crustal structure of the java margin from seismic wide angle and multichannel reflection data seismic investigations across the convergent sunda margin off indonesia provide a detailed image of the crustal architecture of the sunda plate boundary the combined analysis and interpretation of wide angle and reflection seismic data along two coincident profiles across the subduction zone are complemented by additional lines within the forearc domain which yield some three dimensional 3 d constraints on the velocity depth structure across the margin a detailed cross section of the subduction zone is presented which is confirmed by supplementary gravity modeling the sunda convergence zone is a prime example of an accretionary margin where sediment accretion has led to the formation of a massive accretionary prism with a total width of 110 km between the trench and the forearc basin it is composed of a frontal wedge which documents ongoing accretion and a fossil part behind the present backstop structure which constitutes the outer high moderate seismic velocities derived from wide angle modeling indicate a sedimentary composition of the outer high the subducting oceanic slab is traced to a depth of almost 30 km underneath the accretionary prism the adjacent forearc domain is characterized by a pronounced morphological basin which is underlain by a layer of increased seismic velocities and a shallow upper plate moho at 16 km depth we speculate that remnant fragments of oceanic crust might be involved in the formation of this oceanic type crust found at the leading edge of the upper plate beneath the forearc basin

deformation and sedimentation along a developing terrane suture eastern sunda forearc indonesia the collision of the eastern sunda arc with northwest australia has resulted in the development of a suture between the sumba ridge and sawu timor terranes along a zone of intraforearc convergence the developing suture varies from the low angle sawu thrust with attendant mud diapirs in the sumba basin to high angle reverse faults near a basement high of the underthrust sumba ridge terrane bottom currents associated with the flow of pacific ocean deep water into the indian ocean have eroded the terranes and subsequently deposited the detritus in an assemblage of contourites along the suture this study reveals the high structural variability of a terrane suture and the oceanographic influence on the deposition of overlap assemblages

influence of solar and lunar tides on the mesopause region as observed in polar mesosphere summer echoes characteristics long term observations of polar mesosphere summer echoes pmse from 2002 to 2012 are investigated with the aim to statistically study the effects of solar thermal migrating and lunar gravitational tides on aerosol layers and their environment at altitudes 80 90 km the solar and lunar tidal periodicities are clearly present in pmse data for the first time both amplitudes and phases of solar and lunar tides are estimated using pmse data from the esrad radar located at esrange sweden the diurnal semidiurnal and terdiurnal solar migrating tides show pronounced periodicities in the pmse strength and wind velocity components lunar tides demonstrate clear oscillations in the pmse strength and wind velocities as well canonical lunar gravitational tides corresponding to the lunar gravitational potential produce rather large amplitudes and are comparable to the solar thermal tides whereas noncanonical lunar oscillations have minor effects on pmse layers but are still statistically significant the influence of diurnal semidiurnal tides and monthly semimonthly tidal components is studied separately our estimations of solar thermal and lunar tidal amplitudes are in good agreement with those of previous model and experimental studies a new mechanism of quadratic demodulation of the solar semidiurnal and lunar semidiurnal tides is shown to be valid at the summer mesopause and can explain periodical pmse oscillations due to the lunar synodic semimonthly tide with period of 14 77 days two harmonics with periods of 27 0 and 13 5 days supposedly representing the solar rotation cycle are also clearly present in pmse data

crustal structure of the central sunda margin at the onset of oblique subduction summary the convergent margin of the central sunda arc in indonesia was the target of a reflection and refraction seismic survey conducted in 1998 and 1999 along two seismic lines across the subduction complex off southern sumatra and off sunda strait coincident multichannel and wide angle data were collected complemented by two refraction strike lines in the forearc basin off sumatra the combined analysis of the acquired data allows us to present a detailed model of the subduction zone where initiation of strain partitioning occurs due to the onset of oblique subduction the dip of the subducted plate is well defined along both dip lines and a lateral increase from 5 to 7 from beneath the outer high off sumatra to sunda strait is supported by complementary gravity modelling the downgoing slab is traced to a depth of more than 30 km on both reflection dip lines a clearly developed backstop structure underlying a trench slope break defines the landward termination of the active accretionary prism and separates it from the outer high active subduction accretion is supported by laterally increasing velocities between the deformation front and the active backstop structure seismic velocities of the outer high are moderate along both lines 5 8 km s 1 at 20 km depth suggesting a sedimentary composition reduced reflectivity beneath a rugged top basement traced along the outer high of both dip lines supports a high degree of deformation and material compaction several kilometres of sediment has accumulated in the forearc domain although a distinct morphological basin is only recognized off southern sumatra and is not developed off sunda strait the bathymetric elevation of the java shelf that is encountered in the southern sunda strait corresponds to increased velocities of a basement high there and is connected to extensional structures of the sunda strait transtensional basin differences observed in the morphology of the forearc domain are also reflected in the lower crustal structure off southern sumatra the velocity depth model clearly indicates a continental type crust underlying the forearc basin whereas lower velocities are found beneath the sunda strait forearc domain off sumatra some 3 d constraint on the upper plate structure is gained from the refraction strike lines which in addition is supported by synthetic data modelling

a global view of the atmospheric lunar semidiurnal tide 1 atmospheric lunar semidiurnal tides are studied using 10 years of temperature data collected by the thermosphere ionosphere mesosphere energetics and dynamics sounding of the atmosphere using broadband emission radiometry satellite the amplitudes and phases in the temperature field are calculated by performing least mean square fit in a data set of about 60 day interval combining ascending and descending data together the mean tidal structures are studied for the height range from 20 to 120 km between 50 latitude and centered on each month from february 2002 to january 2012 a clear signature of the 12 42 h lunar semidiurnal tide is observed in the data characteristic of propagating waves is observed in the vertical amplitude and phase profiles in almost all heights the best conditions of propagation for the lunar semidiurnal tide are reached in the lower thermosphere region asymmetry between the hemispheres and seasonal variability is observed in the amplitudes of the tide longitudinal variations are also observed which reveals the existence of nonmigrating components in addition to the dominant migrating lunar tide

subduction of seamounts at the java trench a view with long range sidescan sonar abstract we describe here a 1300 km by 45 km gloria long range sidescan sonar swath along the eastern java trench the swath images the trench axis a narrow strip of oceanic crust to the south and the toe of the accretionary wedge to the north between 108 and 120 e sonar images of the ocean crust show a pattern of normal faults typical of the outer wall of trenches these result from tension related to the bending of the oceanic lithosphere into the subduction zone a number of sub circular seamounts are also seen some of which are currently being subducted isolated ponds of flat lying sediments occur in the trench axis although along much of its length the trench is devoid of such sediment accumulations on the inner trench wall the accretionary wedge is recognised by its distinctive grainy texture with the grain aligned sub parallel to the deformation front where subducting seamounts are colliding with the wedge large crescentic areas of very high backscattering correlate with re entrants in the deformation front and large indentations in the wedge the high backscattering within these collision scars is interpreted to arise from outcropping strata and talus covered slopes resulting from erosion of an inner trench wall shortened and oversteepened by collision with a seamount all of the sediment ponds in the trench axis occur in close association with collision scars strongly suggesting localised erosion of the accretionary wedge in the scar areas however the volume of the indentations appears to be an order of magnitude greater than the volume of eroded sediments deposited in the trench indicating that erosion cannot be the primary mechanism by which indentations are created most of the missing material must be displaced landward by thrusting and folding ahead of the seamount our observations at the java trench are broadly comparable with those made at the japan trench by french and japanese workers however some differences in the detail of the collision process are evident in particular oversteepening and erosion occur from the earliest stage of collision at the java trench while uplift and understeepening initially dominate at the japan trench differences in the effects of subducting seamounts in the two areas are attributed to contrasts between the relatively unlithified strata of the java trench inner wall and the more lithified strata of the non accreting japan trench inner wall

fine details of the wadati benioff zone under indonesia and its geodynamic implications using about 5200 handpicked p s pp sp pcp and scp phases from digitally recorded seismograms together with international seismological centre reported phases we obtain improved hypocentral locations for 1790 earthquakes 983 of them having 90 confidence limits 50 km in the period 1962 to september 1996 along the indonesian subduction zone we use an improved joint hypocenter determination method in which the solution is more stable than in the original one we show that for deep earthquakes use of the core reflected phases is as good as use of depth phases and since such core phases often have larger amplitudes and sharper onsets than the depth phases their arrival times can be read very accurately the positions of the relocated hypocenters show that 1 a portion of the indonesian arc between 110 e and 123 e longitude and deeper than 500 km is dipping southward at an angle of 75 that is in a direction opposite to the upper part of the north dipping slab and 2 east of about 108 e the seismic zone is wider near 670 km than near the 500 km depth the first suggests southward lateral flow in the mantle relative to the plate motion vector here from the contortion of the seismic zone along the eastern portion of the indonesian arc we can estimate the average lateral shear strain rate in the 300 to 670 km depth range to be of the order of 10 16s 1 over the last 10 20 myr

determinations of focal depths of earthquakes associated with the bending of oceanic plates at trenches abstract the earthquakes examined in this paper are all within the oceanic lithosphere and are associated with the bending of plates before subduction accurate determinations of the depth of these earthquakes are needed to study the stress pattern within a bending plate routinely determined depths of shallow sub oceanic earthquakes published in bulletins are unreliable the depths can be accurately determined to within a few kilometers if the original seismograms from these events are studied in some cases the reflected phases pp and pwp can be clearly identified there exists the possibility that the wave reflected at the water air interface pwp may be misidentified as pp leading to erroneous estimates of depth additional methods of analysis such as surface wave radiation patterns or the apparent frequency dependence of reflection at the crust water interface can remove this possible source of confusion one of the most powerful techniques for depth analysis is the modelling of long period waveforms the pattern of stresses within the bending oceanic lithosphere revealed by the depths and focal mechanisms of these intraplate earthquakes is one of horizontal deviatoric tension down to a depth of about 25 km with horizontal compression at greater depths

seismic structure of the upper mantle beneath the northern canadian cordillera from teleseismic travel time inversion abstract teleseismic tomography is used to image upper mantle structure beneath the northern canadian cordillera with the objective of determining the physical state of the upper mantle along the western half of the snorcle lithoprobe transect the resulting three dimensional p wave velocity model resolves structure beneath the southern yukon and northernmost british columbia between 100 and 600 km depth two significant anomalies are identified the first a relatively shallow high velocity feature located at the western edge of the model is interpreted as being the edge of the pacific slab from the southern alaska subduction zone the second is a large tabular low velocity anomaly centred at 60 n by 136 w elongate northwest southeast dipping southwest and reaching a depth of 450 500 km this low velocity anomaly is judged to reflect a thermal anomaly of 100 200 c with a possible compositional component its northeastern boundary is particularly sharp and is interpreted to represent the boundary between thin cordilleran lithosphere and a colder cratonic mantle root our preferred explanation for the low velocity feature is a thermal anomaly resulting from the advective upflow produced by the opening of a slab window beneath the northern cordillera a possible alternative is dense downward percolating partial melt generated by sub orogenic heating as past work e g stolper et al j geophys res 86 1981 6261 6271 suggests that basic partial melts may be denser than peridotite below 200 km depth

plate convergence measured by gps across the sundaland philippine sea plate deformed boundary the philippines and eastern indonesia summary the western boundary of the philippine sea ph plate in the philippines and eastern indonesia corresponds to a wide deformation zone that includes the stretched continental margin of sundaland the philippine mobile belt pmb extending from luzon to the molucca sea and a mosaic of continental blocks around the ph australia sunda triple junction the gps geodyssea data are used to decipher the present kinematics of this complex area in the philippines the overall scheme is quite simple two opposing rotations on either side of the left lateral philippine fault clockwise to the southwest and counterclockwise to the northeast transfer 55 per cent of the ph sundaland convergence from the manila trench to the northwest to the philippine trench to the southeast further south 80 per cent of the ph sunda convergence is absorbed in the double subduction system of the molucca sea and less than 20 per cent along both continental margins of northern borneo finally within the triple junction area between the sundaland ph and australia plates from sulawesi to irian jaya preferential subduction of the celebes sea induces clockwise rotation of the sulu block which is escaping toward the diminishing celebes sea oceanic space from the eastwardadvancing ph plate to the south we identify an undeformed banda block that rotates counterclockwise with respect to australia and clockwise with respect to sundaland the kinematics of this block can be defined and enable us to compute the rates of southward subduction of the banda block within the flores trench and of eastward convergence of the makassar straits with the banda block the analysis made in this paper confirms that this deformation is compatible with the eastward motion of sundaland with respect to eurasia determined by the geodyssea programme but is not compatible with the assumption that sundaland belongs to eurasia as was often assumed prior to this study

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

collisional melange development geologic associations of active melange forming processes with exhumed melange facies in the western banda orogen indonesia analysis of block assemblages matrix clay mineral composition and microfauna and offshore seismic reflection profiles reveal that the bobonaro melange in the timor region is sourced from mud rich australian continental margin sequences that are remobilized during accretion and form various facies depending on the structural conditions of emplacement melange facies include broken formation matrix rich mud injections and classic mixed block in clay facies each of these are distinguished by varying degrees of remobilization mixing and dispersion at different structural positions across the orogenic wedge the most important structural control is whether melange was generated beneath or in front of upper plate banda forearc basement banda terrane at the present collisional deformation front in the timor trough seismic reflection profiles show that melange forms mostly by stratal detachment and fluid assisted remobilization above a basal decollement propagating laterally along overpressured jurassic to cretaceous clay rich sequences of the distal australian continental margin the broken clay rich material injects upward through faults to form intrusive bodies at the base of slope cover sediment to form mud ridges at the surface similar patterns of stratal disruption are exposed onshore in the pliocene kolbano fold and thrust wedge of southern timor which is structurally contiguous with the timor trough deformation front melange in the kolbano mountains is mostly broken formation and matrix rich injections of mud from jurassic and cretaceous units deformation mechanisms include intense layer parallel extension associated with emplacement by mud diapirs that rise from near the decollement upward to the surface along fault conduits in the hinterland of the orogenic wedge east timor and northern west timor melange is dominantly of mixed block in clay facies with large blocks derived from roof thrust sheets of intermixed banda terrane and maubisse formation units at the structural base of these thrust sheets is the sonnebait disruption zone sdz which formed the initial suture between the banda terrane and structurally underthrust australian continental margin sequences during the late miocene to early pliocene the thickest accumulations of mixed block in clay melange in the timor region are found at the southern edge outlet of the sdz near the central and viqueque synorogenic basins the extent of block dispersion and mixing in the sdz is indicative of intense shear strains perhaps induced by an oversupply of accretable material when the suture zone was clogged by underthrusting of the australian continental margin

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

source process of the great 1977 sumba earthquake in order to investigate the applicability of the asperity model to intraplate earthquakes we have studied the rupture process of the great 1977 sumba normal faulting earthquake mw 8 2 8 3 one of the largest earthquakes since 1963 this event has been variously interpreted as a plate detachment event i e rupture through the entire lithosphere or a shallow plate bending event we have analyzed long period body waves in order to determine the spatiotemporal rupture characteristics including the depth extent of the rupture area visible depth phases in the initial stage of weak radiation beginning about 15 s before the main pulse suggest that the earthquake nucleated near 29 km depth which corresponds to the maximum depth of the aftershock sequence the excitation of a strong tsunami implies that rupture extends to the surface while deconvolutions of long period p waves suggest a relatively shallow 50 km maximum depth extent however the existence of slip below this depth cannot be ruled out particularly if it preferentially radiates frequencies below the passband of the body waves used 0 02 hz for undiffracted phases the source time function of the principal rupture which initiated 30 km west of the epicenter of the precursor comprises a dominant initial short duration 24 s triangular pulse followed by several smaller pulses however slightly diffracted phases indicate a simple basic underlying character for the rupture consisting of the initial 24 s triangle superimposed on a longer duration 42 44 s trapezoid the absence of observable directivity in the deconvolved source time functions suggests a bilateral rupture mode although the body waves do not require a fault length greater than 80 km the aftershock area and surface wave results of zhang and kanamori 1988 imply a total length of at least 200 km the body wave source functions are well modeled by a 200 km long fault extending to 30 50 km depth on which slip nucleates at the center of the fault and has variable displacement along strike the peak moment release of the deconvolved source functions indicates higher displacement in the hypocentral area than in other areas of the fault the spatial relationship of the precursor and the main pulse is suggestive of rupture initiating at and propagating along the edge of an asperity prior to the rupture of the asperity itself the large size of the event may be due to an unusual stress environment arising from strong lateral gradients in seismic interplate coupling along the java timor arc

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

evidence for a large scale remnant of subducted lithosphere beneath fiji we combine spatial variations of p and s wave speeds 1000 fault plane solutions and 6600 well determined hypocenters to investigate the nature of subducted lithosphere and deep earthquakes beneath the tonga back arc we show that perplexing patterns in seismicity and fault plane solutions can be accounted for by the juxtaposition of a steep dipping wadati benioff zone and a subhorizontal remnant of slab that is no longer attached to the actively subducting lithosphere the detached slab may be from a previous episode of subduction along the fossil vitiaz trench about 5 to 8 million years ago the juxtaposition of slabs retains a large amount of subducted material in the transition zone of the mantle such a configuration if common in the past would allow the preservation of a primordial component in the lower mantle

lunar tidal winds measured in the upper atmosphere 78 105 km at saskatoon canada abstract six years of winds data measured by the partial reflection drifts technique have been analyzed for lunar tides data are available at 3 km intervals of height and are separately analyzed in two year datasets to cheek consistency a month by month seasonal variation is derived largest amplitudes of the lunar tide occur in january february with a smaller maximum in summer the vertical wavelength is longest in summer and the tide then resembles that predicted for a pure 2 2 mode in winter vertical wavelengths range from 25 to 81 km in different years several of these results do not agree with the model of forbes an o1 component of the lunar tide could not be detected

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

the 1994 java tsunami earthquake and its normal aftershocks 1 we compare the source spectra of the 1994 java tsunami earthquake mw 7 9 and its two largest aftershocks the source spectra of the aftershocks from teleseismic p waves can be fit remarkably well by a standard 2 model however the mainshock shows a lower moment release at periods of 1 20 sec than its aftershocks although its total moment is 1000 times larger we analyze this discrepancy by exploring two mechanisms that in a simple haskell rupture model will decrease one of the corner frequencies of the source spectrum 1 lowering the rupture velocity and 2 lowering the particle slip velocity both changes maintain an identical spectral drop off and static stress drop and result in the characteristic spectral shape of a slow earthquake these kinematic models can be related to physical rupture parameters by considering the earthquake energy budget in both cases the radiated seismic energy is lowered either due to a higher frictional stress during the break down phase increasing the fracture energy case 1 or by an increase in the sliding stress case 2 we do not suggest that either of these simplified models is the only possible interpretation but want to illustrate the danger in directly interpreting slow earthquakes as having a low rupture velocity

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

field survey of the east java earthquake and tsunami of june 3 1994 a field survey of the june 3 1994 east java earthquake tsunami was conducted within three weeks and the distributions of the seismic intensities tsunami heights and human and house damages were surveyed the seismic intensities on the south coasts of java and bali islands were small for an earthquake with magnitude m 7 6 the earthquake caused no land damage about 40 minutes after the main shock a huge tsunami attacked the coasts several villages in east java province were damaged severely and 223 persons perished at pancer village about 70 percent of the houses were swept away and 121 persons were killed by the tsunami the relationship between tsunami heights and distances from the source shows that the hatori s tsunami magnitude was m 3 which seems to be larger for the earthquake magnitude but we should not consider this an extraordinary event because it was pointed out by hatori 1994 that the magnitudes of tsunamis in the indonesia philippine region generally exceed 1 2 grade larger than those of other regions

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

thermochronology in southeast alaska and southwest yukon implications for north american plate response to terrane accretion abstract this study presents the first comprehensive dataset of low temperature thermochronology from 43 bedrock samples collected north of the active yakutat north american plate boundary our apatite and zircon u th he and fission track data reveal the cooling history of the inboard wrangellia composite terrane that is dominated by rapid cooling after late jurassic to early cretaceous arc magmatism followed by very little cooling and exhumation until today deformation resulting in rock exhumation due to the collision of the yakutat microplate is spatially very limited 20 30 km and is concentrated mainly in the chugach prince william terrane and rocks near the border ranges fault focused exhumation from greater depths of ca 10 km with very high rates 5 km myr is localized at the syntaxis region starting ca 10 ma and shifted south through time the rapid exhumation rates are explained by the development of strong feedbacks between tectonically driven surface uplift and erosion which started already before glaciation of the area the shift in the location towards the south is a consequence of continuous readjusting between tectonics and climate which is changing on local and global scales since the late miocene

a dual doubly vergent orogen in the banda arc continent arc collision zone as observed on deep seismic reflection profiles new deep seismic reflection profiles across the banda arc of indonesia reveal reflectors in the uppermost 50 km of the lithosphere combined with existing earthquake hypocenter locations and focal mechanisms the new structural geometries inferred from the reflectors yield a more complete analysis of deformation during the past 10 m y and provide insights into how strain is partitioned across an orogenic belt in which volcanic arcs and continents converge a clearly defined wadati benioff zone and recent deformation of shelf sediments observed on older shallow seismic profiles indicated to previous workers that substantial convergence occurred at the timor trough a few focal mechanisms seafloor escarpments and recent geodetic surveying indicate that convergence at 7 cm yr 1 currently last 200 kyr occurs at the northern margin of the now inactive volcanic arc the wetar thrust zone reflectors on the new seismic profiles are interpreted as thrust faults and folds that occur throughout the crust and within the uppermost mantle between the timor trough and wetar thrust specifically basement reflectors beneath the toe of the accretionary complex have reverse sense offsets that imply blind thrusts the whole crust is horizontally shortened not only the sedimentary cover rocks that previously deformed into duplexes above a decollement reflectors dipping away from both margins of the forearc basin and at the northern margin of the volcanic arc are interpreted as evidence of thrusting thus each arc represents a doubly vergent fold and thrust belt but only the northern one is currently active crustal thicknesses inferred from seismic velocities reflectors and gravity anomalies are consistent with the merging of a thinned continental shelf margin with oceanic lithosphere to form an orogenic belt with at present 3 4 km of topographic relief in the region of eastern timor

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

ocean trench blocked and obliterated by banda forearc collision with australian proximal continental slope abstract the bathymetry and abrupt changes in earthquake seismicity around the eastern end of the java trench suggest it is now blocked south east of sumba by the australian jurassic rifted continental margin forming the largely submarine roti savu ridge plate reconstructions have demonstrated that from at least 45 ma the java trench continued far to the east of sumba from about 12 ma the eastern part of the java trench called banda trench continued as the active plate boundary located between what was to become timor island then part of the australian proximal continental slope and the banda volcanic arc this banda trench began to be obliterated by continental margin arc collision between about 3 5 and 2 ma the present position of the defunct banda trench can be located by use of plate reconstructions earthquake seismology deep reflection seismology dsdp 262 results and geological mapping as being buried under the para autochthon below the foothills of southern timor locating the former trench guides the location of the apparently missing large southern part of the banda forearc that was carried over the australian continental margin during the final stage of the period of subduction of that continental margin that lasted from about 12 ma to about 3 5 ma tectonic collision is defined and distinguished from subduction and rollback collision in the southern part of the banda arc was initiated when the overriding forearc basement of the upper plate reached the proximal part of the australian continental slope of the lower plate and subduction stopped collision is characterised by fold and thrust deformation associated with the development of structurally high decollements this collision deformed the basement and cover of the forearc accretionary prism of the upper plate with part of the unsubducted australian cover rock sequences from the lower plate together with parts of the forearc basement they now form the exposed banda orogen the conversion of the northern flank of the timor trough from being the distal part of the banda forearc accretionary prism carried over the australian continental margin into a foreland basin was initiated by the cessation of subduction and simultaneous onset of collisional tectonics this reinterpretation of the locked eastern end of the java trench proposes that from its termination south of sumba to at least as far east as timor and probably far beyond the java banda trench and forearc overrode the subducting australian proximal continental slope locally to within 60 km of the shelf break part of the proximal forearc s accretionary prism together with part of the proximal continental slope cover sequence were detached and thrust northwards over the java banda trench and forearc by up to 80 km along the southwards dipping savu thrust and wetar suture these reinterpretations explain the present absence of any discernible subduction ocean trench in the southern banda arc and the narrowness of the forearc reduced to 30 km at atauro north of east timor

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

polar mesosphere summer echoes at wasa antarctica 73 s first observations and comparison with 68 n 1 polar mesosphere summer echoes pmse have been observed for the first time at wasa antarctica 73 s 13 w 61 geomagnetic a new 54 5 mhz radar mara operated first in kiruna 68 n during late summer 2006 and then at wasa between 18 january and 5 february 2007 operation in kiruna allowed accurate cross calibration with the permanent 52 mhz radar esrad pmse at 73 s are found to have very similar characteristics to pmse at 68 n when observations from the same part of the summer season are compared volume reflectivities show very similar distributions over different intensities over height and over local time pmse at 68 n 65 geomagnetic are stronger in the midnight sector likely due to the different geomagnetic latitudes above 85 km altitude weak pmse have a higher occurrence rate at 73 s the height of peak pmse occurrence is 1 km higher at 73 s compared to 68 n

tectonic features of the southern sumatra western java forearc of indonesia 1 multichannel reflection seismic profiles along the active sunda arc where the indo australian plate subducts under the overriding eurasian margin revealed two accretionary wedges the inner wedge i is of assumed paleogene age and the outer wedge ii is of neogene to recent age the inner wedge i is composed of tectonic flakes stretching from southeast sumatra across the sunda strait to northwest java implying a similar plate tectonic regime in these areas at the time of flake development during upper oligocene today wedge i forms the outer arc high and the backstop for the younger outer wedge ii the missing outer arc high of the southern sunda strait is explained by a combination of neogene transtension due to a clockwise rotation of sumatra with respect to java and by arc parallel strike slip movements the rotation created transtensional pull apart basins along the western sunda strait semangka graben as opposed to transpression and inversion on the eastern sunda strait within the new detected krakatau basin the arc parallel transpressional mentawai strike slip fault zone mfz was correlated from the sumatra forearc basin to the northwest java forearc basin off the sunda strait northward bending branches of the mfz are connected with the right lateral sumatra fault zone sfz along the volcanic arc segment on sumatra it is speculated that the sfz was attached to the cimandiri pelabuhan ratu strike slip fault of java prior to the presumed rotation of sumatra and that since the late lower miocene the main slip movement shifted from the volcanic arc position to the forearc basin area due to increasingly oblique plate convergence

seismic response to recent tectonic processes in the banda arc region abstract internal structure and recent tectonics of the geologically complex banda arc region latitude 1 9 s longitude 124 135 e have been studied by means of the analysis of global seismological data relocated hypocentral determinations of the international seismological center ehb data and fault plane solutions of the global centroid moment tensor project have been used together with previously published information on regional geology and dynamics the analysis considered earthquakes in the lithospheric wedges above subducting slabs and earthquakes in the uppermost portions of the wadati benioff zones focal depth

neogene sutures in eastern indonesia five suture zones are described from the zone of collision between the eurasian indian australian and pacific philippine sea plates within the eastern indonesia region these are the molucca sorong sulawesi banda and borneo sutures each of these sutures has a relatively short history compared to most pre neogene orogenic belts but each preserves a record of major changes in tectonics including subduction polarity reversals elimination of volcanic arcs changing plate boundaries and important extension within an overall contractional setting rapid tectonic changes have occurred within periods of less than 5 ma many of these events although important would be overlooked in older orogenic belts because the age resolution required to identify them even when the evidence is preserved is simply not possible q 2000 elsevier science ltd all rights reserved

a 1200 km long eocene metamorphic plutonic belt in the northwestern cordillera evidence from southwest yukon distinctive regional eocene metamorphic plutonic units of the coast belt in southwestern yukon match similar units in southeastern alaska and british columbia and possibly in the eastern alaska range and together form a belt originally 1200 km long the final high grade metamorphic event in the aishihik and kluane assemblages between the ruby range batholith and the denali fault zone occurred in latest paleocene to early eocene time structural petrologic and geochronologic evidence indicates that metamorphism occurred during a major period of west southwest vergent deformation and metamorphism the final phase of consumption of the kula plate at 43 ma may be linked to the culmination of metamorphism intrusion and deformation along the early cenozoic cordilleran margin

backstop geometry and accretionary mechanics of the sunda margin the convergent sunda margin off indonesia displays all geological features characteristic of an accretion dominated subduction zone a combined interpretation of prestack depth migrated seismic reflection data and velocity information gained from refraction studies is supplemented by high resolution bathymetric data and for the first time allows the exact mapping of backstop regimes initially the outer high evolved as material was pushed against a static rigid arc framework backstop underlying a forearc basin increasing material strength of the outer high due to lithification formed a dynamic backstop which controls accretion today an out of sequence thrust marks the transition from the recent active frontal accretionary prism to the outer high and may be traced in the seismic and bathymetric data over the whole extent of the study area the existence of a static as well as a dynamic backstop controls the forearc geometry and is associated with the segmentation of the forearc which is observed in regimes of frontal as well as of oblique subduction mass balance calculations which account for porosity changes and metamorphism indicate a subduction history dominated by accretionary processes since the late eocene accretion is associated with the low values of basal friction inferred for the sunda margin structural investigations of conjugate fault planes indicate a very weak basal detachment effective stress analyses reveal that intrinsically weak material causes the high strength ratio of the detachment to the overlying sediments whereas overpressuring within the frontal accretionary prism is negligible

geomagnetic field anomalies over the lombok island region an attempt to understand the local tectonic changes during the last years several investigations on the earthquakes and related tectonic structures along the java trench have been conducted in this study we focus on the lombok island west nusa tenggara indonesia which lies between the centres of the highest intensity of contiguous negative positive geomagnetic anomalies in this region the geological and tectonic structures however are not known in detail for this island whereas a better knowledge of these conditions could lead to better estimate the potential earthquake risks and thus a possible improvement of the existing early warning system we have performed a ground based geomagnetic survey at 56 stations in the lombok island during october november 2006 for a detailed mapping and interpretation of geomagnetic anomalies related to the geological and tectonic characteristics the 2d and 3d magnetic maps show a general geomagnetic anomaly pattern in the lombok island which consists of repeated contiguous negative positive anomalies two forward models have been proposed for a profile connecting a strongest apparent dipolar structure the first model assumes a uniformly magnetized sphere as the source of the anomaly and could be interpreted as a specific local structure composed by a quite large magnetic body the second model considers several rocks with different susceptibilities and magnetizations and could be interpreted as a discontinuity in the geological structures this model agrees with the local geological surface conditions and the known large scale regional tectonic structure therefore it is used to interpret our results in terms of tectonic characteristics which suggests the potential existence of a new tectonic element e g a local normal fault in this region

lower plate structure and upper plate deformational segmentation at the sunda banda arc transition indonesia the sunda banda arc transition at the eastern termination of the sunda margin indonesia represents a unique natural laboratory to study the effects of lower plate variability on upper plate deformational segmentation neighboring margin segments display a high degree of structural diversity of the incoming plate transition from an oceanic to a continental lower plate presence absence of an oceanic plateau variability of subducting seafloor morphology as well as a wide range of corresponding fore arc structures including a large sedimentary basin and an accretionary prism outer arc high of variable size and shape here we present results of a combined analysis of seismic wide angle refraction multichannel streamer and gravity data recorded in two trench normal corridors located offshore the islands of lombok 116 e and sumba 119 e on the incoming plate the results reveal a 8 6 9 0 km thick oceanic crust which is progressively faulted and altered when approaching the trench where upper mantle velocities are reduced to 7 5 km s the outer arc high located between the trench and the fore arc basin is characterized by sedimentary type velocities vp 5 5 km s down to the top of the subducting slab 13 km depth the oceanic slab can be traced over 70 100 km distance beneath the fore arc a shallow serpentinized mantle wedge at 16 km depth offshore lombok is absent offshore sumba where our models reveal the transition to the collisional regime farther to the east and to the sumba block in the north our results allow a detailed view into the complex structure of both the deeper and shallower portions of the eastern sunda margin

atmospheric tide 2 the solar and lunar semidiurnal components solar and lunar semidiurnal wind and temperature oscillations from the surface to 400 km are simulated for average solar activity conditions utilizing the numerical tidal model described in part 1 hough mode decomposition of the solstitial solar semidiurnal tide excited by h2o and o3 insolation absorption below 80 km indicates that it is characterized by a predominance of 2 2 below 60 km about equal contributions of 2 2 2 3 and 2 4 between 70 and 90 km mostly 2 4 with some 2 5 and 2 2 between 90 and 120 km and a predominance of 2 2 above 140 km with secondary contributions from 2 3 and 2 5 the solstitial lunar semidiurnal tide is characterized by a predominance of 2 2 below 70 km 2 4 with secondary contributions from 2 2 2 3 and 2 5 between 80 and 110 km and by 2 2 with a fairly strong secondary contribution from 2 3 above 120 km similar descriptions for both the solar and lunar oscillations apply at equinox except that the asymmetric 2 3 and 2 5 modes are absent relative to the solar component lunar temperature and wind amplitudes are sufficiently large 20 in the lower and upper thermosphere to account for some of the observed variability previously attributed to the solar tide amplitudes of the 2 4 and 2 5 modes above 100 km are significantly affected by mesospheric eddy diffusion coefficients in excess of 2 106 cm s 1 the total solar semidiurnal exospheric temperature oscillation for average solar conditions ranges from 10 20 k poleward of 40 n to 40 60 k equatorward of 30 n and has its origin in three sources of excitation all of comparable importance 1 euv solar radiation absorption in the lower thermosphere 100 200 km 2 in situ momentum coupling due to the interaction of diurnal winds and diurnally varying ion drag and 3 tides propagating upwards from below 100 km in addition the calculations are compared with rocket meteor radar partial reflection thomson scatter and satellite data to evaluate the consistency of the model with observations

the 1977 sumba earthquake series evidence for slab pull force acting at a subduction zone the great 1977 sumba earthquake occurred at the eastern sunda trench just west of the collision of australian continental lithosphere with the island arc the length of the aftershock zone of this normal faulting earthquake is about 200 km aftershocks are concentrated 65 115 km east of the main shock epicenter with very few aftershocks in a 50 km long segment that spans the main shock epicenter relocated hypocenters and focal mechanism data are consistent with normal faulting throughout the upper 28 km of the oceanic lithosphere there is no evidence for thrust faulting of the deeper aftershocks these data imply that the neutral bending surface must be at least 35 40 km deep a second aftershock zone about 180 km northwest of the main shock became active immediately following the main shock but events were concentrated during days 50 52 this zone is a 70 km long lineation that trends toward the main shock epicenter and reflects right lateral strike slip faulting within the subducted oceanic plate seismicity exists to a depth of about 650 km in the very old plate beneath the sunda banda arc and that plate s negative buoyancy causes very large slab pull forces great interface thrust earthquakes are absent at the sumba region and slab pull forces are inferred to have partially decoupled the subducted plate from the overriding plate this decoupling permits slab pull stresses to be guided updip to the region of the sumba main shock such shallow acting slab pull provides a bending moment at the trench and explains the deformation and timing observed for the entire sumba earthquake series in this model slab pull forces stretch the subducted plate until the increasing stresses at the shallow subduction zone lead to a subduction zone earthquake postseismically the released oceanic plate undergoes a pulse of downdip strain returning the plate to a less extended state the moment of this downdip plate motion could exceed the seismic moment of the main shock

structure evolution and tectonic activity of the eastern sunda forearc indonesia from marine seismic investigations forearc structures of the eastern sunda arc are studied by new multichannel reflection seismic profiling we image a high along strike variability of the subducting oceanic plate the interface between subducting and overriding plate the accretionary wedge the outer arc high and forearc basins we highlight ongoing tectonic activity of the entire outer arc high active out of sequence thrust faults connecting the plate interface with the seafloor slope basins showing tilted sedimentary sequences on the outer arc high vertical displacement of young seafloor sediments and tilted sedimentary sequences in the lombok forearc basin while frontal accretion plays a minor role the growth of the outer arc high is mainly attributed to oceanic sediments and crustal fragments which are attached to the base of the upper plate and recycled within the forearc we image ongoing large scale duplex formation of the oceanic crust the incoming oceanic crust is dissected by normal faulting into 5 10 km wide blocks within a 50 70 km wide belt seaward of the deep sea trench these blocks determine the geometry and evolution of duplexes attached to the base of the overriding plate landward of the trench long lasting and ongoing subsidence of the lombok basin is documented by distinct seismic sequences in the lombok basin we image mud diapirs fed from deeply buried sediments which may have been mobilized by rising fluids we propose a wrench fault system in the eastern lombok forearc basin that decouples the subduction regime of the sunda arc from the continent island arc collision regime of the western banda arc the observed tectonic activity of the entire forearc system reflects a high earthquake and tsunami hazard similar to the western part of the sunda arc

time dependent interaction between subduction dynamics and phase transition kinetics summary numerical subduction models are presented that account for the kinetics of the olivine spinel transformation and the equilibrium transformation of spinel into perovskite and magnesiowustite temperature depth and stress dependent rheology is used buoyancy due to temperature and the olivine spinel and magnesiowustite perovskite phases leads to free subduction into the transition zone and retarded penetration into the lower mantle a dynamic feed back mechanism is found between the different buoyancy forces the kinetics of the phase transition and the release of latent heat this mechanism modulates the parachute effect of the metastable olivine mo in a subducting slab and leads to characteristic temporal variations of the depth of mo and with a time delay variations of the subduction velocity time periods are of the order of 3 4 myr this mechanism allows to explain variations of the depths of the deepest earthquakes in otherwise similar subduction zones further conclusions are as follows the maximum depth of mo increases roughly linearly with lithospheric thickness and the maximum depth may reach as deep as 720 750 km different subduction zones may represent different stages of velocity depth phase loops of mo

terdiurnal tide in the extended canadian middle atmospheric model cmam 1 we use the extended canadian middle atmosphere model cmam a general circulation model gcm to investigate the nature of the terdiurnal tide temperature and horizontal winds from a model run are analyzed to delineate the character of this tide for zonal wave numbers s 5 to 5 descriptions of the annual mean amplitudes seasonal variations and total tide superposed from the migrating and 10 nonmigrating components are provided the amplitudes and vertical wavelengths of the various components and the total terdiurnal tide are found to depend strongly on season latitude and altitude the migrating terdiurnal component maximizes at mid and high latitudes with significant amplitudes annual mean amplitude in wind temperature 10 m s k in the upper mesosphere and lower thermosphere mlt region between 80 and 100 km maximum amplitudes occur in winter in both hemispheres whereas above 100 km maximum amplitudes occur during solstices for the zonal wind field the nonmigrating terdiurnal components te5 te3 te4 tw4 and tw5 tend to peak at 50 n s with amplitudes between 2 and 8 m s the other nonmigrating components maximize in the polar regions with amplitudes of 2 10 m s possible generation mechanisms solar heating and nonlinear interactions for the migrating terdiurnal tide in the mlt region are also examined correlation analysis indicates that nonlinear interactions between the migrating diurnal and semidiurnal tides are unlikely to be the source of the migrating terdiurnal tide

focal depths and moment tensor representations of shallow earthquakes associated with the great sumba earthquake focal depths in the range 8 to 24 km below the seafloor were determined for seven of the larger shocks associated with the great sumba earthquake of august 19 1977 depth control was achieved by modeling digitized long period p waves recorded by the world wide standard seismic network if the base of the rupture at the time of the mainshock were no greater than the depth of the deepest aftershock the stress drop would be nearly 500 bars amplitude and first motion data from the p waves were inverted for point source moment tensors the inversion of rayleigh and love wave spectra computed from digital seismograms recorded by the seismic research observatories sro and the abbreviated seismic research observatories asro broadened the source study to include earthquakes with moments as small as 1024 dyn cm too small for either traditional first motion solutions or p wave modeling the inversion procedure was applied to data in the passband from 30 to 120 s the propagation phase for the love and the rayleigh waves was calibrated with signals from two earthquakes for which the source phase was inferred from the p wave solutions agreement with the corresponding p wave solutions is nearly the same whether or not the smaller eigenvalues of the inner product matrix are retained in the inversions the double couple components generally account for more than two thirds of the total moment normal faulting along an east to northeasterly strike characterizes the mechanisms in the principal zone of aftershock activity strike slip mechanisms consistent with horizontal compression normal to the arc prevail in the delayed aftershock zone located 200 km northwest of the mainshock of the earthquakes subjected to this surface wave analysis the foreshock stood out as having felt a significantly higher apparent stress perhaps as much as one half an order of magnitude higher than the others these results suggest that accurate source parameters for moderate to small magnitude earthquakes can be determined from surface waves recorded by the sro and asro in particular the mechanisms of small magnitude foreshocks could be obtained in this way

microearthquake seismicity and fault plane solutions related to arc continent collision in the eastern sunda arc indonesia the collision of australia with the eastern sunda and banda arcs of indonesia represents a modern example of the early stages of arc continent collision in order to obtain a more detailed view of the tectonics of the collision zone a microearthquake survey was conducted around the savu sea the region that encompasses the transition from subduction of indian ocean lithosphere on the west to collision or subduction of australian continental litho sphere on the east intermediate depth earth quakes were concentrated near pantar island the easternmost active volcano of the sunda arc and outline a northwest dipping zone that strikes n65oe from 70 to 150 km depth the seismic zone probably marks the western edge of the collision zone and its more northerly strike and the orientations of nodal planes from fault plane solutions indicate a 25 o bend in the subducted slab to a depth of at least 150 km because the convergence rate and the timing of collision from geologic observations on timor suggest that the oart of the slab now at 150 km depth was at the trench when australia first collided with timor we infer that continental crust or at least rifted continental margin crust caused the bend in the convergent margin and has been subducted to 150 km depth fault plane solutions of several events show nearly vertical nodal planes that trend parallel to the strike of the seismic zone along which a northwest side down sense of dis placement is indicated these events are concentrated at the southern top side of the seismic zone and suggest that the subducted lithosphere is presently detaching in the 50 100 km depth range beneath the eastern savu sea fault plane solutions for earthquakes within the upper part of the detaching slab 70 100 km depth have p and t axes whose trends lie parallel to the strike of the seismic zone and horizontal southeast trending b axes these earthquakes are interpreted as due to stresses caused by the bend in the subducting plate

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

seismicity pattern an indicator of source region of volcanism at convergent plate margins abstract the results of detailed investigation into the geometry of distribution of earthquakes around and below the volcanoes korovin cleveland makushin yake dake oshima lewotobi fuego sangay nisyros and montagne pelee at convergent plate margins are presented the isc hypocentral determinations for the period 1964 1999 based on data of global seismic network and relocated by engdahl van der hilst and buland have been used the aim of this study has been to contribute to the solution of the problem of location of source regions of primary magma for calc alkaline volcanoes spatially and genetically related to the process of subduction several specific features of seismicity pattern were revealed in this context i a clear occurrence of the intermediate depth aseismic gap idag in the wadati benioff zone wbz below all investigated active volcanoes we interpret this part of the subducted slab which does not contain any teleseismically recorded earthquake with magnitude greater than 4 0 as a partially melted domain of oceanic lithosphere and as a possible source of primary magma for calc alkaline volcanoes ii a set of earthquakes in the shape of a seismically active column sac seems to exists in the continental wedge below volcanoes korovin makushin and sangay the seismically active columns probably reach from the earth surface down to the aseismic gap in the wadati benioff zone this points to the possibility that the upper mantle overlying the subducted slab does not contain large melted domains displays an intense fracturing and is not likely to represent the site of magma generation iii in the continental wedge below the volcanoes cleveland fuego nisyros yake dake oshima and lewotobi shallow seismicity occurs down to the depth of 50 km the domain without any earthquakes between the shallow seismically active column and the aseismic gap in the wadati benioff zone in the depth range of 50 100 km does not exclude the melting of the mantle also above the slab iv any earthquake does not exist in the lithospheric wedge below the volcano montagne pelee the source of primary magma could be located in the subducted slab as well as in the overlying mantle wedge v frequent aftershock sequences accompanying stronger earthquakes in the seismically active columns indicate high fracturing of the wedge below active volcanoes vi the elongated shape of clusters of epicentres of earthquakes of seismically active columns as well as stable parameters of the available fault plane solutions seem to reflect the existence of dominant deeply rooted fracture zones below volcanoes these facts also favour the location of primary magma in the subducting slab rather than in the overlying wedge we suppose that melts advancing from the slab toward the earth surface may trigger the observed earthquakes in the continental wedge that is critically pre stressed by the process of subduction however for definitive conclusions it will be necessary to explain the occurrence of earthquake clusters below some volcanoes and the lack of seismicity below others taking into account the uncertainty of focal depth determination from global seismological data in some regions

earthquake occurrence along the java trench in front of the onset of the wadati benioff zone beginning of a new subduction cycle 1 spatial distribution of earthquake foci in the central part of the sunda arc was analyzed using global seismological data the analysis revealed the existence of a distinct strip of earthquakes distributed along the java trench separated by a trench parallel 50 150 km wide aseismic link from seismicity belonging to the wadati benioff zone of the recently subducting slab the seismicity pattern at the plate margin corresponds well with the morphology of the seafloor the along trench seismicity correlates with the position of the java trench and the onset of the wadati benioff zone correlates with the java trough the gps measurements performed in three analogous structural units of the neighboring sumatran convergent margin point to substantial differences in velocities of movement of the respective units and correlate with the spatial distribution of earthquake foci we interpret the distinct along trench seismicity as a consequence of the onset of a new subduction cycle due to the rapid convergent movement of the indo australian plate relative to the aseismic lithospheric link

back arc thrusting in the eastern sunda arc indonesia a consequence of arc continent collision the structure of the eastern sunda back arc region is dominated by two large north directed thrusts the wetar and flores thrusts and one or more minor thrusts which may represent early stages of subduction polarity reversal of the arc the relationships between thrusting and magmatic activity surface slopes cross arc faulting uplift forearc structure and collision by the australian continental margin provide constraints on the likely driving mechanisms of thrust formation driving mechanisms are considered in two broad categories one set of possible mechanisms originates within the upper plate and includes gravity sliding gravity spreading and magmatic intrusion the other set focuses on stress propagation between the upper and lower plates and for this arc system the major mechanism is that of continental collision while no one mechanism explains the range of observations we see in the back arc region all of these aspects play some role in the development of the thrusts we can eliminate upper plate mechanisms as primary driving forces because slope effects are similar in areas of both thrusting and nonthrusting in addition the wetar thrust shows a negative relation between thrusting and volcanism and side looking airborn radar images show no evidence of postvolcanic rifting that could accompany intrusion without volcanism collision between the arc and the australian continent provides the clearest driving mechanism but it does not explain the discontinuous nature or the particular location of the thrusts we suggest a sequence that appears to account for the data and to provide insight into the controversies often associated with other such thrust belts thrusting was initiated in those areas where the crust of the forearc region was thick a factor that facilitated stress propagation across the arc and where the crust of the back arc was thin which facilitated back arc thrusting thrusting concentrated at the base of the slope where the slope stress is maximum the early thrusting may have been helped also by thermal weakening of the crust due to volcanism as convergence proceeded volcanism waned then ceased in the eastern part of the arc the crust then strengthened and thrusting required higher stress to maintain and propagate this later stage should show higher seismic energy release which appears to be the case for the wetar thrust region displacement on the flores thrust appears to be matched by deflection of the volcanic arc we have estimated shortening in the back arc from interpretation of reflection profiles and for the flores thrust the value of approximately 30 km is consistent with that estimated for deflection of the arc compressional deformation continues west of the collision zone across the bali basin and into java it is reported in ne sumatra as well this deformation involves much less convergence than the eastern sunda thrusts and it may be related to magmatic processes to subduction of oceanic plateaus such as the roo rise or in the case of the bali basin to efficient lateral propagation of the flores thrust