post eocene extensional tectonics in southern new caledonia sw pacific insights from onshore fault analysis and offshore seismic data ductile to brittle extensional deformation following thrusting of the peridotites nappe during the upper eocene has been shown to play a major role in the tertiary tectonic evolution of the northern part of the main island of new caledonia and its eastern and western margins in this study we provide new tectonic data from southern new caledonia that allow to better constrain the tectonic evolution of the southern part of the main island we present a kinematic analysis of faults and striations obtained mainly from exposures of sedimentary rocks in the region of noumea with complements from measurements made farther north at nepoui within post obduction middle miocene deposits we also present additional results of an interpretation of seismic lines from the lagoon south of the noumea peninsula which provide constraints on the current tectonic regime of southern new caledonia extensional faults in the noumea region have been studied within terranes of various ages including pre and syn obduction deposits and ophiolites hence we demonstrate that important extensional events have affected the southern part of the new caledonia block after the obduction of the peridotite nappe the direction of maximum extension is variable at the scale of the region both high angle and low angle normal faults are present and block rotation is observed at some localities this suggests that detachments accommodating significant displacements are cutting through the sedimentary pile the average final strain pattern of the region can be regarded as the results of a multidirectional flattening a hypothesis consistent with vertical uplift associated with regional extension these results are in good agreement with conclusions of earlier workers showing late extensional evolution of the ophiolites along

the metamorphic sole of new caledonia ophiolite 40ar 39ar u pb and geochemical evidence for subduction inception at a spreading ridge amphibolite lenses that locally crop out below the serpentinite sole at the base of the ophiolite of new caledonia termed peridotite nappe recrystallized in the high temperature amphibolite facies and thus sharply contrast with blueschists and eclogites of the eocene metamorphic complex amphibolites mostly display the geochemical features of morb with a slight nb depletion and thus are similar to the youngest late paleocene eocene babb components of the allochthonous poya terrane thermochronological data from hornblende 40ar 39ar zircon and sphene u pb suggest that these mafic rocks recrystallized at 56ma using various geothermobarometers provides a rough estimate of peak recrystallization conditions of 0 5gpa at 800 950c the thermal gradient inferred from the metamorphic assemblage 60 ckm 1 geometrical relationships and geochemical similarity suggest that these mafic rocks belong to the oceanic crust of the lower plate of the subduction obduction system and recrystallized when they subducted below young and hot oceanic lithosphere they were detached from the down going plate and finally thrust onto unmetamorphosed poya terrane basalts this and the occurrence of slab melts at 53ma suggest that subduction inception occurred at or near to the spreading ridge of the south loyalty basin at 56ma 2012 american geophysical union all rights reserved

geologic and kinematic constraints on late cretaceous to mid eocene plate boundaries in the southwest pacific abstract starkly contrasting tectonic reconstructions have been proposed for the late cretaceous to mid eocene 85 45 ma evolution of the southwest pacific reflecting sparse and ambiguous data furthermore uncertainty in the timing of and motion at plate boundaries in the region has led to controversy around how to implement a robust southwest pacific plate circuit it is agreed that the southwest pacific comprised three spreading ridges during this time in the southeast indian ocean tasman sea and amundsen sea however one and possibly two other plate boundaries also accommodated relative plate motions in the west antarctic rift system wars and between the lord howe rise lhr and pacific relevant geologic and kinematic data from the region are reviewed to better constrain its plate motion history during this period and determine the time dependent evolution of the southwest pacific regional plate circuit a model of 1 west dipping subduction and basin opening to the east of the lhr from 85 55 ma and 2 initiation of northeast dipping subduction and basin closure east of new caledonia at 55 ma is supported west dipping subduction and basin opening were not driven by convergence as has previously been proposed our plate circuit analysis suggests that between at least 74 ma and subduction initiation at 55 ma there was little net relative motion between the pacific plate and lhr

rate and state friction properties of the longitudinal valley fault from kinematic and dynamic modeling of seismic and aseismic slip the longitudinal valley fault lvf taiwan is a fast slipping fault 5 cm yr which exhibits both seismic and aseismic slip geodetic and seismological observations 1992 2010 were used to infer the temporal evolution of fault slip thomas et al 2014a this kinematic model is used here to estimate spatial variations of steady state velocity dependence of fault friction and to develop a simplified fully dynamic rate and state model of the lvf based on the postseismic slip we estimate that the rate and state parameter a b over bar decreases from 1 2 mpa near the surface to near velocity neutral at 19 km depth the inferred a b values are consistent with the laboratory measurements on clay rich fault gouges comparable to the lichi melange which borders the lvf the dynamic model that incorporates the obtained a b over bar estimates as well as a vw patch with tuned rate and state properties produces a sequence of earthquakes with some realistic diversity and a spatio temporal pattern of seismic and aseismic slip similar to that inferred from the kinematic modeling the larger events have moment magnitude m w 6 7 similar to the 2003 chenkung earthquake with a range of smaller events the model parameterization allows reproducing partial overlap of seismic and aseismic slip before the earthquake but cannot reproduce the significant postseismic slip observed in the previously locked patch we discuss factors that can improve the dynamic model in that regard including the possibility of temporal variations in a b due to shear heating such calibrated dynamic models can be used to reconcile field observations kinematic analysis and laboratory experiments and assess fault behavior

mountain building in taiwan a thermokinematic model the taiwan mountain belt is classically viewed as a case example of a critical wedge growing essentially by frontal accretion and therefore submitted to distributed shortening however a number of observations call for a significant contribution of underplating to the growth of the orogenic wedge we propose here a new thermokinematic model of the taiwan mountain belt reconciling existing kinematic thermometric and thermochronological constraints in this model shortening across the orogen is absorbed by slip on the most frontal faults of the foothills crustal thickening and exhumation are sustained by underplating beneath the easternmost portion of the wedge tananao complex tc where the uplift rate is estimated to 6 3 mm a 1 and beneath the westernmost internal region of the orogen hsueshan range units hr where the uplift rate is estimated to 4 2 mm a 1 our model suggests that the tc units experienced a synchronous evolution along strike despite the southward propagation of the collision it also indicates that they have reached a steady state in terms of cooling ages but not in terms of peak metamorphic temperatures exhumation of the hr units increases northward but has not yet reached an exhumational steady state presently frontal accretion accounts for less than 10 of the incoming flux of material into the orogen although there is indication that it was contributing substantially more 80 before 4 ma the incoming flux of material accreted beneath the tc significantly increased 1 5 ma ago our results also suggest that the flux of material accreted to the orogen corresponds to the top 7 km of the upper crust of the underthrust chinese margin this indicates that a significant amount 76 of the underthrust material has been subducted into the mantle probably because of the increase in density associated with metamorphism we also show that the density distribution resulting from metamorphism within the orogenic wedge explains well the topography and the gravity field by combining available geological data on the thermal and kinematic evolution of the wedge our study sheds new light onto mountain building processes in taiwan and allows for reappraising the initial structural architecture of the passive margin

seismic stratigraphic record of transition from mesozoic subduction to continental breakup in the zealandia sector of eastern gondwana abstract the southwest pacific between australia new zealand and new caledonia is a block of continental crust zealandia that moved away from australia and antarctica after a long period of subduction beneath eastern gondwana we use 100 000 line km of seismic reflection profiles to identify intra continental basins related to the gondwana active margin overlain with erosional unconformity by retrogradational strata we interpret this regional scale first order unconformity the eastern gondwana composite surface and seismic stratigraphic megasequence pattern to represent the transition from subduction to continental breakup and separation of eastern gondwana rocks that make up the lower seismic stratigraphic megasequence zealandia 3 permian to early cretaceous have been drilled near new zealand and can be correlated with murihiku supergroup rocks farther north on the lord howe rise we correlate this megasequence with triassic to jurassic rocks of the clarence moreton basin of eastern australia we reinterpret the fairway aotea basin to be underlain by a wedge of zealandia 3 deposits thrust in a retro arc like foreland basin that was active immediately prior to breakup the lower rift and retrogradational megasequence zealandia 2 late cretaceous to eocene we correlate with the pakawau and kapuni groups of taranaki basin new zealand and the formation a charbon and phtanites of new caledonia the boundary with the shallowest megasequence zealandia 1 late eocene to present is the eocene oligocene unconformity which is primarily overlain by pelagic carbonate rocks this regional unconformity likely represents the onset of the modern tonga kermadec subduction system

discovery of early cretaceous rocks in new caledonia new geochemical and u pb zircon age constraints on the transition from subduction to marginal breakup in the southwest pacific abstract new u pb dating of detrital zircon and geochemical features of permian mesozoic arc derived volcanic rocks and volcaniclastic turbidites graywackes when compared with those of the volcanic rocks associated with unconformable late cretaceous shallow water sediments reveal that subduction in new caledonia once thought to be extinct in the late jurassic ca 150 ma was still active at least from ca 130 to 95 ma the accumulation of volcanic arc derived sediments during the late early cretaceous suggests that as in new zealand active margin activity went on for a short time in spite of the assumed subduction jamming by the hikurangi plateau at ca 100 ma meanwhile the rift related magmatic activity that preceded the marginal breakup migrated eastward from ca 130 ma 130 95 ma in eastern australia to 110 ma 110 82 ma in new zealand and finally to ca 89 ma 89 83 ma in new caledonia and generated large volumes of silicic magma in contrast marginal basins opened synchronously at

ion microprobe dating of paleozoic granitoids devonian magmatism in new zealand and correlations with australia and antarctica abstract precise ion microprobe u pb zircon ages have been obtained from a representative set of paleozoic igneous rocks from the western province of the south island new zealand granitoid rocks forming the karamea batholith and related plutons in the buller terrane all yield crystallisation ages that are indistinguishable within a 5 ma uncertainty at 375 ma middle late devonian previous workers have suggested that the batholith was emplaced over a long time interval and comprises rocks ranging in age from 370 to 310 ma with the bulk in the early carboniferous granitoid rocks with carboniferous ages 330 ma do occur further to the west and younger cretaceous granitoids occur within the karamea batholith but these are not volumetrically significant a sample from the ultramafic mafic riwaka complex in the adjacent takaka terrane gave a crystallisation age of 376 9 5 6 ma 2 indicating emplacement coeval with the karamea batholith the paleozoic granitoids contain a large amount of inherited zircon with distinct 390 500 600 and 1000 ma components the 390 ma age corresponds to widespread plutonism in the lachlan fold belt in se australia the 500 600 ma ross delamerian age and 1000 ma grenville age age components have also been observed in granitoids from the lachlan fold belt and in ordovician metasedimentary rocks from se australia and new zealand the inherited zircons in the karamea batholith could be derived from continental basement at depth from the incorporation of upper crustal material in the granitoid magmas or both the devonian granitoids in new zealand can now be correlated with rocks of similar age in northern victoria land admiralty intrusives and marie byrd land ford granodiorite in west antarctica in ne tasmania and in the central part of the lachlan fold belt in se australia on a reconstruction of the sw pacific margin of gondwana prior to later break up it is possible to trace out a semi continuous magmatic belt in excess of 2000 km in length

u pb zircon dating of post obduction volcanic arc granitoids and a granulite facies xenolith from new caledonia inference on southwest pacific geodynamic models in new caledonia the occurrence of one of the world s largest and best exposed subduction obduction complex is a key point for the understanding of the geodynamic evolution of the whole southwest pacific region within the ophiolite pre and post obduction granitoids intrude the ultramafic allochthon and provide new time constraints for the understanding of obduction processes at 27 4 ma a new east dipping subduction generated the active margin magmatism along the western coast of the island saint louis massif at 24 3 ma the eastward shift of the magma activity and slightly different geochemical features koum borindi massif was either related to the older slab break off or alternatively due to the eastward migration of the mantle wedge following the collision of the eastern margin of the low howe rise finally the occurrence of a granulite facies xenolith in the koum borindi massif with comparable 24 5 ma u pb zircon age and isotopic features initial end 5 1 suggests that these evolved magmas were generated within the lithospheric mantle beneath a continental crust of normal thickness geochronological evidence for continuous convergence during the oligocene infers an east dipping eocene oligocene subduction obduction system to have existed in the southwest pacific from the d entrecasteaux zone to the north island of new zealand

seismogenic structure in a tectonic suture zone with new constraints from 2006 mw6 1 taitung earthquake 1 a mw 6 1 earthquake occurred on april 1st 2006 near taitung eastern taiwan it produced significant coseismic ground displacements and a large number of aftershocks in the ensuing month this event provides an opportunity to diagnose the seismogenic structure in the southern longitudinal valley lv of eastern taiwan long viewed as one of the collision sutures between the philippine sea and the eurasian plates with precisely relocated main and aftershock hypocenters focal mechanisms for m 3 8 events and coseismic ground displacements from strong motion records we determine a main shock dislocation model our results indicate that the main shock occurred on a high angle fault azimuth 198 dip 77 the model comprises a fault with two segments the main shock and a large number of aftershocks are associated with the northern segment that exhibited predominantly left lateral strike slip motion in agreement with p wave first motions and waveform usgs solutions the southern segment exhibits a slightly larger thrust component in agreement with cmt solutions tectonically this event highlights a nne trending fault on the west side of the lv which is predominantly strike slip the aftershocks clustered to the east of the main shock which exhibit mainly thrust mechanisms indicate that shortening is still acting on the sedimentary materials deposited between the coastal and central ranges prior to collision as a result the southern lv is undergoing slip partitioning along different faults which has never been specified before

under the hood of the earthquake machine toward predictive modeling of the seismic cycle advances in observational laboratory and modeling techniques open the way to the development of physical models of the seismic cycle with potentially predictive power to explore that possibility we developed an integrative and fully dynamic model of the parkfield segment of the san andreas fault the model succeeds in reproducing a realistic earthquake sequence of irregular moment magnitude m w 6 0 main shocks including events similar to the ones in 1966 and 2004 and provides an excellent match for the detailed interseismic coseismic and postseismic observations collected along this fault during the most recent earthquake cycle such calibrated physical models provide new ways to assess seismic hazards and forecast seismicity response to perturbations of natural or anthropogenic origins

a comparative study of late cretaceous ophiolitic basalts from new zealand and new caledonia implications for the tectonic evolution of the sw pacific abstract our understanding of the tectonic evolution of the sw pacific between the cretaceous and the miocene is incomplete during this period there were a number of ophiolitic complexes formed and emplaced including the tangihua ophiolite complex of new zealand and the poya terrane ophiolites of new caledonia both ophiolitic complexes contain rocks from only the uppermost levels of the oceanic crust have a similar age of formation and were emplaced during the eocene consequently it is thought that the two systems are somehow related however the poya terrane and the tangihua ophiolite complex have significantly different geochemistry the poya terrane basalts are predominantly p and n morb tholeiites generated during the opening of a small marginal basin north east of new caledonia whereas the tangihua basalts range from back arc tholeiites to calc alkaline arc basalts suggesting formation in an arc back arc setting the similarities in age emplacement and stratigraphy between the two systems must be a result of the tectonic regime operating within the sw pacific as the new geochemical information clearly shows that the poya terrane and the tangihua ophiolite complex are not directly related

geochemical evolution and tectonic significance of boninites and tholeiites from the koh ophiolite new caledonia the central chain ophiolites in new caledonia are fragments of a supra subduction zone ssz ophiolite now preserved from the upper layered gabbros through to volcanics and overlain by pelagic cherts and a thick middle triassic to upper jurassic volcaniclastic sequence most of the fragments were formed by a single tholeiitic magmatic episode but one of these the koh ophiolite was formed by two tholeiitic magmatic episodes separated by boninites the first event in the koh ophiolite formed cumulate gabbros dolerites plagiogranites and the first pillow lava sequence from a tholeiitic magma with strong depletion in the light rare earth elements lree and abnormally low tio2 0 5 at mg 60 shortly after their eruption these tholeiitic lavas were overlain by a high ca boninitic unit with a basal section of boninite pillows flows and breccias and an upper section of boninitic dacites and tuffs the last magmatic phase involved eruption of evolved tholeiitic basalts as pillows above the boninites and as dykes and sills intruding the older plutonic and volcanic sections of the ophiolite this second phase of tholeiitic magmatism is compositionally distinct from the first and is closest to back arc basin basalts babb erupted during the early rifting history of modern back arc basins the boninitic volcanics belong to a high ca series with slightly lower sio2 al2o3 and tio2 compared to those from modern island arc systems and they lack the positive zr spike relative to adjacent rare earth elements ree in normalised element variation patterns these boninites were formed shortly after the production of back arc basin crust represented by the depleted tholeiites and shortly before a second spreading event which caused 40 60 extension of the initial basin crust and eruption of the upper tholeiites the dominance of babb like tholeiites throughout the central chain ophiolites in new caledonia the restricted occurrence of boninites and the stratigraphy and chemistry of the koh ophiolite suggest that the boninites were erupted in response to an exceptional tectonic situation we suggest that this boninite generation event was driven by adiabatic decompression of hot depleted mantle residual from the production of the lower tholeiites during initiation of rifting of young oceanic crust intimately associated with propagation of a back arc basin spreading centre the occurrence of a thick blanket of calc alkaline volcaniclastic sediments above the ophiolite indicates proximity to a mature arc and suggests that the koh boninites were not associated with the initiation of subduction a close modern analogy for the koh ophiolite exists on the hunter ridge protoisland arc between southernmost vanuatu new hebrides island arc and the fijian islands there high ca boninites lacking positive zr spikes occur together with low ti tholeiites and more typical babb tholeiites where the southern spreading centre of the north fiji basin is propagating into the protoarc crust of the hunter ridge

uranium lead ages from the dun mountain ophiolite belt and brook street terrane south island new zealand the dun mountain ophiolite and overlying maitai group is discontinuously exposed for 480 km in south island new zealand zircon u pb dates from plagiogranite are presented for relatively intact ophiolite ophiolitic melanges and for more silicic volcanic plutonic assemblages in the southern part of the belt where a typical ophiolite association is lacking step wise dissolution experiments on slightly discordant plagiogranite zircon produce more concordant residues that indicate the zircons have lost from 1 to more than 5 of their radiogenic pb relatively recently high precision 207 pb 206 pb dates establish the age of ophiolite formation for at least 350 km along strike to a narrow interval between about 275 and 285 ma the zircon u pb data confirm correlation of petrologically distinct segments of the dun mountain ophiolite and show that mafic ultramafic ophiolite assemblages and moderately potassic high level granitoids developed within a short time interval probably during the extension of a volcanic arc marginal basin thick lenses of polymictic breccia and bio clastic limestone of the maitai group locally rest in depositional contact on relatively intact ophiolite within the dun mountain ophiolite comparison of inferred biostratigraphic ages from the limestone with the 280 ma ages from the plagiogranites indicate a gap of 20 m y following ophiolite formation a granite clast from conglomerate higher in the maitai group yielded a near concordant u pb date of 265 ma and provides a maximum age for this part of the sequence attenuation of the dun mountain ophiolite by extensional faulting and erosion may have occurred during the interval between ophiolite formation and maitai group sedimentation the dun mountain ophiolite and overlying maitai group are bounded to the west by triassic and jurassic volcanogenic sedimentary rocks of the murihiku terrane and in turn by the brook street terrane which is interpreted as remnants of an early permian oceanic arc a hornblende gabbronorite associated with a layered mafic ultramafic intrusion in the brook street terrane yielded a date of 265 ma significantly younger than dun mountain ophiolite such intrusions may represent the plutonic roots for ankaramitic volcanic rocks that comprise a conspicuous component of the brook street terrane but which are not represented by detritus in the maitai group biotite granite occurs locally in the brook street terrane and is dated at 260 ma the absence of any clear stratigraphic correlation or provenance linkage between the brook street terrane and dun mountain maitai terrane suggests strike slip displacements on intervening terrane boundary faults

significance of palaeomagnetic data from the oceanic poya terrane new caledonia for sw pacific tectonic models results from a palaeomagnetic study of pillow basalts and associated pelagic sediments of the late cretaceous palaeocene poya terrane of new caledonia are presented the poya terrane forms a nappe that was thrust sw over the island i e the pacific side in the middle eocene data from four outcrops nine sites spread over 250 km yield a normal polarity tilt corrected mean inclination of 57 2 where 95 11 2 and k 67 4 which suggests formation at 37 8 12 1 s the between outcrop declinations are unfortunately too scattered to be used in regional tectonic discussions they indicate rotations that are localised and sometimes very large following reference to sw pacific late cretaceous palaeogene plate tectonic reconstructions the inclination data suggest that the poya terrane formed close to the new caledonian portion of the indo australia plate this interpretation is consistent with tectonic models where the poya terrane is generated in a marginal basin immediately to the northeast of new caledonia during the break up of east gondwana the terrane was thrust over new caledonia in the middle eocene possibly in response to a change in relative motion of the australian and pacific plates at about this time a short time later it was overthrust by a supra subduction zone ultramafic nappe and together they have since drifted northwards as passengers on the australia plate

source model of an earthquake doublet that occurred in a pull apart basin along the sumatran fault indonesia summary on 2007 march 6 an earthquake doublet occurred along the sumatran fault indonesia the epicentres were located near padang panjang central sumatra indonesia the first earthquake with a moment magnitude m w of 6 4 occurred at 03 49 utc and was followed two hours later 05 49 utc by an earthquake of similar size m w 6 3 we studied the earthquake doublet by a waveform inversion analysis using data from a broadband seismograph network in indonesia jisnet the focal mechanisms of the two earthquakes indicate almost identical rightlateral strike slip faults consistent with the geometry of the sumatran fault both earthquakes nucleated below the northern end of lake singkarak which is in a pull apart basin between the sumani and sianok segments of the sumatran fault system but the earthquakes ruptured different fault segments the first earthquake occurred along the southern sumani segment and its rupture propagated southeastward whereas the second one ruptured the northern sianok segment northwestward along these fault segments earthquake doublets in which the two adjacent fault segments rupture one after the other have occurred repeatedly we investigated the state of stress at a segment boundary of a fault system based on the coulomb stress changes the stress on faults increases during interseismic periods and is released by faulting at a segment boundary on the other hand the stress increases both interseismically and coseismically and may not be released unless new fractures are created accordingly ruptures may tend to initiate at a pull apart basin when an earthquake occurs on one of the fault segments the stress increases coseismically around the basin the stress changes caused by that earthquake may trigger a rupture on the other segment after a short time interval we also examined the mechanism of the delayed rupture based on a theory of a fluidsaturated poroelastic medium and dynamic rupture simulations incorporating a rheological velocity hardening effect these models of the delayed rupture can qualitatively explain the observations but further studies especially based on the rheological effect are required for quantitative studies

tectonic history of northern new caledonia basin from deep offshore seismic reflection relation to late eocene obduction in new caledonia southwest pacific new high quality multichannel seismic reflection data from the western new caledonia offshore domain allow for the first time the direct continuous connection of seismic reflectors between the deep sea drilling project 208 drill hole on the lord howe rise and the new caledonia basin a novel seismic interpretation is hence proposed for the northern new caledonia basin stratigraphy which places the eocene oligocene unconformity deeper than previously thought and revisits the actual thickness of the pre oligocene sequences a causal link is proposed between the obduction of the south loyalty basin over new caledonia nc and the tectonic history of the northern new caledonia basin here it is suggested that as the south loyalty basin was being obducted during early oligocene times the nc basin subsided under the effect of the overloading and underthrusted to accommodate the compressional deformation which resulted in 1 the uplift of the northern fairway ridge and 2 the sinking of the western flank of new caledonia this event also had repercussions farther west with the incipient subsidence of the lord howe rise

regional implications of u pb shrimp age constraints on the tectonic evolution of new caledonia abstract u pb shrimp ages for zircons from plagiogranites indicate a late carboniferous age of formation for ophiolitic basement of the koh terrane in the central chain mountains of new caledonia samples from ophiolites at koh and koua yielded ages of 302 7 ma and 290 5 ma respectively the similarity of these ages to those of plagiogranites in the dun mountain ophiolite belt maitai terrane of new zealand and the comparable structural positions of the two terranes potentially constrain reconstructions of the cretaceous sw pacific margin detrital zircons from late mesozoic sediments that overlap the koh terrane also provide potential constraints on the location of new caledonia prior to its break up and dispersal from eastern australia

shallow marine to pelagic sediments from a dismembered ophiolite kandra southern india glimpses of ancient subduction zone related sedimentation abstract a suprasubduction zone oceanic back arc setting for the paleoproterozoic kandra ophiolite complex koc in southern india has been suggested from geochemical signatures the telescoped segments of thin deformed sedimentary successions of shallow marine to pelagic affinity overlying a basaltic substrate and preserved within thrust slices of the koc are tectonically juxtaposed against the eastern dharwar craton margin in the northern thrust slice kandra village succession about 150 m of sedimentary strata show intercalation of quartz arenite and basaltic flow in the lower part grading upwards to heterolithic sandstone mudstone deposited above the storm wave base in the southeastern part of the koc gurramkonda succession deep water greywacke turbidite pelagic chert mafic tuff and volcaniclastics and quartz arenite deposited below the storm wave base are preserved as thrust bound packets intermittent basaltic outpourings punctuated deeper water deposition as evidenced by alternate metachert and metabasalt layers and emplacement of basaltic rocks along small thrusts which transpose stratification craton margin sediments consists of immature coarse terrigenous clastics intercalated with thin mafic tuff suggesting influence of mass flow processes giving way to fluvial sedimentation in the lower part of the udaigiri group further up fine grained plane laminated siltstone shale with rippled sandstone lenses grade upward to compositionally mature quartz arenite deposited close to the craton margin with signatures of tidal and wave reworking the association of stratigraphic successions of two contrasting depositional environments in the koc adds to the spectrum of variation of sedimentary collage of the ocean plate stratigraphy the kandra village and gurramkonda successions of the koc possibly represent ancient arc trench milieu and shallower part of oceanic marginal basin respectively paleoproterozoic subduction accretion process led to collapse of these basins and tectonic emplacement of the koc against the eastern dharwar craton margin which hosted near shore sedimentary succession of the udaigiri group occurring west of the koc

the development of the sw pacific margin of gondwana correlations between the rangitata and new england orogens prior to formation of the tasman sea the late paleozoic mesozoic rangitata orogen of new zealand and new caledonia abutted the paleozoic new england orogen of eastern australia comparison of the record of permian cretaceous igneous and deformational events from the two orogens suggests that their tectonic evolution was interrelated and is a consequence of convergent plate interaction along the southwest pacific margin of gondwana the following relations are proposed 1 termination of arc volcanism and widespread sedimentation in new england together with the onset of regional deformation and crustal anatexis were synchronous with the commencement of volcanism and sedimentation within the rangitata orogen 2 early permian andesitic volcanism in eastern new england represents an along strike extension of the brook street terrane of new zealand 3 late permian regional deformation in new england coincides with both a break in subduction related igneous activity in the new england and rangitata orogens and a shift in the locus of this activity 4 late permian triassic calc alkaline igneous activity in new england correlates with a phase of relatively continuous accumulation of pyroclastic material in the forearc basin of the rangitata orogen 5 cessation of plutonism in new england corresponds with commencement of formation of the esk head melange in new zealand and the probable commencement of juxtaposition of the te anau and alpine assemblage 6 late cretaceous epizonal plutons intruded into the new england orogen are similar in character and age to those emplaced during the final phases of rangitata orogenesis and both appear to mark initial stages of rifting associated with formation of the tasman sea the generation of permian and triassic igneous activity in eastern new england by convergent plate interaction results on present reconstructions of the gondwana margin in an excessively wide arc trench gap succession for the position of the trench is constrained to east of new caledonia from the permian onward this suggests there may have been some rearrangement of tectonic elements along the margin resulting in widening of the lord howe rise between australia and new caledonia in the period between termination of igneous activity in new england and formation of the tasman sea in the late cretaceous

melange rheology and seismic style shear displacements in crustal fault zones are accommodated by a range of seismic styles including standard earthquakes non volcanic tremor and continuous and transitory aseismic slip subduction channel shear zones containing highly sheared fluid saturated trench fill sediments intermingled with fragments of oceanic crust are commonly inferred to occur along active subduction megathrusts if this interpretation is correct these plate boundary faults are not discrete planes but may resemble the melange shear zones commonly found in exhumed subduction related rock assemblages melange deformation appears to depend critically on the ratio of competent to incompetent material with shear surfaces localized along lithological contacts or within competent domains while matrix flow accommodates shearing by distributed strain if the style of strain and or displacement accommodation in a melange reflects the partitioning between aseismic and seismic slip the proportion of competent material seems likely to be a significant factor affecting seismic style within subduction channel shear zones and along comparable mixed lithology fault zones

frictional properties of olivine at high temperature with applications to the strength and dynamics of the oceanic lithosphere 1 faulting and brittle deformation of mantle rocks occurs in many tectonic settings such as oceanic transform faults oceanic detachment faults subduction zones and continental rifts however few data exist that directly explore the frictional properties of peridotite rocks improved constraints on the brittle deformation of peridotite is important for a more complete understanding of the rheological properties of the lithosphere furthermore our comparatively detailed understanding of plastic deformation in olivine allows us to explore the possible role of thermally activated intracrystalline deformation mechanisms in macroscopically brittle processes it has been hypothesized and some experimental data indicate that plastic yielding by dislocation glide low temperature plasticity determines the direct effect in the rate and state frictional constitutive formulation plastic flow may also have important implications for the blunting or necking at asperity contacts that influences the time and or displacement dependent friction evolution effect and frictional healing we present results from saw cut experiments on fine grained synthetic olivine fault gouge conducted in a gas medium deformation apparatus in the temperature range of 400 1000 c with 100 mpa confining pressure we conducted velocity stepping tests to explore the rate and temperature dependence of sliding stability we also conducted slide hold slide experiments to investigate the time and temperature dependence of fault zone restrengthening frictional healing the mechanical data and microstructural observations allow us to explore the role of thermally activated processes in frictional sliding the data indicate systematic temperature dependenceof rate and state variables that can be attributed to plastic yielding at grain to grain contacts we explore the implications of such temperature dependent behavior for controlling the base of the seismogenic zone in the oceanic lithosphere and we seek insight into possible mechanistic models for the interactions between fracture and flow that could lead to improved constraints on the strength of the lithosphere

the gravity fields of palawan and new caledonia insights into the subsurface geometries of ophiolites abstract new gravity data from palawan in the western philippines emphasize resemblances to new caledonia on both islands ophiolites derived from root zones just offshore rest on basal surfaces that change abruptly in depth by as much as 5 km the subsurface geometries of these thrust sheets are as important to an understanding of their emplacement histories as are their exposure patterns

shear concentration in a collision zone kinematics of the chihshang fault as revealed by outcrop scale quantification of active faulting longitudinal valley eastern taiwan abstract repeated measurements of active deformation were carried out at three sites along the active chihshang fault a segment of the longitudinal valley fault zone of eastern taiwan the present day plate boundary between the philippine sea plate and eurasia reliable annual records of displacement along an active fault were obtained based on detailed surveys of faulted concrete structures along the active chihshang fault striking n18 e we determined average motion vectors trending n37 w with an average shortening of 2 2 cm yr thus the transverse component of motion related to westward thrusting is 1 8 cm yr whereas the left lateral strike slip component of motion is 1 3 cm yr the fault dips 39 45 to the east so that the vertical displacement is 1 5 3 cm yr and the actual oblique offset of the fault increases at a rate of 2 7 3 7 cm yr this is in good agreement with the results of regional geodetic and tectonic analyses in taiwan and consistent with the n54 w trend of convergence between the northernmost luzon arc and south china revealed by gps studies our study provides an example of extreme shear concentration in an oblique collision zone at chihshang the whole horizontal shortening of the longitudinal valley fault 2 2 cm yr on average occurs across a single narrow fault zone so that the whole reverse slip about 2 7 3 7 cm yr depending on fault dip was entirely recorded by walls 20 200 m long where faults are tightly localized this active faulting accounts for more than one fourth 27 of the total shortening between the luzon arc and south china recorded through gps analyses further surveys should indicate whether the decreasing shortening velocity across the fault is significant revealing increasing earthquake risk due to stress accumulation or not revealing continuing fault creep and weak behaviour of the chihshang fault

frictional properties of a low angle normal fault under in situ conditions thermally activated velocity weakening the zuccale fault is a regional low angle normal fault exposed on the isle of elba in central italy that accommodated a total shear displacement of 6 8 km the fault zone structure and fault rocks formed at 8 km crustal depth the present day fault structure is the final product of several deformation processes superposed during the fault history in this study we report results from a series of rotary shear experiments performed on 1 mm thick powdered gouges made from several fault rock types obtained from the zuccale fault the tests were done under conditions ranging from room temperature to in situ conditions i e at temperatures up to 300 c applied normal stresses up to 150 mpa and fluid saturated the ratio of fluid pressure to normal stress was held constant at either 0 4 or 0 8 to simulate an overpressurized fault the samples were sheared at a constant sliding velocity of 10 m s for at least 5 mm after which a velocity stepping sequence from 1 to 300 m s was started to determine the velocity dependence of friction this can be represented by the rate and state parameter a b which was determined by an inversion of the data to the rate and state equations friction of the various fault rocks varies between 0 3 and 0 8 similar to values obtained in previous studies and decreases with increasing phyllosilicate content friction decreases mildly with temperature whereas normal stress and fluid pressure do not affect friction values systematically all samples exhibited velocity strengthening conditionally stable behavior under room temperature conditions and a b increased with increasing sliding velocity in contrast velocity weakening accompanied by stick slips was observed for the strongest samples at 300 c and sliding velocities below 10 m s an increase in fluid pressure under these conditions led to a further reduction in a b for all samples so that they exhibited unstable stick slip behavior at low sliding velocity the results suggest that phyllosilicate bearing fault rocks can deform by stable aseismic creep at low resolved shear stress and low shear rate conditions an increase in fluid pressure or loading of stronger portions could lead to a runaway instability the runaway instability might be limited in size because of 1 the fault heterogeneity 2 the observed strengthening at higher sliding velocities and 3 a co seismic drop in pore fluid pressure

eocene arc continent collision in new caledonia and implications for regional southwest pacific tectonic evolution new caledonia preserves evidence that constrains models for the tectonic evolution of the southwest pacific region onland geology reflects four main tectonic phases 1 early mesozoic development of subduction related terranes and their accretion to the gondwana margin 2 cretaceous passive margin development and sea floor spreading during the gondwana breakup 3 foundering of an oceanic basin and the eocene arrival of thinned gondwana margin crust at a southwest facing subduction zone resulting in collisional orogenesis and obduction of an ophiolitic nappe from the northeast and 4 detachment faulting during extensional collapse resulting in unroofing of metamorphic core complexes the last phase explains supposedly anomalous metamorphic gradients in the northeast of the island

eclogites and blueschists of the pam peninsula ne new caledonia a reappraisal high p rocks of the pam peninsula ne new caledonia are divided into three zones 1 an uppermost ferroglaucophane lawsonite zone of cretaceous to eocene metasediments and metavolcanics of the diahot terrane that experienced peak conditions involving p 7 9 kbar and t 400 58 c 2 albite epidote omphacite zone diahot terrane rocks that experienced blueschist facies conditions of p 12 6 1 2 kbar and t 570 36 c 3 lowermost metabasic eclogites of uncertain age that form the pouebo terrane which experienced high p conditions of p 23 9 3 0 kbar and t 600 c eclogite occurs as metre to kilometre scale pods in coarse grained hydrous mineral rich glaucophanite formed during hydration and decompression of the pouebo terrane metamorphism and deformation were consequent to 44 51 ma eocene convergence when sedimentary and ophiolitic nappes were thrust over the eclogites in a sw direction white mica ages constrain metamorphism to have ended by 37 1 ma large steps in metamorphic grade are coincident with sw dipping and ne dipping faults that separate the three zones and were formed during two stages 1 comparatively slow uplift and hydration of the pouebo terrane before it was juxtaposed with the albite epidote omphacite zone at p 14 kbar 2 comparatively rapid uplift of both the pouebo terrane and the albite epidote omphacite zone to form a domal core of eclogite flanked by significantly lower grade rocks to the sw and ne

tectonic mode switches and the nature of orogenesis abstract the birth and death of many mountain belts occurs in lithosphere that over rides major subduction zones here the tectonic mode shortening versus extension can abruptly switch even during continuous and otherwise smooth convergence if the hinge line of the foundering slab rapidly retreats i e rolls back the foundering slab creates a gravitational potential well into which the orogen collapses this motion coupled with stress guides can pull the orogen apart a slowing of roll back or of hinge retreat means that the subduction flexure may subsequently begin to be pushed back or be pushed over by the advancing orogen the consequence of such changes in relative motion is that orogenic belts are affected by abrupt tectonic mode switches the change from push to pull leads to a sudden change from horizontal extension to horizontal shortening potentially throughout the entire mass of the orogenic lithosphere that over rides the subducting slab the sequencing of these tectonic mode switches affects the thermal evolution of the orogen and thus fundamentally determines the nature of orogenesis this insight led to us to our quite different views as to how orogens work it is evident that orogens affected by abrupt push pull mode switches are characterized by high pressure metamorphism whereas orogens affected by abrupt pull push mode switches are characterized by high temperature metamorphism magmatism and anatexis

permian evidence for trans tasman relationships between east australia new caledonia and new zealand abstract basaltic to basaltic andesitic tuff breccias agglomerates and subordinate lavas together with cogenetic dacitic tuffs and glassy flows comprise the tectonomorphically anomalous early permian submarine volcanic sequence of the gympie group southeast queensland the least accumulative gympie basalts and basaltic andesites show geochemical features which typify island arc tholeiites the absence of andesitic eruptives i e the essential bimodality of the volcanic sequence together with low levels of large ion lithophile elements lile and the absence of compelling evidence for amphibole or garnet fractionation are consistent with an immature submarine tholeiitic stage of arc development on relatively thin oceanic crust by contrast the mid carboniferous to permian calc alkaline camboon arc to the west is inferred to have developed at least in part on early carboniferous continental crust the volcanics and overlying sediments of the gympie group are compared with those of the volcanic arc and adjoining formations of the nelson eglinton takitimu areas of new zealand to reveal some striking geochemical and lithostratigraphic similarities dacitic volcanics in new caledonia may also have formed a relatively young part of the same volcanic arc we analyse the overlying permian sediments to show further similarities and facial differences between the three regions essentially we propose new zealand was locus for an actively spreading mid ocean ridge dun mountain ultramafics and patuki ophiolite complex which received a substantial thickness of marine sediment gympie lay towards the end of the mid ocean ridge and new caledonia close to the terminus of the volcanic arc and received more terrestrial sediment we analyse original and subsequent spatial interrelationships that developed before and during the late cretaceous opening of the tasman sea and suggest that the history of separation was complicated by strike slip and or transform movements

petrogenesis of gympie group volcanics evidence for remnants of an early permian volcanic arc in eastern australia mafic ohenocryst rich basalt to basaltic andesite tuff breccias agglomerates and subordinate lavas together with sparsely quartz and plagiophyric dacitic tuffs and glassy flows comprise the tectonomorphically anomalous lower permian submarine volcanic sequence of the gympie group southeast queensland geochemical data imply three distinct crystallisation stages for the main volcanic series these are 1 initial olivine cr spinel clinopyroxene removal that caused rapid mgo cao ni and cr depletion in the ascending mantle derived magma 2 extensive clinopyroxene dominated olivine clinopyroxene plagioclase fractionation that gave rise to tholeiitic feo1 tio2 al2o3 p2o5 zr and y enrichment in the basalt basaltic andesite range and 3 plagioclase dominant augite magnetite apatite crystallisation that resulted in decreasing al2o3 tio2 feo1 p2o5 v nb and sr levels in the dacites identical degrees of rare earth element ree fractionation for the basalts and dacites suggest their comagmatic origin and preclude significant amphibole involvement in their petrogenesis low mg numbers mg1 ni cr ree and high field strength cation hfsc abundances in the gympie basalts along with low zry tiy and nbzr ratios are features typical of island arc tholeiites the gympie suite represents an immature submarine tholeiitic stage of development of a portion of a major intra oceanic arc that bordered gondwana but was fragmented by opening of the tasman sea the presence of coarse clinopyroxene phyric ankaramites together with highly differentiated dacites may relate to a phase of strike slip tectonics that exerted important control on magma supply and volumetric eruptive rates during the early permian evolution of the gondwana margin

provenance of permian triassic and ordovician metagraywacke terranes in new zealand evidence from 40ar 39ar dating of detrital micas single crystal 40 ar 39 ar ages of detrital micas from greenland group ordovician low grade metagraywackes of the west coast south island new zealand indicate a source area having muscovite age patterns of 490 515 ma the detrital muscovite ages are characteristic of granitoid and gneiss terranes of the ross adelaide fold belt of antarctica therefore the source area for the greenland group sedimentary rocks was the immediately adjacent pacific margin of gondwana similar age determinations for rakaia terrane permian triassic torlesse supergroup metagraywackes of the wellington and canterbury regions of new zealand indicate that their source area included rocks having prominent muscovite cooling ages populations of 210 290 ma 80 and 410 460 ma 15 the torlesse detrital muscovite age data thus suggest that the source area of the metagraywackes was not within the lachlan fold belt of southeast australia and analogues in antarctica nor in the adjacent ross adelaide fold belt rather the rakaia terrane of the torlesse metagraywackes is a true suspect terrane derived from a source area within the hunter bowen fold belt of northeast australia and the immediately adjacent older orogens of eastern queensland

seismicity on a fault controlled by rate and state dependent friction with spatial variations of the critical slip distance 1 we perform systematic simulations of slip using a quasi dynamic continuum model of a two dimensional 2 d strike slip fault governed by rate and state dependent friction the depth dependence of the a b and l frictional parameters are treated in an innovative way that is consistent with available laboratory data and multidisciplinary field observations various realizations of heterogeneous l distributions are used to study effects of structural variations of fault zones on spatiotemporal evolution of slip we demonstrate that such realizations can produce within the continuum class of models realistic features of seismicity and slip distributions on a fault we explore effects of three types of variable l distributions 1 a depth dependent l profile accounting for the variable width of fault zones with depth 2 uncorrelated 2 d random distributions of l with different degrees of heterogeneity and 3 a hybrid distribution combining the depth dependent l profile with the 2 d random l distributions the first type of l distribution with relatively small l over the depth range corresponding to the seismogenic zone and larger l elsewhere generates stick slip events in the seismogenic zone and ongoing creep above and below that region the 2 d heterogeneous parameterizations generate frequency size statistics with event sizes spanning 4 orders of magnitude our results indicate that different degrees of heterogeneity of l distributions control 1 the number of simulated events and 2 the overall stress level and fluctuations other observable trends are 3 the dependency of hypocenter location on l and 4 different nucleation phases for small and large events in heterogeneous distributions

tectonic accretion and underplating of mafic terranes in the late eocene intraoceanic fore arc of new caledonia southwest pacific geodynamic implications this paper deals with the tectonic events that result in the accretion of mafic terranes in the fore arc region and a close juxtaposition of ultramafic rocks low grade and high grade mafic terranes in many collisional orogens the example is taken from new caledonia where tectonic accretion subduction underplating and obduction of mafic terranes took place during the late eocene in an intra oceanic forearc setting the late eocene tectonic complex comprised three major terranes an overlying ultramafic mainly harzburgitic allochthon named the ophiolitic nappe an intermediate mafic mainly basaltic off scraped melange composed of kilometre scale slices of oceanic upper crust called the poya terrane parts of which have been metamorphosed into an eclogite blueschist facies complex the pouebo terrane and a lower continental basement formed by the norkolk ridge terranes based upon exhaustive sampling of the mafic terranes and field surveys our tectonic micropaleontologic and geochemical data reveal that poya and pouebo terranes rocks originally formed within one single campanian to late paleocene oceanic basin floored by tholeiitic basalt associated with some minor seamount related intraplate alkali basalt the tholeiitic basalt displays a continuous range of compositions spanning between undepleted and depleted end members the former being volumetrically predominant the overall geochemical and isotopic features indicate an origin from a prominently heterogeneous mantle source during the opening of a marginal basin the south loyalty basin which almost completely disappeared during eocene convergence the opening of this basin originally located to the east of the norfolk ridge was synchronous with that of tasman sea basin as a consequence of oceanward migration of the west dipping pacific subduction zone establishing the origin of the ultramafic ophiolitic nappe is beyond the scope of this paper however it appears to be genetically unrelated to the mafic poya and pouebo terranes although it was located in the late eocene fore arc the ophiolitic nappe and the corresponding oceanic lithosphere originated before the late cretaceous to the east of the south loyalty basin in a back arc setting or alternatively in a much older trapped basin for reasons that remain unclear a new east dipping subduction started in the eocene and consumed most of the south loyalty basin forming the intra oceanic loyalty arc due to a changing subduction regime underplating of the diahot terrane the mafic slices that now form the poya terrane were tectonically accreted in the loyalty fore arc region and remained under low pressure low temperature conditions possibly at the subsurface until the norfolk ridge reached the subduction zone diachronously this resulted in the final obduction of the fore arc area the two step obduction involved first the mafic complex forming the poya terrane and thereafter the lithospheric mantle that now forms the ophiolitic nappe in contrast pieces of the accretionnary complex were dragged down into the subduction zone underplated at depth ca 70 km and metamorphosed into high temperature eclogite to form the pouebo terrane metamorphics that display the same geochemical features as the poya terrane basalt a mid to late eocene syntectonic piggy back sedimentary basin the nepoui flysch basin mainly filled with mafic clastic material and shallow water carbonates that record the progressive uplift of the fore arc region due to the accretion and underplating of mafic ocean related and other material in contrast a slightly younger foreland basin located upon the norfolk ridge the priabonian bourail flysch basin received a massive input of detrital material derived from the norfolk ridge itself and a time increasing amount of mafic poya derived material that recorded the first step of obduction thereafter the bourail flysch was overthrust by the poya terrane and finally by the ophiolitic nappe at the same time buoyancy driven uplift and exhumation of the high pressure metamorphic complex occurred as a consequence of the diachronous blocking of the subduction zone finally for a short time a new subduction started along the west coast of new caledonia and generated small amounts of active margin related magmas these events have resulted in the close juxtaposition of unmetamorphosed and highly metamorphosed mafic and ultramafic terranes that may represent a good pre collision analogue of mafic ultramafic belts found in many collisional mountain ranges

prograde sulfide metamorphism in blueschist and eclogite new caledonia in new caledonia blueschist and eclogite preserve as inclusions in porphyroblastic minerals a record of sulfide present during prograde subduction processes sulfide inclusions in prograde garnet and lawsonite became chemically isolated from the matrix whereas sulfide minerals in the matrix continued to equilibrate with matrix fluids or grew later during retrogression cu fe sulfide mineral inclusions have been found across metamorphic grade within silicate defined metamorphic mineral zones spanning a crustal profile of 30 km bulk area scans of sulfide inclusions provide compositions that represent mixtures of the solid sulfide that were included as the host silicate minerals grew in general single sulfide inclusion compositions and aggregate sulfide assemblages are distinct from those of matrix phases high cu contents in sulfide inclusions are interpreted to be a consequence of fe lost from sulfide to growing garnet rather than the result of intrinsically high cu in the bulk rock the distribution of sulfide inclusion compositions across metamorphic grade considered together with the available thermodynamic data suggests that covellite nukundamite bearing inclusions in lawsonite high in both cu and s disappear at higher grades as these sulfide minerals are no longer stable similarly clustering near the ratio fe cu 1 1 may cease with increasing grade owing to the replacement of chalcopyrite intermediate solid solution iss by the denser assemblage pyrite pyrrhotite bornite digenite

investigation of the records of earthquake slip in carbonaceous materials from the taiwan chelungpu fault by means of infrared and raman spectroscopies this research was supported by a grant in aid for young scientists a from the japan ministry of education science sports and culture 23684039 2013

long term temperature records following the mw 7 9 wenchuan china earthquake are consistent with low friction this is the publisher s final pdf the published article is copyrighted by the geological society of america and can be found at http geology gsapubs org

linking active margin dynamics to overriding plate deformation synthesizing geophysical images with geological data from the norfolk basin the tonga kermadec subduction system in the southwest pacific preserves a series of crustal elements and sediments which have recorded subduction initiation rift and back arc basin formation the norfolk basin is the farthest landward of all back arc basins formed in the tonga kermadec region and may preserve the earliest record of subduction initiation regionally for the norfolk basin we use a set of multibeam bathymetry magnetic and seismic reflection and refraction data to constrain basin structure and the mode and timing of formation a structural interpretation reveals a two stage tectonic evolution 1 a convergent tectonic regime until 38 34 ma alternatively related to island arc collision or subduction initiation and 2 lithospheric extension after 34 ma these observations may help to constrain mechanical models that predict rapid extension following convergence of the overriding plate during subduction initiation or arc reversals

coseismic versus interseismic ground deformations fault rupture inversion and segmentation revealed by 2003 mw 6 8 chengkung earthquake in eastern taiwan 1 the 2003 chengkung earthquake mw 6 8 provided diagnostic evidence for a source model showing the deformation process of the seismogenic chihshang fault in eastern taiwan the aftershocks show a fault bend at a depth of 18 km coseismic ground displacements recorded by strong motion records allow us to deduce instant rupturing of this event our resulting model shows a fault length of 33 km and dip slip dominant rupture on fault plane deeper than 18 km estimated coseismic displacements constrain two fault planes one at 5 18 km depth dipping 60 e and 18 36 km depth dipping 45 e the uppermost fault plane of the chihshang fault 0 5 km did not break immediately after the main shock however it may have a major role in after slip and even interseismic ground deformation the taiyuan basin developed in the hanging wall is a geomorphic feature consistent with and adequately explained by coseismic ground displacements

modeling afterslip and aftershocks following the 1992 landers earthquake one way to probe the rheology of the lithosphere and fault zones is to analyze the temporal evolution of deformation following a large earthquake in such a case the lithosphere responds to a known stress change that can be assessed from earthquake slip models constrained from seismology and geodesy here we model the postseismic response of a fault zone that is assumed to obey a rate strengthening rheology where the frictional stress varies as a ln e e being the deformation rate and a 0 a rheological parameter the model is simple enough that these parameters can be estimated by inversion of postseismic geodetic data we apply this approach to the analysis of geodetic displacements following the m w 7 3 1992 landers earthquake the model adjusts well the measured displacements and implies a 0 47 0 53 mpa in addition we show that aftershocks and afterslip follow the same temporal evolution and that the spatiotemporal distribution of aftershocks is consistent with the idea that they are driven by reloading of the seismogenic zone resulting from frictional afterslip

interactions and triggering in a 3 d rate and state asperity model we present a 3 d continuous quasi dynamic rate and state model of multiple seismic asperities forced by surrounding aseismic creep and motivated by observations of coplanar multiplets our model allows to study the physics of interactions among a set of asperities first we show that the amount of interactions and clustering characterized by the omori law and interevent time distribution depends on how far the system is from a critical density of asperities which is related to the friction properties of the barriers separating the sources this threshold controls the ability of a population of asperities to destabilize the creeping barriers between them and therefore determines whether dynamic sequences including several asperities in the same event might occur in agreement with what is expected from observed magnitude frequency distributions therefore the concept of critical density of asperity provides a mechanical interpretation of statistical properties of seismicity as an illustration we used our numerical results in the specific case of parkfield in the period preceding the mw 6 2004 earthquake in order to infer the steady state friction parameter a b characterizing the creep of this part of the san andreas fault we estimate a value of a b that locally exceeds 0 001 which is in the upper range of what has already been proposed for the postseimic period of the mw 6 2004 parkfield earthquake