flexure of the india plate underneath the bhutan himalaya 1 we investigate flexural geometry and rheology of the india plate beneath the eastern himalaya from a new gravity data set acquired in bhutan compared to the well studied nepal himalaya the obtained bouguer anomaly profiles across the range show shorter wavelength flexure of the lithosphere with a narrower and shallower foreland basin this new data set and seismic moho constraints are interpreted together in terms of lithospheric flexure using a 2 d thermomechanical model our results suggest that the strongest layer of the continental lithosphere beneath bhutan is the upper mantle as it is beneath nepal the observed west to east decrease in flexural wavelength is associated with weakening mantle rheology the simulations show that this decrease can be related to ductile mantle behavior either hydrated wet dunite or dry and hot olivine rheology both models display decoupled lithospheric layers leading to an eastward decrease of flexural rigidity from 10 24 to 5 10 22 n m in nepal and bhutan respectively

primary surface ruptures of the great himalayan earthquakes in 1934 and 1255 it is unclear where plate boundary thrusts generate giant rather than great earthquakes along the himalayas the source sizes and recurrence times of large seismic events are particularly uncertain since no surface signatures were found for those that shook the range in the twentieth century here we challenge the consensus that these events remained blind and did not rupture the surface we use geomorphological mapping of fluvial deposits palaeo seismological logging of river cut cliffs and trench walls and modelling of calibrated 14c ages to show that the mw 8 2 bihar nepal earthquake on 15 january 1934 did break the surface traces of the rupture are clear along at least 150 km of the main frontal thrust fault in nepal between 85 50 and 87 20 e furthermore we date collapse wedges in the sir valley and find that the 7 june ad 1255 earthquake an event that devastated kathmandu and mortally wounded the nepalese king abhaya malla also ruptured the surface along this stretch of the mega thrust thus in the past 1 000 years two great earthquakes 679 years apart rather than one giant eleventh century ad event contributed to the frontal uplift of young river terraces in eastern nepal the rare surface expression of these earthquakes implies that surface ruptures of other reputedly blind great himalayan events might exist the recurrence times of great himalayan earthquakes are difficult to assess because they rarely rupture the surface field mapping and 14c dating of offset fluvial deposits are used to identify two great himalayan quakes that ruptured the surface along the main plate boundary fault in ad 1255 and 1934

lateral uniformity of india plate strength over central and eastern nepal the current understanding of the himalayan lithosphere stems mostly from cross sections through the range at the longitude of the kathmandu basin in this paper we laterally extend the analyses of structures and rheology along the nepal himalayas between the pokhara valley and the arun river we take advantage of available information and a new data set including gravity measurements and a receiver function profile it appears that the geometry of the moho inferred from seismological profiles and long wavelength gravity anomalies does not exhibit major east west variations within the 350 km wide study area using thermomechanical modelling we show that the northward deepening of the moho observed along profiles perpendicular to the main thrust faults can be interpreted simply as the bending of a strong india plate this result suggests a gradual mechanical decoupling between the crust and the mantle leading to a northward decrease of the effective elastic thickness of the indian lithosphere from 75 km to 25 km beneath the ganga basin and the tibetan plateau respectively our results also confirm partially eclogitized lower indian crust beneath southern tibet at shorter wavelengths the observed gravity profiles exhibit some small lateral variations that can be interpreted in terms of east west variations of the thickness of subsurface geological structures such as the ganga basin and the tethyan sedimentary sequence

geomagnetic field for 0 3 ka 2 a new series of time varying global models 1 steadily increasing numbers of archeomagnetic and paleomagnetic data for the holocene have allowed development of temporally continuous global spherical harmonic models of the geomagnetic field extending present and historical global descriptions of magnetic field evolution the current work uses various subsets of improved data compilations details of which are given in a companion paper by donadini et al 2009 and minor modifications of standard modeling strategies using temporally and spatially regularized inversion of the data and cubic spline parameterizations for temporal variations to produce five models with enhanced spatial and temporal resolution for 0 3 ka spurious end effects present in earlier models are eliminated by enforcing large scale agreement with the gufm1 historical model for 1650 1990 a d and by extending the model range to accommodate data older than 3 ka age errors are not considered as a contribution to data uncertainties but are included along with data uncertainties in an investigation of statistical uncertainty estimates for the models using parametric bootstrap resampling techniques we find common features but also significant differences among the various models indicating intrinsic uncertainties in global models based on the currently available holocene data model cals3k 3 based on all available archeomagnetic and sediment data without a priori quality selection currently constitutes the best global representation of the past field the new models have slightly higher dipole moments than our previous models virtual axial dipole moments vadms calculated directly from the data are in good agreement with all corresponding model predictions of vadms these are always higher than the spherical harmonic dipole moment indicating the limitations of using vadms as a measure of geomagnetic dipole moments

results of rock magnetic investigations and relative paleointensity determinations on lacustrine sediments from birkat ram golan heights israel i detailed rock magnetic investigations including the analysis of the laboratory installed magnetizations the measurement of hysteresis parameters and the high temperature dependency of the saturation magnetization were carried out on sediments from birkat ram golan heights israel the 550 cm long composite profile composed of three single cores is supposed to span the late holocene i e the last 4400 years at least titanomagnetites in the pseudo single domain range were identified as the main magnetic carrier minerals in the homogenous sediments the variations in concentration and grain size of the magnetic fraction are only partly reflected in the sediment lithology the relative paleointensity was estimated by normalizing the intensity of the natural remanent magnetization nrm after demagnetization at 20 mt j nrm 20 mt by different concentration parameters the median destructive field of the nrm mdf nrm is coherent with the relative paleointensity estimates indicating that a sedimentary effect has not sufficiently been removed by the normalization process the morphologies of these estimates however correspond to the archeomagnetic records from bulgaria and greece therefore a second normalization based on the linear relationship between the paleointensity estimates and the mdf nrm was applied resulting in an improvement of the records

imaging the moho and the main himalayan thrust in western nepal with receiver functions the crustal structure of western nepal is studied for the first time by performing receiver function analysis on teleseismic waveforms recorded at 16 seismic stations the moho geometry is imaged as it deepens from 40 km depth beneath the foothills and the lesser himalaya to 58 km depth beneath the higher himalayan range a midcrustal low velocity zone is detected at 15 km depth along 55 km horizontal distance and is interpreted as the signature of fluids expelled from rocks descending in the footwall of the main himalayan thrust our new image allows structural comparison of the moho and of the main himalayan thrust geometry along strike of the himalayas and documents long wavelength lateral variations the general crustal architecture observed on our images resembles that of central nepal therefore western nepal is also expected to be able to host large m w 8 megathrust earthquakes as the 1505 ce event plain language summary we investigate the earth s crust in western nepal we use 16 stations to detect waves from faraway earthquakes and using these we make an image of the structure of the crust we find that the crust is getting thicker beneath the himalaya and that fluids are locally present in the upper part of the crust as this image is similar to the one we know in central nepal where major earthquakes happened it is possible that major earthquakes will also happen in western nepal in the future without knowing when

variations of the geomagnetic field during the holocene relative paleointensity and inclination record from the west pacific odp hole 1202b abstract we conducted detailed rock magnetic investigations on 36 m of drill core collected during ocean drilling program leg 195 at hole 1202b 24 48 24 n 122 30 00 e in the southern okinawa trough with the goal of extracting a reliable paleointensity signal with centennial resolution an age depth model was established from a chronology obtained by accelerator mass spectromety 14c dating the sedimentary section spans almost the entire holocene 0 9 4 kyr and exhibits sedimentation rates close to 400 cm kyr the magnetic properties are dominated by stable pseudo single domain magnetite high field hysteresis data and the grain size sensitive ratio of anhysteretic remanent magnetization arm to low field magnetic susceptibility indicate a narrow range of grain sizes and concentrations magnetic parameters vary by a factor of 4 thereby fulfilling the usual criteria for a relative paleointensity study the relative geomagnetic paleointensity was obtained by normalizing the intensity of natural remanent magnetization nrm by the arm and the low field magnetic susceptibility both normalizations yield nearly identical results r 0 89 spectral analysis indicates that the record is not significantly affected by local environmental conditions comparison of this west pacific paleointensity curve with other curves suggests a geomagnetic origin for the signal millennial scale features of our record correlate to variations of the archeomagnetic dipole moment this suggest that the sediments at hole1202b recorded changes of the geomagnetic field over the studied time interval

a palaeomagnetic secular variation record for new zealand during the past 2500 years abstract a record of the secular variation of the geomagnetic field over new zealand for the past 2500 years has been compiled by measuring and averaging logs of the primary magnetization of five cores of lacustrine sediment from lake pounui a time scale is provided by four radiocarbon age determinations the record is constrained by historical observations for the last 350 years and is in good agreement with instantaneous palaeomagnetic directions from lava flows this is the first continuous record of secular variation from new zealand and one of only a few from the southern hemisphere together with existing australian records the results show significant evidence of westward drift of the geomagnetic field over the past 2500 years it contains new information for modelling the geomagnetic secular variation in the southern hemisphere and will also be valuable for dating applications within new zealand

a new rock magnetic approach to selecting sediments for geomagnetic paleointensity studies application to paleointensity for the last 4000 years the hypothesis that the ratio of detrital remanent magnetization to anhysteretic remanent magnetization drm arm for sediment samples is a measure of relative geomagnetic paleointensity is critically evaluated by two distinct approaches one approach is a detailed rock magnetic examination of the implicit assumptions of the drm arm method and the construction of a selection process by which to identify sediments that conform to requirements satisfying these assumptions sediments are uniform with respect to drm arm ratio if they contain magnetite in the 1 15 ym particle size range as the predominant magnetic mineral and have variations in magnetite content of less than 20 30 times the minimum concentration the drm arm ratios of these sediments should provide estimates of relative geomagnetic paleointensity relative particle size variations in magnetite are detected with a plot of anhysteretic susceptibility xarm versus low field susceptibility x and the size range 1 15 m is approximately identified by high field hysteresis parameters a rock magnetic evaluation of leboeuf lake sediments with these techniques indicates that these sediments are suitable for a relative plaeointensity study the second approach to evaluating the drm arm ratio as a measure of relative paleointensity is direct comparison with absolute paleointensity data a comparison between the leboeuf lake estimates and thellier thellier results from the western united states supports the conclusion that suitable sediments can record geomagnetic paleointensity fluctuations

interseismic strain accumulation on the himalayan crustal ramp nepal the departement of mines and geology has been monitoring the seismicity of the central himalayas of nepal since 1985 intense microseismicity and frequent medium size earthquakes ml 4 tend to cluster beneath the topographic front of the higher himalaya this 10 20km deep seismicity also correlates with a zone of localized uplift that has been evidenced from geodetic data both microseismic and geodetic data indicate strain accumulation on a mid crustal ramp that had been previously inferred from geological and geophysical evidence this ramp connects a flat decollement under the lesser and sub himalaya with a deeper decollement under the higher himalaya and probably acts as a geometric asperity where strain and stress build up during the interseismic period the large himalayan earthquakes could nucleate there and probably activate the whole flat and ramp system up to the blind thrusts of the sub himalaya

mean mixed depth of sediments the wherefore and the why the activities and consequently the bioturbational effects of deposit feeding organisms are largely restricted to a narrow surficial zone of marine sediments with a worldwide environmentally invariant mean of 9 8 cm with a standard deviation of 4 5 cm currently available theories of infaunal behavior cannot predict quantitatively this observation a new simple model that accounts for the feedback between resource food abundance its reactivity and the intensity of bioturbation leads to a quantitative estimate of 9 7 cm this model constitutes a fundamental advance in our understanding bioturbation

paleosecular variations since 9000 yr bp as recorded by sediments from maar lake shuangchiling hainan south china abstract high resolution paleosecular variation psv can play an important role in sediment dating and for understanding the temporal characteristics of the geodynamo of the earth s magnetic field in this article based on magnetic susceptibility correlation a composite sediment profile has been compiled from a 16 m long core hn 2 and a 8 m deep well hn 3 in shuangchiling maar lake a crater basin located on hainan island southern china fine and homogeneous silty clay corroborates with a stable continuous and undisturbed deposition a u channel based paleomagnetic study constrained by ams14c chronology derived from leaves plant debris and woods and supported by rock magnetic data indicates that the lake sediments document a reliable paleosecular variation psv record since 9000 cal year bp comparison of our psv features with other records from lakes biwa japan erhai china baikal russia as well as archaeomagnetic records demonstrate that the inclination pattern is generally synchronous within chronological uncertainties suggesting further psv dating may be valuable for stratigraphic correlation on a regional scale

an 84 kyr paleomagnetic record from the sediments of lake baikal siberia we have conducted a paleomagnetic study of sediment cores obtained from the selenga prodelta region of lake baikal russia this record which spans approximately the last 84 kyr contributes to a better understanding of the nature of geomagnetic field behavior in siberia and is a useful correlation and dating tool we demonstrate that the lake baikal sediments are recording variations in the geomagnetic field the directional record displays secular variation behavior with a geomagnetic excursion at 20 ka and additional excursions appearing as large amplitude secular variation at 41 61 and 67 ka smoothing of the geomagnetic excursion behavior occurs in lake baikal sediments owing to the intermediate sedimentation rate 13 cm kyr 1 the lake baikal relative paleointensity record correlates to absolute paleointensity data for the last 10 kyr and to relative paleointensity records from the mediterranean sea and indian ocean for the last 84 kyr this correlation suggests a strong global i e dipole component to these records and further supports the reliability of sediments as recorders of relative geomagnetic paleointensity we show that a relative geomagnetic intensity stratigraphy has a potential resolution of 7 kyr by correlating continental and marine records the geomagnetic intensity stratigraphy helps constrain the age of the difficult to date lake baikal sediments

crustal structure of the pannonian basin the alcapa and tisza terrains and the mid hungarian zone abstract the pannonian basin of central europe is one of the key examples of miocene continental extension that is easily accessible to surface seismological investigation it comprises two major crustal blocks alcapa and tisza which abut along a poorly understood structure referred to as the mid hungarian zone mhz the whole being surrounded by the arc of the carpathian mountains the alps and the dinarides using data from the cbp carpathian basins project temporary broadband seismic array of 46 stations deployed across the western pannonian basin in 2006 2007 we calculated receiver functions that constrain the variation of crustal thickness across the basin and derive a map of moho depth across a nw se oriented swath about 450 km long and 75 km wide the measured moho depths show no significant change in crustal thickness between alcapa and tisza terrains but the moho is not or very weakly imaged along a ca 40 km wide strip centred on the mhz moho depths within the pannonian basin are typically in the range 25 30 km and increase toward the periphery of the basin our measurements are generally consistent with earlier vp models from controlled source seismic surveys and recent vs models determined by tomographic analysis of ambient noise signals the lack of a sharp moho image beneath the mhz suggests that the crust mantle boundary in that zone may consist of a gradual increase in velocity with depth the relatively constant crustal thickness across the two domains of the pannonian basin suggests that thinning to the same final state is controlled thermally this structural characteristic seems to be governed by a large scale balance of gravitational potential energy that is insensitive to the separate prior histories of the two regions

high resolution paleomagnetic records from holocene sediments from the palmer deep western antartic peninsula thick holocene sedimentary sections 45 m cored in the palmer deep by the united states antarctic program usap and during ocean drilling program odp leg 178 provide the first opportunity to examine past geomagnetic field behavior at high southern latitudes after removal of a low coercivity drilling overprint the sediments display a stable single component remanent magnetization two short cores that recovered the uppermost 2 6 m of sediment have inclinations that fluctuate about the present day inclination 57 measured at faraday station and several features with wavelengths of 10 to 20 cm appear to be correlative however shipboard measurements of inclination fluctuations on split core samples from three holes drilled at odp site 1098 do not correlate well with each other even though the intensity and susceptibility data correlate very well and the overall mean inclination for cores from each hole is consistent with the expected geocentric axial dipole gad inclination the correlation is improved dramatically by using inclinations measured on u channels taken from the pristine center of a split core consequently the anomalous directions and the resulting poor between hole correlation of inclinations obtained from shipboard data can be attributed to coring induced deformation which is common on the outer edge of odp piston cores and or measurement artifacts in the split core data our preferred inclination record is thus derived from u channel results the upper 25 m represents continuous sedimentation over the past 9000 yr with an average sedimentation rate exceeding 250 cm kyr 0 25 cm yr given that remanence measurements on u channels average over an interval 7 cm long we obtained independent measurements of the paleo geomagnetic field that average over only 30 yr this high resolution record is characterized by an inclination that fluctuates within 15 of the current gad inclination

stratigraphy structure and tectonic evolution of the himalayan fold thrust belt in western nepal regional mapping stratigraphic study and 40ar 39ar geochronology provide the basis for an incremental restoration of the himalayan fold thrust belt in western nepal tectonostratigraphic zonation developed in other regions of the himalaya is applicable with minor modifications in western nepal from south to north the major structural features are 1 the main frontal thrust system comprising the main frontal thrust and two to three thrust sheets of neogene foreland basin deposits 2 the main boundary thrust sheet which consists of proterozoic to early miocene lesser himalayan metasedimentary rocks 3 the ramgarh thrust sheet composed of paleoproterozoic low grade metasedimentary rocks 4 the dadeldhura thrust sheet which consists of medium grade metamorphic rocks cambrian ordovician granite and granitic mylonite and early paleozoic tethyan rocks 5 the lesser himalayan duplex which is a large composite antiformal stack and hinterland dipping duplex and 6 the main central thrust zone a broad ductile shear zone the major structures formed in a general southward progression beginning with the main central thrust in late early miocene time eocene oligocene thrusting in the tibetan himalaya north of the study area is inferred from the detrital unroofing record on the basis of 40ar 39ar cooling ages and provenance data from synorogenic sediments emplacement of the dadeldhura thrust sheet took place in early miocene time the ramgarh thrust sheet was emplaced between 15 and 10 ma the lesser himalayan duplex began to grow by 10 ma simultaneously folding the north limb of the dadeldhura synform the main boundary thrust became active in latest miocene pliocene time transport of its hanging wall rocks over an 8 km high footwall ramp folded the south limb of the dadeldhura synform thrusts in the subhimalayan zone became active in pliocene time the minimum total shortening in this portion of the himalayan fold thrust belt since early miocene time excluding the tibetan zone is 418 493 km the variation depending on the actual amounts of shortening accommodated by the main central and dadeldhura thrusts the rate of shortening ranges between 19 and 22 mm yr for this period of time when previous estimates of shortening in the tibetan himalaya are included the minimum total amount of shortening in the foldthrust belt amounts to 628 667 km this estimate neglects shortening accommodated by small scale structures and internal strain and is therefore likely to fall significantly below the actual amount of total shortening

a late quaternary geomagnetic secular variation record from lake waiau hawaii and the question of the pacific nondipole low a continuous paleomagnetic record for the last 13 000 years was obtained from the sediments of lake waiau located near the summit of mauna kea volcano on the island of hawaii the secular variation sv of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector the hypothesis that there has been anomalously low geomagnetic sv in the central pacific was tested using angular dispersion analysis the inclination record has a mean value of 27 that is much lower than the 35 predicted by the geocentric axial dipole hypothesis the spectrum obtained from spectral analysis shows major inclination peaks at periodicities of approximately 3600 and 7900 years and major declination peaks at periodicities of approximately 1100 2000 3300 and 7800 years the approximately 8000 and 3500 year periodicities shown in both inclination and declination spectrums may represent the dipole and nondipole variation respectively the approximately 1100 and 2000 year periodicities are probably derived from either the sources that affect declination only or the offsets between the core sections in addition bauer plots of the magnetic vector are dominated by clockwise motion the angular dispersion calculated from lake sediments is 5 9 with respect to the mean virtual geomagnetic pole vgp and 9 1 with respect to the geographic pole both values are much lower than the 13 5 expected from paleosecular variation model g which separates the angular dispersion into components from the dipole and the quadruple families our results support the hypothesis that an anomalously low secular variation is a characteristic feature of the central pacific furthermore this geomagnetic behavior persists on time scales of 104 years regional anomalies in temperature topography or electrical conductivity at the core mantle boundary are inferred to cause the low sv

a lacustrine record of paleomagnetic secular variations from birkat ram golan heights israel for the last 4400 years abstract detailed paleo and rock magnetism investigations were carried out on three sediment cores from birkat ram golan heights israel based on high resolution logs of magnetic susceptibility a 5 4 m long composite profile was created that spans the last 4400 years the time interval covered by a single sample is about 26 years characteristic remanent magnetisation chrm of all 288 samples was determined by analysis of the results of progressive alternating field af demagnetisation the brown to olive coloured homogenous sediments show a fairly stable magnetisation and the obtained inclination and declination records agree with the archaeomagnetic records from iraq egypt and israel comparison of the psv records from birkat ram with those from bulgaria and hungary yielded a different behaviour of the earth s magnetic field vector over the near east and southeast europe during the last 1000 years

seismic imaging of deep hydrocarbon reservoirs this paper examines those aspects of reflection seismology which require special consideration when imaging deeper hydrocarbon reservoirs including the constraints imposed by vertical resolution lateral resolution and velocity analysis we derive quantitative expressions relating the uncertainties in stacking velocities and in interval velocities derived from stacking velocities to acquisition parameters as well as expressions for the lateral resolution which can theoretically be achieved for migrated seismic images this analysis shows that the most significant limitations of seismic imaging at depth involve the finite lateral resolution of the seismic method and the proper lateral positioning of seismic images these difficulties are overcome in large measure through the proper migration of a seismic dataset which becomes more critical as deeper horizons are imaged if these horizons are suspected of having significant 3 d structure a strong argument may be made for acquiring a 3 d seismic survey over the prospect migration of this dataset will then generate an image of the subsurface with good lateral resolution in both the x and y directions

configuration of the indian moho beneath the nw himalaya and ladakh 1 teleseismic receiver function analysis of seismograms recorded on a 700 km long profile of 17 broadband seismographs traversing the nw himalaya shows a progressive northward deepening of the indian moho from 40 km beneath delhi south of the himalayan foredeep to 75 km beneath taksha at the karakoram fault similar studies by wittlinger et al 2004 to the north of the karakoram fault show that the moho continues to deepen to 90 km beneath western tibet before shallowing substantially to 50 60 km at the altyn tagh fault the continuity of the indian moho imaged in the receiver functions reported here along with those of wittlinger et al 2004 suggest that in this part of the himalayan orogen the indian plate may penetrate as far as the bangong suture and possibly as far north as the altyn tagh

the aftershock sequence of the 2015 april 25 gorkha nepal earthquake l b adhikari 1 u p gautam 1 b p koirala 1 m bhattarai 1 t kandel 2 r m gupta 1 c timsina 1 n maharjan 1 k maharjan 2 t dahal 2 r hoste colomer 3 4 y cano 3 m dandine 3 a guilhem 3 s merrer 3 p roudil3 and l bollinger3 1national seismological centre department of mines and geology lainchaur kathmandu nepal e mail adhikari research gmail com 2regional seismological centre department of mines and geology surkhet birendranagar nepal 3cea dam dif f 91297 arpajon france 4laboratoire de geologie ecole normale superieure cnrs 24 rue lhomond f 75004 paris france

palaeosecular variation of the earth s magnetic field during the last 10000 years based on the annually laminated sediment of lake nautajarvi central finland a palaeomagnetic study of the lake nautajarvi sediment sequence in central finland demonstrates that varved lake sediments can provideregionally applicable secular variations curves for holocene stratigraphic correlation and age control based on x ray radiography and digital image analysis techniques we constructed an inherent and continuous varve chronology for the lake nautajarvi varve sequence which covers nearly 10000 years with an estimated counting error of less than 1 and a mean sedimentation rate of 0 66 mm yr 1 we reconstructed a record of the palaeomagnetic secular variation psv of the earth s magnetic field in this nearly 7 m long section of clastic organic varves mineral magnetic measurements indicated that pseudosingle domain magnetite is the major carrier of the remanence psv shows many of the familiar features of declination and inclination that have previously been recorded in northern europe in addition the lake nautajarvi record contains a continuous record of relative palaeoi

crustal deformation in the india eurasia collision zone from 25 years of gps measurements the india eurasia collision zone is the largest deforming region on the planet direct measurements of present day deformation from global positioning system gps have the potential to discriminate between competing models of continental tectonics but the increasing spatial resolution and accuracy of observations have only led to increasingly complex realizations of competing models here we present the most complete accurate and up to date velocity field for india eurasia available comprising 2576 velocities measured during 1991 2015 the core of our velocity field is from the crustal movement observation network of china i ii 27 continuous stations observed since 1999 56 campaign stations observed annually during 1998 2007 1000 campaign stations observed in 1999 2001 2004 and 2007 260 continuous stations operating since late 2010 and 2000 campaign stations observed in 2009 2011 2013 and 2015 we process these data and combine the solutions in a consistent reference frame with stations from the global strain rate model compilation then invert for continuous velocity and strain rate fields we update geodetic slip rates for the major faults some vary along strike and find that those along the major tibetan strike slip faults are in good agreement with recent geological estimates the velocity field shows several large undeforming areas strain focused around some major faults areas of diffuse strain and dilation of the high plateau we suggest that a new generation of dynamic models incorporating strength variations and strain weakening mechanisms is required to explain the key observations seismic hazard in much of the region is elevated not just near the major faults

global geomagnetic field models for the past 3000 years transient or permanent flux lobes psvmod1 0 is a compilation of globally distributed palaeodirectional data from archaeomagnetic artefacts lava flows and lake sediments at 24 sites evaluated at 100 year intervals from 1000 bc to ad 1800 we estimate uncertainty in these measures of declination and inclination by comparison with predictions from standard historical models in time intervals of overlap and use the 100 year samples and their associated uncertainties to construct a sequence of minimum structure global geomagnetic field models global predictions of radial magnetic field at the coremantle boundary cmb as well as inclination and declination anomalies at the earth9s surface provide an unprecedented view of geomagnetic secular variations over the past 3000 years and demonstrate a consistent evolution of the field with time resolution of the models is poorest in the southern hemisphere where only six of the 24 sites are located several with incomplete temporal coverage low flux regions seen in the historical field near the north pole are poorly resolved but the northern hemisphere flux lobes are clearly visible in the models these lobes are not fixed in position and intensity but they only rarely venture into the pacific hemisphere the pacific region is seen to have experienced significant secular variation a strong negative inclination anomaly in the region like that seen in 0 5 ma models persists from 1000 bc until ad 1000 and then gradually evolves into the smaller positive anomaly seen today on average between 1000 bc and ad 1800 the non axial dipole contribution to the radial magnetic field at the core mantle boundary is largest in the north central pacific and beneath central asia with clear non zonal contributions at the earth9s surface average inclination anomalies are large and negative in the central pacific and most positive slightly to the east of central africa inclination anomalies decrease with increasing latitude average declinations are smallest in equatorial regions again with strong longitudinal variations largest negative departures are centred over australia and eastern asia secular variation at the earth9s surface is quantified by standard deviation of inclination and declination about their average values and at the cmb by standard deviation in radial magnetic field all three show significant geographical variations but appear incompatible with the idea that secular variation in the pacific hemisphere is permanently attenuated by greatly enhanced conductivity in d 00 beneath the region

line of sight displacement from alos 2 interferometry mw 7 8 gorkha earthquake and mw 7 3 aftershock interferometric synthetic aperture radar insar is a key tool for the analysis of displacement and stress changes caused by large crustal earthquakes particularly in remote areas a challenge for traditional insar has been its limited spatial and temporal coverage especially for very large events whose dimensions exceed the typical swath width of 70 100 km this problem is addressed by the alos 2 satellite whose palsar 2 instrument operates in scansar mode enabling a repeat time of 2 weeks and a swath width of 350 km here we present insar line of sight displacement data from alos 2 palsar 2 observations covering the mw 7 8 gorkha nepal earthquake and its mw 7 3 aftershock that were acquired within 1 week of each event the data are made freely available and we encourage their use in models of the fault slip and associated stress changes the mw 7 3 aftershock not only extended the rupture area of the main shock toward the east but also left a 20 km gap where the fault has little or no coseismic slip we estimate this unslipped fault patch has the potential to generate a mw 6 9 event

icelandic holocene palaeolimnomagnetism abstract sediments spanning the last 9000 y from two sites in lake vatnsdalsvatn lat 66 n long 23 e in northwest iceland hold repeatable palaeomagnetic direction records the vatnsdalsvatn sediments have mean palaeomagnetic inclinations of 76 close to that expected for a geocentric axial dipole field and direction fluctuations of around 20 from the mean the palaeomagnetic directions are stable under alternating field partial demagnetization experiments a time scale for the vatnsdalsvatn sediments has been estimated from 14 c dating the pattern of palaeomagnetic secular change shows few similarities with british records 2000 km distant and a central north american record 5000 km distant

palaeomagnetism of holocene and late pleistocene sediments from lago di mezzano and lago grande di monticchio italy initial results abstract palaeomagnetic records of the geomagnetic secular variation reaching back to 31 and 102 kyr cal bp respectively were obtained from two sediment cores from lago di mezzano central italy and two cores from lago grande di monticchio southern italy intra lake correlation was based on continuous high resolution susceptibility measurements and discrete dry density samples characteristic remanent magnetization chrm of all 4800 samples was determined by analysis of the results of progressive alternating field af demagnetization intra lake comparison of the resulting chrm directions confirms that the inclination and declination records reflect the palaeosecular variation of the local geomagnetic field composite curves of geomagnetic palaeosecular variations psv were created for each lake in order to compare the reconstructed psv records with those from lac du bouchet massif central france and lac de joux switzerland the good agreement in the general patterns of the inclination and declination records of all lakes mentioned above confirms the reconstructed psv records of the italian lakes investigated

joint approach combining damage and paleoseismology observations constrains the 1714 a d bhutan earthquake at magnitude 8 0 5 the region of bhutan is thought to be the only segment of the himalayas not having experienced a major earthquake over the past half millennium a proposed explanation for this apparent seismic gap is partial accommodation of the india asia convergence further south across the shillong plateau yet the seismic behavior of the himalayan megathrust is unknown here we present historical documents from the region reporting on an earthquake in 1714 ad and geological evidence of surface rupture to constrain the latest large event in this area we compute various earthquake scenarios using empirical scaling relationships relating magnitude with intensity source location and rupture geometry our results constrain the 1714 ad earthquake to have ruptured the megathrust in bhutan most likely during a m7 5 8 5 event this finding reclassifies the apparent seismic gap to a former information gap and implies that the entire himalayan arc has a high level of earthquake potential

from mountain summits to roots crustal structure of the eastern alps and bohemian massif along longitude 13 3 e abstract the crustal structure of the eastern alps and adjacent tectonic units investigated in this work sheds new light on the relationship of surface geology to geodynamic processes operating at depth of particular interest are the nature of a previously proposed moho gap south and east of the tauern window the plate tectonic affinity of the steeply dipping eastern alpine slab and the relationship of the alps to the neogene sedimentary basins and the bohemian massif to address these questions we use various seismological approaches based on converted waves from the temporary passive experiment easi eastern alpine seismic investigation a complementary experiment of the alparray project the easi is a densely spaced 540 km long seismic network along 13 3 e we operated for more than a year the uppermost crustal structures in and near the alps exhibit dipping layers and or tilted anisotropy that correlate well with surface geology observations the moho despite its variable appearance is clearly identified along most of the swath the variscan lithospheric blocks beneath the bohemian massif are imaged with sub vertical boundaries beneath the eastern alps the shape of the moho is consistent with bi vergent orogenic thickening with a steeper and deeper reaching adriatic plate plunging northwards beneath the european plate in the north at the junction of these plates at depth around the previously proposed moho gap the root of the eastern alps is a broad trough characterized by a zone of low velocity gradient that is up to 20 km thick transitioning between crust and mantle our receiver function results corroborate earlier lithosphere upper mantle seismic tomography images and highlight the adriatic affinity of the eastern alpine slab the zigzag deployment pattern of stations in the easi experiment also allows distinction of short wavelength variations perpendicular to the profile both within the shallow and the deep crust this underlines the importance of applying 3d imaging in complex geodynamic systems

a paleomagnetic approach toward refining holocene radiocarbon based chronologies paleoceanographic records from the north iceland md99 2269 and east greenland md99 2322 margins 1 we report the intercalibration of paleomagnetic secular variation psv and radiocarbon dates of two expanded postglacial sediment cores from geographically proximal but oceanographically and sedimentologically contrasting settings the objective is to improve relative correlation and chronology over what can be achieved with either method alone core md99 2269 was taken from the hunafloaall trough on the north iceland shelf core md99 2322 was collected from the kangerlussuaq trough on the east greenland margin both cores are well dated with 27 and 20 accelerator mass spectrometry 14c dates for cores 2269 and 2322 respectively paleomagnetic measurements made on u channel samples document a strong stable single component magnetization the temporal similarities of paleomagnetic inclination and declination records are shown using each core s independent calibrated radiocarbon age model comparison of the psv records reveals that the relative correlation between the two cores could be further improved starting in the depth domain tie points initially based on calibrated 14c dates are either adjusted or added to maximize psv correlations radiocarbon dates from both cores are then combined on a common depth scale resulting from the psv correlation support for the correlation comes from the consistent interweaving of dates correct alignment of the saksunarvatn tephra and the improved correlation of paleoceanographic proxy data percent carbonate these results demonstrate that psv correlation used in conjunction with 14c dates can improve relative correlation and also regional chronologies by allowing dates from various stratigraphic sequences to be combined into a single higher dating density age to depth model

is burial velocity a master parameter for bioturbation abstract the intensity of biological mixing in a marine sediment is widely believed to be related to the flux of labile organic matter at the same time this flux has been shown to be strongly correlated to the burial velocity one would then expect a significant correlation between biological mixing coefficient d b and burial velocity a nonlinear regression of existing data with a power law eqns 2 and 3 of the text produces a statistically significant correlation the statistical significance of the regression in no way implies causation and in fact it accounts for only about 22 of the total variance in the dataset thus reducing its physical significance a number of additional processes contribute to the large observed variance including timing of mixing events temporal and spatial heterogeneity differences in temporal scales sampling artifacts and specific particle associations with due care the d b relationship may prove useful in defining the likely range of d b values in a particular environment a similar analysis of the tracer identified surface mixed depth shows that it is essentially independent of burial velocity with a worldwide mean of 9 8 4 5 cm depth of mixing is probably more closely related to the energetic costs of deep burrowing

himalayan megathrust geometry and relation to topography revealed by the gorkha earthquake the himalayan mountain range has been the locus of some of the largest continental earthquakes including the 2015 magnitude 7 8 gorkha earthquake competing hypotheses suggest that himalayan topography is sustained and plate convergence is accommodated either predominantly on the main plate boundary fault or more broadly across multiple smaller thrust faults here we use geodetic measurements of surface displacement to show that the gorkha earthquake ruptured the main himalayan thrust fault the earthquake generated about 1 m of uplift in the kathmandu basin yet caused the high himalaya farther north to subside by about 0 6 m we use the geodetic data combined with geologic geomorphological and geophysical analyses to constrain the geometry of the main himalayan thrust in the kathmandu area structural analyses together with interseismic and coseismic displacements are best explained by a steep shallow thrust fault flattening at depth between 5 and 15 km and connecting to a mid crustal steeper thrust we suggest that present day convergence across the himalaya is mostly accommodated by this fault no significant motion on smaller thrust faults is required furthermore given that the gorkha earthquake caused the high himalayan mountains to subside and that our fault geometry explains measured interseismic displacements we propose that growth of himalayan topography may largely occur during the ongoing post seismic phase

paleosecular variations recorded by holocene pleistocene sediments from lake el trebol patagonia argentina paleomagnetic studies carried out on six cores from the bottom sediments from lake el trebol south argentina are described measurements of directions declination and inclination d and i and intensity of natural remanent magnetisation nrm magnetic susceptibility at low and high frequency specific x and volumetric k isothermal remanent magnetisation irm saturation isothermal remanent magnetisation sirm back field and anhysteric remanent magnetisation arm were carried out stability of the nrm was investigated by alternating field demagnetisation rock magnetic studies suggest that the main carriers of magnetisation are ferrimagnetic minerals predominantly pseudo single domain magnetite records of nrm and k show a good correlation with the sedimentological description and also with those of shorter cores previously studied the tephra layers were identified from the lithologic profiles and also from the magnetic susceptibility logs due to their different chronological meaning and their rather bad behaviour as magnetic recorder these layers were removed from the sequence and the gaps that were produced along the profiles by the removal were closed obtaining a shortened depth radiocarbon age estimates from these cores and from earlier studies allow us to construct a paleosecular variation psv record for the past 24 000 years these results show good correlation with the previous one the spectrum obtained from spectral analysis shows major peaks at periodicities of about 1150 1500 2490 3630 5240 and 11 810 years both clockwise and counterclockwise precession of the geomagnetic vector is evident from analysis of the bauer plots with a preponderance of clockwise movement

structural interpretation of the great earthquakes of the last millennium in the central himalaya abstract a major question about the himalaya remains open does a great earthquake like the mw 8 1 1934 earthquake release all the strain stored by the tibet india convergence during the preceding interseismic period and only that strain or can it also release a background store of energy that remained unreleased through one or more earlier earthquakes and so potentially engender giant events or a relatively random sequence of events to consider this question the history of the great earthquakes of the last millennium is investigated here by combining data provided by the historical archives of kathmandu trenches through surface ruptures isoseismal damage mapping seismites and the instrumental record in the kathmandu basin the location of the epicenter of the 1934 earthquake was determined from the arrival of high energy p waves that caused sedimentary dikes and ground fractures perpendicular to the epicenter azimuth the epicenter of the mw 7 6 1833 earthquake can therefore be determined analogously from dike orientation and its location to the ne of kathmandu indicates an overlap with the mw 8 1 1934 rupture the 1934 earthquake released strain not released by the 1833 earthquake comparison of the historical records of earthquakes in kathmandu with 14c ages from paleo seismic trenches along the himalayan front suggests that 1 the 1344 kathmandu event ruptured the surface as far away as kumaon and was therefore a giant mw 8 6 earthquake and 2 the 1255 event that destroyed kathmandu is attested by surface ruptures in central and western nepal and by seismites in soft sediment as far away as kumaon geometric and rheologic controls for the different types of ruptures during the medium mw 7 great mw 8 and giant mw 8 4 earthquakes are illustrated in structural cross sections it is found that the epicenters of great himalayan earthquakes are located on the basal thrust farther north or close to the locked zone which is defined from geodetic measurements of regional deformation during the interseismic period this suggests that great earthquakes initiate in a wide transition zone between exclusively brittle and exclusively creeping regimes the extent of which depends on the dip of the main himalayan thrust the succession of the great earthquakes during the last millennium has released all the 20 m millennial himalayan convergence even in the central seismic gap which has been locked since 1505 the millennial seismic release rate is close to the convergence rate nonetheless no evidence of a succession of characteristic earthquakes has been found the 1100 1833 and 1934 earthquakes in the eastern himalaya are characterized neither by constant displacement nor by constant recurrence furthermore some great earthquakes do not release all the strain elastically stored by the himalayan and tibetan upper crust after the 1255 event there was still the potential for a slip of several meters for the mw 8 1 1505 event this suggests a rather random release of seismic energy great earthquakes could occur anytime and in any part of the central himalaya furthermore a future giant earthquake of mw 8 6 cannot be excluded

continuous geomagnetic field models for the past 7 millennia 2 cals7k 1 we present two continuous global geomagnetic field models for recent millennia cals3k 2 covering the past 3000 years and cals7k 2 covering 7000 years from 5000 bc to 1950 ad the models were determined by regularized least squares inversion of archeomagnetic and paleomagnetic data using spherical harmonics in space and cubic b splines in time they are derived from a greatly increased number of paleomagnetic directional data compared to previous efforts and for the first time a significant amount of archeointensity data is used in this kind of global model allowing the determination of evolution of geomagnetic dipole strength while data accuracy and dating uncertainties remain a limitation reliable low resolution global models can be obtained the results agree well with previous results from virtual axial dipole moment vadm studies from archeomagnetic intensity data apart from a systematic offset in strength a comparison of model predictions with the previous 3000 year model cals3k 1 gives general agreement but also some significant differences particularly for the early epochs the new models suggest that the prominent two northern hemisphere flux lobes are more stationary than cals3k 1 implied extending considerably the time span of stationary flux lobes observed in historical models between 5000 bc and 2000 bc there are time intervals of weak dipole moment where dipole power is exceeded by low degree nondipole power at the core mantle boundary model coefficients and evaluation code can be obtained from the earthref digital archive erda together with animations and snapshots plots for every 100 years at http www earthref org detailed urls for the different material are listed in appendix a

spline analysis of holocene sediment magnetic records uncertainty estimates for field modeling 1 sediment and archeomagnetic data spanning the holocene enable us to reconstruct the evolution of the geomagnetic field on time scales of centuries to millennia in global field modeling the reliability of data is taken into account by weighting according to uncertainty estimates uncertainties in sediment magnetic records arise from 1 imperfections in the paleomagnetic recording processes 2 coring and sub sampling methods 3 adopted averaging procedures and 4 uncertainties in the age depth models we take a step toward improved uncertainty estimates by performing a comprehensive statistical analysis of the available global database of holocene magnetic records smoothing spline models that capture the robust aspects of individual records are derived this involves a cross validation approach based on an absolute deviation measure of misfit to determine the smoothing parameter for each spline model together with the use of a minimum smoothing time derived from the sedimentation rate and assumed lock in depth departures from the spline models provide information concerning the random variability in each record temporal resolution analysis reveals that 50 of the records have smoothing times between 80 and 250 years we also perform comparisons among the sediment magnetic records and archeomagnetic data as well as with predictions from the global historical and archeomagnetic field models combining these approaches we arrive at individual uncertainty estimates for each sediment record these range from 2 5 to 11 2 median 5 9 interquartile range 5 4 to 7 2 for inclination 4 1 to 46 9 median 13 4 interquartile range 11 4 to 18 9 for relative declination and 0 59 to 1 32 median 0 93 interquartile range 0 86 to 1 01 for standardized relative paleointensity these values suggest that uncertainties may have been underestimated in previous studies no compelling evidence for systematic inclination shallowing is obtained from the analysis of the available database of holocene sediment magnetic records the analysis highlights the importance of collecting oriented cores publishing and archiving unprocessed raw paleosecular variation determinations and presenting a detailed chronology so that changes in the sedimentation rate can be assessed with regard to future field models workers should consider rejection of anomalous cores through comparisons to other sources and ensure that realistically large uncertainties are allocated to high latitude declination records

electrical structure of the himalaya of central nepal high conductivity around the mid crustal ramp along the mht twelve broadband magnetotelluric mt soundings were performed across the himalaya of central nepal in 1996 in order to determine the electrical structure of the crust and its relation to geological structures and active tectonics the mt impedance tensors were obtained for frequencies between 0 001 and 500 hz the 2 d section derived from joint inversion of te and tm mode after rri and groom bailey decomposition shows high conductivity in the foreland basin 30 m that contrasts with the resistive indian basement 300 m and lesser himalaya 1000 m in addition our mt sounding reveals a major conductive feature beneath the front of the higher himalaya also characterized by intense microseismic activity and the position of a mid crustal ramp along the major active thrust fault mht this high conductivity zone probably reflects metamorphic fluids released during underthrusting of the indian basement and pervading well connected microcracks induced by interseismic stress build up or distributed brittle deformation around the ramp

crustal structure of the darjeeling sikkim himalaya and southern tibet analysis of data from nine temporary broadband seismic stations operated across west bengal and sikkim along with publicly available data from seismographs in the surrounding region provides the first image of the descending indian plate beneath the darjeeling sikkim himalaya the down going indian crust is imaged by receiver function common conversion point stacking using data from 32 sites in combination with more detailed analyses from simultaneous modelling of receiver function data and rayleigh wave group velocity dispersion at 13 stations compared to locations farther south on the indian shield our southernmost station shows evidence for thickened crust beneath the mahanadi rift basin with a possible mafic basal layer north of the mahanadi rift the indian moho is 38 km deep below the archean terranes of the northeast part of the indian shield the moho then dips gently northward beneath the himalayan foreland basin reaching a depth of 44 48 km below the himalayan foothills below sikkim the moho continues to deepen but there are indications of secondary structures in the receiver function image and modelling results suggesting some imbrication of the crust as it flexes downward the crust thickens further beneath the greater himalaya and southern tibet reaching depths of 65 70 km below the southern tibet detachment std below the lhasa terrane north of the std a double discontinuity exists with interfaces at 55 60 km and 80 km depth there is a significant reduction in the average shear wave velocity of the crystalline crust between sites to the south of and on the himalayan foreland basin and sites in the himalaya and to the north below the himalaya and southern tibet the p to s conversion ps has a lower amplitude compared to that observed at sites on the undeformed indian shield this decrease in amplitude of the moho ps phase could arise from a lower impedance contrast across the crust mantle boundary or from scattering due to deformation of the crust and moho a coherent negative arrival beneath the darjeeling sikkim himalaya indicate the presence of a low velocity zone lvz possibly associated with the main himalayan thrust this lvz can be traced beneath the darjeeling sikkim himalaya but disappears beneath the greater himalaya

great earthquakes seismicity gaps and potential for earthquake disaster along the himalaya plate boundary abstract analysis of the space time patterns of seismicity in the himalaya plate boundary has established the existence of three seismic gaps 1 1 the kashmir gap lying west of the 1905 kangra earthquake 2 2 the central gap situated between the 1905 kangra and the 1934 bihar earthquakes 3 3 the assam gap between the 1897 and 1950 assam earthquakes this study has shown that the above great earthquakes were preceded as well as followed by long periods 19 years of decreased levels of seismic activity in the epicentral regions remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the central gap as well as in the assam gap local seismic investigation in the assam gap confirms this feature and the seismicity suggests the existence there of an asperity the local seismic investigations in garhwal himalaya have shown that the small earthquakes are confined to the upper 6 8 km of the crust and may have strike slip motions these earthquakes occur in a region where teleseismically recorded events were few

measurement of the degree of smoothing in sediment paleomagnetic secular variation records an example from late quaternary deep sea sediments of the bermuda rise western north atlantic ocean abstract replicate paleomagnetic secular variation psv records for the last 15 000 yr have been recovered from two deep sea sediment gravity cores on the bermuda rise western north atlantic ocean the records have been correlated using several different parameters and dated by correlation to a nearby piston core which has a high resolution 14 c chronology the psv records are systematically subdued with respect to the expected local magnetic field variability during the holocene when sedimentation rates were about 10 cm kyr during the late pleistocene when sedimentation rates were a factor of 2 3 higher the psv variability was significantly larger we attribute this to smoothing of the psv records by a depositional post depositional remanence drm pdrm acquisition process with a 10 20 cm lock in interval the degree of psv smoothing was evaluated by comparing the vgp angular dispersion and vector spectral content of the bermuda rise cores with high resolution psv records from north america and great britain these results suggest a 50 reduction in the drm pdrm recording of vector variability during the holocene on the bermuda rise with most of the psv reduction occurring for features of less than 2000 yr in duration we can reproduce the subdued psv pattern with a mathematical model that simulates the site drm pdrm remanence acquisition process finally the replicate gravity cores document that psv records may be reproducible on a local scale even though they only retain a low pass filtered record of true magnetic field variability

lateral variations of the midcrustal seismicity in western nepal seismotectonic implications abstract the midcrustal seismicity along the himalayas depicts some lateral variations this seismicity is often related to stress build up at depth along the downdip extent of the fault segments producing large and great earthquakes to better characterize these variations we deployed the first temporary seismological network in west nepal hiknet as a complement to the nepalese national network we used automatic picks manually validated to perform absolute and relative location of the earthquakes the resulting catalog contains 2190 local events shallow to midcrustal 8 16 km the comparison between the seismicity and the geologic balanced cross sections shows that most earthquakes occur within the hanging wall of the main himalayan thrust fault nearby ramps or suspected contacts between lesser himalayan slivers some of the events associated with these geological structures are clustered within weeks long earthquake swarms with seismic envelopes migrating at 35 50 m day these transients are possibly related to fluid migrations or geodetically unresolved slow slip events the lateral variations of some of the structures associated to this seismicity are likely partially controlling the extent of the coseismic ruptures during intermediate earthquakes that break partly the locked fault zone in a similar way to what was reported after the mw7 8 2015 gorkha nepal earthquake a better characterization of the faults segmentation including a better location and extent of the seismogenic segments at depth is an important input for seismic hazard studies

a paleomagnetic record from lake lama northern central siberia abstract two cores from lake lama northern central siberia with lengths of 19 and 11 m respectively were subjected to detailed magnetostratigraphic investigations directions of the characteristic remanent magnetisation chrm were derived from vector analysis of the results from alternating field a f demagnetisation yielding records for the last 18 000 years bp the sediments show a distinct change in sedimentation pattern at around 14 500 years bp from a highly variable to a monotonous sedimentation with anoxic conditions in the lake sediments during the last 11 500 years bp the oxic anoxic boundary is reflected in all rock magnetic parameters measured and the magnetic mineral fraction is affected by reductive dissolution of iron bearing minerals here mainly magnetite therefore no record of relative paleointensity could be achieved but as intra and inter lake comparison of the obtained inclination and declination records have shown the directions of the geomagnetic field recorded in the sediments from lake lama were not severely affected by the partial dissolution of the remanence carrying minerals

paleoseismic evidence of great surface rupture earthquakes along the indian himalaya 1 toward understanding the relationship between strain accumulation and strain release in the context of the mechanics of the earthquake and mountain building process and quantifying the seismic hazard associated with the globes largest continental thrust system we describe the late quaternary expression and paleoseismic evidence for great surface rupture earthquakes at six sites along the himalayan frontal thrust hft system of india our observations span a distance of 250 km along strike of the hft uplifted and truncated fluvial terrace deposits resulting from the holocene displacements on the hft are preserved along canyons of the ghaggar markanda shajahanpur and kosi rivers dividing the elevation of the bedrock straths at each site by their ages yields estimates of the vertical uplift rate of 4 6 mm yr which when assumed to be the result of slip on an underlying thrust dipping at 20 45 are equivalent to fault slip rates of 6 18 mm yr or shortening rates of 4 16 mm yr trench exposures reveal the hft to fold and break late holocene surface sediments near the cities and villages of chandigarh kala amb rampur ganda lal dhang and ramnagar radiocarbon ages of samples obtained from the displaced sediments indicate surface rupture at each site took place after a d 1200 and before a d 1700 uncertainties attendant to the radiocarbon dating currently do not allow an unambiguous definition of the capping bound on the age of the displacement at each site and hence whether or not the displacements at all sites were contemporaneous trench exposures and vertical separations measured across scarps at rampur ganda lal dhang and ramnagar are interpreted to indicate single event displacements of 11 38 m dividing the observed single event vertical components of displacement by the estimated longer term uplift rates indicates 1330 3250 or more years should be required to accumulate the slip sufficient to produce similar sized displacements surface rupture appears to not have occurred during the historical 1905 kangra mw 7 7 1934 bihar nepal mw 8 1 and 1950 assam mw 8 4 earthquakes which also occurred along the himalayan front yet we observe clear evidence of fault scarps and displacements in young alluvium and progressive and continued offset of fluvial terrace deposits along the hft we suggest on this basis and the size and possible synchroneity of displacements recorded in the trenches that there exists the potential for earthquakes larger than recorded in the historical record and with the potential to rupture lengths of the hft greater than the 250 km we have studied

geomagnetic field for 0 3 ka 1 new data sets for global modeling 1 paleomagnetic and archeomagnetic records are used in both regional and global studies of earth s magnetic field we present a description and assessment of five newly compiled data sets also used in the companion paper by korte et al 2009 to produce a series of time varying spherical harmonic models of the geomagnetic field for the last 3000 years data are drawn from our compilation of lake sediment records and from the online database geomagia50v2 the five selections are available from the earthref digital archive at http earthref org cgi bin erda cgi n 944 data are grouped according to the source of material and we conducted separate assessments of reliability for archeomagnetic artifacts and lava flows the arch3k dat data set and for sediments sed3k dat the overall number of data is 55 greater than in previous compilations constrained data sets were selected using different criteria for each group winnowing of archeological data was based on uncertainties supplied by the original data providers the lake sediment data assessment relied on preassigned age uncertainties and one or more of the following comparisons with archeomagnetic data from the same region regional consistency among several lakes and consistency with global archeomagnetic models we discuss relative merits of a larger unconstrained data set or a smaller possibly more reliable one the constrained data sets eliminate a priori up to 35 of the available data in each case and rely on potentially subjective assessments of data quality given the limited data available our analyses indicate that iterative rejection of a small number 1 1 5 of outlying data during global field modeling is a preferable approach specific regional comparisons among the models and data support the conclusion that korte et al s outlier free cals3k 3 model based on all available measurements from sediments and archeological artifacts currently provides the best global representation of the 0 3 ka field the arch3k 1 model provides a better fit to the denser european archeomagnetic data and may be better in that region

palaeomagnetic study of the holocene and upper pleistocene sediments from lake barombi mbo cameroun first results abstract the analyses of the stable deposition and post depositional remanent magnetization carried by the lacustrine sediments contained in a 24 m sequence collected from the bottom of the maar lake barombi mbo cameroun yield well defined declination and inclination oscillations which can be attributed to palaeosecular variations of the local geomagnetic field the transformation to a time scale based on the interpolation and extrapolation of 14 c ages allows comparison of this record with contemporaneous records obtained in other parts of the world the successive inclination peaks can be individually identified with those found in western europe in spite of small chronological discrepancies which are in the range of the standard deviation of the ages normalization of the nrms by anhysteretic magnetization provides a profile of relative palaeointensities which shows similarities with that reconstructed from the same time interval in a sequence from western europe although an important phase shift appears

gravity anomalies flexure of the indian plate and the structure support and evolution of the himalaya and ganga basin bouguer gravity anomalies along four profiles across the western himalaya and ganga basin show large deviations from local isostatic equilibrium a deficit of mass characterizes the ganga basin and an excess underlies the lesser himalaya both can be understood if the indian plate is flexed down by the distributed load of part of the mountains the cross sectional shape of the ganga basin seems to be controlled by the deflection of the indian plate which we compute assuming the indian plate to overlie an inviscid fluid from the shapes of both bouguer anomaly profiles and the basement topography we place bounds on the flexural rigidity of such a plate if the ganga basin is a steady state feature then the age of the basal sediments in a given locality should be proportional to the distance of that locality from the southern edge of the basin if the rate of convergence of india and the himalaya were constant that rate should equal the distance divided by the corresponding age we find a rate of 10 to 15 mm a for the last 15 to 20 ma which is consistent with a large part of the 50 mm a rate of convergence between india and eurasia being absorbed by the eastward extrusion of parts of tibet profiles of bouguer gravity anomalies show only a small peak or plateau over the southern edge of the lesser himalaya implying that the boundary between the light sediments of the ganga basin and the heavier crustal rocks of the lesser himalaya is not sharp and that there exists some light material beneath the range we infer that some sediment deposited in the ganga basin has been underthrust beneath the lesser himalaya but the quantity is small most of this sediment probably is scraped off the indian plate to make the foothills of the range we find that the load of the high himalaya is too large to be supported solely by elastic stress in the indian plate if the flexural rigidity of the plate is constant and if no other external forces act on the plate the observed gradient in bouguer gravity anomalies increases from an average of about 1 mgal km over the ganga basin and lesser himalaya to about 2 mgal km over the high himalaya this increase in the gravity gradient implies that the moho dips more steeply 10 15 beneath the high himalaya than beneath the lesser himalaya 2 3 we interpret this steepening of the moho to be due to a weakening of the plate which allows it to bend more sharply beneath the high himalaya than farther south with the inclusion of a weak segment of indian plate beneath the high himalaya calculated anomalies show a somewhat increased gradient beneath the high himalaya but when the weight of the entire himalaya is used as a load on the plate calculated anomalies are more negative than observed therefore an external force system is needed to support much of the weight of the high himalaya as well as to bend the plate sufficiently beneath the high himalaya the magnitudes of the bending moment and the force per unit length that must be applied to the end of the plate are compatible with their sources being gravity acting on a part of india s mantle lithosphere stripped of its crust and underthrust beneath southern tibet

seismic imaging of a mid crustal low velocity layer beneath the northern coast of the south china sea and its tectonic implications abstract low velocity layer lvl within the continental crust is usually closely associated with tectonic events thus it may reflect ongoing processes or offer a chance to backtrack the evolutional history mid crustal lvl has been reported in the northern coast of the south china sea scs by several geophysical studies but the 3d distribution of lvl in the whole coastal area is still poorly known here we perform a receiver function study based on 67 broadband seismological stations we use the common conversion point method to construct structures of the moho as well as intra crustal interfaces we image sharp intra crustal negative velocity gradient broadly distributed in the eastern cathaysia block with depth increasing from 10 km in the nw to 12 16 km in the se the corresponding amplitude of the negative interface shows variable values from 0 03 to 0 1 with an evidential trend of strengthening eastwards we interpret the negative gradient as top of the lvl produced by accumulation of fluids from dehydration of the paleo pacific subduction plate the mid crustal lvl tends to act as weak domains during continental rift and the lateral variation of the lvl may be one possible reason explaining the along strike variation in crustal stretching in the northern scs rifted margin

crustal structure of the himalayan orogen at 90 east longitude from project indepth deep reflection profiles international deep profiling of tibet and the himalaya indepth deep seismic reflection profiles show that the indian lithosphere is underthrusting the central himalaya along a gently north dipping decollement that is traceable northward beneath the tethyan belt to 28 6 n and to a depth of about 45 km the decollement carries in its hanging wall a near crustal thickness slice of internally deformed indian continental basement and cover represented in outcrop by the greater himalayan belt and structurally overlying tethyan belt geometric relationships suggest that the decollement probably ramps downward beneath the northern tethyan belt to near the base of the crust and that the hanging wall crustal slice was detached from indian mantle lithosphere that presently underlies southern tibet to the north the north himalayan anticlinorium kangmar dome appears to be a large duplex ramp anticline in the hanging wall of the decollement the south tibetan detachment appears to have been imaged in two areas in the wagye la area it appears to follow the tethyan belt greater himalayan belt contact northward in the subsurface and to have been folded over the kangmar dome in the zherger la area it appears to have been active relatively recently as a 30 north dipping normal fault that cuts deeply into the greater himalayan belt allochthon palinspastic reconstruction indicates a minimum of about 326 km of shortening of the indian basement across the himalaya since the initiation of the main central thrust hence indian continental lithosphere largely stripped of its overlying crust can extend northward beneath the tibetan plateau to at least 32 n where earthquake seismological observations show that the properties of the upper mantle change markedly e g mcnamara et al 1995 taken together the seismic reflection and earthquake seismological observations lend support for the view that the indian mantle lid mechanically underplates roughly the southern half of the tibetan plateau the indepth reflection data do not show that indian crust attached to this lithosphere extends north of southernmost tibet kangmar dome nor do they negate this possibility similarly the reflection data do not yield direct evidence for or against lower crustal subduction beneath the himalaya

millenary mw 9 0 earthquakes required by geodetic strain in the himalaya the himalayan arc produced the largest known continental earthquake the m w 8 7 assam earthquake of 1950 but how frequently and where else in the himalaya such large magnitude earthquakes occur is not known paleoseismic evidence for coseismic ruptures at the front of the himalaya with 15 to 30 m of slip suggests even larger events in medieval times but this inference is debated here we estimate the frequency and magnitude of the largest earthquake in the himalaya needed so that the moment released by seismicity balances the deficit of moment derived from measurements of geodetic strain assuming one third of the moment buildup is released aseismically and the earthquakes roughly follow a gutenberg richter distribution we find that m w 9 0 events are needed with a confidence level of at least 60 and must return approximately once per 800 years on average

regional modeling of the geomagnetic field in europe from 6000 to 1000 b c we have developed a first low degree regional geomagnetic model for the european continent valid for the period 6000 1000 b c from a selected compilation of sedimentary and archeomagnetic data the scha dif 8k model this model provides information about both direction declination and inclination and intensity of the earth s magnetic field by connecting it with our previous model scha dif 3k valid from 1000 b c to 1900 a d and the igrf we furnish continuous geomagnetic field information for the last 8000 years in europe it has been developed using the revised spherical cap harmonic analysis in 2 dimensions technique r scha2d and using the norm of the earth s magnetic field to constrain the inversion problem the size of the cap is 22 and the maximum degree of the expansion is 2 the linearization problem was solved by using the truncated taylor s series applied to the expressions representing the relationship between the declination inclination and intensity data and the cartesian components of the geomagnetic field we used the geocentric axial dipole gad field as our initial or reference field for time we used the classical sliding overlapping window method the size of the window was set to 100 years shifted by 50 years we compared the model s prediction with the input data with the global cals7k 2 model and with new independent data the regional model shows a better fit to the input and to the independent data than the global model especially in terms of intensity and agrees with the virtual axial dipole moment given by other studies for the last 8000 years the european geomagnetic field has recorded rapid changes or archeomagnetic jerks the average field for the last 8000 years in europe is indistinguishable from the gad field

imaging the indian subcontinent beneath the himalaya new seismic images reveal the geometry of the indian plate as it passes beneath the himalayan plateau several important subsurface features of vanished india are revealed including a shear zone above the base of the indian crust beneath the himalaya and conversion of the deep indian crust into denser rock the rocks of the indian subcontinent are last seen south of the ganges before they plunge beneath the himalaya and the tibetan plateau they are next glimpsed in seismic reflection profiles deep beneath southern tibet1 yet the surface seen there has been modified by processes within the himalaya that have consumed parts of the upper indian crust and converted them into himalayan rocks2 3 the geometry of the partly dismantled indian plate as it passes through the himalayan process zone has hitherto eluded imaging here we report seismic images both of the decollement at the base of the himalaya and of the moho the boundary between crust and mantle at the base of the indian crust a significant finding is that strong seismic anisotropy develops above the decollement in response to shear processes that are taken up as slip in great earthquakes at shallower depths north of the himalaya the lower indian crust is characterized by a high velocity region consistent with the formation of eclogite a high density material whose presence affects the dynamics of the tibetan plateau

holocene palaeomagnetic secular variation recorded in multiple lake sediment cores from eastern finland summary holocene palaeomagnetic secular variation psv in inclination and declination recorded in the sediment remanent magnetization of two small lakes lake lehmilampi 63 37 n 29 06 e and lake kortejarvi 63 37 n 28 56 e in eastern finland is presented as an outcome of systematic coring eight cores 300 753 cm in length were investigated all samples lehmilampi n 1320 kortejarvi n 943 were subjected to palaeo and mineral magnetic analyses the directions of the characteristic remanent magnetization chrm were obtained from progressive alternating field demagnetization of the natural remanent magnetization nrm followed by principle component analysis the younger sections of the sediment columns in the studied lakes are annually laminated providing detailed chronologies for dating psv features back to 5100 cal bp the underlying older sections of the cores were dated by palaeomagnetic pattern matching in respect to varve dated lake nautajarvi psv data ojala saarinen 2002 thus yielding a composite age model covering nearly the whole holocene epoch average sedimentation rates ranging from 0 68 to 0 74 mm yr 1 enabled recording of changes in the geomagnetic field at decadal resolution the carriers of remanence are dominantly magnetite of stable single domain to pseudo single domain grain size accompanied by magnetic minerals of harder coercivity the sediments from both lakes exhibit strong and stable single component magnetizations nearly throughout the whole cores the sediment magnetization lock in delay is estimated to range between 80 and 100 yr psv data were transformed into time series and subsequently stacked to comprise north karelian stack and fisher statistics were used to calculate mean directions together with the 95 per cent confidence level 95 a comparison of declination and inclination features of the north karelian stack with previously published data expresses remarkable similarity therefore confirming the similar source behind the changes in the nrm directional records the high quality of the psv data extracted from lehmilampi and kortejarvi in terms of dating as well as amplitude reconstruction have a high potential to improve existing and future geomagnetic field models

mountain building in the nepal himalaya thermal and kinematic model we model crustal deformation and the resulting thermal structure across the nepal himalaya assuming that since 20 ma shortening across the range has been primarily taken up by slip along a single thrust fault the main himalayan thrust mht fault and that the growth of the himalayan wedge has resulted mainly from underplating and to the development of a duplex at midcrustal depth we show that this process can account for the inverse thermal metamorphic gradient documented throughout the lesser himalaya lh the discontinuity of peak metamorphic temperatures across the mct as well as the distribution of age of exhumation across the range this study suggests that the metamorphic evolution of the range over about the last 20 million years is compatible with the kinematics of recent crustal deformation deduced from morphotectonic and geodetic studies

continuous global geomagnetic field models for the past 3000 years abstract several global geomagnetic field models exist for recent decades but due to limited data availability models for several centuries to millennia are rare we present a continuous spherical harmonic model for almost 3 millennia from 1000 b c to 1800 a d based on a dataset of directional archaeo and paleomagnetic data and axial dipole constraints the model named continuous archaeomagnetic and lake sediment geomagnetic model for the last 3k years cals3k 1 can be used to predict both the field and secular variation comparisons and tests with synthetic data lead to the conclusion that cals3k 1 gives a good general large scale representation of the geomagnetic field but lacks small scale structure due to the limited resolution of the sparse dataset in future applications the model can be used for comparisons with additional new data for that time span for better resolved regions the agreement of data with cals3k 1 will provide an idea about the general compatibility of the data with the field and secular variation in that region of the world for poorly covered regions and time intervals we hope to iteratively improve the model by comparisons with and inclusion of new data animations and additional snapshot plots of model predictions as well as the model coefficients and a fortran code to evaluate them for any time can be accessed under http www mahi ucsd edu cathy holocene holocene html the whole package is also stored in the earthref digital archive at http www earthref org

the 2015 gorkha earthquake a large event illuminating the main himalayan thrust fault the 2015 gorkha earthquake sequence provides an outstanding opportunity to better characterize the geometry of the main himalayan thrust mht to overcome limitations due to unaccounted lateral heterogeneities we perform centroid moment tensor inversions in a 3 d earth model for the main shock and largest aftershocks in parallel we recompute s top and p to s receiver functions from the hi climb data set inverted centroid locations fall within a low velocity zone at 10 15 km depth and corresponding to the subhorizontal portion of the mht that ruptured during the gorkha earthquake north of the main shock hypocenter receiver functions indicate a north dipping feature that likely corresponds to the midcrustal ramp connecting the flat portion to the deep part of the mht our analysis of the main shock indicates that long period energy emanated updip of high frequency radiation sources previously inferred this frequency dependent rupture process might be explained by different factors such as fault geometry and the presence of fluids

characterizing the main himalayan thrust in the garhwal himalaya india with receiver function ccp stacking abstract we use common conversion point ccp stacking of ps receiver functions to image the crustal structure and moho of the garhwal himalaya of india our seismic array of 21 broadband seismometers spanned the himalayan thrust wedge at 79 80 e between the main frontal thrust and the south tibet detachment in 2005 2006 our ccp image shows the main himalayan thrust mht the detachment at the base of the himalayan thrust wedge with a flat ramp flat geometry seismic impedance contrasts inferred from geologic cross sections in garhwal imply a negative impedance contrast velocity decreasing downward for the upper flat located beneath the lower himalaya and a positive impedance contrast velocity increasing downward for the ramp located beneath the surface trace of the munsiari thrust or mct i at the lower flat located beneath the higher himalaya spatially coincident measurements of very high electrical conductivities require the presence of free fluids and we infer a negative impedance contrast on the mht caused by ponding of these fluids beneath the detachment our seismic image indicates that the upper flat of the mht is 10 km below sea level and dips north at 2 connecting to a mid crustal ramp which is 10 km high and dips at 16 the lower flat is 20 25 km below sea level and dips at 4 the main central thrust mct appears as a negative impedance contrast dipping at 16 the moho is nearly horizontal at 35 45 km depth beneath the sub himalaya and lower himalaya deepening to 50 km or more beneath the higher himalaya this depth is 10 25 km shallower than in the nw indian himalaya and 5 10 km shallower than in central nepal requiring significant along strike variations in crustal thickness the observed thickness of subducted indian crust in garwhal is 20 28 km

palaeomagnetic and 210pb estimates of sedimentation in lake turkana east africa abstract sediment cores from lake turkana preserve a record of the historical geomagnetic secular variation in this part of east africa and therefore can be used to estimate sedimentation rates within the lake the results are supported by estimates based on 210pb measurements in several cores and annual lamination counts in one core and indicate a very high sedimentation rate about 1 cm yr 1 0 2 g cm 2 yr 1 during the last few hundred years a single radiocarbon age from near the base of a 12 m core from the south basin gives an average sedimentation rate of 0 19 cm yr 1 over the last 5600 years we conclude that the present lake and drainage pattern are very young the present day flow of the omo river into the lake is not a permanent feature of the basin and that a high lake level postulated at around 3500 years ago is unlikely though not ruled out the very rapid accumulation rate of sediment and burial of interstitial water in lake turkana provides an excellent opportunity to study the geochemistry of closed basin lake evolution

detailed configuration of the underthrusting indian lithosphere beneath western tibet revealed by receiver function images we analyze the teleseismic waveform data recorded by 42 temporary stations from the y2 and antilope 1 arrays using the p and s receiver function techniques to investigate the lithospheric structure beneath western tibet the moho is reliably identified as a prominent feature at depths of 55 82 km in the stacked traces and in depth migrated images it has a concave shape and reaches the deepest location at about 80 km north of the indus yarlung suture iys an intra crustal discontinuity is observed at 55 km depth below the southern lhasa terrane which could represent the upper border of the eclogitized underthrusting indian lower crust underthrusting of the indian crust has been widely observed beneath the lhasa terrane and correlates well with the bouguer gravity low suggesting that the gravity anomalies in the lhasa terrane are induced by topography of the moho at 20 km depth a mid crustal low velocity zone lvz is observed beneath the tethyan himalaya and southern lhasa terrane suggesting a layer of partial melts that decouples the thrust fold deformation of the upper crust from the shortening and underthrusting in the lower crust the sp conversions at the lithosphere asthenosphere boundary lab can be recognized at depths of 130 200 km showing that the indian lithospheric mantle is underthrusting with a ramp flat shape beneath southern tibet and probably is detached from the lower crust immediately under the iys our observations reconstruct the configuration of the underthrusting indian lithosphere and indicate significant along strike variations

late quaternary paleomagnetic record of the goderich basin lake huron paleomagnetic analysis of two cores taken of the late quaternary sequence of the goderich basin lake huron resulted in high resolution declination inclination intensity of magnetization j magnetic susceptibility k and q ratio j k curves there was a consistent relative relationship of the features along the curves of all five parameters for both cores studied which confirms the reproducibility of the method and suggests that paleomagnetic curves can be used for time parallel correlation of the late quaternary sequence of the goderich basin

structural evolution of orogenic wedges interplay between erosion and weak decollements orogenic wedges commonly display an inner wedge where crystalline units have been exhumed and an outer wedge formed by imbricated sedimentary units detached from the basement analog experiments have shown that similar structures can emerge naturally in the presence of weak decollements due to the interplay between erosion and deformation in this study we further investigate this hypothesis using two dimensional visco elasto plastic numerical models our experiments assume a basal and an intermediate decollement within the wedge experiments with a frictional strength of the basal decollement lower or equal to that of the intermediate decollement show a structural evolution of fold and thrust belts dominated by out of sequence thrusting conversely when the intermediate decollement is weaker than the basal decollement distinct outer and inner wedges are formed this process leads to episodic migration of midcrustal ramps tectonic underplating and antiformal stacking facilitated by erosion comparison between our models and the himalayan wedge suggests a low effective friction 0 10 which is probably due to dynamic weakening during large m8 himalayan earthquakes the deeper decollement along which the lower plate thrusts beneath the high himalaya must be a thermally activated ductile shear zone with an apparent friction of 0 18 fold and thrust belts worldwide exhibit various architectures in which different decollement levels might be activated thus our study provides a framework to help assess under which conditions a variety of structures observed in orogenic systems can arise

underplating in the himalaya tibet collision zone revealed by the hi climb experiment we studied the formation of the himalayan mountain range and the tibetan plateau by investigating their lithospheric structure using an 800 kilometer long densely spaced seismic array we have constructed an image of the crust and upper mantle beneath the himalayas and the southern tibetan plateau the image reveals in a continuous fashion the main himalayan thrust fault as it extends from a shallow depth under nepal to the mid crust under southern tibet indian crust can be traced to 31 n the crust mantle interface beneath tibet is anisotropic indicating shearing during its formation the dipping mantle fabric suggests that the indian mantle is subducting in a diffuse fashion along several evolving subparallel structures

estimating the return times of great himalayan earthquakes in eastern nepal evidence from the patu and bardibas strands of the main frontal thrust the return times of large himalayan earthquakes are poorly constrained despite historical devastation of cities along the mountain range definitive links between events and specific segments of the main frontal thrust mft are not established and paleoseismological records have not documented the occurrence of several similar events at the same location in east central nepal however recently discovered primary surface ruptures of that megathrust in the a d 1255 and 1934 earthquakes are associated with flights of tectonically uplifted terraces we present here a refined longer slip history of the mft s two overlapping strands patu and bardibas thrusts in that region based on updated geomorphic neotectonic mapping of active faulting two 1 3 km long shallow seismic profiles and logging of two river cut cliffs three paleoseismological trenches and several pits with constraints from 74 detrital charcoals and 14 cosmogenic nuclide ages the amount of hanging wall uplift on the patu thrust since 3650 450 years requires three more events than the two aforementioned the uplift rate 8 5 1 5mm yr thrust dip 25 5 n and apparent characteristic behavior imply 12 17 5m of slip per event on the bardibas thrust discrete pulses of colluvial deposition resulting from the coseismic growth of a flexural fold scarp suggest the occurrence of six or seven paleo earthquakes in the last 4500 50 years the coeval rupture of both strands during great himalayan earthquakes implies that in eastern nepal the late holocene return times of such earthquakes probably ranged between 750 140 and 870 350 years

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

testing the fidelity of sediment chronology comparison of varve and paleomagnetic results from holocene lake sediments from central finland abstract a careful construction of independent varve and paleomagnetic chronologies from three varved lake sediment records from central finland resulted in detailed and continuous age depth profiles cumulative varve calculation errors were estimated to be 3 for lake alimmainen savijarvi 10 295 340 varve years and 1 for lakes nautajarvi 9898 97 varve years and korttajarvi 9590 103 varve years paleomagnetic secular variation psv curves demonstrate good consistency between these sites and within a margin of varve chronology error they show similar declination and inclination features commonly described in the uk and sweden the timing of psv patterns from finnish varved sites agree well with uk curves between the present and 2000 bc and in pre 6000 bc deposits and with swedish data between the present and 5000 bc combined inclination records from three independently dated finnish varved sites possess an opportunity for accurate paleomagnetic comparisons within the margin of varve chronology errors and throughout the last 10 000 years

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

lower edge of locked main himalayan thrust unzipped by the 2015 gorkha earthquake faults are unlocked by earthquakes analysis of seismic data from the 2015 nepal earthquake shows that only part of the main himalayan thrust fault was unzipped by the quake leaving much of the fault locked and ready to slip in a future event

medieval pulse of great earthquakes in the central himalaya viewing past activities on the frontal thrust the himalaya has experienced three great earthquakes during the last century1934 nepal bihar 1950 upper assam and arguably the 1905 kangra focus here is on the central himalayan segment between the 1905 and the 1934 ruptures where previous studies have identified a great earthquake between thirteenth and sixteenth centuries historical data suggest damaging earthquakes in a d 1255 1344 1505 1803 and 1833 although their sources and magnitudes remain debated we present new evidence for a great earthquake from a trench across the base of a 13m high scarp near ramnagar at the himalayan frontal thrust the section exposed four south verging fault strands and a backthrust offsetting a broad spectrum of lithounits including colluvial deposits age data suggest that the last great earthquake in the central himalaya most likely occurred between a d 1259 and 1433 while evidence for this rupture is unmistakable the stratigraphic clues imply an earlier event which can most tentatively be placed between a d 1050 and 1250 the postulated existence of this earlier event however requires further validation if the two earthquake scenario is realistic then the successive ruptures may have occurred in close intervals and were sourced on adjacent segments that overlapped at the trench site rupture s identified in the trench closely correlate with two damaging earthquakes of 1255 and 1344 reported from nepal the present study suggests that the frontal thrust in central himalaya may have remained seismically inactive during the last similar to 700years considering this long elapsed time a great earthquake may be due in the region

palaeomagnetic investigations on lake sediments from ne china a new record of geomagnetic secular variations for the last 37 ka summary detailed palaeomagnetic investigations were carried out on two 23 m long sediment cores from erlongwan maar lake ne china the sediment composition of both cores is nearly identical based on a macroscopical inspection of the cores 410 graded layers intercalated into the laminated sediments were identified measurements of the anisotropy of the magnetic susceptibility revealed that these layers have not disturbed the sediment structure in general but only in intervals where their thicknesses exceeds 50 cm the age model for erlongwan is based on 15 ams 14c datings on bulk sediment showing that the sediment profile spans the last 37 ka cal bp although one of the sediment cores has been slightly deformed during core recovery similar inclination and declination records could be obtained by standard palaeomagnetic methods the stacked inclination and declination records show both variations similar to those known from palaeosecular variation records from eastern china and japan therefore the presented study is a contribution to the ongoing process of compiling a psv mastercurve for east asia

when and where did india and asia collide timing of the collision between india and asia is the key boundary condition in all models for the evolution of the himalaya tibetan orogenic system thus it profoundly affects the interpretation of the rates of a multitude of associated geological processes ranging from tibetan plateau uplift through continental extrusion across eastern asia as well as our understanding of global climate change during the cenozoic although an abrupt slowdown in the rate of convergence between india and asia around 55 ma is widely regarded as indicating the beginning of the collision most of the effects attributed to this major tectonic episode do not occur until more than 20 ma later refined estimates of the relative positions of india and asia indicate that they were not close enough to one another to have collided at 55 ma on the basis of new field evidence from tibet and a reassessment of published data we suggest that continent continent collision began around the eocene oligocene boundary 34 ma and propose an alternative explanation for events at 55 ma

very high resolution paleosecular variation record for the last 1200 years from the aral sea 1 a record of geomagnetic paleosecular variation psv spanning the last 1200 years has been obtained from two lacustrine sediment cores from the north part of aral sea kazakhstan magnetic susceptibility and nrm intensity have been used for correlating between cores and reconstructing composite core data the main swings and fine details of declination and inclination records correlate well between both cores a very high sedimentation rate up to 25 mm per year due to recent tectonic activity of the region provides a very high resolution psv record for the interval from 450 100 years bp to 655 65 years bp the results which have been dated by eight ams radiocarbon age determinations suggest that a 200 400 years secular variation period with amplitudes in declination and inclination up to 10 15 existed regularly during the time interval 0 1200 bp amplitudes of the psv record from aral sea are not reduced and smoothed by postdetrital magnetization processes they adjoin to the historical data model and are considered to represent a reliable paleosecular variation record for the aral sea region for the last 1200 years

rupture process of the mw 7 9 2015 gorkha earthquake nepal insights into himalayan megathrust segmentation we investigate the rupture process of the 25 april 2015 gorkha earthquake mw 7 9 using a kinematic joint inversion of teleseismic waves strong motion data high rate gps static gps and synthetic aperture radar sar data the rupture is found to be simple in terms of coseismic slip and even more in terms of rupture velocity as both inversion results and a complementing back projection analysis show that the main slip patch broke unilaterally at a steady velocity of 3 1 3 3 km s this feature likely contributes to the moderate peak ground acceleration 0 2 g observed in kathmandu the 15 km deep rupture occurs along the base of the coupled portion of the main himalayan thrust and does not break the area ranging from kathmandu to the front the limitation in length and width of the rupture cannot be identified in the preearthquake interseismic coupling distribution and is therefore discussed in light of the structural architecture of the megathrust

tectonic evolution of the himalayan thrust belt in western nepal implications for channel flow models we present a new geologic map of western nepal and three balanced regional cross sections in the himalayan thrust belt the minimum shortening between the south tibetan detachment and the main frontal thrust is 485 743 km and suggests that total himalayan shortening may exceed 900 km all rocks involved in the thrust belt are of upper crustal affinity implying that a comparable length of indian lower crust and mantle lithosphere was subducted beneath tibet major structural features are the subhimalayan thrust system lesser himalayan imbricate zone dadeldhura thrust sheet lesser himalayan duplex ramgarh thrust sheet main central thrust sheet and a north dipping normal sense shear zone possibly related to the south tibetan detachment these structures are continuous along the entire nepalese portion of the himalayan thrust belt new 40 ar 39 ar ages from the ramgarh thrust zone greater himalayan rocks and the lower part of the tethyan sequence support a kinematic model in which major thrust systems in nepal propagated southward from early miocene time onward the geometry and kinematic history of the thrust belt in western nepal are not compatible with recent models for southward ductile extrusion of greater himalayan rocks in a mid crustal channel instead the thrust belt in western nepal behaved like a typical forward propagating thrust system involving unmetamorphosed brittlely deformed rocks in its frontal part and ductilely deformed higher grade metamorphic rocks in its hinterland region although our results do not support published versions of the channel flow model they provide additional geological and geo chronological data that will assist future attempts to develop geodynamic models for the himalayan tibetan orogenic system

paleointensity studies on holocene pleistocene sediments from lake escondido argentina abstract relative changes in geomagnetic field intensity over the last 16 000 years bp were recovered from the study of four cores obtained from lake escondido south argentina rock magnetic analysis shows that the main magnetic mineral is magnetite the concentrations being mainly between 0 01 and 0 1 and the grain size between 1 and 8 m in order to fulfil the criteria for assessing the reliability of paleointensity data derived from sediments rev geophys 31 1993 319 the samples whose concentrations and size are beyond this range were rejected the remanent magnetisation at 20 mt nrm20 mt was normalised using the anhysteric remanent magnetisation arm100 mt the saturation of the isothermal remanent magnetisation sirm and the low field magnetic susceptibility k coherence function analysis indicates that the records are not significantly affected by local environmental conditions this suggests that the variations in normalised remanence are mostly likely due to geomagnetic paleointensity fluctuations arm100 mt is the best normaliser for the lake escondido sediments the record of relative paleointensity nrm20 mt arm100 mt shows peaks and troughs whose amplitudes are similar to those in the st lawrence estuary lake baikal lake pepin and larsen a ice shelf data set and a stack of archeomagnetic data given as virtual axial dipole moment vadm

the underthrusting indian crust and its role in collision dynamics of the eastern himalaya in bhutan insights from receiver function imaging most of the convergence rate between the indian and eurasian plate is assumed to be absorbed along a major basal thrust beneath the himalaya the main himalayan thrust mht deformation along this basal thrust in combination with frontal accretion results in the formation of the upper crustal fold thrust belt the role of the underthrusting indian crust and its impact on the long term growth of the himalaya are only poorly understood partly due to the lack of high resolution seismic images of the crust to improve the imaging of lithospheric structures we developed an 3 d migration scheme for receiver functions using seismic data from the temporary gansser network in bhutan extending the 2 d high frequency ray approximation and common conversion point stacking to 3 d including linear phase weighting and a quality assessment we reveal significant along strike differences in the lithospheric structure beneath bhutan in western bhutan the moho geometry shows an increased dip south of the higher himalaya reaching almost 70 km depth thereafter whereas in eastern bhutan the moho is almost subhorizontal at 50 km depth across our network the appearance of distinct listric structures beneath the mht indicates intra crustal deformation up to crustal imbrication down to the lower crust we propose that these variations in the crustal thickness and in intra crustal structures influence the upper crustal kinematics of the bhutan himalayan orogeny and are primarily driven by an indian mantle slab northwest of bhutan and its absence northeast of bhutan