plate kinematics in the western pacific derived from geodetic observations 1 plate kinematics have been derived from gps site velocities spanning australasia and the western pacific and define a framework in which deformation fields at plate boundaries can be investigated the australian plate appears to be rigid from cocos island in the west to noumea in the east and incorporating all of the australian continent a revision of the angular velocity vector of the pacific plate using six site velocities has led to the detection of significant relative motion between the pacific plate and sites in northern papua new guinea this provides strong evidence in support of a north bismarck plate between the south bismarck and pacific plates and we model the motion of the north bismarck plate with the angular velocity vector 45 0 s 126 4 e 0 85 myr these new angular velocity vectors model the rigid plate motions of a substantial part of the australasian and western pacific regions with an accuracy better than 3 mm yr

the mw 8 2 17 february 1996 biak indonesia earthquake rupture history aftershocks and fault plane properties moment of 2 7 10 21 n m the rupture propagated bilaterally at an average speed of 90 of the shear wave speed on a fault extending 180 km west and 50 km east of the hypocenter with very variable width ranging from 30 to 100 km at different locations along strike the mean slip over a 230 km 100 km fault area was 4 m and the mean stress drop 1 9 mpa the slip distribution is very nonuniform over the fault with the largest slip of 12 m being near the hypocentral depth 10 km the rupture is very complex propagating first to the west and then after a 15 s delay to the east we interpret this delay as being due to the existence of a inhomogeneous barrier just east of the hypocenter which initially acted as a barrier to rupture propagation toward the east but subsequently failed due to stress increase on it generated by the rupture to its west and with the rupture then continuing to propagate eastward this barrier acted as a stress concentrator before the earthquake giving rise to foreshocks and was also the initiator of rupture for this earthquake the aftershock zone closely corresponds to the region in which rupture occurred the area with greatest aftershock density lying entirely within the area of highest moment release index terms 7209 seismology earthquake dynamics and mechanics 7230 seismology seismicity and seismotectonics 8123 tectonophysics dynamics seismotectonics 7215 seismology earthquake parameters keywords earthquake dynamics and mechanics new guinea trench seismotectonics earthquake parameters

glacier shrinkage across high mountain asia an assessment of glacier shrinkage reductionof area for all of high mountain asia requires a complete compilation of measured rates of change and also a methodology for objective comparison of rates i present a compilation from 155 publications reporting glacier area changes and also a method ology that overcomes the main obstacles hindering comparison glacier areas are not always assigned uncertainties and this problem is addressed with an error model derived from published estimates the problem of discordant survey dates is addressed by interpolating measured areas to fixed dates at pentadal intervals interpolation error depends only incoherently on the time span between measure ments but strongly on glacier size smaller glaciers in addition to changing more rapidly on average exhibit more variable rates of change the overlapping boundaries of study regions are reconciled by mapping all of the information to a 0 5 geographical grid when coupled with glacier area information from the randolph glacier inventory the widely observed inverse dependence of shrinkage rates on glacier size shows promise as a tool for treating incomplete spatial coverage over high mountain asia as a whole from 1960 to 2010 the unweighted average shrinkage rate is 0 57 a 1 but corrections for variable glacier size raise the average to 0 34 a 1 and filling unmeasured gridcells with rates based on size dependence alters the latter estimate to 0 40 a 1 the uncertainties in these rates are large the karakoram anomaly is found to be a zonal feature extending well to the east of the karakoram proper

gps measurements of crustal deformation within the pacific australia plate boundary zone in irian jaya indonesia abstract global positioning system gps measurements made in 1991 1992 and 1993 provide preliminary estimates of slip distribution between the australian and pacific plates in irian jaya indonesia we interpret the gps results with constraints from earthquake mechanisms and slip vectors recent marine surveys and geology three gps sites in southeastern irian jaya show motions that are within 10 mm yr of the expected motion of australia a coast to coast n s baseline along 140 5 e crosses all known onland regions of active deformation but reveals no more than 15 mm yr of shortening and 20 mm yr of left lateral shear in the 27 month period the remaining 40 mm yr of expected convergence between the pacific and australian plates probably occurs at the new guinea trough gps sites on the island of biak at 136 e and at sorong near the western tip of bird s head at 131 e both move 90 100 mm yr in a wsw direction relative to irian jaya but less than 15 mm yr relative to each other these sites are on either side of the sorong fault and demonstrate that it is not presently the major boundary between the australian and pacific plates instead the plate boundary is now south of the sorong and biak sites earthquakes suggest possible structures that accomodate motion between bird s head and australia but the relative importance of them remains uncertain

glacier regime on the northern slope of the himalaya xixibangma glaciers abstract the mass energy exchange components and ice thickness of the xixibangma glacier massif were evaluated during the chinese russian glaciological expedition to the northern himalaya in 1991 long term data from two chinese meteorological stations were used to analyze the glacier climatic regime in the surrounding area it was determined that solar radiation income during the summer autumn monsoon is half that theoretically possible because of cloudiness melting of the glaciers on the northern slopes of the himalaya is driven by solar radiation up to 86 continuous cold katabatic winds decrease turbulent exchange resulting in only a minor contribution from sensible heat transfer to the heat balance of glaciers strong katabatic winds suppress precipitation but favor evaporation reducing glacier melting even in the ablation zone evaporation is very important in the heat balance consuming up to 57 of the heat and so limiting glacier melting autumn ice formation occurs as refrozen melt water in a thin snow layer on the ice surface the mean mass balance index for the period from 1956 to 1990 of the xixibangma glacier was negative amounting to 34 kg m 2

the 1998 papua new guinea earthquake and its fault plane estimated from relocated aftershocks the 1998 papua new guinea earthquake of m w 7 0 occurred near the wewak trench where the north bismarck plate is subducting beneath the australian plate its mechanism is thrust type and one of the nodal planes is almost parallel to the plate interface to determine which of the two nodal planes of the main shock is the fault plane we relocated the main shock and aftershocks using a method of modified joint hypocenter determination we combined and employed two types of data in this study firstly we used data reported by the national earthquake information center neic of the u s geological survey usgs which includes three stations at the northeastern edge of irian jaya and one station in northern papua new guinea from which the epicentral distances are less than 2 degrees secondly in addition to the above permanent station data we used data from temporary aftershock observations near the epicentral area around the sissano lagoon carried out by tsuji et al 1998 using three component seismometers they carried out observations from august 2 to october 2 1998 at three sites although the network did not record the main shock and immediate aftershocks the data obtained by temporary observation sites can clearly assist in identifying their absolute locations since it is possible to apply the joint hypocenter determination jhd method hypocenters were relocated between the coastline and the wewak trench distributed along a nodal plane dipping shallowly to the southwest therefore we can conclude that this nodal plane is the main shock fault and that the 1998 papua new guinea earthquake was an interplate earthquake between the north bismarck and australian plates

evidence for active subduction at the new guinea trench 1 recent seismic tomography imaging shows clear evidence for southwestward subduction along the entire length of the new guinea trench ngt in indonesia and papua new guinea viewed in conjunction with the occurrence of large mw 7 thrust earthquakes that are known to have occurred on the trench this confirms conclusions of earlier studies that the ngt is an active inter plate boundary the 650 km long slab is visible to a depth of about 300 km and subducts with a dip angle that varies from 30 at 136 e to 10 at 143 e the improved clarity of the seismic tomography in this region stems from the use of a more accurate data set of p and s wave arrival times and hypocentral locations

upper plate stressing and seismicity in the subduction earthquake cycle we investigate upper plate stressing during the earthquake cycle in a subduction segment using three dimensional 3 d elastic models to address the effects of strongly heterogeneous coupling along strike of the interplate interface we show how heterogeneity controls the locations and mechanisms of seismicity in the upper plate oblique subduction segments two from the aleutians andreanof islands 1986 and rat islands 1965 and one from indonesia biak 1996 are studied all examples of upper plate seismicity from the aleutians represent events occurring toward the beginning of a new cycle while in biak indonesia the examined events occur both toward the end of one cycle and the beginning of the next in the majority of cases studied the location and mode of the upper plate seismicity are consistent with space and time dependent stressing as predicted by modeling this confirms earlier observations that seismicity in the vicinity of large great subduction earthquakes toward the outer rise at intermediate depth and now in the upper plate depends in an interpretable manner on the stage in the earthquake cycle as well as on distribution of coupling along the interplate interface

climatic and hydrologic changes in the tien shan central asia abstract the authors analyze climatic and hydrologic data from 110 sites collected from the middle of the twentieth century to the present in the tien shan one of the largest mountain systems of central asia in spite of a few confounding interregional variations in the temporal changes of surface air temperature precipitation runoff glacier mass and snow thickness in the tien shan it has been possible to establish statistically significant long term trends in these key hydroclimatic variables the average rise in air temperature was 0 01 c yr 1 over the range with slightly lower values below 2000 m elevation the precipitation in the tien shan increased 1 2 mm yr 1 over the past half century the precipitation increase is larger at low altitudes in the northern and western regions than at altitudes above 2000 m a decrease in snow resources occurred almost everywhere in the tien shan the maximum snow thickness and snow duration have decreased on average 10 cm and 9 days respectively the annual

historical seismicity and seismotectonic context of the great 1979 yapen and 1996 biak irian jaya earthquakes we present relocations of over 220 historical and recent earthquakes in the northwestern part of irian jaya in the context of the large earthquakes of 1979 and 1996 our results document continuous activity on a 420 km segment of the sorong fault with a possible extension over an additional 330 km to the west we also show that some level of activity did take place on the new guinea trench prior to the 1996 biak earthquake and relocate a large m pas 7 4 event on 02 april 1947 to the trench at 138 e we speculate that the large earthquake of 26 may 1914 may also have taken place on the new guinea trench we study the pattern of activity following the 1979 yapen earthquake which triggered stress release in the pandaidori islands also the location of stress transfer following the 1996 biak earthquake

seismotectonics of new guinea a model for arc reversal following arc continent collision the structure and evolution of the northern new guinea collision zone is deduced from international seismological center isc seismicity 1964 1985 new and previously published focal mechanisms and a reexamination of pertinent geological data a tectonic model for the new guinea margin is derived which illustrates the sequential stages in the collision and suturing of the bewani toricelli adelbert finisterre huon new britain arc to central new guinea followed by subduction polarity reversal in the west east of 149 e the solomon plate is being subducted both to the north and south bringing the new britain and trobriand forearcs toward collision west of 149 e the forearcs have collided and together they override a fold in the doubly subducted solomon plate lithosphere which has an axis that is parallel to the strike of the ramu markham suture and that plunges westward at an angle of 5 beneath the coast ranges of northern new guinea active volcanism off the north coast of new guinea is related to subduction of the solomon plate beneath the bismarck plate active volcanism of the papuan peninsula and quaternary volcanism of the new guinea highlands are related to slow subduction of the solomon plate beneath the indo australian plate along the trobriand trough and the trough s former extension to the west respectively from 144 148 e seismicity and focal mechanisms reveal that convergence between the sutured bismarck and indo australian plates is accommodated by thrusting within the finisterre and adelbert ranges and compression of the new guinea orogenic belt together with basement involved foreland folding and thrusting to the south the finisterre block overthrusts the new guinea orogenic belt whereas the adelbert block is sutured to new guinea and overthrusts the oceanic lithosphere of the bismarck sea along the new guinea trench west of 144 e seismicity defines a southward dipping wadati benioif zone and focal mechanisms indicate oblique subduction only this oldest westernmost portion of the collision has progressed past suturing to a full reversal in subduction polarity

a seismological study of the eastern new guinea and the western solomon sea regions and its tectonic implications summary we use new and pre existing seismological data to study the neotectonics and the state of stress in the seismic zones of eastern papua new guinea and the western solomon sea regions earthquake hypocentres for the period 1964 90 were relocated using the joint hypocentre determination jhd technique we show that the t axes of earthquakes in the 100 250km depth range beneath eastern papua new guinea are aligned parallel to the seismic zone with no seismicity below 250 km this intermediate depth seismic zone forms an inverted u shaped zone with limbs dipping to the north and south and is interpreted to be seismicity along the subducted solomon sea plate the northern and southern limbs of the seismic zone are connected by a flattened zone of seismicity which is marked by predominantly strike slip and a few normal fault mechanisms we suggest that the solomon sea plate at depth beneath the finisterre mountains is no longer influenced by the tectonic forces acting at the surface but breaking up and sinking under its own gravitational forces a significant north dipping seismic zone is imaged above the deeper seismic zone this feature characterized by thrust mechanisms extrapolates to the surface along the ramu markham valley and is attributed to the ramu markham fault rmf the rmf has an average dip of about 40 to the north east but its detailed geometry would appear to be complex the rmf is interpreted to ramp steeply in the uppermost 10 20 km flattening out sharply to a dip of 15 at a depth of about 20km the rmf marks the suture between the finisterre terrane and the australia new guinea plate and may extend to a depth of 90km beneath the western limit of the finisterre mountains there is a clear gap in seismicity between the rmf and the deeper solomon sea plate seismic zone beneath the finisterre mountains which together with the alignment of the t axes of earthquakes along the seismic zone at depths 100km indicates that these are indeed two distinct features the seismicity in the depth range 50 80 km along the new britain arc follows the trend of the 2000m bathymetric contour of the new britain trench and the finsch deep far more closely than it does the trend of the surface plate boundary indicating that the increase in the distance between the solomon sea south bismarck plate boundary and the active volcanos along the new britain arc west of 6 83 150 o e is only a shallow phenomenon and does not reflect the geometry of the solomon sea plate at depths greater than 50 km

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

hydrological cycles on the north and south peripheries of mountain glacial basins of central asia four high mountain glacial basins of the northern and southern periphery of central asia were studied to determine their interaction with the external hydrological cycle over the eurasian continent two of them located in the northern periphery are closed drainage basins with continental climate and the other two are open basins located in the southern periphery calculations of mass energy exchange glacial runoff and components of the hydrological cycles were conducted for glaciers with a continental climate the calculations of snow ice melt and runoff were based on solar parameters for glaciers with a marine climate regime glacier melt and runoff were based on air temperature the relative errors of simulated annual flows were on average 8 14 the components of the regional hydrological cycles precipitation condensation runoff and evaporation were quantified for each glacial system and their share in total atmospheric moisture was determined the closed basins of the northern periphery in central asia stored annually about 0 1 2 4 of the total external atmospheric moisture in the aralo caspian and tarim hydrographic systems about 0 22 0 24 of the external water cycle is transferred annually in open glacial basins of the southern periphery the glaciers of these regions return 0 25 0 30 of the external water cycle per year to the pacific and indian oceans 0 03 and 0 06 of this external moisture is taken from the glacial resources of the gongga and xixibangma glaciers

subducted slabs beneath the eastern indonesia tonga region insights from tomography tomographic images of mantle structure beneath the region north and northeast of australia show a number of anomalously fast regions these are interpreted using a recent plate tectonic reconstruction in terms of current and former subduction systems several strong anomalies are related to current subduction the inferred slab lengths and positions are consistent with neogene subduction beneath the new britain and halmahera arcs and at the tonga and the new hebrides trenches where there has been rapid rollback of subduction hinges since about 10 ma there are several deeper flat lying anomalies which are not related to present subduction and we interpret them as former subduction zones overridden by australia since 25ma beneath the bird s head and arafura sea is an anomaly interpreted to be due to north dipping subduction beneath the philippines halmahera arc between 45and 25ma a very large anomaly extending from the papuan peninsula to the new hebrides and from the solomon islands to the east australian margin is interpreted to be the remnant of south dipping subduction beneath the melanesian arc between 45and 25ma this interpretation implies that a flat lying slab can survive for many tens of millions of years at the bottom of the upper mantle in the lower mantle there is a huge anomaly beneath the gulf of carpentaria and east papua new guinea this is located above the position where the tectonic model interprets a change in polarity of subduction from north dipping to south dipping between 45and 25ma we suggest this deep anomaly may be a slab subducted beneath eastern australian during the cretaceous or subducted north of australia during the cenozoic before 45ma the tomography also supports the tectonic interpretation which suggests little neogene subduction beneath western new guinea since no slab is imaged south of the new guinea trench however one subduction zone in the tectonic model and many others that associated with the trobriand trough east of papua new guinea and the miocene maramuni arc is not seen in the tomographic images and may require reconsideration of currently accepted tectonic interpretations 4 2002 elsevier science b v all rights reserved

active deformation in eastern indonesia and the philippines from gps and seismicity data in this study we combine global positioning system gps velocities with information on the style of regional seismicity to obtain a self consistent model velocity and strain rate field for the entire eastern indonesia and philippines region in the process of interpolating 93 previously published gps velocities the style and direction of the seismic strain rate field inferred from earthquakes with m0 1 1020 n m from the harvard centroid moment tensor catalog are used as constraints on the style and direction of model strain rates within the plate boundary zones the style and direction of the seismic strain rate field are found to be self similar for earthquakes up to m0 1 1020 n m equivalent to mw 7 3 our inversion result shows the following the java trench which lacks any significant historic seismicity delineates the australian plate au sunda block sunda plate boundary west of the island of sumba east of sumba convergence is distributed over the back arc and banda sea and there is no subduction at the timor trough suggesting that the northern boundary of the au plate runs north of this part of the banda arc through the banda sea in new guinea most motion is taken up as strike slip deformation in the northern part of the island delineating the pacific plate pa au boundary however some trench normal convergence is occurring at the new guinea trench evidence that the strain is partitioned in order to accommodate oblique pa au motion pa au motion is consistent with nuvel 1a direction but 8 mm yr 1 slower than the nuvel 1a estimate for pa au motion the sulawesi trench and molucca sea delineate zones of high strain rates consistent with high levels of active seismicity the sulawesi trench may take up some of the au sunda motion philippine sea plate motion is in a direction slightly northward of the nuvel ia estimate and is partitioned in some strike slip strain rates along the philippine fault and relatively larger trench normal convergence along the philippine trench and on the philippine mainland in the southern philippines and along the manila trench in the northern philippine islands the high level of strain rate along the manila trench is not released by any significant historic seismic activity for the entire eastern indonesia philippines region seismicity since 1963 has taken up 40 of the total moment rate inferred from our model

non european palaeomagnetic directions from the carpathian foredeep at the southern margin of the european plate terra nova 23 134 144 2011 abstract a palaeomagnetic study carried out at 33 geographically distributed localities in the miocene fill of the 600 km long moravian and polish segment of the carpathian foredeep revealed an overall more than 20 ccw rotation of the area these new palaeomagnetic results can be best interpreted in terms of ccw rotation starting at around 17 ma the rotations must have affected not only the sedimentary fill of the carpathian foredeep but also the basement owing to the dextral shift on nw se trending block bounding faults observed in the basement and in the miocene sediments this evidence for non european palaeomagnetic directions north of the alpine carpathian mountain chain together with previously published indications question the rigidity of the european plate during the last 20 ma at least near the thrust front of the alps and carpathians

origin and tectonic evolution of the caroline ridge and the sorol trough western tropical pacific from admittance and a tectonic modeling analysis abstract an independent caroline sea plate surrounded by prominent seismotectonic features is said to exist in the western tropical pacific the caroline sea plate is a transient feature existing only when the caroline philippine sea plate boundary is jumping to the caroline pacific boundary the origin and the tectonic evolution of the caroline ridge sorol trough region which forms the northern part of the caroline pacific plate boundary are examined using a standard admittance analysis a tectonic modeling study and additional direct gravity and magnetic analyses the observed admittance function is fitted well by shallow airy model in the 250 125 km 0 025 k 1 wavelength region whose average crustal thickness t c is 20 km and also by thin plate flexure model of isostasy within the diagnostic waveband of 250 80 km 0 025 k 1 with an effective elastic thickness t e of 5 7 km a simple interpretation of the observed admittance function is that the local airy model of isostasy is the main support mechanism in the study region for the longer wavelength more fundamental topography corresponding to that of the caroline ridge the caroline ridge is inferred to have formed in a near ridge tectonic setting on top of oceanic lithosphere which was young thin and weak at the time of emplacement the tectonic model study after an explanation for rifting along the mendana fracture zone in the nazca plate suggests that the sorol trough formed in the 17 7 ma interval splitting the caroline ridge into two longitudinal halves the rifting along the sorol trough which took place in the manner described in weissel and karner 1989 flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension j geophys res 94 13 919 13 950 necking of unbroken lithosphere post dated the formation of the caroline ridge by 10 15 m y during which time t e in the region increased to 5 10 km the rifting necking along the sorol trough represents a second loading event in the region the combined gravity effects of the rifting as well as the increase in the t e in the region from essentially nil to 5 10 km is reflected in the agreement between the observed admittance and the regional model with a 5 7 km t e in the wavelength region 80 km these results are consistent with the findings and the suggestions of the previous investigators in the region in that 1 the caroline ridge was constructed in the late oligocene by hot spot volcanism on top of oligocene seafloor of the caroline sea back arc basin 2 the eauripik rise genetically related to the caroline ridge formed on young and weak caroline basin lithosphere and is supported by airy manner crustal thickening and that 3 the lithosphere of the caroline ridge was young at the time of rifting necking along the sorol trough on the basis of the current results and the findings of the previous workers a tentative hypothetical rheological model for the crustal density structure of the caroline ridge sorol trough is also given the caroline sea plate appears to be bounded in the north and south by e w trending boundaries that deform diffusely while more normal narrow n s trending boundaries exhibiting more localized albeit slow deformation bound the plate in the east and west

the manokwari trough and the western end of the new guinea trench the new guinea trench is a sparsely surveyed seafloor depression which runs parallel to the north coast of new guinea for a distance of some 700 km its western end lies about 600 km east of the philippine trench the intervening region is occupied by a complex series of north trending ridges and troughs of which the ayu trough and the tobi and mapia ridges are the most prominent it has been suggested and is now widely accepted that the trench marks a site of subduction but the degree of present day activity is disputed the western termination has recently been defined by combined single channel seismic and long range sidescan sonar surveys as lying at the ridge system which culminates in mapia island the trench contains as much as 1 km of flat lying undisturbed sediments within the area surveyed and the southern slopes are extensively channeled suggesting a lack of recent deformation the same survey has also shown that for a distance of some 400 km west of the western end of the trench the north coast of new guinea is flanked at a distance of only a few tens of kilometers by a deep trough the sonar imagery of this manokwari trough suggests recent convergence as well as transcurrent movement both the existence of this trough and the abrupt termination of the new guinea trench are consequences of the seafloor spreading which took place in the ayu trough after subduction had ceased at the trench

active deformation in the new guinea fold and thrust belt seismological evidence for strike slip faulting and basement involved thrusting the new guinea fold and thrust belt forms a 1000 km long mountain chain running the length of new guinea but its trend is oblique to the predicted convergence direction a large component of left lateral shear across the mountain belt is expected but geological evidence for such motion is ambiguous surface structures in the fold and thrust belt show mountain building by folding and thrusting supposedly thin skinned of pre pliocene continental shelf sediments although some evidence indicates that active faulting penetrates the basement we examine the active deformation of this mountain belt by using teleseismic long period p and sh waveforms short period p waveforms and p wave first motions to determine reliable focal mechanisms and source depths for the 18 largest earthquakes in the new guinea fold and thrust belt since 1964 eight thrust events with seismic moments m0 between 1017 and 2 1018 n m are distributed throughout the thrust belt at depths ranging from 0 5 to 45 km and have steeply dipping fault planes that strike parallel to surface structural trends six of the eight events are between 11 and 25 km deep the steep dips of nodal planes the depths of these earthquakes and the known thicknesses of the sedimentary section show that thrust faulting is not exclusively thin skinned i e confined above a shallow detachment surface but penetrates the crystalline basement at high angles most earthquakes in the western half of the thrust belt including the three largest earthquakes examined m0 5 1018 n m show strike slip faulting with the probable fault plane oriented east west so that displacement is left lateral the nine strike slip earthquakes account for almost 90 of the observed seismic moment in the period 1964 1985 and indicate a seismic slip rate of 5 25 mm a all but one of these strike slip earthquakes are shallower than the thrust earthquakes suggesting that east northeast convergence across the fold and thrust belt is accommodated by a decoupled system of strike slip and dip slip faults while the great height of the mountain belt is an obvious indication that crustal thickening is an important consequence of plate motion in new guinea seismological evidence suggests that translation by strike slip faulting may play a much greater role than previously recognized by analogy in older collisional orogens whose motions can be inferred only from remnant structures and not from seismicity strike slip faulting may have been equally important in accommodating convergence we estimate from seismic moments of earthquakes and from the volume of the mountains that deformation of the new guinea highlands may account for 5 20 of the total convergence between the pacific plate and australia in new guinea