structure and evolution of the northern potwar deformed zone pakistan the northern potwar deformed zone npdz is part of the active foreland fold and thrust belt of the salt range and potwar plateau in northern pakistan about 500 km of seismic reflection profiles are integrated with surface geologic and drilling data to examine the deformation style and structure of the npdz with particular emphasis on history of deformation of the dhurnal oil field the seismic lines suggest that the overall structure of the eastern npdz is a duplex structure developed beneath a passive roof thrust the roof thrust is generated from a tipline in the miocene murree formation and the sole thrust is initiated from the same eocambrian evaporite zone that extends 80 km southward beneath the soan syncline and salt range the dhurnal oil field structure is a pop up at the southern margin of the npdz and developed beneath the passive roof thrust the passive roof thrust crops out just north of dhurnal on the steep northern limb of the soan syncline an overstep passive roof thrust sakhwal fault is interpreted west of dhurnal this fault developed due to

landward and seaward directed thrusting accompanying the onset of subduction beneath new zealand a short 5 m y episode of deformation accompanied the onset of the present phase of subduction beneath northern and eastern new zealand in the earliest miocene at many places along the continental margin the structures produced were dominated by subhorizontal thrust sheets with tens of kilometres of displacement thrusting was directed both landward with or without involvement of the upper part of the downgoing plate and seaward the structures are different in style from those typical of active trench slopes which are predominantly seaward directed imbricate thrusts and associated folds the structures show that delamination of the downgoing plate occurred at some places and suggest that a high degree of coupling between upper and lower plates occurred at others

seismic potential revealed by surface folding 1983 coalinga california earthquake the 2 may 1983 coalinga california earthquake magnitude 6 5 failed to rupture through surface deposits and instead elastically folded the top few kilometers of the crust the subsurface rate of fault slip and the earthquake repeat time are estimated from seismic geodetic and geologic data three larger earthquakes up to magnitude 7 5 during the past 20 years are also shown to have struck on reverse faults concealed beneath active folds

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

glacio meteorological and isotopic studies along the egig line central greenland the geographical distribution of firn temperature annual accumulation rate as well as deuterium and oxygen 18 content in the firn were determined along an east west transect through central greenland this study is based on isotopic and chemical analyses of shallow firn cores at 18 sites along the egig line and high precision firn temperature measurements in 17 steam drilled boreholes along the eastern part of the transect the firn temperatures at 15 m depth range from 31 6 c at dome grip 3230 m a s l to 11 4 c at caecilia nunatak eastern ice margin at 1600 m a s l and 18 c at t05 near the western ice margin at 1900 ma s l the temperature altitude gradient changes from 0 7 c 100 m 1 in the ice divide region to 1 1 c 100 m 1 in the eastern part of the dry snow zone the temperature latitude gradient in the central part of the egig line is 0 7 c lat 1 the average annual accumulation decreases significantly from the west 47 cm a 1 water equivalent at t05 towards the ice divide 20 25 cm a 1 water equivalent from t99 to t43 accumulation rates are constantly low east of the ice divide 23 17 cm a 1 water equivalent thus dividing central greenland into two climatologically different regions the average 18 o and d values along the whole egig line reflect the well known temperature dependence for greenland very well e g 18 o t m 0 69 c 1 different regression lines for the western and eastern part however should be applied unlike the mean annual temperature the isotopic minimum along the egig line lies east of the ice divide this geographical distribution supports the choice of different water vapour trajectories in central greenland for the west and for the east significant parts of the water precipitated over the western slope are attributed to cyclonic systems entering greenland from the west the deuterium excess shows no significant geographical trend but a uniform seasonal variation at all sites along the egig line suggesting equal contributions from vapour source areas of the water precipitated over central greenland

bed by bed fold growth by kink band migration sant llorenc de morunys eastern pyrenees ahstract rowth strata deposited over and against the flank of the sant llorenc de morunys fold during its final stages of deformation have been mapped at high resolution as the basis for unraveling the kinematics of fold growth we use restoration techniques based on normal balancing assumptions to decipher the detailed kinematic history of folding the progressive restorations as well as balanced forward modeling show that the last few hundred meters of fold growth were dominated by kink band migration of a sort that is typical of much faultrelated folding the kink band migration has produced complex anticlinal hinge zone geometry including segmented fold hinges linked by disconformities and unconformities which has direct and detailed explanation in terms of fluctuations in deposition rate relative to curved hinge kink band migration rate large fluctuations in the convolution of non steady sedimentation and deformation are demonstrated although the absolute fluctuations in deformation and sedimentation are unknown at a length scale of 100 m kink band migration with little or no deposition is interspersed with sedimentation with little or no deformation at the length scale of 500 m deposition ranges from 200 to 50 of uplift 0 1997 elsevier science ltd all rights reserved

a mechanism for the generation of the lunar mare basalts summary according to the magma ocean or magmasphere model of lunar formation rapid accretion would result in the formation of a solid primitive core of undifferentiated material surrounded by a spherical shell of molten silicate as the outer layers of the moon cool by radiation of heat to space the deep interior will warm due to the decay of trace radionuclides this will lead to compression of the remnant magmasphere producing excess pressure in the fluid magma it is proposed that relief of this excess pressure through vents opened by the excavation of the mascon basins was sufficient to drive the major episodes of mare volcanism between 3 9 3 2 ga thermal models of the moon are constructed and a range of initial conditions based on the magmasphere model are identified which satisfy known constraints on lunar evolution the rate at which radial thermoelastic stress accumulates within the moon is calculated and from this estimates of the maximum volume of basaltic magma which could be produced by this mechanism are obtained by comparing these calculated magma generation rates with estimates of the volume of mare basalts residing on the lunar surface we are able to identify a set of initial temperature profiles which both satisfy the known constraints on lunar evolution and are able to produce the observed volume of mare basalts these models are characterised by deep magmaspheres and or initially warm central temperatures

distribution age and deformation of late pleistocene marine terraces at mahia peninsula hikurangi subduction margin new zealand a sequence of seven marine terraces of late pleistocene age constitutes approximately 40 of the area of mahia peninsula in eastern north island the peninsula is one of the closest land areas to the hikurangi trough approximately 80 km further east where the pacific plate is being subducted beneath the australian plate terrace ages of 40 59 81 106 124 176 and 212 ka are assigned by correlation with the marine terrace sequence of huon peninsula papua new guinea paleontological data and amino acid dating of marine components of the 124 ka terrace at mahia peninsula provide a basis for correlation to the huon peninsula sequence loess and tephra stratigraphy constrain the ages of older and younger terraces the marine terrace sequence is tilted to the wnw on the flank of the nne trending lachlan anticline uplift of at least 130 m of the circa 124 kyr old shoreline indicates uplift rates of at least 1 mm yr at the axis of the anticline younger marine terraces have been uplifted more rapidly about 3 mm yr and there is a progressive increase in rate to the youngest holocene shoreline structural contours normalized to the circa 124 ka terrace illustrate the tilt on the flank of the lachlan anticline and on a secondary structure the aurora point fold seismic profiling has confirmed the presence of a reverse fault the lachlan fault at the eastern margin of the lachlan anticline the lachlan fault is inferred to be responsible for growth of the anticline and deformation of the marine terraces the relationship of the reverse fault to the subduction thrust which separates the two crustal plates at about 20 km depth below mahia peninsula and dips about 6 12 to the nw is uncertain however the late pleistocene and holocene growth of the lachlan anticline indicates substantial coupling across the plate interface deforming the inner part of the frontal wedge of the australian plate

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

age height and deformation of holocene marine terraces at mahia peninsula hikurangi subduction margin new zealand mahia peninsula is a prominent coastal landmark in eastern north island and is the closest point of land in the north island to the hikurangi trough where the pacific plate plunges beneath the subduction complex at the eastern margin of the australian plate uplifted holocene marine deposits of both estuarine and open beach affinities are found in many parts of the peninsula and provide the basis for holocene tectonic characterization estuarine deposits record the later part of the postglacial transgression that culminated about 6500 years b p in new zealand the deposits have been differentially uplifted since that time at a rate of 2 5 0 3 mm yr in the central north coast area decreasing to 0 7 0 2 mm yr about 6 km to the west the coastal plain is characterised in many places by a stepped sequence of emergent shore platforms overlain by fossiliferous beach deposits extensive radiocarbon dating of samples from beach deposits shows that terraces in widespread parts of the peninsula are of five distinct ages each of the terraces is inferred to have formed in conjunction with a large prehistoric earthquake because of the stepped terrace morphology clustering of ages on each terrace differential uplift of terraces across the peninsula and historic coseismic uplift events in this tectonic setting paleoseismic events of mw 7 5 8 0 are estimated to have occurred approximately 250 1600 1900 3500 and 4500 years b p uplift distribution of the holocene and late pleistocene marine terraces shows that the peninsula lies on the west gentle flank of the active lachlan anticline which is cored by a major west dipping reverse fault the lachlan fault holocene active deformation at mahia peninsula and other coastal areas of eastern north island is a continuation of structures developed in pleistocene time in the landward part of the subduction complex adjacent to the hikurangi subduction zone

shallow morphology of the subducted pacific plate along the hikurangi margin new zealand abstract along the east coast of the north island new zealand the pacific plate is subducted beneath the australian plate the seismicity associated with this subduction has been determined using the results from a number of temporary and permanent microearthquake networks a synthesis of the microearthquake seismicity the depths of thrust events the depth of s to p conversions and deep reflection seismic studies leads to a coherent picture of the subducting slab both in terms of its mechanical structure and in terms of the general morphology the slab is initially subducted at a low angle of a few degrees is bent through a circular arc of few hundred kilometre radius and then becomes planar again below 120 km depth the radius of curvature varies along strike from about 280 km just north of wellington to 240 km north of hawke bay the slab shape between depths of 15 45 km is thus approximately conical it also approximates within the errors of hypocentre location a surface of constant gaussian curvature as would be geometrically expected from the simple bending of a thin spherical lithospheric shell observed seismicity is primarily concentrated within what is interpreted as the subducted crust of the pacific plate with a lower level of activity within the subducted mantle normal fault mechanisms at the top of the plate probably reflect tensional stress associated with the plate bending whereas thrust events observed at the lower bound of the observed seismicity probably reflect compression below the neutral plane

a late holocene marine terrace on the kidnappers coast north island new zealand some implications for shore platform development processes and uplift mechanism abstract a marine terrace up to 6 m above present mean sea level is preserved along 15 km of the kidnappers coast hawke s bay north island new zealand radiocarbon dates for 10 shell samples collected from intertidal marine deposits overlying an uplifted shore platform have a total age range of 590 yr from 2280 50 to 2750 70 yr b p sample age decreases landward suggesting a small relative sea level rise probably as a result of tectonic subsidence prior to uplift rates of contemporary shore platform formation preclude the preservation of a marine terrace subjected to constant aseismic uplift preservation of a subhorizontal uplifted shore platform mantled by intertidal marine deposits with in situ fauna is best explained by abrupt coseismic uplift 2300 yr b p and preceded by tectonic subsidence the presence of a single marine terrace does not permit the calculation of past earthquake magnitude or recurrence but the nne tilt of the 2300 yr old marine terrace indicates continued growth of the north trending late pleistocene kidnappers anticline

an elusive blind thrust fault beneath metropolitan los angeles seismic reflection profiles petroleum wells and relocated earthquakes reveal the presence of an active blind thrust fault beneath metropolitan los angeles a segment of this fault likely caused the 1987 whittier narrows magnitude 6 0 earthquake mapped sizes of other fault segments suggest that the system is capable of much larger magnitude 6 5 to 7 and more destructive earthquakes

splay fault slip during the mw 8 8 2010 maule chile earthquake splay faults are thrusts that emerge from the plate boundaries of subduction zones such structures have been mapped at several convergent margins and their activity commonly ascribed to large megathrust earthquakes however the behavior of splay faults during the earthquake cycle is poorly constrained because typically these structures are located offshore and are difficult to access here we use geologic mapping combined with space and land geodesy as well as offshore sonar data to document surface fault ruptures and coastal uplift at isla santa maria in south central chile 37 s caused by the 27 february 2010 maule earthquake m w 8 8 during the earthquake the island was tilted parallel to the margin and normal faults ruptured the surface and adjacent ocean bottom we associate tilt and crestal normal faulting with growth of an anticline above a blind reverse fault rooted in the nazca south america plate boundary which slipped during the maule earthquake the splay fault system has formed in an area of reduced coseismic plate boundary slip suggesting that anelastic deformation in the upper plate may have restrained the 2010 megathrust rupture surface fault breaks were accompanied by prominent discharge of fluids our field observations support the notion that splay faulting may frequently complement and influence the rupture of subduction zone earthquakes

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

submarine paleoseismology of the northern hikurangi subduction margin of new zealand as deduced from turbidite record since 16 ka abstract paleoseismic studies seek to characterise the signature of pre historical earthquakes by deriving quantitative information from the geological record such as the source magnitude and recurrence of moderate to large earthquakes in this study we provide a 16 000 yr long paleo earthquake record of the 200 km long northern hikurangi margin new zealand using cm thick deep sea turbidites identified in sediment cores cores were collected in strategic locations across the margin within three distinct morphological re entrants the poverty ruatoria and matakaoa re entrants the turbidite facies vary from muddy to sandy with evidence for rare hyperpycnites interbedded with hemipelagites and tephra we use the oxal probabilistic software to model the age of each turbidite using the sedimentation rate of hemipelagite deduced from well dated tephra layers and radiocarbon ages measurements on planktonic foraminifera turbidites are correlated from one core to the other using similarity in sedimentary facies petrophysical properties and ages results show that 46 turbidites are synchronous along the entire margin amongst them 41 are interpreted as originating from the upper continental slope in response to earthquake triggered slope failures between 390 170 to 16 450 310 yr bp using well established empirical relationships that combine peak ground acceleration magnitude and location of earthquakes we calculate that synchronous slope failures were triggered by the rupture of 3 of the 26 known active faults in the region each capable of generating mw 7 3 to 8 4 earthquakes two are crustal reverse faults and one is the subduction interface the 41 mw 7 3 earthquakes occurred at an average recurrence interval of 400 yr over the last 16 000 yr among them twenty are interpreted as subduction interface earthquakes that occurred at an average recurrence interval of 800 yr with alternating periods of high activity and low return times 305 610 yr and quiescence periods with high return times 1480 2650 yr based on turbidite paleoseismology we propose that subduction interface earthquakes were of lower magnitude during active periods mw 7 5 than during quiescence periods mw 8 2

micropaleontological evidence of large earthquakes in the past 7200 years in southern hawke s bay new zealand abstract foraminiferal and diatom assemblages in 11 cores 3 7 5 m deep of holocene sediment from brackish marine ahuriri inlet in southern hawke s bay new zealand provide a record of 8 5 m of subsidence followed by 1 5 m of uplift in the last 7200 cal years in a region overlying the subduction zone between the australian and pacific plates modern analogue technique was used to estimate paleotidal elevation of the 97 richest foraminiferal assemblages the most precise estimates are for high tidal salt marsh assemblages cored in marginal settings in the north and south of the former inlet the least precise estimates are from low tidal and subtidal assemblages from cores in the middle of the inlet these paleoelevation estimates combined with sediment thicknesses age determinations from tephrostratigraphy and radiocarbon dates the new zealand holocene sea level curve and estimates of compaction identify the holocene land elevation changes and earthquake displacement events in each core the following major earthquake related displacements are inferred ca 7000 cal yr bp 0 6 m displacement ca 5800 cal yr bp 0 5 m ca 4200 cal yr bp ca 1 5 m ca 3000 cal yr bp 1 4 to 1 8 m ca 1600 cal yr bp ca 1 7 m ca 600 cal yr bp ca 1 m 1931ad napier earthquake 1 5 m further smaller events involving regional subsidence or earthquake shake compaction are indicated during the 7000 3000 yr bp interval but cannot be identified precisely the six possibly subduction interface subsidence events in the last 7000 years have had a return time of 1000 1400 years identified displacement events have a range of sedimentary expressions from an eroded and burrowed hiatus surface to an abrupt lithologic switch from mud to sand or peat to shelly mud or in some places no change in sediment character whatsoever

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

strain partitioning between structural domains in the forearc of the hikurangi subduction zone new zealand the pacific plate obliquely converges with the australian plate at latitude 39 50 s along the hikurangi margin off the east coast of the north island of new zealand an extensive and youthful subaerially exposed forearc on the east coast of the north island in the hawke s bay area provides the opportunity to document contemporaneous forearc deformation in this obliquely convergent margin setting geologic mapping and analysis of strain at both mesoscale and megascale indicates that strain is partitioning into domains of extension contraction and strike slip the domains are elongate and trend parallel to the margin measurements of net shortening and transcurrent slip in the forearc show that the obliquely convergent motion is transferred across the plate interface deformation rates calculated for the past 1 2 m y for structures in all six forearc domains account for 50 70 of the margin parallel motion required by pacific australian plate convergence and about 6 of the plate motion perpendicular to the plate boundary at the surface in the forearc this obliquely convergent motion is manifest not by transpressional faults but rather by paired structural domains that consist of a strike slip fault zone and an accompanying contractional fault and fold zone on the trenchward side there are two such transcurrent faulting and contraction couplets one where the backstop daylights at the arcward edge of the forearc and another couplet trenchward of a relatively undisturbed forearc basin the small amount of shortening relative to strike slip in the onshore part of the forearc suggests that shortening perpendicular to the plate boundary may be concentrated offshore and that most of the component of plate motion perpendicular to the plate boundary may be accommodated by slip along the subduction zone megathrust

pervasive near surface stratal disruption in an accretionary prism setting kaczawa complex sw poland the tectonized and metamorphosed mudrocks within the variscan accretionary prism of the kaczawa mountains in sw poland comprise sedimentary melanges together with more coherent stratigraphic units some represent large olistoliths deposited in a submarine trench we infer a trend of progressive near surface stratal disruption in mud dominated deposits due to dewatering that forms a continuum with subduction related tectonic structures imposed on unconsolidated sediment during deeper burial the assemblage of characters suggests that an accretionary prism environment can influence and leave characteristic traces of the total burial history of a trench succession

a geometric model to estimate slip rates from terrace rotation above an offshore listric thrust fault kaikōura new zealand abstract the kaik ura peninsula lies at the transition from subduction to continental collision at the southern end of the hikurangi subduction system this study uses a 2012 lidar survey over the kaik ura peninsula to re map a flight of four uplifted late pleistocene marine terraces at high resolution the lidar shows that the terraces are being progressively tilted landwards in a manner consistent with listric thrust faulting offshore the fault known as the kaik ura peninsula fault dips shallowly at c 30 to the northwest at depth and probably truncates the seaward segment of the hope fault in the footwall of the jordan thrust geometric analysis of the tilt using ages based on previous dating and a regional sea level curve suggests that slip rates on the kaik ura peninsula fault have ranged between 2 3 1 5 mm yr and 4 1 1 3 mm yr over the late pleistocene the elevations of late holocene fringing beaches track regional sea level changes apart from a departure indicating a single uplift event penultimate earthquake in the late 18th to earliest 19th century 1702 1838 ce followed by uplift in the 2016 kaik ura earthquake the slip rate calculated from beach uplift including the kaik ura earthquake is consistent with longer term rates the accumulation of the slip over only c 220 years following 2000 years of quiescence suggests that the offshore thrust and associated faults exhibit clustered behavior possibly as a result of keystone faulting

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

holocene paleoseismicity in the fold and thrust belt of the hikurangi subduction zone eastern north island new zealand abstract along the 500 km long eastern coastline of the north island new zealand there are at most seven distinct holocene marine terraces aged 7 ka b p or less the highest of the terraces is 27 m above present day mean sea level the coastal region is subdivided into fourteen distinct subregions based on radiocarbon ages of marine deposits overlying wave cut shore platforms and geographic distribution of similarly aged terraces holocene marine terraces are the result of uplift associated with large earthquakes co seismic deformation this conclusion is based on characteristic stepped terrace morphology clustering of ages of terrace deposits within subrogions and the occurrence of co seismic uplift in historic time differential uplift across structures and distinct age variations at subregion boundaries are also characteristic recurrence intervals of uplift in any one terrace sequence vary from 0 4 ka to 2 0 ka and individual amounts of uplift vary from 1 0 m to 4 0 m in the past 2 5 ka ages from all terraces within subrogions indicate at least 21 paleoseismic events affecting coastal areas of eastern north island in that period these events cluster in time and in separate parts of eastern north island several earthquakes occurred 0 3 0 6 1 0 1 5 2 1 and 2 3 ka b p our data strongly support the concept of segmentation of deformation along the subduction margin the likely cause of coastal uplift is movement on steep reverse faults local structures rather than the subduction thrust that propagate from or near the subduction thrust some 20 25 km below the region earthquakes of moment magnitude 7 3 8 0 are estimated to be associated with these fault movements

a review of the milankovitch climatic beat template for plio pleistocene sea level changes and sequence stratigraphy the milankovitch theory of climate change predicts that global ice volume and hence sea level changes were controlled by long term quasi periodic variations in the earth s orbital parameters obliquity precession and eccentricity d 18 o records from deep sea cores are a proxy for sea level changes and have an orbitally tuned chronology covering the last 5 ma the sea level signal in d 18 o data from east equatorial pacific core v19 30 is well calibrated with sea level data from coral terraces on huon peninsula new guinea over the last 140 ka and with less certainty back to 340 ka over the last 140 ka the sea level contribution to benthic glacial interglacial isotopic variation is about 1 2 1 3 or 0 011 m 1 and for core v19 30 the glacial age temperature contribution from deep ocean cooling of 1 7oc is 0 4 independent constraints on late pliocene sea level changes interpreted from shallow marine continental margin records indicate that the sea level d 18 o calibration may not have been the same over the last 2 6 ma and the temperature correction is unlikely to have been the same in all glacial periods and all ocean settings nevertheless the astronomically tuned isotopic records from deep sea cores provide an accurate chronology and approximate the magnitudes of sea level changes over the last 2 6 ma against which the facies architecture of stratigraphic sequences can be analysed and the concepts of sequence stratigraphy properly evaluated 1998 elsevier science b v all rights reserved

grouping and migration of surface faulting and variations in slip rates on faults in the great basin province abstract nonuniformity of the occurrence of large slip events producing surface ruptures on seismogenic faults and variations in slip rate probably characterize seismogenic faulting in the great basin province western united states examples include the grouping of faulting events along the lost river fault idaho changes in tilt rates of the east range and cortez mountains nevada extension of slip along a fault on the northwest flank of the humboldt range nevada and migration or shifting of slip back and forth from one fault to another along subparallel range front faults in dixie valley nevada

late cenozoic evolution and earthquake potential of an active listric thrust complex above the hikurangi subduction zone new zealand in the center of the frontal wedge of the hikurangi subduction zone new zealand mahia peninsula and its submarine continuation lachlan ridge are being uplifted and folded above an active landward dipping thrust fault complex that is 80 km long high quality marine seismic reflection profiles reveal complex deformation of a cretaceous to holocene sedimentary section and enable a detailed analysis of the stratigraphy structural evolution deformation rates and future earthquake potential the structural analysis is facilitated by uplifted marine terraces on mahia peninsula and by 14 submarine unconformities in the hanging wall sequence five of which are correlated across the eroded crest of lachlan ridge and into the footwall basin the ages of the unconformities are determined by seismic ties to an offshore exploration well onshore outcrops on the peninsula and seabed samples dated by pollen coccolith nannoflora and foraminifera biostratigraphy nine regional quaternary unconformities which developed in response to eustatic fluctuations in sea level and are not older than ca 1 ma are correlated with oxygen isotope stages in equatorial pacific ocean drilling project core 677 the ages of fault growth strata and progressive restorations of deformed stratigraphy indicate that lachlan ridge developed during three phases of deformation since subduction of the pacific plate commenced beneath the australian plate in the early miocene these include an initial phase of thrust faulting a subsequent phase dominated by extensional faulting and the current mainly pleistocene to holocene phase of structural inversion reactivated listric thrust faulting and folding early to middle miocene thrusts in the deeper core of the complex developed out of sequence by sequentially stepping up into the hanging wall section creating an imbricate fan with emerging thrust tips now buried within the forelimb basin in the middle miocene early pliocene listric extensional faults developed in the active thrust wedge possibly as a result of substantial relief on the subducted pacific plate and controlled the development of lachlan basin to the west of the ridge the principal active thrust is the lachlan fault a listric extensional detachment reactivated to accommodate thrust movement and consisting of at least three right stepping segments depth converted seismic profiles indicate that the fault dips westward at 15 20 6 8 km beneath the western flank of lachlan ridge and steepens to 55 70 or even steeper in the upper 1 2 km of section beneath the eastern flank syninversion pleistocene fault growth strata on both flanks of the associated anticline provide an exceptional record of progressive fold limb rotation resulting from the listric fault geometry a geometric analysis of the fault growth strata and deformed terraces was used to derive a maximum dip slip displacement rate of as fast as 3 0 6 5 mm yr the implied shortening rate of 2 6 6 3 mm yr represents 8 20 of the total 31 mm yr of orthogonal plate convergence across this part of the upper plate of the hikurangi subduction zone the top of the pre fault growth paleogene section reveals as much as 5 8 1 5 km of vertical separation in the north decreasing to 30 50 of this value in the south temporal 10 3 10 6 yr and spatial 10 3 10 4 m of strike length variations in vertical deformation rate have occurred during the past 1 m y maximum rates occurred in the holocene and middle quaternary a long term increase in vertical separation rate on all segments during the pleistocene largely reflects a change in thrust kinematics associated with structural inversion the relatively greater increase in uplift rate on the northern part of the fault during the past 1 m y could be related to the possibility that a subducted seamount lies 10 km beneath the peninsula estimates of earthquake source parameters incorporating paleoseismic uplift data from mahia peninsula indicate a potential moment magnitude of up to m w 7 6 8 0 for an earthquake that ruptures all three segments of the lachlan fault the average recurrence interval for such events is estimated to be 615 2333 yr which is consistent with a mean recurrence interval of 1062 yr for four late holocene earthquakes thus the uplift and folding of mahia peninsula and lachlan ridge results from coseismic displacements on a major listric thrust fault that ruptures the upper plate frequently in association with large magnitude earthquakes

coastal deformation and great subduction earthquakes isla santa maria chile 37 s isla santa maria at the active margin of south central chile is the result of earthquake related uplift and deformation in the forearc since at least late pleistocene time field mapping dating of key depositional horizons and analysis of seismic refl ection profi les reveal ongoing deformation in this sector of the chilean forearc the 30 km 2 island is located 12 km above the interplate seismogenic zone and 75 km landward of the trench it is situated near the southern termination of the concepcion earthquake rupture segment where charles darwin measured 3 m of coseismic uplift during a m 8 megathrust earthquake in 1835 permanent postearthquake deformation from this earthquake and an earlier event in 1751 is registered by emerged landward tilted abrasion surfaces uplift at 2 m k y and tilting at 0 025 k y of the island have been fairly constant throughout the late quaternary and have resulted in emergence of the island above sea level 31 k y ago the island is composed of a late pleistocene upper tilted surface with two asymmetric tilt domains and holocene lowlands characterized by uplifted and tilted strandlines industry offshore seismic refl ection profi les covering an area of 1800 km 2 and crustal seismicity reveal active reversefault cored anticlines surrounding isla santa maria the principal fault apparently roots in the plate interface thrust these reverse faults in the upper plate result from inversion of late cretaceous to early pliocene normal faults and rift structure of the arauco forearc basin positive inversion of these inherited structures started between 3 6 and 2 5 ma and resulted in continuous shortening rates of 0 8 mm yr the seismic refl ection profi les show that the asymmetric tilt domains and progressive syntectonic sedimentation are linked to the position of the island in the forelimbs of two converging anticlines whereas their backlimbs have been removed by cliff retreat the 2 m uplift contour of the 1835 earthquake is parallel to the strike of active faults and antiforms in the arauco concepcion region the close relation among the asymmetric uplift and tilt of the island modern deformation patterns and reverse faults rooted in the plate interface suggests that slip on the plate interface thrust infl uences localizes and segments surface deformation during large interplate earthquakes furthermore the link between positive inversion of pre existing structures uplift and tilt patterns in the forearc emphasizes the importance of inherited structural fabrics in guiding plate boundary deformation

dynamic rupture activation of backthrust fault branching we perform dynamic rupture simulations to investigate the possible reactivation of backthrust branches triggered by ruptures along a main thrust fault simulations with slip weakening fault friction and uniform initial stress show that fast propagation speed or long propagation distance of the main rupture promotes reactivation of backthrust over a range of branch angles the latter condition may occur separately from the former if rupture speed is limited by an increasing slip weakening distance towards the junction direction the results suggest a trade off between the amplitude and duration of the dynamic stress near the main rupture front for backthrust reactivation termination of the main rupture by a barrier can provide enhanced loading amplitude and duration along a backthrust rooted near the barrier facilitating its reactivation especially with a high frictional resistance the free surface and depth dependent initial stress can have several additional effects the sign of the triggered motion along the backthrust can be reversed from thrust to normal if a deeply nucleated main rupture breaks the free surface while it is preserved as thrust if the main rupture is terminated by a barrier at depth the numerical results are discussed in relation to several recent megathrust earthquakes in sumatra chile and japan and related topics such as branch feedbacks to the main fault the dynamic view on backthrust fault branching provided by the study fills a gap not covered by quasi static models or observations a specific examined case of antithetic fault branching may be useful for indicating a barrier like behavior along the main fault

structural evolution along the inner forearc of the obliquely convergent hikurangi margin new zealand the accretionary margin of the hikurangi forearc on the southeast coast of the north island of new zealand is part of the leading edge of the australian plate which is overriding the obliquely converging pacific plate we investigate the last 10 m y of deformation history of the innermost western quarter of the total width of the forearc through analysis of the sedimentologic and structural evolution of the eketahuna area on the east coast of the north island the eketahuna area is ideal for such a study because emergence of the margin in the quaternary has exposed a complete late neogene rock record this record has allowed us to chronicle the strain history from 10 ma to about 2 5 ma this forearc region was the locus of subsidence and marine deposition in the latest pliocene this part of the margin began to shorten through folding and reverse faulting bringing an end to basin filling the period of shortening was brief and by the late pleistocene reverse faulting had ceased and was immediately succeeded by dextral strike slip faulting in some cases along the same faults presently the dominant strain regime in the inner quarter of the forearc is strike slip faulting this structural history illustrates that over time the pattern of strain partitioning has changed in the hikurangi forearc the switch from crustal shortening to dextral shear along the major faults in this area in the last 1 m y may be a response to more than 10 of clockwise rotation in the southern hikurangi forearc in pliocene and pleistocene time this rotation is a consequence of the fact that the accretionary margin is undergoing continuous deformation between the obliquely converging australian and pacific plates in this area at the southernmost end of the kermadec hikurangi subduction system the inboard portion of this young accretionary margin is exceptionally well exposed today probably in part because of the late neogene subduction of relatively thick buoyant crust of the hikurangi chatham plateau

listric thrusts in the western transverse ranges california some of the main faults accommodating current shortening in the western transverse ranges are probably listric because 1 they are associated with progressive tilting and 2 they may be preexisting normal faults that accommodated miocene extension these faults have been reactivated in the pliocene quaternary transpressive regime we propose a listric thrust model where slip is proportional to backlimb dip this model requires relatively little fault slip to account for progressive tilting and for wide in the dip direction and gently dipping backlimbs in contrast widely applied fault bend fold and fault propagation fold models relate fault slip to limb width alone and typically predict more shortening by the blind thrusts that can be accounted for by folding in the cover above them we trace the southernmost structural high in the transverse ranges from the santa monica mountains through the southern santa barbara channel the north dipping backlimb of this anticline is 20 30 km wide and 220 km long its presence suggests a very large north dipping thrust that could generate very large earthquakes the slip rate for this fault however is substantially lower for a listric thrust model than for a single step ramp flat model

growth stratal records of instantaneous and progressive limb rotation in the precordillera thrust belt and bermejo basin argentina analysis of synorogenic deposits preserved near the thrust front zone of the precordillera fold and thrust belt and in the bermejo foreland basin in central argentina documents the evolution of deformation during the last 5 myr as well as the thrust system kinematics seismic lines across the area display examples of progressive and instantaneous limb rotations the easternmost thrust plate of the central precordillera the niquivil thrust experienced episodic motion in two main stages a first thrust movement as a fault propagation fold and a second movement as a high angle anticlinal breakthrough fault after a period of quiescence growth strata deposited in the la pareja intermontane basin and the las salinas and bermejo anticline recorded continuous growth of eastern precordilleran structures beginning at 2 7 ma with uplift rates of 0 3 mm yr for the niquivil anticline 1 08 mm yr for the las salinas anticline and between 0 6 and 0 38 mm yr during the last 2 myr for the bermejo anticline once the eastern precordillera began to grow the propagation of the niquivil thrust stopped restricting the deformation to the young vallecito out of sequence thrust the complex geometry of growth strata deposited on the back limb of the las salinas anticline can be explained by using a model of a two step fault propagation fold with constant layer thickness the bermejo anticline of the eastern precordillera is formed by the simultaneous propagation of a shallow fault responsible for the fold shape and a deep fault that produced vertical uplift a growth triangle that documents instantaneous forelimb rotation for a fault propagation fold is recorded for the first time in a published seismic line

deciphering the late cretaceous cenozoic structural evolution of the north peruvian forearc system the link between plate tectonics and the evolution of active margins is still an ongoing task to challenge since the acceptance of plate tectonic paradigm this paper aims at deciphering the structural architecture and uplift history of the north peruvian forearc system to better understand the evolution and the mechanics that govern the late cretaceous cenozoic building of this active margin in this study we report surface structural geology data interpretation of seismic reflection profiles apatite fission track data and the construction of two offshore onshore crustal scale balanced cross sections the structure of the north peruvian forearc system is dominated by an accretionary style with northwestward propagation of thrust related structural highs involving continental oceanic basement rocks and off scrapped sediments the thrust systems bound thick thrust top forearc depocenters mainly deformed by crustal normal to strike slip faults and thin skinned gravitational instabilities the sequential restoration of the margin calibrated with apatite fission track data suggests a correlation between uplift shortening and plate convergence velocity during late cretaceous and miocene pliocene quaternary shortening and uplift of the coastal zone is rather related to the subduction of asperities during convergence rate decrease the development of crustal normal to strike slip faulting and subsidence zones might be the consequence of slab flexure local basal erosion along subduction fault and or oblique subduction associated with sediment loading control we conclude that the evolution of the north peruvian forearc system was controlled by subduction dynamics strong sediment accumulation and recent ridge subduction and it recorded the orogenic loading evolution of the andes over the cenozoic

temporal variations in latest quaternary slip across the australian pacific plate boundary northeastern south island new zealand rates of latest quaternary slip from stream terraces and moraines displaced by faults of the alpine shear system in ne south island new zealand vary in space and time detailed histories of fault slip are obtained from combining displacement data with estimates of the age of the surface from weathering characteristics precision in surface ages is 5 20 using rock weathering rinds and 15 50 using soil properties the oldest surfaces examined are 15 20 ka and have right lateral fault offsets up to 400 600 m the main faults of the in the ne south island the wairau awatere clarence hope kekerengu and porters pass faults have average latest quaternary right lateral slip rates of 3 10 5 10 7 10 25 40 5 7 and 3 4 mm yr respectively every fault has undergone a substantial decrease in lateral slip rate in the last 3 5 kyr summed across the plate boundary the average latest quaternary slip rates are comparable to long term rates of horizontal slip across the australian pacific plate boundary around 40 mm yr parallel to the boundary and rates of geodetic strain and seismic moment release over the last 50 100 years approximately the same however sums of lateral fault slip rates over the interval from 15 to 5 ka exceed the plate motions whereas late holocene lateral fault slip rates are less than half the long term average the best explanation of these variations is slip across the plate boundary is episodic varying over perhaps 5 kyr intervals this implies that 15 20 kyr is the time interval necessary to average out shorter 5 kyr episodic variations in plate boundary motions

kinematic model of detachment folding including limb rotation fixed hinges and layer parallel strain abstract detachment anticlines formed above a stratigraphically fixed detachment horizon and without thinning in the syncline will in general require layer parallel shortening a kinematic model for detachment folds is presented that has planar limbs and is area balanced but requires bed length changes that can be expressed as layer parallel strain the fold grows primarily by limb rotation not by limb lengthening at constant dip the kinematic evolution of the geometry and strain is examined fold geometry is well predicted and the strain estimated in applications of the model to two map scale detachment folds a triangle zone from the front of the wyoming thrust belt and a duplex cored anticline from the appalachian plateau

glacial interglacial control of terrigenous and biogenic fluxes in the deep ocean off a high input collisional margin a 139 kyr record from new zealand abstract sediment input to the deep ocean off the new zealand collisional plate boundary is large and variable as revealed by a 139 kyr old record from the 34 92 m long core md97 2121 mass accumulation rates mars were derived for terrigenous and biogenic carbonate and silica sedimentary components with temporal control from a stable isotope age model verified by tephra and radiocarbon ages terrigenous mars changed in phase with glacio eustatic fluctuations of sea level highest rates 30 g cm 2 kyr coincided with the late regressive lowstand early transgressive phase of marine isotope stage mis 2 when rivers discharged at or near the shelf edge lesser but still high terrigenous rates 20 30 g cm 2 kyr characterized peak warm phases of early mis 5 and 1 when a strengthened subtropical inflow probably introduced sediment from fluvial and seabed sources to the north of md97 2121 however during prolonged highstands the flux declined as more sediment was retained on a tectonically subsiding shelf with a shore parallel current paradoxically the lowest mars 10 5 g cm 2 kyr occurred in mis 4 either sea level was too high to allow much sediment to escape off shelf or the fluvial input was modest or both these factors despite the terrigenous dominance biogenic mars are high and are 2 4 times larger than sw pacific ocean rates mars were lowest during mis 4 and 3 possibly due to reduced marine production under a lowered input of fluvial micronutrients in contrast mars increased irregularly though glacial maxima to peak at 5 6 g cm 2 kyr carbonate and 2 2 5 g cm 2 kyr silica in early mid mis 5 and 1 such rates reflected the interaction of macronutrient rich subantarctic waters sourced from the south with local micronutrient rich subtropical waters production also responded to warmer temperatures elevated nutrient runoff and a more stratified surface ocean later in mis 5 and 1 fluxes reduced as less productive subtropical waters prevailed that biogenic and aeolian mar profiles are out of phase suggests fe fertilization by aerosolic dust was not a major influence

paleoseismology of an active reverse fault in a forearc setting the poukawa fault zone hikurangi forearc new zealand the poukawa fault zone on the north island of new zealand within the forearc of the hikurangi subduction zone consists of a series of en echelon reverse faults and companion hanging wall anticlines the geomorphically expressed length of the fault zone is 34 km however on the basis of coseismic deformation associated with an m s 7 8 earthquake in 1931 and the presence of blind faults north of the geomorphically expressed fault zone it appears that the seismogenic length of the fault zone may be as much as 130 km on the basis of chronostratigraphic horizons identified in each of three trenches evenly distributed along the exposed fault zone from which a paleoseismological record for the past 25 k y can be determined there is not a characteristic rupture length for earthquakes some slip events are confined to the 10 20 km long southern part of the fault zone whereas other slip events may have ruptured the entire 34 km length of the geomorphically expressed fault zone at least two slip events that occurred in the northern part of the fault zone did not occur in the southern part of the zone the largest earthquake recorded in the trenches had a maximum reverse slip in excess of 10 m we infer that this prehistoric earthquake similar to the 1931 earthquake entailed slip on faults along the geomorphically expressed fault zone and on blind faults to the north this prehistoric earthquake may have had a rupture length surface plus subsurface in excess of 100 km average earthquake repeat times on the fault zone range from 3 7 5 k y for the southern and middle part of the zone to 7 12 k y for the northern part of the fault zone average single event slip ranges from 3 m to as much as 6 m slip was initially accommodated at the surface primarily by folding with successive slip events however coseismic displacements propagated to the surface and surface deformation became increasingly dominated by reverse slip on fault planes the poukawa fault zone is part of a foreland propagating fold and thrust belt in the forearc of the hikurangi subduction zone older actively eroding hanging wall anticlines are present to the west of the fault zone toward the volcanic arc whereas younger folds are developing above blind reverse faults east of the main fault trace in addition to propagating to the east the fault zone is propagating northward beneath the heretaunga plains this active propagation testifies to ongoing and evolving contractional forearc deformation in response to oblique plate convergence

basement balancing of rocky mountain foreland uplifts restorable cross sections of foreland basement uplifts must contain faults whose curvatures are consistent with the relative slip and tilt between adjacent basement blocks cylindrical fault surfaces can explain the uniform dip of strata on the back side of foreland uplifts local zones of shortening and extension occur in hinge zones above transitions in fault curvature high curvature fault splays form fault wedges of basement which ease the transition from thrust and reverse faulting of basement blocks to folding in the sedimentary cover 20 references 4 figures

geometric and numerical model of progressive limb rotation in detachment folds a simple area balanced geometric model of progressive limb rotation in detachment folds allows the quantification of displacement uplift and rotation and the assessment of their effect upon growth strata geometries translation of this geometric model into a velocity model of deformation allows the modeling of associated growth strata resulting from background sedimentation and local erosion transport and deposition we show that with constant displacement and sedimentation rate this model predicts a progressive unconformity indicating the onlap and eventual overlap of the fold limb caused by a decreasing uplift rate this decrease is a consequence of the kinematics of progressive limb rotation increases in displacement rate with sedimentation rate kept constant can lead to offlap and angular unconformities although subsequent onlap does not necessarily reflect a return to a lower displacement rate modeled growth strata geometries exhibit many of the features reported from the literature

extensional deformation across an active margin relations with subsidence uplift and rotations the hikurangi subduction new zealand on the basis of field studies in the forearc domain of the hikurangi subduction margin in the eastern north island of new zealand we analyze the evolution of the subduction since its onset 25 myr ago analyses of brittle deformation within this forearc domain have revealed evidence of extensional deformation contemporaneous with the subduction of the pacific plate beneath the north island the type and origin of extensional deformation during the development of the active margin are discussed the problem is crucial because this forearc domain was previously considered as having undergone almost continuous compression during the late cenozoic two distinct events of late cenozoic extensional deformation are identified the youngest one is quaternary in age it affects limited areas where important uplift prevails the orientation of extensional paleostress axes is perpendicular to that of uplift axes hence consistent with the classical hypothesis of gravitational collapse affecting the upper part of the margin of particular interest is the older extensional event middle late miocene in age it affected most of the forearc domain during a long time span that was also characterized by widespread margin subsidence some structures attributed to this event are syndepositional including rollover structures and there are mainly high angle normal faults that affect not only the miocene sediments but also the pre miocene basement the orientations of paleostress axes obtained by inversion of fault data sets are multiple after corrections taking into account the rotational history of the margin during the late cenozoic they are found to be generally consistent with two major trends because these extensional structures developed throughout a long period of the margin subsidence it is proposed that they reflect the process of tectonic erosion that affected the hikurangi active margin during the middle and late miocene between about 15 and 5 myr ago

fault displacement gradient folds and the structure at lost hills california u s a abstract geometric models of fault propagation folds require that the underlying fault tip propagate upward across layering however related folds can be generated if the tip remains stationary or even moves back along the ramp as a pre existing fault is reactivated fault propagation folds detachment folds as well as those produced when there is no propagation are generated by a displacement gradient along the underlying fault and as a general class can be called fault displacement gradient folds new geometric equations are derived which relate fold shape to displacement gradient and fault propagation folds are a special case of these more general equations growth sequences associated with these structures have been used to distinguish fault propagation folds from fault bend folds when the underlying structure is obscured a displacement gradient fold in which the fault tip retreats back down the ramp generates a growth sequence that in some cases could be confused with that of a fault bend fold the structure at lost hills in the san joaquin valley of california u s a has been interpreted as a fault bend fold but it may be a displacement gradient fold which formed as a pre existing fault was reactivated during a pliocene change in plate motion

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

the influence of sea level and tectonics on late pleistocene through holocene sediment storage along the high sediment supply waipaoa continental shelf abstract we present geophysical and core evidence showing how subsidence caused by forearc shortening has accommodated late pleistocene and holocene sediments supplied to the tectonically active waipaoa shelf nz limiting off shelf export during the early sea level highstand the last glacioeustatic fall and subsequent rise exposed and then flooded a shelf segmented into subbasins separated by zones of uplift leaving key stratigraphic markers of shoreline regression and transgression that vary strongly in character across the shelf highstand sediment isopachs tied to piston cores dated using tephra correlation and a radiocarbon age model provide a sediment budget at 2000 yr intervals from the mid holocene 5500 cal yr bp to present sediment load estimates from our shelf budget are in agreement with published model estimates for suspended sediment discharge from the waipaoa river for the past 3000 yr but importantly do not show the 6 fold increase in the waipaoa s sediment output that began with human settlement 700 yr ago and accelerated with deforestation over the last century bypassing of waipaoa sediment to the slope may therefore be a recent phenomenon caused by unnaturally high sediment loads a conclusion supported by data reported elsewhere in this volume our study also reveals evidence for 1 a relatively thick mid shelf transgressive section deposited during the last eustatic rise that may correlate to estuarine sequences reported from numerous sites on the modern coastline of the north island 2 a slight decrease in total basin filling rates during the highstand and 3 variability in the partitioning of highstand sediments between individual subbasins that may reflect differing degrees of tectonic accommodation

coastal uplift mechanisms at pakarae river mouth constraints from a combined holocene fluvial and marine terrace dataset abstract one of the major environmental controls on sedimentary systems is tectonics and thus in order to make quantitative explanations and predictions of the behaviour of sedimentary systems it is important to quantify tectonic rates and mechanisms in this study we show how a combined holocene fluvial and marine terrace dataset can be used to place constraints on coastal uplift mechanisms at pakarae river mouth to the east of the waipaoa sedimentary system mapping and surveying of fluvial terraces shows that the terraces can be divided into three sets i pgt a fill terrace formed during post glacial sea level rise 10000 7000 cal yr bp ii a sequence of post 7000 cal yr bp degradation terraces and iii historical post ad 1880 flood terraces a conceptual model of terrace evolution proposes that coseismic uplift has resulted in the observed back tilting downstream divergence and successive abandonment of tectonic terraces coastal uplift mechanisms are then examined by comparing the fluvial and marine terrace uplift distribution and the uplift per event from the marine terraces with those predicted by forward elastic dislocation models the models agree with the interpretation that the terrace uplift can be explained by coseismic slip on a steeply west dipping reverse fault located close to the shore possibly in combination with rupture of the hikurangi margin subduction interface 10 24 km below this study also provides insights into the tectonic drivers and impacts on the adjacent waipaoa sedimentary system including the possible role of subduction earthquakes growth of structures on the shelf and upper slope and the role that the interplay between sea level and tectonic controls has on sediment dispersal

seafloor structural geomorphic evolution of the accretionary frontal wedge in response to seamount subduction poverty indentation new zealand abstract high quality swath bathymetry and seismic reflection data reveal that the steep forearc slope along the northern sector of the obliquely convergent hikurangi subduction zone is characteristic of non accretionary and tectonically eroding continental margins with reduced sediment supply in the trench relative to further south and the presence of subducting seamount relief on the hikurangi plateau these seamounts influence the subduction process and the structurally driven geomorphic development of the over riding margin of the australian plate frontal wedge the origin of the poverty indentation on the inboard trench slope is attributed to multiple seamount impacts over the last c 1 myr period accompanied by canyon incision thrust fault propagation into the trench fill and numerous large scale gravitational collapse structures with multiple debris flow and avalanche deposits ranging in downslope length from a few hundred metres to more than 40 km the indentation is directly offshore of the waipaoa river which is currently estimated to have a high sediment yield into the marine system the poverty canyon stretches 70 km from the continental shelf edge directly offshore from the waipaoa to the trench floor incising into the axis of the indentation the sediment delivered to the margin from the waipaoa catchment and elsewhere during sea level high stands including the holocene has remained largely trapped in a large depocentre on the poverty shelf while during low stand cycles sediment bypassed the shelf to develop a prograding clinoform sequence out onto the upper slope the formation of the indentation and the development of the upper branches of the poverty canyon system has led to the progressive removal of a substantial part of this prograding wedge by mass movements and gully incision sediment has also accumulated in the head of the poverty canyon and episodic mass flows contribute significantly to continued modification of the indentation by driving canyon incision and triggering instability in the adjacent slopes prograding clinoforms lying seaward of active faults beneath the shelf and overlying a buried inactive thrust system beneath the upper slope reveal a history of deformation accompanied by the creation of accommodation space the middle to lower poverty canyon represents a structural transition zone within the indentation coincident with the indentation axis the lower to mid slope south of the canyon conforms more closely to a classic accretionary slope deformation style with a series of east facing thrust propagated asymmetric anticlines separated by early stage slope basins north of the canyon system seamount impact has resulted in frontal tectonic erosion associated with the development of an over steepened lower to mid slope margin fault reactivation and structural inversion and over printing

temporal stability of deformation rates comparison of geological and geodetic observations hikurangi subduction margin new zealand abstract we examine how well contemporary horizontal velocity fields from global positioning system gps geodetic measurements describe long term deformation rates million year rates of extension shortening strike slip and vertical axis rotations are compared with modelling of gps velocities from the last 10 15 years in the hikurangi subduction margin new zealand within measurement uncertainties of mainly 50 the rates of deformation and vertical axis rotations for each time interval are usually indistinguishable the comparable deformation rates are consistent with the notion of near constant rates since 1 5 ma during this time oblique relative plate motion was partitioned with the majority 85 of margin normal motion accommodated on the plate interface and most 60 margin parallel motion by strike slip faulting and vertical axis rotations in the upper plate prior to 1 5 ma gps velocities cannot be reliably used to describe deformation and rotations of the hikurangi margin because at this time the taupo rift commenced opening the boundary between raukumara and wairoa rotational domains was abandoned and the rates of upper plate shortening increased the broad compatibility of gps and geological deformation and rotation rates since 1 5 ma suggests that the build up of contemporary elastic strains in the north island measured by gps is largely uniform for much of the duration of each seismic cycle the good agreement between the gps and geological deformation rates in the north island is consistent with the view that contemporary elastic strains will mainly be converted to permanent dip slip on the subduction thrust and to displacement on upper plate faults during future large magnitude earthquakes

submarine gas seepage in a mixed contractional and shear deformation regime cases from the hikurangi oblique subduction margin gas seepage from marine sediments has implications for understanding feedbacks between the global carbon reservoir seabed ecology and climate change although the relationship between hydrates gas chimneys and seafloor seepage is well established the nature of fluid sources and plumbing mechanisms controlling fluid escape into the hydrate zone and up to the seafloor remain one of the least understood components of fluid migration systems in this study we present the analysis of new three dimensional high resolution seismic data acquired to investigate fluid migration systems sustaining active seafloor seepage at omakere ridge on the hikurangi subduction margin new zealand the analysis reveals at high resolution complex overprinting fault structures i e protothrusts normal faults from flexural extension and shallow 1 km arrays of oblique shear structures implicated in fluid migration within the gas hydrate stability zone in an area of 2x7 km in addition to fluid migration systems sustaining seafloor seepage on both sides of a central thrust fault the data show seismic evidence for sub seafloor gas rich fluid accumulation associated with proto thrusts and extensional faults in these latter systems fluid pressure dissipation through time has been favored hindering the development of gas chimneys we discuss the elements of the distinct fluid migration systems and the influence that a complex partitioning of stress may have on the evolution of fluid flow systems in active subduction margins

seep bubble characteristics and gas flow rates from a shallow water high density seep field on the shelf to slope transition of the hikurangi subduction margin abstract we analyse an area of high density submarine methane gas seeps situated on the shelf to slope transition 130 420 m water depth on the northern region of new zealand s hikurangi margin off poverty bay multibeam and singlebeam echo sounder data collected in 2014 and 2015 revealed 600 seeps at much greater density than any previously mapped areas of seepage on the hikurangi margin to broadly constrain the output of methane from these seeps we have estimated the flow of methane at individual seeps utilising perspective measurements applied to still frames from a deep towed camera system to measure the dimensions of rising bubbles we combine bubble size and rise rate distributions with singlebeam acoustic data to estimate gas flow rates at six selected seeps sites our results predict a wide range 3 0 2249 ml min of methane release into the water column if we assume that the six seeps we analysed are representative of the entire seep population and that gas flow is constant we can extrapolate across the seep field and infer a gas release of 30 to 2415 t of methane per year into the ocean

duplex structures and imbricate thrust systems geometry structural position and hydrocarbon potential duplexes and imbricate thrust systems form some of the most complex hydrocarbon traps in overthrust belts the geometry of a duplex is controlled by the ramp angle thgr and height hr the final spacing between adjacent thrusts a prime and the relative displacements on them d1 d2 for constant thgr and hr three different classes are recognized 1 independent ramp anticlines and hinterland sloping duplexes 2 true duplexes and 3 overlapping ramp anticlines imbricate thrust systems consist of several thrust faults each of which loses displacement upsection and eventually dies out by progressively transferring its displacement to a fold at its tip or by distributing it among several splays hybrid duplexes are ormed from systems of fault propagation folds that are subsequently carried over ramps so they have a more complex geometry and a greater structural relief these different types of thrust systems occur as outcrops and prospect scale structures and they define the regional structural styles of most fold and thrust belts second and third order duplexes and imbricate thrust systems occur in specific structural positions such as footwalls hanging walls and frontal zones of major thrust ramps and in cores of major anticlines several types of duplexes and imbricate thrust systems form important hydrocarbon traps examples include the system of independent anticlines of the turner valley and highwood oil and gas fields the hinterland sloping duplex consisting of the chestnut ridge sandy ridge system of the ben hur oil field the partly overlapping anticlines of the waterton and savanna creek gas fields and the completely overlapping anticlines of the rose hill oil field