging folds of the south dabieshan domain an intense cretaceous magmatism accounts for thermal resetting of most of the 40ar 39ar dates a lithosphere scale exhumation model involving continental subduction synconvergence extension with inversion of southward thrusts into nw ward normal faults and crustal melting is presented

crust mantle structure difference across the gravity gradient zone in north china craton seismic image of the thinned continental crust the archean north china craton ncc has been tectonically modified and lost its thick lithospheric keel during the mesozoic and cenozoic the processes and mechanisms of the lithospheric modification and its appearance in and the relation between different subregions of the ncc are still poorly understood seismic data from 45 stations along a 470 km long profile cross the bohai bay basin bbb and the taihangshan mountain range tmr in the ncc were employed to construct a coherent structural image of the crust and uppermost mantle an integrated receiver function imaging technique combining the common conversion point stacking approach with waveform inversion and forward modeling was proposed to extract the structural information beneath the study region modeling of bouguer gravity anomalies was also applied to constrain the density distribution the imaging result reveals distinct structural features between the mountain range and the basin area and presents a picture of uneven crust thinning within the study region in the east bbb the crust is significantly thinned due mainly to the reduction in the thickness of the lower crust including the crust mantle transition zone by up to 12 km the west tmr in contrast is characterized by a relatively thick lower crust of 20 km the teleseismic waveform data and the gravity observation suggest a thicker crust and a buoyant mantle lithosphere beneath the tmr compared with the bbb the contrasting crustal structural features appear coupled with the lithospheric processes and possibly reflect that different tectonic mechanisms and deformation regimes dominated the evolution of the two regions the north south gravity lineament lying between the tmr and bbb might represent a deep intra continental boundary separating the ncc into topographically and tectonically different regions

global change eruptions linked to el nino statistical validation of a relationship between explosive volcanic eruptions and the el nino southern oscillation is a step forward in understanding the effects of such eruptions on climate

u pb zircon ages of granites from the southern margin of the yangtze block timing of neoproterozoic jinning orogeny in se china and implications for rodinia assembly abstract neoproterozoic jinningian bendong granodiorite and sanfang and yuanbaoshan granites occurred in northern guangxi southern margin of the yangtze block se china and were generally considered to be of orogenic origin that is the collision between the yangtze and huanan blocks during the jinning orogeny these granites were intruded into the mesoproterozoic sibao metamorphic basement and covered unconformably by the neoproterozoic danzhou metasediments they are dominantly peraluminous asi 1 18 1 29 and have low initial end values of 4 8 to 7 6 indicating derivation from a supracrustal source with strong enrichment in rb k and th and relatively low zr hf and higher rare earth elements they are similar to post collision granites zircon u pb ages of 819 9 826 10 and 824 4 ma were obtained for the bendong granodiorite and the sanfang and yuanbaoshan granites respectively by both shrimp and conventional dating methods the age result precludes the existence of any late mesoproterozoic grenville age granitic magmatism in the southern margin of yangtze block together with previous age determinations of ophiolites along the southern margin of the yangtze block the jinning orogeny is referred to the neoproterozoic orogeny which took place between 1 0 and 0 80 ga and likely ended at 0 82 ga the granite formation age of 0 82 ga also supports the basal boundary age of 0 80 ga for the post orogenic sinian system which is probably stratigraphically correlated with the adeladean system in south australia as the link between australia east antarctica and laurentia in the configuration of the supercontinent rodinia the collision between the yangtze and huanan blocks during the neoproterozoic jinning orogeny probably marks the termination of the rodinia assembly

a detailed receiver function image of the sedimentary structure in the bohai bay basin abstract if the site at which receiver functions are constructed is filled by sediments then the waveforms from these receiver functions are dominantly controlled by the sedimentary structures within the first few seconds after the direct p arrival based on this observation waveform data collected at 44 temporary seismic stations have been used to image the sedimentary structure of the bohai bay basin a major continental petroliferous basin in eastern china an adapted hybrid global waveform inversion method was applied to the receiver functions to extract structural information beneath each of the stations the derived s velocity structure provides for the first time a basin scale seismic image of detailed sedimentary stratification the sedimentary cover of the basin is about 2 12 km thick consisting of cenozoic mesozoic and paleozoic strata from top to bottom the structural features presented in the s velocity image coincide quite well with the depression uplift type of tectonic system in the bohai bay basin the reconstructed morphology of the sedimentary layers provides seismological evidence for the two stage evolution of the intracontinental basin that were caused by an intensive tectonic regime transition in late mesozoic immediately following the lithospheric reforming of the eastern china continent

insight into the geodynamics of cratonic reactivation from seismic analysis of the crust mantle boundary 1 the reactivation of craton is a crucial issue for the understanding of continent lithosphere although the partial loss of the thick lithospheric root of the north china craton ncc was documented its mechanism remains a contentious topic in the study of cratonic evolution in this paper we imaged the crust mantle structures by using the data from 36 permanent stations with fine spatial coverage in the yanshan tectonic belt ystb and the taihangshan region tsr in the northern ncc two tectonic units with distinct crust mantle structures were recognized and their junction zone was identified the results reveal distinct features of the crust mantle boundaries of the ystb and the tsr which are characterized by a sharp interface and a thick transition zone respectively based on the analysis of the seismic structures of the crust mantle boundary and the upper mantle we propose that the ncc reactivation was possibly derived by a slow secular ascension of hydrated asthenospheric material atop the stagnant pacific slab which influenced the formation of crust mantle transition zone in the eastern ncc on the other hand regional delamination of the deep crust after orogenic thickened and or magmatic underplating beneath the ystb caused the spatial variation of the crust mantle boundary both of the mantle processes possibly changed the nature of the lithospheric mantle

age and origin of the tanghu granite southeast china results from u pb single zircon and nd isotopes u pb single zircon and sm nd whole rock isotopic data for the tanghu granite of the zhuguangshan batholith suggest that a basement either composed of or derived from middle proterozoic to late archean rocks underlies southeast china the granite contains two kinds of inherited zircon components whole anhedral zircons and small cores within younger magmatic zircons the u pb data for a single analysis of four magmatic zircons yielded a concordant age of 433 2 ma whereas single zircons yielded two linear arrays with lower intercepts of 435 1 and 434 14 ma and upper intercepts of 1415 3 and 2516 6 ma respectively xenocrystic zircons of archean age had not previously been recognized in any rocks from southeast china two whole rock samples from the granite yielded nd values of 7 1 and 8 3 at 434 ma and nd model ages of 1750 ma relative to a depleted mantle we conclude from this isotope data that the tanghu granite crystallized at 434 1 6 ma weighted average and was derived from a source of unknown age but had an average crustal residence age of 1750 ma and was partially composed of a mixture of continental crustal material of at least two ages 1400 and 2500 ma

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

insight into modification of north china craton from seismological study in the shandong province 1 the study region is located in the southeast edge of the north china craton ncc which is an archean craton that underwent removal and modification of the lithospheric mantle during the late mesozoic cenozoic teleseismic data from the ncisp 1 experiment were used to image the velocity structures in lithosphere and to investigate the upper mantle anisotropy seismological results revealed that the present lithosphere consists of two parts with different structural features throughout including crustal fabric lithospheric velocity stratification and anisotropic patterns the formation of the contrasting structure is attributable to one of two possibilities the trans lithospheric tanlu fault zone tlfz operated as an asthenospheric upwelling channel and facilitated the ncc reactivation or the tlfz separates the study region into two lithospheric blocks with the ancient lithospheric materials remaining within the rejuvenated lithospheric mantle these two possibilities suggest that thermal chemical erosion may have played critical roles in the ncc reactivation

the 73 ka toba super eruption and its impact history of a debate abstract toba volcano in northern sumatra is located at the intersection of two major tectonic lineaments in one of the most seismically active regions in the world and its caldera is considered the largest quaternary caldera on earth the most recent toba explosive eruption at 73 ka was an order of magnitude larger than that of tambora in 1815 and has a volcanic explosivity index of 8 the exceptional magnitude of this super eruption and the widespread distribution of the younger toba tuff ytt in marine cores in the indian ocean the arabian sea and the south china sea have prompted sustained debate as to its global and regional impact on climate ecosystems and prehistoric human populations however despite climate modelling and appeals to a variety of proxy climatic data including geochemistry pollen analysis archaeology and stable isotopes the extent of the impact remains unclear in order to achieve better progress in the future greater care is needed to obtain higher resolution and more precise chronologies from the marine and terrestrial proxy records used to test whether or not the 73 ka toba super eruption had a significant environmental impact records from speleothems and ice cores have much to offer in this regard