evolution of faulting and plate boundary deformation in the southern taranaki basin new zealand abstract faulting and folding in the southern taranaki basin constrain the evolution of the new zealand plate boundary since 80 ma sedimentary rocks up to 8 km thick record multiple phases of deformation which have been examined using 2d and 3d seismic reflection data resulting in fault displacement time curves and basin wide isopach maps with temporal resolutions of 5 10 myr and 1 4 myr pre and post 23 ma respectively three main phases of tectonic activity have been recognised late cretaceous and palaeocene extension 80 55 ma mainly oligocene and younger contraction and plio pleistocene 3 7 0 ma extension most of the largest faults e g cape egmont fault accrued displacement during the late cretaceous and were reactivated one or more times during subsequent episodes of deformation the oldest phase of extension occurred during gondwana break up and was ubiquitous throughout the basin contraction along the eastern boundary of the basin associated with the onset of hikurangi margin subduction commenced as early as late eocene the zone of contraction widened and migrated westward during the miocene with reverse faults and folds in westernmost parts of the basin formed in the late miocene 7 5 ma initiation and episodic widening of this zone of contraction may have been partly triggered by changes in the rate of plate convergence contraction is now mainly confined to the northern south island and has been succeeded to the north by plio pleistocene extension the present day transition zone between extension in the north and contraction in the south is defined by a wnw trending line across the basin the extension contraction transition migrated southward during the late miocene and pliocene consistent with steepening of the subducting plate and associated southward movement of the southern termination of the hikurangi subduction system

from partial to full strain partitioning along the indo burmese hyper oblique subduction abstract the andaman nicobar trench and its onshore prolongation the indo burmese wedge is the least studied segment of the india australia subduction new offshore geological and geophysical data have recently been collected along the burma scarp during a marine survey conducted with the r v marion dufresne andaman cruise swath bathymetric mapping combined with shallow and deep seismic show that the dominant active tectonics is dextral strike slip faulting accompanied by various amounts of shortening the southern portion of the burma scarp is transpressive north andaman islands the central portion is pure strike slip on nne oriented segments southern myanmar the northern portion shows sedimentary wedge growth along nw segments both onshore and offshore arakan yoma prism further north the wedge bends to the west while dextral shear faults more or less parallel to the sagaing fault develop within the internal part of the wedge and elongated ns folds form in its external part abutting onto the shillong plateau we propose a simple kinematic model involving evolution from partial to full partitioning from south to north along the west burma scarp wbs and we test it quantitatively using the most recent geodetic results in the south half of the 3 5 cm year of india motion is taken at the trench itself the other half being accommodated onto a single shear fault the sagaing fault in myanmar in the north where the bangladesh fold system developed dextral strike slip faults are activated within the arakan yoma belt and at the accretionary prism backstop contact resulting in full partitioning there faults accommodating the oblique component of motion of india are progressively migrating in space from far field faults andaman sagaing to near trench faults arakan yoma belt and trench itself the burma sliver being buttressed by the eastern himalayas this kinematic extends back to 4 ma which is the time of initiation of the last pulse of oceanic accretion in the andaman basin

oblique slip on the puysegur subduction interface in the 2009 july mw 7 8 dusky sound earthquake from gps and insar observations implications for the tectonics of southwestern new zealand summary the mw 7 8 dusky sound earthquake of 2009 july 15 was the largest earthquake in new zealand in the past 80 yr and is the only major subduction interface earthquake in the new zealand historical record we have estimated the coseismic and early post seismic slip distribution in the earthquake by inversion of gps and differential interferometric synthetic aperture radar dinsar observations we show that slip during the earthquake was highly obliqueandessentiallyintheaustralia pacificrelativeplatemotiondirection failureoccurred onaca 80by50kmpatchofthesubductioninterfacewithmaximumslip5 6m inthisregion the offshore alpine fault carries up to 30 mm yr 1 of slip before terminating at resolution ridge near the southern end of the 2009 slip patch the southernmost part of the alpine fault trace lies near the up dip end of the 2009 slip patch and the fault probably exists only within the crust of the over riding plate in this region terminating at shallow depth where it meets the subduction interface there is no evidence for rupture of the alpine fault during the 2009 event however coulomb stress changes from the subduction earthquake have brought this section of the alpine fault closer to failure in contrast to many subduction zones undergoing oblique subduction where the slip in major earthquakes is partitioned into more or less pure thrustearthquakesonthesubductioninterfaceandstrike slipearthquakesinthebackarc thisis a case where the majority of the subduction interface slip is not partitioned with only a shallow convergence zone west of the strike slip alpine fault undergoing contraction approximately normal to subduction zone strike north of the 2009 earthquake region the alpine fault lies further east relative to the subduction interface and partitioning between strike slip on the alpine fault and trench normal thrusting on the subduction interface takes place in a more typical fashion our results provide the first clear demonstration of non partitioned oblique slip between the australian and pacific plates offshore of southern new zealand

megathrust splay faults at the focus of the prince william sound asperity alaska 1 high resolution sparker and crustal scale air gun seismic reflection data coupled with repeat bathymetric surveys document a region of repeated coseismic uplift on the portion of the alaska subduction zone that ruptured in 1964 this area defines the western limit of prince william sound differencing of vintage and modern bathymetric surveys shows that the region of greatest uplift related to the 1964 great alaska earthquake was focused along a series of subparallel faults beneath prince william sound and the adjacent gulf of alaska shelf bathymetric differencing indicates that 12 m of coseismic uplift occurred along two faults that reached the seafloor as submarine terraces on the cape cleare bank southwest of montague island sparker seismic reflection data provide cumulative holocene slip estimates as high as 9 mm yr along a series of splay thrust faults within both the inner wedge and transition zone of the accretionary prism crustal seismic data show that these megathrust splay faults root separately into the subduction zone decollement splay fault divergence from this megathrust correlates with changes in midcrustal seismic velocity and magnetic susceptibility values best explained by duplexing of the subducted yakutat terrane rocks above pacific plate rocks along the trailing edge of the yakutat terrane although each splay fault is capable of independent motion we conclude that the identified splay faults rupture in a similar pattern during successive megathrust earthquakes and that the region of greatest seismic coupling has remained consistent throughout the holocene

crustal structure and neotectonics of the puysegur oblique subduction zone new zealand abstract eocene oligocene rifting followed by miocene quaternary strike slip and obliquely convergent tectonics are responsible for crustal thinning in the solander basin and subsequent development of the puysegur oblique subduction zone southwest new zealand highly oblique convergence at a rate of 35 mm yr is being partitioned between oblique subduction at the puysegur trench thrusting within the trench slope strike slip faulting on the puysegur bank and minor shortening within the solander basin subduction is young and a volcanic arc is not yet well developed we present seismic reflection data recorded across the puysegur subduction zone and solander basin three strike slip fault zones are recognised on the basis of seismic and bathymetric data in the puysegur bank region north of the profile some displacement on the eastern fault is transferred eastward to the hauroko fault but most strike slip motion is inferred to be west of fiordland south of the profile strike slip faults merge with faults of the puysegur ridge active thrusting dominates the trench slope where a thick sedimentary section is evident and bottom simulating reflectors are common the relatively steep average slope angle of 6 suggests the sediments are moderately well cemented possibly similar to sediments found in the solander basin the small amount of sediment found on the subducting plate is consistent with little or no accretion at the margin patches of reflectivity we interpret as sediment at the top of the subducted plate suggest that the slab has a moderate dip of 10 20 to 20 km depth in the solander basin seismic reflection data clearly image the sedimentary section and show well developed crustal and upper mantle reflections to depths of 30 35 km 12 13 s twt on the basis of lower crustal reflectivity and gravity modelling the base of the crust beneath the adjacent stewart island shelf is at 30 km 9 s twt and rises to a depth of 20 km 8 s twt beneath the solander basin prominent dipping reflections which we interpret as an active fault can be traced to 30 km depth 12 s twt where they merge into a zone of strong reflectivity in the upper mantle

paleogene seafloor spreading in the southeast tasman sea magnetic anomalies 11 18 have been identified in the southeast tasman sea the area of ocean crust southwest of fiordland new zealand west of the puysegur trench the present plate boundary and southeast of the older 80 58 ma ocean crust of the tasman sea basin structures associated with two changes in spreading direction are preserved in the area spreading between the australian and pacific plates began in the eocene about 40 ma in this area orthogonal to cretaceous paleocene spreading between them in the tasman sea the boundary between the two ages of ocean crust is abrupt and associated with what we have interpreted as marginal uplift blocks and rift basins of the resolution ridge system rifting appears to have propagated northeast along a fracture zone the northern blocks of the resolution ridge system may be isolated fragments of continental crust of the campbell plateau between anomalies 18 and 11 40 30 ma the spreading rate was about 1 5 cm yr swath mapping and satellite altimetry data show that a second change in relative plate motion direction began shortly after anomaly 11 about 30 ma and led to a change from tension to transcurrent motion along the plate boundary the timing of the changes in spreading direction agrees with tectonic events interpreted from onshore data

paleogene evolution of the kodiak islands alaska consequences of ridge trench interaction in a more southerly latitude the kodiak islands of alaska are principally composed of a late cretaceous and paleogene complex of accreted deep sea rocks an early paleocene magmatic event invaded the accretionary complex with mid ocean ridge basalt morb andesite and granodiorite geochemical evidence suggests both the andesite and granodiorite are mixtures of morb and sediment the volcanic rocks are interlayered with coarse clastic sediments and deformed with the latter the granodioritic intrusions with k ar ages as old as 62 ma postdate emplacement of the early paleocene sedimentary and volcanic rocks interaction of the subduction complex with the kula farallon ridge most simply explains this early paleocene magmatic episode paleomagnetic studies of the volcanic rocks indicate this interaction occurred at 40 3 6 north latitude which is 25 3 9 south of the expected position of the kodiak islands relative to north america the magmatic arc presently northwest of the kodiak accretionary complex was active during the late cretaceous and early paleocene diminished after the ridge trench interaction and resurged from late eocene into miocene time the magmatic resurgence is coeval with the obductive offscraping of eocene to oligocene submarine fan deposits in the kodiak islands the petrology of these fan deposits indicates they are the most likely proximal equivalent for the zodiac fan thereby limiting its relative motion with respect to the kodiak islands possible models accounting for the northward motion of the kodiak accretionary complex include 1 coupling the accretionary complex and possibly related arc to the northward moving kula plate and closing an ocean basin north of the arc in paleogene time 2 emplacing the kodiak accretionary complex at the northward limit of the paleomagnetic data with subsequent northward motion accomplished by closure of a small back arc basin and or intracontinental shortening and 3 transcurrent faulting and northward motion of the kodiak accretionary complex without the presently adjacent arc

crustal structure of accreted terranes in southern alaska chugach mountains and copper river basin from seismic refraction results seismic refraction data were collected along a 320 km long transect line in southern alaska crossing the prince william chugach peninsular and wrangellia terranes and along several shorter lines within individual terranes velocity structure in the upper crust less than 9 km depth differs among the four terranes in contrast layers in the middle crust 9 to 25 km depth in some cases extend across projected terrane boundaries the following observations can be made 1 an intermediate velocity layer 6 4 km s at 9 km depth extends across the deep projection of the suture between the chugach and peninsular terranes suggesting that the northern chugach and southern peninsular terranes are detached and rest on a deeper terrane of unknown origin 2 the top of a gently north dipping sequence of low and high velocity layers 5 7 7 8 km s more than 10 km thick extends from near the surface in the southern chugach terrane to more than 20 km depth beneath the southern peninsular terrane this sequence truncated by the suture between the prince william and chugach terranes is interpreted to be an underplated terrane made up of fragments of the kula plate and its sedimentary overburden that were accreted during subduction in the late mesozoic and or early tertiary during or between times of accretion of the prince william and chugach terranes 3 a thick crustal root with a laminated sequence at its top extends from a depth of 19 km to as much as 57 km beneath the northern peninsular and wrangellia terranes this root extends across the deep projection of the suture between the peninsular and wrangellia terranes although resolution of this apparent crosscutting relationship is relatively poor this root may represent tectonically or possibly magmatically emplaced rocks the lower crust beneath the prince william chugach and southern peninsular terranes includes a north dipping 3 to 8 km thick section of subducting oceanic crust

model for the origin of the yakutat block an accreting terrane in the northern gulf of alaska a composite oceanic and continental terrane the yakutat block is currently colliding with and accreting to north america in the northern gulf of alaska marine geophysical data indicate that the block has moved with the pacific plate during pliocene and quaternary time but are indeterminant about its previous movement history a model that explains some observed geologic and structural features of the block is that it originated as a result of subduction of the kula farallon spreading center beneath north america in this model the spreading center that formed the basaltic basement of the yakutat block was offset from a spreading center to the south by a left lateral transform fault 400 500 km long subduction of the northern spreading center about 45 m y ago sliced off part of the north america continental margin attached it to the kula plate and initiated northward movement of the composite terrane as the yakutat block during eocene and oligocene time migration of the southern spreading center toward north america truncated the yakutat block on the south and left a fossil fracture zone that is now seen as the transition fault the southern spreading center subducted about 25 m y ago and the yakutat block has since traveled with the pacific plate to southern alaska

the oligocene miocene pacific australia plate boundary south of new zealand evolution from oceanic spreading to strike slip faulting abstract since the eocene the pacific australia plate boundary south of new zealand has evolved from a spreading system into a transform boundary swath data acquired in the southeast tasman oceanic crust between the macquarie ridge complex and the resolution ridge system show that the spreading fabric changes orientation southwards along the puysegur trench striking successively n60 e n85 e and n120 e this reflects the reorganisation of the plate boundary in response to changes in relative plate motion a comparison of these orientations with the positions of the pacific australia relative poles of rotation enables us to estimate the age of stoc where there are no identified magnetic anomalies the youngest age of the oceanic crust is ca 12 ma at the south end of the puysegur trench this age is consistent with spreading rates and the amount of crust generated since 31 ma curved fracture zones on either side of the macquarie ridge complex suggest a continuous reorientation of transform faults between 31 ma and ca 15 ma small scale seafloor morphology shows a 13 change of orientation in the l atalante fracture zone that indicates incremental rather than continuous changes in azimuth of the transform faults patterns of fanning ridges indicate that periods of asymmetric spreading accompanied the spreading segment reorientations using swath data and plate reconstruction models we infer that between 31 and 12 ma the plate boundary reorganisation resulted in a continuous increase in the ratio of the cumulative length of transform faults over the cumulative length of spreading segments along the whole plate boundary this indicates that since 14 15 ma the plate boundary has become progressively predominantly transcurrent allowing strike slip motion to develop along a line of merging transform faults that connected to the intracontinental alpine fault

a multiscale approach to high resolution ocean profile observations within a 4dvar analysis system abstractmost ocean data assimilation systems are tuned to process and assimilate observations to constrain features on the order of the mesoscale and larger typically this involves removal of obse

a viscoelastic and afterslip postseismic deformation model for the 1964 alaska earthquake 1 we developed a 3 d viscoelastic model in concert with an afterslip model to describe the postseismic deformation following the 1964 alaska earthquake our model incorporates a realistic geometry including an elastic slab with very low dip angle these geometric factors are important and require a reanalysis of the 1964 coseismic model our coseismic model differs from previous models in that the montague island splay fault extends farther along the kenai peninsula coast and as a result slip on the megathrust in that region is smaller we computed postseismic deformation models using a range of mantle viscosities with maxwell relaxation time of 1 to 50 years with a best estimate of 20 years the viscoelastic model explains most of the trenchward motion observed in the present velocity field but has little impact on cumulative 1965 to present uplifts after removing the viscoelastic response the largest residual cumulative uplifts were located downdip from areas of largest coseismic slip area and we explain them using an afterslip model constrained in space by the observed cumulative postseismic uplifts and in time by tide gauge records no single mechanism can explain both the 30 years of cumulative uplift and the present velocities but a combination of viscoelastic relaxation afterslip interseismic elastic deformation and motion of southern alaska relative to north america explains the first order features of the observations forty years after the earthquake the present day velocities contain a significant component of postseismic deformation so very long lived postseismic deformation plays an important role in the subduction zone earthquake cycle for great earthquakes

quantifying offshore fore arc deformation and splay fault slip using drowned pleistocene shorelines arauco bay chile most of the deformation associated with the seismic cycle in subduction zones occurs offshore and has been therefore difficult to quantify with direct observations at millennial time scales here we study millennial deformation associated with an active splay fault system in the arauco bay area off south central chile we describe hitherto unrecognized drowned shorelines using high resolution multibeam bathymetry geomorphic sedimentologic and paleontologic observations and quantify uplift rates using a landscape evolution model along a margin normal profile uplift rates are 1 3 m ka near the edge of the continental shelf 1 5 m ka at the emerged santa maria island 0 1 m ka at the center of the arauco bay and 0 3 m ka in the mainland the bathymetry images a complex pattern of folds and faults representing the surface expression of the crustal scale santa maria splay fault system we modeled surface deformation using two different structural scenarios deep reaching normal faults and deep reaching reverse faults with shallow extensional structures our preferred model comprises a blind reverse fault extending from 3 km depth down to the plate interface at 16 km that slips at a rate between 3 0 and 3 7 m ka if all the splay fault slip occurs during every great megathrust earthquake with a recurrence of 150 200 years the fault would slip 0 5 m per event equivalent to a magnitude 6 4 earthquake however if the splay fault slips only with a megathrust earthquake every 1000 years the fault would slip 3 7 m per event equivalent to a magnitude 7 5 earthquake

fjords as temporary sediment traps history of glacial erosion and deposition in muir inlet glacier bay national park southeastern alaska glacimarine sedimentary deposits within the basins of muir inlet a 48 km long silled fjord are interpreted from complimentary sets of high resolution seismic reflection profiles using known glacial advance and retreat history two prominent glacial erosion surfaces are identified the lowest attributed to the last glacial maximum lgm advance and the upper coincident with the little ice age lia advance the lgm ice sheet which advanced onto the continental shelf was 1700 m thick in muir inlet and eroded bedrock whereas the thinner lia ice did not lgm deposits 300 m thick occur beneath the lia erosion surface in the deepest basins evidence for earlier neoglacial advances is present in subaerial deposits however neoglacial sediments preserved within the marine record are restricted to one depositional package on the entrance sill volumes of lia retreat sediments were calculated within basins an average annual sediment flux was calculated by modeling the duration of sediment contributed from muir glacier and from tributary glaciers and side entry sources the annual sediment flux ranged from 1 3 10 6 m 3 yr to 4 6 10 7 m 3 yr and increases logarithmically with increasing drainage basin area similar to fluvial systems this sediment flux does not only represent bedrock erosion additional sediment is contributed from persistent tributary glaciers and from lgm sediment stored within deeper basins basin wide reflections characterize the most common seismic facies and indicate that strata are horizontal and continuous across each basin confirming the importance of sediment gravity flows originating from sills and sloping fjord walls

oblique collision and evolution of large scale transcurrent shear zones in the kaoko belt nw namibia abstract early structures in the central part of the kaoko orogenic belt of nw namibia suggest that the initial stage of collision was governed by underthrusting of the medium grade central kaoko zone below the high grade western kaoko zone resulting in the development of an inverted metamorphic gradient in the western zone early structures were overprinted by a second phase of deformation which is associated with localization of the transcurrent puros shear zone along the contact between the western and central zones during this second phase extensive partial melting and intrusion of 550 ma granitic bodies occurred in the high grade western zone in the central zone the second phase of deformation led to complete overprinting of the early foliation in the zone adjacent to the puros shear zone and to the development of kilometre scale folds in the more distal parts strain partitioning into transcurrent deformation along the puros shear zone and ne sw oriented shortening in the central zone is consistent with a sinistral transpressional regime during the second phase of deformation transcurrent deformation continued during cooling of the entire belt giving rise to the localized low temperature village mylonite zone that separates a segment of elevated mesoproterozoic basement from the rest of the western zone in which only pan african ages have so far been observed the data suggest that the boundary between the western and central kaoko zones represents a modified thrust zone controlling the tectonic evolution of the pan african kaoko belt

rupture process of the 1964 prince william sound alaska earthquake from the combined inversion of seismic tsunami and geodetic data 1 four great earthquakes 1952 1960 1964 and 2004 have occurred since seismic monitoring began and only two since the installation of a global seismic network a reexamination of the 1964 m 9 2 prince william sound pws alaska earthquake is timely due to the 2004 sumatra earthquake because it adds constraints to the potential range of source parameters for these types of infrequent events and aids in the ability to predict the ground motions for other subduction zone including cascadia we first measured the durations of high frequency energy radiation from teleseismic p wave codas recorded by short period world wide standardized seismographic network wwssn sp instruments to put constraints on the earthquake rupture length the durations ranged between 250 and 600 s and are shorter in time between azimuths of 190 and 260 the fault length is estimated to range from 540 to 740 km rupturing at average speeds of 1 4 2 km s in a 220 238 direction we developed a multiple time window kinematic rupture model for the pws earthquake from the least squares inversion of teleseismic p waves tsunami tide gauge records and geodetic leveling survey observations based on the green s function technique we assume three major fault segments for the subduction zone dipping 6 12 based on geologic data the subfault size on the megathrust was set to 50 50 km the patton bay fault pbf imbricate thrust was assigned a 60 dip with a subfault size of 20 20 km we estimated a seismic moment of 5 52 1022 n m mw9 12 we identified three areas of major moment release on the pws segment near montague and middleton islands extending out to the trench beneath the portlock anticline on the cook segment between 58 n fracture zone and the kodiak bowie seamount chain and finally on the katmai segment off the coast of kodiak island extending to the trench our preferred rupture model has a peak slip of 14 9 m along the megathrust and 17 4 m along the pbf the addition of the pbf resulted in an 8 improvement in residuals and also had a significant effect on the overall slip distribution moment release occurred as deep as 50 km depth slab contour near the 350 c isotherm and mantle fore arc wedge which is about 10 20 km deeper than previous coupling depths

tectonic block motion and glacial isostatic adjustment in southeast alaska and adjacent canada constrained by gps measurements 1 we use data from campaign and continuous gps sites in southeast alaska and the neighboring region of canada to constrain a regional tectonic block model that estimates block angular velocities and derives a self consistent set of fault slip rates from the block motions present day tectonics in southeast alaska is strongly influenced by the collision of the yakutat block our model predicts a velocity of 50 3 0 8 mm a toward n22 9 0 6 w for that block our results suggest that the eastern edge of the yakutat block is deforming along this edge the fairweather fault accommodates a large portion of the pacific north america relative plate motion through 42 9 0 9 mm a of dextral slip further south along the queen charlotte fault our model predicts an average of 43 9 0 6 mm a of dextral slip and a southward increasing amount of transpression strain from the yakutat collision is transferred far to the east of the strike slip system this strain transfer causes the region north of glacier bay to undergo a clockwise rotation south of glacier bay and inboard of the queen charlotte fault a smaller but clearly defined clockwise rotation is observed the heterogeneous block motion north and south of glacier bay may indicate the area is undergoing internal deformation and could explain regional patterns of diffuse seismicity the northern cordillera of canada displays a small northeasterly motion our block model suggests that the entire southeastern alaska northwestern canada margin is mobile

accretion in the wake of terrane collision the neogene accretionary wedge off kenai peninsula alaska subduction accretion and repeated terrane collision shaped the alaskan convergent margin the yakutat terrane is currently colliding with the continental margin below the central gulf of alaska during the neogene the terrane s western part was subducted after which a sediment wedge accreted along the northeast aleutian trench this wedge incorporates sediment eroded from the continental margin and marine sediments carried into the subduction zone on the pacific plate prestack depth migration was performed on six seismic reflection lines to resolve the structure within this accretionary wedge and its backstop the lateral extent of the structures is constrained by high resolution swath bathymetry and seismic lines collected along strike accretionary structure consists of variably sized thrust slices that were deformed against a backstop during frontal accretion and underplating toward the northeast the lower slope steepens the wedge narrows and the accreted volume decreases notwithstanding a doubling of sediment thickness in the trench in the northeasternmost transect near the area where the terrane s trailing edge subducts no frontal accretion is observed and the slope is eroded the structures imaged along the seismic lines discussed here most likely result from progressive evolution from erosion to accretion as the trailing edge of the yakutat terrane is subducting

abrupt strike slip fault to subduction transition the alpine fault puysegur trench connection new zealand swath bathymetry and other geophysical data collected over the fiordland margin southwest of new zealand are used to investigate the mechanism of transform subduction transition between the alpine fault and the puysegur trench two segments of the pacific australian plate boundary in this region the cenozoic southeast tasman basin which obliquely underthrusts fiordland at the puysegur trench is separated from the cretaceous tasman basin by the resolution ridge system a major lithospheric discontinuity of the downgoing plate interpretation of seafloor morphology shows that the alpine fault extends offshore along the fiordland coast and splits into west and east branches the west branch cuts obliquely across the margin and connects sharply to the puysegur subduction front at the northeastern tip of the resolution ridge system earthquake and seismic reflection data indicate that the west branch is genetically controlled by downgoing plate structures associated with the resolution ridge system hence the west branch is interpreted as the surface trace of the plate boundary segment extending between the alpine fault and the puysegur trench we conclude that the development of the strike slip segment of the plate boundary and its sharp transition to the puysegur subduction are controlled by inherited structures of the australian plate furthermore according to geophysical data presented here a tearing of the downgoing plate can be interpreted beneath the west branch a review of geophysical data along the region of the alpine fault hikurangi trough northeast new zealand shows a progressive transform subduction transition that is accommodated by motion partitioning between the subduction interface and strike slip faults this transition is accounted for by an interplate coupling that progressively increases toward the alpine fault in relation with a gradual thickening of the downgoing crust the comparison between the fiordland and the hikurangi strike slip subduction transitions show that presence of inherited downgoing plate crustal faults properly oriented with respect to the plate motion facilitates a sharp strike slip subduction transition

focal mechanisms of large earthquakes in the south island of new zealand implications for the accommodation of pacific australia plate motion b the plate motion model nuvel 1 predicts oblique convergence between the pacific and australian plates in the south island of new zealand we used p and sh body waveform analysis to constrain the focal mechanisms of the 15 largest earthquakes ms 5 8 that have occurred in this region since 1964 in order to see how the plate motion is accommodated at the southern end of the alpine fault convergence is achieved by oblique slip movement along a concentrated zone of deformation in the southern offshore region one event may be related to thrusting of the australian plate beneath the pacific plate and another strike slip event probably demonstrates movement on an active strike slip fault system parallel to but offset from the southern limit of the alpine fault this geometry provides a possible mechanism for the rapid uplift of the fiordland region deformation in the northern south island is more distributed in the south west marlborough region partitioning occurs between strike slip faulting in the se and reverse faulting farther nw in the buller region we suggest that the partitioning developed as a consequence of an increasing component of shortening that was accommodated by slip on reactivated pre existing normal faults in the buller region shortening in the buller region may have deflected the ne end of the alpine fault towards the nw forming the prominent bend the marlborough fault system with its youngest and most active faults to the se probably developed in an attempt to maintain a through going strike slip structure as each of the strike slip faults was transported towards the north west partitioning of the opposite polarity with reverse faulting se of the strike slip faulting occurs in north east marlborough the boundary between the two different styles of partitioning in ne and sw marlborough appears to coincide with a change in the nature of the downgoing slab and a change in strike of faults of the marlborough fault system a normal faulting earthquake on the northern edge of the chatham rise probably results from a complex interaction of the buoyant continental crust in that region with the subduction zone and the overlying marlborough fault system

landslides and megathrust splay faults captured by the late holocene sediment record of eastern prince william sound alaska abstract we present new marine seismic reflection profiles and bathymetric maps to characterize holocene depositional patterns submarine landslides and active faults beneath eastern and central prince william sound pws alaska which is the eastern rupture patch of the 1964 m w 9 2 earthquake we show evidence that submarine landslides many of which are likely earthquake triggered repeatedly released along the southern margin of orca bay in eastern pws we document motion on reverse faults during the 1964 great alaska earthquake and estimate late holocene slip rates for these growth faults which splay from the subduction zone megathrust regional bathymetric lineations help define the faults that extend 40 70 km in length some of which show slip rates as great as 3 75 mm yr we infer that faults mapped below eastern pws connect to faults mapped beneath central pws and possibly onto the alaska mainland via an en echelon style of faulting moderate m w 4 upper plate earthquakes since 1964 give rise to the possibility that these faults may rupture independently to potentially generate m w 7 8 earthquakes and that these earthquakes could damage local infrastructure from ground shaking submarine landslides regardless of the source of initiation could generate local tsunamis to produce large run ups along nearby shorelines in a more general sense the pws area shows that faults that splay from the underlying plate boundary present proximal perhaps independent seismic sources within the accretionary prism creating a broad zone of potential surface rupture that can extend inland 150 km or more from subduction zone trenches

joint hypocentre determination of intermediate depth earthquakes in fiordland new zealand abstract relocation of well observed intermediate depth earthquakes in the fiordland region by the method of joint hypocentre determination has revealed some fine structure in the benioff zone the earthquakes occur in three groups the central group is the largest and occupies a planar volume less than 15 km thick striking n40 e and dipping at 80 the deepest events in the region at depths of 150 km occur at the northeast end of this group the two smaller groups lie to the northeast and to the south of the main group the focal mechanism of the majority of the main group is that of thrust faulting we suggest that the main group lies within a section of indian plate lithosphere which has been broken off and rotated into its observed position and that the northern edge of the unbroken subducted indian plate is indicated by the southern group we suggest that the small northeastern group has quite a different tectonic origin and is similar to a group of earthquakes further north which are at a similar distance from and presumably related to the alpine fault use has also been made of the travel time information which is a by product of the joint hypocentre method to construct upper mantle velocity models for p and s waves in the south island the features of this model are a high velocity region in the vicinity of the benioff zone and a subcrustal zone of high seismic velocities running east west across the center of the south island in an otherwise normal mantle

the 1964 prince william sound earthquake joint inversion of tsunami and geodetic data the 1964 prince william sound alaska earthquake mw 9 2 ruptured a large area beneath the continental margin of alaska from prince william sound to kodiak island a joint inversion of tsunami waveforms and geodetic data consisting of vertical displacements and horizontal vectors gives a detailed slip distribution two areas of high slip correspond to seismologically determined areas of high moment release the prince william sound asperity with average slip of 18 m and the kodiak asperity with average slip of 10 m the average slip on the fault is 8 6 m and the seismic moment is estimated as 6 3 1022 n m or over 75 of the seismic moment determined from long period surface waves

incipient subduction at the contact with stretched continental crust the puysegur trench a seismic benioff zone and plate kinematics show puysegur trench south of new zealand transitioning to subduction because the local structure and its influence on subduction initiation is poorly understood we conducted a seismic survey with ocean bottom seismometers and multichannel seismic profiles our early results show that the overriding pacific plate beneath the solander basin is composed of block faulted and thinned continental crust and the inner trench wall of northern puysegur ridge is composed of folded and faulted sediment the megathrust interface has been imaged and shows 500 m of downgoing undisturbed sediments combining plate kinematic history with seismic velocity inferred density we show that the density difference across the plate boundary changed as oblique strike slip plate motion juxtaposed dense oceanic crust with thinned continental crust the density difference rapidly increased 18 to 15 ma coincident with subduction initiation suggesting that compositional differences have a large influence on subduction initiation

evolution of macquarie ridge complex seamounts implications for volcanic and tectonic processes at the australia pacific plate boundary south of new zealand abstract the macquarie ridge complex mrc coincides with the australia pacific plate boundary south of new zealand and is characterised by a rugged bathymetry that comprises numerous seamounts along its length tectonic plate reconstructions show that the australia pacific plate boundary evolved from a spreading centre to a transpressional boundary from ca 40 to 6 ma however limited sampling and high resolution mapping of the region have meant that the composition and morphology of the mrc remain relatively unknown here we present results from multibeam mapping photographic investigation and petrologic and geochemical analyses from 10 seamounts along the mrc dredge samples collected from the seamounts are alkaline to sub alkaline basalts containing 45 1 50 8 wt sio2 3 5 12 0 wt mgo and 1 9 4 9 wt total alkalis all samples are enriched mid ocean ridge basalts that have k ti 0 15 which originated as low degree partial melts during the late stages of mid ocean ridge volcanism this oceanic crust has been sheared and accreted along the plate boundary since ca 6 ma by cumulative transpressional relative plate motion such that lavas from distinct magma chambers have been juxtaposed at individual seamounts along the ridge mrc seamounts have formed as discrete elevations as a result of dip slip and strike slip faulting of the ridge axis three guyot type seamounts have flat top summit plateaux that were presumably formed by wave erosion via relative sea level lowering due to uplift of the ridge these seamounts have since subsided due to extension associated with the step over fault geometry of the transform plate boundary along the mcdougall and macquarie ridge segments while the seamounts are of volcanic origin they are manifestations of tectonic and geomorphic processes seamounts distal from the ridge axis however are not subjected to plate boundary deformation and instead have morphologies formed through volcanic processes

transition from strike slip faulting to oblique subduction active tectonics at the puysegur margin south new zealand abstract south of new zealand the pacific australia pac aus plate boundary runs along the intracontinental alpine fault the puysegur subduction front and the intraoceanic puysegur fault the puysegur fault is located along puysegur ridge which terminates at ca 47 s against the continental puysegur bank in a complex zone of deformation called the snares zone at puysegur trench the australian plate subducts beneath puysegur bank and the fiordland massif east of fiordland and puysegur bank the moonlight fault system mfs represents the eocene strike slip plate boundary interpretation of seafloor morphology and seismic reflection profiles acquired over puysegur bank and the snares zone allows study of the transition from intraoceanic strike slip faulting along the puysegur ridge to oblique subduction at the puysegur trench and to better understand the genetic link between the puysegur fault and the mfs seafloor morphology is interpreted from a bathymetric dataset compiled from swath bathymetry data acquired during the 1993 geodynz survey and single beam echo soundings acquired by the nz royal navy the snares zone is the key transition zone from strike slip faulting to subduction it divides into three sectors namely east nw and sw sectors a conspicuous 3600 m deep trough the snares trough separates the nw and east sectors the east sector is characterised by the ne termination of puysegur ridge into right stepping en echelon ridges that accommodate a change of strike from the puysegur fault to the mfs between 48 s and 47 s in the nw sector and the snares trough a series of transpressional faults splay northwards from the puysegur fault between 49 50 s and 48 s thrusts develop progressively at puysegur trench into a decollement north of 48 s the snares trough develops between two splays of the puysegur fault indicating superficial extension associated with the subsidence of puysegur ridge seismic reflection profiles and bathymetric maps show a series of transpressional faults that splay northwards across the snares fault and terminate at the top of the puysegur trench slope between ca 48 s and 46 30 s the relative plate motion appears to be distributed over the puysegur subduction zone and the strike slip faults located on the edge of the upper plate conversely north of ca 46 s a lack of active strike slip faulting along the mfs and across most of puysegur bank indicates that the subduction in the northern part of puysegur trench accounts for most of the oblique convergence hence active transpression in the snares fault zone indicates that the relative pac aus plate motion is transferred from strike slip faulting along the puysegur fault to subduction at puysegur trench the progressive transition from thrusts at puysegur trench and strike slip faulting at the puysegur fault to oblique subduction at puysegur trench suggests that the subduction interface progressively developed from a western shallow splay of the puysegur fault it implies that the transfer fault links the subduction interface at depth a tectonic sliver is identified between puysegur trench and the puysegur fault its northwards motion relative to the pacific plate implies that is might collide with puysegur bank

influence of cumulative convergence on lithospheric thrust fault development and topography along the australian pacific plate boundary south of new zealand the development of faulting and topography resulting from initial convergence within oceanic lithosphere is largely unknown we explore relationships among convergence structural development and topography along 1500 km of the submarine australian pacific plate boundary south of new zealand the macquarie ridge complex mrc due to the variable orientation of the boundary and close proximity of the australian pacific poles of rotation individual segments of the plate boundary have experienced different convergence histories since 10 95 ma chron 5o because interaction along the oceanic extent of the boundary involves oceanic lithosphere of broadly the same age and therefore thermal structure structural and morphologic differences can be attributed primarily to variations in angles and rates of convergence with respect to the plate boundary orientation since 10 95 ma we relate plate boundary normal convergence determined from stage pole rotations to structural development focusing on transitions from purely strike slip faulting to partitioned thrust and strike slip faulting between 47 s and 60 s since 10 95 ma our results indicate that boundary normal convergence of 100 km marks the transition from strike slip dominated faulting to partitioned underthrusting and strike slip faulting incipient subduction establishment of subduction at the puysegur trench and incipient subduction at the hjort trench corresponds to convergence at rates between 2 and 4 cm yr angles 30 and with durations of at least 10 m y resulting in 100 km of boundary normal convergence anomalous topographic volumes resulting from tectonic deformation are quantified from swath bathymetry and compared to convergence history results from analysis of the central mrc suggest that prior to lithospheric scale thrust faulting 100 km of boundary normal convergence can be accommodated by crustal deformation 6 km relief from ridge crest to adjacent trough and strike slip faulting our research supports induced forced intraoceanic initiation of subduction

fracture zone subduction and reactivation across the puysegur ridge trench system southern new zealand a two dimentional kinematic model for lithospheric thrusting that considers the flexural interaction between the underriding and overriding plates was used to assess the mechanical implications of subducting trench parallel fracture zones on the topography and free air gravity anomalies of the puysegur ridge trench system fracture zones in the underriding plate are simulated by vertical discontinuities across which bending and shearing stresses cannot be supported the implication of reactivating fracture zones on the outer trench slope is to suppress the flexural bulge creating topographic relief between the fracture zone and the trench and reducing the trench gravity anomaly in the studied region the trench subparallel l atalante fracture zone accounts for the lack of a flexural bulge strong outer trench slope and gravity gradients the southward decrease of the trench fracture zone distance results in a decrease of the trench gravity anomaly the effect of subducting and vertically reactivating fracture zones within the underriding plate is to segment the load of the overriding plate creating a trough located above the underthrust fracture zone the vertical offset and gravity modifications are functions of the fracture zone position relative to the trench this model explains the 3500 m deep troughs and the 1700 m subsidence observed at the puysegur ridge we speculate that reactivating underthrust fracture zones can facilitate strike slip faults development within the upper plate in case of oblique subduction and are conducive to the formation and dispersion of terranes at convergent margins this process can account for basal tectonic erosion

the mid cenozoic challenger rift system of western new zealand and its implications for the age of alpine fault inception analysis of the structure and sedimentary geology of western new zealand has identified a middle eocene to early miocene continental rift system 1 200 km long and 100 200 km wide named here the challenger rift system four phases of rift development occurred 1 infra rift subsidence 2 active axial trough subsidence 3 expanded rift subsidence involving collapse of the rift shoulders and 4 incipient sea floor spreading the spatial and temporal distribution of these phases identifies a north island and a south island rift segment and shows that rifting propagated toward the center of the rift from both ends the northern segment shows a simple pattern of rifting that is comparable with vink9s model of rift propagation the southern segment with locked zones and rift nucleation segments is comparable to courtillot9s model of rift propagation the sea floor spreading history of the southwest pacific shows that the northern rift segment probably linked with a sea floor spreading center in the norfolk basin and the southern segment linked with the southeast indian ridge this is corroborated by the good correlation between the ages of sea floor magnetic anomaly lineations that are aligned with the rift and the biostratigraphic ages of rifting the probable continuity of the rift system in its early development precludes pre miocene transcurrent displacement on the alpine fault an early miocene 23 m y b p age of alpine fault inception is indicated by the age and pattern of rift disruption attributed to compression that originated at the australia pacific plate boundary the modern australia and pacific plates were not discrete entities therefore until the early miocene

morphostructure of an incipient subduction zone along a transform plate boundary puysegur ridge and trench multibeam bathymetric and geophysical data reveal a major strike slip fault that extends along the summit of the puysegur ridge east of the puysegur trench the northward structural development of this ridge trench system illustrates the evolution of an incipient subduction zone along a transform plate boundary that has been subjected to increasing transverse shortening during the past 10 m y at the southern end of the trench where subduction has not yet started the puysegur ridge has a narrow 50 km steep sided cross section and the axial strike slip fault separates a shallow 125 625 m flat topped eastern crest from a deeper 400 1600 m western crest these characteristics indicate differential uplift during the initial stage of shortening on the lower plate an incipient 5 2 km deep trench developed in conjunction with normal and reverse faults suggesting strong interplate coupling across the trench northward the ridge broadens linearly to 80 km wide its western flank has locally collapsed and the ridge summit has subsided possibly by 1 5 km suggesting that the interplate coupling decreases and that a benioff zone is being formed concomitant to the northward ridge evolution the trench deepens to 6 2 km and normal fault throws increase along its outer wall indicating greater flexure of the downgoing plate

opposing gradients of permanent strain in the aseismic zone and elastic strain across the seismogenic zone of the kodiak shelf and slope alaska an industry acquired seismic reflection line from the aleutian arc to the alaska trench was prestack depth migrated and further constrained with wide angle ocean bottom hydrophone seismic velocity data and swath mapping from the seismic reflection image individual thrust slices the backstop and the forearc basin were resolved sufficiently well to balance the section tectonic shortening and age estimates provided rates of permanent contraction in five discrete segments over 150 km during the past 3 myr about 70 of the plate convergence is measured as contraction across the 40 km wide neogene accretionary prism which composes less than 10 of the forearc permanent contraction is minimal above the 1964 alaska earthquake aftershock zone indicating dominently elastic strain since elastic strain is poorly recorded in the geological record it was approximated from the historical record of the 1964 alaska earthquake the 1964 coseismic vertical deformation displays an inverse pattern to the permanent strain consistent with the earthquake cycle concept elastic deformation is dominant beneath the shelf and upper slope rapid permanent deformation is concentrated beneath the lower slope and a transition between them occurs beneath the middle slope

slip on the suckling hills splay fault during the 1964 alaska earthquake abstract the suckling hills in southern alaska experienced localized anomalously large coseismic uplift in the m w 9 2 1964 alaska earthquake large uplift at the suckling hills can be explained by increased slip or an asperity on the alaska aleutian megathrust however this paper suggests that increased uplift may be a result of slip on the suckling hills splay fault we present a series of models that demonstrate how the inclusion of the suckling hills fault improves the fit between modeled vertical displacement and measured coseismic uplift in comparison to slip on the alaska aleutian megathrust alone our results suggest that 3 m of average slip on the suckling hills fault during the 1964 earthquake can help explain the large coseismic uplift data these results are consistent with recent studies indicating pleistocene slip on the suckling hills fault and together highlight the potential seismic and tsunami risk associated with this segment of the alaskan subduction complex

edge deep seismic reflection transect of the eastern aleutian arc trench layered lower crust reveals underplating and continental growth an edge deep crustal seismic reflection transect of the eastern aleutian arc trench traces oceanic crust and moho more than 200 km beneath the accretionary prism to depths of more than 30 km these horizons project beneath a prominent sequence of layered reflectors that extends from about 9 to 35 km beneath the mesozoic core of the prism earthquake hypocenters imply continuity of the downgoing lithosphere from the base of the layered reflectors to beneath and beyond the active augustine volcano rapid lateral growth of the prism in eocene oligocene time coincided with uplift of the mesozoic core of the prism during lateral growth maintenance of critical taper requires thickening either by internal deformation or underplating because exposed rocks show only modest postemplacement shortening thickening most likely occurred by underplating probably of the layered reflectors the overall geometry of the layered reflectors is reminiscent of nappe structures and their emplacement may represent crustal scale duplexing associated with underplating the edge reflection data and borehole results indicate that the self edge is marked by an active out of sequence thrust that separates the paleogene and neogene prisms this thrust apparently developed in response to the prism s need to maintain critical taper and demonstrates that contrasts inmore lithology can result from mechanisms other than terrane emplacement less

the rupture process and tectonic implications of the great 1964 prince william sound earthquake we have determined the rupture history of the march 28 1964 prince william sound earthquake m w 9 2 from long period wwssn p wave seismograms source time functions determined from the long period p waves indicate two major pulses of moment release the first and largest moment pulse has a duration of approximately 100 seconds with a relatively smooth onset which reaches a peak moment release rate at about 75 seconds into the rupture the second smaller pulse of moment release starts at approximately 160 seconds after the origin time and has a duration of roughly 40 seconds because of the large size of this event and thus a deficiency of on scale digitizable p wave seismograms it is impossible to uniquely invert for the location of moment release however if we assume a rupture direction based on the aftershock distribution and the results of surface wave directivity studies we are able to locate the spatial distribution of moment along the length of the fault the first moment pulse most likely initiated near the epicenter at the northeastern down dip edge of the aftershock area and then spread over the fault surface in a semi circular fashion until the full width of the fault was activated the rupture then extended toward the southwest approximately 300 km ruff and kanamori 1983 the second moment pulse was located in the vicinity of kodiak island starting at 500 km southwest of the epicenter and extending to about 600 km although the aftershock area extends southwest past the second moment pulse by at least 100 km the moment release remained low we interpret the 1964 prince william sound earthquake as a multiple asperity rupture with a very large dominant asperity in the epicentral region and a second major but smaller asperity in the kodiak island region

accretionary prisms in subduction earthquake cycles the theory of dynamic coulomb wedge 1 we expand the theory of critically tapered coulomb wedge for accretionary prisms by considering stress changes in subduction earthquake cycles building on the coulomb plasticity of the classical theory we assume an elastic perfectly coulomb plastic rheology and derive exact stress solutions for stable and critical wedges the new theory postulates that the actively deforming most seaward part of an accretionary prism the outer wedge overlies the updip velocity strengthening part of the subduction fault and the less deformed inner wedge overlies the velocity weakening part the seismogenic zone during great earthquakes the outer wedge is pushed into a compressively critical state with an increase in basal and internal stresses and pore fluid pressure after the earthquake the outer wedge returns to a stable state the outer wedge geometry is controlled by the peak stress of the updip velocity strengthening part of the subduction fault achieved in largest earthquakes the inner wedge generally stays in the stable regime throughout earthquake cycles acting as an apparent backstop and providing a stable environment for the formation of forearc basins the new theory has important implications for the studies of the updip limit of the seismogenic zone the evolution of accretionary prisms and forearc basins activation of splay faults and tsunami generation evolution of the fluid regime and mechanics of frontal prisms at margins dominated by tectonic erosion

combined effects of tectonic and landslide generated tsunami runup at seward alaska during the mw 9 2 1964 earthquake we apply a recently developed and validated numerical model of tsunami propagation and runup to study the inundation of resurrection bay and the town of seward by the 1964 alaska tsunami seward was hit by both tectonic and landslide generated tsunami waves during the m rm w 9 2 1964 megathrust earthquake the earthquake triggered a series of submarine mass failures around the fjord which resulted in landsliding of part of the coastline into the water along with the loss of the port facilities these submarine mass failures generated local waves in the bay within 5 min of the beginning of strong ground motion recent studies estimate the total volume of underwater slide material that moved in resurrection bay to be about 211 million m3 haeussler et al in submarine mass movements and their consequences pp 269 278 2007 the first tectonic tsunami wave arrived in resurrection bay about 30 min after the main shock and was about the same height as the local landslide generated waves our previous numerical study which focused only on the local landslide generated waves in resurrection bay demonstrated that they were produced by a number of different slope failures and estimated relative contributions of different submarine slide complexes into tsunami amplitudes suleimani et al in pure appl geophys 166 131 152 2009 this work extends the previous study by calculating tsunami inundation in resurrection bay caused by the combined impact of landslide generated waves and the tectonic tsunami and comparing the composite inundation area with observations to simulate landslide tsunami runup in seward we use a viscous slide model of jiang and leblond j phys oceanogr 24 3 559 572 1994 coupled with nonlinear shallow water equations the input data set includes a high resolution multibeam bathymetry and lidar topography grid of resurrection bay and an initial thickness of slide material based on pre and post earthquake bathymetry difference maps for simulation of tectonic tsunami runup we derive the 1964 coseismic deformations from detailed slip distribution in the rupture area and use them as an initial condition for propagation of the tectonic tsunami the numerical model employs nonlinear shallow water equations formulated for depth averaged water fluxes and calculates a temporal position of the shoreline using a free surface moving boundary algorithm we find that the calculated tsunami runup in seward caused first by local submarine landslide generated waves and later by a tectonic tsunami is in good agreement with observations of the inundation zone the analysis of inundation caused by two different tsunami sources improves our understanding of their relative contributions and supports tsunami risk mitigation in south central alaska the record of the 1964 earthquake tsunami and submarine landslides combined with the high resolution topography and bathymetry of resurrection bay make it an ideal location for studying tectonic tsunamis in coastal regions susceptible to underwater landslides

tsunami hazards along the eastern australian coast from potential earthquakes results from numerical simulations australia is surrounded by the pacific ocean and the indian ocean and thus may suffer from tsunamis due to its proximity to the subduction earthquakes around the boundary of australian plate potential tsunami risks along the eastern coast where more and more people currently live are numerically investigated through a scenario based method to provide an estimation of the tsunami hazard in this region we have chosen and calculated the tsunami waves generated at the new hebrides trench and the puysegur trench and we further investigated the relevant tsunami hazards along the eastern coast and their sensitivities to various sea floor frictions and earthquake parameters i e the strike the dip and the slip angles and the earthquake magnitude rupture length the results indicate that the puysegur trench possesses a seismic threat causing wave amplitudes over 1 5 m along the coast of tasmania victoria and new south wales and even reaching over 2 6 m at the regions close to sydney maria island and gabo island for a certain worse case while the cities along the coast of queensland are potentially less vulnerable than those on the southeastern australian coast

the 2011 tohoku oki earthquake displacement reaching the trench axis we detected and measured coseismic displacement caused by the 11 march 2011 tohoku oki earthquake moment magnitude mw 9 0 by using multibeam bathymetric surveys the difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the japan trench suggesting that the fault rupture reached the trench axis the sea floor on the outermost landward area moved about 50 meters horizontally east southeast and 10 meters upward the large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement

late cenozoic exhumation model of new zealand impacts from tectonics and climate abstract late cenozoic convergence between the australian and pacific plates has led to extensive crustal deformation and exhumation in new zealand over the past five decades the convergence associated exhumation history of the palaeozoic mesozoic new zealand basement has been studied using various thermochronometric techniques here we compile 992 published ages and invert them to estimate the temporal and spatial variation in exhumation rates since 25 ma which we then interpret with a plate tectonic reconstruction model the results reveal widespread increases in the exhumation rates at 6 4 ma a time correlated with accelerations in the relative plate motion the absolute increases in exhumation rates are however not uniformly distributed over new zealand since the plio pleistocene the inferred models suggest variable response of exhumation to global cooling in the non glaciated eastern north island the hikurangi subduction margin the million year average exhumation rates have remained relatively low 5 km myr have been observed in the collision zone of the central southern alps of south island where both tectonic deformation and precipitation rates are highest in fiordland the puysegur subduction margin despite the weak crustal deformation the exhumation rates have been high 0 5 3 km myr which we suggest is due to intensified glacial erosion our findings highlight the determining role of tectonics in setting up the regional exhumation pattern but both strong tectonic deformation and efficient erosion are required to maintain rapid exhumation rates the influence of climate on mountain erosion can only be distinguished in regions under slow to mediate exhumation

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

continuous uplift near the seaward edge of the prince william sound megathrust middleton island alaska middleton island located at the seaward edge of the continental shelf 50 km from the base of the inner wall of the aleutian trench affords an opportunity to make land based measurements of uplift near the toe of the prince william sound megathrust site of the 1964 m 9 2 alaska earthquake leveling surveys 1973 1993 on middleton island indicate roughly uniform tilting 1 rad a down to the northwest of the island and gps surveys 1993 2012 show an uplift rate of 14 mm a of the island relative to fixed north america the data are consistent with a combined coseismic and postseismic uplift in meters due to the 1964 earthquake as a function of time years after the earthquake u 3 5 1 21 log10 1 1 67 h where 3 5 is the coseismic uplift and h is 0 for 0 and 1 otherwise the current uplift on middleton island is attributed to continuous slip on a fault splaying off from the megathrust and the long term uplift is the superposition of the effects of past earthquakes each earthquake being similar to the 1964 event then the predicted uplift at time t due to a sequence of earthquakes at times ti would be iut ti from studies of strandlines associated with the uplifted terraces on middleton island plafker et al 1992 estimated the occurrence times of the last six earthquakes and measured the present day elevations of those strandlines the predicted uplift is in rough agreement with those measurements about half of the predicted uplift is due to postseismic relaxation from previous earthquakes

holocene glacier fluctuations in alaska abstract this review summarizes forefield and lacustrine records of glacier fluctuations in alaska during the holocene following retreat from latest pleistocene advances valley glaciers with land based termini were in retracted positions during the early to middle holocene neoglaciation began in some areas by 4 0 ka and major advances were underway by 3 0 ka with perhaps two distinct early neoglacial expansions centered respectively on 3 3 2 9 and 2 2 2 0 ka tree ring cross dates of glacially killed trees at two termini in southern alaska show a major advance in the ad 550s 720s the subsequent little ice age lia expansion was underway in the ad 1180s 1320s and culminated with two advance phases respectively in the 1540s 1710s and in the 1810s 1880s the lia advance was the largest holocene expansion in southern alaska although older late holocene moraines are preserved on many forefields in northern and interior alaska tidewater glaciers around the rim of the gulf of alaska have made major advances throughout the holocene expansions were often asynchronous with neighboring termini and spanned both warm and cool intervals suggesting that non climatic factors were important in forcing these advances however climatic warming appears to have initiated most rapid iceberg calving retreats large glaciers terminating on the forelands around the gulf of alaska may have had tidewater termini early in the holocene but have progressively become isolated from the adjacent ocean by the accumulation and subaerial exposure of their own sediments

changes in crustal seismic deformation rates associated with the 1964 great alaska earthquake we calculated seismic moment rates from crustal earthquake information for the upper cook inlet region including anchorage alaska for the 30 yr prior to and 36 yr following the 1964 great alaska earthquake our results suggest over a factor of 1000 decrease in seismic moment rate in units of dyne centimeters per year following the 1964 mainshock we used geologic information on structures within the cook inlet basin to estimate a regional geologic moment rate assuming the structures extend to 30 km depth and have near vertical dips the geologic moment rates could underestimate the true rates by up to 70 since it is difficult determine the amount of horizontal offset that has occurred along many structures within the basin nevertheless the geologic moment rate is only 3 7 times lower than the pre 1964 seismic moment rate suggesting the 1964 mainshock has significantly slowed regional crustal deformation if we compare the geologic moment rate to the post 1964 seismic moment rate the moment rate deficit over the past 36 yr is equivalent to a moment magnitude 6 6 7 0 earthquake these observed differences in moment rates highlight the difficulty in using seismicity in the decades following a large megathrust earthquake to adequately characterize long term crustal deformation

the seismic coupling of subduction zones revisited 1 the nature of seismic coupling for many of the world s subduction zones has been reevaluated geodetic estimates of seismic coupling obtained from gps measurements of upper plate deformation during the interseismic period are summarized we compared those with new estimates of seismic coupling obtained from seismological data the results show that with a few notable exceptions the two methods agree to within about 10 the seismological estimates have been greatly improved over those made 20 30 years ago because of an abundance of paleoseismological data that greatly extend the temporal record of great subduction earthquakes and by the occurrence in the intervening years of an unusual number of great and giant earthquakes that have filled in some of the most critical holes in the seismic record the data also again with a few notable exceptions support the frictional instability theory of seismic coupling and in particular the test of that theory made by scholz and campos 1995 overall the results support their prediction that high coupling occurs for subduction zones subjected to high normal forces with a switch to low coupling occurring fairly abruptly as the normal force decreases below a critical value there is also considerable variation of coupling within individual subduction zones earthquake asperities correlate with areas of high coupling and hence have a semblance of permanence but the rupture zones and asperity distributions of great earthquakes may differ greatly between seismic cycles because of differences in the phase of seismic flux accumulation

seismic reflection characteristics of glacial and glacimarine sediment in the gulf of alaska and adjacent fjords abstract glaciation together with tectonism have been dominant factors affecting sedimentation in the gulf of alaska area from at least the late miocene throughout the quaternary the effects of tectonism are apparent in high mountains that border the gulf raised terraces of middleton island and the eastern gulf coastal zone and numerous active faults and related earthquakes glacial evidence includes magnificent glaciers and their onshore deposits spectacular fjords large sea valleys incised in the continental shelf submarine morainal ridges at mouths of bays and sea valleys and thick glacimarine sedimentary sequences diamicts that are exposed onshore and at the sea floor along the outer shelf seismic reflection profiling and sampling of the uppermost marine sedimentary sequences in the gulf of alaska and adjacent fjords and bays have allowed identification of three discrete glacially related stratigraphic units these units were delineated on the basis of seismic signature geometry physiographic location stratigraphic position and sedimentologic characteristics the oldest unit a quaternary diamict is portrayed on seismic profiles by irregular discontinuous reflections this unit probably includes till outwash and glacimarine sediment a geographically restricted unit one incorporating holocene end moraines at bay mouths and associated with some sea valleys consists of jumbled masses of discontinuous reflections and very irregular surface morphology the youngest unit a blanket of holocene sand to clayey silt prograding as a sediment wedge across the shelf contains nearly horizontal parallel reflections except where disrupted by mass movement although seismic reflection data alone cannot provide definitive proof of the presence of glacial sediment when combined with sea floor sampling seismic profiling is a powerful tool for determining the continuity of marine sedimentary units and relationships to past and modern glaciers

mesoscale to submesoscale transition in the california current system part ii frontal processes this is the second of three papers investigating the regime transition that occurs in numerical simulations for an idealized equilibrium subtropical eastern boundary upwelling current system similar to the california current the emergent upper ocean submesoscale fronts are analyzed from phenomenological and dynamical perspectives using a combination of composite averaging and separation of distinctive subregions of the flow the initiating dynamical process for the transition is near surface frontogenesis the frontal behavior is similar to both observed meteorological surface fronts and solutions of the approximate dynamical model called surface dynamics i e uniform interior potential vorticity q and diagnostic force balance in the intensification of surface density gradients and secondary circulations in response to a mesoscale strain field however there are significant behavioral differences compared to the surface dynamics model wind stress acts on fronts through nonlinear ekman transport and creation and destruction of potential vorticity the strain induced frontogenesis is disrupted by vigorous submesoscale frontal instabilities that in turn lead to secondary frontogenesis events submesoscale vortices and excitation of even smaller scale flows intermittent submesoscale breakdown of geostrophic and gradient wind force balance occurs during the intense frontogenesis and frontal instability events

mapping the megathrust beneath the northern gulf of alaska using wide angle seismic data in the northern gulf of alaska and prince william sound we have used wide angle seismic reflection refraction profiles earthquake studies and laboratory measurements of physical properties to determine the geometry of the prince william and yakutat terranes the aleutian megathrust and the subducting pacific plate in this complex region the yakutat terrane is underthrust beneath the prince william terrane and both terranes are interpreted to be underlain by the pacific plate wide angle seismic reflection refraction profiles recorded along five seismic lines are used to unravel this terrane geometry modeled velocities in the upper crust of the prince william terrane to 18 km depth agree closely with laboratory velocity measurements of orca group phyllites and quartzofeldspathic graywackes the chief components of the prince william terrane to hydrostatic pressures as high as 600 mpa 6 kbar a landward dipping reflector at depths of 16 24 km is interpreted as the base of the prince william terrane this reflector corresponds to the top of the wadati benioff zone seismicity and is interpreted as the megathrust immediately beneath the megathrust is a 4 km thick 6 9 km s refractor which we infer to be the source of a prominent magnetic anomaly and which is interpreted by us and previous workers to be gabbro in eocene age oceanic crust of the underthrust yakutat terrane wide angle seismic data magnetic anomaly data and tectonic reconstructions indicate that the yakutat terrane has been underthrust beneath the prince william terrane for at least a few hundred kilometers wide angle seismic data are consistent with a 9 to 10 landward dip of the subducting pacific plate beneath the outer shelf and slope distinctly different from the inferred average 3 to 4 dip of the overlying 6 9 km s refractor and the wadati benioff seismic zone beneath the inner shelf our preferred interpretation of the geophysical data is that one composite plate composed of the pacific plate of a fairly uniform thickness and the yakutat plate of varying thickness is subducting beneath southern alaska

terrane motion by strike slip faulting of forearc slivers forearc slivers bounded by a trench and an active strike slip fault occur in about 50 of modern subduction zones analysis of earthquake slip vectors indicates that modern sliver terranes typically migrate at rates of 1 2 cm yr tertiary transport of some forearc slivers by 1000 km or more is therefore expected as a consequence of normal subduction active arc parallel strike slip faulting occurs whenever interplate coupling is strong and convergence is somewhat oblique strike slip rate increases with greater convergence obliquity

the yakutat terrane dramatic change in crustal thickness across the transition fault alaska we present new constraints on the crustal structure of the yakutat terrane and evidence of the role of the transition fault in southern alaska the yakutat terrane south of yakutat bay includes crystalline crust that is 24 27 km thick overlain by sedimentary units that are 4 5 7 5 km thick the yakutat terrane crustal thickness and velocity structure are consistent with an oceanic plateau origin the southern edge of the yakutat terrane is bounded by the transition fault which is imaged as a near vertical fault zone 1 km wide the transition fault is coincident with a dramatic change in moho depth from 32 km for yakutat oceanic plateau crust to 11 5 km for pacific ocean crust occurring over a horizontal distance of 0 5 km there is no evidence for underthrusting of the pacific ocean crust beneath the yakutat terrane at the transition fault we argue that the yakutat terrane formed on the kula or farallon plate and was later juxtaposed next to younger pacific ocean crust by the transition fault

seismic and geodetic constraints on plate boundary deformation across the northern macquarie ridge and southern south island of new zealand summary in the southern new zealand region the boundary between the australian and pacific plates changes from oblique continental convergence in the central south island of new zealand to interoceanic transcurrent motion along the macquarie ridge source parameters of recent post 1964 upper crustal events mw 5 3 in the region 43 53 s 155 175 e are determined using p and sh waveform analysis in order to investigate the nature of strain accommodated seismically throughout the region repeated occupation of three geodetic networks across the southern south island provides estimates of contemporary crustal strain seismicity over the last 35 years shows uneven spatial and temporal distribution with clusters of events occurring in regions along the plate boundary that exhibit structural variation focal mechanisms of individual earthquakes vary widely but are consistent with the accommodation of long term estimates of the relative plate motion across the southern south island geodetically measured principal contraction directions are consistent with p axis orientations the mode of accommodation of the relative plate motion varies throughout the region influenced by the change in crustal composition on either side of the plate boundary the underlying structure as a relic of previous relative motions and the variation of obliquity of the relative motion with respect to these structures

underthrusting at the hjort trench australian pacific plate boundary incipient subduction 1 the southernmost portion of the macquarie ridge complex mrc comprises the hjort ridge trench and plateau the topographic expression of the australian pacific plate boundary south of new zealand on the basis of marine geophysical swath bathymetry reflectivity seismic reflection gravity magnetic data teleseismic data and gravity modeling we argue that the australian plate is actively underthrusting the pacific plate along the hjort trench but self sustaining subduction does not yet appear to have commenced we interpret a crustal discontinuity in the trench as a shallowly dipping thrust splay off a sub vertical transform fault in the crest of the hjort ridge hjort fault the hjort fault separates oceanic crust generated at the southeast indian ridge seir crust located to the south from oceanic crust generated at the extinct australian pacific spreading center located to the north mrc crust oblique convergence on the transform has initiated a significant plate boundary decollement in the trench but our estimate of 50 km of underthrusting does not support the existence of an eastwardly dipping australian slab below 20 km depth for the length of the hjort ridge and trench system oblique convergence is partitioned between the decollement in the trench and the hjort fault south of 57 5 s the trench decollement accommodates thrusting north of 57 5 s the boundary parallel component of convergence becomes dominant the trench gradually shallows and the trench decollement evolves into a low angle oblique slip fault the trench decollement and strike slip system in the hjort ridge are structural boundaries that contain tectonic slivers of inferred seir crust of the western flank of the hjort ridge that currently belong to neither the australian nor the pacific plates

the deglacial transition on the southeastern alaska margin meltwater input sea level rise marine productivity and sedimentary anoxia 1 oxygen isotope data from planktonic and benthic foraminifera on a high resolution age model 44 14c dates spanning 17 400 years document deglacial environmental change on the southeast alaska margin 59 33 32 n 144 9 21 w 682 m water depth surface freshening i e 18o reduction of 0 8 began at 16 650 170 cal years b p during an interval of ice proximal sedimentation likely due to freshwater input from melting glaciers a sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14 790 380 cal years b p abrupt warming and or freshening of the surface ocean i e additional 18o reduction of 0 9 coincides with the bolling interstade of northern europe and greenland cooling and or higher salinities returned during the allerod interval coincident with the antarctic cold reversal and continue until 11 740 200 cal years b p when onset of warming coincides with the end of the younger dryas an abrupt 1 reduction in benthic 18o at 14 250 290 cal years b p likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater a regional megaflood event or brine formation associated with sea ice two laminated opal rich intervals record discrete episodes of high productivity during the last deglaciation these events precisely dated here at 14 790 380 to 12 990 190 cal years b p and 11 160 130 to 10 750 220 cal years b p likely correlate to similar features observed elsewhere on the margins of the north pacific and are coeval with episodes of rapid sea level rise remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia

transition of accretionary wedge structures around the up dip limit of the seismogenic subduction zone the nankai accretionary prism is divided into three segments outer and inner wedges and their transition zone these wedges reflect different aspects of wedge taper internal deformation and basal plate boundary fault the outer wedge is characterized by narrow critical taper internal deformation by in sequence fold and thrust and aseismic decollement the inner wedge represents a stable narrow taper weakly deformed internal structure and seismogenic plate boundary fault along its base the transition zone between the two wedges shows large critical taper with steep surface slope internal structure of out of sequence thrust and step down of decollement onto the sediment oceanic basement interface the trench slope break and oceanward margin of forearc basin is located around the landward edge of this transition zone these common aspects might be related to the lithification of both accreted and underthrust sediments and the resultant switch of the plate boundary fault deformation and lithification process recorded in exhumed on land melange of accretionary complexes suggest that the step down of the plate boundary decollement occurs around the up dip limit of seismogenic subduction zone

a 4dvar system for the navy coastal ocean model part 1 system description and assimilation of synthetic observations in monterey bay abstracta 4d variational data assimilation system was developed for assimilating ocean observations with the navy coastal ocean model it is described in this paper along with initial assimilation experiments in monterey bay using synthetic observations the assimilation system is tested in a series of twin data experiments to assess its ability to fit assimilated and independent observations by controlling the initial conditions and or the external forcing while assimilating surface and or subsurface observations in all strong and weak constraint experiments the minimization of the cost function is done with both the gradient descent method in the control space and the representer method observation space the accuracy of the forecasts following the analysis and the relevance of the retrieved forcing correction in the case of weak constraints are evaluated it is shown that the assimilation system generally fits the assimilated and nonassimilated observations well in all experiments yielding lowe

the age and origin of miocene pliocene fault reactivations in the upper plate of an incipient subduction zone puysegur margin new zealand

a comprehensive study of the seismicity of the kenai peninsula cook inlet region south central alaska abstract we compare 30 yr of background seismicity of the kenai peninsula cook inlet region extending from eastern prince william sound kayak island to west of the cook inlet volcanic arc to potential field gravity magnetics tomographic global positioning system geodesy and geologic information to better determine factors controlling seismicity we also compare the occurrence of m w 5 events over the past 80 100 yr to background seismicity in an effort to determine how reflective background seismicity is of the regional seismic hazard our results indicate that contrasts in upper plate rheology leading to changes in density magnetic susceptibility and velocity of the upper plate serve to concentrate seismicity the southwestern edge of the subducting yakutat microplate has a strong influence on both upper and lower plate seismicity density and velocity contrasts also indicate changes in lower plate rheology that influence the location of deeper 30 km seismicity and the occurrence of a double seismic zone within the subducting pacific plate

tectonic implications of out of sequence faults in an accretionary prism prince william sound alaska the chugach and prince william terranes constitute a mesozoic through tertiary accretionary complex bordering the gulf of alaska faults of the contact fault system juxtapose the two terranes across the previously mapped trace of the contact fault in western prince william sound we studied three belts of alternately higher and lower deformation intensity and metamorphism out of sequence reverse faults separate these belts until recently researchers assumed that the prince william terrane was accreted to the chugach terrane along the contact fault however our work supports an emerging view that the chugach and prince william terranes represent older and younger parts of a continuously evolved accretionary prism best considered a single terrane we found that we cannot distinguish the chugach from the prince william terrane on the basis of lithology deformation or metamorphism therefore we cannot precisely identify the local strand of the contact fault system furthermore the major faults in the study area are relatively late stage features related not to initial accretion but rather to internal deformation of the prism west northwest shortening characterizes the deformation along the contact fault system in western prince william sound whereas dextral slip faulting characterizes the deformation along the contact fault system in eastern prince william sound we ascribe this difference to development of the alaska orocline coeval with changes in plate motions during eocene time which resulted in convergence in western prince william sound remaining relatively orthogonal while convergence in eastern prince william sound became increasingly oblique

synthesis of the structural evolution and associated gold mineralization of the cadillac fault abitibi canada abstract the cadillac fault zone cfz is a 250 km long east trending crustal discontinuity associated with numerous world class gold deposits in the archean abitibi subprovince in quebec the fault follows the boundary between the abitibi and the pontiac subprovinces and can be divided into four segments 1 rouyn 2 joannes 3 malartic and 4 val d or each displays different attitudes and structural styles the malartic segment strikes se whereas the other segments are e trending abrupt changes in strike or smaller scale faults represent limits between the segments structural styles include four generations of foliation with numerous shear sense indicators and folding specifically related to each foliation structural features can be correlated from one segment to another but display clear variations in attitude or expression a stretching lineation signature is definitely associated with each segment in the malartic segment the predominant e trending schistosity displays an angular relationship with the contact between groups and bedding suggesting that the se trending architecture of this segment was already emplaced prior to ductile deformation the evidence suggests a model where the cfz originates from several independent structures inherited from volcanism prior to timiskaming deformation and abitibi pontiac accretion the proto cfz was then linked up during the timiskaming deposition forming high strain zones inherited structures form the frame on which each deformation event was overprinted with different responses depending on segmentation the structural styles of each segment can be integrated in a structural evolution model for the cfz the n s shortening led to the development of a dominantly e striking penetrative foliation and folding during the subsequent extensional stage the cfz was reactivated with normal kinematics during the pontiac uplift a third deformation event is represented by the local development of nw trending cleavage axial planar to the s shaped minor folds finally a late nw se shortening event produced a dextral strike slip movement with ne striking vertical foliation and development of z shaped folds on bedding surfaces and anterior fabrics linkage of the cfz had a major impact on hydrothermal activity in the southern abitibi as it channeled fluids along large scale pathways distribution of gold bearing intrusions can also be related to segmentation and inherited structures of the cfz this association is expressed by gold mineralization styles present in several longitudinal fields reflecting fault segmentation

on the nature of buttressing in margin parallel strike slip fault systems margin parallel strike slip faults commonly develop along convergent plate margins where an oceanic plate subducts obliquely beneath a continental plate such faults detach a sliver of continental crust from the leading edge of the overriding plate fault motion then causes the sliver to move parallel to the continental margin in the direction of the transverse component of relative plate motion however few slivers move as rapidly as predicted by simple analyses of the forces acting on them this discrepancy must be due principally to the buttress effect resistance to displacement of the sliver arising from a space problem at its leading edge more simply a sliver can move only if it has somewhere to go buttresses can be geometrical as when the continental margin changes trend abruptly or they can arise from changes in the physical properties of the overriding plate or in other factors such as subduction angle and angle of obliquity that help determine whether sliver motion will occur a strongly buttressed sliver will move only insofar as the buttress can be overcome obvious ways in which a buttress can be overcome are by thickening the crust or widening the sliver examples of both are known crustal thickening entails elevation increase sliver motion is opposed by both gravity and friction widening the sliver is a more complex process that results in areas of extension and compression forming within the sliver as well as a characteristic pattern of overlapping curved fault segments this latter response may be the cause of curvature in many strike slip fault systems

subduction initiation with vertical lithospheric heterogeneities and new fault formation how subduction initiates with mechanically unfavorable lithospheric heterogeneities is important and rarely studied we investigate this with a geodynamic model for the puysegur incipient subduction zone pisz south of new zealand the model incorporates a true free surface elasto visco plastic rheology and phase changes our predictions fit the morphology of the puysegur trench and ridge and the deformation history on the overriding plate we show how a new thrust fault forms and evolves into a smooth subduction interface and how a preexisting weak zone can become a vertical fault inboard of the thrust fault during subduction initiation consistent with two fault system at pisz the model suggests that the pisz may not yet be self sustaining we propose that the snares zone or snares trough is caused by plate coupling differences between shallower and deeper parts the tectonic sliver between two faults experiences strong rotation and low density material accumulates beneath the snares zone

the updip and downdip limits to great subduction earthquakes thermal and structural models of cascadia south alaska sw japan and chile this study examines thermal and structural controls of the updip and downdip rupture limits of great subduction thrust earthquakes data on past great earthquake seismic limits have been compiled for four continental subduction zones cascadia sw japan south alaska and chile these limits have then been compared to the predictions of several models for what constrains great earthquake rupture temperatures on the subduction thrusts have been estimated by finite element numerical models the landward limits of the observed updip aseismic zones correspond to the position where the thrust temperature reaches about 100 c that is depths of about 2 to 10 km for the subduction zones studied this temperature agrees with the dehydration of stable sliding smectite clays to illite chlorite the temperatures in this region are controlled mainly by the thickness of sediment on the incoming crust and by the crustal age and thus heat flow the downdip limits correspond to the depth on the thrust where either 1 the temperature reaches about 350 c which corresponds to thermally activated stable sliding behavior for crustal rocks with a transition to 450 c or 2 about 40 km depth if 350 c is reached at greater depth depths of about 40 km approximately correspond to the intersection of the thrust with the continental forearc moho and this downdip limit may be a consequence of stable sliding serpentinite or talc and other hydrated forearc mantle rocks the primary temperature controls on the downdip region are the age of the subducting oceanic plate and the thrust dip profile secondary control comes from the thickness of incoming sediment the convergence rate and the radioactive heat generation in the overlying forearc the 100 c updip limit occurs near the trench for young subducting plates with a thick sediment section such as cascadia 6 8 ma and up to 80 km landward for older oceanic crust such as south alaska 50 ma the 350 c downdip thermal limit is applicable for young oceanic plates e g cascadia and nankai whereas the forearc mantle limit applies for older plates e g south alaska and chile except near the chile rise for the margins studied that have experienced great earthquakes there is generally good agreement between the postulated thermal and moho limits and the rupture or seismogenic zone as defined by the distribution of aftershocks and by waveform tsunami and dislocation modeling the downdip limit of the interseismic locked zone from dislocation modeling is also in agreement with these limits

seismicity of the prince william sound region for over thirty years following the 1964 great alaskan earthquake in this paper we present results of body wave form modeling of 19 earthquakes generally m b 5 7 occurring from 1964 to 1983 in the vicinity and down dip of the large asperity within the prince william sound region that ruptured in 1964 these data are supplemented with source parameters from studies of more recent post 1980 events our results suggest that moderate earthquakes which occurred in the region between 1964 and 1984 were predominantly located in the vicinity of the prince william sound asperity and could be assigned to two groups the first group consists of events occurring above the plate interface within prince william sound along reverse faults or low angle thrusts the second group occurs at 35 to 60 km depth in the region north of prince william sound and represents normal to normal oblique faulting within the subducted pacific crust or upper mantle these earthquakes occur below the northern edge of the 1964 asperity in a region where the subducting plate undergoes a rapid change in strike and dip a third group of events occurs in cook inlet well down dip of the 1964 asperity and below the plate interface these events exhibit a variety of mechanisms and many at depths of 50 to 70 km may be associated with complexities in the shape of the downgoing slab most of the cook inlet events occurred after 1984 whereas a few events of similar magnitude have occurred in the vicinity of the prince william sound asperity since 1984

exhumation rates in the st elias mountains alaska abstract reprocessing and interpretation of seismic profiles from the gulf of alaska in the vicinity of the st elias mountains indicate that over 3000 km 3 of sediment were deposited on the ocean shelf since the end of the last glacial epoch approximately 10 000 years ago this estimate of the sediment volume does not include material moved out of the region by long shore currents transportation from the shelf to deeper waters or material trapped in fiords and basins on and near land thus an estimated sedimentation rate offshore of 7 9 mm year and the average erosion rate of 5 1 mm year from the st elias mountains derived from the estimated sedimentation rate represent minimum estimates we infer that these estimated rates are not typical of the approximately 5 m y history of mountain building in the area but rather they represent the result of efficient erosion by glaciers during this interglacial period

near field modeling of the 1964 alaska tsunami the role of splay faults and horizontal displacements near field observations of tsunami waves generated by the mw9 2 1964 alaska earthquake reveal a complex relationship between coseismic slip and the tsunami wavefield in the source area the documen

on the mechanism of tectonic transport in zones of oblique subduction abstract many cases of oblique subduction are known throughout the world today and many more must have existed in the past in at least one modern case sumatra the over riding plate has responded to oblique subduction by forming a strike slip fault that traverses the magmatic arc and displaces its leading edge in the direction of the transverse component of oblique convergence conditions favoring this sort of tectonic response are shown to be 1 1 a high angle of oblique convergence 2 2 a low angle of subduction and 3 3 relative thermal softening of the magmatic arc this mechanism may have been responsible in part for northward transport of western cordilleran magmatic arc and subduction zone rocks in the late cretaceous and earliest tertiary it also may help to explain evidence of southward transport and left lateral shear in northern mexico and the caribbean region in pre jurassic time

national seismic hazard model for new zealand 2010 update a team of earthquake geologists seismologists and engineering seis mologists has collectively produced an update of the national probabilistic seismic hazard psh model for new zealand national seismic hazard model or nshm the new nshm supersedes the earlier nshm published in 2002 and used as the hazard basis for the new zealand loadings standard and numerous other end user applica tions the new nshm incorporates a fault source model that has been updated with over 200 new onshore and offshore fault sources and utilizes new new zealand based and international scaling relationships for the parameterization of the faults the dis tributed seismicity model has also been updated to include post 1997 seismicity data a new seismicity regionalization and improved methodology for calculation of the seismicity parameters probabilistic seismic hazard maps produced from the new nshm show a similar pattern of hazard to the earlier model at the national scale but there are some significant reductions and increases in hazard at the regional scale the national scale differences between the new and earlier nshm appear less than those seen between much earlier national models indicating that some degree of consis tency has been achieved in the national scale pattern of hazard estimates at least for return periods of 475 years and greater online material table of fault source parameters for the 2010 national seismic hazard model

three dimensional elastic dislocation modeling of the postseismic response to the 1964 alaska earthquake 1 gps velocity observations from the kenai peninsula and kodiak island alaska display a pattern of spatial variability suggesting the presence of multiple active processes on the underlying pacific north american plate interface velocities of sites on the eastern kenai peninsula and kodiak island are consistent with elastic strain accumulation at the plate interface whereas velocities of sites on the western kenai peninsula and cook inlet are oriented in the opposite direction and suggest an ongoing postseismic response to the 1964 alaska earthquake we can reproduce the observed velocities using a three dimensional elastic dislocation model to estimate the variation in coupling between the pacific and north american plates two different inversion schemes are examined to check the robustness of the results we find that the gps data can be satisfied by the presence of a locked area near southwest prince william sound a locked area near southwest kodiak island and an area of postseismic reverse slip beneath and north of the western kenai peninsula the shallow plate interface trenchward of the western kenai peninsula does not appear to be locked the locked areas correspond to the prince william sound and kodiak island asperities that ruptured in 1964 and the area of postseismic slip lies downdip of the 1964 rupture area the correspondence between the present shallow coupling distribution and the 1964 slip distribution suggests that the locked regions repeat from one earthquake cycle to another

constraints on macquarie ridge tectonics provided by harvard focal mechanisms and teleseismic earthquake locations in this study we evaluate teleseismically determined focal mechanisms and epicenters for earthquakes along the macquarie ridge complex mrc from 45os to 61 os and 155oe to 168oe a region characterized by some previous investigators as undergoing subduction initiation from 65 centroid moment tensors reported by harvard we develop statistical guidelines for choosing 26 which represent better determined more reliable focal mechanisms for tectonic analysis although thrust mechanisms occur in the north near fiordland elsewhere along the mrc the better determined mechanisms virtually all indicate that present day motion along most of the mrc is strike slip this is consistent with sidescan sonar and multichannel reflection data collected between 50os and 57os on 1994 and 1996 cruises the active plate boundar3 zone appears to be quite narrow 5 km wide and no active compressional features can be observed on the seafloor if we determine a rotation pole for plate boundary motion using only slip vectors from better determined harvard mechanisms along the mrc the best fitting instantaneous pole is at 57 4os 179 4oe about 2 5 o north of the nuvel i australian pacific pole which averages motion over the last 3 0 my if the mrc pole was formerly farther south than at present this could explain the existence of relict features associated with crustal shortening such as bathymetric highs and troughs yet the absence of active features such as thrust faults etc suggests ongoing compression or subduction initiation we also carefully read arrival times for p phases for 53 earthquakes at 16 teleseismic stations selected to represent a range of azimuths surrounding the earthquakes we relocated these earthquakes using standard joint epicentral determination jed methods while most of the better quality relocations lie on or very close to the australia pacific boundar3 as determined on the 1994 cruise a few epicenters occur well away from the boundar3 apparently on cenozoic fracture zones thus on the macquarie ridge complex and other major strike slip boundaries e g in california it appears that the very largest earthquakes occur on the principal plate boundar3 fault but that other earthquakes some quite large may occur away from the boundary along zones of preexisting weakness

oblique subduction and collision forearc tectonics of the kuril arc the tectonics of the southwestern kuril arc are a result of the oblique subduction of the pacific plate at the kuril trench in association with forearc sliver migration caused by the oblique subduction collision tectonics occur at the leading margin of the sliver and tensional tectonics take place at the tapering margin as a result of the collision a deep crustal section of island arc is observed at the leading margin of the forearc sliver tectonics of the kuril arc related to oblique subduction are different from those of the western sunda arc where backarc spreading occurs at the leading margin this difference is due to margin morphology of the oblique subduction zone