correction to strong ferrimagnetic resonance signal and magnetic susceptibility of the nojima pseudotachylyte in japan and their implication for coseismic electromagnetic changes 1 pseudotachylyte is a glassy fault rock providing certain evidence of ancient seismic fault movement i examine the nojima pseudotachylyte found along the nojima fault which caused the 1995 kobe earthquake m 7 2 in japan using the electron spin resonance technique the nojima pseudotachylyte has a strong ferrimagnetic resonance fmr signal derived from bulky trivalent iron ions in ferrimagnetic iron oxides this fmr signal appears by heating the surrounding fault gouge that is the source material of the nojima pseudotachylyte furthermore the magnetic susceptibilities of the nojima pseudotachylyte are 10 2 10 3 times larger than those of the surrounding fault gouge and are proportional to the fmr signal intensities here i reconstruct the magnetization process of fault gouge during ancient seismic fault slip using the fmr signal the results indicate that the instantaneous magnetization of the nojima fault gouge may have induced instantaneous geomagnetic changes and that the instantaneous geomagnetic changes may have further induced geoelectric changes by electromagnetic induction

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

southern california permanent gps geodetic array continuous measurements of regional crustal deformation between the 1992 landers and 1994 northridge earthquakes the southern california permanent gps geodetic array pgga was established in 1990 across the pacific north america plate boundary to continuously monitor crustal deformation we describe the development of the array and the time series of daily positions estimated for its first 10 sites in the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes we compare displacement rates at four site locations with those reported by feigl et al 1993 which were derived from an independent set of global positioning system gps and very long baseline interferometry vlbi measurements collected over nearly a decade prior to the landers earthquake the velocity differences for three sites 65 100 km from the earthquake s epicenter are of order of 3 5 mm yr and are systematically coupled with the corresponding directions of coseismic displacement the fourth site 300 km from the epicenter shows no significant velocity difference these observations suggest large scale postseismic deformation with a relaxation time of at least 800 days the statistical significance of our observations is complicated by our incomplete knowledge of the noise properties of the two data sets two possible noise models fit the pgga data equally well as described in the companion paper by zhang et al this issue the pre landers data are too sparse and heterogeneous to derive a reliable noise model under a fractal white noise model for the pgga data we find that the velocity differences for all three sites are statistically different at the 99 significance level a white noise plus flicker noise model results in significance levels of only 94 43 and 88 additional investigations of the pre landers data and analysis of longer spans of pgga data could have an important effect on the significance of these results and will be addressed in future work

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

india and sunda plates motion and deformation along their boundary in myanmar determined by gps using a regional gps data set including 190 stations in asia from nepal to eastern indonesia and spanning 11 years we update the present day relative motion between the indian and sundaland plates and discuss the deformation taking place between them in myanmar revisiting measurements acquired on the main boundary thrust in nepal it appears that points in southern nepal exhibit negligible deformation with respect to mainland india including these points using a longer time span than previous studies and making an accurate geodetic mapping in the newest reference frame allows us to refine the present day indian motion our results confirm that the current motion of india is slower than predicted by the nuvel 1a model and in addition our india eurasia motion is significantly 5 mm yr slower than previous geodetic determinations this new indian motion combined with a refined determination of the sundaland motion gives way to a relative india sunda angular velocity of 20 2 n 26 1 e 0 370 myr in itrf2000 predicting a relative motion of 35 mm yr oriented n10 at the latitude of myanmar there the sagaing fault accommodates only 18 mm yr of right lateral strike slip only half of the shear component of motion we present two models addressing how and where the remaining deformation may occur a first model of distributed deformation implies convergence on the arakan subduction the northern continuation of the now famous sumatra andaman trench and wrench faulting in the arakan wedge the second model uses localized deformation where deformation observed west of the sagaing fault is entirely due to elastic loading on a faster and oblique arakan subduction 23 mm yr this latter model predicts that a major earthquake of mw 8 5 may occur every century on this segment of the subduction

application of the global positioning system to crustal deformation measurement 1 precision and accuracy in this paper we assess the precision and accuracy of interstation vectors determined using the global positioning system gps satellites these vectors were between stations in california separated by 50 450 km using data from tracking the seven block i satellites in campaigns from 1986 through 1989 we examine the precision of gps measurements over time scales of a several days and a few years we characterize gps precision by constant and length dependent terms the north south component of the interstation vectors has a short term precision of 1 9 mm 0 6 parts in 108 the east west component shows a similar precision at the shortest distances 2 1 mm with a larger length dependence 1 3 parts in 108 the vertical precision has a mean value of 17 mm with no clear length dependence for long term precision we examine interstation vectors measured over a period of 2 2 to 2 7 years when we include the recent results of davis et al 1989 for distances less than 50 km we can describe long term gps precision for baselines less than 450 km in length as 3 4 mm 1 2 parts in 108 5 2mm 2 8 parts in 108 11 7mm 13 parts in 108 in the north south east west and vertical components accuracy has been determined by comparing gps baseline estimates with those derived from very long baseline interferometry vlbi a comparison of eight interstation vectors shows differences ranging from 5 to 30 mm between the mean gps and mean vlbi estimates in the horizontal components and less than 80 mm in the vertical a large portion of the horizontal differences can be explained by local survey errors at two sites in california a comparison which suffers less from such errors is between the rates of change of the baselines the horizontal rates estimated from over 4 years of vlbi data agree with those determined with 1 2 years of gps data to within one standard deviation in the vertical both gps and vlbi find insignificant vertical motion

u pb dating of a terminal pliocene coral from the indonesian seaway abstract pristine detrital platygyra corals were discovered in an exhumed package of syn orogenic marine sediments on the island of timor in the eastern indonesian region and dated using u pb techniques a single coral from the upper part of the sequence yields a 238 u 206 pb 207 pb 206 pb concordia age of 2 66 0 14 2 ma that is supported by coral 87 sr 86 sr chemostratigraphy and foraminiferal biostratigraphy from bounding strata minor u series disequilibrium is best explained by u mobility within the last 150 ka as pore water chemistry was altered during exhumation and is unlikely to have affected 238 u 206 pb and the apparent sample age by more than 1 2 the ability to date corals beyond the limits of 14 c and u th techniques provides the opportunity to improve the temporal resolution of associated marine chronostratigraphic records in this instance we refine the timing of timor s emergence from beneath the waters of the indonesian seaway is and the initiation of turbiditic deposition at the study site to between ca 3 35 and 2 66 ma these results have implications for the evolution of topography and is oceanic pathways in the active orogenic belts along the northern fringes of the australian plate

one century of tectonic deformation along the sumatran fault from triangulation and global positioning system surveys an analysis combining historical triangulation and recent global positioning system gps survey measurements in west and north sumatra indonesia reveals a detailed slip history along the central part of the sumatran fault the arc parallel components of the combined velocity field are consistent with slip rates inferred from gps data ranging from 23 to 24 mm yr between 1 0 s and 1 3 n the sumatran fault appears to be characterized by deep locking depths of the order of 20 km and the occurrence of large mw 7 earthquakes the long term 1883 1993 strains show simple right lateral shear with rates similar to gps measured 1989 1993 strain rates coseismic deformation due to the 1892 tapanuli and 1926 padang panjang earthquakes estimated from triangulation measurements taken before and after the events indicates that the main shocks were significantly larger than previously reported the 1892 earthquake had a likely magnitude of mw 7 6 while the 1926 events appear to be comparable in size to the subsequent m 7 1943 events and an order of magnitude higher than previously reported

strain partitioning during oblique plate convergence in northern sumatra geodetic and seismologic constraints and numerical modeling global positioning system gps measurements along the subduction zone of northern sumatra 2 s to 3 n reveal that the strain associated with the oblique convergence of the australian plate with eurasia is almost fully partitioned between trench normal contraction within the forearc and trench parallel shear strain within a few tens of kilometers of the sumatran fault kinematic analyses of interplate earthquake slip vectors provide slip rates on the sumatran fault within a few millimeters per year of gps and geologic rates giving us more confidence in the use of slip vectors for inferring slip partitioning elsewhere the inferred slip rate on the sumatran fault is 1 3 less than the full margin parallel component of plate motion an across forearc rotation in the slip vectors suggests that the missing arc parallel shear occurs seaward of the geodetic network between the forearc islands and the trench simple finite element models are used to explore the conditions under which the change in the principal strain rate directions between the forearc and the arc region can occur modeling suggests that neither a preexisting strike slip fault nor a zone of thermally induced lithospheric weakness in the overriding plate is needed for strain partitioning to occur in general forearc slivers form over the region of interplate coupling and are driven along strike by the basal shear a volcanic arc can help the partitioning process by localizing the margin parallel shear strain in the upper plate if its crust and mantle are weaker than its surroundings interplate slip vectors and geodetic results from sumatra together suggest that the highest coupling on the plate boundary occurs beneath and seaward of the forearc islands consistent with inferences about the rupture zones of great nineteenth century earthquakes there the sumatra example suggests that geodetic measurements of interseismic margin parallel shear strain at oblique convergent margins can be used to map the landward extent of the relatively high basal stress beneath the overriding plate if one can correct for strain localization caused by weak upper plate strike slip faults

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

geodetic observations of interseismic strain segmentation at the sumatra subduction zone deformation above the sumatra subduction zone revealed by global positioning system gps geodetic surveys shows nearly complete coupling of the forearc to the subducting plate south of 0 5 s and half as much to the north the abrupt change in plate coupling coincides with the boundary between the rupture zones of the 1833 and 1861 mw 8 thrust earthquakes the rupture boundary appears as an abrupt change in strain accumulation well into the interseismic cycle suggesting that seismic segmentation is controlled by properties of the plate interface that persist through more than one earthquake cycle structural evidence indicates that differences in basal shear stress may be related to elevated pore pressure in the north

stratigraphic record of holocene coseismic subsidence padang west sumatra 1 stratigraphic evidence is found for two coseismic subsidence events that underlie a floodplain 20 km south of padang west sumatra along the mentawai segment 0 5 s 0 3 s of the sunda subduction zone each earthquake is marked by a sharp soil mud contact that represents a sudden change from mangrove to tidal flat the earthquakes occurred about 4000 and 3000 cal years b p based on radiocarbon ages of detrital plant fragments and seeds the absence of younger paleoseismic evidence suggests that late holocene relative sea level fall left the floodplain too high for an earthquake to lower it into the intertidal zone our results point to a brief few thousand year window of preservation of subsidence events in tidal wetland stratigraphic sequences a result that is generally applicable to other emergent coastlines of west sumatra

distribution of slip at the northern sumatran fault system we model spatial variations in horizontal displacements of 117 geodetic sites measured during annual surveys in 1989 1996 with the global positioning system gps as elastic strain across a locked strike slip fault to infer the contemporary slip rate locking depth and location of the sumatran fault sf in northern sumatra 1 s 3 n gps derived slip rate estimates increase slightly northward from 23 plus or minus 3 mm yr at 0 8 deg s to 26 plus or minus 2mm yr at 2 7 n they agree with geologic estimates north of the equator but at 0 5 s they are about 10 mm yr higher strain appears to be distributed asymmetrically about the fault south of 2 n about 5 mm yr of shear is required within the offshore forearc west of the fault to achieve a closer agreement of fault locations inferred from gps velocities with geologically identified traces of the sf locking depth estimates are on the order of 10 20 km the western branch of the major fault bifurcation near 1 n slips at a rate five times higher than the eastern branch the two main strands of the fault at the northwestern tip of sumatra 5 5 n appear to be nearly free of horizontal strain significant slip must occur away from the two strands probably further east at two other geologically active branches the banda aceh embayment is extruded to the northwest at a rate of 5 plus or minus 2 mm yr within the estimated velocity uncertainties of several mm yr fault normal deformation along the sf is insignificant almost strain free the northern part of the back arc basin is part of a rigid sunda shelf while the northern forearc is subjected to 8 plus or minus 5 x 10 exp 8 yr of extension nearly parallel to the arc

slip vectors and stretching of the sumatran fore arc slip vectors from thrust earthquakes at the java trench southwest of sumatra demonstrate that the sumatran fore arc is not a single rigid plate that is translated to the northwest by oblique plate convergence instead they indicate arc parallel stretching of the fore arc at a uniform strain rate of 3 4 x 10 8 yr the northwestward motion of the fore arc relative to the upper plate southeast asia increases from near zero at the sunda strait to 45 60 mm yr in northwest sumatra and should result in variable slip rates on the sumatran fault

geomorphological evidence for late quaternary tectonic deformation of the cape region coastal west central australia abstract a late pleistocene marine isotope stage 5e emergent marine sequence fringes the coastline of the cape region of coastal west central australia and provides elevation and age control to characterize the locations and rates of crustal deformation there is a systematic measurable change in relative paleo sea level elevations across the cape region high precision leveling of modern and pleistocene shoreline features indicates the minimum elevation range of mis 5e shoreline features along the coast is 10 4 m this compares with the 2 5 m elevation range for observed modern shoreline analogs the lack of continuity of mis 5e shoreline elevations along 300 km of coastline demonstrates continuing tectonic deformation along coastal anticlines in the cape region topographic expression of mis 5e features indicates tectonic uplift consistent with late neogene to quaternary deformation on the cape cuvier and cape range anticlines post mis 5e tectonic uplift rates are up to 0 054 0 035 mm yr at fold axial locations estimated subsidence rates are 0 013 0 034 mm yr on fold limbs while the estimated vertical tectonic deformation is small and the rates are low the geomorphological data also demonstrate tectonic activity not stability

observing plate motions in s e asia geodetic results of the geodyssea project this paper presents the final geodetic results of the geodyssea project the gps data from a 42 station network observed during two field campaigns 1994 1996 were analyzed by four groups using different software packages and analysis strategies the precision of both campaign coordinate solutions was found to be 4 7 mm for the horizontal and 1 cm for the vertical component the campaign solutions were merged into one unique solution which was accurately mapped into the itrf 96 reference frame the global accuracy of this solution with respect to itrf 96 is 1 cm while the resolution of the relative horizontal velocities is estimated to be at the level of 2 3 mm yr this solution was used as the basis for all scientific interpretations which are published in separate papers the velocity estimates of a part of the network provided the first direct measurement of a relative motion of the sundaland block with respect to eurasian plate

accretion of the southern banda arc to the australian plate margin determined by global positioning system measurements global positioning system geodetic measurements at thirteen locations in indonesia and four in australia reveal that the australian continent has accreted the banda island arc to its margin small relative velocities of five sites on west java south kalimantan bali and south sulawesi define a rigid sunda shelf that moves relative to northern australia in a manner consistent with pole locations from nuvel 1 australia eurasia but at a rate that is about 7 slower block like northward motion of the southern banda arc toward the sunda shelf at nearly the same rate as australia suggests that the timor trough is now inactive as a thrust little of the convergence of australia with eurasia is accommodated by strain within the banda arc structure most of the convergence appears to occur as northward translation of the rigid arc with shortening on the flores and wetar thrusts and possibly on faults within the back arc basin

tests of the rigid plate hypothesis and bounds on intraplate deformation using geodetic data from very long baseline interferometry the geodetic results of ma et al 1994 from very long baseline interferometry are used to assess rates of intraplate deformation we analyze the resulting set of velocities of 18 plate interior sites nine on the north american plate four western european sites on the eurasian plate three on the pacific plate and two on the australian plate we formulate three alternative error budgets based partly on the work of ryan et al 1993a an optimistic error budget a conservative error budget and an upper bound error budget all three budgets assume the existence of a previously unmodeled error that is inversely proportional to the time span of observations at a site use of the conservative error budget indicates no significant motion between sites on any one of the four plates use of the upper bound error budget designed to be precisely large enough to be consistent with rigid plates places a usefully small upper bound on how fast any site might be moving relative to the rest of its plate speeds faster than 2 mm yr are excluded at the 95 confidence level for seven of the 18 plate interior sites adjustments of the site velocities for motion due to postglacial rebound as predicted from the model of tushingham and peltier 1991 give an insignificant improvement to the fit of the horizontal velocities to the rigid plate model the velocities of six sites near the western margin of the interior of the north american plate were also analyzed use of the conservative error budget indicates that a site near fairbanks alaska has an upper bound of 3 mm yr on its speed a site in nome alaska has an upper bound on its speed of 8 mm yr and a site in penticton british columbia has an upper bound on its speed of 4 mm yr of three sites on the colorado plateau two move marginally significantly and one moves insignificantly relative to stable north america upper limits on their speeds relative to stable north america range from 4 to 5 mm yr we conclude that the data do not yet demonstrate significant velocities between sites in the stable interior of any one plate but do provide useful and small upper bounds of 2 mm yr or less on the speeds of the best observed intraplate sites six sites near the western margin of the north american interior have upper bound speeds of 3 to 8 mm yr

gps compared to long term geologic motion of the north arm of sulawesi geodetic data acquired in the north arm of sulawesi are compared with geologic and palaeomagnetic data from north sulawesi and the celebes sea the objective of this study is to assess whether the long term motion deduced from palaeomagnetic and geological studies is coherent with the extrapolation of the current motions measured by gps palaeomagnetic data that have been collected in the north arm of sulawesi indicate that since 5 ma about 20 to 25o of semi rigid rotation occurred about a pole located north of manado this suggests 200 to 250 km of left lateral displacement along the palu koro fault with a displacement rate of 4 cm year a rather similar displacement on the palu fault is derived using the distribution of the asymmetric magnetic anomalies of the celebes seafloor the distribution implies that 200 to 250 km of oceanic crust was subducted at the north sulawesi trench another marker for the rotation is derived from the opening of the gulf of tomini and the nw migration of the calc alkaline subduction related volcanism the far field observation by gps of 4 cm year of left lateral strike slip motion over 17 months and the 5 year average of 3 4 0 3 cm year on a transect across the palu fault fit well with the geological observations that indicate a motion of 4 to 5 cm year of the north arm we therefore conclude that the current rates deduced from gps measurements approximate the long term rates and may hence be extrapolated over a few million years 1998 elsevier science b v all rights reserved

depth dependent azimuthal anisotropy in the western us upper mantle abstract we present the results of a joint inversion of long period seismic waveforms and sks splitting measurements for 3d lateral variations of anisotropy in the upper mantle beneath the western us incorporating recent datasets generated by the usarray deployment as well as other permanent and temporary stations in the region we find that shallow azimuthal anisotropy closely reflects plate motion generated shear in the asthenosphere in the shallow upper mantle 70 150 km depth whereas at depths greater than 150 km it is dominated by northward and upward flow associated with the extension of the east pacific rise under the continent constrained to the east by the western edge of the north american craton and to the north by the presence of the east west trending subduction zone in particular the depth integrated effects of this anisotropy explain the apparent circular pattern of sks splitting measurements observed in nevada without the need to invoke any local anomalous structures

gps determined eastward sundaland motion with respect to eurasia confirmed by earthquakes slip vectors at sunda and philippine trenches abstract gps measurements acquired over southeast asia in 1994 and 1996 in the framework of the geodyssea program revealed that a large piece of continental lithosphere comprising the indochina peninsula sunda shelf and part of indonesia behaves as a rigid sundaland platelet a direct adjustment of velocity vectors obtained in a eurasian frame of reference shows that sundaland block is rotating clockwise with respect to eurasia around a pole of rotation located south of australia we present here an additional check of sundaland motion that uses earthquakes slip vectors at sunda and philippine trenches seven sites of the geodyssea network are close to the trenches and not separated from them by large active faults two at sumatra trench three at java trench and two at the philippine trench the difference between the vector at the station and the adjacent subducting plate vector defines the relative subduction motion and should thus be aligned with the subduction earthquake slip vectors we first derive a frame free solution that minimizes the upper plate or sundaland motion when corrected for australia eurasia and philippines eurasia nuvel1 a motion the misfit between gps and slip vectors azimuths is significant at 95 confidence indicating that the upper plate does not belong to eurasia we then examine the range of solutions compatible with the slip vectors azimuths and conclude that the minimum velocity of sundaland is a uniform 7 10 mm a eastward velocity however introducing the additional constraint of the fit of the geodyssea sites with the australian igs reference ones or tie with the ntus singapore station leads to a much narrower range of solutions we conclude that sundaland has an eastward velocity of about 10 mm a on its southern boundary increasing to 16 18 mm a on its northern boundary

neotectonics of the sumatran fault indonesia the 1900 km long trench parallel sumatran fault accommodates a significant amount of the right lateral component of oblique convergence between the eurasian and indian australian plates from 10 n to 7 s our detailed map of the fault compiled from topographic maps and stereographic aerial photographs shows that unlike many other great strike slip faults the sumatran fault is highly segmented cross strike width of step overs between the 19 major subaerial segments is commonly many kilometers the influence of these step overs on historical seismic source dimensions suggests that the dimensions of future events will also be influenced by fault geometry geomorphic offsets along the fault range as high as 20 km and may represent the total offset across the fault if this is so other structures must have accommodated much of the dextral component of oblique convergence during the past few million years our analysis of stretching of the forearc region near the southern tip of sumatra constrains the combined dextral slip on the sumatran and mentawai faults to be no more than 100 km in the past few million years the shape and location of the sumatran fault and the active volcanic arc are highly correlated with the shape and character of the underlying subducting oceanic lithosphere nonetheless active volcanic centers of the sumatran volcanic arc have not influenced noticeably the geometry of the active sumatran fault on the basis of its geologic history and pattern of deformation we divide the sumatran plate margin into northern central and southern domains we support previous proposals that the geometry and character of the subducting investigator fracture zone are affecting the shape and evolution of the sumatran fault system within the central domain the southern domain is the most regular the sumatran fault there comprises six right stepping segments this pattern indicates that the overall trend of the fault deviates 4 clockwise from the slip vector between the two blocks it separates the regularity of this section and its association with the portion of the subduction zone that generated the giant m w 9 earthquake of 1833 suggest that a geometrically simple subducting slab results in both simple strike slip faulting and unusually large subduction earthquakes

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

k ar age of the ranau tuffs implications for the ranau caldera emplacement and slip partitioning in sumatra indonesia the sumatran subduction is an example of oblique convergence which is partitioned into a component normal to the plate boundary and a wrench component taken up by strike slip deformation within the overriding plate indeed off sumatra the approximately nne trending convergence is mechanically accommodated both by subduction processes and strike slip deformation partly localised on the great sumatran dextral fault gsf the gsf parallels the trench and follows approximately the magmatic arc where major calderas are installed the ranau caldera is one of those located along the gsf in south sumatra a ranau tuff sample yielded 40k 40ar ages of 0 55 0 15 ma for its separated feldspars which places the major ranau caldera collapse between 0 7 and 0 4 ma a period of paroxysmal calderic activity along the sumatran arc geomorphic features affecting the ranau tuff and offset by the gsf yield a long term dextral slip rate of 5 5 1 9 mm yr at 5 s consequently south sumatra represents an intermediate case between complete slip partitioning and purely oblique thrusting where the leading edge is characterised by a low convergence obliquity 20 accommodated by strike slip deformation in the overriding plate this demonstrates that even for low obliquity slip partitioning can exist

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

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

very broadband seismic analysis of the 1992 flores indonesia earthquake mw 7 9 the december 12 1992 flores island earthquake m w 7 9 which caused a destructive tsunami is located in the back arc of the transition zone between the sunda and banda arcs a region in active collision with the australian continental margin we study the earthquake using four seismological techniques spanning a period range of 1 1000 s and infer that the flores event may be characterized as a shallow back arc thrust with fault plane strike 70 30 dip 28 10 and rake 80 to 140 linear trade off with strike a rupture consisting of three discrete pulses with a total duration of 70 s centroid time 26 3 s and an estimated moment release between 7 5x10 20 and 8 0x10 20 n m from the slip vector we infer that compressional forces play an important role in the deformation mechanism of the back arc north of flores island body waves constrain the hypocentral depth to be 16 km with rupture mainly propagating updip to shallow depth and bilaterally along strike with most subevents located toward the northeast evidence for rupture directivity from surface wave deconvolutions is inconclusive but the overall source function is consistent with body wave results our body wave finite fault model is in rough agreement with two models proposed to explain tsunami run up observations normal mode modeling of w phase observations at periods longer than 70 s shows that slow slip is negligible from this and the slip distribution determined from the body wave analysis we infer that the seismic source is an unlikely candidate to explain anomalously high tsunami run ups measured on northeastern flores island

motion and rigidity of the pacific plate and implications for plate boundary deformation 1 using up to 11 years of data from a global network of global positioning system gps stations including 12 stations well distributed across the pacific plate we derive present day euler vectors for the pacific plate more precisely than has previously been possible from space geodetic data after rejecting on statistical grounds the velocity of one station on each of the pacific and north american plates we find that the quality of fit of the horizontal velocities of 11 pacific plate pa stations to the best fitting pa euler vector is similar to the fit of 11 australian plate au velocities to the au euler vector and 20 better than the fit of nine north american plate na velocities to the na euler vector the velocities of stations on the pacific and australian plates each fit a rigid plate model with an rms residual of 0 4 mm yr while the north american velocities fit a rigid plate model with an rms velocity of 0 6 mm yr our best fitting pa au relative euler vector is located 170 km southeast of the nuvel 1a pole but is not significantly different at the 95 confidence level it is also close 70 km in position and 3 in rate to a pole derived from transform faults identified from satellite altimetry suggesting that the vector has not changed significantly over the past 3 myr our relative euler vector is also consistent with all known geological and geodetic evidence concerning the au pa plate boundary through new zealand the gps sites offshore of southern california are presently moving 4 5 1 mm yr relative to predicted pacific velocity with their residual velocities in approximately the opposite direction to pa na relative motion likewise the easternmost sites in south island new zealand are moving 3 1 mm yr relative to predicted pacific velocity with the residuals in approximately the opposite direction to pa au relative motion these velocity residuals are in the same sense as predicted by elastic strain accumulation on known plate boundary faults but are of a significantly higher magnitude in both southern california and new zealand implying that the plate boundary zones in both regions are wider than previously believed index terms 1206 geodesy and gravity crustal movements interplate 8155 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8158 tectonophysics evolution of the earth plate motions present and recent 3040 8159 tectonophysics evolution of the earth rheology crust and lithosphere keywords pacific plate motion plate rigidity plate boundary deformation

crustal motion and block behaviour in se asia from gps measurements results acquired using global positioning system gps data taken over a large part of se asia indicate that sundaland i e indochina along with the western and central part of indonesia constitutes a stable tectonic block moving approximately east with respect to eurasia at a velocity of 12 3 mm yr 31 with respect to india and australia this block moves due south significant motion has not been detected along the northern boundary to south china i e along the red river fault whereas nearly 50 mm yr 31 of right lateral motion has to be accommodated between india and sundaland in the andaman burma region fl 2001 elsevier science b v all rights reserved

microplate versus continuum descriptions of active tectonic deformation whether deformation of continents is more accurately described by the motions of a few small rigid plates or by quasi continuous flow has important implications for lithospheric dynamics fault mechanics and earthquake hazard assessment actively deforming regions of the western united states central asia japan and new zealand show features that argue for both styles of movement but new observations are necessary to determine which is most appropriate and at what scale the description applies geologic geodetic seismic and paleomagnetic measurements tend to sample complementary aspects of the deformation field so an integrated observation program can utilize the strengths of each method and overcome their separate spatial or temporal biases provided the total relative motion across each region is known and the distribution of active faults is well mapped determination of fault slip rates can provide potentially decisive constraints reconnaissance geological studies supply useful slip rate estimates but precise values depend upon detailed intensive investigation of individual sites geodetic survey measurements can determine the spatial pattern of contemporary movements and extract slip rate information but the sometimes elusive effects of cyclic elastic strain buildup and relief must be accounted for in relating current movements to the long term deformation pattern earthquake catalogs can be applied to determine seismic strain rates and relative velocities but must be averaged over large regions and are usually limited by the inadequate duration of historical or instrumental seismicity catalogs paleomagnetic determinations of vertical axis rotations provide estimates of block rotation rates but are often locally variable and averaged over many millions of years which of the two descriptions of continental tectonics is more nearly correct depends on the local rheological stratification of the lithosphere especially the strength and thickness of the elastic crust relative to the ductile lithosphere and dynamical models can provide contrasting forecasts of observable features with testable consequences

orogeny in arc continent collision the banda arc and western new guinea eastern indonesia contains a modern continent island arc collision that demonstrates how a complex juxtaposition of continental and oceanic elements can occur in an orogenic belt shallow earthquakes show that strike slip faulting transports large crustal blocks into out of and along the collision zone while crustal shortening and thickening occur by steep angle thrust faulting near the strike slip faulting whereas strike slip faulting is paramount in positioning australian continental rocks so as to enclose the oceanic and island arc rocks of eastern indonesia its role may be overshadowed by the contemporaneous thrusting and may confuse geologic interpretations of the resulting orogenic belt

earthquakes and ophiolite emplacement in the molucca sea collision zone indonesia the molucca sea in eastern indonesia is the site of an active arc arc collision and among its interesting features is the exposure of ophiolitic rocks on islands of the talaud mayu ridge tmr a largely submarine ridge formed of highly deformed rocks that bisects the collision zone to explore the relationship between earthquakes and uplift of the ophiolite the centroid depths and fault plane solutions of 18 large earthquakes occurring in the past 20 years beneath the tmr are constrained by inversion of their teleseismic long period p and sh waveforms centroid depths range from 16 to 36 km but uncertainties allow a range of 10 to 45 km all events show thrust faulting nodal planes strike parallel to the nne trending tmr and dip 40 9 to the ese and 53 9 to the wnw published seismic refraction and gravity data support the inference that the wnw dipping steeper nodal planes are the fault planes dips do not change with depth indicating either that the fault flattens below 40 km depth or that the steeply dipping fault penetrates the entire thickness of the lithosphere i conclude that the molucca sea ophiolite is being lifted by high angle thrust faults 45 to 60 that extend at least 15 km into the upper mantle summing seismic moment tensors and assuming uniformly distributed deformation suggest that the closure across the molucca sea collision zone may account for 14 to 59 of the pacific eurasia convergence vector or 15 to 63 of the philippine eurasia convergence moment tensor sums provide estimates of crustal thickening rates beneath the tmr of 7 to 20 mm yr and these imply uplift rates of 2 to 6 mm yr if the increase in crustal thickness is isostatically compensated hence the ophiolite and an enormous volume of melange are being lifted higher than the flanks of the island arcs and will be emplaced on them by gravity i suggest that ophiolites occur in this tectonic setting because the concave down shape of the subducted oceanic lithosphere beneath the molucca sea increases its effective buoyancy preventing it from sinking out of the way of the encroaching island arcs this case suggests a family of convergent margin settings in which normal oceanic lithosphere is buoyed up so that ophiolites can be stripped from it and emplaced on a continental margin or island arc these settings include those where 1 slab geometry restricts asthenospheric flow away from the convergent margin 2 subduction of younger less dense lithosphere decreases its negative buoyancy 3 a passive continental margin resists subduction or 4 the presence of a thick thermal boundary layer beneath a passive continental margin inhibits asthenospheric flow necessary to accommodate the sinking oceanic lithosphere

the field of crustal velocity in asia calculated from quaternary rates of slip on faults rates of quaternary faulting when treated as measures of strain rates within regions several times larger than the depths of brittle faulting yield a velocity field for asia that matches the average relative velocity between the indian and eurasian plates over the past 2 myr nuvel 1a and the velocity of shanghai with respect to eurasia measured with very long baseline interferometry vlbi by using rates of slip on discrete surfaces faults to define average strain rates we explicitly assume that the large scale deformation can be treated as that of a continuum depending on the jcales over which strain rates are averaged 87 to 93 per cent of the assumed strain ites are fit within assigned 1 sigma uncertainties and 97 to 99 per cent are fit within 2 sigma the internal consistency of these data and the agreement with independent rates nuvel 1a and vlbi test the validity of treating large scale deformation of continents as that of a continuum in the calculated velocity field a large fraction 85 per cent of india s convergence with eurasia is absorbed by crustal or lithospheric thickening among consistently misfit assumed strain rates are those dominated by high rates of strike slip faulting strain associated with 20 30 mm a 1 of slip on the altyn tagh karakax and karakorum faults is inconsistent with the distributions of strain in surrounding regions we conclude that these rates all of which are based on correlations of ages of offset landforms with changes in global climate and not on radiometric dating have been systematically overestimated lateral transport out of india s northward path is relatively minor south china is calculated to move east southeast at less than 10 mm a 1

seismic history and seismotectonics of the sunda arc historic records of the last 300 years reveal two great interplate earthquakes 1833 mw 8 1861 mw 8 8 which ruptured major segments of the sumatra fore arc in western indonesia a significant percentage of interplate slip along this portion of the plate boundary appears to occur seismically the ends of these rupture zones are coincident with clusters of large ms 7 and moderate 6 ms 7 shocks and with heterogeneities in the plate interface as inferred from geologic and geophysical data the northern extent of the 1833 rupture zone is coincident with a group of moderate and large earthquakes a structural arch in the fore arc and a fracture zone on the subducted plate the southern portion is coincident with a very prominent cluster and the along strike extension of a sediment filled trough on the subducted plate prior to this study sumatra was characterized as relatively aseismic as inferred from the lack of great earthquakes in the instrumental record of this century java and the lesser sunda islands had major ms 6 earthquakes in the historic record but none are of the same magnitude as the great events near sumatra there is no clear evidence that shocks in the java fore arc were interplate events yet geophysical data indicate recent uplift of the trench slope break and a change in strike of the trench axis where the northernmost flank of the roo rise a prominent bathymetrie high appears to be interacting with the fore arc this feature was formed at a ridge crest and is more buoyant and thus more difficult to subduct than the surrounding seafloor there is no increase in seismicity associated with this tectonism however that may indicate a lack of contact between the crystalline portions of the plates at this time we infer that a majority of slip on the plate interface near java occurs aseismically the variation in occurrence of great interplate earthquakes along the sunda arc may be interpreted in terms of a model that attributes variation in interplate coupling to the age of the subducted lithosphere great interplate earthquakes occur near sumatra where the age of the youngest crust is 46 ma the characteristics of the sunda arc and analogies with pacific arcs imply that the entire length of sumatra has the potential to produce great thrust earthquakes its seismic potential should be considered high as there has been no recurrence of the great events of 1833 and 1861 in contrast no such events have been reported off java and the lesser sunda islands where the oldest crust is 152 ma the plate interface near java and the lesser sunda islands should be considered to have low seismic potential

active tectonics of the eastern sunda and banda arcs the tectonics of the eastern sunda and banda arcs of eastern indonesia are inferred from the centroid depths seismic moments and fault plane solutions of 63 large earthquakes that occurred between 1962 and 1984 source parameters are estimated by inverting long period teleseismic p and sh waves earthquakes show that the collision of the australian continent with the banda arc shortens the upper plate beneath the forearc and back arc basin over the broad area between the timor and seram troughs along the eastern end of the sunda arc and along the southern banda arc earthquakes reveal that the arc and forearc respond to collision by shortening in the direction of convergence by elongating in the direction perpendicular to convergence and by thrusting over the back arc basin shallow thrust and strike slip earthquakes beneath the banda basin the back arc basin demonstrate that deformation within the back arc accommodates some of the northward motion of the australian continent the rate of north south shortening of the entire upper plate at the longitude of timor calculated from the seismic moments of the earthquakes over the 22 year period is roughly 20 of the predicted convergence rate between australia and southeast asia strike slip faulting within the banda basin results also in eastward motion of the banda arc with respect to western indonesia and australia eastward extrusion of the banda arc results in thrusting at the aru trough earthquakes due to thrusting of the back arc basin beneath the volcanic arc are too shallow to corroborate that the arc s polarity has reversed although the wetar back arc thrust zone at present has a high seismic slip rate earthquakes and their mechanisms provide evidence that the lithosphere of the weber basin a 7500 m deep forearc basin rests on the subducting lithosphere without intervening asthenosphere so that the weber basin subsides in response to sinking of the subducting lithosphere closure of the banda basin is geometrically incompatible with the australian plate subducting simultaneously beneath both the timor and seram troughs instead the bird s head which subducts beneath seram is decoupled from the australian plate in western new guinea and probably moves west or southwest with respect to australia in the eastern indonesian example strike slip faulting plays a major role in the evolution of the collision zone and clearly demonstrates the complexity in three dimensions of continental accretion and mountain building by arc continent collision

the geometry of back arc thrusting along the eastern sunda arc indonesia constraints from earthquake and gravity data the flores earthquake of december 23 1978 represents the first seismological evidence for active back arc thrusting behind the eastern sunda arc this mb 5 8 earthquake occurred north of flores island where seismic reflection profiling has revealed back arc thrusting interpreted to be a reaction to compression of the arc following collision with the australian continent we investigate the source mechanism and depth of the flores earthquake by inversion of long period p waveforms and relocate the earthquake s epicenter incorporating arrival time data from local stations we find that this event occurred beneath the accretionary prism south of the back arc thrust zone at a depth of 11 5 km 7 km below the seafloor the best fitting fault plane solution is consistent with active southward thrusting of the floor of the flores basin beneath the volcanic arc along a 30 dipping fault plane the morphology of the thrust zone and the free air gravity profile over the flores basin in the epicentral region resemble those of oceanic trenches and the observed gravity field is best interpreted if the crust of the flores basin dips smoothly below the accreted wedge at an average angle of about 6 the position of the earthquake hypocenter south of the flores thrust and the fault plane solution suggest that the 1978 earthquake is analogous to thrust events at subduction zones and represents slip between the subducting and overriding plates the flores thrust is thus the surface expression of a deep seated thrust zone and may represent the initial stage of polarity reversal of the eastern sunda arc

crustal motion in indonesia from global positioning system measurements terrestrial reference frame 2000 we compute poles of rotation for the australia eurasia and pacific plates based on our analysis of the global gps data we find that regional tectonics is dominated by the interaction of four discrete rotating blocks spanning significant areas of the sunda shelf the south banda arc the bird s head region of new guinea and east sulawesi the largest the sunda shelf block ssh is estimated to be moving 6 3 mm yr se relative to eurasia the south banda block sbb rotates clockwise relative to both the ssh and australia plate resulting in 15 8 mm yr of motion across the timor trough and 60 3 mm yr of shortening across the flores sea southern new guinea forms part of the australia plate from which the bird s head block bhb moves rapidly wsw subducting beneath the seram trough the east sulawesi block rotates clockwise about a nearby axis with respect to the sunda shelf thereby transferring east west shortening between the pacific and eurasia plates into north south shortening across the north sulawesi trench except for the sunda shelf the crustal blocks are all experiencing significant internal deformation in this respect crustal motion in those regions does not fit the microplate tectonics model index terms 1206 geodesy and gravity crustal movements interplate 8155 1243 geodesy and gravity space geodetic surveys 8150 tectonophysics plate boundary general 3040 8158 tectonophysics plate motions present and recent 3040 9320 information related to geographic region asia keywords crustal motion indonesia tectonics gps current plate motions southeast asia

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

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

western irian jaya the end product of oblique plate convergence in the late tertiary abstract the island of new guinea is the surface expression of the deformed northern margin of the australian continental block to the south undeformed continental crust is overlain by flat lying platform sediments that form a conformable sequence from late palaeozoic to late tertiary along the new guinea cordillera these platform sediments have been tightly folded and overthrust to the south as a result of crustal shortening caused by convergence between the australian plate and the pacific plate the earth movements resulting from this convergence started at the end of the miocene and continue to the present day it is postulated that all the major structures of western irian jaya were caused by this orogeny and can be explained by the convergence directed southwest northeast between the australian and pacific plates it is further postulated that the convergence has remained essentially constant since the start of the earth movements this convergence is consistent with that postulated in the circum pacific plate tectonic map aapg 1981 of 12 5 cm yr directed about 15 south of west only if the effects of the sorong yapen fault system are taken into account this complex east west trending fault system forms the southern boundary of the pacific plate and has responded to the convergence by left lateral strike slip displacement of at least 370 km since the late miocene as a consequence south of the sorong yapen fault system the convergence has been directed more to the south i e at least 45 south of west in this region south of the fault zones the north south component of the convergence has been accommodated in the east by folding and overthrusting over a wide zone of interaction called the new guinea mobile belt dow 1977 in the west on the other hand the australian continental crust has been a stable buttress kepala burung fig 2 which following convergence has protruded into the pacific plate its northeastern margin has therefore been exposed to the full brunt of collision with the pacific plate and large segments of continental crust have been broken off and rafted westwards in order to accommodate the difference in crustal shortening between the new guinea mobile belt and kepala burung two fundamental crustal fractures formed in the intervening region the waipoga and wandamen faults these fractures make angles of about 65 with the regional structural trend fig 2 and they were the focus of most of the resulting differential crustal displacement two of the more spectacular examples of this differential movement have been the thrusting of large slabs of crustal rocks tens of kilometres southwards over the australian continental crust weyland overthrust and lengguru fold belt

southern california permanent gps geodetic array error analysis of daily position estimates and site velocities we analyze time series of daily positions estimated from data collected by 10 continuously monitoring global positioning system gps sites in southern california during the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes each time series exhibits a linear tectonic signal and significant colored noise spectral power at frequencies in the range 5 yr 1 to 0 5 d 1 is dominated by white noise or possibly fractal white noise and is several orders of magnitude higher than what would be expected from random walk noise in this short period range attributed by others to geodetic monument motions estimating a single slope for the time series power spectra suggests fractal white noise processes with spectral indices of about 0 4 site velocity uncertainties assuming this fractal white noise model are 2 4 times larger than uncertainties obtained assuming a purely white noise model a combination white noise plus flicker noise spectral index of 1 model also fits the data and suggests that the velocity uncertainties should be 3 6 times larger than for the white noise model we cannot adequately distinguish between these two noise models nor can we rule out the possibility of a random walk signal at the lowest frequencies these questions await the analysis of longer time series in any case reducing the magnitude of low frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments otherwise rate uncertainties estimated from continuous gps measurements may not be improved significantly compared to those estimated from infrequent campaign mode measurements

rapid rotations about a vertical axis in a collisional setting revealed by the palu fault sulawesi indonesia global positioning system gps measurements from 1992 to 1995 indicate that the left lateral palu fault in central sulawesi slips at a rate of 38 8 mm a with a locking depth between 2 and 8 km from the measured slip rate and the historic seismicity of the fault we estimate that the palu fault currently has stored enough strain to produce a mw 7 earthquake the palu and other nearby faults accommodate rapid clockwise rotation of nearly 4 ma of e sulawesi relative to eastern sunda the rotation of east sulawesi transfers e w shortening between the pacific and eurasian plates to n s subduction of the celebes basin beneath sulawesi

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

rupture along the great sumatran fault indonesia during the earthquakes of 1926 and 1943 while investigating features of quaternary displacement along the great sumatran fault zone in the padang highlands of sumatra indonesia figure 1 the authors incidentally came across heretofore unreported evidence of significant surficial displacements along the fault during the m s 6 earthquake of 28 june 1926 and the m s 7 6 earthquake of 9 june 1943 in both cases eyewitness reports by long term local residents allowed unequivocal documentation of the location and nature of the surficial fault displacements associated with the earthquakes although it was only through the use of vertical aerial photographs to locate the active fault trace that it was possible to concentrate the questioning in promising areas in every case it was thus possible to locate the primary active fault trace to within a few hundred meters before commencing the search for local eyewitnesses