the seismic cycle in the area of the 2011 mw9 0 tohoku oki earthquake we model seismic and aseismic slip on the japan megathrust in the area of the m w9 0 2011 tohoku oki earthquake based on daily time series from 400 gps stations of the geonet network and campaign measurements of six sea floor displacements the coseismic and postseismic slip distributions are inverted simultaneously using principal component analysis based inversion method pcaim exploring a wide range of boundary conditions and regularization constraints we found the coseismic slip distribution to be quite compact with a peak slip between 30 and 50 m near the trench our model shows deep afterslip fringing the downdip edge of the coseismic rupture but also a dominant zone of shallow afterslip afterslip over the first 279 days following the main shock represents about 40 of the coseismic moment we compare the coseismic and postseismic models with an interseismic coupling model derived from inland and sea bottom measurements determined in a self consistent manner assuming that seismic and aseismic slip had to match the long term slip rate along the megathrust the recurrence time of m w9 0 earthquakes is estimated to 100 300 years while historical and paleotsunami records suggest a return period more of the order of 1000 years the discrepancy is smaller if the shallower portion of the megathrust is assumed to produce both aseismic slip as the afterslip model suggests and seismic slip during occasional large tsunamigenic earthquakes

rupture kinematics of the 2005 mw 8 6 nias simeulue earthquake from the joint inversion of seismic and geodetic data the 2005 mw 8 6 nias simeulue earthquake was caused by rupture of a portion of the sunda megathrust offshore northern sumatra this event occurred within an array of continuous global positioning system gps stations and produced measurable vertical displacement of the fringing coral reefs above the fault rupture thus this earthquake provides a unique opportunity to assess the source character istics of a megathrust event from the joint analysis of seismic data and near field static co seismic displacements based on the excitation of the normal mode data and geodetic data we put relatively tight constraints on the seismic moment and the fault dip where the dip is determined to be 8 to 10 with corresponding moments of 1 24 10 22 to 1 00 10 22 n m respectively the geodetic constraints on slip distribution help to eliminate the trade off between rupture velocity and slip kine matics source models obtained from the inversion of various combinations of the teleseismic body waves and geodetic data are evaluated by comparing predicted and observed long period seismic waveforms 100 500 sec our results indicate a rela tively slow average rupture velocity of 1 5 to 2 5 km sec and long average rise time of up to 20 sec the earthquake nucleated between two separate slip patches one beneath nias and the other beneath simeulue island the gap between the two patches and the hypocentral location appears to be coincident with a local geological disrup tion of the forearc coseismic slip clearly tapers to zero before it reaches the trench probably because the rupture propagation was inhibited when it reached the accre tionary prism using the models from joint inversions we estimate the peak ground velocity on nias island to be about 30 cm sec an order of magnitude slower than for thrust events in continental areas this study emphasizes the importance of util izing multiple datasets in imaging seismic ruptures

geodetic imaging of plate motions slip rates and partitioning of deformation in japan 1 interseismic deformation in japan results from the combined effects of tectonic processes including rotation of crustal blocks and the earthquake cycle process of elastic strain accumulation about upper plate faults and subduction zone interfaces we use spherical linear block theory constrained by geodetic observations from densely spaced global positioning system gps stations to estimate plate motions fault slip rates and spatially variable interplate coupling on the japan kuril sagami and nankai subduction zones the reference model developed in this paper consists of 20 blocks produces a mean residual velocity magnitude of 1 84 mm yr at 950 stations and accounts for 96 of the observed interseismic deformation signal we estimate fault slip rates in excess of 15 mm yr along the niigata kobe tectonic zone and itoigawa shizuoka tectonic line through central japan confirming their hypothesized roles as major tectonic boundaries oblique convergence across the nankai trough is partitioned with 3 4 of the 30 mm yr of trench parallel motion accommodated by strike slip motion on the subduction interface and the remaining 1 4 accommodated by right lateral slip on the median tectonic line in contrast our models suggest negligible slip partitioning in eastern hokkaido where oblique slip on the japan kuril subduction interface accommodates all of the trench parallel component of relative plate motion inferred spatial variations in the rake and magnitude of slip deficit on subduction zone interfaces reflect the influences of megathrust geometry and earthquake cycle processes such as enhanced elastic strain accumulation about seismic asperities and coseismic sense fault motion indicative of silent slip events or afterslip following large earthquakes

three dimensional elastic dislocation modeling of the postseismic response to the 1964 alaska earthquake 1 gps velocity observations from the kenai peninsula and kodiak island alaska display a pattern of spatial variability suggesting the presence of multiple active processes on the underlying pacific north american plate interface velocities of sites on the eastern kenai peninsula and kodiak island are consistent with elastic strain accumulation at the plate interface whereas velocities of sites on the western kenai peninsula and cook inlet are oriented in the opposite direction and suggest an ongoing postseismic response to the 1964 alaska earthquake we can reproduce the observed velocities using a three dimensional elastic dislocation model to estimate the variation in coupling between the pacific and north american plates two different inversion schemes are examined to check the robustness of the results we find that the gps data can be satisfied by the presence of a locked area near southwest prince william sound a locked area near southwest kodiak island and an area of postseismic reverse slip beneath and north of the western kenai peninsula the shallow plate interface trenchward of the western kenai peninsula does not appear to be locked the locked areas correspond to the prince william sound and kodiak island asperities that ruptured in 1964 and the area of postseismic slip lies downdip of the 1964 rupture area the correspondence between the present shallow coupling distribution and the 1964 slip distribution suggests that the locked regions repeat from one earthquake cycle to another

submergence and uplift associated with the giant 1833 sumatran subduction earthquake evidence from coral microatolls the giant sumatran subduction earthquake of 1833 appears as a large emergence event in fossil coral microatolls on the reefs of sumatra s outer arc ridge stratigraphic analysis of these and living microatolls nearby allow us to estimate that 1833 emergence increased trenchward from about 1 to 2 m this pattern and magnitude of uplift are consistent with about 13 m of slip on the subduction interface and suggest a magnitude mw of 8 8 9 2 for the earthquake the fossil microatolls also record rapid submergence in the decades prior to the earthquake with rates increasing trenchward from 5 to 11 mm yr living microatolls show similar rates and a similar pattern the fossil microatolls also record at least two less extensive emergence events in the decades prior to 1833 these observations show that coral microatolls can be useful paleoseismic and paleogeodetic instruments in convergent tectonic environments

san andreas fault earthquake chronology and lake cahuilla history at coachella california the southernmost 100 km of the san andreas fault has not ruptured historically it is imperative to determine its rupture history to better predict its future behavior this paleoseismic investigation in coachella california establishes a chronology of at least five and up to seven major earthquakes during the past 1100 yr this chronology yields a range of average recurrence intervals between 116 and 221 yr depending on assumptions with a best estimate average recurrence interval of 180 yr the most recent earthquake occurred c 1690 more than 300 yr ago suggesting that this stretch of the fault has accumulated a large amount of tectonic stress and is likely to rupture in the near future assuming the fault follows a stress renewal model this study also establishes the timing of the past 5 6 highstands of ancient lake cahuilla since a d 800 we found that earthquakes do not tend to occur at any particular stage in the lake cycle

convergence rate across the nepal himalaya and interseismic coupling on the main himalayan thrust implications for seismic hazard we document geodetic strain across the nepal himalaya using gps times series from 30 stations in nepal and southern tibet in addition to previously published campaign gps points and leveling data and determine the pattern of interseismic coupling on the main himalayan thrust fault mht the noise on the daily gps positions is modeled as a combination of white and colored noise in order to infer secular velocities at the stations with consistent uncertainties we then locate the pole of rotation of the indian plate in the itrf 2005 reference frame at longitude 1 34 3 31 latitude 51 4 0 3 with an angular velocity of 0 5029 0 0072 myr the pattern of coupling on the mht is computed on a fault dipping 10 to the north and whose strike roughly follows the arcuate shape of the himalaya the model indicates that the mht is locked from the surface to a distance of approximately 100 km down dip corresponding to a depth of 15 to 20 km in map view the transition zone between the locked portion of the mht and the portion which is creeping at the long term slip rate seems to be at the most a few tens of kilometers wide and coincides with the belt of midcrustal microseismicity underneath the himalaya according to a previous study based on thermokinematic modeling of thermochronological and thermobarometric data this transition seems to happen in a zone where the temperature reaches 350 c the convergence between india and south tibet proceeds at a rate of 17 8 0 5 mm yr in central and eastern nepal and 20 5 1 mm yr in western nepal the moment deficit due to locking of the mht in the interseismic period accrues at a rate of 6 6 0 4 10 19 nm yr on the mht underneath nepal for comparison the moment released by the seismicity over the past 500 years including 14 m w 7 earthquakes with moment magnitudes up to 8 5 amounts to only 0 9 10 19 nm yr indicating a large deficit of seismic slip over that period or very infrequent large slow slip events no large slow slip event has been observed however over the 20 years covered by geodetic measurements in the nepal himalaya we discuss the magnitude and return period of m 8 earthquakes required to balance the long term slip budget on the mht

persistent termini of 2004 and 2005 like ruptures of the sunda megathrust to gain insight into the longevity of subduction zone segmentation we use coral microatolls to examine an 1100 year record of large earthquakes across the boundary of the great 2004 and 2005 sunda megathrust ruptures simeulue a 100 km long island off the west coast of northern sumatra indonesia straddles this boundary northern simeulue was uplifted in the 2004 earthquake whereas southern simeulue rose in 2005 northern simeulue corals reveal that predecessors of the 2004 earthquake occurred in the 10th century ad in ad 1394 2 and in ad 1450 3 corals from southern simeulue indicate that none of the major uplifts inferred on northern simeulue in the past 1100 years extended to southern simeulue the two largest uplifts recognized at a south central simeulue site around ad 1422 and in 2005 involved little or no uplift of northern simeulue the distribution of uplift and strong shaking during a historical earthquake in 1861 suggests the 1861 rupture area was also restricted to south of central simeulue as in 2005 the strikingly different histories of the two adjacent patches demonstrate that this boundary has persisted as an impediment to rupture through at least seven earthquakes in the past 1100 years this implies that the rupture lengths and hence sizes of at least some future great earthquakes and tsunamis can be forecast these microatolls also provide insight into megathrust behavior between earthquakes revealing sudden and substantial changes in interseismic strain accumulation rates

the tsunami of 2007 september 12 bengkulu province sumatra indonesia post tsunami field survey and numerical modelling summary the m w 8 4 earthquake on 2007 september 12 offshore of the bengkulu province of sumatra indonesia generated a moderate tsunami with run up heights of up to 4 m as measured by indonesian and international researchers in the days following the earthquake the tsunami was observed along 250 km of coastline and caused damage at several locations the largest wave heights and most severe inundation were observed about 50 km to the northwest of bengkulu elsewhere the effects were less severe with the exception of substantial inundation at a site 150 km to the south in addition to presenting the field data we conduct a modelling study and compare the run up heights and water level predictions from four different seismic deformation models used to initialize a tsunami propagation and inundation model our comparative results suggest that for this event the estimates of fault parameters available immediately after determination of the earthquake size and location predicted the near field run up heights and distribution and far field wave equally well as estimates obtained using more detailed descriptions of the seafloor deformation as typically available hours or days after an event we conclude that while detailed slip patterns can be important to the near field run up distribution simple fault models can be used to rapidly assess the likely near and far field tsunami effects of a particular earthquake

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

the earthquake deformation cycle recurrence and the time predictable model geodetic and geologic observations from a handful of well studied great plate boundary earthquakes provide a basis for exploring those features of the deformation cycle having the strongest influence on recurrence estimation in ideal circumstances the time predictable model requires knowledge of only the seismic slip and time of the last earthquake and the rate of relative plate motion or fault slip practically indirect measurements must usually suffice local coseismic strain changes rather than seismic slip and local deformation rate rather than slip rate permanent nonrecoverable deformation often roughly half the coseismic strain offset near great thrust earthquakes complicates the inference of interplate seismic slip owing to short and long term postseismic transients commonly 20 40 of the coseismic strain drop deformation rates are variable and not simply related to the plate motion rate at strike slip plate boundaries these complications can sometimes be avoided and seismic slip and slip rate can be obtained more or less directly when these favorable circumstances are absent and when knowledge of the deformation cycle is incomplete recurrence accuracy can be improved by empirically correcting for unknown elements of the cycle systematic features in the spatial distribution of the transients and permanent deformation near subduction zones help identify the regions where these corrections are largest and where the shortcomings of the empirical approach are most severe

crustal deformation at the sumatran subduction zone revealed by coral rings analyses of coral rings grown in the interval 1970 1997 reveal a geographically distinct pattern of interseismic uplift off sumatra s western coast at distances less than 110 km from the sumatran trench coral reefs are submerging as fast as 5 mm y at 130 and 180 km distance from the trench they are emerging at similar rates we suggest that a locked or partially locked patch located above 30 km depth on the upper surface of the subducting oceanic plate generates this pattern

towards inferring earthquake patterns from geodetic observations of interseismic coupling ultimately seismotectonic studies seek to provide ways of assessing the timing magnitude and spatial extent of future earthquakes ample observations document the spatial variability in interseismic coupling defined as a degree of locking of a fault during the period of stress build up between seismic events fully or nearly locked fault patches are often surrounded by aseismically creeping areas however it is unclear how these observations could help assess future earthquakes here we simulate spontaneous seismic and aseismic fault slip with a fully dynamic numerical model our simulations establish the dependence of earthquake rupture patterns and interseismic coupling on spatial variations of fault friction we consider the long term evolution of slip on a model fault where two seismogenic locked segments are separated by an aseismically slipping patch where rupture is impeded we find that the probability for a large earthquake to break through the rupture impeding patch is correlated with the interseismic coupling averaged over this patch in addition the probability that an earthquake breaks through the rupture impeding patch and interseismic coupling are both related to fault friction properties through a single non dimensional parameter our study opens the possibility of predicting seismic rupture patterns that a fault system can produce on the basis of observations of its interseismic coupling and suggests that regions of low interseismic coupling may reveal permanent barriers to large earthquakes

velocity and temperature structure functions in the upper troposphere and lower stratosphere from high resolution aircraft measurements abstract high resolution measurements obtained from noaa best atmospheric turbulence bat probes mounted on an egrett high altitude research aircraft were used to characterize turbulence in the upper troposphere and lower stratosphere at scales from 2 m to 20 km focusing on three dimensional behavior in the sub kilometer scale range data were analyzed for 129 separate level flight segments representing 41 h of flight time and 12 600 km of wind relative flight distances the majority of flights occurred near the tropopause layer of the winter subtropical jet stream in the southern hemisphere second order structure functions for velocity and temperature were analyzed for the separate level flight segments individually and in various ensembles a 3d scaling range was observed at scales less than about 100 m with power law exponents for the structure functions of the velocity component in the flight direction varying mostly between 0 4 and 0 75 for the separate flight segments but close to for the

high precision and high resolution carbonate 230th dating by mc icp ms with sem protocols abstract to facilitate the measurement of u th isotopic compositions suitable for high precision and high resolution 230th dating of coral and speleothem carbonates secondary electron multiplier sem protocol techniques for multicollector inductively coupled plasma mass spectrometry mc icp ms have been developed the instrumental sensitivities are 1 2 with a precision of 1 2 2 for abundance determination of 50 200 fg 234u 1 4 ng 238u or 230th this method features chemistry refinements improvements to procedural and instrumental blanks spectral inference reductions and careful consideration of non linear sem behavior measurement consistency of this mc icp ms combined with previous mass spectrometric results on u th standards and a variety of carbonates demonstrates the validity of the sem protocol method for fossil corals a routine u th isotopic determination at permil level precision requires only 10 50 mg of carbonate as little as 200 mg of young coral with an age of less than 20 yr can be dated with a precision of 0 3 0 8 yr about 20 200 mg speleothem samples with sub ppm to ppm u are required to earn a 5 precision on ages from 5 to 100 kyr requirement of small sample size 10 100s mg carbonate can permit high temporal resolution to date speleothems with slow growth rates i e 1 10 mm kyr this high precision 230th chronology is critical to accurately establish age models date events and splice geochemical proxy time series records from multiple samples in the fields of paleoclimatology and paleoceanography the u th isotopic determination techniques described here can also be applied to different environmental samples such as waters rocks and sediments

evaluation of wasatch fault segmentation and slip rates using lake bonneville shorelines 1 analysis of lake bonneville shorelines using lidar digital elevation data challenges accepted models of wasatch fault deformation since the late pleistocene while footwall deformation of the weber segment of the wasatch fault is consistent with back rotation of the footwall block and greatest displacement rate toward the center of the segment shorelines along the footwall of the salt lake city segment decrease in elevation toward the interior and are highest at the segment boundaries an opposite pattern of footwall deformation than predicted for boundaries arresting or strongly inhibiting displacement during earthquakes the spatial pattern of footwall rebound implies that some of the proposed persistent fault segment boundaries do not stop earthquake ruptures that originate on adjacent fault segments nor constrain ruptures initiated within the salt lake city segment net vertical fault displacement at the boundary between the salt lake and provo segments is 16 20 m over the past 16 3 18 5 ka corresponding to a vertical displacement rate of 0 8 1 2 mm yr a net fault slip rate of 2 0 2 8 mm yr and horizontal extension rate of 1 8 2 6 mm yr on the 25 west southwest dipping fault that forms the southern salt lake city segment boundary shoreline analysis suggests isostatic rebound caused by a drop in lake level was concentrated during a relatively short 2000 year time period following the bonneville flood at 16 ka lidar derived topography in conjunction with robust geomorphic datums improves our ability to map deformation associated with lithospheric flexure and faulting while demonstrating the limitation of lacustrine shorelines in this type of analysis

a comprehensive model of postseismic deformation of the 2004 sumatra andaman earthquake deduced from gps observations in northern sumatra abstract we investigate the postseismic deformation of the 2004 sumatra andaman earthquake sae using 5 years of global positioning system gps data located in northern sumatra continuous gps data from northern sumatra suggest that the relaxation time in the vertical displacement is longer than horizontal displacements this implies that there are multiple physical mechanisms that control the postseismic deformation which refer to afterslip and viscoelastic relaxation in this study we introduce an analysis strategy of postseismic deformation to simultaneously calculate multiple mechanisms of afterslip and viscoelastic relaxation the afterslip inversion results indicate that the distribution of the afterslip and the coseismic slip are compensatory of each other also afterslip has a limited contribution to vertical deformation in northern sumatra in our rheology model we use a gravitational maxwell viscoelastic response and the result indicates that the elastic layer thickness is 65 5 km and the maxwell viscosity is 8 0 1 0 1018 pa s we find that afterslip plus maxwell viscoelastic relaxation are appropriate to explain the deformation in northern sumatra we also find that our rheology model reproduces the long term features of the gps time series in thailand applying our rheology model to the data in andaman islands our afterslip estimation is located at the down dip part of the plate boundary finally we showed that our rheology model is applicable to the gps datasets of postseismic deformation of the 2004 sae located in northern sumatra thailand and andaman nicobar respectively

heterogeneous plate locking in the south central chile subduction zone building up the next great earthquake abstract we use global positioning system gps velocities and kinematic finite element models fe models to infer the state of locking between the converging nazca and south america plates in south central chile 36 s 46 s and to evaluate its spatial and temporal variability gps velocities provide information on earthquake cycle deformation over the last decade in areas affected by the megathrust events of 1960 m w 9 5 and 2010 m w 8 8 our data confirm that a change in surface velocity patterns of these two seismotectonic segments can be related to their different stages in the seismic cycle accordingly the northern 2010 segment was in a final stage of interseismic loading whereas the southern 1960 segment is still in a postseismic stage and undergoes a prolonged viscoelastic mantle relaxation after correcting the signals for mantle relaxation the residual gps velocity pattern suggests that the plate interface accumulates slip deficit in a spatially and presumably temporally variable way towards the next great event though some similarity exist between locking and 1960 coseismic slip extrapolating the current decadal scale slip deficit accumulation towards the 300 yr recurrence times of giant events here does neither yield the slip distribution nor the moment magnitude of the 1960 earthquake this suggests that either the locking pattern is evolving in time to reconcile a slip deficit distribution similar to the 1960 earthquake or that some asperities are not persistent over multiple events the accumulated moment deficit since 1960 suggests that highly locked patches in the 1960 segment are already capable of producing a m 8 event if triggered to fail by stress transfer from the 2010 event

aftershocks of the campania lucania italy earthquake of 23 november 1980 abstract the result of a study of 1130 aftershocks of the 1980 campania lucania earthquake are presented the data were collected primarily with a dense array of portable smoked drum seismographs deployed in the epicentral region a few days after the main shock tests performed on subsets of the data to establish the location accuracy are described in detail and epicentral maps and cross sections are presented and discussed one hundred and sixty well constrained fault plane solutions using upward traveling rays are presented the distribution of aftershocks forms an elongate cloud which does not define a plane this is not because the events are poorly located a subset of events located with epicentral errors of less than 1 km and depth errors less than 2 km forms a similar cloud to the complete aftershock set the aftershock mechanisms are very varied some are similar to the main event but many differ profoundly these include events on shallow or vertical planes and thrust events the latter include some events which require contraction in the direction in which the main event indicates extension the aftershocks of all mechanisms are intermixed in space in such a way that no simple system of faults can explain them a model to explain the aftershocks and the lack of surface ruptures in the main event is offered it is proposed that the main shock cuts between two aseismic detachment surfaces and that the aftershocks are a consequence of the complicated deformation that such a geometry demands whatever interpretation is adopted the results are a challenge to the commonly accepted view that aftershocks even approximately define simple fault planes or that aftershock mechanisms replicate the mechanism of the main shock defects in interpretations of the main shock and aftershocks process arise largely from a lack of information about the geometry of structures at depth in the epicentral region suitable deep reflection profiles could help to resolve this problem

postseismic deformation of the andaman islands following the 26 december 2004 great sumatra andaman earthquake 1 two years after the great sumatra andaman earthquake the 3 1 m wsw coseismic displacement at port blair andaman islands had increased by 32 cm postseismic uplift initially exceeded 1 cm per week and decreased to 1 mm week by 2007 points near port blair had risen more than 20 cm a 24 reversal of coseismic subsidence uplift at eight gps sites suggests a gradual eastward shift of the coseismic neutral axis separating subsidence from uplift simulations of the gps postseismic displacements as viscoelastic relaxation of coseismic stress change and as slip on the plate interface indicate that slip down dip of the seismic rupture dominates near field deformation during the first two years postseismic slip beneath the andaman islands released moment equivalent to a magnitude mw 7 5 earthquake and the distribution suggests deep slip in the stable frictional regime accelerated to catch up to the coseismic rupture

frictional afterslip following the 2005 nias simeulue earthquake sumatra continuously recording global positioning system stations near the 28 march 2005 rupture of the sunda megathrust moment magnitude m w 8 7 show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust with a major fraction of this slip in the up dip direction from the main rupture eleven months after the main shock afterslip continues at rates several times the average interseismic rate resulting in deformation equivalent to at least a m w 8 2 earthquake in general along strike variations in frictional behavior appear to persist over multiple earthquake cycles aftershocks cluster along the boundary between the region of coseismic slip and the up dip creeping zone we observe that the cumulative number of aftershocks increases linearly with postseismic displacements this finding suggests that the temporal evolution of aftershocks is governed by afterslip

source parameters of the great sumatran megathrust earthquakes of 1797 and 1833 inferred from coral microatolls large uplifts and tilts occurred on the sumatran outer arc islands between 0 5 and 3 3 s during great historical earthquakes in 1797 and 1833 as judged from relative sea level changes recorded by annually banded coral heads coral data for these two earthquakes are most complete along a 160 km length of the mentawai islands between 3 2 and 2 s uplift there was as great as 0 8 m in 1797 and 2 8 m in 1833 uplift in 1797 extended 370 km between 3 2 and 0 5 s the pattern and magnitude of uplift imply megathrust ruptures corresponding to moment magnitudes m w in the range 8 5 to 8 7 the region of uplift in 1833 ranges from 2 to at least 3 2 s and judging from historical reports of shaking and tsunamis perhaps as far as 5 s the patterns and magnitude of uplift and tilt in 1833 are similar to those experienced farther north between 0 5 and 3 n during the giant nias simeulue megathrust earthquake of 2005 the outer arc islands rose as much as 3 m and tilted toward the mainland elastic dislocation forward modeling of the coral data yields megathrust ruptures with moment magnitudes ranging from 8 6 to 8 9 sparse accounts at padang along the mainland west coast at latitude 1 s imply tsunami runups of at least 5 m in 1797 and 3 4 m in 1833 tsunamis simulated from the pattern of coral uplift are roughly consistent with these reports the tsunami modeling further indicates that the indian ocean tsunamis of both 1797 and 1833 unlike that of 2004 were directed mainly south of the indian subcontinent between about 0 7 and 2 1 s the lack of vintage 1797 and 1833 coral heads in the intertidal zone demonstrates that interseismic submergence has now nearly equals coseismic emergence that accompanied those earthquakes the interseismic strains accumulated along this reach of the megathrust have thus approached or exceeded the levels relieved in 1797 and 1833

paleogeodetic records of seismic and aseismic subduction from central sumatran microatolls indonesia we utilize coral microatolls in western sumatra to document vertical deformation associated with subduction microatolls are very sensitive to fluctuations in sea level and thus act as natural tide gauges they record not only the magnitude of vertical deformation associated with earthquakes paleoseismic data but also continuously track the long term aseismic deformation that occurs during the intervals between earthquakes paleogeodetic data this paper focuses on the twentieth century paleogeodetic history of the equatorial region our coral paleogeodetic record of the 1935 event reveals a classical example of deformations produced by seismic rupture of a shallow subduction interface the site closest to the trench rose 90 cm whereas sites further east sank by as much as 35 cm our model reproduces these paleogeodetic data with a 2 3 m slip event on the interface 88 to 125 km from the trench axis our coral paleogeodetic data reveal slow submergence during the decades before and after the event in the areas of coseismic emergence likewise interseismic emergence occurred before and after the 1935 event in areas of coseismic submergence among the interesting phenomenon we have discovered in the coral record is evidence of a large aseismic slip or silent event in 1962 27 years after the 1935 event paleogeodetic deformation rates in the decades before after and between the 1935 and 1962 events have varied both temporally and spatially during the 25 years following the 1935 event submergence rates were dramatically greater than in prior decades during the past four decades however rates have been lower than in the preceding decades but are still higher than they were prior to 1935 these paleogeodetic records enable us to model the kinematics of the subduction interface throughout the twentieth century

three dimensional fem derived elastic green s functions for the coseismic deformation of the 2005 mw 8 7 nias simeulue sumatra earthquake using finite element models fems we examine the sensitivity of surface displacements to the location of fault slip topography and three dimensional variations in elastic moduli in the context of a 2 d infinite thrust fault we then evaluate the impact of these factors and fault geometry on surface displacements and estimates of the distribution of coseismic slip associated with the 2005 m w 8 7 nias simeulue sumatra earthquake topographic effects can be significant near the trench where bathymetric gradients are highest and the fault is closest to the free surface variations in young s modulus can significantly alter predicted deformation surface displacements are relatively insensitive to perturbations in poisson s ratio for shear sources but may play a stronger role when the source has a dilatational component if we generate synthetic displacements using a heterogeneous elastic model and then use an elastic half space or layered earth model to estimate the slip distribution and fault geometry we find systematic residuals of surface displacements and different slip patterns compared to the input fault slip model the coseismic slip distributions of the 2005 earthquake derived from the same fault geometry and different material models show that the rupture areas are narrower in all tested heterogeneous elastic models compared to that obtained using half space models this difference can be understood by the tendency to infer additional sources in elastic half space models to account for effects that are intrinsically due to the presence of rheological gradients although the fit to surface observations in our preferred 3 d fem model is similar to that from a simple half space model the resulting slip distribution may be a more accurate reflection the true fault slip behavior

a 20th century acceleration in global sea level rise 1 multi century sea level records and climate models indicate an acceleration of sea level rise but no 20th century acceleration has previously been detected a reconstruction of global sea level using tide gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea level rise but no significant acceleration over this period here we extend the reconstruction of global mean sea level back to 1870 and find a sea level rise from january 1870 to december 2004 of 195 mm a 20th century rate of sea level rise of 1 7 0 3 mm yr 1 and a significant acceleration of sea level rise of 0 013 0 006 mm yr 2 this acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed if this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm consistent with projections in the ipcc tar

a reassessment of global and regional mean sea level trends from topex and jason 1 altimetry based on revised reference frame and orbits 1 mean sea level trends from topex and jason 1 altimeter data are recomputed using unified geophysical modeling and the new itrf2005 terrestrial reference frame for the entire altimetric time series with consistent orbits based on satellite laser ranging slr and doris tracking data we obtain a global rate of 3 36 0 41 mm yr over the 14 year period from 1993 to 2007 the regional sea level trends computed with the new reference frame show significant north south hemispherical offsets of 1 5 mm yr relative to trends based on the previous 1995 era frame regional sea level trend comparisons for the time periods of 1993 1999 and 1999 2005 reveal strong basin scale polarities and pronounced inter decadal variability with a relative increase in the global mean sea level trend of 1 5 0 7 mm yr in the latter seven years

partial rupture of a locked patch of the sumatra megathrust during the 2007 earthquake sequence the great sumatra andaman earthquake and tsunami of 2004 was a dramatic reminder of the importance of understanding the seismic and tsunami hazards of subduction zones 1 2 3 4 in march 2005 the sunda megathrust ruptured again producing an event 5 of moment magnitude mw 8 6 south of the 2004 rupture area which was the site of a similar event in 1861 ref 6 concern was then focused on the mentawai area where large earthquakes had occurred in 1797 mw 8 8 and 1833 mw 9 0 6 7 two earthquakes one of mw 8 4 and twelve hours later one of mw 7 9 indeed occurred there on 12 september 2007 here we show that these earthquakes ruptured only a fraction of the area ruptured in 1833 and consist of distinct asperities within a patch of the megathrust that had remained locked in the interseismic period this indicates that the same portion of a megathrust can rupture in different patterns depending on whether asperities break as isolated seismic events or cooperate to produce a larger rupture this variability probably arises from the influence of non permanent barriers zones with locally lower pre stress due to the past earthquakes the stress state of the portion of the sunda megathrust that had ruptured in 1833 and 1797 was probably not adequate for the development of a single large rupture in 2007 the moment released in 2007 amounts to only a fraction both of that released in 1833 and of the deficit of moment that had accumulated as a result of interseismic strain since 1833 the potential for a large megathrust event in the mentawai area thus remains large

rupture and variable coupling behavior of the mentawai segment of the sunda megathrust during the supercycle culmination of 1797 to 1833 we refer to periods of subduction strain accumulation beneath the mentawai islands sumatra as supercycles because each culminates in a series of partial ruptures of the megathrust in its final decades the finale of the previous supercycle comprised two giant earthquakes in 1797 and 1833 and whatever happened in between this behavior between two great ruptures has implications for how the megathrust will behave between its more recent partial failure during the m w 8 4 earthquake of 2007 and subsequent large ruptures we synthesize previously published coral microatoll records and a large new coral data set to constrain not only these two giant ruptures but also the intervening interseismic megathrust behavior we present detailed maps of coseismic uplift during the two earthquakes and of interseismic deformation during the periods 1755 1833 and 1950 2000 as well as models of the corresponding slip and coupling on the underlying megathrust the large magnitudes we derive m w 8 6 8 8 for 1797 and m w 8 8 8 9 for 1833 confirm that the 2007 earthquakes released only a fraction of the moment released during the previous rupture sequence whereas megathrust behavior leading up to the 1797 and 2007 earthquakes was similar and comparatively simple behavior between 1797 and 1833 was markedly different and more complex several patches of the megathrust became weakly coupled following the 1797 earthquake we conclude that while major earthquakes generally do not involve rupture of the entire mentawai segment they may significantly change the state of coupling on the megathrust for decades to follow influencing the progression of subsequent ruptures

irregular recurrence of large earthquakes along the san andreas fault evidence from trees old trees growing along the san andreas fault near wrightwood california record in their annual ring width patterns the effects of a major earthquake in the fall or winter of 1812 to 1813 paleoseismic data and historical information indicate that this event was the san juan capistrano earthquake of 8 december 1812 with a magnitude of 7 5 the discovery that at least 12 kilometers of the mojave segment of the san andreas fault ruptured in 1812 only 44 years before the great january 1857 rupture demonstrates that intervals between large earthquakes on this part of the fault are highly variable this variability increases the uncertainty of forecasting destructive earthquakes on the basis of past behavior and accentuates the need for a more fundamental knowledge of san andreas fault dynamics

inverting geodetic time series with a principal component analysis based inversion method 1 the global positioning system gps system now makes it possible to monitor deformation of the earth s surface along plate boundaries with unprecedented accuracy in theory the spatiotemporal evolution of slip on the plate boundary at depth associated with either seismic or aseismic slip can be inferred from these measurements through some inversion procedure based on the theory of dislocations in an elastic half space we describe and test a principal component analysis based inversion method pcaim an inversion strategy that relies on principal component analysis of the surface displacement time series we prove that the fault slip history can be recovered from the inversion of each principal component because pcaim does not require externally imposed temporal filtering it can deal with any kind of time variation of fault slip we test the approach by applying the technique to synthetic geodetic time series to show that a complicated slip history combining coseismic postseismic and nonstationary interseismic slip can be retrieved from this approach pcaim produces slip models comparable to those obtained from standard inversion techniques with less computational complexity we also compare an afterslip model derived from the pcaim inversion of postseismic displacements following the 2005 8 6 nias earthquake with another solution obtained from the extended network inversion filter enif we introduce several extensions of the algorithm to allow statistically rigorous integration of multiple data sources e g both gps and interferometric synthetic aperture radar time series over multiple timescales pcaim can be generalized to any linear inversion algorithm

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

deformation cycles of subduction earthquakes in a viscoelastic earth subduction zones produce the largest earthquakes over the past two decades space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes the short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle piecing together geodetic snapshots from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short term years and long term decades and centuries viscous behaviour of the mantle traditional views based on elastic models such as coseismic deformation being a mirror image of interseismic deformation are being thoroughly revised snapshots of subduction zones using space geodesy reveal that the viscous behaviour of the mantle controls crustal deformation requiring the revision of traditional elastic models for earthquake risk assessment space geodesy the use of satellites to monitor earth has revolutionized our view of crustal deformation between consecutive earthquakes however the brevity of such measurements means that studies must be done by comparing multiple subduction zones at different stages of the earthquake cycle by piecing together geodetic snapshots from the sumatra chile and cascadia subduction zones this review presents a unifying picture in which deformation is controlled by the viscous behaviour of the mantle in both the short term years and the long term decades to centuries

a comparative study of the sumatran subduction zone earthquakes of 1935 and 1984 a m s 7 7 earthquake struck the western equatorial coast of sumatra in december 1935 it was the largest event in the region since the two devastating giant earthquakes of 1833 and 1861 historical seismograms of this event from several observatories around the world provide precious information that constrains the source parameters of the earthquake to more precisely quantify the location geometry and mechanism of the 1935 event and to estimate the coseismic deformation we analyze the best of the available teleseismic historical seismograms by comparing systematically the records of the 1935 earthquake with those of a smaller event that occurred in the same region in 1984 first we constrain the source parameters of the 1984 event using teleseismic records then we compare the records of the 1935 event with those of 1984 from the same sites and instruments to do this we choose several time windows in the corresponding seismograms that contain clearly identifiable phases and deconvolve the modern event from the older one the deconvolutions result in very narrow pulses with similar sizes thus confirming similar locations and mechanisms for the events the initiation of the 1984 event was on the subduction interface at a depth of 27 2 km its m 0 is 6 5 x 10 19 n m m w is 7 2 the sense of slip was nearly pure thrust on a plane dipping 12 the 1935 event also involved rupture of the shallow subduction interface but was about five times larger m 0 3 3 x 10 20 n m m w 7 7 and initiated a few kilometers to the southeast along strike the 1935 rupture propagated unilaterally toward the southeast the along strike rupture length was about 65 km from these source parameters we calculate the surface deformations assuming an elastic multilayered medium these deformations compare favorably with those actually recovered from paleoseismic data in the form of coral microatolls

deformation and slip along the sunda megathrust in the great 2005 nias simeulue earthquake seismic rupture produced spectacular tectonic deformation above a 400 kilometer strip of the sunda megathrust offshore northern sumatra in march 2005 measurements from coral microatolls and global positioning system stations reveal trench parallel belts of uplift up to 3 meters high on the outer arc islands above the rupture and a 1 meter deep subsidence trough farther from the trench surface deformation reflects more than 11 meters of fault slip under the islands and a pronounced lessening of slip trenchward a saddle in megathrust slip separates the northwestern edge of the 2005 rupture from the great 2004 sumatra andaman rupture the southeastern edge abuts a predominantly aseismic section of the megathrust near the equator

interseismic deformation above the sunda megathrust recorded in coral microatolls of the mentawai islands west sumatra past half century vary from 2 to 14 mm yr 1 and increase southwestward toward the subduction trench the pattern is consistent with rates of subsidence measured by a sparse network of continuously recording global positioning system cgps stations and with locking of a 400 km long section of the underlying subduction megathrust between about 1s and 4s this record of subsidence and tilting extending nearly a century into the past implies that the region is advancing toward the occurrence of another giant earthquake however evidence of episodic rather than steady subsidence reflects a behavior that is more complex than simple elastic strain accumulation and relief most prominent of these episodes is an extensive emergence subsidence couplet in about 1962 which may be the result of rapid aseismic slip on the megathrust between the islands and the trench lower subsidence rates recorded by the corals since about 1985 may reflect failure on many small patches within the locked section of the megathrust

coral evidence for earthquake recurrence and an a d 1390 1455 cluster at the south end of the 2004 aceh andaman rupture coral records of relative sea level change provide a history of vertical interseismic and coseismic deformation along the coast of northern simeulue island sumatra and reveal details about earthquakes in the 10th and 14th 15th centuries a d along the southern end of the december 2004 m w 9 2 sunda megathrust rupture over a 56 year period between a d 1390 and 1455 northern simeulue experienced a cluster of megathrust ruptures associated with total uplift that was considerably more than in 2004 uplifted corals at two sites constrain the first event of the cluster to a d 1393 3 and 1394 2 2 a smaller but well substantiated uplift occurred in northern simeulue in 1430 3 an inferred third uplift in a d 1450 3 killed all corals on the reef flats of northern simeulue the amount of uplift during this third event though confirmed only to have exceeded 28 and 41 cm at two sites probably surpassed the 100 and 44 cm that occurred respectively at those sites in 2004 and it was likely more than in 2004 over all of northern simeulue the evidence for past earthquake clustering combined with the inference of considerably greater uplift in a d 1390 1455 than in 2004 suggests that strain may still be stored along the southernmost part of the 2004 rupture interseismic subsidence rates recorded by northern simeulue coral microatolls have varied by up to a factor of 4 at some sites from one earthquake cycle to another

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

invited review paper seismicity along the south american subduction zone review of large earthquakes tsunamis and subduction zone complexity abstract earthquakes along the shallow south american subduction zone exhibit heterogeneous rupture characteristics going back several centuries of the earthquake record in this area this heterogeneity is manifest in several ways such as changes in rupture mode from magnitude 8 events during one century followed by smaller ones in other time periods as well as unusual tsunami events there is also an apparent interaction between earthquake rupture and subducting plate complexity in this region significant complexity exists on the subducting nazca plate including fracture zones and ridges such as the large nazca ridge several large magnitude earthquakes have occurred in the region of ridge subduction but no earthquake rupture has ruptured through these features into adjacent regions suggesting that these subducting features act to segment the margin other features such as fracture zones and variable sediment thickness on the nazca plate appear to influence earthquake behavior over a wide range of magnitude scales upper plate features such as crustal faults also lead to heterogeneous earthquake behavior here i provide an overview of seismicity along the margin since 1850 in the context of the subduction zone structures this includes great earthquakes such as the 1906 ecuador and 1960 chile events i also present results showing increased rupture complexity in moderate magnitude earthquakes that can also be linked to certain nazca plate features

modern vertical deformation above the sumatran subduction zone paleogeodetic insights from coral microatolls coral microatolls from the coast and outer arc islands of western sumatra retain a stratigraphic and morphologic record of relative sea level change which is due in large part to vertical tectonic deformation above the sumatran subduction zone low water levels whose fluctuations produce measurable changes in coral morphology limit the upward growth of the microatolls annual rings derived from seasonal variations in coral density serve as an internal chronometer of coral growth the microatolls act as natural long term tide gauges recording sea level variations on time scales of decades field observations and stratigraphic analysis of seven microatolls five from the outer arc islands and two from the mainland coast indicate that the mentawai islands have been submerging at rates of 4 10 mm yr over the last four or five decades while the mainland has remained relatively stable the presence of fossil microatolls up to several thousand years old in the intertidal zone indicates that little permanent vertical deformation has occurred over that time thus most of the strain accumulated in the past few decades represents interseismic deformation that is recovered during earthquakes elastic dislocation models using these submergence data suggest that elastic strain is being accumulated in the interseismic period and that the subduction zone in this region is fully coupled

geodetic observations of an earthquake cycle at the sumatra subduction zone role of interseismic strain segmentation 1 we use survey mode and continuous gps data from 1991 to 2007 to examine fault segmentation in the earthquake cycle at the sumatra megathrust site of the 26 december 2004 mw 9 1 sumatra andaman the 28 march 2005 mw 8 7 nias simeulue and the 12 september 2007 mw 8 4 mentawai earthquakes these data including new observations from 2006 and 2007 allow us to observe the final few years of one earthquake cycle and the beginning of the next our analysis reveals that the megathrust is segmented a characteristic that may persist through multiple earthquake cycles the nias simeulue earthquake ruptured approximately the same region that broke in 1861 a 300 km long segment abutting the sumatra andaman rupture zone farther southeast the mentawai segment of the megathrust 0 5 s 5 s which produced m 8 earthquakes in 1797 and 1833 is fully locked in the interseismic period but is flanked by two freely slipping regions the batu islands in the nw and enggano in the se the 12 september 2007 mentawai earthquake sequence ruptured only the southern one third of the 1833 rupture zone we model postseismic deformation from the sumatra andaman and nias simeulue earthquakes and find that afterslip was concentrated updip and downdip respectively from the main shocks comparing the velocity fields before and after 2001 we find the subduction zone underneath the batu islands and enggano which prior to the earthquakes was partially to fully coupled appears now to be slipping freely thus while the segmentation of the subduction zone is preserved interseismic coupling on the subduction fault may vary with time

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

segmentation of megathrust rupture zones from fore arc deformation patterns over hundreds to millions of years arauco peninsula chile 1 this work explores the control of fore arc structure on segmentation of megathrust earthquake ruptures using coastal geomorphic markers the arauco nahuelbuta region at the south central chile margin constitutes an anomalous fore arc sector in terms of topography geology and exhumation located within the overlap between the concepcion and valdivia megathrust segments this boundary however is only based on 500 years of historical records we integrate deformed marine terraces dated by cosmogenic nuclides syntectonic sediments published fission track data seismic reflection profiles and microseismicity to analyze this earthquake boundary over 10 2 10 6 years rapid exhumation of nahuelbuta s dome like core started at 4 1 2 ma coeval with inversion of the adjacent arauco basin resulting in emergence of the arauco peninsula here similarities between topography spatiotemporal trends in fission track ages pliocene pleistocene growth strata and folded marine terraces suggest that margin parallel shortening has dominated since pliocene time this shortening likely results from translation of a fore arc sliver or microplate decoupled from south america by an intra arc strike slip fault microplate collision against a buttress leads to localized uplift at arauco accrued by deep seated reverse faults as well as incipient oroclinal bending the extent of the valdivia segment which ruptured last in 1960 with an mw 9 5 event equals the inferred microplate we propose that mechanical homogeneity of the fore arc microplate delimits the valdivia segment and that a marked discontinuity in the continental basement at arauco acts as an inhomogeneous barrier controlling nucleation and propagation of 1960 type ruptures as microplate related deformation occurs since the pliocene we propose that this earthquake boundary and the extent of the valdivia segment are spatially stable seismotectonic features at million year scale

variation of initial 230th 232th and limits of high precision u th dating of shallow water corals one hundred eighty u th data including 23 isochrons on 24 pristine modern and holocene corals and 33 seawater samples were analyzed using sector field mass spectrometry to understand the variability of initial 230th 232th 230th 232th0 this dataset allows us to further assess the accuracy and precision of coral 230th dating method by applying quality control including careful sampling and subsampling protocols and the use of contamination free storage and workbench spaces the resulting low procedural blanks give an equivalent uncertainty in age of only 0 2 0 3 yr for 1 2 g of coral sample using site specific 230th 232th0 values or isochron techniques our study demonstrates that corals with an age less than 100 yrs can be 230th dated with precisions of 1 yr six living subtidal coral samples were collected from two continental shelf sites nanwan off southern taiwan in the western pacific and son tra off central vietnam in the south china sea one coral core was drilled from an open ocean site santo island vanuatu in the western tropical pacific and modern and fossil intertidal coral slabs 17 in total were cut from six sites around the islands of simeulue lago north pagai and south pagai of sumatra in the eastern indian ocean the results indicate that the main source of thorium is the dissolved phase of seawater with variation of 230th 232th0 depending on local hydrology with intense input of terrestrial material low 230th 232th0 atomic ratios of 4 9 10 6 and 3 2 10 6 with a 10 variation are observed in nanwan and son tra respectively at the santo site we find a value of 5 6 10 6 at 4 horizons and one high value of 24 10 6 in a sample from ad 1974 6 0 5 likely due to the upwelling of cold water during a la nina event between ad 1973 and 1976 the natural dynamics of 230th 232th0 recorded in the intertidal corals at sites in the sumatran islands are complicated so that this value varies significantly from 3 0 to 9 4 10 6 three of the 141 modern coral 230th ages differ from their true ages by 23 to 4 indicating the presence of detrital material with anomalous 230th 232th values duplicate measurement of coeval subsamples is therefore recommended to verify the age accuracy this improved high precision coral 230th dating method raises the prospects of refining the age models for band counted and tracer tuned chronologies and of advancing coral paleoclimate research

the 2010 mw 7 8 mentawai earthquake very shallow source of a rare tsunami earthquake determined from tsunami field survey and near field gps data 1 the mw 7 8 october 2010mentawai indonesia earthquake was a tsunami earthquake a rare type of earthquake that generates a tsunami much larger than expected based on the seismicmagnitude itproducedalocallydevastatingtsunami withrunupcommonlyinexcess of 6 m we examine this event using a combination of high rate gps data from instruments located on the nearby islands and a tsunami field survey the gps displacement time series are deficient in high frequency energy and show small coseismic displacements 16 m our modeling results show that the combination of the small gps displacements and large tsunami can only be explained by high fault slip at very shallow depths far from the islands and close to the oceanic trench inelastic uplift of trench sediments likely contributed to the size of the tsunami recent results for the 2011 mw 9 0 tohoko oki earthquake have also shown shallow fault slip but the results from our study which involves a smaller earthquake provide much stronger constraints on how shallow the rupture can be with the majority of slip for the mentawai earthquake occurring at depths of 6 km this result challenges the conventional wisdom that the shallow tips of subduction megathrusts are aseismic and therefore raises important questions both about the mechanical properties of the shallow fault zone and the potential seismic and tsunami hazard of this shallow region

dating earthquakes with high precision thorium 230 ages of very young corals mass spectrometric techniques have recently yielded significant increases in precision and sensitivity over previous methods for measuring 230 th abundance in corals to assess the accuracy of 230 th ages three corals from vanuatu whose ages were known from counting annual growth bands were analyzed for each sample the date of growth determined by 230 th analysis a d 1969 3 1932 5 and1806 5 2 uncertainties based on analytical error was indistinguishable from the date determined by counting bands a d 1971 1973 1935 1937 and 1804 1810 indicating that the 230 th dates are accurate 230 th dates were also determined for two adjacent emerged heads from santo is vanuatu which were thought to have died when they were raised above sea level during coseismic uplift the dates a d 1864 4 1866 4 were the same indicating that the heads died at the same time and consistent with the idea that they were killed by coseismic emergence around a d 1865 the difference between this date and the date of the only major historically documented earthquake that caused uplift a d 1973 m s 7 5 suggests a seismic recurrence interval of108 4y for santo analogous emerged corals from malekula is vanuatu yielded 230 th dates that were similar to each other a d 1729 3 1718 5 and are inferred to have died during coseismic emergence around a d 1729 in conjunction with the date of the only large historically documented earthquake that caused uplift a d 1965 m s 7 5 the recurrence interval for malekula is236 3y if similar emerged corals can be found this appraoch may be extended back in time and to other localities because it appears that such features can now be dated both accurately and precisely

an ancient shallow slip event on the mentawai segment of the sunda megathrust sumatra the outer arc islands of western sumatra rise during great megathrust earthquakes due to large slip on the underlying megathrust in contrast the islands subsided up to a few centimeters during the recent tsunamigenic earthquake of october 2010 due to slip far updip near the trench coral microatolls on one of the islands recorded a much larger subsidence at least 35 cm during an event in approximately a d 1314 we calculate a suite of slip models slightly deeper and or larger than the 2010 event that are consistent with this large amount of subsidence sea level records from older coral microatolls suggest that these events occur at least once every millennium but likely far less frequently than their great downdip neighbors the revelation that shallow slip events are important contributors to the seismic cycle of the mentawai segment further complicates our understanding of this subduction megathrust and our assessment of the region s exposure to seismic and tsunami hazards

persistent elastic behavior above a megathrust rupture patch nias island west sumatra we quantify fore arc deformation using fossil reefs to test the assumption commonly made in seismic cycle models that anelastic deformation of the fore arc is negligible elevated coral microatolls paleoreef flats and chenier plains show that the sumatran outer arc island of nias has experienced a complex pattern of relatively slow long term uplift and subsidence during the holocene epoch this same island rose up to 2 9 m during the mw 8 7 sunda megathrust rupture in 2005 the mismatch between the 2005 and holocene uplift patterns along with the overall low rates of holocene deformation reflects the dominance of elastic strain accumulation and release along this section of the sunda outer arc high and the relatively subordinate role of upper plate deformation in accommodating long term plate convergence the fraction of 2005 uplift that will be retained permanently is generally 4 for sites that experienced more than 0 25 m of coseismic uplift average uplift rates since the mid holocene range from 1 5 to 0 2 mm a and are highest on the eastern coast of nias where coseismic uplift was nearly zero in 2005 the pattern of long term uplift and subsidence is consistent with slow deformation of nias along closely spaced folds in the north and trenchward dipping back thrusts in the southeast low holocene tectonic uplift rates provide for excellent geomorphic and stratigraphic preservation of the mid holocene relative sea level high which was under way by 7 3 ka and persisted until 2 ka