simultaneous rupture along two conjugate planes of the wharton basin earthquake analysis of broadband teleseismic data shows that the 18 june 2000 wharton basin earthquake a moment magnitude 7 8 intraplate event in the region of diffuse deformation separating the indian and australian plates consisted of two subevents that simultaneously ruptured two near conjugate planes this mode of rupture accommodates shortening by a mechanism different from that previously known elsewhere in the region the larger subevent occurred on a fossil fracture zone with a relatively high stress drop of about 20 megapascals showing that large stresses can accumulate in regions of distributed deformation

multi fault rupture and successive triggering during the 2012 mw 8 6 sumatra offshore earthquake 1 on april 11 2012 a mw 8 6 strike slip earthquake struck the northern sumatra offshore region and became the largest intraplate event ever recorded there preliminary study results show a remarkably complex rupture pattern on a fault system manifested by north south trending paleo transform faults and east west striking abyssal hill fabric to image the rupture pattern of the earthquake we back projected teleseismic p wave recordings observed at three regional seismic networks eu au and f net our results indicate that the earthquake ruptured on a conjugate fault system composed of two subparallel wnw ese trending faults and a nne ssw striking fault in between for a duration of at least 120 s the rupture started at the wnw end of the first wnw ese trending fault located at the east of the conjugate fault system and propagated toward ese it then jumped to the second nne ssw trending fault located west of the first fault and first extended sswward and 15 s later nneward after its end on the second fault the rupture jumped onto the third wnw ese trending fault and continued wnwward the static coulomb stress changes calculated from the rupture of the first and then the second faults based on simplified uniform slip models suggest that initiation of the rupture on the second fault could be statically and dynamically triggered by the first fault however the third fault was primarily dynamically triggered by s or even love waves radiated from the southern branch of the second fault

inversion for seismic slip rate history and distribution with stabilizing constraints application to the 1986 andreanof islands earthquake we develop and present a method of inverting seismograms including their absolute amplitudes to obtain the complete seismic slip time history and distribution using the method of linear programming a rectangular fault is discretized into cells and the source duration into time steps the inversion for the slip rate distribution on the fault as a function of time reduces to the solution of a system of linear equations the influence on the solution of constraining different source parameters such as the sign of the slip rate and the seismic moment is investigated it is found that the constraint of positiveness of slip rate and the constraint that the seismic moment determined from the solution should be close to that obtained from the centroid moment tensor cmt solution are very strong constraints and are essential to obtaining a physically reasonable solution since the inverse problem is unstable instead of presenting only one particular solution we examine several solutions equally well fitting the data for all practical purposes we find that when both constraints are applied the solution becomes quite stable the method is applied to a data set consisting of the vertical component of available digitally recorded teleseismic p waves at stations within a chosen distance window for the 1986 andreanof islands earthquake mw 8 0 the preferred solution is the one in which the slip rate is constrained to be positive and the moment is set to the cmt value the average rupture speed in the 90 km segment to the east of the hypocenter was 3 2 km s and in the 190 km section to the west was 2 km s the maximum slip in the area of large moment release to the west was 5 m and the maximum slip rate which occurs in the same place as the maximum slip was 6 5 m s the slip distribution on the fault shows a corrugated pattern with the long axis in the direction of the plate convergence rather than normal to the arc which was the slip vector direction for the earthquake with most of the slip occurring pn a region of the fault to the west of the rupture nucleation zone this region continued to slip for about 55 s the total source duration being about 80 s the results of this analysis suggest that the long term motion on this portion of the aleutian arc is indeed in the direction of plate convergence

exchange of carbon with biological apatite abstract the validity of using carbon isotopes in biological apatite from bone for dietary studies has been questioned because of diagenetic alterations and supposed exchange of carbon from the burial environment laboratory and natural experiments have been devised to test the integrity of carbon isotope ratios in biological apatite with respect to isotopic exchange of carbon with natural waters the laboratory experiment subjected a sample of bone to a synthetic groundwater whose carbon isotopic composition had been adjusted to 9750 analyses indicate that simple carbonates exchanged rapidly with the groundwater but that the actual biological apatite exchanged very little if any of its carbon even with 2 years exposure the natural experiment involved analysis of mammoth and mastodon teeth that had been submerged in sea water for 11 000 years with proper cleaning the original dietary signals were well preserved despite the long exposure to oceanic dissolved carbonate of much different isotopic composition these experiments suggest that properly cleaned biological apatite is an appropriate analytical phase for dietary studies on bone or teeth as old as 10 000 years

direct evidence of active deformation in the eastern indian oceanic plate conventional plate tectonics theory postulates that plates only deform on their boundaries to the contrary there is ample evidence of intraplate deformation in the equatorial indian ocean west of the ninetyeast aseismic ridge prior to this study no direct evidence of deforma tion east of the ninetyeast ridge was available we present the results of a multipurpose geo physical cruise showing that intraplate deformation also occurs in this area long at least 1000 km left lateral north south strike slip faults are active and reactivate fossil fracture zones this style of deformation is strikingly different from the east west folds and reverse faults that affect the region west of the ninetyeast ridge contrasting processes of convergence at the northern plate boundaries can account for the two styles of deformation west of the ninetyeast ridge there is a continent continent collision and east of the ridge oceanic lithosphere subducts along the sumatra trench the ninetyeast aseismic ridge therefore appears to be a mechanical border separating two distinct deformed areas

coseismic offsets due to the 11 april 2012 indian ocean earthquakes mw 8 6 and 8 2 derived from gps measurements 1 the 11 april 2012 earthquake mw 8 6 in the indian ocean about 100 km west off the sumatra subduction zone is the largest intraplate strike slip earthquake in the known history two hours later it triggered another great earthquake of mw 8 2 in its vicinity the earthquakes reflect the internal deformation of the diffused plate boundary between india and australia caused by the differential plate motion between them the slip occurred on conjugate planes and the presence of some of them has been reported from the swath bathymetry and satellite magnetic anomalies we estimate coseismic offsets due to these earthquakes at continuous gps sites in the andaman nicobar region and at other international gnss service igs sites around the earthquakes source region the sites on the andaman islands which are about 900 1200 km to the north of the earthquake epicenters experienced predominantly southward coseismic offset of up to 3 cm the nearest site campbell bay on great nicobar island about 500 km to the north of the earthquake documented an ese offset of about 4 cm the coseismic offsets are consistent with the finite fault slip models derived from back projection of the seismic waves recorded by the global networks

the 2005 and 2010 earthquakes on the sumatra andaman trench evidence for post 2004 megathrust intraplate rejuvenation great earthquakes on oblique subduction zones accommodate slip on strike slip faults on the overriding and subducting plates leading to increased intraplate seismicity after the 2004 sumatra earthquake there was an increase in activity in the wharton basin wb which is considered to be part of a diffuse plate boundary here the intraplate deformation occurs in response to northwest southeast directed compression as opposed to the north northeast south southwest directed plate motion along the sumatra andaman subduction zone earthquakes here mostly occur by left lateral strike slip on north south n s trending fossil fractures although ruptures on east west planes are not uncommon here we discuss the 24 july 2005 m w 7 2 and the 12 june 2010 m w 7 5 earthquakes both of which were left lateral strike slip events sourced in the northern wb our source models for these events based on teleseismic waveform inversion favor slip on the n s fossil fracture systems consistent with previous studies in the wb although the former sourced at similar to 16 km depth was not tsunamigenic the latter similar to 34 km triggered a small tsunami possibly due to its oblique slip at similar to 5 km depth we use conceptual models of plate deformation to suggest that both these events have resulted from post 2004 redistribution of stresses and rejuvenation of intraslab fracture systems within the wb an actively deforming oceanic intraplate region

stability of earthquake moment tensor inversions effect of the double couple constraint abstract we show that spurious large non double couple components can be obtained in inversions for the full deviatoric moment tensor for shallow crustal earthquakes due to inaccurate earth models the traditional best double couple solution does not in general provide an optimal estimate of a double couple mechanism and is only reliable when the non double couple component of the full deviatoric solution is small the inverse problem for the moment tensors of the 1998 antarctic plate and 2000 wharton basin strike slip earthquakes is shown in each case to have two well fitting minima in the misfit function of pure double couple solutions such pairs of solutions are most likely to exist for earthquakes which are close either to vertical strike slip or to dip slip on a fault plane dipping at 45 it is shown theoretically that these pairs of solutions arise from the combination of the pure double couple constraint and the instability of two elements of the moment tensor no significant non double couple component is found for the shallow thrusting 1996 biak indonesia earthquake

deep seismic reflection images of the wharton basin oceanic crust and uppermost mantle offshore northern sumatra relation with active and past deformation 1 we present deep seismic reflection images along two profiles collected in 2006 in the wharton basin offshore northern sumatra the main profile is located subparallel to the sumatran trench at a distance of 32 66 km faulting of the entire sedimentary section strike slip deformation sometimes accompanied by a dip slip component is imaged over two fracture zones of the extinct wharton spreading center that prior studies have shown to be reactivated as left lateral faults the western fracture zone is associated with a wide region of strong basement topography a difference in crustal thickness of 1 5 km and an age offset of 9 ma the epicenters of the 11 april 2012 mw 8 6 great strike slip earthquake its mw 7 2 foreshock and mw 8 2 aftershock align along this major structure 100 km south of the profile intersection our high quality long offset seismic reflection data also reveal bright dipping reflections extending down to a maximum of 24 km into the oceanic mantle 37 km below sea level apparent dips are mostly 25 35 corresponding to 30 55 along either n s to nne ssw or e w to wnw ese directions which encompass the directions of plate fabric and nodal planes of the mw 8 6 event we suggest that these enigmatic reflections arise from presently inactive dip slip fault planes reaching for the deepest ones to the base of the brittle layer possible origins include extension related to plate bending or an episode of now inactive thrust type deformation reactivating paleonormal faults similar to that taking place in the central indian basin

evidence of active backthrusting at the ne margin of mentawai islands sw sumatra summary the indo australian plate subducts obliquely beneath the sunda plate leading to a slip partitioning into pure thrust and strike slip motion just in the last 5 yr three pure thrust earthquakes of mw 8 4 have occurred along this subduction interface the great sumatra fault traversing the sumatra continental block takes up a significant part of the strike slip motion but the mentawai fault bounding the ne margin of mentawai islands has been suggested to accommodate a part of the strike slip motion although the great sumatra fault is active no seismicity has been observed along the mentawai fault using a combination of high resolution seismic reflection and bathymetry data here we show that the mentawai fault seems to be characterized by active sw dipping backthrusts the presence of recent steeply dipping thrust earthquakes suggests that these faults should be active combined with results from north in 2004 earthquake region and south of this study area our results suggest that backthrusting should play an important role in forearc evolution sw of sumatra we also observed several mass wasting sites at ne margin of the mentawai islands which could be erosional features or landslides triggered by earthquake activities localized uplift along the steeply dipping backthrusts at the ne margin of mentawai islands in the fully locked region could pose serious seismic and tsunami risks to the sw coast of sumatra in the future

strike slip intraplate earthquakes in the western philippine sea plate abstract on 26 april 2010 a strike slip earthquake mw 6 5 occurred in the western philippine sea plate we deployed 14 ocean bottom seismometers to record the corresponding aftershocks to acquire information regarding these intraplate events our results show that the aftershocks were located along two linear features that intersect with an angle of approximately 120 and are considered a conjugate fault set the p axis of the mainshock focal mechanism is consistent with the compressive stress direction induced by the arc continent collision occurring in eastern taiwan the pre existing oceanic fracture zones and tectonic fabrics do not appear to be reactivated based on the distinct rupture directions determined from the relocated aftershocks however the abrupt halt of the aftershocks at the border of the fracture zone suggests that pre existing weak zones could act as a barrier to rupture propagation moreover most large earthquakes have occurred near fracture zones indicating that the pre existing weakness may favor the generation of earthquakes compared to the other portion of the oceanic plate due to the relatively low rock strength of this zone

site specific ground motion simulation and seismic response analysis at the proposed bridge sites within the city of addis ababa ethiopia in this study synthetic ground motion time histories have been generated at rock sites simulating earthquakes of moment magnitudes 6 8 6 0 and 5 2 and epicentral distances of 25 50 80 120 and 200 km applying these rock time histories as input motions at the base of the soil columns determined using surface seismics a one dimensional equivalent linear analysis was used to propagate the input motions through the soil columns to determine the ground motions at the ground surface the goal is to determine the seismic responses of the sites chosen for bridge construction in the framework of the addis ababa city ring road project the computed acceleration time histories response spectra and amplification spectra will be most useful for design engineers

sudden productivity collapse associated with the triassic jurassic boundary mass extinction the end triassic mass extinction is one of the five most catastrophic in phanerozoic earth history here we report carbon isotope evidence of a pronounced productivity collapse at the boundary coincident with a sudden extinction among marine plankton from stratigraphic sections on the queen charlotte islands british columbia canada this signal is similar to though smaller than the carbon isotope excursions associated with the permian triassic and cretaceous tertiary events

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

en echelon and orthogonal fault ruptures of the 11 april 2012 great intraplate earthquakes the magnitude 8 7 earthquake that occurred off the coast of the sumatra subduction zone on 11 april 2012 is shown to have had an extraordinarily complex four fault rupture these great ruptures represent large lithospheric deformation that may eventually lead to a localized boundary between the indian and australian plates on 11 april 2012 two of the largest strike slip earthquakes ever recorded at magnitudes of 8 7 and 8 2 occurred in the northeastern indian ocean a few hundred kilometres off the coast of sumatra three groups now report the analysis of seismic data from the days and months before and after these events as well as the events themselves matthias delescluse and co authors show that these earthquakes are part of the ongoing boost of intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes they conclude that the australian plate driven by slab pull forces at the sunda trench is gradually detaching from the indian plate han yue and colleagues show that the 11 april event involved a complex four fault rupture lasting several minutes followed two hours later by a magnitude 8 2 aftershock these great ruptures on a lattice of strike slip faults that extends through the crust and into the upper mantle represent large lithospheric deformation that may eventually create a localized boundary between the indian and australian plates fred pollitz and colleagues show that in the six days following 11 april the global rate of remote earthquakes with magnitudes greater than 5 5 increased nearly fivefold and events up to magnitude 7 seem to have been triggered the unprecedented delayed triggering power of this earthquake may arise from its strike slip source geometry or because it struck at a time of an unusually low global earthquake rate and increased the number of nucleation sites that were very close to failure the indo australian plate is undergoing distributed internal deformation caused by the lateral transition along its northern boundary from an environment of continental collision to an island arc subduction zone1 2 on 11 april 2012 one of the largest strike slip earthquakes ever recorded seismic moment magnitude mw 8 7 occurred about 100 200 kilometres southwest of the sumatra subduction zone occurrence of great intraplate strike slip faulting located seaward of a subduction zone is unusual it results from northwest southeast compression within the plate caused by the india eurasia continental collision to the northwest together with northeast southwest extension associated with slab pull stresses as the plate underthrusts sumatra to the northeast here we use seismic wave analyses to reveal that the 11 april 2012 event had an extraordinarily complex four fault rupture lasting about 160 seconds and was followed approximately two hours later by a great mw 8 2 aftershock the mainshock rupture initially expanded bilaterally with large slip 20 30 metres on a right lateral strike slip fault trending west northwest to east southeast wnw ese and then bilateral rupture was triggered on an orthogonal left lateral strike slip fault trending north northeast to south southwest nne ssw that crosses the first fault this was followed by westward rupture on a second wnw ese strike slip fault offset about 150 kilometres towards the southwest from the first fault finally rupture was triggered on another en echelon wnw ese fault about 330 kilometres west of the epicentre crossing the ninetyeast ridge the great aftershock with an epicentre located 185 kilometres to the ssw of the mainshock epicentre ruptured bilaterally on a nne ssw fault the complex faulting limits our resolution of the slip distribution these great ruptures on a lattice of strike slip faults that extend through the crust and a further 30 40 kilometres into the upper mantle represent large lithospheric deformation that may eventually lead to a localized boundary between the indian and australian plates

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

the energy release in earthquakes energy calculations are generally made through an empirical application of the familiar gutenberg richter energy magnitude relationships the precise physical significance of these relationships is somewhat uncertain we make use here of the recent improvements in knowledge about the earthquake source to place energy measurements on a sounder physical basis for a simple trapezoidal far field displacement source time function with a ratio x of rise time to total duration t 0 the seismic energy e is proportional to 1 x 1 x 2 m 0 2 t 0 3 where m 0 is seismic moment as long as x is greater than 0 1 or so the effect of rise time is not important the dynamic energies thus calculated for shallow events are in reasonable agreement with the estimate e 5 10 5 m 0 based on elastostatic considerations deep events despite their possibly different seismological character yield dynamic energies which are compatible with a static prediction similar to that for shallow events studies of strong motion velocity traces obtained near the sources of the 1971 san fernando 1966 parkfield and 1979 imperial valley earthquakes suggest that even in the distance range of 1 to 5 km most of the radiated energy is below 1 to 2 hz in frequency far field energy determinations using long period wwssn instruments are probably not in gross error despite their band limited nature the strong motion record for the intermediate depth bucharest earthquake of 1977 also suggests little teleseismic energy outside the pass band of a long period wwssn instrument

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

alteration of enamel carbonate environments during fossilization an understanding of enamel diagenesis is necessary to ensure sound isotopic palaeodietary and palaeoenvironmental reconstructions although carbon isotope signals of browsing and grazing herbivores remain distinct in enamel even after millions of years subtle alteration of isotopic signatures does occur to better understand this change we analysed modern and fossil enamel from a number of south african sites using fourier transform infra red spectroscopy our results indicate that while there is little evidence of increased crystallinity in fossil enamel there is a small but significant change in the proportion of carbonate ions occupying hydroxyl and phosphate sites this seems to occur early in the process of fossilization after which there is no noticeable change it is also important to note that the degree of alteration varies significantly within and between sites we suggest that this change results from one or some combination of three mechanisms exogenous carbonate incorporation endogenous carbonate loss and endogenous carbonate reorganization determining which mechanism s contribute to this alteration is important because all three are likely to affect biogenic carbon isotope ratios differently ftir spectroscopy promises to increase our knowledge of diagenesis and in so doing should improve our palaeodietary and palaeoenvironmental reconstructions

a rare great earthquake on an oceanic fossil fracture zone first motion solution found in this study and has a strike consistent with the fracture zone north of the bend the southern fault plane with strike 178 d ip 54 and rake 65 has a strike consistent with the portion of the fracture zone to the south of the bend and has a dip which can be explained by the style of deformation that the region is undergoing the centroid moment tensor solution of the broad band model is calculated and found to be consistent with the region of low misfit in mantle wave solution space the broad band solution has a moment of 1 53 10 21 nm mw 8 1 again consistent with the mantle wave data slip propagated bilaterally with an approximate rupture velocity of 3k ms 1 80 per cent of local shear wave speed the rupture front is less well resolved to the south of the epicentre than to the north the majority 75 per cent of moment originated from slip on the northern fault the broad band data requires significant slip below the oceanic moho with as much as 70 per cent of moment due to slip in the brittle uppermost mantle in the preferred model

tectonic interpretation of aftershock relocations in eastern papua new guinea using teleseismic data and the arrival pattern method summary the arrival pattern ap method and teleseismic data have been used to relocate aftershocks following three major mw 7 8 interplate earthquakes that occurred in eastern papua new guinea in 2000 november the first event was an mw 8 0 strike slip earthquake that ruptured the weitin fault over a length of 100 km no aftershocks were located in the upper 15 km suggesting that the accumulated strain was fully released in this event the two subsequent mw 7 8 thrust events occurred on the new britain trench wadati benioff zones dipping 20 define the locations of the thrust events at 152 e and 153 e on fault planes with strikes of 75 and 65 respectively the plot of aftershocks defines a complex seismic zone beneath new ireland where events have occurred in the overriding pacific and south bismarck plates above the deeper zone of subduction of the solomon sea plate these events cluster in a broad zone to the northeast of the weitin fault rather than defining a linear feature that might have been expected following a near vertical major strike slip event

the 2012 mw 8 6 wharton basin sequence a cascade of great earthquakes generated by near orthogonal young oceanic mantle faults we improve constraints on the slip distribution and geometry of faults involved in the complex multisegment mw 8 6 april 2012 wharton basin earthquake sequence by joint inversion of high rate gps data from the sumatran gps array sugar teleseismic observations source time functions from broadband surface waves and far field static gps displacements this sequence occurred under the indian ocean 400 km offshore sumatra the events are extraordinary for their unprecedented rupture of multiple cross faults deep slip large strike slip magnitude and potential role in the formation of a discrete plate boundary between the indian and australian plates the sugar recorded static displacements of up to 22 cm along with time varying arrivals from the complex faulting which indicate that the majority of moment release was on young wnw trending right lateral faults counter to initial expectations that an old lithospheric nne trending fracture zone played the primary role the new faults are optimally oriented to accommodate the present day stress field not only was the greatest moment released on the younger faults but it was these that sustained very deep slip and high stress drop 20 mpa the rupture may have extended to depths of up to 60 km suggesting that the oceanic lithosphere in the northern wharton basin may be cold and strong enough to sustain brittle failure at such depths alternatively the rupture may have occurred with an alternative weakening mechanism such as thermal runaway

the plate tectonic approximation plate nonrigidity diffuse plate boundaries and global plate reconstructions the central assumption of plate tectonics that plate interiors are rigid remains a useful but uncertain approximation strain rates of stable plate interiors are bounded between 10 i12 10 i11 year i1 and 4 10 i10 year i1 the narrowness of all plate boundaries the other main assumption of plate tectonics as originally conceived is contradicted by many observations both in the continents and in the oceans some diffuse plate boundaries in both continents and oceans exceed dimensions of 1000 km on a side diffuse plate boundaries cover 15 of earth s surface the maximum speed of relative plate motion across any one diffuse plate boundary ranges from 2t o 15 mm year which is faster than some upper bounds on intraplate motion across stable plate interiors 2m m year i1 strain rates in diffuse plate boundaries can be as high as 10 i8 year i1 25 times higher than the upper bound on strain rates of stable plate interiors but 600 times lower than the lowest strain rates across typical narrow plate boundaries the poles of rotation of the plates flanking a diffuse oceanic plate boundary tend to be located in the diffuse boundary which is a consequence of the strong coupling across the boundary

fault interactions and triggering during the 10 january 2012 mw 7 2 sumatra earthquake the 10 january 2012 mw 7 2 sumatra earthquake in the wharton basin occurred 3 months before the great mw 8 6 and mw 8 2 earthquakes in the same region which had complex ruptures and are the largest strike slip earthquakes ever recorded teleseismic p wave back projection of the mw 7 2 earthquake images a unilateral rupture lasting 40 s without observable frequency dependency low frequency 0 05 0 3 hz high frequency 0 3 1 hz in addition to radiation bursts during the mw 7 2 main shock coherent energy releases from 50 to 75 s and from 100 to 125 s are observed about 143 km northeast of the main shock rupture and landward of the trench analysis of globally recorded p waves in both 0 02 0 05 hz velocity records and 1 5 hz stacked envelope functions confirms the presence of coherent sources during the time windows the observed energy bursts are likely to be large early aftershocks occurring on or near the subduction interface both dynamic and static triggering could have induced these early aftershocks as they initiated after the surface wave passed by and the coulomb stress perturbations from the mw 7 2 main shock promote earthquakes in the observed locations the earthquake sequence is a clear example of a seaward intraplate strike slip earthquake triggering landward intraplate earthquakes in the same region in contrast to previously reported normal reverse or reverse normal interactions at subduction zones

spacing of faults at the scale of the lithosphere and localization instability 2 application to the central indian basin 1 tectonic deformation in the central indian basin cib is organized at two spatial scales long wavelength 200 km undulations of the basement and regularly spaced faults the fault spacing of order 7 11 km is too short to be explained by lithospheric buckling we show that the localization instability derived by montesi and zuber 2003 provides an explanation for the fault spacing in the cib localization describes how deformation focuses on narrow zones analogous to faults the localization instability predicts that localized shear zones form a regular pattern with a characteristic spacing as they develop the theoretical fault spacing is proportional to the depth to which localization occurs it also depends on the strength profile and on the effective stress exponent ne which is a measure of localization efficiency in the brittle crust and upper mantle the fault spacing in the cib can be matched by ne 300 if the faults reach the depth of the brittle ductile transition bdt around 40 km or ne 100 if the faults do not penetrate below 10 km these values of ne are compatible with laboratory data on frictional velocity weakening many faults in the cib were formed during seafloor spreading the preexisting faults near target locations separated by the wavelength of the localization instability were preferentially reactivated during the current episode of compressive tectonics the long wavelength undulations may result from the interaction between buckling and localization index terms 8010 structural geology fractures and faults 8020 structural geology mechanics 8159 tectonophysics evolution of the earth rheology crust and lithosphere keywords faults central indian basin fault spacing folds strength envelope diffuse plate boundary

rupture characteristics of the 2003 mw 7 6 mid indian ocean earthquake implications for seismic properties of young oceanic lithosphere 1 analysis of broadband seismograms from the 15 july 2003 large earthquake m 7 6 in the central indian ocean reveals an unusual source process the source duration of longer than a minute is more than twice as long as expected from earthquake scaling relations yet 80 of the moment release occurred in two energetic asperities near the end of the rupture these two asperities were located in lithosphere with an age of 7 ma or greater a previous study has suggested that strike slip earthquakes in oceanic lithosphere having much longer than expected source durations also have a slow dissipative rupture process characterized by low radiated seismic energy and therefore low apparent stress we find no evidence for a slow rupture process to the 2003 earthquake instead the long duration appears to be due only to nucleation close to the actively spreading carlsberg ridge in lithosphere younger than 7 ma younger oceanic lithosphere may be able to generate small to moderate earthquakes but be unable to sustain slip in a large event due to steady release of strain in aseismic creep events large strike slip earthquakes within oceanic lithosphere may occur only in the central portions of long transform faults or in intraplate regions rupturing energetic asperities like those that failed in the mid indian ocean earthquake and leading to the observation that oceanic strike slip earthquakes have the largest apparent stresses among the global population of shallow earthquakes

rupture of the indian slab in the 2011 mw 6 9 sikkim himalaya earthquake and its tectonic implications unlike the other himalayan plate boundary segments the eastern nepal to bhutan himalayan region is not known to have generated prominent shallow thrust faulting earthquakes typical of the ongoing convergence this region features strike slip earthquakes over the depth ranges of 40 120 km indicating intraslab deformation here we present for the first time a slip distribution model for the largest recorded intraslab strike slip earthquake in this region the mw 6 9 sikkim event that occurred on 18 september 2011 relying on kinematic source process modeling our results indicate a ne sw trending steeply dipping sinistral source zone within the underthrusting indian slab the rupture propagated radially with a low rupture velocity of 1 7 km s breaking a large asperity of 20 a 20 km 2 with a maximum slip of 1 6 m the rupture nucleated at a depth of 45 km and reached upper mantle depths the computed coseismic stress drop value is 13 6 mpa we suggest that most of the aftershocks occurred on the conjugate plane possibly due to stress triggering stress inversion of focal mechanisms indicates a transpressive stress regime throughout the crust and pure strike slip regime in the upper mantle we observed a unimodal distribution of earthquakes beneath the higher himalaya this indicates a strong brittle indian slab and unravels a scenario of an eventual breakup of the lithosphere the key trigger might be variation in the convergence rates along the himalayan arc 2019 american geophysical union all rights reserved

the 2014 mw 6 1 bay of bengal indian ocean earthquake a possible association with the 85 e ridge oceanic intraplate earthquakes are known to occur either on active ridge transform structures or by reactivation of their inactive counterparts generally referred to as fossil ridges or transforms the indian ocean one of the most active oceanic intraplate regions has generated large earthquakes associated with both these types of structures the moderate earthquake that occurred on 21 may 2014 m w 6 1 in the northern bay of bengal followed an alternate mechanism as it showed no clear association either with active or extinct ridge transform structures its focal depth of 50 km is uncommon but not improbable given the similar to 90 ma age of the ocean floor with 12 km thick overlying sediments no tectonic features have been mapped in the near vicinity of its epicenter the closest being the 85 degrees e ridge located similar to 100 km to its west hitherto regarded as seismically inactive the few earthquakes that have occurred here in the past are clustered around its southern or northern limits and a few are located midway at around 10 degrees n the 2014 earthquake sourced close to the northern cluster seems to be associated with a northwest southeast oriented fracture located on the eastern flanks of the 85 degrees e ridge if this causal association is possible we believe that reactivation of fossil hotspot trails could be considered as another mechanism for oceanic intraplate seismicity

reassessing the complexity of the rupture of the 2010 jia shian earthquake mw 6 2 in southwestern taiwan by inverting jointly teleseismic strong motion and cgps data abstract a new interpretation is proposed for the 2010 jia shian earthquake mw 6 2 which occurred on march 4 2010 in southwestern taiwan among the few tens of cgps stations which recorded the mainshock at a distance less than 50 km we identified a few stations displaying horizontal displacements in disagreement with the dominant pattern of horizontal coseismic motion based on this observation we find that a secondary rupture plane explains these peculiar motions and helps improving the modeling of the overall set of cgps stations we also model the teleseismic and strong motion records to refine the rupture model finally we obtain the slip distribution on a two fault model by the joint inversion of all three datasets cgps teleseismic and strong motion the main fault plane is consistent with previous studies it corresponds to a n311 e fault dipping 33 to the ne with left lateral reverse oblique slip likely related to the chishan transfer fault zone ctfz we find that the earthquake started with a sharp slip patch localized at the hypocenter the secondary rupture plane is a n20 e thrust fault related to the lungchuan anticline faulting on the main nw se plane during the jia shian earthquake and stress inversions from previous studies both suggest a direction of maximum horizontal compression oriented ne sw in the area of the earthquake very different from the dominant nw se compression direction in taiwan we propose that such a variation can be related to a stress deviation in the immediate vicinity of the ctfz in a similar way as observed along the san andreas fault in california on the other hand rupture on the secondary fault plane associated with the lungchuan anticline appears to be compatible with the dominant compression in taiwan

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

the 1987 1992 gulf of alaska earthquakes abstract we present a study of the 1987 1992 gulf of alaska earthquake sequence using relocated seismicity data together with body wave analysis of selected larger events most of the sequence is located on a n s trending fault directly south of the yakataga seismic gap and consists of four main events of mw 7 2 7 8 7 7 and 6 8 and associated aftershocks the first earthquake is of left lateral strike slip type on an ene wsw trending fault the second event is a right lateral strike slip earthquake on the n s trending fault the fault plane of the third strike slip event was identified as an ene wsw trending fault located to the south of that for the first event in a previous study using body wave analysis we show that though the body wave study cannot unambiguously identify the fault plane the temporal development of the seismicity together with the pattern of aftershock distribution on the conjugate fault suggests that this event also occurred on the n s trending fault and is of right lateral type the seismicity on the conjugate fault is interpreted as being triggered by the increase of the shear stress in the direction of the normal to the fault plane due to the main shock the occurrence of the fourth main shock a right lateral strike slip event in 1992 which itself can be considered an aftershock of the 1987 1988 sequence with epicentres distributed along a n s trending fault favours this conclusion the first three events of the sequence have been described in earlier studies as having too short a rupture length for their seismic moment if the rupture lengths inferred from the aftershock zones in this study are used we find that this is not the case the events in the 1987 1992 sequence lie along magnetic anomaly 13 and related conjugate fracture zones indicating that the oceanic crust is rupturing along pre existing zones of weakness in response to plate boundary stresses at the southern end the seismic activity terminates near a seamount which rises 1 km above an otherwise relatively low relief ocean floor and close to a fracture zone perpendicular to the n s trend of the earthquake sequence suggesting that the n s striking rupture along the n s trending fault is terminated here by a barrier at the northern end the sequence terminates at the alaska trench near the yakataga seismic gap where there is a right lateral offset in the bathymetry along the transition fault this offset also being visible on the gravity map of the region thus this offset has the same right lateral sense as the n s trending strike slip fault planes of three of the main shocks and suggests that though there was no significant seismic activity in this region of the gulf of alaska since 1964 faulting here has been active in the past

spatial relation between main earthquake slip and its aftershock distribution 1 we examine where aftershocks occur relative to the spatial distribution of the main shock slip using data from several recent large earthquakes no universal relation between high and low moment regions and high or low aftershock occurrence or vice versa is found we generally find that few and usually the smaller aftershocks occur in the high slip regions of the fault a notable exception to this being the great 1996 biak indonesia subduction zone earthquake in all cases aftershocks occur on favorably oriented planes of weakness in regions of increased postseismic stress generally they are clustered at both ends of faults but examples where aftershocks occur only at one end or where there is no clustering at the ends are found aftershock clusters are also found at the edge of unbroken barriers and regions of rapid transition from high to low slip within the main fault area we identify examples of geometrical and inhomogeneous barriers and sharp and dull stress concentrations rupture in the main shock is generally found to nucleate in the region of low slip or at the edge of high slip regions the 1996 biak earthquake again being the only exception nucleating in a very high slip region off fault aftershocks are found for all earthquakes in this study and they sometimes rupture the nodal plane conjugate to the main shock fault plane

the great march 25 1998 antarctic plate earthquake moment tensor and rupture history we use broadband body and mantle wave data to study the 1998 antarctic intraplate earthquake the centroid moment tensor cmt has a large non double couple component there exist two pure double couple constrained solutions that fit the data almost equally well the frequent practice of taking the best double couple gives a far from optimal solution we use p and sh body waves to determine the rupture parameters of the first and larger of the two observed subevents the best rupture plane with strike 96 dip 69 and rake 18 is compatible with only one of the two cmt solutions strike 96 dip 64 rake 23 centroid location 63 1 s 148 4 e 10 km depth centroid time 0313 02 ut and m0 1 3 1021 n m mw 8 0 the first subevent is a simple primarily westward propagating 140 km rupture of 45 s duration with average velocity 3 km s 1 it has a seismic moment of 1 2 1021 n m mw 8 0 with 75 of its moment released between 10 and 27 s and a stress drop of 240 bars the rupture is physically bounded by two fracture zones at 147 5 e and 150 e the second subevent lasted from 70 to 90 s on a fault extending from 210 to 270 km west of the epicenter with a moment of 0 3 0 6 1021 n m mw 7 6 7 8 this is a spectacular example of dynamic stress triggering over a 100 km separation distance with a time delay of 40 s the complex pattern of aftershocks is primarily controlled by preexisting fracture zones on the ocean floor

diagenesis of bones from eland s bay cave abstract archaeological bone specimens have been shown in a number of studies to have increased mineral crystallinity when measured both by xrd and ir spectrometry in this study we investigated the relative dating potential of ir crystallinity measurements based on the splitting factor or sf on a sample of 54 specimens from the holocene sequence at eland s bay cave south africa in addition to sf c and n measurements were obtained using a carlo erba elemental analyser results of the study indicate that i a reasonably good correlation between sf and time exists in bones under 20 000 years bp but that the increase in sf levels off after this period and ii correlations between diagenetic indicators such as sf c and n are better than those between any indicator and time an excellent correlation r2 0 81 was obtained between sf residing in the inorganic phase and n residing in the organic phase suggesting that diagenesis of the two phases of bone are linked implications of the data for monitoring stratigraphic anomalies at archaeological sites are discussed

interseismic strain and rotation rates in the northeast mojave domain eastern california 1 the northeast mojave domain a type locality for bookshelf faulting is a region of east striking left lateral faults in the northeast corner of the mojave block a block otherwise dominated by n40 w striking right lateral faults paleomagnetic evidence suggests that blocks within the domain have rotated clockwise about a vertical axis as much as 60 since 12 8 ma schermer et al 1996 in 1994 and again in 2002 the u s geological survey surveyed an array of 14 geodetic monuments distributed across the northeast mojave domain the 2002 survey results were adjusted to remove the coseismic offsets imposed by the nearby hector mine earthquake 16 october 1999 mw 7 1 the adjusted deformation across the array appears to be uniform and can be approximated by the principal strain rates e1 28 9 9 1 n77 2 w 4 8 and e2 48 2 8 9 n12 8 e 4 8 nstrain yr 1 extension reckoned positive and quoted uncertainties are standard deviations that strain accumulation could be released by slip on faults striking n32 w but not by bookshelf faulting on the east striking faults alone the vertical axis rotation rate of the northeast mojave domain as a whole relative to fixed north america is 71 0 6 4 nrad yr 1 4 07 0 37 myr 1 clockwise about twice the maximum tensor shear strain rate the observed rotation rate acting over 12 8 myr would produce a clockwise rotation of 52 1 4 7 exclusive of possible coseismic rotations that rotation is in rough agreement with the paleomagnetic rotation accumulated in the individual fault blocks within the northeast mojave domain since 12 8 ma

source parameters of selected earthquakes on the central and western margin of afar abstract spectral analysis of 196 short period and long period vertical and horizontal component seismograms from ten earthquakes on the central and western margin of afar is performed to determine source parameters and discuss their tectonic implications for the earthquakes in the regions under study the stress drop varies from 2 to 31 bar while the seismic moment varies from 2 10 24 to 154 10 24 dyn cm in general low stress drop values are obtained indicating the presence of softer material especially for central afar at a shallower depth it is observed that there is an increase in stress drop with the increase in moment magnitude which in turn is obtained from the calculated average seismic moment energy estimates show that the mode of energy release is different in the two regions indicating that different tectonic processes are involved in the two regions the slip rate obtained for the serdo area is of the order of 1 6 cm yr and is in close agreement with the spreading rate already obtained for central afar spreading rates obtained earlier and that of the present study show a low spreading rate for afar and neighbouring regions as compared to those of the other regions of the world

the 2 march 2016 wharton basin mw 7 8 earthquake high stress drop north south strike slip rupture in the diffuse oceanic deformation zone between the indian and australian plates the diffuse deformation zone between the indian and australian plates has hosted numerous major and great earthquakes during the seismological record including the 11 april 2012 m w 8 6 event the largest recorded intraplate earthquake on 2 march 2016 an m w 7 8 strike slip faulting earthquake occurred in the northwestern wharton basin in a region bracketed by north south trending fracture zones with no previously recorded large event nearby despite the large magnitude only minor source finiteness is evident in aftershock locations or resolvable from seismic wave processing including high frequency p wave backprojections and love wave directivity analysis our analyses indicate that the event ruptured bilaterally on a north south trending fault over a length of up to 70 km with rupture speed of 2 km s and a total duration of 35 s the estimated stress drop 20 mpa is high comparable to estimates for other large events in this broad intraplate oceanic deformation zone

a unified gps based earthquake catalog for the sumatran plate boundary between 2002 and 2013 we have compiled the first self consistent gps based earthquake catalog for the sumatran plate boundary using continuous daily position time series from the sumatran gps array sugar we document 30 earthquakes which occurred within or outside the sugar network from august 2002 through the end of 2013 and we provide estimates of both vertical and horizontal coseismic offsets associated with 1 m9 2 3 m8 6 m7 19 m6 and 1 m5 9 earthquakes as well as postseismic decay amplitudes and times associated with 9 m 7 earthquakes and 1 m6 7 earthquake for most of the previously studied earthquakes our geodetic catalog provides more complete coseismic displacements than those published showing consistent patterns of motion across a large range of distances for many of the moderate to large earthquakes we publish their coseismic displacements for the first time providing new constraints on their locations and slip distributions for the postseismic time series we have tackled the challenge of separating the signals for individual events from the overlapping effects of many other earthquakes as a result we have obtained either new or much longer time series than previously published based on our long time series we find logarithmic decay times ranging from several days to more than 20 years and sometimes a second decay time is needed suggesting that when studying large to great sumatran earthquakes we need to consider multiple postseismic mechanisms our geodetic catalog provides rich spatial and temporal sumatran earthquake cycle information for future studies of the physics and dynamics of the sumatran plate boundary

fault identification for buried strike slip earthquakes using insar the 1994 and 2004 al hoceima morocco earthquakes summary the 1994 m w 6 0 and 2004 m w 6 5 al hoceima earthquakes are the largest to have occurred in morocco for 100 yr and give valuable insight into the poorly understood tectonics of the area bodywave modelling indicates the earthquakes occurred on near vertical strike slip faults with the nodal planes oriented nw se and ne sw distinguishing between the primary fault plane and auxiliary planes using either geodetic or seismic data is difficult due to the spatial symmetry in deformation fields and radiation pattern of moderately sized buried strikeslip earthquakes preliminary studies using aftershock locations and surface observations have been unable to identify the orientation of the primary fault plane for either earthquake conclusively we use radar interferometry and aftershock relocation of the earthquake sequence to resolve the ambiguity for the 2004 earthquake inverting the interferograms for a uniform slip model based either of the two potential nodal planes results in similar misfits to the data however the ne sw best fit fault plane has an unrealistically high fault slip to length ratio and we conclude the nw se striking nodal plane is the primary fault plane and slip was right lateral we carry out tests on synthetic data for a buried strike slip earthquake in which the orientation of the fault plane is known a priori independent of geometry missing data and correlated noise models produced assuming the auxiliary plane to be the fault plane have very high fault slip to length ratios the 1994 earthquake had a smaller magnitude and comparisons of model misfits and slip to length ratios do not conclusively indicate which of the nodal planes is the primary fault plane nonetheless the insar data provides valuable information by improving the accuracy of the earthquake location by an order of magnitude we carry out a multiple event relocation of the entire earthquake sequence including aftershocks making use of the absolute locations for the 1994 and 2004 main shocks from our insar study the aftershock locations are consistent with a nw se orientated fault plane in 2004 and suggests that the 1994 earthquake occurred on a ne sw fault perpendicular to the fault which ruptured in 2004 previous tectonic models of the area proposed a bookshelf model of block rotation with nne ssw left lateral faults this model requires modification to accommodate the observation of right lateral slip on a nw se fault plane for the 2004 earthquake and we prefer to interpret the fault orientations as due to a zone of distributed shear with a right lateral fault striking at 115 and conjugate clockwise rotating left lateral faults striking at 25

macrofracturing of oceanic lithosphere in complex large earthquake sequences major earthquakes in oceanic lithosphere seaward of the subduction zone outer trench slope are relatively uncommon but several recent occurrences have involved very complex sequences rupturing multiple nonaligned faults and or having high aftershock productivity with diffuse distribution this includes the 21 december 2010 m w 7 4 ogasawara bonin 11 april 2012 m w 8 6 indo australia 23 january 2018 m w 7 9 off kodiak island and 20 december 2018 m w 7 3 nikol skoye northwest pacific earthquakes major oceanic intraplate event sequences farther from plate boundaries do not tend to be as complex in faulting or aftershocks outer trench slope extensional faulting can involve complex distributed sequences particularly when activated by great megathrust ruptures such as 11 march 2011 m w 9 1 tohoku and 15 november 2006 m w 8 3 kuril islands intense faulting sequences also occur near subduction zone corners with many fault geometries being activated including some in nearby oceanic lithosphere as for the 29 september 2009 m w 8 1 samoa 6 february 2013 m w 8 0 santa cruz islands and 16 november 2000 m w 8 0 new ireland earthquakes the laterally varying plate boundary stresses from heterogeneous locking recent earthquakes or boundary geometry influence the specific faulting geometries activated in nearby major intraplate ruptures in oceanic lithosphere preexisting lithospheric structures and fabrics exert secondary influences on the faulting intraplate stress release in oceanic lithosphere near subduction zones favors distributed macrofracturing of near critical fault systems rather than localized single fault failures both under transient loading induced by plate boundary ruptures and under slow loading by tectonic motions and slab pull

examples of chemical changes during fossilisation abstract during fossilisation bone tissue is modified by various chemical changes bone mineral can be decomposed both by ionic substitution and by dissolution and recrystallisation processes this is demonstrated by the examples of the formation of brushite calcite and vivianite in archaeological bones due to soil processes soil living microorganisms are also able to decompose the bone tissue either by general demineralisation or by focal destruction besides this they may modify the composition of interred bones by leaving organic microbial mebolites within the hard tissue

the macquarie ridge earthquake of 1989 summary a study of the seismicity on the central portion of the macquarie ridge before and after the 1989 may 23 macquarie ridge earthquake mw 8 2 and the solution of the inverse problem to obtain the moment release time history during the earthquake are presented the aftershock study shows that there were remarkably few and small aftershocks on the main fault the aftershocks were distributed along a 220 km portion of the india australia pacific plate boundary and indicate that the motion was bilateral on a vertical fault in addition the earthquake reactivated a 175 km section of a fault to its west which had been dormant since at least 1964 and 44 per cent of the aftershocks occurred on this feature moreover the largest aftershocks in the five month period following the event occurred not on the main fault plane but on the reactivated one based on available bathymetry gravity and magnetic anomaly data from the region this reactivated feature is interpreted as being an old oceanic fracture zone and hence a pre existing zone of weakness the aftershock distribution and their focal mechanisms are interpreted in terms of the tectonics of the region and suggest that a triangular piece of crust to the west of the macquarie ridge is being squeezed to the north and west the centroid moment tensor solution was obtained using both gdsn and geoscope data simultaneously it shows that the motion was primarily strike slip on a vertical fault with a moment of mo 1 5 x lo2 n m and a centroid depth of 19 5 km the moment release distribution and time history were obtained by inversion of broad band body waves recorded digitally by the gdsn and geoscope networks the rupture is found to be bilateral with the propagation first starting towards the north east and a few seconds later towards the south west the moment release was low in the hypocentral area with the higher areas of moment located towards the north east and south west of this the average rupture speed was approximately the shear wave speed no simple relation between the moment release pattern and the distribution of aftershocks on the fault plane was found instead the aftershock distribution is seen to be dominated by the intersection of the reactivated fault and the main fault plane with most aftershocks occurring to the north of this intersection

the mw 7 8 2001 kunlunshan earthquake extreme rupture speed variability and effect of fault geometry 1 by analyzing body wave seismograms we show that the rupture speed on the main kunlun fault during the mw 7 8 2001 kunlunshan tibet earthquake was highly variable and the rupture process consisted of three stages in the first stage the rupture accelerated from rest to an average speed of 3 3 km s over a distance of 120 km the rupture then propagated for another 150 km at an apparent rupture speed exceeding the p wave speed in the final stage the earthquake fault bifurcates and the rupture front slowed down the region of highest rupture velocity is found to coincide with the region of highest fault slip has the longest slip duration and is where off fault ground cracking is observed in the field stress drops are found to be higher in regions of higher rupture speeds the greatest concentration of aftershocks is located near the fault bifurcation zone and hence coincides with the region of highest fault slip highest stress drop and highest rupture velocity the fault width is no more than 10 km in most places and is about 20 km in the region of highest slip this narrow fault width is attributed to the fact that crust below this depth is sufficiently warm not to permit brittle failure to occur the remarkable similarity of this earthquake with the 1906 california earthquake in spite of occurring in very different tectonic regimes is discussed

active faulting on the ninetyeast ridge and its relation to deformation of the indo australian plate 1 the 4500 km long ninetyeast ridge ner in the northeastern indian ocean crosses a broad zone of deformation where the indo australian plate is fracturing into three smaller plates india capricorn australia separated by diffuse boundaries whose extents are poorly defined new multichannel seismic reflection profiles image active faults along the entire length of the ner and show spatial changes in the style of deformation along the ridge the northern ner 0 n 5 n displays transpressional motion along wnw ese faults observed fault patterns confirm strike slip motion at the western extent of the april 2012 wharton basin earthquake swarm in the central ner 5 s 8 s deformation on wnw ese trending thrust faults implies nearly n s compression an abrupt change in fault style occurs between 8 and 11 s with modest extension characterizing the southern ner 11 s 27 s although extension is dominant narrow zones of faults with strike slip or compressional character also occur in the southern ner suggesting a complex combination of fault motions at all sites active faulting is controlled by the reactivation of original spreading center formed normal faults implying that deformation is opportunistic and focused along existing zones of weakness even when original fault trend is oblique to the direction of relative plate motion observed faulting can be interpreted as india australia deformation in the northern ner and capricorn australia deformation in the southern ner the india capricorn boundary is directly adjacent to the northern ner and this juxtaposition combined with a different style of faulting to the east of the ner imply that the ridge is a tectonic boundary

aftershock zones of large shallow earthquakes fault dimensions aftershock area expansion and scaling relations summary we determine the aftershock areas from relocated hypocentres for 64 dip slip and eight strike slip earthquakes in the period 1977 1996 together with those for three recent earthquakes the 1998 antarctic plate earthquake the 1999 izmit turkey earthquake and the 2000 wharton basin earthquake we also include the data for 27 strike slip earthquakes from pegler das 1996 we find that the location of the hypocentre is essentially random along strike for both strike slip and dip slip earthquakes subduction zone earthquakes appear to initiate more frequently towards the down dip edge of the fault whereas the non subduction zone dip slip earthquakes do not have any preferred depth of initiation the aftershock zones of subduction zone earthquakes often expand substantially along strike and up dip but far less in the down dip direction whereas those for non subduction zone earthquakes do not expand significantly in either the up or the down dip direction subduction zone thrust earthquakes have larger and more numerous aftershocks than earthquakes in all other tectonic settings for strikeslip earthquakes we find that slip increases at least linearly with length for dip slip earthquakes we find that the ratio of length to width increases systematically with length for lengths 40 km indicating that there is some restriction on fault width slip is found to be proportional to length over the moment range 10 17 nm m0 3r10 21 nm

diversity of solutions of the problem of earthquake faulting inversion application to sh waves for the great 1989 macquarie ridge earthquake abstract we use the sh waves generated by the great 1989 macquarie ridge earthquake to investigate the non uniqueness of the inverse problem of earthquake faulting the details of the method of linear programming developed for this problem of solution of a constrained set of equations is described protective measures necessary to remove loss of accuracy when solving the problem for large numbers of unknowns and constraints are developed it is shown that solutions which look very different fit the data almost equally well a method is presented for choosing solutions with desirable properties e g with the most uniformly distributed moment along the fault or with the most concentrated moment release on the fault from among available solutions the results show that the data may equally well be interpreted as representing an asperity model of faulting or a propagating crack model of faulting the common feature of all the models is that the hypocentral region is a region of low moment release with regions of higher release being located to its northeast and its southwest along the fault clearly this earthquake did not initiate by the rupture of an asperity

dynamic source parameters of the march may 1969 serdo earthquake sequence in central afar ethiopia deduced from teleseismic body waves long period teleseismic p and s waveforms for the largest four earthquakes in the serdo sequence are compared with synthetic seismograms to infer mechanisms focal depths source time functions and dynamic energy release for all four events studied the mechanisms are predominantly strike slip depth estimates obtained for the four earthquakes by matching synthetic seismograms to the observations are found to lie between 5 and 8 km the azimuthal variation of observed body wave duration for the main event indicates that the rupture propagated from ne to sw average seismic moments obtained from body wave synthetics vary from 4 6 1017 to 2 5 1018 n m average final displacements stress drops and lengths of the fault are found to lie between 0 16 and 0 56 m 0 45 and 1 56 mpa and 10 and 16 km respectively the low stress drop value obtained may indicate the presence of softer materials near the source the energy release shows that the mode of energy release during the sequence took place in two steps mainly by the two largest shocks

stress transfer in the tokai subduction zone from the 2009 suruga bay earthquake in japan a large earthquake has been a national hazard concern for decades in the tokai region of japan the 2009 suruga bay earthquake increased seismic stress in strongly locked patches of the tokai fault plane potentially increasing the likelihood of a major earthquake in the region southwestern japan lies at the boundary between the subducting philippine sea plate and the overriding eurasian plate a magnitude 8 megathrust earthquake ruptured the tonankai and nankai segments in 1944 and 1946 respectively but the neighbouring tokai segment of the plate boundary remained locked1 a large megathrust earthquake in the tokai region has therefore been expected in 2009 a magnitude 6 4 earthquake took place in suruga bay within the philippine sea subducting plate close to the tokai segment here we use a fault slip model to examine the impact of the stress changes2 caused by the suruga bay event on the tokai segment we show that the occurrence rate of plate boundary seismicity increased following the earthquake most of the presumed strongly locked patches of the tokai segment are located within areas of increased stress rupturing of a locked patch following a threshold level of seismic stress could trigger the rupture of the entire tokai segment leading to a megathrust earthquake

the motion and boundary between the capricorn and australian plates the motions between the somalian antarctic and australian plates the three plates believed to meet at the rodrigues triple junction in the indian ocean are inconsistent with the assumption that all three plates are rigid the discrepancy is best explained if the australian plate contains two component plates thus the traditionally defined indo australian plate consists of three component plates and multiple diffuse plate boundaries the pattern of present deformation indicates that the boundaries between the three component plates are two unconnected zones accommodating divergence and a larger zone which we interpret as three diffuse convergent plate boundaries and a diffuse triple junction

the 2012 mw 8 6 sumatra earthquake evidence of westward sequential seismic ruptures associated to the reactivation of a n s ocean fabric 1 the 11 april 2012 mw 8 6 earthquake offshore sumatra is the largest of the rare great intraplate earthquakes of the instrumental era this major strike slip event occurred in the diffuse zone of deformation that accommodates differential rotation between indian and australian plates we perform a back projection analysis calibrated with well located aftershocks of short period teleseismic p waves recorded by the european array to image the rupture process during the mainshock in complement a love wave analysis is conducted for tracking azimuthal change in the apparent global source duration due to the source spatio temporal extent the combined analysis reveals a complex rupture pattern characterized by three main episodes of energy release the latest being located 370 km west of the epicenter on the ninety east ridge with a delay of 120 s we interpret the 11 april 2012 mw 8 6 offshore sumatra earthquake as a complex westward propagating sequence of dynamically triggered strike slip fault ruptures associated to the reactivation of the inherited nne striking sea floor fabric the dynamic triggering mechanism could result from the interaction between transient surface wave stress perturbations and fluids

insight into complex rupturing of the immature bending normal fault in the outer slope of the japan trench from aftershocks of the 2005 sanriku earthquake mw 7 0 located by ocean bottom seismometry 1 the distribution of aftershocks of a large mw 7 0 normal faulting earthquake beneath the outer slope of the japan trench in 2005 measured in 2007 using ocean bottom seismographs indicates that the earthquake was involved with a set of conjugate normal faults although the faults reach to the upper mantle the estimated vp and vp vs show no remarkable changes that can be related to extensive hydration in the crust or uppermost mantle the absence of horst graben topographic structure in the rupture area suggests that immaturity of the bending fault system is responsible for the relatively unhydrated lithosphere several earthquakes below the aftershock zone may belong to the lower plane seismicity of the shallow double seismic zone because no earthquakes were recorded in the area for more than 80 years before the 2005 event shallow extensional and deep compressive earthquakes may be activated concurrently in the focal area of this earthquake

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

seismic imaging of forearc backthrusts at northern sumatra subduction zone forearc tectonics at accretionary convergent margins has variously been studied using analogue and numerical modelling techniques numerous geophysical investigations have targeted the subsurface structure of active forearc settings at convergent margins however several critical details of the structure mode of tectonic evolution and the role forearcs play in the subduction seismic cycle remain to be further understood especially for large accretionary margins in this study we present a high resolution deep seismic reflection image of the northern sumatran subduction forearc near the 2004 december 26 sumatra earthquake epicentral region the profile clearly demarcates the backthrust branches at the seaward edge of the aceh forearc basin along which the inner forearc continues to evolve sharp bathymetric features at the seafloor suggest that the imaged backthrusts are active coincident wide angle seismic tomographic image of the sumatra forearc allows us to image the geometry of the seaward dipping backstop buttress with which the imaged backthrust branches are associated the presence of forearc backthrusting confirms model predictions for the development of backthrusting over seaward dipping backstops the west andaman fault at the seaward edge of aceh basin appears to be a shallow tributary of the backthrust and sheds light on the complex deformation of the forearc uplifting along the backthrust branches may explain the presence of forearc islands observed all along sumatran margin and help further constrain the tectonic models for their evolution moreover if these backthrusts slip coseismically they would contribute to tsunamigenesis and seismic risk in the region

earth science when an oceanic tectonic plate cracks analyses of two recent earthquakes of great magnitude show how complex the breaking of the oceanic lithosphere can be how it is linked to earlier great events and how it triggers seismicity worldwide see letters p 240 p 245 p 250 on 11 april 2012 two of the largest strike slip earthquakes ever recorded at magnitudes of 8 7 and 8 2 occurred in the northeastern indian ocean a few hundred kilometres off the coast of sumatra three groups now report the analysis of seismic data from the days and months before and after these events as well as the events themselves matthias delescluse and co authors show that these earthquakes are part of the ongoing boost of intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes they conclude that the australian plate driven by slab pull forces at the sunda trench is gradually detaching from the indian plate han yue and colleagues show that the 11 april event involved a complex four fault rupture lasting several minutes followed two hours later by a magnitude 8 2 aftershock these great ruptures on a lattice of strike slip faults that extends through the crust and into the upper mantle represent large lithospheric deformation that may eventually create a localized boundary between the indian and australian plates fred pollitz and colleagues show that in the six days following 11 april the global rate of remote earthquakes with magnitudes greater than 5 5 increased nearly fivefold and events up to magnitude 7 seem to have been triggered the unprecedented delayed triggering power of this earthquake may arise from its strike slip source geometry or because it struck at a time of an unusually low global earthquake rate and increased the number of nucleation sites that were very close to failure

multifaulting in a tectonic syntaxis revealed by insar the case of the ziarat earthquake sequence pakistan on 28 29 october 2008 within 12 h two similar mw 6 4 strike slip earthquakes struck baluchistan pakistan as part of a complex seismic sequence interferometric synthetic aperture radar insar data reveal that the peak of surface displacement is near the ziarat anticline a large active fold affected by quaternary strike slip faulting all coseismic interferograms integrate the deformation due to both earthquakes as their causative faults ruptured close to each other the individual signals cannot be separated according to their focal mechanisms each earthquake may have activated a ne sw sinistral or a nw se dextral fault segment which leads to four possible scenarios of fault orientations a nonlinear inversion of the insar data set allows rejecting two scenarios the best slip distributions on the two fault segments for the two remaining scenarios are determined by linear inversion stress change modeling favors a scenario involving two abutting conjugate strike slip faults two other fault segments accommodated left lateral strike slip during the seismic sequence the activated fault system includes multiple fault segments with different orientations and little surface expression this may highlight at a smaller scale the distributed possibly transient character of deformation within a broader right lateral shear zone it suggests that the activated faults delineate a small tectonic block extruding and subtly rotating within the shear zone it occurs in the vicinity of the local tectonic syntaxis where orogenic structures sharply turn around a vertical axis these mechanisms could participate in the long term migration of active tectonic structures within this kinematically unstable tectonic syntaxis

indian ocean actively deforms according to plate tectonics plates are rigid and deform only at narrow boundaries but studies have shown that intraplate deformation can occur in continental plates in her perspective deplus discusses recent evidence for active deformation in the indian ocean offering a rare opportunity to study intraplate deformation of oceanic lithosphere

earthquake in a maze compressional rupture branching during the 2012 mw 8 6 sumatra earthquake seismological observations of the 2012 moment magnitude 8 6 sumatra earthquake reveal unprecedented complexity of dynamic rupture the surprisingly large magnitude results from the combination of deep extent high stress drop and rupture of multiple faults back projection source imaging indicates that the rupture occurred on distinct planes in an orthogonal conjugate fault system with relatively slow rupture speed the east southeast west northwest ruptures add a new dimension to the seismotectonics of the wharton basin which was previously thought to be controlled by north south strike slip faulting the rupture turned twice into the compressive quadrant against the preferred branching direction predicted by dynamic coulomb stress calculations orthogonal faulting and compressional branching indicate that rupture was controlled by a pressure insensitive strength of the deep oceanic lithosphere

the 2012 mw 8 6 indian ocean earthquake deep nucleation on a listric like fault abstract the 2012 mw 8 6 indian ocean earthquake the largest instrumentally recorded strike slip event has been described as a westward rupture on orthogonal faults that are part of the original oceanic fabric of the region reported estimates of its depth vary from 10 to 45 km while the maximum depth of its inferred rupture extends to 50 60 km the complexity of the earthquake is undeniable both in terms of fault geometry and rupture propagation with debates on the geometry of the causative faults results from recent seismic surveys enable a fresh look at the earthquake fault geometry nucleation depths and lithospheric rheology in the present study these new findings are incorporated into 22 forward models using a revised velocity structure and n s geometries that flatten with depth the rupture initiation is modeled in the uppermost mantle 25 30 km as well as in the upper mantle at 45 km the latter of which is 15 20 km below the commonly accepted values of maximum depth for frictional failure our study shows that the westward directionality of wave propagation is achieved for strike slip failure on a listric like fault in contrast to subvertical geometries as previously suggested this propagation is persistent for a strike slip failure only for events nucleating at upper mantle depths 45 km rather than for those set to originate at depths between 25 and 30 km however for a dip slip failure the westward propagation is found to be consistent at both nucleation depths on a listric like fault this study highlights a deep nucleation within the lithospheric mantle for the 2012 mw 8 6 earthquake that could be due to strain localization induced by fluid rock interaction and or mineral transformation crystallization near the 680 c isotherm at 45 km depth 1 4 gpa which correlates with deep serpentinization on faults

interferometric synthetic aperture radar observations of the 1994 double spring flat nevada earthquake m5 9 main shock accompanied by triggered slip on a conjugate fault 1 the 1994 double spring flat dsf earthquake m5 9 was the largest earthquake to strike nevada in more than 30 years it occurred in the sierra nevada basin and range transition zone within a step over region between two major normal faults descending and ascending ers interferograms show a maximum range change of 8 5 cm which is the coseismic ground displacement associated with this normal oblique slip moderatesized earthquake elastic inverse modeling and surface displacements across coseismic ground cracks suggest that two different event sources could account for the observed deformation the first source was the main shock with right oblique slip on the northnorthwest striking dsf fault the second source was normal faulting on a shallow northnortheast striking elongated plane conjugate to the dsf fault these two sources are consistent with the pattern of postevent seismicity and we suggest that the second source represents seismic and aseismic slip triggered by the main shock calculations of changes in coulomb failure stress show that the main shock encouraged normal slip on this plane index terms 1206 geodesy and gravity crustal movements interplate 8155 1241 geodesy and gravity satellite orbits 1242 geodesy and gravity seismic deformations 7205 1299 geodesy and gravity general or miscellaneous 7212 seismology earthquake ground motions and engineering

recent seismicity of the east african rift system and its implications abstract the seismicity of the east african rift system and southern red sea is studied here location of earthquake epicenters in east africa shows that there is a seismicity gap in space and time between the main ethiopian rift system and the eastern rift however distribution of earthquake epicenters together with the energy mapping suggest a continuity of seismic activity or stress field from the main ethiopian rift system to the western rift system via the southernmost rifts of ethiopia in general except for some earthquakes which occurred at different complex tectonics regions mechanisms of earthquakes studied here show dominantly normal faulting suggesting that the rift system is an extensional zone on the continent the presence of greater focal depth earthquakes to the southern part of the rift system may indicate that softer materials at a shallower depth are present in afar and neighboring regions than in the remaining part of the east african rift system this interpretation is supported by other geophysical studies low electrical resistivity and gravity data performed in afar it is also supported by low and high stress drops found for the northern part afar depression and southern part of the east african rift system respectively

the april 2012 indian ocean earthquakes seismotectonic context and implications for their mechanisms the 11 april 2012 earthquakes m w 8 6 and m w 8 2 were sourced within the northern wharton basin in the northeastern part of the indo australian diffuse plate boundary this unusually active oceanic intraplate region has generated many large earthquakes in the past most of which are believed to have occurred by strike slip motion triggered by the nw se oriented compressional stresses acting across the indian and australian plates in the aftermath of the 2004 megathrust earthquake along the nearby sunda trench increased seismicity in the northern wharton basin is attributed to the stress transfer from the sumatra andaman plate boundary models proposed for the april 2012 earthquakes differ somewhat in details but partly attribute their complex rupture to the reactivation of pre existing structures these structures include previously mapped n s trending fracture zones within the northern wharton basin and e w lineations across the ninetyeast ridge in this paper we review the regional tectonics and past seismicity on the indo australian plate in order to understand the seismotectonic setting of the april 2012 indian ocean earthquakes c 2014 elsevier b v all rights reserved