temporal variation of large intraplate earthquakes in coupled subduction zones the focal mechanisms of intraplate earthquakes within subducting lithosphere are frequently used to infer large scale stress regimes induced by slab pull bending or unbending and lateral segmentation and undulations of the slab numerous studies have further postulated that the intraplate activity is influenced by transitory regional stress regimes such as those associated with interplate thrust events temporal variations of the latter type may potentially play an important role in assessing regions of uncertain seismic potential and possibly even in earthquake forecasting a systematic analysis of 1130 focal mechanisms for intraplate earthquakes with m b 5 0 in the depth range 0 300 km is conducted for nine circum pacific subduction zones all of which are known to have large interplate thrust events the spatial and temporal relationships of the earthquakes within the subducting slab to the large thrust events in each region are appraised the earthquake catalog assembled contains all published focal mechanisms and is probably complete for m b 6 5 for the years 1963 1986 for many of the localized regions considered in detail the catalog is complete to lower thresholds of m b 6 0 or m b 5 5 this analysis provides compelling evidence for a temporal link between large interplate thrust activity and intraplate seismicity for the seismically coupled regions considered here outer rise compressional events have occurred prior to several large thrust events or are associated with seismic gaps while outer rise tensional events generally only follow interplate ruptures in the intermediate depth range large down dip tensional events generally precede interplate thrusts and are often concentrated at the down dip edge of the coupled zone a transition to down dip compressional stress or diminished tensional activity at intermediate depth is observed after several large thrust events e g 1960 chile 1974 peru 1957 aleutian 1971 new britain these examples support the notion that the intraplate stress environment responds viscoelastically to the temporally varying interplate stress regime assuming that this concept is correct the seismic potential of several seismic gaps is considered on the basis of both outer rise and intermediate depth earthquake activity

mineralogical and spectroscopic investigation of the tagish lake carbonaceous chondrite by x ray diffraction and infrared reflectance spectroscopy abstract we have carried out a sample correlated spectroscopic and mineralogical investigation of samples from seven different collection sites of the tagish lake c2 chondrite rietveld refinement of high resolution powder x ray diffraction xrd data was used to determine quantitative major mineral abundances thermal infrared 400 4500 cm 1 2 2 25 0 m spectra of the same samples were obtained using diffuse biconical reflectance infrared fourier transform spectroscopy drifts our results are in good agreement with previous studies of the mineralogy of the tagish lake meteorite we find however that tagish lake is more varied in major mineralogy than has previously been reported in particular we observed two new distinct lithologies an inclusion poor magnetite and sulfide rich lithology and a carbonate rich siderite dominated lithology in addition to the previously documented carbonate rich and carbonate poor lithologies grain density for each tagish lake sample was calculated from the measured mineral modal abundances and known mineral densities for powders from three originally intact inclusion rich samples the calculated grain density is 2 77 0 05 g cm 3 in excellent agreement with those reported in the literature for other intact inclusion rich tagish lake samples tagish lake disaggregated samples have a significantly higher calculated grain density due to their lower saponite serpentine content likely a result of mineral separation in the meltwater holes from which they were collected the disaggregated samples may not therefore adequately represent bulk samples of the tagish lake meteorite the predominance of very fine grained material in the tagish lake samples investigated in this study is expected to produce infrared spectra representative of asteroidal regolith gypsum and talc have been found by xrd in powders from the inclusion rich intact tagish lake samples in this study and may have been present in the parent body if present these hydrous sulfates would complicate the interpretation of possible hydrated mineral features in asteroid infrared spectra

carboniferous permian tectonic evolution and sedimentation of the turpan hami basin nw china implications for the closure of the paleo asian ocean abstract the tectonic evolution and sedimentary characteristics of the carboniferous permian rocks of the turpan hami basin have been analysed initially a joint inversion of gravity magnetic seismic data and the established model of electrical profiles was synthesized to create a new geological interpretation discussion on the tectonic characteristics of piedmont zone in the northern part of the basin then followed according to the analysis of balanced cross sections the tectonic evolutionary history of carboniferous permian sedimentary rocks of the turpan hami basin can be divided into three stages an extensional stage in the carboniferous a tectonic transition stage in the early permian and a compression and inversion stage after the middle permian it is found that the tectonic evolution controlled the sedimentary facies under these three stages and the sedimentation evolution has undergone marine facies marine lacustrine transitional facies and lacustrine facies meanwhile based on the recent seismic gravity magnetic and electrical data and combined with the field surveying of outcrops the residual distribution of carboniferous permian strata is characterized by the widely distributed residual upper carboniferous except for the southern liaodun uplift and locally in the eastern area and the denudation of middle permian strata mainly distributed in the turpan depression and the turpan hami depression after comprehensive analysis of the sedimentary facies and erosion of permian strata it is concluded that the tectonic evolution and sedimentation of the turfan hami basin can be used as a constraint on permian subduction related accretionary orogenesis of northern xinjiang nw china and the closure time of the paleo asian ocean

modal mineralogy of cm2 chondrites by x ray diffraction psd xrd part 1 total phyllosilicate abundance and the degree of aqueous alteration abstract cm carbonaceous chondrites are samples of incompletely serpentinized primitive asteroids using position sensitive detector x ray diffraction psd xrd and a pattern stripping technique we quantify the modal mineralogy of cm2 chondrites mighei murray murchison nogoya and cold bokkeveld there is a narrow range in the combined modal volume vol of the most abundant phases mg serpentine 25 33 and fe cronstedtite 43 50 cold bokkeveld is anomalous in containing more mg serpentine 49 59 than fe cronstedtite 19 27 even including cold bokkeveld the range in modal total phyllosilicate is 73 79 average 75 total phyllosilicate abundance provides a non ambiguous measure of the degree of aqueous alteration and indicates that these meteorites have all experienced essentially the same degree of aqueous alteration this reflects pervasive hydration of matrix across cm2 samples apparent differences in the alteration of chondrules observed in petrographic studies represent various stages in the progression towards complete hydration of all components but are not manifest in significant differences in modal mineralogy for all samples there is a limited range in olivine 6 9 and pyroxene 5 abundances modal abundances of the remaining identified phases also show a limited range calcite 0 1 3 gypsum 0 1 6 magnetite 1 1 2 4 pentlandite 0 2 1 and pyrrhotite 1 3 8 as expected we observe a strong negative correlation in the modal abundance of anhydrous fe mg silicates olivine pyroxene and total phyllosilicate mg serpentine fe cronstedtite consistent with the idea that phyllosilicate is forming by aqueous alteration of the anhydrous components the negative correlation in the modal abundance between mg serpentine and fe cronstedtite indicates a mineralogic transformation of fe cronstedtite to mg serpentine by fluid driven recrystallisation or b that these meteorites had different initial abundances of olivine and pyroxene the observed positive correlation in the relative proportion of mg serpentine with increasing total phyllosilicate abundance reflects the evolution of increasingly mg rich phyllosilicate during aqueous alteration fe cronstedtite is the dominant phyllosilicate while cm chondrule olivines are forsteritic and will form mg serpentine during aqueous alteration this implies that matrix olivine was more fe rich than chondrule olivine prior to aqueous alteration

light element geochemistry of the tagish lake ci2 chondrite comparison with ci1 and cm2 meteorites we have studied the carbon and nitrogen stable isotope geochemistry of a small pristine sample of the tagish lake carbonaceous chondrite by high resolution stepped combustion mass spectrometry and compared the results with data from the orgueil ci1 eet 83334 cm1 and murchison cm2 chondrites the small chip of tagish lake analysed herein had a higher carbon abundance 5 81 wt than any other chondrite and a nitrogen content 1220 ppm between that of ci1 and cm2 chondrites owing to the heterogeneous nature of the meteorite the measured carbon abundance might be artificially high the carbon inventory and whole rock carbon isotopic composition 13c 24 4 of the chip was dominated by 13c enriched carbon from the decomposition of carbonates between 1 29 wt and 2 69 wt 13c 67 and 18o 35 in the proportions 4 1 dolomite to calcite in addition to carbonates tagish lake contains organic carbon 2 6 wt 13c 9 1033 ppm n 15n 77 a level intermediate between ci and cm chondrites around 2 of the organic material is thermally labile and solvent soluble a further 18 of the organic species are liberated by acid hydrolysis tagish lake also contains a complement of presolar grains it has a higher nanodiamond abundance 3650 4330 ppm than other carbonaceous chondrites along with 8 ppm silicon carbide whilst carbon and nitrogen isotope geochemistry is not diagnostic the data are consistent with classification of tagish lake as a ci2 chondrite

depositional style and subsidence history of the turpan basin nw china the turpan basin has a complex polycyclic sedimentary and tectonic history from late permian to late tertiary time main stratigraphic boundaries are unconformities that bound tectonically induced sedimentary cycles the depositional style reflects a continental environment exhibiting changes from alluvial fan fluvial to lacustrine conditions within each cycle more than 7000 m of clastic sediments accumulated during the evolution of the basin paleocurrent analysis reveals a complex pattern of sediment dispersal pathways into the basin on the southern margin of the basin the transport direction is always directed from south to north indicating sediment sources in the jueluotage shan while in the northern part the late jurassic uplift of the bogda shan provided an important source area from the early cretaceous onwards with transport directions from north to south after basin formation during the late permian the turpan basin underwent first thermal subsidence and then flexural subsidence the thermal subsidence took place during the late permian and early triassic following the period of magmatic activities in this region the flexural subsidence was throughout the middle triassic to early tertiary induced by collisions and accretions onto the south asian continental margin of the qiangtang block in the late triassic early jurassic the gangdise block in latest jurassic earliest cretaceous and the indian subcontinent in the latest cretaceous early cenozoic

influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas abstract dmowska r and lovison l c 1992 influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 23 43 we have investigated the influence of large scale fault inhomogeneities in large subduction earthquakes on the style of deformation and seismic behavior of the incoming oceanic plate and slab at intermediate depths during the earthquake cycle the zones of the large subduction events of rat islands 1965 alaska 1964 and valparaiso 1985 have been searched for earthquakes with m b 5 0 if available and for time periods as long as possible it has been found that in general the seismicity in the incoming oceanic plate clusters in front of asperities areas of highest seismic moment release and strongest locking and is positioned relative to them in the direction of plate motion it is usually lacking in areas adjacent to non asperities that is to zones that slip during the main event but with appreciably smaller seismic moment release and possibly slip seismically aseismically during the whole cycle similar behavior occurs in the downgoing slab at intermediate depths where seismicity during the cycle clusters but less strongly than in the oceanic crust next to asperities and down dip from them we infer that the locking of asperities causes higher stresses associated with the earthquake cycle itself to occur in areas adjacent to asperities both up dip and down dip from them along the direction of plate motion and that such stressing is much less pronounced in the areas adjacent to non asperities this opens the possibility of identifying the areas of highest seismic moment release in future subduction earthquakes and carries implications for where the highest deformation and possibly precursory phenomena and or nucleation of a future event might occur

mineralogy of tagish lake an ungrouped type 2 carbonaceous chondrite in this paper we describe the recovery handling and preliminary mineralogical investigation of the tagish lake meteorite tagish lake is a type 2 carbonaceous chondrite which bears similarities to ci1 and cm chondrite groups but is distinct from both abundant phyllosilicates as well as chondrules however sparse and common olivine grains in the matrix preclude any other classification the bulk density of tagish lake 1 67 g cc which is far lower than ci or cm chondrites 2 2 2 3 and 2 6 2 9 g cc respectively or any other meteorite for that matter we have identified two lithologies a dominant carbonate poor lithology and a less abundant carbonate rich lithology the meteorite is a breccia at all scales we have noted similarities between tagish lake and some clasts within the enigmatic meteorite kaidun possibly there are genetic relationships here worth exploring in the paper we describe a clast of cm1 material within tagish lake which is very similar to a major lithology in kaidun

the fall recovery orbit and composition of the tagish lake meteorite a new type of carbonaceous chondrite the preatmospheric mass of the tagish lake meteoroid was about 200 000 kilograms its calculated orbit indicates affinity to the apollo asteroids with a semimajor axis in the middle of the asteroid belt consistent with a linkage to low albedo c d and p type asteroids the mineralogy oxygen isotope and bulk chemical composition of recovered samples of the tagish lake meteorite are intermediate between cm and ci meteorites these data suggest that the tagish lake meteorite may be one of the most primitive solar system materials yet studied

the june 2000 mw 7 9 earthquakes south of sumatra deformation in the india australia plate 1 two large mw 7 9 earthquakes occurred on 4 and 18 june 2000 south of sumatra beneath the indian ocean both earthquakes were predominantly left lateral strike slip on vertical n s trending faults that we interpret to be reactivated fracture zones the 4 june enggano earthquake occurred at the edge of the rupture area of the 1833 subduction earthquake the first strike slip subevent within the subducting plate triggered a thrust subevent on the plate interface which comprised at least 35 of the total moment and ruptured se away from the 1833 earthquake the 18 june earthquake in the wharton basin is one of the largest shallow strike slip faulting earthquakes ever recorded a small second subevent with reverse slip is required to fit the body waves the orientation of both subevents in our preferred model is consistent with the current stress field in the region both the june 2000 earthquakes are consistent with recent models of distributed deformation in the india australia composite plate the occurrence of the enggano earthquake implies that the stress field within the indian plate continues to a depth of 50 km in the subducting slab the purely strike slip source model of the wharton basin earthquake obtained by robinson et al 2001 matches the p waves very poorly and fits the s waves no better than our preferred model the strike slip subevents of both earthquakes had few aftershocks and higher stress drops than the subduction thrust subevent of the enggano earthquake this difference is consistent with previous observations of oceanic and subduction earthquakes

polyphase deformation of a paleozoic forearc arc complex in the beishan orogen nw china abstract the lebaquan complex in the central beishan nw china plays a significant role in understanding the subduction accretion collision processes of the southern central asian orogenic belt four stages of deformation have been identified the d1 deformation is characterized by a pervasive foliation s1 defined by metamorphic layering and intrafolial isoclinally folded quartz veins f1 the d2 deformation is marked by a crenulation cleavage s2 mainly developed in the schists widespread tight to open folds and asymmetric folds f2 as well as pinch and swell structures boudins the d3 deformation is characterized by high strain ductile shears that modified the earlier structures small scale asymmetric folds type porphyroclasts and s c fabrics in the schists metacherts and pegmatites indicate dextral shearing in an east west direction the d4 deformation is represented by semi ductile to brittle structures including open gentle folds kink folds and small scale thrusts which overprinted earlier structures the overall deformation pattern of this complex indicates a tectonic regime that changed from an earlier ns directed compression to a later ew directed transpression and finally to an ew extension geochemical data show that the protoliths of the metasedimentary rocks were sourced from an active margin new la icp ms zircon u pb dates indicate that the youngest age peak of detrital zircons from a garnet mica quartz schist is 424 ma which constrains the depositional age of the rocks protoliths a syn deformation leucogranitic dyke which underwent d2 but not d1 formed at 423 ma and a post deformation mafic dyke that intruded all the lithologies formed at 280 ma these data indicate that d1 occurred in the time interval of 424 423 ma that d2 took place at or shortly after 423 ma and that d3 and d4 formed in the period of 423 280 ma combined with other published data we conclude that the lebaquan complex represents a subduction accretionary complex formed in a forearc setting

the fall and recovery of the tagish lake meteorite the tagish lake c2 ungrouped carbonaceous chondrite fall of january 18 2000 delivered 10 kg of one of the most primitive and physically weak meteorites yet studied in this paper we report the detailed circumstances of the fall and the recovery of all documented tagish lake fragments from a strewnfield at least 16 km long and 3 to 4 km wide nearly 1 kg of pristine meteorites were collected one week after the fall before new snow covered the strewnfield the majority of the recovered mass was collected during the spring melt ground eyewitnesses and a variety of instrument recorded observations of the tagish lake fireball provide a refined estimate of the fireball trajectory from its calculated orbit and its similarity to the remotely sensed properties of the d and p class asteroids the tagish lake carbonaceous chondrite apparently represents these outer belt asteroids the cosmogenic nuclide results and modeled production indicate a prefall radius of 2 1 2 4 m corresponding to 60 90 tons consistent with the observed fireball energy release the bulk oxygen isotope compositions plot just below the terrestrial fractionation line tfl following a trend similar to the cm meteorite mixing line the bulk density of the tagish lake material 1 64 0 02 g cm 3 is the same within uncertainty as the total bulk densities of several c class and especially d and p class asteroids the high microporosity of tagish lake samples 40 provides an obvious candidate material for the composition of low bulk density primitive asteroids

sequence of strong intraplate earthquakes in the kodiak island region alaska in 1999 2001 a sequence of strong earthquakes was registered in 1999 2001 in the kodiak island region of the alaska aleutian subduction zone two mw 7 earthquakes occurred in december 1999 and january 2001 and an mw 6 5 event occurred in july 2000 these events and their aftershocks recorded by the regional seismograph network were relocated using a joint hypocenter determination jhd method regional broadband data were used to obtain seismic moment tensors for the main shocks and their largest aftershocks relocation and moment tensor inversion results indicate that these events originated inside the subducting pacific plate the focal mechanisms indicate down dip tension with the fault planes being nearly vertical and parallel to the strike direction of the subducting plate the 1999 and 2000 events were located down dip of the locked portion of the megathrust while the 2001 event was located directly beneath it

high interseismic coupling of the alaska subduction zone sw of kodiak island inferred from gps data we use global positioning system gps measurements to make the first geodetic study of the semidi segment of the alaska aleutian subduction zone this segment which sustained an mw 8 2 earthquake in 1938 lies between kodiak island where the subduction interface appears to presently be fully locked and the shumagin islands segment where substantial aseismic slip occurs we invert the gps station velocity estimates using a nonlinear least squares algorithm to solve for the width of the locked zone the dip and the interseismic coupling of a model subduction interface the data are consistent with a shallow plate interface dipping 6 a locking depth of 23 km and high interseismic coupling of 80

studies of wadati benioff zone seismicity of the anchorage alaska region we have relocated over 8600 earthquakes occurring between 1964 and 1999 at depths 25 km within 100 km of anchorage alaska using the double difference technique the relocated seismicity reveals important details of the subducting pacific plate and yakutat blocks including clustering of seismicity within the pacific plate mantle northeast and northwest striking near vertical faults within the pacific plate crust and a region of intense deformation associated with the southwestern edge of the yakutat block stress analyses from the direct inversion of first motion data and from inversion of focal mechanisms for 713 events indicates a rotation of the maximum compressive stress direction from a trench parallel direction northeast in the southwestern portion of the study area to an east west direction near the southwestern edge of the yakutat block located just north of anchorage regions of the pacific plate mantle that produced m w 6 4 earthquakes in 1934 and 1954 continue to be seismically active

intracontinental orogenic transition insights from structures of the eastern junggar basin between the altay and tianshan orogens abstract detailed subsurface structure of the eastern junggar basin is investigated using a large number of high resolution two dimensional reflection seismic profiles and well data our results reveal thrust faults some of which are with strike slip component and fault related folds dominating the subsurface structure of the study area the thrust faults mainly show a divergent pattern towards the west and convergence towards the east we divide these thrust faults and folds into three structural systems the north thrust system located in the north of the study area is characterized by top to the southwest imbricate thrusts initiated from late paleozoic the central transpression system dominating the central study area mainly consists of thrust faults with visible strike slip component active from early mesozoic until cretaceous the south thrust system includes top to the southeast thrusts in the southern part of the study area the existence of these structural systems indicates that the eastern junggar basin underwent obvious intracontinental deformation in mesozoic probably due to the continuous convergence between the altay and the tianshan orogens after the main collision accretion processes of the central asian orogenic belt

modeling earthquake cycles in the shumagin subduction segment alaska with seismic and geodetic constraints deformation associated with the earthquake cycle in the shumagin islands segment of the alaska aleutian subduction zone is analyzed with the use of a two dimensional finite element model the model consists of an oceanic plate dipping under an upper plate both of which respond elastically to stress fluctuations in the earthquake cycle and these are underlain by asthenospheric mantle and mantle wedge regions which respond viscoelastically it is tailored to the geometry of the shumagin islands region by using seismicity to define the position of the interplate interface and partially coupled region along it the model is preconditioned by forcing this interface to undergo periodically repeated slips up to and including the time of the may 31 1917 event ms 7 4 in that region with each chosen to be consistent with the moment and estimated rupture area of that event we investigated the dependence of model results for geodetic signals on the strength of seismic coupling between the plates and viscoelastic relaxation of deviatoric stresses in the mantle including in the mantle wedge close to the plate junction and along the aseismic downdip continuation of the thrust interface in models with significant relaxation in the wedge or downdip thrust zone results show that as the intraseismic stage matures there is a region of diminished compressional strain rates and even of locally extensional rates on the earth s surface above the downdip end of the seismically coupled zone based on the seismic estimates of the location of the coupled zone this region is in the area of the shumagin islands we find that if approximately 20 of the convergence takes place seismically compatible with the previous seismic history and if an extensive region of relaxed deviatoric stress is assumed to be present in the wedge and or along the downdip interface then deformations predicted by the model can be made consistent with the measured strain data from the shumagin islands geodetic network lisowski et al 1988 larson and lisowski 1994 as well as uplift and tilt data savage and plafker 1991 beavan 1992 our model simulations here suggest that the shumagin segment is capable of large earthquakes the hypothesis of totally aseismic subduction is not similarly consistent with all geodetic constraints

spatial variations in present day deformation kenai peninsula alaska and their implications from four years of global positioning system gps measurements we find significant spatial variations in present day deformation between the eastern and western kenai peninsula alaska sites in the eastern kenai peninsula and prince william sound move to the nnw relative to north america in the direction of pacific north america relative plate motion velocities decrease in magnitude from nearly the full plate rate in southern prince william sound to about 30 mm yr at seward and to about 5 mm yr near anchorage in contrast sites in the western kenai peninsula move to the sw in a nearly trenchward direction with a velocity of about 20 mm yr the data are consistent with the shallow plate interface offshore and beneath the eastern kenai and prince william sound being completely locked or nearly so with elastic strain accumulation resulting in rapid motion in the direction of relative plate motion of sites in the overriding plate the velocities of sites in the western kenai along strike to the southwest are opposite in sign with those predicted from elastic strain accumulation these data are incompatible with a significant locked region in this segment of the plate boundary trenchward velocities are found also for some sites in the anchorage area we interpret the trenchward velocities as being caused by a continuing postseismic transient from the 1964 great alaska earthquake there may be significant along strike differences in the long term behavior of the plate interface between the western and eastern kenai based on roughly coincident boundaries in the coseismic slip distribution cumulative postseismic uplift present day plate coupling and stress field the present postseismic response appears to generate purely trenchward motion suggesting a creep process that is purely dip slip our observations suggest that postseismic processes after the largest earthquakes can influence patterns of deformation for decades after the event

seismic response of the katmai volcanoes to the 6 december 1999 magnitude 7 0 karluk lake earthquake alaska a sudden increase in earthquake activity was observed beneath volcanoes in the katmai area on the alaska peninsula immediately following the 6 december 1999 magnitude m w 7 0 karluk lake earthquake beneath southern kodiak island alaska the observed increase in earthquake activity consisted of small m l 1 3 shallow z 5 0 km events these earthquakes were located beneath mount martin mount mageik trident volcano and the katmai caldera and began within the coda of the karluk lake mainshock all of these earthquakes occurred in areas and magnitude ranges that are typical for the background seismicity observed in the katmai area seismicity rates returned to background levels 8 to 13 hours after the karluk lake mainshock the close temporal relationship with the karluk lake mainshock the onset of activity within the mainshock coda and the simultaneous increase beneath four separate volcanic centers all suggest these earthquakes were remotely triggered modeling of the coulomb stress changes from the mainshock for optimally oriented faults suggests negligible change in static stress beneath the katmai volcanoes this result favors models that involve dynamic stresses as the mechanism for triggered seismicity at katmai

the western central asian orogenic belt a window to accretionary orogenesis and continental growth abstract the architecture of accretionary orogens is a key to understand continental growth here we present an overview of the orogenic components and their amalgamation in the western central asian orogenic belt caob the caob records the convergence and interactions among various types of orogenic components including the japan type mariana type and alaska aleutian type arc systems as well as the active marginal sequences of the siberia craton which incorporated wide accretionary complexes and accreted arcs and terranes during construction of the caob the kazakhstan arc chain was characterized by multiple subduction whereas the northern fringe of the tarim craton remained mostly as a passive margin the multiple convergence and accretions among these various orogenic components generated huge orogenic collages in the late paleozoic and even in the early triassic involving parallel amalgamation circum microcontinent amalgamation and oroclinal bending the preservation of trapped basins played a significant role in orogenesis with some parts of the oceanic plate being subducted and others behaving as rigid units the orogenesis in the caob was long lived lasting for more than 800 m y involving multiple subduction and long continuous accretion and featuring the complexity of accretionary orogenesis and continent growth

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

middle cambrian to permian subduction related accretionary orogenesis of northern xinjiang nw china implications for the tectonic evolution of central asia abstract middle cambrian to permian subduction related records are widely distributed in northern xinjiang which can be grouped into the chinese altay east junggar eastern tien shan west junggar yili and tarim domains by integrating paleogeographic and geological data we suppose that the chinese altay east junggar eastern tien shan domain was more closely located to siberia while the west junggar and yili domains occupied an intermediate position near the kazakhstan block in the early paleozoic paleoasian ocean distribution of andean type magmatic arcs island arcs accretionary wedges ophiolitic slices and or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences the tarim domain was on the opposite side of the early paleozoic paleoasian ocean remaining passive margin these tectonic units drifted northwards and approached the southern active margin of the siberian craton in the late paleozoic leading to termination of the paleoasian ocean and formation of a complicated orogenic collage between siberian craton and the tarim block between the end permian and triassic these multiple accretion processes significantly contributed to the lateral growth of central asia

deformation across the alaska aleutian subduction zone near kodiak the kodiak katmai geodetic array nine monuments distributed along a profile trending north northwestward across kodiak island and the alaska peninsula was surveyed in 1993 1995 and 1997 to determine the deformation at the alaska aleutian subduction zone velocities on kodiak island measured relative to the stable north american plate decrease with distance from the alaska aleutian trench distance range 106 to 250 km whereas no appreciable deformation was measured on the alaska peninsula distances 250 to 370 km from the trench the measured deformation is reasonably well predicted by the conventional dislocation representation of subduction with the model parameters determined independently i e not simply by fitting the observations the deformation of kodiak island is in striking contrast to the very minor deformation measured in the similarly situated shumagin islands 450 km southwest of kodiak along the alaska aleutian trench

earthquake location in island arcs abstract a comprehensive data set of selected teleseismic p wave arrivals and local network p and s wave arrivals from large earthquakes occurring at all depths within a small section of the central aleutians is used to examine the general problem of earthquake location in island arcs reference hypocenters for this special data set are determined for shallow earthquakes from local network data and for deep earthquakes from combined local and teleseismic data by joint inversion for structure and location the high velocity lithospheric slab beneath the central aleutians may displace hypocenters that are located using spherically symmetric earth models the amount of displacement depends on the position of the earthquakes with respect to the slab and on whether local or teleseismic data are used to locate the earthquakes hypocenters for trench and intermediate depth events appear to be minimally biased by the effects of slab structure on rays to teleseismic stations however locations of intermediate depth events based on only local data are systematically displaced southwards the magnitude of the displacement being proportional to depth shallow focus events along the main thrust zone although well located using only local network data are severely shifted northwards and deeper with displacements as large as 50 km by slab effects on teleseismic travel times hypocenters determined by a method that utilizes seismic ray tracing through a three dimensional velocity model of the subduction zone derived by thermal modeling are compared to results obtained by the method of joint hypocenter determination jhd that formally assumes a laterally homogeneous velocity model over the source region and treats all raypath anomalies as constant station corrections to the travel time curve the ray tracing method has the theoretical advantage that it accounts for variations in travel time anomalies within a group of events distributed over a sizable region of a dipping high velocity lithospheric slab in application jhd has the practical advantage that it does not require the specification of a theoretical velocity model for the slab considering earthquakes within a 260 km long by 60 km wide section of the aleutian main thrust zone our results suggest that the theoretical velocity structure of the slab is presently not sufficiently well known that accurate locations can be obtained independently of locally recorded data using a locally recorded earthquake as a calibration event jhd gave excellent results over the entire section of the main thrust zone here studied without showing a strong effect that might be attributed to spatially varying source station anomalies we also calibrated the ray tracing method using locally recorded data and obtained results generally similar to those obtained by jhd

the 13 january 2001 el salvador earthquake a multidata analysis 1 on 13 january 2001 a large normal faulting intermediate depth event mw 7 7 occurred 40 km off the el salvadorian coast central america we analyze this earthquake using teleseismic regional and local data we first build a kinematic source model by simultaneously inverting p and sh displacement waveforms and source time functions derived from surface waves using an empirical green s function analysis in an attempt to discriminate between the two nodal planes 30 trenchward dipping and 60 landward dipping we perform identical inversions using both possible fault planes after relocating the hypocentral depth at 54 km we retrieve the kinematic features of the rupture using a combination of the neighborhood algorithm of sambridge 1999 and the simplex method allowing for variable rupture velocity and slip we find updip rupture propagation yielding a centroid depth around 47 km for both assumed fault planes with a larger variance reduction obtained using the 60 landward dipping nodal plane we test the two possible fault models using regional broadband data and near field accelerograms provided by universidad centro americana 2001 near field data confirm that the steeper landward dipping nodal plane is preferred rupture propagated mostly updip and to the northwest resulting in a main moment release zone of approximately 25 km 50 km with an average slip of 3 5 m the large slip occurs near the interplate interface at a location where the slab steepens dip significantly the occurrence of this event is well explained by bending of the subducting plate

seismicity of the kodiak island region 1964 2001 and its relation to the 1964 great alaska earthquake earthquake relocation first motion and waveform modeling studies of m 5 5 earthquakes are used to examine the seismicity associated with the kodiak island region since the 1964 great alaska earthquake our results indicate that the most intense seismicity and moment release in this region occurred within the pacific plate and along the plate interface of the southwestern edge of the kodiak segment where slip during the 1964 mainshock was less than 5 m few earthquakes have occurred within the north american plate the intense seismicity correlates well with the northern edge of a zone of high plate interface coupling detected by global positioning system geodesy studies our studies suggest that during 1964 1974 faulting within the pacific plate was characterized by normal and normal oblique faulting however since 1974 reverse oblique faulting has become more common in the pacific plate seismic moment release has been over 6 times greater in the kodiak region than in the prince william sound cook inlet region during the past 37 years unlike the prince william sound region there is also a lack of down dip migration of seismicity since 1964 manuscript received 23 october 2001

new constraints on tectonics of interior alaska earthquake locations source mechanisms and stress regime we used the joint hypocenter determination jhd method to relocate 3611 crustal earthquakes that occurred from 1988 to 1999 in central alaska the new earthquake locations provide more details on the structure of the kantishna cluster and better locations for the aftershock sequence of the 29 november 2000 m l 5 6 earthquake in the minto flats seismic zone the jhd locations for the aftershocks of the 1995 m w 6 0 minto flats earthquake and 22 october 1996 m w 5 8 earthquake near the denali fault are also available a catalog of 196 fault plane solutions consisting of the moment tensor solutions for the earthquakes with magnitude 4 0 or above and p wave first motion solutions for the earthquakes with magnitude 3 4 and above that occurred from 1988 to 2000 was composed moment tensor solutions were calculated using regional broadband data this catalog was used to calculate principal stress orientations in the crust the stress orientations change across central alaska in particular the maximum principal stress orientation rotates clockwise from se nw to ssw nne direction as one moves from west to east these stress orientations are consistent with the stress field transferred from the plate convergence in southern alaska in addition we tested different velocity structures in the moment tensor inversion procedure to identify velocity models for calculating the green s functions the moment tensor inversion study shows that it is possible to obtain a reliable moment tensor solution for moderate sized earthquakes m l 4 using three component records from a single broadband station when the epicentral distances are between 50 and 300 km manuscript received 8 june 2001

an extension of the bus asteroid taxonomy into the near infrared the availability of asteroid spectral measurements extending to the near infrared resulting from the development of new telescopic instruments such as spex rayner 2003 provides a new basis for classifying asteroid reflectance spectra we present an asteroid taxonomy classification system based on reflectance spectrum characteristics for 371 asteroids measured over the wavelength range 0 45 to 2 45 microns this system of 24 classes is constructed using principal component analysis following most closely the visible wavelength taxonomy of bus 1999 which itself builds upon the system of tholen 1984 nearly all of the bus taxonomy classes are preserved with one new class sv defined for each class we present boundary definitions spectral descriptions and prototype examples a flow chart method is presented for classifying newly acquired data spanning this wavelength range when data are available only in the near infrared range 0 85 to 2 45 microns classification is also possible in many cases through an alternate flow chart process within our sample several classes remain relatively rare only 6 objects fall into the a class 349 dembowska and 3628 boznemcova reside as the only objects in their respective r and o classes eight q class objects are all near earth asteroids we note 1904 massevitch as an outer main belt v type while 15 other v type objects have inner main belt orbits consistent with an association with vesta

variability absorption features and parent body searches in spectrally featureless meteorite reflectance spectra case study tagish lake abstract reflectance spectra of many asteroids and other solar system bodies are commonly reported as featureless here we show that weak but consistently detectable absorption bands are observable in 200 2500 nm spectra of the tagish lake meteorite a likely compositional and spectral analogue for low albedo spectrally featureless asteroids tagish lake presents a rare opportunity to study multiple lithologies within a single meteorite reflectance spectra of tagish lake display significant variation between different lithologies the spectral variations are due in part to mineralogical variations between different tagish lake lithologies ultraviolet reflectance spectra 200 400 nm few of which have been reported in the literature to date reveal albedo and spectral ratio variations as a function of mineralogy similarly visible near infrared reflectance spectra reveal variations in albedo spectral slope and the presence of weak absorption features that persist across different lithologies and can be attributed to various phases present in tagish lake these observations demonstrate that significant spectral variability may exist between different lithologies of tagish lake which may affect the interpretation of potential source body spectra it is also important to consider the spectral variability within the meteorite before excluding compositional links between possible parent bodies in the main belt and tagish lake tagish lake materials may also be spectral compositional analogues for materials on the surfaces of other dark asteroids including some that are targets of upcoming spacecraft missions tagish lake has been proposed as a spectral match for ultra primitive d or p type asteroids and the variability reported here may be reflected in spatially or rotationally resolved spectra of possible tagish lake parent bodies and source objects in the near earth asteroid population a search for objects with spectra similar to tagish lake has been carried out among the near earth asteroids we have identified three possible spectral matches the best of which are asteroids 326732 2003 hb6 and 17274 2000 lc16

segmentation of the aleutian plate boundary derived from stress direction estimates based on fault plane solutions we propose a new method to investigate stress homogeneity along plate boundaries based on the cumulative misfit of individual fault plane solutions calculated using assumed stress tensors using this method some segments of faults can be defined without the time consuming inversions for stress directions from earthquake fault plane solutions we assume that the misfits are relatively constant within segments of uniform stress orientation but that they change abruptly at boundaries of segments this assumption is supported by the pattern of misfits observed for about 400 earthquakes located along the aleutian subduction zone from 170 e to 145 w which occurred between 1964 and 1993 the efficacy of the approach is confirmed by stress inversion analysis of moving windows the cumulative misfit as a function of strike along the aleutian arc shows there are five first order boundaries where the stress directions change significantly the first one is near 177 5 e which corresponds to the northward projection of the rat fracture zone the second one falls on the adak fracture zone the third is near the locus where the amlia fracture zone intersects the trench the fourth lies on the easternmost end of the 1957 aftershock zone the last is located where the two major asperities of the 1964 rupture are separated the segmentation boundaries found in our analysis may be controlled by the fracture zones in the subducted plate this observation may be interpreted as due to decoupling within the underthrusting plate along the zones of weakness the fracture zones across which stress may not be transmitted fully the boundaries defined by our method may also be related to the asperity and aftershock distributions of great earthquakes the focal mechanism data in the segments defined as stress homogeneous by our method are then used to invert for the principal stress orientations by employing the focal mechanism stress inversion fmsi computer programs of gephart we find that the stress directions within these segments are different from each other where they can be defined well and the average misfits in these volumes are very small 2 8 and 5 5 the method is not robust enough to detect all the stress segmentation boundaries based on only one reference stress tensor analyses with different reference stress models help to define most or all the stress segmentation boundaries

testing variations within the tagish lake meteorite i mineralogy and petrology of pristine samples four samples tl5b tl11h tl11i and tl11v from the pristine collection of the tagish lake meteorite an ungrouped c2 chondrite were studied to characterize and understand its alteration history using epma xrd and tem we determined that samples tl11h and tl11i have a relatively smaller proportion of amorphous silicate material than sample tl5b which experienced low temperature hydrous parent body alteration conditions to preserve this indigenous material the data suggest that lithic fragments of tl11i experienced higher degrees of aqueous alteration than the rest of the matrix based on its low porosity and high abundance of coarse and fine grained sheet silicates suggesting that tl11i was present in an area of the parent body where alteration and brecciation were more extensive we identified a coronal flower like microstructure consisting of a fine grained serpentine core and coarse grained saponite serpentine radial arrays suggesting varied fluid chemistry and crystallization time scales we also observed pentlandite with different morphologies an exsolved morphology formed under nebular conditions a nonexsolved pentlandite along grain boundaries a bulls eye sulfide morphology and rims around highly altered chondrules that probably formed by multiple precipitation episodes during low temperature aqueous alteration 100 c on the parent body on the basis of petrologic and mineralogic observations we conclude that the tagish lake parent body initially contained a heterogeneous mixture of anhydrous precursor minerals of nebular and presolar origin these materials were subjected to secondary nonpervasive parent body alteration and the samples studied herein represent different stages of that hydrous alteration i e tl5b the least altered tl11h tl11i the most altered sample tl11v encompasses the petrologic characteristics of the other three specimens

seismic potential of the queen charlotte alaska aleutian seismic zone the 5000 km long queen charlotte alaska aleutian seismic zone is subdivided into 17 unequally sized segments their boundaries are delineated based on the prior distribution of large and great earthquakes the 17 segments are chosen to represent areas likely to be ruptured by characteristic earthquakes this term usually implies repeated breakage of a plate boundary segment by either a large or great earthquake whose source dimensions remain consistent from cycle to cycle this definition does not exclude the possibility that occasionally adjacent characteristic earthquake segments may break together in a single giant event that is larger than the characteristic size outlined conversely a segment can also sometimes break in a series of smaller ruptures formal computations of the conditional probabilities for future large and great earthquakes in the 17 segments of the queen charlotte alaska aleutian seismic zone are based on the following data sets and findings 1 recurrence intervals from historic and geologic data 2 direct recurrence time estimates based on rates of relative plate motion and the size or displacement of the most recent characteristic event in each segment and 3 the application of a lognormal distribution of recurrence times for large and great earthquakes results of these computations indicate seven areas that have high i e 60 conditional probabilities for the recurrence of either large or great earthquakes within the next 20 years 1988 2008 these areas include cape st james yakataga the shumagin islands unimak island and the fox delarof and near islands segments of the aleutian arc when a shorter time interval is considered 1988 1998 those segments more likely to rupture in large ms 7 7 7 rather than great earthquakes have a high conditional probability these areas include the unimak fox and delarof islands segments the largest uncertainties in these forecasts stem from the short historic record providing a single recurrence time estimate for some segments or widely varying estimates for others from the unknown importance of aseismic slip and from a vague definition of characteristic earthquake size in fact characteristic earthquake size may not be a time invariant quantity

absence of strain accumulation in the western shumagin segment of the alaska subduction zone gps measurements in the western shumagin segment of the alaska subduction zone show no significant strain the elastic dislocation model that best fits the data has the entire plate interface slipping freely the simplest explanation is that steady slip at the plate convergence rate is occurring on the entire plate interface although we cannot rule out the existence of a shallow locked patch close to the trench large enough to generate a m 7 earthquake the 99 confidence upper bound on the down dip width of the locked patch is 55 km assuming the trench is the the updip limit of the locked zone unless there is significant temporal variability in the locking of the plate interface or viscoelastic effects from a past earthquake the shumagin segment cannot by itself release enough moment to generate a great m 8 earthquake

relocation of earthquakes in the cook inlet area south central alaska using the joint hypocenter determination method abstract the joint hypocenter determination jhd method was used to relocate 1604 earthquakes that occurred during 1988 to 1993 in the wadati benioff zone wbz beneath the cook inlet in south central alaska the study utilizes both p and s wave arrivals recorded by a recently improved regional seismic network and it provides an improvement over previous studies the jhd locations of the events allowed improved delineation of the geometry of the subducted slab and the detection of a double seismic zone within the wbz in the 40 to 100 km depth range the jhd station corrections obtained correlate with the major surface geological features in the study area slow velocity sedimentary basins as well as with crustal and mantle structure high velocity subducting slab and low velocity anomalies beneath the active volcanoes to investigate the dependence of the jhd relocation procedure on factors such as the hypocentral depths of the events used the velocity model the p s ratio and random and systematic errors in travel time readings synthetic travel times were calculated using an exact raytracing technique a three dimensional tomographic p wave velocity model the present network configuration and the actual seismicity distribution then the synthetic events were located with the jhd algorithm the synthetic experiments showed that the jhd procedure is rather insensitive to the choice of plane layered velocity model and p s ratio preserves relative hypocenter locations well and can handle systematic and large random reading errors effectively

the oxygen isotope composition of chondrules and isolated forsterite and olivine grains from the tagish lake carbonaceous chondrite abstract the oxygen isotope compositions obtained by laser fluorination of hand picked separates of isolated forsterite isolated olivine and chondrules from the tagish lake carbonaceous chondrite describe a line 17o 0 95 18o 3 24 r2 0 99 similar to the trend known for chondrules from other carbonaceous chondrites the isolated forsterite grains fo99 6 99 8 18o 7 2 to 5 5 17o 9 6 to 8 2 are more 16o rich than the isolated olivine grains fo39 6 86 8 18o 3 1 to 5 1 17o 0 3 to 2 2 and have chemical and isotopic characteristics typical of refractory forsterite chondrules contain olivine fo97 2 99 8 with oxygen isotope compositions 18o 5 2 to 5 9 17o 8 1 to 1 2 that overlap those of isolated forsterite and isolated olivine an inverse relationship exists between the 17o values and fo contents of tagish lake isolated forsterite and chondrules the chondrules likely underwent greater exchange with 16o poor nebular gases than the forsterite the oxygen isotope compositions of the isolated olivine grains describe a trend with a steeper slope 1 1 0 1 r2 0 94 than the carbonaceous chondrite anhydrous mineral line ccamslope 0 95 the isolated olivine may have crystallized from an evolving melt that exchanged with 16o poor gases of somewhat different composition than those which affected the chondrules and isolated forsterite the primordial components of the tagish lake meteorite formed under conditions similar to other carbonaceous chondrite meteorite groups especially cms its alteration history has its closest affinities to ci carbonaceous chondrites

joint hypocentral location in media with lateral velocity variations and interpretation of the station corrections abstract the application of a new implementation of the joint determination of hypocenters origin times and station correction terms jhd technique to data from the arkansas swarm usa the campi flegrei italy and the nazca plate argentina throws new light onto the problem of earthquake location in all these cases good quality p and s wave arrival times were available the main results are as follows 1 large lateral velocity variations llvv are generally associated with relatively large station corrections these corrections in turn are usually much larger than the average of the station residuals determined when the same set of events is located using a single event location sel method 2 the locations determined by the jhd and sel methods may be substantially different 3 since the effect of llvv on jhd locations is not well established simple 3 d velocity models are constructed so that the jhd technique applied to synthetic data generated using these models produce station corrections similar to those observed 4 the analysis of the synthetic data also shows that the locations determined by the jhd method are much closer to the true locations than the locations determined with the sel method the use of the weighted average of the sel station residuals as station corrections does not give better located events although there is a large decrease in the r m s residual computed for each event therefore the use of r m s residuals to estimate the quality of event locations is not always warranted in view of these results it is possible to conclude that the jhd station corrections can be used to detect lateral velocity variations and to produce locations substantially less affected by these variations than the locations determined by the sel method furthermore under appropriate conditions the jhd station corrections can also be used in a forward modeling scheme to get a semiquantitative velocity model such a model may be the only information that can be obtained from a data set when the station and event distributions are not adequate for 3 d velocity inversion

historical seismicity 1918 1964 of the kodiak island region i have relocated 35 earthquakes and conducted waveform modeling studies of 12 events located primarily within the kodiak portion of the 1964 great alaska earthquake rupture zone and the northeasternmost portion of the 1938 semidi earthquake rupture zone these results show that there is considerable similarity between earthquakes occurring before the 1964 mainshock pre 1964 mainshock seismicity and after the 1964 mainshock post 1964 mainshock seismicity persistent seismicity has occurred for the past 85 years at the southwestern end of the 1964 rupture zone a region where global positioning system gps geodesy studies indicate the plate interface is currently locked earthquakes also occurred frequently within the kennedy entrance region where the transition between the kodiak and kenai block of the subducting pacific plate occurs the seismic moment rate for post 1964 mainshock seismicity is about two times larger than for premainshock seismicity this is in contrast to the prince william sound portion of the 1964 rupture zone where post 1964 mainshock moment rates are orders of magnitude lower than pre 1964 mainshock rates and the pattern of seismicity has changed considerably with time these observations reinforce previous studies that indicate the behavior of plate subduction beneath the kodiak island region is much different from that beneath the prince william sound region

modal mineralogy of carbonaceous chondrites by x ray diffraction and mossbauer spectroscopy carbonaceous chondrites are among the most analyzed geological materials on earth however despite this attention and unlike most terrestrial rocks little is known on the abundance of individual phases within them here we show how a combination of several novel x ray diffraction xrd techniques including a high brightness x ray microsource and mssbauer spectroscopy allows a complete modal mineralogy to be ascertained from even the most highly unequilibrated fine grained chondrites for all minerals of abundance 1 wt knowledge of the modal mineralogy of a sample also allows us to calculate grain density we analyzed allende murchison tagish lake and orgueil based on our modal data the grain density estimates for allende murchison and orgueil are close to literature values in the case of tagish lake there is no published grain density although a bulk density measurement does exist taking our estimate of grain density and the measured bulk density we calculate an exceptionally high porosity of 41 for this meteorite similar to some chondritic idps and in line with a porosity calculated from an entry model for the tagish lake fireball although it is an oxidized cv magnetite is present in allende at a level of 0 5 wt or 0 3 vol a result that is substantiated by several other instrumental studies this may be an oxidized meteorite but that oxidation is not manifested in abundant magnetite in addition we note appreciable fayalitic olivine in orgueil detected by both xrd and mossbauer we employed microsource xrd to look at heterogeneity in mineral abundance in orgueil and found substantial variation with phyllosilicates varying inversely with olivine the data suggest that orgueil was initially composed primarily of anhydrous materials which have been partially but not completely altered although the data are preliminary comparison between our xrd modal assessment bulk chemistry grain density and mossbauer data suggests that our estimates of mineral abundance are robust the advent of microsource xrd allows similar modal data to be acquired from samples as small as a few hundred micrograms

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

crustal deformation and the seismic cycle across the kodiak islands alaska 1 the kodiak islands are located 120 to 250 km from the alaska aleutian trench and are within the southern extent of the 1964 prince william sound mw 9 2 earthquake rupture and aftershock zone here we report new campaign gps results 1993 2001 from northeastern kodiak and reprocessed gps results 1993 1997 from southwestern kodiak the rate and orientation of the horizontal velocities relative to a fixed north america range from 29 7 1 7 mm yr at n30 3 w 3 3 located 120 km from the deepest point of the trench to 8 0 1 3 mm yr at n62 4 w 9 3 located 230 km from the trench we evaluated alternate models of coseismic and interseismic slip to test the importance of the mechanisms that account for surface deformation rates near the gulf of alaska coastal region of kodiak the horizontal velocity can be accounted for primarily by the viscoelastic response to plate motion and a locked main thrust zone mtz downdip creep and to a lesser extent slip in the 1964 earthquake farther inland the dominant mechanisms that account for post 1964 uplift rates are time dependent downdip creep and a locked mtz for the horizontal velocity component southwest translation of western kodiak may be important as well on the basis of the pre 1964 and post 1964 earthquake pattern of interseismic earthquakes we suggest that between the occurrences of great earthquakes like the 1964 event more moderate to large earthquakes occur in the southwestern kodiak region than near northeastern kodiak