new absolute time scale for the quaternary climate in the chinese loess region by grain size analysis continuous loess sequences in china provide not only information for paleoclimatic reconstructions but also permit the establishment of a reliable absolute time scale for the quaternary an empirical relationship is developed between the grain size of the loess and the sedimentation rate in a short well dated reference section step 1 this relationship is extrapolated to the complete quaternary section step 2 after derivation of the sedimentation rate by measuring the grain size in all the layers of the sequence the duration of deposition of each layer is obtained by dividing thickness by sedimentation rate and subsequently the age of each point in the sequence is calculated by adding together all the duration values of the overlying layers the chronology of the extrapolated part of the section obtained in this way is independent of dates provided by other methods and may also be checked by them

reverse and normal drag along a fault an analysis of the theoretical displacement field around a single dip slip fault at depth reveals that normal and reverse fault drag develop by perturbation flow induced by fault slip we analytically model the heterogeneous part of the instantaneous displacement field of an isolated two dimensional mode ii fault in an infinite homogeneous elastic body in response to fault slip material on both sides of the fault is displaced and opposing circulation cells arise on opposite sides of the fault with displacement magnitudes increasing towards the center of the fault both normal and reverse drag can develop at the fault center depending on the angle between the markers and the fault normal drag develops there for low angles 30 408 and reverse drag for higher angles a comparison of the theoretical results with published models and natural examples reveals that the characteristics of normal and reverse fault drag are largely insensitive to the scale and rheology of the faulted rocks and that drag forces generated by frictional resistance need not be the primary cause of fault drag fault drag has some interesting geometric implications for normal and reverse fault terminology emphasizing the importance for discrimination of vertical separation and throw furthermore our results lead us to propose an alternative model for the formation of rollover anticlines above normal faults

high resolution fault displacement mapping from three dimensional seismic data evidence for dip linkage during fault growth abstract detailed mapping using high resolution three dimensional seismic data has revealed a number of sub horizontal anomalies in the distribution of vertical displacement throw on the planes of growth faults in the gulf of mexico recognition of these anomalies is highly sensitive to the interval at which the fault displacements are sampled because they represent local decreases in throw which are confined to small discrete parts of the fault planes the distribution of the anomalies is inconsistent with model displacement fields of quasi elliptical concentric contours and is therefore incompatible with models of fault growth by uniform slip distribution and radial tip line propagation an alternative model is proposed whereby the evolution of a fault plane is established by the propagation and linkage of precursor fault segments in the dip direction dip linkage overlap and linkage of fault tips in the dip direction results in relay structures that are sub parallel to fault strike and therefore displacement minima that are sub horizontal on normal and thrust faults however since they are orthogonal to the main slip direction on the fault these structures have a low preservation potential and are therefore unlikely to be well resolved on cross sectional seismic profiles

chronology and dynamics of a large silicic magmatic system central taupo volcanic zone new zealand the central taupo volcanic zone in new zealand is a region of intense quaternary silicic volcanism accompanying rapid extension of continental crust at least 34 caldera forming ignimbrite eruptions have produced a complex sequence of relatively short lived nested and or overlapping volcanic centers over 1 6 m y silicic volcanism at taupo is similar to the yellowstone system in size longevity thermal flux and magma output rate however taupo contrasts with yellowstone in the exceptionally high frequency but small size of caldera forming eruptions this contrast reflects the thin rifted nature of the crust which precludes the development of long term magmatic cycles at taupo 11 refs 4 figs 1 tab

five thousand years of surface ruptures on the wellington fault new zealand implications for recurrence and fault segmentation new paleoseismic studies have been undertaken on the wellington hutt valley w hv segment of the wellington fault to characterize its late holocene record of surface rupturing earthquakes trenches and radiocarbon dates from te kopahou and te marua have provided evidence and improved timing for the four most recent earthquake ruptures these events have been recognized on the basis of upward terminating faults coseismic deposition progressive displacement and faulting of colluviums at te kopahou colluvial and scree deposition resulting from surface rupture and strong earthquake shaking buries old ground surfaces associated with peat and or soil development at te marua the timing of the two youngest events has been refined by bracketing the ages of the youngest faulted and unfaulted alluvial terraces of the hutt river assuming that the w hv segment acts as a rupture segment along its length the approximate timings of these faulting events is as follows the most recent faulting event event i occurred between 110 and 310 cal yr b p a d 1640 1840 the penultimate faulting event event ii between 790 and 930 cal yr b p event iii occurred between 1835 and 2340 cal yr b p and event iv between 2460 and 4900 yr b p the minimum and maximum earthquake recurrence intervals derived from the four youngest events are 715 and 1575 yr respectively with a median value of 1145 yr revisions of the earthquake timing recurrence interval data and recently the single event displacement and slip rate collectively reduce the seismic hazard for the w hv segment of the wellington fault a four event paleoearthquake record from the pahiatua section of the wellington fault is statistically similar to that from the w hv segment this has significant implications with respect to the rupture length and magnitude or clustering of future surface rupturing earthquakes on the wellington fault

influence of rift obliquity on fault population systematics results of experimental clay models abstract we use clay models to simulate how fault population systematics vary as a function of rift obliquity rift obliquity is related to the acute angle between the rift trend and the displacement direction so that the value of is inverse to the degree of obliquity the range of azimuths in a fault population increases as rift obliquity increases i e as decreases the length of the longest faults the sum of fault lengths and the width of the deformed zone all increase as rift obliquity decreases i e as increases the majority of faults in our models are segmented and have highly tortuous traces tortuosity is maximum when 30 as segments of widely varying azimuth link during fault growth significant changes occur in the fault patterns between 30 and 45 at 30 two fault populations of equal importance develop in the center of the rift zone one approximately rift parallel and the other displacement normal between 30 and 45 the number of faults more than doubles and between 45 and 60 summed fault length more than doubles fault patterns for all models are fractal with fractal dimensions that increase with increasing and that are comparable to those found in the field fault populations are not multi fractal because the cumulative frequency distributions of fault lengths do not generally follow a power law relationship an exponential distribution best describes the data for whole faults with the characteristic length increasing with increasing segment lengths also follow an exponential distribution with characteristic length varying very little with the fault patterns in our models resemble the spatial pattern of brittle deformation observed at oblique mid ocean ridge segments and are similar in geometry to those in oblique continental rift basins at the rift margins tensional stresses are modulated and reoriented by a secondary stress field related to a change in boundary conditions resulting in the formation of two distinct sub populations of faults during oblique rifting

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

oblique slip deformation in extensional terrains a case study of the lakes tanganyika and malawi rift zones the east african rift system ear is the archetypal continental rift and a widely proposed analogue for the early stages of evolution of passive continental margins the three dimensional structure of parts of the ear has been recently elucidated by a multifold seismic mfs survey of lakes tanganyika and malawi project probe analysis of fault geometries displayed on the probe mfs data coupled with the more extensive 28 khz echosounder data has improved understanding of the geometry and kinematics of the linked fault systems that underlie the lakes in particular it has been recognized that profiles across i e at high angles to the rift elongation commonly display fault geometries that are not readily retrodeformable there must therefore be significant displacement out of the plane of what would conventionally be regarded as dip lines that is perpendicular to rift elongation and parallel to the tectonic transport or extension direction careful determination of fault plane dip and the dip of synrift reflectors in the hanging wall demonstrates that the dip directions of the shallowest faults and the steepest hanging wall sediment dips are oriented either nw or se this defines the direction of maximum fault block rotation and therefore the direction of extension or tectonic transport as nw se oblique to the trend of the regional rift axis and to the apparent strike of many of the major border faults in the survey area the border faults and many other faults imaged on the probe mfs data must therefore have significant components of strike slip motion and the tanganyika and malawi rift zones have undergone extension oblique to and not perpendicular to their axes near dip slip normal faults steeply dipping oblique slip faults and subvertical strike slip or transfer faults have all been recognized in a complex linked fault system that accomplishes the extension the overall orientation of the rift lakes and their internal segmentation are influenced by major preexisting subvertical fault zones within the basement complex accommodation zones act principally as transfer zones that allow switches in gross polarity of the border fault system the detailed geometries of the accommodation zones result from the specific relations between juxtaposed half graben and the strike and internal geometry of the influencing basement structure the variations in fault geometry subsidence water depth and basin or rift morphology can be better explained by an oblique slip extensional model influenced by basement structures than by a simple orthogonal extensional model

loess stratigraphy in central china abstract loess sequences in central china provide a detailed record of climate changes during the last 2 5 million years at least 44 major shifts from glacial to interglacial conditions occurred during this time in china prolonged loess deposition lasting more than 40 millennia occurred eleven times with only four of these intervals in brunhes chron the climate oscillations took place with increased frequency between 2 4 and 0 5 ma compared to the last half million years major shifts toward cooler and drier climates occurred at about 2 4 ma 1 2 ma and 0 5 ma while less pronounced shifts are dated to 1 65 ma 0 8 ma and 0 2 ma three of the last four reversals of the earth s magnetic field whose lithostratigraphic position has been detail are recorded in a glacial deposit the low field magnetic susceptibility of loess and soils which reflects the concentration of ultrafine magnetite is related to the degree of pedogenesis and serves as a proxy measure of climate the accumulation rate of the magnetite was fairly constant throughout the last 1 2 million years and can serve as a measure of time susceptibility records from localities near xifeng and luochuan located 160 km apart are compared and used to define informal lithostratigraphic units in the loess plateau of china

stacked 2 6 ma grain size record from the chinese loess based on five sections and correlation with the deep sea δ18o record 1 this study aims to establish a stacked climate record of the quaternary period from the chinese loess sequence and to address the forcing mechanisms for the regional climate history of the loess plateau by correlating the stacked record with a composite 18o record in deep sea sediments a total of 18 352 samples were obtained from five loess sections located at baoji lingtai jingchuan puxian and pingliang in the southern and middle loess plateau these yielded high resolution grain size records between section correlation of these shows that although small depositional hiatuses are present in places within a single section most parts of the sections display near continuous dust deposition throughout the quaternary the grain size records were tuned simultaneously to the theoretical variations in obliquity and precession of the earth s orbit the grain size records plotted on their orbital timescales were then averaged to form a stacked loess grain size time series termed the chiloparts record this resolves most of the orbital timescale paleoclimate events buried in the loess soil sequences of the southern and middle loess plateau and can be used as a regional archive of the pleistocene climate history in the loess plateau comparison of the chiloparts record with a composite marine 18o record shows that for the past 1 8 ma the loess paleosol record can be correlated almost cycle by cycle with the marine record several discrepancies in the climatic events between the two records have also been identified implying that regional forcing mechanisms may have played a part in the climatic evolution of the chinese loess plateau

quaternary environmental change in equatorial regions with particular reference to vegetation history a bibliography abstract it was thought for a long time that equatorial regions had remained virtually unchanged at least since the tertiary period it is only from the late tertiary that we can talk of the present disposition of land and sea about the equator our teaching has supposed that these regions were the hearth from which general spread to the remainder of the planet s surface by gradual adaptation and speciation this warm humid zone has been seen as a refuge for species unable to maintain temperature ranges in the face of stresses and fluctuations to north and south the diversity of species in rain forest environments was assumed to reflect their essential stability so indeed it may but not in quite the manner supposed originally by ecologists the variety of species present in the various regions of rain forest are greatly different with african exhibiting a relatively poor list compared with south america this as it turns out may well be a function of disturbance during the last 25 years and gathering momentum within the last decade a variety of studies have demonstrated that the concept of equatorial biological stasis is no longer tenable evidence for equatorial environmental changes is derived from theoretical as well as empirical studies regarding the former various attempts have been made to model the earth s atmosphere at different periods of the pleistocene and there is now fairly good agreement about the consequences for equatorial regions of a general global cooling namely a critical drying at lower elevations the empirical evidence is derived on the one hand from stratigraphic studies of peats and lake muds and also the analysis of ocean cores it is also derived from studies of the geographical ranges of plant and animal species

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

grain size of loess palaeosol and red clay deposits on the chinese loess plateau significance for understanding pedogenic alteration and palaeomonsoon evolution abstract to assess pedogenic modification to grain size distributions of loess palaeosol and red clay deposits on the chinese loess plateau and to understand long term evolution of the east asian palaeomonsoon since the late miocene we investigate a continuous loess palaeosol red clay sequence at lingtai south chinese loess plateau and another parallel red clay sequence at zhaojiachuan central chinese loess plateau by analyzing the grain size distributions of bulk samples and chemically isolated quartz samples the relative intensity of pedogenic alteration of the loess palaeosol and red clay deposits can be quantified comparisons of the grain size distributions and contents of different grain size fractions between the bulk and the quartz samples suggest that pedogenic alteration is apparently stronger in the red clay sequence than in the overlying loess palaeosol deposits furthermore grain size parameters derived from the bulk and the quartz samples such as mean grain size coarse fraction content and u ratio exhibit similar variations in the loess palaeosol sequence quaternary 0 2 6 ma whereas these grain size parameters of quartz samples show different variability from those of bulk samples in the red clay sequence late miocene to pliocene 2 6 7 ma grain size of quartz from the loess palaeosol and red clay deposits exhibits distinct and persistent oscillations from the late miocene to the pleistocene implying that significant fluctuations of the palaeomonsoon climate in east asia might have occurred at least since late miocene time

focal mechanisms of large earthquakes in the north island of new zealand slip partitioning at an oblique active margin we have used body wave modelling to determine the source parameters of 22 moderate to large earthquakes that have occurred along the hikurangi subduction margin and elsewhere in the north island of new zealand since 1964 we have also included events from the harvard cmt catalogue since 1977 as that catalogue contains smaller events than can be modelled with body waves we have found that shallow earthquakes occurring in the back arc taupo volcanic zone and its extension to the north show predominantly normal faulting with nodal planes parallel to the regional fabric and t axes indicating extension in a direction in agreement with geodetic measurements a normal faulting solution for the 1974 opunake earthquake is compatible with the mapping of active faults in the offshore taranaki region and the initiation depth of 17 km is close to the expected brittle ductile transition for that area earthquakes within the subducted plate at the southwestern end of the margin are dominated by down dip tension that is rotated towards the deepest part of the subducting plate further north the events in the upper part of the wadati benioff zone 200 km show pure down dip tension while this association is less obvious for the deeper events suggesting that the aseismic part of the subducting slab inferred from plate reconstructions has reached the 670 km discontinuity normal faulting earthquakes associated with plate bending below the region of interplate contact occur along the length of the margin while shallow normal faulting events also occur in the trench indicating that some slab pull propagates to that region we infer that large interplate earthquakes are not imminent because in other similar areas they are preceded by outer rise compressional events that have not been recorded in the region in historical times slip vectors of interplate thrust earthquakes indicate that the oblique plate motion across the margin is fully partitioned that is the plate interface accommodates very little transcurrent motion which is instead accommodated by faults in the overlying australian plate extensional geodetic strain has been measured across the margin in the northeast which has been regarded as unusual in view of the plate convergence we suggest that the topography at this part of the margin is too steep to be supported by the current horizontal forces due to friction on the plate interface this may have occurred due to a reduction in friction because of the subduction of seamounts and the subsequent entrapment of sediments this also being consistent with the idea of underplating at this part of the margin or due to the subduction of less buoyant crust other margins such as japan and mid america where there is known to be subduction of sediments also show extension in the forearc compressional strain observed across the margin in the southwest is more usual for a convergent margin but it does not show the partitioning we see in focal mechanisms these data might only agree after the long term compressional strain accumulation has been averaged over a complete seismic cycle large historical and palaeo earthquakes have occurred along the length of the margin associated with deformation in both the axial and the coastal ranges in addition along the length of the margin the rate of recent interplate thrust activity is low compared to margins that have a high proportion of aseismic slip these factors indicate that the entire length of this margin is capable of producing large earthquakes

crustal seismic reflection measurements across the northern extension of the taupo volcanic zone north island new zealand abstract a crustal seismic reflection profile across the offshore taupo volcanic zone otvz has been reprocessed to improve the lower crust upper mantle image the otvz is underlain by several strong sub horizontal crustal reflections that may correspond to shear zones or mafic sills a reflector interpreted to correspond to moho lies at a depth of about 8 8 5 s twt seconds two way traveltime about 20 km under the western margin of the raukumara peninsula and rises to a depth of about 6 s twt about 16 km under the active eastern part of the otvz and can be traced at about this depth across most of the otvz underlying this inferred moho are two diffuse zones of discontinuous reflectivity one underlying the active eastern otvz and a less well defined one underlying the landward extension of the havre trough they extend from about 15 to 35 km depth within the mantle wedge and are inferred to be imaging a zone of depleted upper mantle associated with crustal extension a localised zone of deep 30 50 km reflectivity and seismicity occurs under the eastern otvz margin and may relate to fluid flow from the hikurangi plateau being subducted further east

faulting and extension rate over the last 20 000 years in the offshore whakatane graben new zealand continental shelf oblique rifting in the offshore taupo volcanic zone new zealand is expressed in widely distributed active normal faulting in the 20 km wide whakatane graben active faults are identified along seafloor scarps and displacements of the post last glacial transgressive ravinement surface 400 faults we derive an extension rate at seismogenic depths 6 10 km across the graben of 13 6 mm yr by summing surface measurements assuming an average crustal fault dip of 45 15o and correcting for the discrepancies between surface and deep crustal extension estimates structural and kinematic data implies an extension direction 20o oblique to the rift axis resulting in up to 4 6 2 1 mm yr of dextral motion parallel to the rift axis the strike slip motion is accommodated by dip slip displacements on oblique faults in the centre of the graben and oblique slip faulting along the rift margins pure dip slip in the graben centre represents 50 of the total slip with the rangitaiki fault accommodating 25 of the total extension in the graben

earthquake histories and holocene acceleration of fault displacement rates displacement rates for normal and reverse faults n 57 are generally higher when averaged for the holocene 10 ka than for the late quaternary 300 ka and longer time scales holocene acceleration of displacement rates could be attributed to geological processes that produce increases of tectonic tempo we propose an alternative model in which the observed rate changes arise from variability in earthquake slip and or recurrence coupled with a sampling bias toward those faults that are best represented at the earth s surface and that accrued displacement fastest during the holocene this model is consistent with displacement rates measured over time intervals of as long as 300 ka for 129 faults from the taupo rift new zealand departures of earthquake parameters and associated displacement rates from their long term 300 ka averages are attributed to fault interactions and occur on time intervals inversely related to these long term displacement rates and to regional strain rates

shallow structure and active tectonism of an offshore continental back arc spreading system the taupo volcanic zone new zealand the taupo volcanic zone tvz the predominant active volcano tectonic structure within the new zealand sub continent marks the zone of quaternary back arc spreading and calc alkaline volcanism associated with the convergence of the pacific and australian plates at the hikurangi plate boundary margin north island new zealand new bathymetric shallow seismic reflection magnetic anomaly and gloria data presented here accurately define for the first time the extent structure and tectonism of the poorly known offshore portion of the tvz these data show that nearly half of the entire ca 40 km wide tvz lies offshore extending northeast for some 150 km seaward to 36 45 s the southeastern and northwestern boundaries of the offshore tvz are significant tectonic and bathymetric features which comprise inward facing normal fault zone the white island and tauranga fault zones respectively three essentially parallel tectono morphological units are identified along the length of the offshore tvz they comprise from southeast to northwest a frontal non volcanic graben a volcanic ridge and a volcanic back arc graben the spatial position of these units with respect to the hikurangi subduction margin is not a simple arc and back arc relationship tectonism within the offshore tvz although pervasive increases from northwest to southeast so that the area of highest extension and subsidence of the non volcanic graben occurs in front of the volcanic ridge geophysical data also suggest the possible tectonic ablation of blocks of the forearc hinterland into the offshore tvz along its southeastern margin the southern havre trough and northern tvz are offset sinistrally by 45 50 km they overlap by 40 km and differ in orientation by ca 7 dextral displacement between these two extensional regimes is accomodated by a series of dextrally oblique and en echelon bookshelf faults the orientation of extensional structures within the offshore tvz is also dextrally oblique by 10 15 to the regional 030 trend of the bounding faults and agree with axes of maximum extension determined elsewhere from geodetic and seismological data

analogue modelling of orthogonal and oblique rifting abstract the three dimensional progressive development of orthogonal and oblique rift systems has been simulated using scaled analogue sandbox models the orientation of the zone of rifting where angle between the rift axis and the extension direction was varied systematically from 90 orthogonal rifting to 75 60 and 45 oblique rifting completed models were impregnated and sectioned both vertically and horizontally orthogonal rift models are characterized by long straight rift border faults and intra rift faults perpendicular to the extension direction oblique rift models are characterized by shorter segmented rift border faults and intrarift faults in the oblique models the rift border faults formed en echelon arrays parallel to the inderlying zone of basement stretching whereas the intra rift faults formed at a high angle to the extension vector increased extension in the moderately oblique and oblique rift systems 60 and 45 caused the intra rift faults to rotate towards parallelism with the rift border faults no strike slip or oblique slip transfer faults were found in any experiments rift border faults and intra rift faults in the models are segmented along strike with relay ramp structures formed between overlapping fault tips along the strike of the rift variations in half graben polarities and offsets of depocentres are accomplished by accommodation zones formed by interlocking conjugate fault arrays the experimental fault patterns compare well with the fault architectures found in those modern or relatively young rift systems where well defined basement controlled strike slip or oblique slip transfer faults are absent an accommodation zone model consisting of interlocking conjugate extension faults is proposed for the along strike switching of half graben asymmetries and offsetting of depocentres in rift systems the fault geometries in the analogue models can be used as templates for recognition of fault styles in both orthogonal and in oblique rift environments

three dimensional velocity structure of the northern hikurangi margin raukumara new zealand implications for the growth of continental crust by subduction erosion and tectonic underplating traveltimes between shots from nine marine seismic reflection lines and nine onshore recorders were used to construct a 3 d p wave velocity model of the northern hikurangi subduction margin new zealand from north to south between raukumara basin and raukumara peninsula the moho of the overriding plate increases in depth from 17 to similar to 35 km low seismic p wave velocities of 3 5 5 0 km s are localized within a similar to 10 km thick prism in the lower crust of the overriding plate immediately updip of the intersection between the subduction thrust and moho and beneath the topographic crest of east cape ridge and the raukumara range southward this region of low seismic velocities and surface uplift increases in distance from the trench as the thickness of the crust in the overriding plate increases we interpret this low velocity volume to be underplated sedimentary rocks and crustal materials that were tectonically eroded by subduction beneath the trench slope the buoyancy and low strength of these subducted materials are proposed to assist the escape from a subduction channel near the base of the crust and drive local rock uplift in the middle crust our observations of very low velocity suggest high fluid filled porosities of 12 18 and the implied buoyancy anomaly may enhance underplating at greater depths the process is driven by the contrast between upper crustal quartz feldspar mineralogy and the denser diabase or olivine rich lithologies of the lower crust and mantle we estimate a rate of lower crustal underplating at the northern hikurangi margin of 20 7 km 3 ma 1 km 1 since 22 ma we suggest that underplating provides an efficient means of accreting subducted sediment and tectonically eroded material to the lower crust and that the flux of forearc crustal rocks into the mantle at subduction zones may be systematically overestimated

active normal faulting and crustal extension a world wide review of fault plane solutions and focal depths for large normal faulting earthquakes on the continents shows that the overwhelming majority of such earthquakes nucleate in the depth range 6 15 km on faults dipping between 30 and 60 in the few cases where levelling or seismic data are good enough these normal faults are shown to be approximately planar from the surface to their nucleation depth at the base of the brittle crust there is evidence that in some cases as a result of the enormous transitory increase in strain rate during large earthquakes rupture continues into the normally ductile lower crust on surfaces with substantially gentler dips these low angle surfaces may be analogous to some of the detachments seen in metamorphic core complexes of the western usa but the nature of the motion on them depends on strain rate as well as on rheological contrasts between the detachments and the blocks on either side such contrasts however are unlikely to introduce substantial curvature to an originally planar shear zone if the observed spread in active normal fault dips is caused by rotation of the faults and the blocks they bound during extension then a maximum value of 1 7 can be accommodated by seismic activity on a single generation of normal faults with continued extension either a new generation of steeper faults cutting the rotated first faults is likely to form or the deformation will continue aseismically on faults dipping at less than 30 large earthquakes have not been observed to nucleate on very low angle 20 normal faults within the continental crust anywhere in the world such faults can of course move aseismically but are unlikely to do so on a large scale within the upper crust in areas where steep normal faults are seismically active thus extensional models that require concentrated simple shear on large sub horizontal faults within the brittle upper crust will also require a spatial separation between aseismic very low angle faulting and seismic highangle faulting since seismogenic high angle faults dominate the topography of extending regions upper crustal very low angle faulting if it occurs on a large scale presumably does so in areas that are relatively fiat

strong seismic reflections and melts in the mantle of a continental back arc basin 1 a program of explosion seismology in central north island new zealand discovered a strong reflector within the upper mantle reflections from this pmp2 are spatially confined to come from an interface 35 km deep and directly beneath a 40 km wide back arc extension zone with active volcanism high heat flow low pn wave speeds and thinned crust on the basis of relative reflection amplitudes the mantle reflections are most readily explained by an interface with a negative seismic impedance contrast a satisfactory fit is obtained for a layer with a 40 90 drop in s wave speed vs compared to the surrounding mantle we interpret this layer to be a 40 km wide reservoir of partial melt pooled at a thermal boundary layer within the upper mantle

active normal faulting along the mt morrone south western slopes central apennines italy in the present work we analyse one of the active normal faults affecting the central apennines i e the mt morrone normal fault system this tectonic structure which comprises two parallel nw se trending fault segments is considered as potentially responsible for earthquakes of magnitude 6 5 and its last activation probably occurred during the second century ad structural observations performed along the fault planes have allowed to define the mainly normal kinematics of the tectonic structure fitting an approximately n 20 trending extensional deformation geological and geomorphological investigations performed along the whole mt morrone south western slopes permitted us to identify the displacement of alluvial fans attributed to middle and late pleistocene by means of tephro stratigraphic analyses and geomorphological correlations with dated lacustrine sequences along the western fault branch this allowed to evaluate in 0 4 0 07 mm year the slip rate of this segment on the other hand the lack of synchronous landforms and or deposits that can be correlated across the eastern fault segment prevented the definition of the slip rate related to this fault branch nevertheless basing on a critical review of the available literature dealing with normal fault systems evolution we hypothesised a total slip rate of the fault system in the range of 0 4 0 07 to 0 8 0 09 mm year moreover basing on the length at surface of the mt morrone fault system i e 22 23 km we estimated the maximum expected magnitude of an earthquake that might originate along this tectonic structure in the order of 6 6 6 7

crust mantle structure of the central north island new zealand based on seismological observations abstract two geophysical features characterise the anomalous crust mantle structure beneath central north island of new zealand the apparent thinning of the felsic crust by a factor of at least 50 and upper mantle p wave velocities pn phase about 10 less than normal 7 3 7 4 km s pn velocities increase slowly to a maximum of 7 8 km s at a depth of about 80 100 km above a depth of 15 km seismic p wave velocities vp are 6 km s or less representing what is likely to be a mix of the original greywacke crust that has been stretched along with an unknown volume of intruded igneous rocks that are in various stages of cooling defining the moho is problematic in this dynamic region below a depth of 15 km there is a continuous increase in vp such that velocities 7 km s are reached at a depth as shallow as 20 km on a east west line and 7 4 km s on a north south line we interpret these wave speeds as a transition zone into low pn velocities rather than high lower crustal values of vp pn wave speeds as low as 7 4 km s are detected by tomographic methods to depths of at least 65 km and laterally over an area of at least 10 000 km2 a 1 4 partial melt in the mantle wedge beneath the central north island is estimated based on qp seismic anisotropy low values of pn and amplitudes of deep reflections these upper mantle features are more indicative of asthenosphere than lithosphere and coupled with the geological evidence for rapid uplift here at 5 ma are consistent with convective removal of the mantle lithosphere from western and central north island in late miocene times

fault scaling relationships deformation rates and seismic hazards an example from the lazio abruzzo apennines central italy abstract spatial variations in the number of seismic shaking events in a given time period frequency implied by measured throw rates associated with active normal faults in central italy are investigated through comparison with models of fault growth and the historical record of earthquake shaking for the region measured offsets of 18 ka glacial features provide a throw rate database averaged over a time period much longer than the reliable portion of the historical earthquake record for the region

extensional hard linkages eastern gulf of suez egypt the araba abu durba area on the eastern margin of the gulf of suez exhibits two superb outcrop examples of extensional hard linkages in a rift basin here three large domino style basement cored northeast dipping fault blocks are formed by a series of major northwest trending normal faults these are offset by two north northeast trending sinistral oblique slip transfer faults that terminate in horsetail normal fault splays the transfer faults do not extend across the entire rift basin detailed mapping and structural analysis show that they developed by breakage of initial low strain relay ramps along reactivated north northeast trending basement fabrics between overlapping northwest trending normal fault segments paleostrain analysis of fault slip indicators shows that both the normal and the sinistral oblique slip transfer faults were formed synchronously in response to northeast southwest extension perpendicular to the main northwest rift trend

inner forearc sequence architecture in response to climatic and tectonic forcing since 150 ka hawke s bay new zealand the influence of eustasy tectonic deformation and sediment flux as controlling parameters on basin stratigraphy and depositional sequence development are largely accepted eustasy is usually considered as the dominant mechanism of sequence generation especially for pleistocene successions in active subduction margin settings the high rates of tectonic deformation are expected to have a stronger influence on basin fill architecture while sediment flux is generally less well constrained and therefore less frequently considered the active hikurangi subduction margin in new zealand offers the opportunity to quantitatively assess the relative roles of tectonic climatic and eustatic drivers we present a quantitative source to sink like study of the late pleistocene succession from the hawke s bay sector of the inner forearc domain c 150 ka to present the interpretation of a grid of high resolution marine seismic data onland and offshore core and well descriptions and the integration of geomorphic studies enabled identification of system tracts in turn these comprise two sea level cycle depositional sequences lps1 and lps2 including one complete 100 ka sequence lps1 isopach maps of both sequences reveal changes in sediment distribution and preservation that reflect the relative roles of tectonic deformation and eustasy eustasy dominates development of sequence architecture at relatively short time scales i e 100 kyrs four long lasting depocenters are identified over the inner forearc domain and located in four subsiding basins kidnappers mahia lachlan and motu o kura basins significant shifts of the depocenter location in the basins are correlated with eustatic sea level changes estimates of sediment volumes and masses from isopach maps indicate higher mass accumulation rates during climato eustatic extremes which we correlated to the onland erosional response sediment distribution and landscape evolution are strongly influenced by the interaction of the structural deformation and sediment flux we present paleogeographic reconstructions for the inner forearc domain coincident with two paleoclimatic extremes last glacial maximum and holocene optimum these illustrate the importance of eustatic changes structural deformation and sediment flux on the pattern of sediment distribution accumulation and sequence architecture

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

submergent shorelines in the sw pacific evidence for an episodic post glacial transgression high resolution seismic profiles supported where possible by radiocarbon dates and regional stratigraphic data indicate that the last post glacial transgression in the sw pacific was episodic comprising major stillstands punctuated by rapid rises in sea level on the terrigenous continental shelf east of south island new zealand a succession of shorelines s8 s1 are recognized as follows s8 c 113 m 18 000 yr bp s7 c 88 m 17 000 yr bp s6 c 75 m 15 000 yr bp s5 c 56 m 12 000 yr bp s4 c 46 m 11 000 yr bp s3 c 28 m 9 500 yr bp s3a c 24 m 9 000yr bp s2 c 9 m 7 500yr s1 0 m 6 500yr bp with the exception of s8 and possibly s2 the shorelines are associated with wedges of sediment the size and presence of which imply that 1 sea level stabilized at some shorelines for a considerable period of time up to i 2 000 yr and 2 the intervening rises of sea level estimated to have been at least 10 12 m lo3 yr were too rapid to allow the reworking of the wedges into a transgressive sediment sheet as favoured in some current models on the great barrier reef shelf off queensland australia shorelines s8 sl have also been recognized with a further shoreline feature s4a occurring at c 39 m shorelines sla 0 m o yr bp slb 2 3 m 6 000 yr bp and slc 0 m 6 500 yr bp are recognized as discrete aspects of the post 6 500 yr bp sea level behaviour in north eastern australia the rapid rise in sea level at least between shorelines s5 12 000 yr bp and 53 9 500 yr bp is known to have outpaced reef growth causing in situ drowning of reefs located along the deeper shorelines all modern reefs so far drilled and dated began their development at or above s3 28 m 9 500 yr bp some of the shorelines particularly s5 appear to correlate between the northern and southern hemispheres on the basis of age succession and general depth of occurrence suggesting 1 that they may be global features controlled by the post glacial pattern of ice sheet decay and 2 that hydro isostatic adjustment may exert only a minor control on the depth of particular shorelines at least during the earlieg parts of the post glacial transgression

paleoenvironmental implications of fixed dune systems in southern africa extensive systems of fixed linear dunes occur in the kalahari region of southern africa from 28 s to 16 30 s they provide evidence for large scale expansion of arid climates in the subcontinent during the quaternary on the basis of differing dune morphologies and alignments three periods of upper pleistocene aridity are recognised patterns of dune alignments reflect paleosand flow regimes and permit deduction of past winds and circulation patterns leading to the conclusion that arid episodes were associated with and probably caused by greater strength and persistence of the south african anticyclone a tentative chronology of the arid periods tends to support the hypothesis that subtropical aridity was contemporaneous with glacial conditions in high latitudes

late quaternary records of the atmospheric input of eolian dust to the center of the chinese loess plateau abstract the concentrations of 15 elements and mineral grain size distributions were determined for late quaternary loess sediments from the chinese loess plateau particle size distributions of the loess were approximately log normal for each of three modes i e 0 04 to 1 m diameter 2 to 20 m and 20 to 200 m that integrate the transport and deposition of eolian dust the mass particle size distributions of typical crustal elements si ca fe ti k mn and v in paleosol and loess samples show patterns similar to those of mineral aerosols but higher concentrations occur in the submicrometer sediment particles absolute principal component analysis of the elemental data suggests that the loess can be described in terms of synsedimentary and postdepositional concentration and subvertical migration of caco3 and various elements through the deposit a variety of geochemical indicators in the loess are apparently sensitive to asian monsoon variations these include the mass ratio of course to fine particles the concentration ratios of certain trace elements the elemental fluxes associated with eolian dust and the bulk concentration of ca in the sediments

spatio temporal associations between dike intrusions and fault ruptures in the tongariro volcanic center new zealand abstract crustal extension of the southern portion of the taupo rift in the central north island of new zealand is mostly accommodated by normal faulting and rare dike intrusions to better understand how extension is accommodated and how volcanoes and faults interact we provide a new integration of the tectonic and volcanic history of this young section of the taupo rift from geological evidence fault acceleration and deceleration apparently coincide with episodes of voluminous volcanic eruptions during the last 100 ka using geological data we detect three modes of volcano fault interactions active during different periods 1 increased volcanism eruptive volume coupled with increased fault slip rate e g 26 11 cal kyr bp 2 increased volcanism but decreased adjacent fault activity e g 11 10 cal kyr bp pahoka mangamate unzipping period and 3 decreased volcanism low rates and volumes but increased fault slip rate e g 45 25 cal kyr bp the availability of melt production at depth is a first order factor controlling the geodynamic processes of coeval fault slip rate and magma volume variations within this rift we hypothesize that progressive shallowing of magma drives transition of mode 1 to 2 i e maintaining high volcanic rates but decreasing fault slip second order interactions such as stress transfer is modelled by simple coulomb stress transfer scenarios to other faults and volcanoes surrounding rift elements our results strongly suggest that fluctuations in magma input through time strongly influence both eruption frequency and seismic cycles in volcanic rifts time dependent seismic hazard models must consider the influence of magmatic processes in fault parameters e g temporal slip rate variations in continental rifting environments

normal fault growth and linkage in the whakatane graben new zealand during the last 1 3 myr determination of fault growth rates and fault network evolution at time scales from 104 106 years has been hampered by a lack of a well constrained stratigraphic succession that provides a high fidelity record of fault development over these time periods here we show how seismic reflection data of different spatial resolutions can be used to constrain the linkage history and displacement rate variations of a single major fault we present data collected in the offshore whakatane graben bay of plenty new zealand where intense normal faulting occurs as a result of active back extension the focus of our study is the rangitaiki fault a linked segmented normal fault which is the dominant active structure in the graben the total linked fault length is c 20 km long and has a displacement of up to 830 130 m in the top 1 5 km of sediments the fault has been actively growing for the last 1 34 0 51 ma and has developed from isolated fault segments to a fully linked fault system initially the dominant process of fault growth was tip propagation with an average and maximum displacement rates of 0 52 0 18 mm yr 1 and 0 72 0 23 mm yr 1 respectively interaction and linkage became more significant as the fault segments grew towards each other resulting in the fault network becoming fully linked between 300 and 18 ka following fault segment linkages the average displacement rate of the fault network increased by almost three fold to 1 41 0 31 mm yr 1 while the maximum displacement rate increased to 2 72 0 61 mm yr 1 this is the first time that the growth rate of unlinked fault segments has been resolved and has been shown to be slower than in the subsequent linked fault system

oblique back arc rifting of taupo volcanic zone new zealand taupo volcanic zone tvz is a back arc rift innorth island new zealand its geometry andkinematics are investigated using shaded reliefimages field examination of faults and offset streamchannels the results show that tvz trends nne is 250 km long by hikurangi margin in the north island of new zealand 20 km wide and consists of fivesegments extension is principally manifest as steeplydipping 60 90 normal faults parallel to tvz these in the last 300 kyr have experienced acomponent of dextral shear tvz is therefore anoblique back arc rift the dextral shear is 37 of thetotal displacement which for previously estimatedspreadingrates 7mm yr correspondsto 2 6mm yr thisvalueissimilartopreviousestimatesofthedextralshear from the back arc to the forearc domains in thenorthisland distributeddextralshearacrosstvzthussuggests that strain partitioning across the plateboundary at latitudes of tvz is less significant thanpreviously thought

changes in mineralogy of loess paleosol sections across the chinese loess plateau quantitative mineralogical analysis of bulk samples and single particles was carried out on three loess sections of different local climate settings on the chinese loess plateau clp mineralogy geochemistry and single particle petrography of loess and paleosols are relatively uniform over the clp however in detail there are mineralogical changes related to eolian process and chemical weathering particle size sorting eastward from western sources led to an eastward increase of the total phyllosilicate contents enriched in fine illitic clay minerals after deposition detrital minerals susceptible to chemical weathering were sequentially altered in a progressive fashion with increasing precipitation in the order of calcite dolomite biotite illite chlorite amphibole and plagioclase the weathering of biotite chlorite and illite resulted in a significant increase of expandable phyllosilicate contents the sequential weathering of the minerals is reflected chemically in the decrease of na and mg and the increase of iron oxidation mineralogy of the chinese loess at individual sites reflects the effects of size fractionation during eolian transportation and progressive sequential weathering along the climatic gradient and it is essential to consider both effects when using mineralogical and dependent chemical data in the paleoclimatic reconstruction of the clp

seismic imaging of the alpine fault near inchbonnie new zealand 1 the transpressive alpine fault is the boundary between the pacific and australian plates across the south island of new zealand earthquakes on the alpine fault and related structures pose a serious risk to many urban centers including the city of christchurch although it is a major feature on satellite images the alpine fault is a difficult target for surface studies along much of its length it mostly traverses densely forested and mountainous terrain and where it occurs in the lowlands it is usually covered by recent sediments to investigate the alpine fault at a rare accessible location inchbonnie we have acquired high resolution seismic reflection data along five 380 1200 m long lines images produced from these data reveal a glacially overdeepened valley containing a thick sequence of diverse glacigenic sediments that have been disrupted by three en echelon strands of the principal alpine fault and several secondary fault strands based on their seismic facies the sedimentary sequence is interpreted to comprise basal lacustrine beds overlain successively by alluvial colluvial deposits that possibly include the remnants of large landslides deltaic fan units and braided river gravels whereas the principal alpine fault strands disrupt the entire post glacial sedimentary section and likely offset basement at depths up to 400 m most of the secondary faults either merge with the principal fault strands at shallow depths or are surficial features limited to the sedimentary section

towards an orbital time scale for chinese loess deposits abstract in this study we analyzed the grain size of the baoji loess soil sequence at 10 cm intervals results show that grain size variations are very sensitive to loess soil alternations with loess units being much coarser than soils such a change in loess soil grains is interpreted as the result of the glacial interglacial cyclic variations in the intensity of the winter monsoon winds out of siberia the grain size record is thus employed as a proxy indicator of the winter monsoon circulation and tuned to the orbital records calculated recently by berger and loutre 1991 under the control of major magnetic reversals the tuning is independent of any correlation with 18o signals in the deep sea sediments the resulting grain size time scale is tightly constrained as suggested by the following facts 1 the filtered obliquity and precession components from the grain size data on the orbital time scale closely match the theoretical orbital records 2 ages of the major magnetic reversals estimated from the grain size time scale are in good agreement with the k ar dated ages 3 there is close coherence between the baoji grain size time series and the orbital variations at the orbital frequency bands over the entire 0 2 5 ma period and 4 the grain size record on the orbital time scale shows a close similarity to the orbitally tuned dsdp site 607 and odp site 677 18o records examination of time dependent characteristics of the grain size record suggests that there are two major shifts of dominant periodicities in the long term monsoonal cycles one occurring at about 0 8 ma bp and the other around 1 7 ma bp

experiments on faulting in a two layer cover sequence overlying a reactivated basement fault with oblique slip abstract two series of experiments were undertaken to investigate the development of faults in a cover sequence overlying a reactivated basement fault with oblique slip the experiments represent physical models properly scaled to account for gravitational forces brittle behaviour of the upper cover and ductile behaviour of evaporites in the lower cover models were made with a coulomb layer sand overlying a newtonian ductile layer silicone putty in each series the thickness of the silicone layer was varied from each experiment to the next in all normal wrench experiments a domain of faults appeared in the brittle layer vertical offsets were mostly of normal sense but some reverse faults occurred in experiments with thick silicone layers the thicker the silicone the wider the fault domain the deformation zone was in all cases limited to the faulted domain in the reverse wrench experiments discrete reverse riedel faults appeared without a silicone layer as the silicone layer became thicker the importance of the reverse faults diminished with the thickest layer of silicone 3 cm no faults appeared in the overburden but a monoclinal flexure accommodated the dip slip component in the presence of silicone the deformation zone was not limited to a faulted domain and the strike slip component was accommodated by a bulk shearing of the overburden in the uplifted compartment these experiments demonstrate that in basins deformed in oblique slip mode any deformation that is localized along discrete faults at the basement level becomes distributed over a much wider zone of overburden when this overlies an interval of evaporites

the importance of microearthquakes in crustal extension of an active rift a case study from new zealand received 24 august 2012 revised 29 november 2012 accepted 19 december 2012 1 the amount of extension accommodated in active rifts by earthquakes that do not rupture the ground surface e g mw 5 5 is often poorly constrained the matata earthquake sequence mes a high quality dataset of 2563 relocated microearthquakes 1 mw 4 7 that ruptured the taupo rift in new zealand over a period of 49 months has been used to quantify the proportion of extension produced by small to moderate sized earthquakes analysis shows that the extension rate across the rift due to the mes is 2 4 0 7 mm yr at 1s standard deviation an average extension rate for small to moderate magnitude earthquakes which also prevailed during the preceding 28 years 1977 2004 and represents up to 30 of the total contemporary deformation recorded across the north taupo rift by gps 15 5 mm yr the bulk of the mes 94 occurred at depths of 1 5 to 6 5 km and may not be observed in geological datasets e g as displacements of the ground or near surface horizons small scale faulting associated with microseismicity may thus record strains not measured by geological datasets and constitute an important component of the 3 10 mm yr disparity between geological and gps rates of extension across the taupo rift

asymmetric rifting in a continental back arc environment north island new zealand marine seismic reflection data have been used to investigate the structure and evolution of the continental back arc basin forming the volcanic region of central north island new zealand the seismic reflection data defines two parts to the volcanic region in the west an older region showing narrow back tilted blocks and a younger rift basin delineated by the white island and tauranga fault zones to the east the younger rift coincides with the offshore trend of the active taupo volcanic zone tvz listric faulting of basement in the eastern part gives rise to about 80 extension for the basin which is consistent with the thinning of the crust from 25 km along the margins of the basin to 15 km under the basin basement in the region is interpreted to be highly extended greywacke the nature of the faulting and the seismic stratigraphy demonstrates that the extension has been asymmetric in nature being progressively younger towards the plate boundary in the east active faulting offsets the seafloor in the younger eastern part of the basin eight major sedimentary sequences delineated by unconformities are recognised in the basin these sequences based on correlation with major onshore rhyolitic eruptions are considered to be up to about 1 6 ma old a major unconformity within the sequences may coincide with a hiatus in volcanic activity from 0 7 0 4 ma ago a caldera structure is tentatively identified under the western part of the younger rift basin offshore tvz from seismic and other data its age is not well constrained but an age corresponding to the initiation of the younger extension episode 1 6 ma ago is preferred older volcanic sequences underlie the oldest tvz volcanic units to the west of the younger basin and probably correspond to the pliocene miocene volcanics onshore in the coromandel peninsula

tsunami hazard assessment and risk in aotearoa new zealand a systematic review ad 1868 2012 abstract this paper presents a systematic review of peer reviewed journal articles scientific reports books and research theses covering tsunami hazard assessment and risk in aotearoa new zealand a nz fifteen electronic databases were examined using an array of keyword search strings to comprehensively gather all available sources of information spanning 1868 2012 ad 222 references were identified as directly relevant to tsunami hazard assessment and risk in a nz with a further 51 references identified by scrutinising the original 222 references the amount of information as well as the emphasis of the science contained in these 273 references differs greatly between documents a meta analysis of this collective scholarship shows six principal areas of scientific endeavour i observation and cataloguing of modern and historical tsunami impacts caused by earthquakes and landslides ii modelling and evaluation of near and far field generated tsunamis iii detailed mapping and assessment of offshore seismic and other geological structures responsible for near field tsunami generation iv investigation and cross referencing of holocene palaeo records of tsunami deposits preserved in wetlands dunes and other coastal landforms v survey and reconnaissance of modern and historical tsunami impacts and vi guidance for tsunami hazard mitigation preparedness and land use planning synthesising all of these references it is clear that a nz has been affected by remote regional and locally generated tsunami during the historic pre written and pre human periods further scientific knowledge of tsunami risk and the forces responsible for tsunami generation has greatly improved however in spite of the many scientific advances detailed in this review much more remains to be done to better understand and deal with the diverse tsunami hazard and risk facing a nz

the geometrical evolution of normal fault systems abstract the purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution we pay particular attention to seismological and surface data from regions of present day active normal faulting as the instantaneous three dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static most normal faults are concave upward or listric this shape can be produced by geometric constraints either because the faults reactivate curved thrusts or because they must be curved to accommodate rotations another effect which will produce curved faults is the variation of rheology with depth brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust an important geometric feature of normal faulting is the uplift of the footwall the amount of such uplift is related not only to the elastic properties of the lithosphere but also to the throw and dip of the fault a striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction this behaviour arises because the faults cannot intersect if they do one must cease to be active the rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed once a new fault cuts pre existing faults the earlier faults become locked and a new set of faults must propagate rapidly across the whole region involved many of these geometric constraints also apply to thrust faulting

high resolution record of displacement accumulation on an active normal fault implications for models of slip accumulation during repeated earthquakes the spatial and temporal accumulation of slip from multiple earthquake cycles on active faults is poorly understood here we describe a methodology that can determine the time period of observation necessary to reliably constrain fault behaviour using a high resolution longtimescale the last 17 kyr fault displacement dataset over the rangitaiki fault whakatane graben new zealand the fault linked at ca 300 ka bp and analysis of time periods within the last 17 kyr gives insight into steady state behaviour for time intervals as short as ca 2 kyr the maximum displacement rate observed on the rangitaiki fault is 3 6g1 1 mm yr k1 measured over 17 kyr displacement profiles of the last 9 ka of fault movement are similar to profiles showing the last 300 ka offault movement in contrast profiles determined for short time intervals 2 3 kyr are highly irregular and show points of zero displacement on the larger segments this indicates temporal and spatial variability in incremental displacement associated with surface rupturing slip events there is spatial variability in slip rates along fault segments with minima at locations of fault interaction or where fault linkage has occurred in the past this evidence suggests that some earthquakes appear to have been confined to specific segments whereas larger composite ruptures have involved the entire fault the short term variability in fault behaviour suggests that fault activity rates inferred from geodetic surveys or surface ruptures from a single earthquake may not adequately represent the longer term activity nor reflect its future behaviour different magnitude events may occur along the same fault segment with asperities preventing whole segment rupture for smaller magnitude events q 2006 elsevier ltd all rights reserved

tectonic controls on taupo volcanic zone geothermal expression insights from te mihi wairakei geothermal field information on structure stress and their interrelationship is essential for understanding structurally controlled geothermal permeability active fault mapping borehole image analysis and well testing in the te mihi geothermal area new zealand allows us to refine structural and fluid flow architecture of this resource the te mihi area is structurally complex comprising a set of nw dipping master faults containing pervasive se dipping antithetic and splay structures in their hanging walls these faults are also intersected by e w striking faults a localized n s striking structural trend is also observed at te mihi in consideration with global navigation satellite system velocity vectors both active ne sw and e w striking faults create biaxial extension at te mihi though the observed ne sw shmax direction suggests that contemporary extension is nw se dominated stress field perturbations coincide with structural complexities like fault splays and intersections and or proximity to recently active e w and ne sw striking structures borehole fluid flow at te mihi is concentrated at nw dipping master fault intersections travel time fractures on acoustic image logs halo fractures on resistivity image logs ne sw and e w striking fractures intervals of high fracture density and spatial concentrations of wide aperture fractures and recently active ne sw and e w striking fractures this study suggests te mihi geothermal expression results from biaxial extension evident from active structural trend intersections and the predominance of ne sw and e w striking structures within permeable well zones biaxial extension is therefore an important control on crustal fluid flow within the taupo volcanic zone and thus geothermal resource delineation

reconstructions of the new zealand region for the neogene abstract the major structural elements of the present day plate boundary zone through new zealand are a subduction zone under the northern half of the country linked by a wide transform zone to the southward extension of the plate boundary through fiordland and the macquarie ridge using finite rotations of the pacific australian plate pair a sequence of reconstructions of the relative positions of the plates is presented reconstructions of the plate boundary zone based on paleomagnetic data involve essentially the same structural elements as today but with large clockwise changes in their trend with time

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

postglacial after 18 ka deep sea sedimentation along the hikurangi subduction margin new zealand characterisation timing and origin of turbidites recent sedimentation along the hikurangi subduction margin off northeastern new zealand is investigated using a series of piston cores collected between 2003 and 2008 the active hikurangi margin lies along the pacific australia subduction plate boundary and contains a diverse range of geomorphologic settings slope basin stratigraphy is thick and complex resulting from sustained high rates of sedimentation from adjacent muddy rivers throughout the quaternary turbidites deposited since c 18 ka in the poverty ruatoria and matakaoa re entrants are central to this study in that they provide a detailed record of the past climatic conditions and tectonic activity here alternating hemipelagite turbidite debrite and tephra layers reflect distinctive depositional modes of marine sedimentation turbidity current debris flow and volcanic eruption respectively turbidites dominate the record ranging in lithofacies from muddy to sandy turbidites and include some basal reverse graded turbidites inferred to be derived from hyperpycnal flows stacked turbidites are common and indicate multiple gravity flows over short time periods the chronology of turbidites is determined by collating an extremely dense set of radiocarbon ages and dated tephra which facilitate sedimentation rate calculation and identification of the origin of turbidites sedimentation rates range from 285 cm ka during late glacial time 18 5 17 ka to 15 to 109 cm ka during postglacial time 17 0 ka turbidite deposition is controlled by 1 the emplacement of slope avalanches reorganising sediment pathways 2 the postglacial marine transgression leading to a five fold reduction in sediment supply to the slope due to disconnection of river mouths from the shelf edge and 3 the holocene pleistocene boundary climate warming resulting in a drastic decrease in the average turbidite grain size flood induced turbidites are scarce nine hyperpycnites are recognised since 18 ka and the youngest is correlated to the largest enso related storm event recorded onland lake tutira other turbidites contain a benthic foraminiferal assemblage which is strictly reworked from the upper slope and which relates to large earthquakes over the last c 7 ka they yield a shorter return time 270 430 years than the published coastal records for large earthquakes c 670 years but the offshore record is likely to be more complete the deep sea sedimentation along the new zealand active margin illustrates the complex interaction of tectonic and climate in turbidite generation climate warming and glacio eustatic fluctuations are well recorded at a millennial timescale 18 ka while tectonic deformation and earthquakes appear predominant in fostering turbidite production at a centennial timescale 270 430 years

holocene changes in tropical wind intensity and rainfall evidence from southeast ghana abstract remnants of a fixed aeolian dune ridge occur along the southeast coast of ghana just behind the present shoreline aeolian sands also cover extensive areas of the accra plains no dunes are present here the sands mainly occurring as sheets which blanket an early holocene landscape the sediments are of mid holocene age and were deposited during the interval 4500 b p 3800 yr b p when the southwesterly winds were stronger than they are at present and much of tropical africa seems to have been subject to marked aridity the onset of drier windier conditions around 4500 yr b p brought to an end the more equable climates than had characterized much of west africa during the earlier holocene aridity intensified winds and desert expansion between 4500 and 3800 yr b p parallel environmental conditions in tropical continental areas at the height of the late pleistocene glaciation

crustal structure of the taupo volcanic zone new zealand stretching and igneous intrusion 1 seismic data from both explosive and earthquake sources have been used to constrain the crustal and upper mantle velocity structure beneath the taupo volcanic zone tvz a back arc basin in north island new zealand a thin 16 km quartzo feldspathic crust is underlain to 30 km depth by material with p wave velocities 6 9 7 3 km s interpreted as heavily intruded or underplated lower crust low seismic velocities of 7 4 7 8 km s are present in the underlying mantle wedge to at least 100 km depth which we attribute to the presence of volatiles from dehydration of the subducting pacific plate a region of high 0 34 poisson s ratio is found in the lower crust beneath the tvz consistent with the presence of partial melt this melt fractionates and assimilates crustal material before migrating into the upper crust where it provides a source for the voluminous rhyolitic magmas of the tvz

multiple origins and interpretations of the magnetic susceptibility signal in chinese wind blown sediments abstract in most chinese loess paleosol sequences high magnetic susceptibility values are found in the soil horizons with low values in the loess layers the susceptibility signal has been widely used as a proxy climatic indicator however both the causes and mechanisms which control susceptibility still remain controversial our recent studies challenge some earlier interpretations of the magnetic susceptibility signal in chinese wind blown sediments first the prevailing hypothesis of pedogenic origin cannot totally account for the susceptibility variations in many sections second in some cases the principal carrier of the magnetization seems not to be the ultrafine pedogenic minerals rather coarse lithogenic magnetic minerals derived from local sources can also contribute significantly to the susceptibility signal finally not all the chinese soils have higher susceptibility values than that of loess or sand layers opposite relationships do exist it is concluded that the source and causes of susceptibility may be different from site to site or even at different times at a given site any single hypothesis cannot completely account for the susceptibility variations in the chinese loess plateau and its surrounding regions besides the previous explanations of carbonate leaching pedogenic processes and organic decomposition the contribution of source materials to magnetic susceptibility must also be taken into account

holocene lake deposits and palaeoenvironments in central sahara northeastern mali abstract extensive and fossiliferous lacustrine deposits have been found in a now hyperarid area south of the tanezrouft 20 30 21 n 1 w between the erg ine sakane and the djebel takabart the assemblage of fish molluscs ostracods and charophytes among which lychnothamnus is observed in africa for the first time testify to fresh water conditions however stable carbon and oxygen isotopic values provide evidence for phases of strong evaporation the presence of limicolaria sp a terrestrial pulmonate first observed in the sahara indicate permanent soil humidity around the palaeolake s the remains of large steppe type mammals elephant antelopes buffalo as well as neolithic sites and burials in brown soils also contribute to evidence a northward shift of the sahel belt 3 4 in latitude this period is radiocarbon dated from 6130 180 b p to 7520 70 b p on molluscan shells the human material could be younger 3750 100 b p on charcoal

kinematics and paleoseismology of the vernon fault marlborough fault system new zealand implications for contractional fault bend deformation earthquake triggering and the record of hikurangi subduction earthquakes the 40 km long vernon fault in the marlborough fault system of new zealand is characterized by dextral slip with subordinate reverse slip and exhibits abrupt variations in strike of up to 90 onshore fieldwork paleoseismic trenching and offshore high frequency seismic reflection data are integrated together to identify the kinematics and paleoseismic history of three sections of the fault 1 the nne striking vernon hills section which branches off from the awatere fault 2 the ne striking big lagoon section which borders big lagoon to the south and extends 9 km offshore to the east and 3 the e w striking wairau basin section which is entirely submarine the vernon fault can be shown to have a dextral slip rate of 0 8 4 9 mm yr with a preferred estimate of 0 9 mm yr on the big lagoon section we infer that a further unrecognized 3 4 mm yr of dextral slip has been accommodated off fault as a result of accumulated slip on small and or blind reverse faults adjacent to a 6 km wide restraining bend in the main fault the onshore and offshore paleoseismic records are in good agreement these indicate three to five events at eight sites and a mean recurrence interval of 3 9 1 2 ka over the past 16 kyr with the last event taking place at 3 3 ka earthquakes on the vernon fault are responsible for 25 of the holocene subsidence rate of big lagoon over the last 13 ka most of the subsidence of this lagoon has been the result of surface deformation related with southern hikurangi megathrust earthquakes

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

pedogenesis and paleoclimate interpretation of the magnetic susceptibility record of chinese loess paleosol sequences in the chinese loess paleosol sequences from luochuan haanxi province china variations in the magnetic susceptibility have been accepted as an excellent proxy for paleoclimate and the standard interpretation is that climatic processes have enhanced the magnetic susceptibility of the paleosols beyond the base line level of the loess by using mineral magnetic properties and a soil chemistry extraction procedure we show that most of the magnetic susceptibility signal in both the paleosols and the loess is due to pedogenesis in effect loess deposition and pedogenesis are competing processes at all times and the presence of a paleosol simply indicates that the latter process was predominant these results imply that any interpretation of the paleoclimate record of loess paleosol sequences must recognize the pedogenic nature of the magnetic susceptibility signal and that the focus of future research must be on the critical role of climate in the development of the paleosols

patterns of tectonic fault interactions captured through geostatistical analysis of microearthquakes 1 historical earthquakes are often strongly clustered in space and time this clustering has been attributed to static stress triggering associated with tectonic fault interactions and or to fluid migration discrimination between these two models requires detailed information on the timing location and size of earthquakes the matata earthquake sequence in the taupo rift new zealand provides a unique opportunity to chart spatial and temporal patterns of earthquakes along individual faults and their relations to other faults in the system over timescales of days to years this is possible because there are 2563 accurately relocated within 5 5 earthquakes that occur over thousand year timescales e g 60 kyr

a fractal evaluation of particle size distributions in an eolian loess paleosol sequence and the linkage with pedogenesis abstract the changes of soil particle size distributions psds can be used as a proxy for soil development intensity and an indicator of soil formation processes the fragmentation fractal dimensions can describe psds of soils in a single parameter the objective of this research is to use mass based fragmentation fractal dimension models to describe psds and evaluate the relationship between the fragmentation fractal dimension values df and pedogenesis in loess paleosol based on the theory of fragmentation fractal dimension particle size data from 837 eolian loess samples from the lower part of chaoyang section uniform loess deposits were analyzed with mass based models using linear regression and piecewise linear regression a single power law exponent can characterize the psds across the domain of 0 1 54 4 m the trend of fragmentation fractal dimension values is consistent with chemical weathering indices magnetic susceptibility and df2 close to 2 the energy dissipation for fragmenting larger particles from coarse silt csi to fine silt fsi is identified in the volume and for fragmenting smaller particles from fine silt fsi to clay cl it is substantially on the surface this research indicated that fragmentation fractal model is a good descriptor for the psds and df can be a value quantifying the intensity of loess paleosol pedogenesis

mineral magnetic record of the chinese loess and paleosols variations in the magnetic susceptiblity of the chinese loess and its interbedded paleosols correlate strikingly well with the deep sea oxygen isotope record low susceptibility values are found for the loess layers and high values are found for the soil horizons two interpretative models have been advanced to account for these magnetic variations both of these models discount any significant in situ formation of magnetite during soil forming periods instead they infer relative concentration of detrital or atmospheric magnetite at these times we critically examine the assumptions made in these models and on the basis of some new mineral magnetic data and fromalized magnetic flux calculations offer an alternative explanation of the loess magnetic record our model identifies pedogenic formation of magnetite as the major contributor to the high magnetic susceptibility of the paleosols the formation and preservation of this pedogenic magnetite is dependent on soil froming conditions and hence reflects the regional climate

linked fault families in basin formation abstract recent models of faulting tectonics in basins and passive margins have emphasized the linked nature of faults in a way that is analogous to that developed for thrust regimes a linked fault system requires three components ramps flats and sidewalls or transfers basins that are the result of other processes are not considered in this contribution and the examples used are drawn from the midland valley and northumberland basins of the u k where existing mapping by the british geological survey as well as field work undertaken by the author indicate that such models are appropriate this paper summarizes the geometric features and constraints of such models and emphasizes the role of each of the three critical components of a linked system for large deformations that result in the formation of major extensional and strike slip basins the principal geometries can be understood by reference to regionally and locally balanced fault models that involve detachment ramp and sidewall or transfer elements tip strains and both lateral and vertical accommodation zones are included in the general model but these probably account for less than 10 of the total upper crustal strain the basic analysis of a linked basin system requires the transfer of displacement on and between the fault and shear zone components the geometry of the stratigraphic units is used to deduce the active linkage on the fault system in oblique slip systems and where the dominant extensional ramp is connected to oblique transfer and detachment systems lateral and sidewall sub basins and intra basin uplifts occur as part of continuing slip on the fault system these control facies distribution and depocentre evolution the existence of a basin forming linked system frequently controls later deformation of basins and margins and an appreciation of basin growth faults and stratigraphic geometry is essential in the interpretation of inverted basins and orogenic belts involving supracrustal formations

millennial scale climatic oscillations during the last interglaciation in central china repeated southward excursions of north atlantic polar water during the last interglaciation 18 o stage 5 130 74 ka are recorded by planktonic foraminifera and ice rafted detritus in north atlantic sediment cores and greenland ice sheet cores display quasi synchronous fluctuations comparable high frequency variations in the east asian winter monsoon climate are discernible in three loess paleosol profiles in central china that span the last interglaciation peak values of the 40 m quartz fraction and bulk sediment samples from the s1 last interglacial accretionary paleosol complex reflect major dust flux events when winter monsoon winds strengthened frequent oscillations of the dust flux and nine significant dust events are recorded six events falling between ca 110 and 70 ka are correlated with cold peaks c19 24 identified in north atlantic cores two comparable dust peaks occur within paleosol s1ss3 substage 5e the older of these dating to ca 121 ka may correlate with a brief cold event recently recognized in high resolution marine and terrestrial climate proxy records

a back arc basin formed within continental lithosphere the central volcanic region of new zealand abstract the central volcanic region is an area of quaternary volcanism and tensional tectonics within the north island of new zealand that appears to be a direct continuation of a young oceanic back arc basin the havre trough into the continental structure of new zealand volcanism is predominantly rhyolitic yet the region possesses many of the geophysical characteristics often associated with oceanic back arc basins upper mantle seismic velocities are low pn and sn velocities of 7 4 and 3 95 km s respectively the crust is anomalously thin for its continental setting and the heat flow almost all of which is expressed in the discharge of hot water through geothermal systems is about 700 mw m2 i e some twelve times greater than normal continental heat flow in order to account for such a high heat flow a large scale mass transfer of heat is required it is proposed therefore that the central volcanic region represents a site of active back arc spreading within a continental lithosphere

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

active upper plate thrust faulting in regions of low plate interface coupling repeated slow slip events and coastal uplift example from the hikurangi margin new zealand 1 contractional fore arc faulting and deformation is a characteristic feature of many subduction systems definition of the three dimensional geometry and displacement rates of active upper plate out of sequence thrust faults along 250 km of the upper hikurangi margin enables us to examine the relationship between fore arc deformation and the subduction interface in light of interseismic coupling estimates and distribution of slow slip events both modeled from gps measurements these mid fore arc structures include the seaward vergent outer shelf lachlan and ariel faults with vertical separation rates up to 5 mm yr and several other major inner shelf faults with rates that are up to 3 8 mm yr and comparable with holocene coastal uplift rates seismic reflection imaging and geometric projection of these faults at depth indicate that they splay from the region of the plate interface where geodetic inversions for interseismic coupling and slow slip events suggest that the plate boundary undergoes aseismic slip this observation may indicate either 1 that frictional properties and interseismic coupling on the plate interface are independent and unrelated to the active splay fault deformation in the inner middle fore arc or 2 that the active splay faulting reflects long term mechanical coupling related to higher shear stress or the relative yield strength of the plate interface to the overriding plate and that the current pattern of interseismic coupling may not be persistent over geological time scales of 20 ka we compare structure and processes on the northern hikurangi and costa rican margins and find similarities and significant differences astride these subduction systems

holocene flooding and species diversity in southwestern amazonia abstract a thick blanket of holocene alluvium lies over southwestern lowland amazonia and may possibly occur throughout much of the amazon basin these deposits resulted from massive seasonal flooding from about 11 000 to about 5000 yr b p that was followed by two cycles of erosion and deposition interpretations based on these geologic data suggest that southwestern lowland amazonia is ecologically an island in a state of supersaturated disequilibrium as a result of colonization from pleistocene refugia on its perimeter and that habitats of highest diversity may be the most recent in origin conservation efforts and studies of amazonian biogeography soils and paleoethnography should be reevaluated in light of the geologic data

a quantitative reconstruction of a loess paleosol sequence focused on paleosol genesis an example from a section at chaoyang china abstract a typical loess paleosol sequence at chaoyang in china deposited continuously since 423 ka bp was examined to quantitatively reconstruct a loess paleosol sequence first particle size distribution was evaluated based on clay free fractions where the sum of sand silt 100 and fine earth fractions and used to characterize the parent material uniformity as well as field morphology geochemical features and micro morphology characteristics second mass balance mb and soil reconstruction sr approaches were employed to examine the linkage between pedogenesis and loess deposition the results indicated a uniform loess deposit below 228 cm depth and the presence of four reddish stratigraphic layers interbedded with four yellowish stratigraphic layers all derived mostly from silt eolian deposits the main soil pedogenic processes following silt deposition were clay eluviation illuviation silification and ferrallitization the strongest pedogenesis occurred for the s3 deposit layer during 225 243 ka bp and was associated with the greatest mass loss of non clay 7 6 na2o 42 cao 21 mgo 28 sio2 10 and at the same time with the greatest gains in clay 42 fe2o3 8 and al2o3 4 together with mass loss changes mc of 620 g 100 cm2 the greatest mass gain changes 234 g 100 cm2 occurred in the l4 deposit layer during 243 311 ka bp and were associated with gains in na2o 18 and p2o5 4 5 indicating the fastest deposition rate during the long period of sedimentation 423 ka bp loess deposition was predominant during dry cold periods whereas paleosol formation from pedogenic processes was predominant during wet warm periods thus the formation of paleosols and loess deposition were dependent on the relative rate of pedogenesis and deposition as controlled by climate change under an east asian summer monsoon eas paleosol formation dominated whereas loess deposition dominated under an east asian winter monsoon eaw quantification of the degree of loess development paleosols or loess deposits aids reconstructing soil genesis and understanding the loess paleosol formation sequence and its linkage to climate change

high frequency pulses of east asian monsoon climate in the last two glaciations link with the north atlantic three loess sections in the loess plateau of china have been studied to characterize the variations of the east asian monsoon climate in the late quaternary period paleo weathering profiles based on two weathering indices reveal a series of spatially correlative intervals of lower weathering intensity lw in the last glacial and late penultimate glacial loess indicating significantly cooler or and drier conditions most of them are identified at or near the transitional boundaries between loess and soil units suggesting that climatic conditions favorable for lw events tended to occur at or near major climatic boundaries twenty eight radiocarbon and thermoluminescence measurements combined with kukla s magnetic susceptibility age model date these events at 14 21 29 38 52 71 135 and 145 ka bp with 5 10 ka frequency inlaid within the orbitally induced 20 ka periodicity the ages of the first six events in the last glacial period are therefore close to those of the coarse grained heinrich layers in the north atlantic ocean which resulted from massive discharges of icebergs the results indicate that the climate in the area affected by the east asian monsoon has experienced high frequency changes more or less synchronous with the heinrich events these high frequency changes have been reported by porter and an based on the grain size time series from the luochuan loess section our data also reveal that similar events also occurred during the penultimate glaciation the mechanisms linking the heinrich events and the east asian monsoon climate may be similar to that driving the younger dryas event which has been identified in a large number of records in china and in the surrounding oceans

terminations of large strike slip faults an alternative model from new zealand the 500 km long strike slip north island fault system nifs intersects and terminates against the taupo rift both fault systems are active with strike slip displacement transferred into the rift without displacing normal faults along the rift margin data from displaced landforms fault trenching gravity and seismic reflection profiles and aerial photograph analysis suggest that within 150 km of the northern termination of the nifs the main faults in the strikeslip fault system bend through 258 splay into five principal strands and decrease their mean dip these changes in fault geometry are accompanied by a gradual steepening of the pitch of the slip vectors and by an anticlockwise swing up to 508 in the azimuth of slip on the faults in the nifs as a consequence of the bending of the strike slip faults and the changes in their slip vectors near their intersection the slip vectors on the two component fault systems become subparallel to each other and to their mutual line of intersection this subparallelism facilitates the transfer of displacement from one fault system to the other accounting for a significant amount of the ne increase of extension along the rift whilst maintaining the overall coherence of the strike slip termination changes in the slip vectors of the strike slip faults arise from the superimposition of rift orthogonal differential extension outside the rift margin resulting in differential motion of the footwall and hanging wall blocks of each fault in the nifs the combination of rift orthogonal heterogeneous extension dip slip and strike slip results in a steepening of the pitch of the slip vectors on the terminating fault system slip vectors on each splay close to their terminations are therefore the sum of strike slip and dip slip components with the total angle through which the pitch of the slip vectors steepens being dependent on the relative values of both these two component vectors in circumstances where interaction of the velocity fields for the intersecting fault systems cannot resolve to a slip vector that is boundary coherent either rotation about vertical axes of the terminating fault relative to the through going fault system may take place to accommodate the termination of the strike slip fault system or the rift may be offset by the strike slip fault system rather than terminating into it at the termination of the nifs an earlier phase of such rotations may have produced the 258 anticlockwise bend in fault strike and contributed up to about one third of the anticlockwise deflection in slip azimuth on the terminating strike slip nifs therefore rotational and nonrotational termination mechanisms have both played a role but at different times in its evolution as the thermal structure the rheology and the thickness of the crust in the rift intersection region

experimental models of extensional forced folds we have used single layer and multilayer clay models to study the development of forced folds above normal faults our modeling results show that the deformation patterns associated with extensional forced folding depend on the dip of the underlying normal fault and the presence of layer parallel detachments in single layer clay models extensional forced folds are upward widening monoclines anticlinal axial surfaces dip in the same direction as underlying master normal faults and synclinal axial surfaces dip in the opposite direction of master normal faults most secondary faults are upward steepening normal faults if master normal faults are steeply dipping however many secondary normal faults become high angle reverse faults at shallow depths the propagation and linkage of secondary faults into through going normal faults terminates the development of extensional forced folds more folding occurs prior to fault linkage if the master normal fault is steeply dipping rather than gently dipping most dipping beds and secondary faults are preserved in the hanging walls of the through oing normal faults in multilayer clay models with layer parallel detachments extensional forced folds are also upward widening monoclines slip on the lowest detachment laterally transfers extension induced by normal faulting and forced folding from the master normal fault to the detachment edge slip on overlying detachments accommodates minor thickness changes associated with upward widening of the fold secondary faults include low angle normal faults near the anticlinal axial surface minor thrust faults near the synclinal axial surface and high angle normal faults above the detachment edge the model predicted deformation patterns are similar to those of extensional forced folds from the gulf of suez and offshore norway this similarity suggests that our modeling results apply to extensional forced folds and can provide guidelines for interpreting field well and seismic data

characterization of the shallow structures of active fault zones using 3 d ground penetrating radar data 1 where they can be correlated with geological exposures and trenches 3 d ground penetrating radar gpr data can contribute critical subsurface information to paleoseismic investigations because active faults are typically characterized by complicated near surface structures that vary with the styles of faulting and the types of rock that are ruptured gpr data can be difficult to interpret we have acquired 3 d gpr data sets across three active fault zones within new zealand that have different deformation styles the strike slip wellington fault zone reverse faults of the ostler fault zone and normal faults of the maleme fault zone to improve our interpretation of the processed gpr volumes we employed two suites of geometric attributes the first suite was computed using a coherence based algorithm it provided estimates of the coherency azimuth and dip of reflections the second suite quantified the volumetric textures of reflections which allowed different reflection facies to be defined objectively we have demonstrated how some attributes were more successful at visualizing certain structural or depositional characteristics than others for example the coherency attribute was an excellent tool for highlighting normal faults within volcanic deposits of the maleme fault zone whereas the texture based attributes were most useful for discriminating between the gravel and metasediment units juxtaposed by the wellington fault zone our gpr data sets and associated attribute volumes showed details of near surface fault geometry that were not obvious from surface mapping and they revealed evidence of off fault deformation gravitational collapse and topple structures

micromorphology and genesis of paleosols in the luochuan loess section china pedostratigraphic and environmental implications the loess paleosol sequence in the well known potou section near luochuan covers the entire pleistocene back to 2 5 ma in a much more complete sequence than any known from europe or north america to deduce a record of the pleistocene climatic history an understanding of the genesis of the paleosols is important main diagnostic features normally observable in surface soils have disappeared in the case of fossil soils therefore micromorphology is of outstanding importance because it enables the reconstruction of original properties and polygenetic soil development especially in pedocomplexes the upper part of the loess paleosol sequence can well be compared with the 18o record shown in the specmap curve of the brunhes epoch although the sequence of paleosols shows partly an even more detailed record of cold and warm stages and allows more specific informations regarding the paleoclimate of the interglacial periods cf fig 2 the last four paleosols represented by the s1 pedocomplex the upper part of the s2 and the s3 are genetically well comparable with the natural holocene soil indicating a similar climate with a tall grass steppe vegetation the s6 is a steppe soil also whereas the five soils of the s4 the s5 complex and the s7 are forest soils indicating more moist and partly warmer interglaciations than the holocene the loess paleosol sequence of the matuyama epoch seems to give more paleoclimatic informations than the deep sea cores known so far the lishi loess below the b m boundary down to 84 m in the section contains two more soils s11 and s13 which are developed under steppe vegetation in interglaciations similar to the present one and four forest soils the s8 complex the upper soil of the s9 and the s10 indicating again more moist interglaciations than the holocene most of the numerous soils in the wusheng loess are probably formed synsedimentarily as alternation of soil formation and addition of loess the red clay at the basis consists of four intensively developed but truncated paleosols the parent material of at least the lower part must be regarded as pliocene loess