evidence for inner core rotation from possible changes with time in pkp coda 1 inner core grazing pkp waves from seven french nuclear tests on mururoa island recorded at norsar appear to change over a decade we compared filtered and stacked signals from the explosions which took place from 1977 to 1987 and were separated by less than 10 km the pkp energy 3 to 10 s after the first arrivals differs greatly between the norsar subarrays and evolves over time the small time shifts of coda arrivals a few tenths of a second are qualitatively consistent with shifts predicted for point scatterers in an inner core that rotates in the range 0 05 to 0 10 per year there are also visible changes in the envelope of the pkp energy although the alternative of systematic shifts in source location cannot be ruled out the apparent time evolution of pkp supports claims of slow inner core rotation song and richards 1996 creager 1997 laske and masters 1999 vidale et al 2000 and offers a powerful new tool for its assessment

secondary palaeoremanence of tethyan sediments from the zanskar range nw himalaya summary palaeomagnetic investigations have been carried out on tethyan sediments from the nw zanskar range 33 9 n 76 5 e a total of 455 oriented samples from 41 sites were drilled from four stratigraphic units of middle cretaceous to early eocene age shillakong formation marpo limestone spanboth formation stumpata quartzarenite spanboth formation kong formation a characteristic remanence chrm could be isolated for 27 sites 254 specimens through detailed thermal and alternating field demagnetization and multicomponent analysis all the chrm directions identified are similar irrespective of geological age they fail the fold test and yield an overall in situ mean direction of d 336 6 i 39 6 with 95 5 9 and k 22 9 this corresponds to a palaeopole position at 66 5 n 323 5 e n pole isothermal remanence irm acquisition and thermal demagnetization of a saturation irm identify pyrrhotite as the dominant ferrimagnetic mineral and carrier of the chrm the pyrrhotite remanence is probably a thermoremanent magnetization acquired when the temperature of low grade metamorphism decreased below about 300 c the chrm directions are thus clearly secondary in origin and a negative conglomerate test carried out on the kong formation demonstrates that remanence acquisition post dates the early eocene the mean chrm inclination suggests that the remanence was acquired at about 20 n cooling events in the higher himalayan crystallines indicate an oligocene age for this remanence acquisition the mean chrm declination shows a counterclockwise rotation of 23 4 since remanence acquisition assuming remanence acquisition at about 30 myr ago a slight counterclockwise rotation of about 10 relative to the stable indian plate can be concluded this does not fit with the general pattern of palaeomagnetic results from neighbouring areas within the western syntaxis of the himalaya from which a clockwise rotation relative to the stable indian plate is expected for the zanskar range

is the rotation real earth9s interior consists of a mantle liquid core and at the very center a solid inner core made of iron one of the inner core9s most peculiar properties is its anisotropy seismic waves travel slightly faster if they are parallel to earth9s rotation axis in her perspective souriau describes recent seismic studies that suggest the inner core rotates faster than earth9s mantle and comments on the current dilemma in interpreting the experimental findings

thermo tectonic history of the tethyan himalayas deduced from the palaeomagnetic record of metacarbonates from shiar khola central nepal abstract palaeomagnetic measurements were carried out on low grade metamorphic carbonates of mesozoic age from the shiar area 85 1 e 28 6 n of the tethyan himalaya th in north central nepal two characteristic remanence components carried by pyrrhotite chrm 1 and magnetite chrm 2 could be identified by their unblocking temperature spectra of 270 340 and 430 580 c respectively fold tests are not significant due to the uniform bedding of all sites however according to results from other areas of the th the pyrrhotite component has been probably acquired as a secondary p trm during exhumation and cooling thus the age of remanence acquisition can be related to the last cooling event 25 17 ma in the surrounding areas the inclination of the magnetite component matches the value expected from the indian apwp this may the primary origin of the chrm 2 pyrrhotite site mean directions show a small circle distribution with a best fit parallel to the n s direction backtilting to the expected inclination i exp by intersection of the remanence small circle with the small circle of constant i exp yields a clockwise block rotation of 30 35 with respect to the indian plate characteristics of the pyrrhotite component small circle distribution of site means secondary origin p trm with unblocking temperatures below about 300 c allow the interpretation of the chronologic order of the thermo tectonic history i an earlier main folding phase at elevated temperatures ii a later event of cooling through about 300 c coinciding with the acquisition of chrm 1 iii clockwise block rotations with respect to the indian plate and iv long wave folding as the youngest tectonic event

support for differential inner core superrotation from earthquakes in alaska recorded at south pole station observational evidence for differential inner core rotation has recently been reported the most convincing evidence has been restricted to one ray path from earthquakes in the south sandwich islands to stations in alaska here we show that the differential travel times between pkp df and pkp bc for a new ray path from earthquakes in southern alaska to the station at the south pole have increased by about 0 6 s over 37 years providing support for a differential inner core rotation we apply a newly developed technique to invert simultaneously for the inner core structure and the rotation rate the rotation rate determined from the new pathway is about 0 6 yr faster than the mantle compatible with the estimates of the rate from earthquakes in the south sandwich islands to stations in alaska we also address some criticisms concerning the reported detection of the differential inner core rotation including biases from event mislocations biases from mantle heterogeneity and uncertainty in the tilt of the inner core anisotropy axis we show that although these potential biases would affect the determination of the rotation rate they are unlikely to account for the observed time dependence in the bc df times we found no evidence for a correlation between bc df residuals and event magnitudes as suggested previously

paleomagnetic evidence for dextral strike slip motion in the pyrenees during alpine convergence mauleon basin france abstract the paleomagnetic study of the aptian albian black marls from the inverted early cretaceous mauleon basin in the northern pyrenees reveals two components of magnetization that both yield negative fold tests the carriers of each component show different unblocking temperatures indicating that ferrimagnetic iron sulphides are the main carriers of the intermediate temperature component itc unblocks around 360 400 c and magnetite is the main carrier of the high temperature component htc unblocks around 460 500 c both components show a clockwise deviation in declination with respect to the reference field directions itc di and htc di both in in situ coordinates the reference direction for stable europe for the cenozoic is d i 001 50 d 5 i 3 however the reversal test for both of the magnetization components in situ is positive the structural evolution of the basin involves transtensional deformation during the main stage of basin formation and inversion during compression with migration of hydrocarbons and development of thrusts and folds with axial planar cleavage secondary magnetizations were acquired at the latest stages of the evolution of the inverted basin post folding as the result of a chemical mechanism and they were blocked during two different and likely close spaced in time polarity chrons the blocking of the two different magnetizations with different carriers implies chemical changes in the environment from anoxic sulphate reduction to oxic inferred clockwise rotation of the paleomagnetic vectors can be interpreted in terms of dextral shear across the north pyrenean zone during the tertiary probably eocene according to the plate tectonic scenario this distributed dextral shear was probably favored by discrete shear along cleavage planes as shown by geologic markers of consistent dextral strike slip motion in non competent units with strong cleavage development there is no evidence of such dextral movement in the south pyrenean zone thus indicating a strong partitioning of deformation during the pyrenean orogeny

paleomagnetism of early paleogene marine sediments in southern tibet china implications to onset of the india asia collision and size of greater india article i nfo we report a paleomagnetic study of paleocene marine sediments in the gamba area of the tethyan himalayan terrane southern tibet which aims to accurately locate the position of the northern margin of greater india and further constrain timing of initial contact between india and asia following detailed rock magnetic and paleomagnetic experiments on a total of 675 drill core samples collected from the zongpu and upper jidula formations characteristic remanent magnetizations chrms were successfully isolated from most samples following alternating field af or integrated thermal and af demagnetization the chrms are of dual polarity and pass fold and reversal tests indicating a pre folding origin together with detailed biostratigraphic investigation of the sampling section a magnetic polarity sequence is constructed from data at 167 sampled horizons and satisfactorily correlates with polarity chrons c24r to c27r dating the zongpu formation between 56 2 and 61 8 ma on the geomagnetic polarity time scale the chrm directions from the zongpu formation are grouped stratigraphically into 33 sites and yield two paleopoles of 71 6 n 277 8 e a95 2 5 and 67 3 n 266 3 e a95 3 5 for the time intervals comprising 56 to 59 ma and 59 to 62 ma respectively these new paleopoles imply that the tethyan himalayan terrane was sited at low latitudes in the northern hemisphere during the interval 62 56 ma suggestingthatinitial contact between thetethyanhimalayaand lhasa terranes was established before60 5 1 5 ma and verylikelyoccurred nearthecretaceous tertiary boundary at least in the central partof the suturezone the results alsoindicate that atleast 1500 480 kmof post collisionalcrustal shortening occurred within the himalayas from the analysis of available paleomagnetic data obtained on both sides of the suture zone we propose a conceptional collision model for the india asia collision

what was the paleogene latitude of the lhasa terrane a reassessment of the geochronology and paleomagnetism of linzizong volcanic rocks linzhou basin tibet the paleogene latitude of the lhasa terrane southern tibet can constrain the age of the onset of the india asia collision estimates for this latitude however vary from 5 n to 30 n and thus here we reassess the geochronology and paleomagnetism of paleogene volcanic rocks from the linzizong group in the linzhou basin the lower and upper parts of the section previously yielded particularly conflicting ages and paleolatitudes we report consistent 40ar 39ar and u pb zircon dates of 52 ma for the upper linzizong and 40ar 39ar dates 51 ma from the lower linzizong are significantly younger than u pb zircon dates 64 63 ma suggesting that the lower linzizong was thermally and or chemically reset paleomagnetic results from 24 sites in lower linzizong confirm a low apparent paleolatitude of 5 n compared to the upper part 20 n and to underlying cretaceous strata 20 n detailed rock magnetic analyses end member modeling of magnetic components and petrography from the lower and upper linzizong indicate widespread secondary hematite in the lower linzizong whereas hematite is rare in upper linzizong volcanic rocks of the lower linzizong have been hydrothermally chemically remagnetized whereas the upper linzizong retains a primary remanence we suggest that remagnetization was induced by acquisition of chemical and thermoviscous remanent magnetizations such that the shallow inclinations are an artifact of a tilt correction applied to a secondary remanence in lower linzizong we estimate that the paleogene latitude of lhasa terrane was 20 4 n consistent with previous results suggesting that india asia collision likely took place by 52 ma at 20 n

localized temporal change of the earth s inner core boundary compressional waves of an earthquake doublet two events occurring in the south sandwich islands on 1 december 1993 and 6 september 2003 recorded at three seismic stations in russia and kyrgyzstan and reflected off earth s inner core boundary arrived at least from 39 to 70 milliseconds earlier in the 2003 event than in the 1993 event such changes indicate that earth s inner core radius enlarged locally beneath middle africa by 0 98 to 1 75 kilometers between the times of these two events changes of the inner core radius may be explained by either a differential motion of the inner core assuming that irregularities are present at the inner core boundary and fixed to the inner core or a rapid growth of the inner core by this amount

coupling of late orogenic tectonics and secondary pyrrhotite remanences towards a separation of different rotation processes and quantification of rotational underthrusting in the western himalaya northern india abstract the total amount of crustal shortening within the indian plate includes straight forward and rotational shortening the complex tectonic history of the western himalaya impedes a direct observation of rotational shortening between india and its northern margin a combination of palaeomagnetic results and tectonic structures along a 300 km nw se section from nw zanskar 33 9 n 76 5 e to malari 30 0 n 79 6 e in northern india enable a separation of rotations on different scales correction of the observed rotations and quantification of uniform rotational shortening new palaeomagnetic results from metacarbonates of the tethyan himalaya in sarchu losar and spiti and earlier studies from nw zanskar and malari reveal a characteristic remanent magnetisation carried by pyrrhotite unblocking spectrum 250 330 c negative fold tests 99 level indicated remanence acquisition after the main folding of the himalaya the formation of pyrrhotite during thermal events t 200 c suggests a remanence acquisition related to exhumation and cooling temperatures of about 200 300 c indicate a thermochemical remanence acquisition with an eohimalayan age dated in two areas by 40k 39ar techniques on illites the resulting rotation angles in respect to stable india show an anomalous counterclockwise rotation in nw zanskar and a trend of decreasing clockwise rotations to the se these variations may be attributed to meso scale 100 km tectonic features and oroclinal bending for the first time block rotations with respect to stable india are separated into local meso scale and regional significant ones after elimination of local and meso scale effects using structural analysis of late orogenic features modelled rotations due to oroclinal bending were subtracted regionally significant rotations of 0 20 clockwise are interpreted to be caused only by uniform rotational underthrusting

polar motion excitations for an earth model with frequency dependent responses 2 numerical tests of the meteorological excitations 1 polar motion excitation involves mass redistributions and motions of the earth system relative to the mantle as well as the frequency dependent rheology of the earth where the latter has recently been modeled in the form of frequency dependent love numbers and polar motion transfer functions at seasonal and intraseasonal time scales polar motions are dominated by angular momentum fluctuations due to mass redistributions and relative motions in the atmosphere oceans and continental water snow and ice in this study we compare the geophysical excitations derived from various global atmospheric oceanic and hydrological models ncep ecco era40 erainterim and ecmwf operational products and construct two model sets ldc1 and ldc2 by combining the above models with a least difference method comparisons between the geodetic excitation derived from the polar motion series iers eop 08 c04 and the geophysical excitations based on those meteorological models imply that the atmospheric models are the most reliable while the hydrological ones are the most inaccurate that the erainterim is in general the best model set among the original ones but the combined models ldc1 and ldc2 are much better than erainterim and that applying the frequency dependent transfer functions to ldc1 and ldc2 improves their agreements with the geodetic excitation thus we conclude that the combined models ldc1 and ldc2 are reliable and the frequency dependent love numbers and polar motion transfer functions are well modeled

time dependence of pkp bc pkp df times could this be an artifact of systematic earthquake mislocations abstract differential inner core rotation was first detected from time dependent observations of differential travel times between pkp df waves which go through the inner core and pkp bc waves which turn at the bottom of the outer core song and richards 1996 criticisms concerning the reported detection have been raised the most significant one being the possible bias from potential systematic earthquake mislocations in this study i examine this issue by comparing both differential ab bc and bc df times between pairs of events with similar locations and waveforms the procedure is very similar to the doublet technique proposed recently by poupinet et al 2000 who concluded that the time dependence of the bc df times from the earthquakes in south sandwich islands recorded at college alaska observed by song and richards 1996 is an artifact of earthquake mislocations because the difference in ray parameters between ab another branch of pkp which turns at the mid outer core and bc is more than twice the difference between bc and df systematic mislocations have much larger effect on differential ab bc times than on differential bc df times my analysis of similar event pairs for the south sandwich islands to college alaska path shows a clear time dependence of increasing bc df times over time the ab bc times of these same event pairs do not show any increasing trend rather they show a decreasing trend the results rule out the possibility that the observed time dependence of the bc df times is caused by earthquake mislocation providing strong support for the differential inner core rotation

multicomponent magnetization in western dolpo tethyan himalaya nepal tectonic implications abstract a palaeomagnetic study has been carried out in the tethyan himalaya th the northern margin of greater india twenty six palaeomagnetic sites have been sampled in triassic low grade metasediments of western dolpo two remanent components have been identified a pyrrhotite component characterized by unblocking temperatures of 270 335 c yields an in situ mean direction of d 191 7 i 30 9 k 29 5 95 5 7 n 23 sites the component fails the fold test at the 99 confidence level kin situ kbed 6 9 and is therefore of postfolding origin for reason of the low metamorphic grade this pyrrhotite magnetization is believed to be of thermo chemical origin geochronological data and inclination matching indicate an acquisition age around 35 ma the second remanence component has higher unblocking temperatures 400 c and up to 500 580 c range and resides in magnetite a positive fold test and comparison with expected triassic palaeomagnetic directions suggest a primary origin the postfolding character of the pyrrhotite component and its interpreted age of remanence acquisition implies that the main himalayan folding is older than 35 ma in the western dolpo area this study also suggests that the second metamorphic event neo himalayan was more significant in the dolpo area than the first eo himalayan one a clockwise rotation of 10 15 is inferred from the pyrrhotite component which is compatible with oroclinal bending and or rotational underthrusting models this rotation is also supported by the magnetite component indicating that no rotation of the tethyan himalaya relative to india took place before 35 ma

collision tectonics in the nw himalayas west himalayan tectonics involve the collision of microplates between the indian and asian plates the kohistan complex consists largely of tightly folded basic volcanics and sediments generated as late jurassic to late cretaceous island arcs these were intruded by post folding mid cretaceous eocene plutonics produced from continued subduction of the indian plate after closure of a suture between kohistan and the karakorum the himalayan structures show major thrust sheets and the kohistan arc is essentially a crustal pop up with southward upright and northward verging structures developed above a thick ductile decoupling zone the indus suture which can be traced for 100 km beneath kohistan on large reentrants this pop up formed by a two stage process closure of the northern suture followed by closure of the southern indus suture granitic rocks of the kohis tan ladakh batholith dated at 100 40 ma post date most of the structures related to the northern suture but were deformed and carried southwards on shear structures related to the indus suture postcollisional deformation carried this kohistan complex on deep decoupling zones over the indian plate on a series of imbricated gneiss sheets the thrusts climbing up section in the movement direction so that in the far s some override their own molasse debris folds above these deep decoupling zones deformed their overlying thrust sheets into large antiforms i e the nanga parbat and hazara syntaxes the nanga parbat syntaxis probably formed due to a shear couple near a branch line where one of the main himalayan thrusts joined the indus suture beneath kohistan crustal delamination to produce the imbricated gneiss sheets could not account for all the displacement of india into asia suggested by palaeomagnetic data there must also have been lateral displacement as demonstrated by the large oblique slip shear zone in the hunza valley n of kohistan

palaeomagnetism of cretaceous to tertiary sediments from southern tibet evidence for the extent of the northern margin of india prior to the collision with eurasia abstract palaeomagnetic studies have been carried out on mid cretaceous to latest palaeocene sediments from the tethyan himalaya on the northern margin of the indian plate near the localities of gamba 28 3 n 88 5 e and duela 28 0 n 89 2 e in southern tibet a total of 61 sites more than 700 cores have been sampled mainly from limestones zongshan formation jidula formation member ii zongpu formation sandstones jidula formation member iii and graywackes gamba group member ii with ages well defined from detailed lithological and biostratigraphic analyses carriers of characteristic remanences are magnetite in limestones and graywackes and hematite in sandstones reliable palaeodirections were obtained from 35 sites 356 specimens positive fold tests antiparallel normal and reverse polarities a northward trend of the palaeolatitudes with decreasing age and absence of any metamorphic overprint indicate a primary origin for the characteristic remanences the results have been compared with expected palaeodirections according to available data for the indian subcontinent based on its present day geometry the late maastrichtian sites fourteen sites 156 specimens and the middle late palaeocene sites fourteen sites 113 specimens yield palaeolatitudes of 5 7 s and 4 0 n for the sampling localities in southern tibet respectively these palaeolatitudes are much further north than expected and imply that crustal shortening between the tethyan himalaya and the indian shield since the time of india eurasia collision has occurred on the order of 1500 km at the longitude of gamba duela comparison of our observed palaeolatitudes with palaeolatitudes for the lhasa block during cretaceous and palaeocene times indicate that initial contact of the northern indian margin with the lhasa block was already established at 65 60 ma with suturing completed at about 55 50 ma

seismic velocity and attenuation structures in the top 400 km of the earth s inner core along equatorial paths 1 we study seismic velocity and attenuation structures in the top 400 km of the earth s inner core based on modeling of differential traveltimes amplitude ratios and waveforms of the pkikp pkikp phases observed at the epicentral distance range of 120 141 and the pkpbc pkikp phases observed at the distance range of 146 160 along equatorial paths our data are selected from the seismograms recorded in the global seismographic network from 1990 to 2001 and many regional seismic networks the observed pkikp pkikp and pkpbc pkikp phases exhibit distinctive east west hemispheric patterns 1 at the distance ranges of 131 141 and 146 151 pkikp phases arrive about 0 3 s earlier than the theoretical arrivals based on the preliminary reference earth model prem for the pkikp phases sampling the eastern hemisphere 40 e 180 e of the inner core and about 0 4 s later for those sampling the western hemisphere 180 w 40 e at the distance range of 151 160 pkikp phases arrive about 0 7 s earlier than the predicted arrivals based on prem for those sampling the eastern hemisphere and about 0 1 s later for those sampling the western hemisphere 2 amplitude ratios of the pkikp pkikp phases at the distance range of 131 141 and of the pkikp pkpbc phases at the distance range of 146 151 are in general smaller for the pkikp phases sampling the eastern hemisphere than for those sampling the western hemisphere at distances greater than 151 the pkikp pkpbc amplitude ratios become indistinguishable for the two hemispheres these observations can be best explained by two different types of seismic velocity and attenuation models along equatorial paths one for each hemisphere in the top 400 km of the inner core for the eastern hemisphere the velocity structure has a velocity increase of 0 748 km s across the inner core boundary icb a small velocity gradient of 0 0042 km s 100 km in the top 235 km followed by a steeper velocity gradient of 0 1 km s 100 km extending from 235 km to 375 km and a velocity gradient of 0 01 km s 100 km in the deeper portion of the inner core the attenuation structure has an average q value of 300 in the top 300 km and an average q value of 600 in the deeper portion of the inner core for the western hemisphere the velocity structure has a velocity increase of 0 645 km s across the icb and a velocity gradient of 0 049 km s 100 km in the top 375 km the attenuation structure has an average q value of 600 in the top 375 km of the inner core our results suggest that the inner core hemispheric variations in velocity extend deeper than 375 km below the icb and the top 235 km of the inner core in the eastern hemisphere is anomalous compared to the rest of the inner core in having a small velocity gradient high velocity and high attenuation

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

the inner core hemispheric boundary near 180 w abstract the inner core ic east west hemispheric dichotomy is widely recognized but the reported position of the hemispheric boundary varies among studies due to uneven sampling coverage and the data analyzed this study investigates the sharpness of the western hemispheric boundary whb near 180 w by analyzing differential time residuals of pkikp pkpdf and pkp bc df for pkpdf phases that sample 155 e 130 w in various azimuthal directions using pkikp pkpdf observations the whb is located at 175 e 180 w in the southern hemisphere based mainly on the lateral isotropy anisotropy transition however based on the lateral isotropic velocity contrast and this isotropy anisotropy transition between the two hemispheres its location is 170 160 w in the northern hemisphere these findings indicate that the whb is sharp and exhibits a latitudinal dependence with a 10 20 kink as well as 1 75 anisotropy in the uppermost ic across the 180 155 w range of the western hemisphere as suggested by pkp bc df the whb could remain at 160 w at depth the isotropic velocity contrast near the whb 160 w between the eastern and western hemispheres is lower than previous estimates using pkpdf phases sampling the bulk part of each hemisphere

examination of systematic mislocation of south sandwich islands earthquakes using station pairs implications for inner core rotation 1 one of the most robust observations for the inner core rotation is that the differential pkp bc df traveltimes from south sandwich islands ssi earthquakes to college alaska and some other stations in alaska have increased systematically over the past 50 years the time shift in the differential time residuals is some 0 3 s over 30 years this temporal change is thought to result from a shift of the inner core structure from a superrotation of the inner core however the observation has been hotly debated and has been suggested to be an artifact of systematic earthquake mislocation here we examine this issue using three mutually independent approaches with a goal to quantify the amount of the systematic mislocation if any all three approaches involve differencing data between north stations at a similar azimuth as the ssi alaska azimuth and south stations at nearly the opposite azimuth mislocation along this azimuth has greatest impact on the pkp differential times in approach 1 we examine how the double difference of p traveltimes between a north station and a south station changes with time because the differential apparent slowness between the p traveltimes of the pairs is 8 to 16 times that of the differential bc df times mislocation would cause a time shift in the double difference an order of magnitude larger than that of bc df times in approach 2 we compare directly difference in p arrival times between two ssi events that are close by and between a north and a south stations which avoids using earthquake locations and earth models entirely in approach 3 we compare pkp traveltime residuals between a group of north and south stations because pkp traveltimes are generally not used for location in earthquake bulletins they provide an independent data set to check earthquake location errors the results from approaches 1 and 2 both of which use p data are generally consistent the mislocation is up to 3 6 4 2 km one standard deviation explaining less than 10 of the observed col temporal change the results from approach 3 using pkp data show a larger mislocation but with a larger error 14 4 10 8 km over 30 years it can explain about 30 22 of the observed col temporal change therefore inner core superrotation is still the best explanation for the observed temporal change in the differential traveltimes

paleomagnetic evidence for clockwise rotation and tilting in the eastern tethyan himalaya se tibet implications for the miocene tectonic evolution of the ne himalaya abstract crustal movement around and away from the namche barwa syntaxis is indicated in the asian velocity field inferred from gps data and quaternary fault slip rates nevertheless there is a limited field based control on the rotational history of the north eastern himalayan arc exploring the poly phase nature of deformation within the cretaceous diorite dykes and their host rock triassic flysch in the eastern tethyan himalaya 90 92 e combined with new remote sensing data and existing thermo geochronological data allow us to unravel the kinematic relationship between paleomagnetic remanence vectors and the deformation phases decay at 325 c in high temperature susceptibility curves and in the thermal demagnetization of the sirm indicate that the characteristic remanent magnetization in the cretaceous diorite dykes is carried by pyrrhotite the pyrrhotite component unblocks at 280 350 c revealing normal and reverse polarities it is of post folding origin with a mean remanence direction of 019 28 and 001 20 in the eastern qonggyai valley and western nagarze part of the sampling area respectively the 22 ma k ar age of the last metamorphic event support that the remanence is post eohimalayan folding and likely of thermoremanent or thermo chemical origin comparison of the declination with respect to the early miocene reference direction yields a trend from no apparent rotation in the west to 20 clockwise rotation in the east with respect to the stable indian plate this result can be kinematically related to the middle to late miocene strain partitioning between far field southeast extrusion of se tibet and near field strike slip faulting and e w extension furthermore the observed pattern of tilting around horizontal axis may reflect concealed north himalayan doming

global seismic body wave observations of temporal variations in the earth s inner core and implications for its differential rotation differential rotation of the earth s inner core has been predicted in some geodynamo models and seismic studies over the past 15 yr have resolved rotation rates up to 1 yr 1 most previous seismic body wave studies have focussed on south sandwich islands events recorded at station col in alaska here we present a globally extended study into temporal variations in the inner core over some 25 yr using pkpbc pkpdf traveltime residuals to test for differential rotation of the inner core displacement of inner core heterogeneities over time is sought we introduce a new method of space flattening to remove the effect of spatial variations on the time variations this allows for the use of both polar semi equatorial and equatorial geometries first we reanalyse polar paths from south sandwich islands events to stations col and ink in north america these stations yield a differential rotation of the inner core at a rate of 0 12 0 38 yr 1 in an eastward direction in agreement with previous studies however station dawy which has a very similar path through the inner core as col yields at best a westward differential rotation of the inner core thus dawy results are incompatible with the col ink inferred rotation secondly earthquakes in the aleutian islands region observed at bosa and lbtb in southern africa exhibit temporal variations that are incompatible with the south sandwich islands col ink inferred rotation rate thirdly kuril islands events recorded in south america at station bdf yield inconclusive results finally our final piece of evidence for the irreconcilability of differential inner core rotation with global data comes from using earthquakes in the vanuatu region recorded at bcao bgca in central africa an equatorial geometry these residuals resolve a westward inner core rotation at a rate of 0 14 yr 1 over the same time period that south sandwich islands events indicate an eastward rotation as any rigid body rotation should yield the same direction and rate independent of where the inner core is sampled our results allow us to reject previously reported inner core differential rotation rates of up to 0 1 0 5 yr 1 instead our results suggest that structure in either the inner or the outer core is varying with time over relatively short timescales and in ways that cannot be explained by and do not support a differentially rotating inner core

regional and teleseismic double difference earthquake relocation using waveform cross correlation and global bulletin data 1 we have developed a double difference algorithm to relocate earthquakes recorded at global seismic networks using differential arrival times for first and later arriving regional and global phases to invert for the vectors connecting the hypocenters differential times are formed from global seismic bulletins and are accurately measured on similar seismograms by time domain waveform cross correlation we evaluate the performance of this spherical multiphase double difference algorithm using three dimensional regional scale synthetic data and two sets of earthquake data in different tectonic settings the first includes 3783 intermediate depth earthquakes that occurred between 1964 and 2000 in the subducting nazca plate beneath northern chile where the relocated seismicity confirms a narrowly spaced double seismic zone previously imaged with temporary local seismic data residual statistics and comparison with accurately known locations indicate mean relative location errors at the 90 confidence level of 2 4 km laterally and 1 8 km vertically later events typically constrained by cross correlation data have errors of 1 6 km laterally and 1 4 km vertically the second data set includes 75 crustal earthquakes in the 1999 izmit and duzce turkey aftershock sequences where the double difference solutions image orientation and dip of individual fault segments that are consistent with focal mechanisms and near surface information fault complexity likely causes a low level of waveform similarity in this aftershock sequence and thus generates fewer correlated events compared to the chile earthquakes differences between the double difference locations and corresponding locations in global seismicity catalogs earthquake data report edr international seismological centre isc engdahl hilst buland ehb are typically greater than 10 km we evaluate the potential of cross correlation and double difference methods to improve hypocenter locations on a global scale

origin of temporal changes of inner core seismic waves abstract temporal changes of inner core ic seismic phases have been confirmed with high quality waveform doublets however the nature of the temporal changes is still controversial we investigated systematically the temporal changes of ic refracted pkikp and reflected pkikp waves with a large data set of waveform doublets we used non ic reference phase mainly skp which eliminated ambiguity where the temporal changes come from we found that the temporal changes have always started at refracted pkikp and the travel time changes correlate better with pkikp changes in reflected pkikp can be easily contaminated by the strong and time varying pkikp and coda wave trains and therefore are not reliable indicators for ic boundary changes combining with previous observations we conclude that the temporal changes come mostly if not all from the ic interior and ic surface changes as the sole source suggested previously can be ruled out the differential rotation of the ic shifting its heterogeneous uppermost structures is the simplest and most reasonable explanation for the origin of the time varying ic waves a rotation rate of about 0 05 0 1 per year with possible decadal fluctuation can reconcile all temporal change observations from body waves ic scattering and normal mode data

wide scale detection of earthquake waveform doublets and further evidence for inner core super rotation summary we report on more than 100 earthquake waveform doublets in five subduction zones including an earthquake nest in bucaramanga colombia each doublet is presumed to be a pair of earthquakes that repeat at essentially the same location these doublets are important for studying earthquake physics as well as temporal changes of the inner core particularly our observation from one south sandwich islands ssi doublet recorded at station ink in canada shows an inner core traveltime change of 0 1 s over 6 yr confirming the innercore differential motion occurring beneath central america observations from one aleutian islands doublet recorded at station bosa in south africa and from one kuril islands doublet recorded at station bdfb in brazil show an apparent inner core traveltime change of 0 1 s over 7 yr and 6 yr respectively providing evidence for the temporal change of inner core properties beneath central asia and canada respectively on the other hand observations from one tonga fiji solomon islands doublet recorded at station ptga in brazil and from one bucaramanga doublet recorded at station wrab in australia and station chto in thailand show no little temporal change no more than 0 005 syr 1 if any of inner core traveltimes for the three corresponding ray paths for which the path in the inner core is nearly parallel to the equatorial plane such a pattern of observations showing both presence and possible absence of inner core traveltime change can be explained by the geometry and relative directions of ray path lateral velocity gradient and inner core particle motion due to an eastward super rotation of a few tenths of a degree per year

magnetic properties of the high himalayan leucogranites structural implications the magnetic properties of the high himalayan leucogranites have been investigated on 527 specimens in three plutons everest makalu 6 sites and manaslu 40 sites in nepal and gangotri 43 sites in india susceptibility varies between 2 and 100 10 6 si with an anisotropy ratio up to 1 16 high field and low temperature magnetic measurements together with comparison with weight percent iron demonstrate that anisotropy of magnetic susceptibility is carried by paramagnetic biotite and tourmaline the latter produces an inverse fabric i e with the minimum axis parallel to mineral lineation the magnetic fabric demonstrates complex patterns of stretching lineations during magmatic emplacement and its usefulness in semi quantitatively estimating petrofabric intensity is demonstrated for the biotite bearing facies natural remanent magnetization was measurable at only two sites in everest makalu where there are well defined reverse directions carried by titanomagnetite and pyrrhotite comparison of these preliminary results with predicted directions for stable india suggests northward tilting of about 10 and a small clockwise rotation of this massif

rotational overthrusting of the northwestern himalaya further palaeomagnetic evidence from the riasi thrust sheet jammu foothills india abstract thermal demagnetization results 316 samples are presented for the tertiary succession of the riasi thrust sheet jammu foothills northwestern himalaya primary and secondary magnetization directions of murree group red beds miocene to upper eocene sampled northeast of jammu indicate for this part of the riasi thrust sheet a clockwise rotation over about 45 with respect to the indian shield since late eocene early miocene time this accords with clockwise rotations of similar magnitude observed in the panjal nappe and the krol belt and is interpreted as representative for the northwestern himalaya results from the western part of the kalakot inlier sampled northwest of jammu i e basal murree claystone middle eocene and carbonate from the subathu group lower middle to lower eocene indicate an aberrant 20 25 counterclockwise rotation which is of local importance only available observations on rotation of himalayan thrust sheets with respect to the indian shield indicate that the himalayan arc has formed through oroclinal bending this supports powell and conaghan s and veevers et al s model of greater india with large scale intracontinental underthrusting along the main central thrust beneath the tibetan plateau minimal magnitudes of underthrusting of 550 km in the krol belt and 650 km in the thakkhola region are concluded palaeolatitude observations herein and in 1 agree with absolute positioning of the indian plate based on india africa relative movement data fixed to a hotspot frame in the atlantic ocean and with palaeolatitude observations from dsdp cores on the indian plate collision related secondary magnetic components observed both to the north and to the south of the indus tsangpo suture zone show palaeolatitudes between the equator and 7 n comparison of both datasets indicates that initial contact between greater india and south central asia had been established in the hindu kush karakorum region by about 60 ma ago whereas eastwards progressive suturing had advanced to the lhasa block segment of the indus tsangpo suture zone before 50 ma ago

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

evidence for inner core super rotation from time dependent differential pkp traveltimes observed at beijing seismic network summary in an effort to confirm and constrain inner core rotation we examine earthquakes from the south sandwich islands recorded at the beijing seismic network we obtained a total of 109 high quality measurements of pkp bc pkp df differential traveltimes by waveform cross correlations from earthquakes spanning over 30 years the results show robust temporal changes in pkp bc pkp df residuals along this pathway providing new support for the differential inner core hypothesis we also observed evidence for a lateral velocity gradient in this part of the inner core assuming that the temporal changes result from a shift of a lateral structure due to an inner core rotation we estimate the inner core rotation rate to be about 0 41 0 12 yr 1 faster than the mantle

using earthquake doublets to study inner core rotation and seismicity catalog precision 1 we report our search for doublets in the south sandwich islands ssi region among 906 earthquakes from january 1982 to december 1998 event pairs with source separation less than 40 km which was calculated using pde locations were checked using vertical component short period and broadband digital records cross correlation coefficients of p or pkp waveforms were computed for similarity comparison whole waveforms of those event pairs with correlation coefficients larger than 0 8 were checked by eye by this process 17 doublets were found some of which form multiplets however only one doublet event pair 14 august 1995 and 28 march 1987 has clear pkp df phases on both records at college alaska col the pkp df travel time change measured by cross correlation is a decrease by 0 15 s with standard deviation 0 02 s over a time period of about 8 years this result strongly supports differential rotation of the earth s inner core relative to the mantle and the crust the estimated rotation rate ranges from 0 4 to 1 per year eastward the special case of a locked inner core can then be ruled out we also checked the precision of pde and isc locations using the 17 doublets results show that both catalogs have relatively high location precision standard deviations in latitude longitude and depth are less than 4 km 6 km and 10 km respectively supporting prior claims of detection of inner core rotation song and richards 1996

seismological evidence for differential rotation of the earth s inner core the travel times of seismic waves that traverse the earth s inner core show a small but systematic variation over the past three decades this variation is best explained by a rotation of the inner core that moves the symmetry axis of its known seismic anisotropy the inferred rotation rate is on the order of 1 per year faster than the daily rotation of the mantle and crust

inner core transition zone and anomalous pkp df waveforms from polar paths 1 short period pkp df waves which travel through the inner core from polar paths nearly ns were observed to have small amplitudes and complex waveforms but the cause has been a mystery here we examine both short period and broadband pkp record sections from a single earthquake in south sandwich islands ssi the data from polar paths show clear evidence for an inner core triplication our waveform modeling suggests a 250 km thick isotropic upper inner core uic overlying an anisotropic lower inner core lic with about 8 anisotropy the synthetics match the observed waveforms and amplitudes well with a normal value of inner core attenuation we propose that such a uic lic transition zone structure may be the cause of anomalous df waveforms along polar paths the inferred level of anisotropy in the lic 2 3 times previous estimates has important implications for understanding physical properties of the inner core and sources of inner core anisotropy

a palaeomagnetic reconnaissance of kashmir northwestern himalaya india abstract thermal demagnetization studies of 800 palaeozoic and lower mesozoic samples mainly carbonates from 14 localities in kashmir showed four magnetic components a a recent field component of normal polarity and large intensity b a middle to late tertiary secondary component of large intensity and of reversed and normal polarity which indicates clockwise rotation of central and eastern kashmir over approximately 45 with respect to peninsular indo pakistan c primary magnetic components of triassic late permian early carboniferous siluro ordovician and middle to early ordovician age the triassic and late permian components show a 20 30 cumulative counterclockwise offset with respect to the indo pakistan apparent polar wander path apwp this indicates a post middle to late triassic counterclockwise rotational movement of kashmir over 65 75 with respect to peninsular indo pakistan d a component of low inclination and predominantly east west declination which is observed only in rocks of pre panjal traps age a secondary origin associated with extrusion of the panjal traps flows is surmised but could not be established beyond doubt alternatively this component may be related to the regional foliation the triassic and late permian primary component directions are predominantly of normal polarity this suggests a pre punjabian late permian upper age limit for the permo carboniferous kiaman reversed polarity interval which is earlier than the early to late tatarian limit observed in the u s s r

estimate of inner core rotation rate from united kingdom regional seismic network data and consequences for inner core dynamical behaviour abstract we analyse over 12 500 records of southwest pacific earthquakes recorded by the uk network for pkpbc and pkpdf phases to seek constraints on the inner core s rotation rate careful analysis and strict rejection criteria yield 655 pkpbc pkpdf differential travel time residuals computed with respect to the ak135 reference model densely sampling a small region of the inner core over a time period of 15 years the data images both lateral and radial velocity heterogeneity in the inner core located geographically beneath the north pacific between radii of 870 and 1080 km the dominant feature is a longitudinal wave speed gradient centred at about 180 longitude in combination with different earthquake catalogues and inner core anisotropy models we explore different techniques to use this gradient to constrain the rotation rate our estimates range from 0 45 0 25 to 0 74 0 29 yr relative to the mantle with two of four estimates including zero rotation at the 95 2 confidence level indicating that rotation is marginally detectable as an alternative to monotonic rotation we find weak evidence for rotational oscillation of the inner core on time scales of about 280 days in consequence these observations suggest that 1 viscous coupling between the outer and inner core simulated using viscous hyperdiffusivity is not appropriate for modelling inner core rotation 2 temperature gradients between the interior and exterior of the tangent cylinder in the core are also small 3 gravitational torques coupling the inner core to the mantle are large on the order of 2 1021 nm and 4 the inner core s viscosity is high 3 9 1019 pas

towards pyrrhotite magnetite geothermometry in low grade metamorphic carbonates of the tethyan himalayas shiar khola central nepal abstract in mesozoic metacarbonates of the tethyan himalayas shiar khola area central nepal two characteristic remanent magnetisations chrm1 and chrm2 were identified by their unblocking temperature spectra the chrm1 is carried by pyrrhotite unblocking temperature 270 360 c and the chrm2 by magnetite unblocking temperature spectra 430 580 c the temperature related formation of pyrrhotite at the expense of primary magnetite during low grade metamorphism in marly carbonates allows the determination of thermal gradients by the pyrrhotite magnetite ratio this new method can be used as a geothermometer for t 300 c in low grade metamorphic carbonates where other methods are not available this method is applied for the first time in the tethyan himalayas of central nepal in the shiar khola valley systematic variations in the ferrimagnetic content of the metacarbonates along an e w profile were detected by the ratio of remanence intensity of pyrrhotite to magnetite derived from natural remanent magnetisation rpyr mag and saturation magnetisation spyr mag over a stretch of 10 km the rpyr mag and spyr mag increase from w to e from 0 42 to 0 91 and 0 48 to 1 0 respectively based on temperature estimates the eastern part experienced upper anchizone epizone 250 300 c conditions while the western part underwent only diagenesis 200 c the temperature gradient and the temperature ranges suggested are consistent with the findings of the calcite twin lamellae geothermometry which is a non magnetic method

palaeomagnetic estimates of crustal shortening in the himalayan thrusts and zangbo suture this article reports new palaeomagnetic results from precisely dated late palaeocene limestones from the former northern margin of the indian subcontinent now in tibet between the major himalayan thrusts and the india tibet suture zone convergence in the suture and intracontinental thrusting can be estimated separately and are respectively found to be of the order of 550 km 650 km and 400 km 400 km comparison with kinematic models derived from magnetic anomalies constrains the age of the collision at about 50 myr

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

the himalayan arc large scale continental subduction oroclinal bending and back arc spreading abstract palaeomagnetic results from the himalayan arc and southern tibet compared with simulated apparent polar wander paths for the indian plate show a consistent pattern of rotations of the himalayan arc relative to the indian shield varying gradually from 45 clockwise in the northwestern himalaya to slightly counterclockwise in the lhasa region this pattern is consistent with continental underthrusting of greater india beneath the tibetan plateau since the early miocene over at least 650 km at the longitude of western nepal and oroclinal bending since the latest miocene available palaeomagnetic observations support the steady state model for the formation of the himalayan arc with refinements as follows 1 collision between greater india s northern boundary and southern asia occurred at equatorial latitudes with progressive suturing from palaeocene in the northwestern himalaya until early eocene in the eastern himalaya 2 continuing convergence and indentation of greater india into southern asia over about 2000 km up to the early miocene resulted in southeastward extrusion of indochina and 3 neogene counterclockwise rotational underthrusting of greater india along the main central thrust with pliocene quaternary oroclinal bending of the himalayan arc

detection of a gravitational oscillation in length of day abstract a high resolution length of day data set spanning approximately the last 42 years is found to contain an oscillation with a period of 5 8 0 8 years this oscillation is interpreted to represent a normal mode of the earth that arises due to gravitational coupling between the mantle and inner core in order to match the observed period of the oscillation the strength of the gravitational coupling between the mantle and inner core must be 3 0 1020 n m this coupling constant depends on the heterogeneous density distribution of the mantle including flow induced deformation of the core mantle boundary the existence of this normal mode requires that the relaxation time of the inner core be sufficiently long on the order of a few years or more that a perturbation from equilibrium results predominantly in solid body rotation not viscous deformation of the inner core the inferred lower bound for the viscosity of the inner core is of the order of 1017 pa s

detection of inner core solidification from observations of antipodal pkiikp pkiikp waves reflected from the underside of the inner core boundary are very sensitive to the s velocity in the uppermost 80 km of the inner core at antipodal distances undergoing a phase change and a factor of 4 amplification as the distance approaches 180 modeled pkiikp waveforms are consistent with a near zero shear modulus in the uppermost inner core in a 20 40 km thick patch beneath the eastern equatorial hemisphere this bright spot of pkiikp reflection correlates with a thin zone of low p velocity inferred from the complexity of pkikp waveforms sampling this patch estimates of grain sizes from seismic attenuation the absence of backscattered pkikp coda in this region and a prediction for enhanced heat flow through this patch suggest that it is a region of solidification rather than melting

palaeomagnetic results from the tibetan sedimentary series of the manang area north central nepal summary the remanent magnetization of palaeozoic and mesozoic carbonates from the tibetan sedimentary series tss of the manang area north of the annapurna range north central nepal has been investigated the tss forms part of the tectonic unit between the indian eurasian plate boundary in the north and the main central thrust mct in the south apart from a present field direction three remanence components have been separated a normal polarity post folding remanence negative fold test is carried by pyrrhotite the core corrected mean direction for five sites with 47 specimens from silurian devonian rocks is decl 312 9 incl 58 3 95 17 6 k 19 8 the origin of this component is not understood a more precisely determined reversed polarity post folding remanence 99 per cent negative fold test is also carried by pyrrhotite the core corrected mean direction for 12 sites with 229 specimens from carboniferous triassic rocks is decl 196 4 incl 65 9 95 3 2 k 183 one site of lower carinan age shows in addition to the pyrrhotite component a second stable remanence direction carried by magnetite the fold test is 99 per cent positive and there is a high probability that the remanence is of detrital origin the bedding corrected direction for one site with 40 specimens is decl 334 3 incl 54 1 95 4 2 k 30 2 palaeolatitude 34 6 s the direction of the magnetite component coincides with other triassic palaeodirection data from the literature and the inclination suggests a palaeoposition of the tss at the northern margin of india at this time the northern extent of india in the triassic cannot be reconstructed from the data because of the strong anticlockwise rotation 48 of stable india since this time the inclination of the reverse polarity pyrrhotite component is 19 steeper than expected from the maximum northern position of the area this suggests a regional northward tilt along the mct which is supported by steep inclinations found in other areas declination data for the reverse polarity pyrrhotite component and for the magnetite component deviate clockwise from expected values for the area by 23 34 calculated from the indian apwp utilizing klootwijk conaghan powell s 1985 rotational underthrusting model the minimum magnitude of continental underthrusting between the tss and stable india at the longitude of central nepal 84 e has been calculated from the declination of our reverse polarity pyrrhotite component a possible range of 520 1100 km results from consideration of different tectonic models

tomographic inversion for three dimensional anisotropy of earth s inner core abstract seismological studies generally suggest that the earth s inner core is anisotropic and the anisotropic structure changes significantly both laterally and with depth previous body wave studies of the inner core have relied on ray tracing or waveform modeling using one dimensional 1d models here we present non linear tomographic inversions of the inner core anisotropy using three dimensional 3d ray tracing spline parameterization and a large collection of pkp differential travel times we adapt a pseudo bending ray tracing pbr method in spherical coordinates for seismic rays that traverse the inner core pkp df phase the method iteratively perturbs each discontinuity point and continuous segment of the ray through 3d earth structure so that its travel time is minimum the 3d anisotropic structure of the inner core is approximated to the first order as 3d heterogeneous but isotropic structure for a given ray the data are corrected using a scaled mantle tomographic model the inner core anisotropy model obtained has the following major features 1 the model has strong hemispherical and depth variation the isotropic velocity in the topmost inner core is greater in quasi eastern hemisphere qeh 40 160 e than in quasi western hemisphere qwh other longitudes the anisotropy is weak in qeh to the depth of 600 700 km below the inner core boundary icb while in qwh the anisotropy increases at much shallower depth about 100 200 km below the icb to about 3 4 then remains at about 2 4 throughout the rest of the inner core 2 the anisotropy form changes abruptly over a depth range of about 150 km at the radius of about 600 km slightly less than half of the inner core radius forming a distinct inner inner core iic the velocity in the iic has maximums at equatorial and polar directions and minimum at an angle of about 40 from the equatorial plane the velocity in the outer inner core oic however changes little for ray directions 0 40 from the equatorial plane 3 despite large variation of the anisotropy the isotropic velocity voigt average throughout the inner core is nearly uniform the results suggest that the oic is likely composed of the same type of iron crystals with uniform chemistry but the iic may be composed of a different type of crystal alignment a different iron phase or a different chemical composition our tests on model parameterization mantle correction and linear and non linear inversion suggest the main features of our model are very robust however fine scale structures are likely to differ particularly in the major transition zones e g in the topmost qwh isotropy to anisotropy between oic and iic change in the form of anisotropy and between qeh and qwh in oic difference in anisotropy strength searches for possible waveform complications from these boundaries need to be aware of the directional dependence and geographical variation to be successful

multicyclic history of the northern india continental margin northwestern himalaya 1 the geologic evolution of northern india is best recorded in the stratigraphic succession of the zanskar range northwestern himalaya which represents the most complete transect through this ancient continental margin sedimentary history began in the late proterozoic and recorded a late pan african orogenic event around the cambrian ordovician boundary when the gondwana supercontinent was eventually assembled the following long period of epicontinental deposition in shallow seas linked to palaeo tethys lasted until the early permian when a neo tethyan rift began to open between paleo india and the cimmerian microcontinents neo tethyan history can be subdivided into two sedimentary megasequences both recording a major tectonic and magmatic event in the lower part the first one began with breakup in the late permian and lasted until the end of the jurassic the second one started in the early cretaceous with the final detachment of india from gondwana and the opening of the indian ocean and ended with the india eurasia collision in the early eocene the two megasequences can be in turn subdivided into six transgressive regressive supersequences bounded by tectonically enhanced unconformities basal sandstone units of early permian late permian norian callovian early cretaceous and paleocene age are invariably associated with oolitic ironstones or reworked glauco phosphorites and mark the transgre sive part of each supersequence next condensed nodular carbonates or shales with pelagic fauna are typically overlain by thick shallowing upward marly units capped by regressive platformal carbonates the six tectono eustatic supercycles reflect successive rifting episodes which punctuated the progressive separation of india from the rest of gondwana and document the combination of plate microplate reorganizations and eustatic climatic and oceanographic changes in the tethyan domain after the onset of collision between india and asia close to the paleocene eocene boundary obduction of the remnants of the neo tethys ocean floor onto the indian margin began and the latter underwent multiphase deformation with fold thrust shortening followed by heating and extension after the main metamorphic event ophiolitic nappes were re thrusted and finally emplaced with their sedimentary sole on top of the passive margin succession

inner core rotation rate from small scale heterogeneity and time varying travel times the time it takes seismic waves to propagate from south atlantic earthquakes through the inner core to station col in alaska has decreased systematically over the past 30 years travel times from three earthquakes in 1991 to an array of 37 seismometers in alaska suggest that lateral gradients in seismic wavespeeds are steep in this part of the inner core this combination of observations can be explained by postulating that the inner core is rotating 0 2 to 0 3 per year faster than the mantle

a review of indian phanerozoic palaeomagnetism implications for the india asia collision abstract an overview is presented of the indian apparent polar wander path apwp for the phanerozoic and in particular for post late palaeozoic times this apwp is compiled on basis of data available at october 1981 from peninsular and extrapeninsular indo pakistan and from dsdp cores from the indian plate one of the more important and newly recognized features of this apwp is a large scale triassic jurassic loop this loop indicates a changeover from a late palaeozoic early mesozoic northwards and counter clockwise rotational movement with greater india reaching moderately low southern latitudes into a southwards and clockwise rotational movement during the early to middle jurassic recognizable likewise in apwp s from other gondwana continents this loop reflects the opening of the neotethys studies of extrapeninsular regions up to and north of the indus tsangpo suture zone have shown wide spread presence of magnetic overprints which delineate two regionally confined age groups younger overprints 20 40 m y predominate in the more external thrust zones older overprints 50 60 m y in contrast are found in the more internal zones both north and south of the indus tsangpo suture zone the latter are interpreted to reflect a late phase of relaxation in the early tertiary collision of greater india with south central asia or off shore island arcs which occurred at equatorial to low northern palaeolatitudes 0 10 n subsequent northwards movement over 2500 3000 km or more and impingement of greater india into southern asia resulted into large scale underthrusting of greater india along the main central thrust beneath southern tibet and to clockwise rotation of thrust units in the western himalaya a discrepancy between indian palaeomagnetic data and results available todate from southern tibet is discussed

structure and dynamics of earth s inner core abstract the seismological exploration of the earth s inner core has revealed unexpected and puzzling structural complexities its elastic anisotropy is now well established and has been shown to vary spatially there is a well defined hemispherical dichotomy in anisotropy and attenuation and significant variations in the radial direction with weaker anisotropy in the uppermost regions and possibly different properties in an innermost inner core of radius 300 600 km perhaps even more puzzling is the observation of a stably stratified layer at the base of the outer core which has recently been proposed to result from melting of inner core material if confirmed the presence of this layer has major implications for our understanding of convection in the outer core inner core differential rotation with respect to the mantle remains controversial we will review here recent progress in understanding the dynamics of the inner core a number of different models have been proposed for the development of the inner core s structure and formation of the stable layer at the base of the outer core and particular care will be taken to clarify under which conditions the proposed mechanisms can be active

can a primary remanence be retrieved from partially remagnetized eocence volcanic rocks in the nanmulin basin southern tibet to date the india asia collision paleomagnetic dating of the india asia collision hinges on determining the paleogene latitude of the lhasa terrane southern tibet reported latitudes range from 5 n to 30 n however leading to contrasting paleogeographic interpretations here we report new data from the eocene linzizong volcanic rocks in the nanmulin basin which previously yielded data suggesting a low paleolatitude 10 n new zircon u pb dates indicate an age of 52 ma negative fold tests however demonstrate that the isolated characteristic remanent magnetizations with notably varying inclinations are not primary rock magnetic analyses end member modeling of isothermal remanent magnetization acquisition curves and petrographic observations are consistent with variable degrees of posttilting remagnetization due to low temperature alteration of primary magmatic titanomagnetite and the formation of secondary pigmentary hematite that unblock simultaneously previously reported paleomagnetic data from the nanmulin basin implying low paleolatitude should thus not be used to estimate the time and latitude of the india asia collision we show that the paleomagnetic inclinations vary linearly with the contribution of secondary hematite to saturation isothermal remanent magnetization we tentatively propose a new method to recover a primary remanence with inclination of 38 1 35 7 40 5 95 significance and a secondary remanence with inclination of 42 9 41 5 44 4 95 significance the paleolatitude defined by the modeled primary remanence 21 n 19 8 n 23 1 n is consistent with the regional compilation of published results from pristine volcanic rocks and sedimentary rocks of the upper linzizong group corrected for inclination shallowing the start of the tibetan himalaya asia collision was situated at 20 n and took place by 50 ma

tidal modulation of plate motions abstract while mantle convection is a fundamental ingredient of geodynamics the driving mechanism of plate tectonics remains elusive are plates driven only from the thermal cooling of the mantle or are there further astronomical forces acting on them gps measurements are now accurate enough that on long baselines both secular plate motions and periodic tidal displacements are visible the now 20 year long space geodesy record of plate motions allows a more accurate analysis of the contribution of the horizontal component of the body tide in shifting the lithosphere we review the data and show that lithospheric plates retain a non zero horizontal component of the solid earth tidal waves and their speed correlates with tidal harmonics high frequency semidiurnal earth s tides are likely contributing to plate motions but their residuals are still within the error of the present accuracy of gnss data the low frequency body tides rather show horizontal residuals equal to the relative motion among plates proving the astronomical input on plate dynamics plates move faster with nutation cyclicities of 8 8 and 18 6 years that correlate to lunar apsides migration and nodal precession the high frequency body tides are mostly buffered by the high viscosity of the lithosphere and the underlying mantle whereas low frequency horizontal tidal oscillations are compatible with the relaxation time of the low velocity zone and can westerly drag the lithosphere over the asthenospheric mantle variable angular velocities among plates are controlled by the viscosity anisotropies in the decoupling layer within the low velocity zone tidal oscillations also correlate with the seismic release

joint inversion for inner core rotation inner core anisotropy and mantle heterogeneity observational evidence for differential rotation of the inner core has recently been reported from time dependent travel times of the seismic inner core phase pkp df these analyses are hindered by potential biases from the mantle heterogeneity and systematic earthquake location errors which have raised doubts about the reality of the inferred differential rotation here we report time dependent pkp df pkp bc differential travel times of a total of 611 measurements obtained from 92 earthquakes in the south sandwich islands ssi over the past nearly half a century recorded at the college alaska station col and alaska seismic network asn the events are relocated using the joint hypercenter determination jhd technique dewey 1971 travel time residuals at col from ssi earthquakes over a period of 45 years and at three additional stations from ssi earthquakes over periods of about 22 years show steady increases with time the temporal trends are demonstrated to be statistically very significant with dense samples of the pathway at different time periods we use a joint inversion technique that allows us to separate the time dependent inner core structure from the time independent mantle biases surprisingly the inner core rotation seems resolvable even from digital data observed at asn in the 1990s spanning over 8 years alone in such a joint inversion the results provide strong support for a differential inner core rotation the inferred rotation rate ranges from 0 3 to 1 1 per year faster than the mantle when we take into account the uncertainty in the tilt of the anisotropy axis of the patch of the inner core that was sampled a westward inner core rotation can be ruled out

kinematics of the crust around the ama drime massif southern tibet constraints from paleomagnetic results abstract secondary magnetic remanences are used to study late orogenic rotation and tilting on a e w transect in southern tibet at 28 5 n sampling was performed on both sides of the ama drime massif adm remanent magnetization resides in pyrrhotite formed during metamorphism and is related to the last cooling event through 325 c curie temperature of pyrrhotite the existence of antipodal ptrms demonstrates that the chrm is of thermoremanent origin and was acquired during cooling of the tethyan metasediments penetrative deformation was still going on in ronghbuk area until ca 250 c whereas it was already completed in dinggye area significant departures from the expected field direction during the age of remanence acquisition cannot be interpreted by consistent vertical axis rotation of blocks antagonist deviations on both sides of the adm are explained as tiltings around an horizontal axis striking n20 these tiltings are estimated to be younger than 13 12 ma and they are related to the adm exhumation initiated since 33 ma

continental underplating model for the rise of the tibetan plateau abstract subduction of continental lithosphere entrained in an oceanic plate for distances of several hundred kilometers can lead to continental underplating whereby the continental crust with or without its lithospheric mantle is detached at depth from the main part of the sinking slab and rises buoyantly beneath the overriding plate the rising continental material causes first extension in the overriding plate as the asthenosphere flows laterally and later rapid isostatic uplift when it reaches the base of the overriding lithosphere this continental underplating model is applied to the geology of the tibetan region and the following stages are identified 100 ma to 50 ma oceanic subduction leading to continental collision 50 ma to 20 ma pause in convergence with possible delamination of indian crust 20 ma to 5 ma continental subduction initially at an angle of 30 of indian lithosphere along the main central thrust 5 ma to 2 ma rise of the continental lithosphere displacing the asthenosphere beneath tibet and causing widespread graben formation 2 ma to present contact between the underplating indian continental lithosphere and the overlying asian crust leading to rapid rise of the surface altitude by 3 4 km present day convergence between india and tibet albeit at a rate much less than the total india eurasia convergence continues as continental underthrusting

garnet tourmaline and muscovite bearing leucogranites gneisses and migmatites of the higher himalayas from zanskar kulu lahoul and kashmir

gravitationally driven inner core differential rotation abstract a heterogeneous heat flux at the core mantle boundary can maintain time averaged convective structures in the fluid core this includes a steady pattern of heterogeneous heat flux at the inner core boundary which leads to aspherical inner core growth if this growth pattern is longitudinally misaligned with the mantle induced geoid the latter would impart a gravitational torque on the newly created topography of the inner core allowing for continuous melting solidification and viscous deformation of the inner core a steady gravitationally driven differential rotation of the inner core with respect to the mantle can be sustained in this work we present calculations of inner core rotation driven by such a mechanism using recently published models of the heat flux at the inner core boundary and of the geoid at the base of the mantle we show that for a fast mean inner core growth rate of 1 mm yr and a bulk viscous relaxation time longer than 100 yr the inner core differential rotation can be as high as 100 deg myr in the westward direction although this is much too slow and in the wrong direction to explain the seismically inferred inner core rotation eastward of the order of 0 2 deg yr this mechanism by itself would rotate the inner core by one full rotation in only a few million years this gravitational torque would then partly offset the viscomagnetic torque from the steady eastward zonal flow near the inner core boundary the driving mechanism typically invoked to explain a steady inner core super rotation under the combined action of these two torques the overall steady differential rotation of the inner core may then be small this would allow the development of an inner core texture with a distinct longitudinal pattern connected to its aspherical freezing rate as has been suggested to explain seismic observations

comment on the existence of an inner core super rotation questioned by teleseismic doublets by georges poupinet annie souriau and olivier coutant abstract poupinet et al j geophys res 89 1984 5719 presented a new methodology for testing whether the pkp travel times observed at college alaska station from south sandwich islands earthquakes indicate inner core rotation they applied the method to seven events and concluded that there is no evidence for pkp df times increasing systematically with event dates and therefore no reason to postulate that the inner core rotates at a different rate than the mantle in a reanalysis of the same seven events i find that their results are systematically biased by the choice of radial earth models and by incorrectly assuming that one of the phases had reversed polarity i also question their choice of events but upon correcting for these biases conclude that these seven events are consistent with the previous model of inner core rotation

inner core differential rotation inferred from antipodal seismic observations abstract the earth s inner core may rotate at a different speed than earth s crust mantle we use observations for antipodal earthquake and station pairs to examine the arrival time shift of the whispering gallery wave which propagates tangentially along the top of the inner core observations of these waves for earthquakes which occurred at the same location reveal that travel times vary by 0 2 s over the past 20 years we propose that these time shifts are caused by the interaction of a zero rigidity patch lateral heterogeneity at the inner core surface with the inner core differential rotation the simplest interpretation infers a rotation rate of 0 05 year which is one order of magnitude smaller than those reported by previous studies our result may also give constraint to the provenance of a zero rigidity patch at the inner core surface the fresnel zone coverage of whispering gallery pkiikp antipodal measurements beneath the inner core boundary extend over 60 of the boundary surface in contrast to pkikp pkp paths which individually measure specular reflections 1 hz from the top of the icb over fresnel zones each encompassing 0 002 of the inner outer core boundary

earth s inner core variable rotation different measurements of inner core rotation have delivered inconsistent results an analysis of seismic data provides a resolution of this discrepancy by suggesting decadal variations in inner core rotation rate

on waveform correlation measurement uncertainty with implications for temporal changes in inner core seismic waves abstract we address the uncertainty related to cross correlation waveform time shift measurements particularly related to temporal changes in inner core seismic waves details of the cross correlation measurement including data processing window length pick time sampling rate and the algorithm itself all affect the calculated time shift by systematically varying measurement parameters for a set of earthquake doublets we find time shift uncertainties of 0 01 s and 0 02 s for differential times and double differential times respectively the uncertainty is of a similar magnitude to reported double differential times of pkikp and pkikp inner core phases accounting for measurement uncertainty results in 80 of values published in a recent study being below the measurement resolution yang and song 2020a while the temporal variations in inner core phases is not in dispute properly accounting for uncertainties is needed for robust data interpretation a re assessment for the origin of inner core temporal changes is therefore warranted and future studies should account for measurement uncertainty

paleogeographic maps of the continents bordering the indian ocean since the early jurassic paleomagnetic data from the african plate from the early jurassic onward are critically re evaluated and updated resulting in a set of 30 paleopoles from which an apparent polar wander path is derived using 20 ma intervals this path is then used in conjunction with kinematic models of the indian and atlantic oceans to place other continents bordering the indian ocean eurasia india islands and plateaus madagascar seychelles mascarene and blocks involved in the collision of india with eurasia south tibet indochina in an absolute paleogeographic frame fixed with respect to africa paleogeographic maps are presented for the early jurassic pre breakup the jurassic cretaceous boundary anomaly ml5 the early cretaceous m2 the late cretaceous a 34 the cretaceous tertiary boundary a 29 the early eocene a 24 the middle eocene a 21 and the oligocene miocene boundary a 6 observed and predicted paleomagnetic directions for landmasses other than africa i e for western europe china korea india and australia which are not used in deriving the maps are found to be in very satisfactory agreement the quality of reconstructions as measured by rms discrepancies between observed and predicted paleolatitudes is of the order of 5 the main features of the paleogeographic maps are discussed with the aim of relating oceanic and on land geodynamic events the constraints provided by tibetan data on the india asia collision and the 20 ma reorganization of geology and plate boundaries in a band extending from the south china sea through tibet to the red sea system are discussed in more detail we emphasize the episodic nature of the breakup of gondwanaland and formation of the indian ocean and subsequent interaction with eurasia in which six major discrete events are identified separated by 30 ma phases of rather uniform plate motion

inner core rotation a test at the worldwide scale abstract in order to determine the angular velocity of a possible inner core differential rotation with respect to the mantle we analyse travel times of waves sampling the inner core at the worldwide scale over a period of about 30 years for situations in which the inner core heterogeneities are dominant with respect to the mantle heterogeneities travel times of summary rays i e bunches of seismic rays with the same geometry must have smaller mean standard deviations when computed in the inner core reference frame than when computed in the mantle reference frame thus we build summary rays by applying a backward rotation of the inner core at angular velocity in order to sum residuals which sample the same inner core region at different times the mean standard deviation of the summary ray residuals computed for different values of should exhibit a minimum for the effective value this method has been applied to absolute pkp df residuals in considering only polar paths for which inner core heterogeneities are dominant with respect to mantle heterogeneities the data used come from a high quality file derived by engdahl et al engdahl e r van der hilst r buland r 1998 global teleseismic earthquake relocation with improved travel times and procedures for depth determination bull seismol soc am 88 722 743 from the catalogs of the international seismological centre isc for the period 1964 1995 the minimum standard deviation is obtained for the null rotation rate a similar analysis on the absolute pkp bc residuals which correspond to paths that do not sample the inner core shows that mantle heterogeneities are not at the origin of the observed minimum the same method has also been applied to a set of more than 1200 worldwide distributed pkp bc pkp df differential travel time residuals hand picked by ourselves or gathered by different authors for specific core studies here again the minimum standard deviation is obtained for the null rotation implying a synchronous rotation of the inner core with the mantle however the limited number of very old data and the geographic distribution of the paths prevent us from obtaining a resolution better than 1 year in particular a small super rotation with 1 year cannot be ruled out with the presently available data the problem of the level of the inner core heterogeneities compared to that of the mantle which is another possible limitation of the method is also discussed

inner core differential motion confirmed by earthquake waveform doublets we analyzed 18 high quality waveform doublets with time separations of up to 35 years in the south sandwich islands region for which the seismic signals have traversed the inner core as pkp df the doublets show a consistent temporal change of travel times at up to 58 stations in and near alaska and they show a dissimilarity of pkp df coda using waveform doublets avoids artifacts of earthquake mislocations and contamination from small scale heterogeneities our results confirm that earth s inner core is rotating faster than the mantle and crust at about 0 3 degrees to 0 5 degrees per year

fine scale heterogeneity in the earth s inner core the seismological properties of the earth s inner core have become of particular interest as we understand more about its composition and thermal state1 2 observations of anisotropy and velocity heterogeneity in the inner core are beginning to reveal how it has grown and whether it convects3 4 the attenuation of seismic waves in the inner core is strong and studies of seismic body waves5 6 have found that this high attenuation is consistent with either scattering or intrinsic attenuation5 the outermost portion of the inner core has been inferred to possess layering and to be less anisotropic than at greater depths7 8 9 10 here we present observations of seismic waves scattered in the inner core which follow the expected arrival time of the body wave reflection from the inner core boundary the amplitude of these scattered waves can be explained by stiffness variations of 1 2 with a scale length of 2 kilometres across the outermost 300 km of the inner core these variations might be caused by variations in composition by pods of partial melt in a mostly solid matrix or by variations in the orientation or strength of seismic anisotropy

the existence of an inner core super rotation questioned by teleseismic doublets abstract the first evidence for a differential rotation of the earth s inner core with respect to the mantle comes from the detection of a variation over 30 years of the differential travel time anomalies of seismic core phases song x richards p g 1996 seismological evidence for differential rotation of the earth s inner core nature 382 221 224 the comparison of teleseismic doublets provides a powerful means to measure such differential travel times and to test their temporal variation contrary to direct measurements of differential travel times this technique does not require to have an accurate location of the seismic events this method is first checked on examples of doublets for which no differential travel time is expected these tests allow us to point out the difficulties such as polarity reversals which may be encountered in the use of the doublet method it is then applied to deep tonga events recorded in france and to the south sandwich islands events recorded at station college col alaska which led song and richards to propose an inner core rotation for the first path we find no time variation in agreement with previous studies for the path from south sandwich island to col the doublet analysis shows that no significant temporal change in pkp travel time can be detected within the resolution of the method which is about 0 05 s the variation of the residuals observed by song and richards about 0 3 s over 30 years is in a large extent ascribable to hypocenter mislocations consequently present seismological observations do not detect the inner core differential rotation because if it exists it is smaller than about 0 2 year the present detection capacity of seismology

paleontological view of the ages of the deccan traps the cretaceous tertiary boundary and the india asia collision volcanism in the deccan traps of india occurred over at most three magnetic chrons centered on a main reversed chron paleontological data indicate that this reversed chron must coincide with 29r which contains the cretaceous tertiary k t boundary recent 40 ar 39 ar data may therefore provide one of the best estimates of the absolute age of the k t boundary 65 7 2 0 ma moreover the eurasian character of k t boundary terrestrial faunas in india suggests that this was also close to the time of india asia collision this is significantly earlier than generally recognized and implies about 4000 km of continental shortening in the collision zone probably absorbed jointly by crustal thickening and strike slip extrusion

using pkikp coda to determine inner core structure 1 synthesis of coda envelopes using single scattering theories 1 previous seismic studies have reported evidence of scattered seismic energy coming from the inner core ic this implies that the ic has lateral variations in structure or composition with a scale length of tens of kilometers in the present study we focus on synthesizing the coda following precritical pkikp and try to determine the location of the heterogeneities that produce this coda using previously reported observations as a guide using a single scattering approximation and ray theory we generate synthetic pkikp coda envelopes from six distinctive places inside the earth within the lower mantle on the source and receiver side along the core mantle boundary on the source and receiver side along the inner core boundary and within the inner core we use two approaches to generate synthetic coda from topography on a boundary surface and one that is appropriate for volumetric scattering in our computations we calculate the arrival time ray parameter and amplitude of the seismic waves and take into account errors in the back azimuth as well as source and receiver effects we find that previously reported spindle shaped or growing coda can only be produced from volumetric heterogeneities located in the shallowest 350 km of the ic however strong trade offs between the different parameters describing the volumetric heterogeneities i e characteristic wavelengths rms velocity or impedance contrast and total volume preclude the determination of a unique model additionally we find that reasonable models of topography at the core mantle boundary can produce large variations of the pkikp amplitude due to focusing and defocusing effects therefore complexity at the inner core boundary is not necessarily required to account for dramatic amplitude variations in the direct pkikp amplitudes

where did rotational shortening occur in the himalayas inferences from palaeomagnetic remagnetisations in metacarbonates of the lesser lh and tethyan th himalayas of kumaon garhwal n india characteristic remanent magnetisations carried by pyrrhotite unblocking temperatures 250 330 c and magnetite demagnetising spectra 15 50 mt have been identified negative fold tests indicate remanence acquisition after the main folding phase which is of short wavelength character and occurs during the early orogenese of the himalayas a thermal or thermochemical origin of magnetisation is likely and the age of remanence acquisition is indicated to be about 40 ma by 40 k 39 ar cooling and 40 ar 39 ar crystallisation ages in the kumaon lh a long wavelength tilting is indicated by a distribution of the remanence directions along a small circle in n s direction steepening of the remanence directions in the th related to ramping on the main central thrust mct was not observed in contrast to other related studies in the alaknanda valley of lh a 38 8 ma age of remanence acquisition is supported by comparison of observed inclinations to the apparent polar wander path of india clockwise rotation of 20 3 11 7 lh alaknanda valley and 11 3 8 5 th with respect to the indian plate is observed indicating that there is no significant evidence for rotational shortening along the mct since about 40 ma our results suggest that most of rotational underthrusting and oroclinal bending has not been accommodated by the mct but by the main thrusts south of it the latest miocene pliocene age of the main boundary thrust indicates that oroclinal bending is a late orogenic process

inner core rotation and its variability from nonparametric modeling 1 we present a new approach for studying the inner core rotation and its variability by separating the underlying structure from its time evolution this is achieved by fitting a large set of existing seismic bc df traveltime data with a smoothing spline analysis which is implemented in the statistics package r this method allows us to separate the time independent mantle contribution from the time dependent core contribution without any a priori constraints and to also estimate the error of the fit we add our newly acquired seismic data from the passcal experiment arctic in northern alaska to pkp differential traveltime measurements previously obtained from south sandwich islands earthquakes and recorded at college col and the alaskan seismic network this nearly doubles the number of measurements to a total of 1165 and increases the data coverage of the inner core structure and our time coverage to about 55 years the large number of measurements allows us to use the standard statistical method of bootstrapping to derive the rotation rate and thus to further separate the core structure from its time evolution this approach has been successfully tested with synthetic data sets that feature both a nonlinear structure and variable rotation rates while sharing the same earthquakes and stations geometry as our real data applying this method to the real data yields an average rotation rate of 0 39 0 090 22 yr 1 at 68 confidence level our results also suggest a nonzero acceleration of the inner core with an apparent change in the rotation rate from 0 24 to 0 56 yr 1 within the last 55 years the minimum torque acting on the inner core is estimated 1 19 1016 n m which could result from the imbalance of the electromagnetic and gravitational torques

rheology of the earth and a thermoconvective mechanism for sedimentary basin formation summary a power law non newtonian fluid is usually assumed to model slow flows in the mantle and in particular convective flows however the power law fluid has no memory in contrast to a real material a new non linear integral having a memory model is proposed to describe the rheology of rocks the model is consistent with the theory of simple fluids with fading memory and with laboratory studies of rock creep the proposed model reduces to the power law fluid model for stationary flows and to the andrade model for flows associated with small strains stationary convection beneath continents has been studied by fleitout yuen 1984 who used the power law fluid model and obtained the cold immobile boundary layer continental lithosphere in a stability analysis of this layer the andrade model must be used the analysis shows that the lithosphere is overstable the period of oscillation is about 200 ma in the present study it is suggested that these thermoconvective oscillations of the lithosphere are a mechanism for sedimentary basin formation the vertical crustal movement in sedimentary basins can be considered as a slow subsidence on which small amplitude oscillations are superimposed the longest period of oscillatory crustal movement is of the same order of magnitude as the period of convective oscillation of the lithosphere found in the stability analysis taking into account the diverence between depositional and erosional transport rates we can explain the permanent subsidence as well as the oscillations

palaeomagnetic study of cretaceous red beds from the eastern hindukush ranges northern pakistan palaeoreconstruction of the kohistan karakoram composite unit before the india asia collision we report palaeomagnetic results obtained from cretaceous red bed samples collected from the eastern hindukush mountains northern pakistan rock magnetic studies revealed specular haematite as the dominant remanence carrier while pigmentary haematite magnetite and goethite are responsible for the acquisition of secondary magnetizations thermal treatment generally revealed three components of magnetization the most unstable component a was removed between 200 c and 500 c which corresponds to the local present field direction the intermediate component b was generally separated between 200 c and 660 c the omnipresence of this complex secondary component across the northern suture zone suggests that movement of chemically active orogenic fluids at or slightly before the time of the india asia collision was probably responsible for the authigenic remagnetization processes the characteristic component c was generally unblocked between 600 c and 685 c the characteristic directions from 12 sites fall into two groups the sites from the purit formation give a tilt corrected mean direction of d 311 2 i 4 4 k 12 4 95 17 8 indicating a counter clockwise rotation of about 66 and 15 relative to eurasia and india respectively the tilt corrected mean direction for the reshun and drosh formations is d 263 0 i 2 2 k 52 7 95 10 6 which indicates that the sampling area experienced a counter clockwise rotation of about 114 and 63 with respect to eurasia and india respectively in both cases the palaeomagnetic rotation is consistent with the regional superstructure of the hindukush pamir karakoram syntaxial bend the difference in rotation between these two groups is probably due to local tectonic movement caused by the net rotation of thrust sheets along the northern suture zone the palaeolatitudes calculated for purit and reshun drosh formations are 2 2 s and 1 1 n respectively this indicates that about 4000 km of convergence has taken place since the mid cretaceous of which about 90 per cent post dates the india asia collision the late cretaceous inclination values across the northern suture zone are almost identical which indicates that suturing had been completed at the time of chrm acquisition

the shuffling rotation of the earth s inner core revealed by earthquake doublets earth s inner core rotates at a different rate than the mantle and discrepancies exist between rotation rates derived from geophysical observations and geodynamical simulations an inverse analysis of seismic data from repeating earthquakes over the past 50 years suggests that the rotation rate of the inner core fluctuates on decadal timescales