simultaneous rupture along two conjugate planes of the wharton basin earthquake analysis of broadband teleseismic data shows that the 18 june 2000 wharton basin earthquake a moment magnitude 7 8 intraplate event in the region of diffuse deformation separating the indian and australian plates consisted of two subevents that simultaneously ruptured two near conjugate planes this mode of rupture accommodates shortening by a mechanism different from that previously known elsewhere in the region the larger subevent occurred on a fossil fracture zone with a relatively high stress drop of about 20 megapascals showing that large stresses can accumulate in regions of distributed deformation

litho1 0 an updated crust and lithospheric model of the earth we present the litho1 0 model which is a 1 tessellated model of the crust and uppermost mantle of the earth extending into the upper mantle to include the lithospheric lid and underlying asthenosphere the model is parameterized laterally by tessellated nodes and vertically as a series of geophysically identified layers such as water ice sediments crystalline crust lithospheric lid and asthenosphere litho1 0 is created by constructing an appropriate starting model and perturbing it to fit high resolution surface wave dispersion maps love and rayleigh group and phase over a wide frequency band 5 40 mhz we examine and discuss the model with respect to key lithospheric parameters such as average crustal velocity crustal thickness upper mantle velocity and lithospheric thickness we then compare the constructed model to those from a number of select studies at regional and global scales and find general consistency it appears that litho1 0 represents a reasonable starting model of the earth s shallow structure crust and uppermost mantle for the purposes in which these models are used such as traveltime tomography or in efforts to create a 3 d reference earth model the model matches surface wave dispersion over a frequency band wider than the band used in the inversion there are several avenues for improving the model in the future by including attenuation and anisotropy as well as making use of surface waves at higher frequency

post critical sspmp and its applications to virtual deep seismic sounding vdss 1 sensitivity to lithospheric 1 d and 2 d structure virtual deep seismic sounding vdss has recently emerged as a novel method to image the moho and potentially other lithospheric boundaries the behaviour of sspmp the post critical reflection phase at the moho that is utilized in vdss is rich with complexities not yet widely considered here motivated by observations from the ordos plateau in north china we use synthetic seismograms computed with a broad range of 1 d models to evaluate how different parts of the lithosphere along the ray path of sspmp affect its phase amplitude and arrival time our findings include 1 when the crust mantle boundary is a sharp discontinuity the sspmp phase shift relative to the direct s wave is controlled by lower crustal v p upper mantle v p and ray parameter this property indicates the possibility of using sspmp to constrain v p in the lower crust and uppermost mantle 2 when the crust mantle boundary is a velocity gradient zone sspmp arrival times vary as different functions of ray parameter from cases with a sharp crust mantle boundary because different rays turn at different depths this feature allows measurement of the vertical velocity gradient in the crust mantle transition zone with sspmp 3 when the virtual source location of s to p conversion at the free surface is in a sedimentary basin sspmp amplitude can be significantly reduced due to low s to p reflected energy at the virtual source this may cause the absence of sspmp despite appropriate source receiver geometry in addition to 1 d models we further conduct 2 d waveform modelling and find that the sspmp arrival time relative to direct s is not only controlled by crustal thickness at the reflection point but also by lateral variation of v s beneath the virtual source and receiver therefore in areas with significant lateral heterogeneity in the lithosphere the accuracy of crustal thickness measurements from sspmp arrival times depends on our knowledge of the variability of lithospheric structure across a broad region

determining crustal structure beneath seismic stations overlying a low velocity sedimentary layer using receiver functions the receiver function rf technique has been widely applied to investigate crustal and mantle layered structures using p to s converted ps phases from velocity discontinuities however the presence of low velocity relative to that of the bedrock sediments can give rise to strong reverberations in the resulting rfs frequently masking the ps phases from crustal and mantle boundaries such reverberations are caused by p to s conversions and their multiples associated with the strong impedance contrast across the bottom of the low velocity sedimentary layer here we propose and test an approach to effectively remove the near surface reverberations and decipher the ps phases associated with the moho discontinuity autocorrelation is first applied on the observed rfs to determine the strength and two way traveltime of the reverberations which are then used to construct a resonance removal filter in the frequency domain to remove or significantly reduce the reverberations the filtered rfs are time corrected to eliminate the delay effects of the sedimentary layer and applied to estimate the subsediment crustal thickness and vp vsusing a h k stacking procedure the resulting subsediment crustal parameters thickness and vp vs are subsequently used to determine the thickness and vp vs of the sedimentary layer using a revised version of the h k stacking procedure testing using both synthetic and real data suggests that this computationally inexpensive technique is efficient in resolving subsediment crustal properties beneath stations sitting on a low velocity sedimentary layer and can also satisfactorily determine the thickness and vp vs of the sedimentary layer

sharpening the tomographic image of the subducting slab below sumatra the andaman islands and burma summary taking advantage of the increased ray coverage due to seismicity following the 2004 december and 2005 march great earthquakes an improved iterative regional global tomographic method was applied to the sumatra andaman and adjacent regions to better constrain the 3 d mantle velocity heterogeneity in the region velocity and hypocentral parameters were iteratively perturbed to sharpen the image of the subducted slab several iterations were performed and the effects of source mislocation were considered in the iterative process an issue usually neglected in global tomography we find that source relocation between iterations increases the amplitudes of slab anomalies and sharpens the definition of slab geometry beyond what can be achieved by a fixed source iterative inversion alone in addition extensive restoration tests of synthetic data were conducted that emphasize enhancements obtained by our iterative process these tests show significant increases in amplitude and decreased smearing of synthetic slab features thus when applied to the real data similar enhancements are inferred in the resulting model which better illustrates the complex slab geometry in the upper mantle and transition zone regions along the sumatra andaman and burma subduction zones

weakly coupled lithospheric extension in southern tibet a b s t r a c t west east extension is a prominent tectonic feature of southern and central tibet despite ongoing north south n s convergence between india and eurasia knowledge of deep structure beneath the n s trending rifts is key to evaluating models proposed for their origin including gravitational collapse oblique convergence along the arcuate plate boundary and mantle upwelling we model direct s and moho reflected sspmp phases at teleseismic distances to constrain variations in crustal thickness across the major rifts crossed by a 900 km long w e broadband array in the lhasa terrane crustal thicknesses are 70 80 km however moho depth decreases by 10 km within a horizontal distance of 100 km west of the yadong gulu rift ygr and nyainquentanghla mountains nqtl this moho uplift taken with deep extensional focal mechanisms and reduced seismic velocity in the upper mantle suggests that asthenospheric upwelling has significantly contributed to the pattern of extension across the ygr and nqtl the 100 km separation between surface rift and moho uplift is likely enabled by partial decoupling across a ductile middle crust 2015 the authors published by elsevier b v this is an open access article under the cc by nc nd license http creativecommons org licenses by nc nd 4 0

using ambient noise seismic interferometry and local and teleseismic earthquakes to determine crustal thickness and moho structure of the northwestern gulf of mexico margin

a 3 d model of the crust and uppermost mantle beneath the central and western us by joint inversion of receiver functions and surface wave dispersion 1 rayleigh wave phase velocity maps from ambient noise and earthquake data are inverted jointly with receiver functions observed at 828 stations from the usarray transportable array west of 100 w longitude for data recorded in the years 2005 through 2010 to produce a 3 d model of shear wave speeds beneath the central and western us to a depth of 150 km eikonal tomography is applied to ambient noise data to produce about 300 000 rayleigh wave phase speed curves and helmholtz tomography is applied to data following 1550 ms 5 0 earthquakes so that rayleigh wave dispersion maps are constructed from 8 to 80 s period with associated uncertainties across the region harmonic stripping generates back azimuth independent receiver functions with uncertainty estimates for each of the stations a nonlinear bayesian monte carlo method is used to estimate a distribution of shear wave speed vs models beneath each station by jointly interpreting surface wave dispersion and receiver functions and their uncertainties the assimilation of receiver functions improves the vertical resolution of the model by reducing the range of estimated moho depths improving the determination of the shear velocity jump across moho and improving the resolution of the depth of anomalies in the uppermost mantle a great variety of geological and tectonic features are revealed in the 3 d model that form the basis for future detailed local to regional scale analysis and interpretation

determining moho depth beneath sedimentary basins using regional pn multiples the study of the moho beneath thick sedimentary basins involving natural earthquakes is challenging as low velocity materials often cause strong reverberations that mask moho signals here we develop a method to determine the depth of the moho by taking advantage of the presence of the sediments the method utilizes the first pn crustal multiple from regional earthquakes pnpn and its differential travel time with respect to pn pnpn is usually weak in amplitude thus it is difficult to identify in regions without a sedimentary cover however pnpn is significantly amplified in the presence of low velocity sediments because of an increase in the near surface p to p reflection coefficient the arrival time amplitude and wave shape of pnpn if normalized by the reference pn are insensitive to earthquake source parameters such as focal mechanism and focal depth we demonstrate the potential of this method using both 1d and 2d waveform simulations synthetic waveforms suggest that pmppn and pnpmp one pn leg merges to pmp near the source or the receiver largely contribute to the pnpn amplitudes which depend on the near surface structure at their free surface p to p reflection points we further validate the method with two field examples in the imperial valley one is near the united states mexico border and the other is in oklahoma in the central united states both examples suggest that the method can be used to study the moho either near the source or the receiver

cocorp deep reflections moho at 50 km 16 s beneath the colorado plateau cocorp deep reflection data on the colorado plateau reveal complex reflections to about 16 s two way travel time 50 km beyond which there is an abrupt decrease of reflectivity this boundary is interpreted to represent the moho an inference consistent with the existing but limited refraction data sets when they are reconciled with the recent independent determination of an 8 10 8 15 km s pn velocity beneath the colorado plateau this 50 km depth to moho and 8 10 8 15 km s pn velocity for the colorado plateau closely resembles that of the high plains just east of the rocky mountains the absence of continuous strong reflections at the moho suggests that the moho beneath the colorado plateau is a transition not a velocity step function on the scale of the reflection experiment the reflection boundary may represent the base of complex and discontinuous reflectors of the crust and crust mantle transition below which the mantle may be largely peridotite with a velocity of 8 1 km s these results strongly reinforce the suggestion that the moho on deep reflection data in relatively stable continental regions is represented by an abrupt decrease in reflectivity below which the mantle is relatively seismically transparent

wave field continuation and decomposition for passive seismic imaging under deep unconsolidated sediments abstract the coastal plains of the central and eastern united states contain deep sections of unconsolidated to poorly consolidated sediments these sediments mask deeper crustal and upper mantle converted phases in teleseismic receiver functions through large amplitude near surface reverberations thick sediments also amplify ambient noise levels to generally reduce data signal to noise ratios removing shallow sediment wave propagation effects is critical for imaging deep lithospheric structures a propagator matrix formalism is used to downward continue the wave field for teleseismic p waves into the midcrust and then to separate the upgoing s wave field from the total teleseismic response of the p wave to expose deep sp conversions this method requires that the earth model from the surface to the reference depth be known teleseismic p wave data for the memphis tennessee station mph are analyzed using a reference station deconvolution technique to produce vertical and radial p wave transfer functions these transfer functions are modeled using a simple model parameterization for sediment structure through grid inversion the inverted earth model is incorporated into the wave field continuation and decomposition technique to estimate the upgoing s wave field at 10 km depth in the crust moho and possible deeper ps conversions are identified with this process

tectonic and stratigraphic controls of hydrocarbon systems in the ordos basin a multicycle cratonic basin in central china the ordos basin is the oldest and still an important hydrocarbon province in central china it is a typical cratonic basin developed on the archean granulites and lower proterozoic greenschists of the north china block the development of the ordos basin during the paleozoic mesozoic can be divided into three evolutionary stages cambrian early ordovician cratonic basin with divergent margins middle ordovician middle triassic cratonic basin with convergent margins and late triassic early cretaceous intraplate remnant cratonic basin two hydrocarbon systems are present in the basin the paleozoic gas and mesozoic oil systems in the paleozoic gas system the lower ordovician marine carbonates and pennsylvanian lower permian coal measures serve as source rocks the lower ordovician karst modified dolomites and pennsylvanian bauxitic mudstones form a significant reservoir seal association and the pennsylvanian lower permian deltaic sandstones and upper permian lacustrine mudstones form another effective reservoir seal association in the mesozoic oil system the upper triassic lacustrine mudstones are mature source rocks the upper triassic deltaic sandstones and overlying shallow lacustrine and swamp mudstones form a reservoir seal association and the lower jurassic fluvial sandstones and overlying shallow lacustrine and swamp mudstones form another reservoir seal association in both hydrocarbon systems the stratigraphic variations provide the principal traps the ordos basin is characterized by a stable tectonic setting that controlled the distribution of depositional systems and the development of erosional surfaces and ultimately governed the distribution of oil and gas fields and trap types

estimating crustal thickness using sspmp in regions covered by low velocity sediments imaging the moho beneath the southeastern suture of the appalachian margin experiment sesame array se atlantic coastal plain

post critical sspmp and its applications to virtual deep seismic sounding vdss 3 back projection imaging of the crust mantle boundary in a heterogeneous lithosphere theory and application

post critical sspmp and its applications to virtual deep seismic sounding vdss 2 1 d imaging of the crust mantle and joint constraints with receiver functions

supershear rupture on multiple faults for the mw 8 6 off northern sumatra indonesia earthquake of april 11 2012 1 we perform a back projection method to image the rupture propagation and short period energy release of the 2012 off northern sumatra earthquake mw8 6 using hi net data recorded in japan the results show a complex pattern of four conjugate faults over about 180 sec there is a striking correspondence between the lengths and orientations of our rupture pattern with the distribution of aftershocks each of the first three stages of the rupture corresponds to a clear lineation in the aftershocks with lengths of 200 to 400 km rupture speeds for several of the fault segments were very high about 5 km s and exceed the local s wave velocity this is the first example of an oceanic earthquake with supershear rupture speed

seismic crustal structure of the north china craton and surrounding area synthesis and analysis we present a new digital model nccrust of the seismic crustal structure of the neoarchean north china craton ncc and its surrounding paleozoic mesozoic orogenic belts 30 45 n 100 130 e all available seismic profiles complemented by receiver function interpretations of crustal thickness are used to constrain a new comprehensive crustal model nccrust the model presented on a 0 25 0 25 grid includes the moho depth and the internal structure thickness and velocity of the crust specified for four layers the sedimentary cover upper middle and lower crust and the pn velocity in the uppermost mantle the crust is thin 30 32 km in the east while the moho depth in the western part of the ncc is 38 44 km the moho depth of the sulu dabie qinling qilian orogenic belt ranges from 31 km to 51 km with a general westward increase in crustal thickness the sedimentary cover is 2 5 km thick in most of the region and typical thicknesses of the upper crust middle crust and lower crust are 16 24 km 6 24 km and 0 6 km respectively we document a general trend of westward increase in the thickness of all crustal layers of the crystalline basement and as a consequence the depth of the moho there is no systematic regional pattern in the average crustal vp velocity and the pn velocity we examine correlation between the moho depth and topography for seven tectonic provinces in the north china craton and speculate on mechanisms of isostatic compensation

constraining sedimentary structure using frequency dependent p wave particle motion a case study of the songliao basin in ne china knowledge on sedimentary structure within a basin is of great importance for exploring petroleum resources and predicting strong ground motions caused by earthquakes although 3 d seismic data acquisition is common nowadays in petroleum industry it is still impossible to conduct dense 3 d seismic surveys at a whole basin scale passive seismic imaging thus can play a significant role in obtaining large scale sedimentary structure of basins with a reasonably good resolution here we present a new method to estimate the sedimentary structure beneath a seismic station using frequency dependent nonlinear particle motion of the teleseismic p wave that is a delay in the p wave arrival time on the horizontal component forward modeling suggests that the delay time and its variations over frequency are caused by interference of the direct p wave with the p to s conversions at the base of the sediments as well as sediment reverberations and hence can be used to constrain the thickness and seismic velocity of the sediments beneath the station we further develop a 2 d grid search technique to estimate the optimum sediment thickness z and surface s wave velocity 0 by minimizing the residuals between the observed and calculated apparent p wave splitting times the grid search yields reasonably robust estimates of z and 0 although it has some trade off between the two parameters in the case of thin and unconsolidated sediments we apply the method to 30 broadband stations inside the songliao basin and the estimated sedimentary structures beneath these stations agree well with previous results

constraints on residual topography and crustal properties in the western united states from virtual deep seismic sounding we use virtual deep seismic sounding vdss and data from 1 000 broadband seismic stations to provide high resolution estimates of crustal structure in the western cordillera of the united states us the most robust result is the geographic distribution of residual topography that is the difference between observed elevation and that expected from crustal buoyancy alone and by implication thermal or petrologic anomalies in the mantle overall residual topography of the western us cordillera varies considerably with contrasts of up to about 3 km across distances of 200 km or less high residual topography indicating large mantle effects is evident along the periphery of the colorado plateau and the surroundings of the great basin in contrast the central colorado plateau and the wyoming basin show low residual topography close to what is expected of a geologically stable lithosphere overall in regions to the east of the wasatch hinge line the eastern limit of significant extension in the north american cratonic basement patterns of high residual topography and anomalies of low seismic wave speeds in the upper mantle are similar suggestive of a common thermal origin in contrast such a similarity is absent in regions to the west of the hinge line suggesting substantial effects of petrological heterogeneities in the mantle finally joint analyses of vdss and conventional receiver functions reveal a wide range of crustal p wave speeds locally as high as 6 7 km s perhaps indicating magmatic modification of the crust

spatial relation between main earthquake slip and its aftershock distribution 1 we examine where aftershocks occur relative to the spatial distribution of the main shock slip using data from several recent large earthquakes no universal relation between high and low moment regions and high or low aftershock occurrence or vice versa is found we generally find that few and usually the smaller aftershocks occur in the high slip regions of the fault a notable exception to this being the great 1996 biak indonesia subduction zone earthquake in all cases aftershocks occur on favorably oriented planes of weakness in regions of increased postseismic stress generally they are clustered at both ends of faults but examples where aftershocks occur only at one end or where there is no clustering at the ends are found aftershock clusters are also found at the edge of unbroken barriers and regions of rapid transition from high to low slip within the main fault area we identify examples of geometrical and inhomogeneous barriers and sharp and dull stress concentrations rupture in the main shock is generally found to nucleate in the region of low slip or at the edge of high slip regions the 1996 biak earthquake again being the only exception nucleating in a very high slip region off fault aftershocks are found for all earthquakes in this study and they sometimes rupture the nodal plane conjugate to the main shock fault plane

the evolution of the seismic aseismic transition during the earthquake cycle constraints from the time dependent depth distribution of aftershocks 1 using the example of the 1992 m 7 3 landers earthquake we show that in the aftermath of a large earthquake the depth extent of aftershocks shows an immediate deepening from pre earthquake levels followed by a time dependent postseismic shallowing we use these seismic data to constrain the change in the depth of the seismic aseismic transition with time throughout the earthquake cycle most studies of the seismic aseismic transition have focussed on the effects of temperature and or lithology on the transition either from brittle faulting to viscous flow or from unstable to stable sliding a strain rate dependent transient deepening of the brittle ductile transition following a major earthquake is predicted by geological and laboratory observations by analyzing the time dependent depth distributions of aftershocks we identify and quantify the temporal evolution of this transition in the example of the landers earthquake its depth changes by as much as 3 km over the course of 4 years

imaging basin structure with teleseismic virtual source reflection profiles 1 we demonstrate a case of using teleseisms recorded on single channel high frequency geophones to image upper crustal structure around the bighorn mountains of north central wyoming usa our approach produces images that are analogous to those from a low frequency version of conventional active source seismic reflection profiles except that wave fields from distant earthquakes are used as sources after the source wavelet is removed from the seismograms a distinct phase pppdp is evident in the resultant record after depth conversion we show that this phase correlates well with the top of the madison formation under the powder river and bighorn basins that flank the bighorn mountains in addition we combine the phases pppdpfrom single channel geophone recordings andpsfrom three component recordings to constrain the averagevp vs ratio for the sedimentary strata

efficient calculation of differential seismograms for lithospheric receiver functions summary a new technique for computing differential seismograms for crustal and upper mantle response to a teleseismic wave receiver functions is developed using the matrix formalism of kennett the work was motivated by the difficulty of modelling teleseismic sv waves and has also proven useful for modelling teleseismic p waves this efficient method for calculating differential seismograms is based on three separate methods for computing synthetic seismograms two of the synthetic seismogram methods save intermediate results then the remaining synthetic seismogram algorithm uses the stored results in an efficient calculation of a new synthetic seismogram for a perturbed velocity model these developments have led to a faster for a 30 layer model a 90 per cent reduction in computation time and more accurate linearized inversion scheme for the determination of velocity models using teleseismic waves

northward thinning of tibetan crust revealed by virtual seismic profiles 1 a new approach of constructing deep penetrating seismic profiles reveals significant regional variations in crustal thickness under near constant elevation of tibet over distances of hundreds of kilometers the crust is as thick as 75 km in southern tibet but shoals to just over 60 km under the qiangtang terrane in central tibet where the deviation from airy isostasy is equivalent to a thickness of over 10 km in missing crust northward thinning of crust occurs gradually over a distance of about 200 km where mechanical deformation instead of pervasive magmatism also seems to have disrupted the crust mantle interface

tracer derived freshwater composition of the siberian continental shelf and slope following the extreme arctic summer of 2007 we investigate the freshwater composition of the shelf and slope of the arctic ocean north of the new siberian islands using geochemical tracer data 18o ba and po 4 collected following the extreme summer of 2007 we find that the anomalous wind patterns that partly explained the sea ice minimum at this time also led to significant quantities of pacific derived surface water in the westernmost part of the makarov basin we also find larger quantities of meteoric water near lomonosov ridge than were found in 1995 dissolved barium is depleted in the upper layers in one region of our study area probably as a result of biological activity in open waters increasingly ice free conditions compromise the quantitative use of barium as a tracer of river water in the arctic ocean

an investigation on slowness weighted ccp stacking and its application to receiver function imaging common conversion point ccp stacking of receiver functions is a widely used technique to image velocity discontinuities in the mantle the ccp imaging technique assumes that receiver functions are composed solely of p to s conversions at velocity boundaries whose depths can be mapped out through their arrival times the multiple reflections at shallow boundaries with large velocity contrasts such as the base of unconsolidated sediments and the moho can lead to artificial structures in the ccp images we develop a refined ccp stacking method that uses relative slowness as a weighting factor to suppress the multiples slowness weighted ccp stacking swccp we conduct extensive numerical tests with synthetic data to seek the best weighting scheme and to verify the robustness of the images we apply this technique to receiver function data of necessarray in china and the transportable array in western us and find most of the events in the depth range of 200 400 km shown in the regular ccp images are eliminated the swccp images on the other hand reveal a clear negative event under some parts of the two arrays indicating the presence of low velocity layer above the 410 km discontinuity which was reported by previous studies

the accuracy of δ11b measurements of foraminifers values of 11b reported in the literature for holocene samples of the same foraminiferal species show large variability 6 relative to cited precision 1 this is indicative of significant inter laboratory biases and raises concerns about the accuracy of foraminiferal proxy ph records to investigate this problem we have measured the 11b of modern ocean carbonates using several different analytical procedures we have used total evaporation negative thermal ionisation mass spectrometry te ntims with various sample preparation and loading procedures and multi collector inductively coupled plasma mass spectrometry mc icpms the 11b of pure boric acid solutions measured by te ntims and mc icpms agree well demonstrating no fundamental biases between the techniques yet the 11b values measured by te ntims for non foraminiferal carbonates are about 2 lighter than those by mc icpms whereas foraminifers measured by the same standard te ntims procedure are 2 to 6 heavier than those by mc icpms significantly we found that foraminiferal samples kept in acidic solution over several months yielded lower 11b values up to 5 lower and better reproducibility when re measured by te ntims we infer that organic material released on foraminiferal dissolution causes biases in ntims measurements no residual organics should be present in the mc icpms measurements as matrix is separated from sample before analysis moreover we demonstrate by standard addition the absence of any matrix influence in the mc icpms procedure beyond the inherent uncertainties in the standard addition approach 0 35 2sigma degradation of the inferred organic residue either by long term storage in acidic solution or by loading samples in 30 h2o2 reduces but does not totally remove the variable bias between te ntims and mc icpms 11b measurements despite these problems careful analysis of similar samples by ntims may permit data to be obtained with consistent relative differences that still yield valuable proxy records but there is clearly considerable potential for inaccuracies to result in such an approach from hard to detect changes in matrix

the motion and boundary between the capricorn and australian plates the motions between the somalian antarctic and australian plates the three plates believed to meet at the rodrigues triple junction in the indian ocean are inconsistent with the assumption that all three plates are rigid the discrepancy is best explained if the australian plate contains two component plates thus the traditionally defined indo australian plate consists of three component plates and multiple diffuse plate boundaries the pattern of present deformation indicates that the boundaries between the three component plates are two unconnected zones accommodating divergence and a larger zone which we interpret as three diffuse convergent plate boundaries and a diffuse triple junction

the 2012 mw 8 6 sumatra earthquake evidence of westward sequential seismic ruptures associated to the reactivation of a n s ocean fabric 1 the 11 april 2012 mw 8 6 earthquake offshore sumatra is the largest of the rare great intraplate earthquakes of the instrumental era this major strike slip event occurred in the diffuse zone of deformation that accommodates differential rotation between indian and australian plates we perform a back projection analysis calibrated with well located aftershocks of short period teleseismic p waves recorded by the european array to image the rupture process during the mainshock in complement a love wave analysis is conducted for tracking azimuthal change in the apparent global source duration due to the source spatio temporal extent the combined analysis reveals a complex rupture pattern characterized by three main episodes of energy release the latest being located 370 km west of the epicenter on the ninety east ridge with a delay of 120 s we interpret the 11 april 2012 mw 8 6 offshore sumatra earthquake as a complex westward propagating sequence of dynamically triggered strike slip fault ruptures associated to the reactivation of the inherited nne striking sea floor fabric the dynamic triggering mechanism could result from the interaction between transient surface wave stress perturbations and fluids

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

thick crust beneath the ordos plateau implications for instability of the north china craton abstract surrounded by seismicity and other manifestations of active deformation the ordos plateau or the western portion of the north china craton ncc is a uniquely stable terrane in asia results from virtual deep seismic sounding and crustal receiver functions suggests that the crust under the eastern ordos is thicker at least 60 km than expected from previous studies and from its modest elevation 1500 m above sea level receiver functions also reveal a pronounced elastic impedance contrast within the crust at 40 km depth which we interpret as the conrad discontinuity the presence of a 20 km thick layer of mafic lower crust between the conrad and moho discontinuities would maintain crustal isostasy the 1000 km long seismic profile from the ordos plateau in the west to the north china basin in the east reveals that crustal thickness changes by almost a factor of two across the active shanxi rift in central ncc over a distance of only about 100 km insofar the current configuration of the lithosphere under the ordos plateau might serve as a proxy for the initial condition prior to reactivation of the eastern part of ncc where a cratonic keel no longer seems to exist our results support the hypothesis that lower crust foundering was due to transformation of a thick mafic lower crust to a garnet rich assemblage possibly caused by hydration associated with subduction during and or before mid mesozoic times

seismological constraints on the density thickness and temperature of the lithospheric mantle in southwestern tibet h m d thanks h fang d forsyth r g green a holt v levin c yu and especially l royden for helpful discussions and to schlumberger for a scholarship he is also grateful to v levin and s roecker for making all seismo grams from the y2 network freely available through the iris data management centre we also thank three anonymous reviewers for thorough constructive reviews data were processed using obspy all figures were prepared using matplotlib alongside the cartopy library for mapping