new insights into the mechanism of postseismic stress relaxation exemplified by the 23 june 2001 mw 8 4 earthquake in southern peru 1 the 2001 mw 8 4 southern peru subduction earthquake marked the beginning of a transient postseismic surface motion in direction of the coseismic displacement at the permanent gps station arequipa in general this motion is assigned to afterslip our hypothesis is that the observed transient signal can be explained by stress relaxation processes in the overriding plate we use a 2d finite element model incorporating non linear viscoelastic maxwell rheology our model results indicate that coseismically induced stresses are relieved by viscoelastic stress relaxation in the lower crust the trenchward directed creep motion is transferred to the upper crust due to elastic coupling leading there to an instantaneous relief of elastic stresses in contrast to the existing conceptual models for stress relaxation which incorporate shear stresses we conclude that tensional elastic stresses throughout the crust and upper mantle are the main driving forces for the transient gps signal

on the effects of thermally weakened ductile shear zones on postseismic deformation 1 we present three dimensional 3 d numerical models of postseismic deformation following repeated earthquakes on a vertical strike slip fault our models use linear maxwell burgers and temperature dependent power law rheology for the lower crust and upper mantle we consider effects of viscous shear zones that result from thermomechanical coupling and investigate potential kinematic similarities between viscoelastic models incorporating shear zones and elastic models incorporating rate strengthening friction on a deep aseismic fault root we find that the thermally activated shear zones have little effect on postseismic relaxation in particular the presence of shear zones does not change the polarity of vertical displacements in cases of rheologies that are able to generate robust postseismic transients stronger rheologies can give rise to an opposite polarity of vertical displacements but the amplitude of the predicted transient deformation is generally negligible we conclude that additional to thermomechanical coupling mechanisms of strain localization are required for a viscoelastic model to produce a vertical deformation pattern similar to that due to afterslip on a deep extension of a fault we also investigate the discriminating power of models incorporating burgers and power law rheology these rheologies were proposed to explain postseismic transients following large m7 earthquakes in the mojave desert eastern california numerical simulations indicate that it may be difficult to distinguish between these rheologies even with high quality geodetic observations for observation periods less than a decade longer observations however may potentially allow discrimination between the competing models as illustrated by the model comparisons with available gps and interferometric synthetic aperture radar data

the link between rossby wave breakings and weather regime transitions abstractthe link between rossby wave breaking rwb and the four wintertime weather regimes over the north atlantic domain is studied in this paper using the 40 yr ecmwf re analysis era 40 data frequencies of occurrence of anticyclonic and cyclonic wave breaking awb and cwb respectively events are computed each weather regime has its own characteristic pattern of rwb frequencies cwb events are found to be most frequent for the greenland anticyclone weather regime whereas awb events occur more for the atlantic ridge and the zonal regimes time lagged composites show that the rwb events characterizing each weather regime occur more often during the formation of the regime rather than during its decay this suggests a reinforcement of the weather regime by rwb an exception is the blocking weather regime which is destroyed by an increase of cwb events south of greenland weather regime transitions are then studied using the low frequency streamfunction tendency budget two types of precursors for th

a high resolution time variable afterslip model for the 2010 maule mw 8 8 chile megathrust earthquake the excellent spatial coverage of continuous gps stations in the region affected by the maule mw 8 8 2010 earthquake combined with the proximity of the coast to the seismogenic zone allows us to model megathrust afterslip on the plate interface with unprecedented detail we invert post seismic observations from continuous gps sites to derive a time variable model of the first 420 d of afterslip we also invert co seismic gps displacements to create a new co seismic slip model the afterslip pattern appears to be transient and non stationary with the cumulative afterslip pattern being formed from afterslip pulses changes in static stress on the plate interface from the co and post seismic slip cannot solely explain the aftershock patterns suggesting that another process perhaps fluid related is controlling the lower magnitude aftershocks we use aftershock data to quantify the seismic coupling distribution during the post seismic phase comparison of the post seismic behaviour to interseismic locking suggests that highly locked regions do not necessarily behave as rate weakening in the post seismic period by comparing the inter seismic locking co seismic slip afterslip and aftershocks we attempt to classify the heterogeneous frictional behaviour of the plate interface

the 1960 chile earthquake inversion for slip distribution from surface deformation summary a total of 166 observations of sea level change 130 measurements of elevation difference and 16 determinations of horizontal strain provide an excellent view of the quasi static source process of the great 1960 chilean earthquake these surface deformation data were employed in classical uniform slip fault models as well as more recently developed models that allow spatial variability of slip the best uniform slip planar usp model is 850km long 130km wide and dips 20 seventeen metres of fault displacement contributed to a usp moment of 9 4 times 1022 n m the variable slip planar vsp model concentrates slip on a 900 km long 150 km wide band parallel to the coast several peaks of slip with dimensions of 50 100 km appear in this band and are thought to represent major subduction zone asperities important fractures of the oceanic lithosphere bound the 1960 rupture and are offered as a potential source of fault segmentation within the chilean subduction zone the vsp moment for 1960 earthquake totals 9 5 times 1022 n m about one fifth of the value estimated for the foreshock mainshock sequence from seismic methods except for areas out to sea geodetic resolution on the fault is fairly uniform thus it is unlikely that slip missed by the network could increase the vsp moment much beyond 1 8 times 1023 n m several patches of moment isolated from the main body at 80 110 km depth are found down dip in the vsp model and are presumably indicative of aseismic slip one patch at the northern end of the rupture is probably associated with the initiation phase of the mainshock although the time sequence of the relationship is unknown tide gauge records suggest that another patch between 40 and 43 s responsible for the observed strain and uplifts inland at those latitudes is not of coseismic origin but derives from in place post seismic creep over several years apparently great 1960 type events are not typical members of the 128 yr earthquake cycle in south central chile the nazca south america boundary here is characterized by a variable rupture mode in which major asperities are completely broken by great earthquakes only once in four or five earthquake cycles the more frequent large earthquakes that geographically overlap the great events fill in between the locked zones

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

localized fault slip to the trench in the 2010 maule chile mw 8 8 earthquake from joint inversion of high rate gps teleseismic body waves insar campaign gps and tsunami observations the 27 february 2010 mw 8 8 maule earthquake ruptured 500 km along the plate boundary offshore central chile between 34 s and 38 5 s establishing whether coseismic fault offset extended to the trench is important for interpreting both shallow frictional behavior and potential for tsunami earthquakes in the region joint inversion of high rate gps teleseismic body waves interferometric synthetic aperture radar insar campaign gps and tsunami observations yields a kinematic rupture model with improved resolution of slip near the trench bilateral rupture expansion is resolved in our model with relatively uniform slip of 5 10 m downdip beneath the coast and two near trench high slip patches with 12 m displacements the peak slip is 17 m at a depth of 15 km on the central megathrust located 200 km north from the hypocenter and overlapping the rupture zone of the 1928 m 8 event the updip slip is 16 m near the trench another shallow near trench patch is located 150 km southwest of the hypocenter with a peak slip of 12 m checkerboard resolution tests demonstrate that correctly modeled tsunami data are critical to resolution of slip near the trench with other data sets allowing but not requiring slip far offshore large interplate aftershocks have a complementary distribution to the coseismic slip pattern filling in gaps or outlining edges of large slip zones two clusters of normal faulting events locate seaward along the plate motion direction from the localized regions of large near trench slip suggesting that proximity of slip to the trench enhanced extensional faulting in the underthrusting plate

prevalence of viscoelastic relaxation after the 2011 tohoku oki earthquake seafloor global positioning system observations immediately after the great 2011 tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than just afterslip on the fault as is commonly assumed this paper presents revised estimates of the afterslip following the 2011 tohoku oki earthquake based on seafloor gps observations made immediately after the earthquake tianhaozhe sun et al obtain unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than elastic afterslip on the fault as is commonly assumed they conclude that models which erroneously assume an elastic earth substantially overestimate afterslip downdip of the rupture zone and underestimate afterslip updip after a large subduction earthquake crustal deformation continues to occur with a complex pattern of evolution1 this postseismic deformation is due primarily to viscoelastic relaxation of stresses induced by the earthquake rupture and continuing slip afterslip or relocking of different parts of the fault2 3 4 5 6 when postseismic geodetic observations are used to study earth s rheology and fault behaviour it is commonly assumed that short term a few years deformation near the rupture zone is caused mainly by afterslip and that viscoelasticity is important only for longer term deformation6 7 however it is difficult to test the validity of this assumption against conventional geodetic data here we show that new seafloor gps global positioning system observations immediately after the great tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation these data reveal fast landward motion of the trench area opposing the seaward motion of gps sites on land using numerical models of transient viscoelastic mantle rheology we demonstrate that the landward motion is a consequence of relaxation of stresses induced by the asymmetric rupture of the thrust earthquake a process previously unknown because of the lack of near field observations our findings indicate that previous models assuming an elastic earth will have substantially overestimated afterslip downdip of the rupture zone and underestimated afterslip updip of the rupture zone our knowledge of fault friction based on these estimates therefore needs to be revised

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

toward understanding tectonic control on the mw 8 8 2010 maule chile earthquake the maule earthquake of 27th february 2010 m w 8 8 affected similar to 500 km of the nazca south america plate boundary in south central chile producing spectacular crustal deformation here we present a detailed estimate of static coseismic surface offsets as measured by survey and continuous gps both in near and far field regions earthquake slip along the megathrust has been inferred from a joint inversion of our new data together with published gps insar and land level changes data using green s functions generated by a spherical finite element model with realistic subduction zone geometry the combination of the data sets provided a good resolution indicating that most of the slip was well resolved coseismic slip was concentrated north of the epicenter with up to 16 m of slip whereas to the south it reached over 10 m within two minor patches a comparison of coseismic slip with the slip deficit accumulated since the last great earthquake in 1835 suggests that the 2010 event closed a mature seismic gap slip deficit distribution shows an apparent local overshoot that highlight cycle to cycle variability which has to be taken into account when anticipating future events from interseismic observations rupture propagation was obviously not affected by bathymetric features of the incoming plate instead splay faults in the upper plate seem to have limited rupture propagation in the updip and along strike directions additionally we found that along strike gradients in slip are spatially correlated with geometrical inflections of the megathrust our study suggests that persistent tectonic features may control strain accumulation and release along subduction megathrusts c 2012 elsevier b v all rights reserved

gradual unlocking of plate boundary controlled initiation of the 2014 iquique earthquake a long foreshock series unlocked the south american plate boundary until eventually initiating the m 8 1 iquique chile earthquake two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure on 1 april 2014 northern chile was struck by a magnitude 8 1 earthquake following a protracted series of foreshocks the integrated plate boundary observatory chile monitored the entire sequence of events providing unprecedented resolution of the build up to the main event and its rupture evolution here we show that the iquique earthquake broke a central fraction of the so called northern chile seismic gap the last major segment of the south american plate boundary that had not ruptured in the past century1 2 since july 2013 three seismic clusters each lasting a few weeks hit this part of the plate boundary with earthquakes of increasing peak magnitudes starting with the second cluster geodetic observations show surface displacements that can be associated with slip on the plate interface these seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion leading up to this earthquake the b value of the foreshocks gradually decreased during the years before the earthquake reversing its trend a few days before the iquique earthquake the mainshock finally nucleated at the northern end of the foreshock area which skirted a locked patch and ruptured mainly downdip towards higher locking peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch we conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure distinguishing the iquique earthquake from most great earthquakes finally only one third of the gap was broken and the remaining locked segments now pose a significant increased seismic hazard with the potential to host an earthquake with a magnitude of 8 5

heterogeneous rheology controlled postseismic deformation of the 2011 tohoku oki earthquake using two dimensional finite element modeling we reproduced the observed postseismic deformation of the 2011 tohoku oki earthquake our model which accounts for the lithosphere asthenosphere boundary and weak zones beneath volcanoes was able to reproduce small scale 20 km perturbations in postseismic deformation observed by the dense geodetic network such as local subsidence around quaternary volcanoes the inverted afterslip has a peak at the downdip limit of the main rupture region on the subducting plate interface consistent with physical predictions the combination of afterslip and viscoelastic relaxation in a heterogeneous rheology model explains the observations well even on small scales

simple coupled midlatitude climate models a set of simple analytical models is presented and evaluated for interannual to decadal coupled ocean atmosphere modes at midlatitudes the atmosphere and ocean are each in sverdrup balance at these long timescales the atmosphere s temperature response to heating determines the spatial phase relation between sst and sea level pressure slp anomalies vertical advection balancing heating produces high low slp lying east of warm cold sst anomalies as observed in the antarctic circumpolar wave acw the decadal north pacific mode and the interannual north atlantic mode zonal advection in an atmosphere with a rigid lid produces low slp east of warm sst however if an ad hoc equivalent barotropic atmospheric response is assumed high slp lies east of warm sst relaxation to heating produces behavior like the observed north atlantic decadal pattern with low slp over warm sst meridional advection in the atmosphere cannot produce the observed sst slp patterns the dominant balance in the ocean s temperature equation determines the phase speed of the modes the coupled mode is nondispersive in all models examined here indicating the need for additional processes for modes with an sst slp offset as observed in the acw and north pacific ekman convergence acting as a heat source causes eastward propagation relative to the mean ocean flow sverdrup response to ekman convergence acting on the mean meridional temperature gradient causes westward propagation relative to the mean ocean flow when the ocean temperature adjusts through surface heat flux alone the mode is advected by the mean ocean flow and is damped relaxation to heating in the atmosphere when operating with sverdrup response in the ocean produces the only complete solution presented here that exhibits growth with an e folding timescale of order 100 days this solution appears appropriate for the north atlantic decadal mode in northern hemisphere basins with meridional boundaries the same sets of dynamics create the observed sst slp phase relation an additional factor is the creation of sst anomalies through variations in the western boundary current strengths which are related to the zonally integrated wind stress curl over the whole basin if barotropic and hence fast adjustment is assumed the resulting positive feedback can maintain or strengthen the coupled anomalies in the north pacific and interannual north atlantic modes

heterogeneous coupling of the sumatran megathrust constrained by geodetic and paleogeodetic measurements geodetic and paleogeodetic measurements of interseismic strain above the sumatran portion of the sunda subduction zone reveal a heterogeneous pattern of coupling annual banding in corals provides vertical rates of deformation spanning the last half of the 20th century and repeated gps surveys between 1991 and 2001 and continuous measurements at gps stations operated since 2002 provide horizontal velocities near the equator the megathrust is locked over a narrow width of only a few tens of kilometers in contrast the locked fault zone is up to about 175 km wide in areas where great interplate earthquakes have occurred in the past formal inversion of the data reveals that these strongly coupled patches are roughly coincident with asperities that ruptured during these events the correlation is most spectacular for rupture of the m w 8 7 nias simeulue earthquake of 2005 which released half of the moment deficit that had accumulated since its previous rupture in 1861 suggesting that this earthquake was overdue beneath the mentawai islands strong coupling is observed within the overlapping rupture areas of the great earthquakes of 1797 and 1833 the accumulated slip deficit since these events is slowly reaching the amount of slip that occurred during the 1833 earthquake but already exceeds the slip that occurred during the 1797 earthquake thus rerupture of part of the mentawai patch in september 2007 was not a surprise in contrast coupling is low below the batu islands near the equator and around enggano island at about 5 s where only moderate earthquakes m w 8 0 have occurred in the past two centuries the correlation of large seismic asperities with patches that are locked during the interseismic period suggests that they are persistent features this interpretation is reinforced by the fact that the large locked patches and great ruptures occur beneath persistent geomorphologic features the largest outer arc islands depth and convergence rate dependent temperature might influence the pattern of coupling through its effect on the rheology of the plate interface but other influences are required to account for the observed along strike heterogeneity of coupling in particular subduction of the investigator fracture zone could be the cause for the low coupling near the equator

post seismic relaxation following the great 2004 sumatra andaman earthquake on a compressible self gravitating earth summary the mw 9 0 2004 december 26 sumatra andaman and mw 8 7 2005 march 28 nias earthquakes which collectively ruptured approximately 1800 km of the andaman and sunda subduction zones are expected to be followed by vigorous viscoelastic relaxation involving both the upper and lower mantle because of these large spatial dimensions it is desirable to fully account for gravitational coupling effects in the relaxation process we present a stable method of computing relaxation of a spherically stratified compressible and self gravitating viscoelastic earth following an impulsive moment release event the solution is cast in terms of a spherical harmonic expansion of viscoelastic normal modes for simple layered viscoelastic models which include a low viscosity oceanic asthenosphere we predict substantial post seismic effects over a region several 100s of km wide surrounding the eastern indian ocean we compare observed gps time series from ten regional sites mostly in thailand and indonesia beginning in 2004 december with synthetic time series that include the coseismic and post seismic effects of the 2004 december 26 and 2005 march 28 earthquakes a viscosity structure involving a biviscous burgers body rheology in the asthenosphere explains the pattern and amplitude of post seismic offsets remarkably well

southern hemisphere blocking onsets associated with upper tropospheric divergence anomalies abstract upper tropospheric divergence anomalies and divergence tendencies prior to and during the onset of blocking have been investigated for selected cases over the southern hemisphere in search of links between the upper tropospheric response to tropical convective activity and the onset of blocking in midlatitudes climatologies of blocking defined by an objective index and divergence are established for the southern hemisphere and the southern pacific respectively relative blocking frequency versus longitude reveals a region of maximum blocking activity between 160 e and 75 w blocking frequencies for each enso phase indicate a shift toward the late austral fall and early winter during the warm phase whereas during the cold and neutral phases the highest frequencies are in june and july respectively composites of area averaged divergence anomalies for the selected blocking cases reveal more anomalous divergence than during nonblocking periods over the blocking regions and the immediate upstre

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

interpreting low frequency modes of southern hemisphere atmospheric variability as the rotational response to divergent forcing abstract the principal modes of southern hemisphere low frequency variability have recently been calculated using a 39 yr record of 300 hpa streamfunction fields from the ncep ncar reanalysis dataset the authors attempt to interpret these modes as the rotational response to some divergent forcing for a range of mean states the linearized barotropic vorticity equation bve is used to solve for the divergent wind that would generate or at least be consistent with the observed vorticity modes several of these low frequency modes can be generated by forcing the bve with fairly simple divergent wind fields that could easily be interpreted as resulting from anomalous tropical convection in particular this is found to be true for streamfunction anomalies with el nino southern oscillation enso high latitude mode south pacific wave and madden julian oscillation structure the authors speculate that it may be possible to relate these calculated divergent wind fields to recently observed olr fields and h

tropical connections to climatic change in the extratropical southern hemisphere the role of atlantic sst trends abstractthe austral spring relationships between sea surface temperature sst trends and the southern hemisphere sh extratropical atmospheric circulation are investigated using an atmospheric general circulation model agcm a suite of simulations are analyzed wherein the agcm is forced by underlying sst conditions in which recent trends are constrained to individual ocean basins pacific indian and atlantic allowing the impact of each region to be assessed in isolation when forced with observed global sst the model broadly replicates the spatial pattern of extratropical sh geopotential height trends seen in reanalyses however when forcing by each ocean basin separately similar structures arise only when atlantic sst trends are included it is further shown that teleconnections from the atlantic are associated with perturbations to the zonal walker circulation and the corresponding intensification of the local hadley cell the impact of which results in the development of atmospheric rossby w

depth of seismic coupling along subduction zones underthrusting at subduction zones can cause large earthquakes at shallow depths but it is always accommodated by aseismic deformation below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding along the plate interface we have determined the depth of this stability transition for the circurn pacific subduction zones of honshu kuriles kamchatka aleutians alaska mexico and chile these subduction zones have experienced great interplate earthquakes and the aftershock regions are well located depth estimates of interplate events that are located at the downdip edge of the aftershock regions are used to determine the maximum depth of seismic coupling for an average p wave velocity of 6 7 km s 1 above the plate interface we find that for most subduction zones the stability transition occurs at 40 5 km depth there are however several exceptions at the hokkaido trench junction where the japan trench and the kurile trench intersect seismic coupling is deep and extends down to 52 55 km deep coupling was also found in the coquimbo region in central chile the mexico subduction zone has shallow coupling the transition occurs at 20 30 km depth previous studies of micro earthquakes in honshu hokkaido the aleutians and alaska show that earthquakes within the upper plate extend no deeper than the downdip edge of the coupled zone that we find given our measurements of seismic coupling depth we then explore the mechanism that may determine coupling depth the concept of critical temperature has been used to explain the depth of seismic coupling in other tectonic environments thus we first test whether a critical temperature can explain our results temperatures at the plate interface are dependent on many variables but two that are poorly determined are shear stress and radiogenic heat generation shear stress has been constrained by inversion of heat flow data assuming a crustal radiogenic heat production rate of 3 1 exp z 8 5 wm 3 and a constant coefficient of friction we find two critical temperatures of about 400 c and 550 c the lower critical temperature may be characteristic of regions with a relatively thick continental crust and the higher temperature of regions with a relatively thin continental crust on the other hand one single critical temperature of about 250 c can explain the coupling depths if shear stresses are constant with depth

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

afterslip and viscoelastic relaxation model inferred from the large scale post seismic deformation following the 2010 mw 8 8 maule earthquake chile

the role of interactions between multiscale circulations on the observed zonally averaged zonal wind variability associated with the madden julian oscillation abstractthe mechanisms driving the upper tropospheric zonal mean intraseasonal zonal wind associated with the madden julian oscillation are examined through budget analysis during boreal winter to diagnose the role of nonlinear and cross scale interactions the wind fields are decomposed into three temporal bands including the intraseasonal time scale 30 100 days and periods shorter and longer than the intraseasonal time scales the intraseasonal zonal mean circulation and its driving mechanisms are first examined based on the leading eofs of the intraseasonal zonal wind consistent with previous studies of intraseasonal atmospheric angular momentum the upper troposphere zonal mean intraseasonal zonal wind anomaly begins in the tropics and propagates poleward results show that interaction between the background state and intraseasonal time scale zonally symmetric and asymmetric circulation helps drive changes in the tropical intraseasonal zonal wind and its poleward propagation the intraseasonal a

horizontal structure and seasonality of large scale circulations associated with submonthly tropical convection the relationship between deep tropical convection and large scale atmospheric circulation in the 6 30 day period range is examined regression relationships between filtered outgoing longwave radiation at various locations in the tropics and 200 and 850 mb circulation are mapped for the standard seasons and the spatial structure and seasonal dependence of the results are interpreted in view of the basic state circulation in regions where the convection is embedded in upper level easterlies anomalous equatorial easterly flow is typically present at 200 mb within and to the west of the convective signal along with patterns of meridional outflow into subtropical anticyclonic perturbations lagged relationships suggest that the convection is forcing the circulation in many of these cases the outflow and subtropical circulations are strongest into the winter hemisphere during the solstitial seasons with more symmetric signals about the equator seen in the equinoctial seasons the longitudinal positioning of the subtropical features with respect to the convection varies but is generally located due poleward or just to the east of the convection there tends to be a first baroclinic mode vertical structure to these circulations such that equatorial westerlies are present at 850 mb within the convection with closed circulations on either side of the equator resembling equatorial rossby modes especially common over the atlantic and pacific sectors as a contrast in regions located within upper level westerlies or along the margin of influence of upper westerly disturbances convection appears to be forced by upper level wave energy propagating into the deep tropics with the heating located in the upward motion region ahead of upper level troughs this occurs over the atlantic and eastern pacific sectors during northern winter and spring and over australia the south pacific and south america during southern summer when upper westerlies are at relatively low latitudes where they can interact with deep tropical convection the results confirm theoretical and modeling ideas that suggest that rossby wave energy is able to propagate into the deep tropics in regions where upper level westerlies exist in the tropics

the 2010 mw 8 8 maule megathrust earthquake of central chile monitored by gps large earthquakes produce crustal deformation that can be quantified by geodetic measurements allowing for the determination of the slip distribution on the fault we used data from global positioning system gps networks in central chile to infer the static deformation and the kinematics of the 2010 moment magnitude m w 8 8 maule megathrust earthquake from elastic modeling we found a total rupture length of 500 kilometers where slip up to 15 meters concentrated on two main asperities situated on both sides of the epicenter we found that rupture reached shallow depths probably extending up to the trench resolvable afterslip occurred in regions of low coseismic slip the low frequency hypocenter is relocated 40 kilometers southwest of initial estimates rupture propagated bilaterally at about 3 1 kilometers per second with possible but not fully resolved velocity variations

three dimensional viscoelastic finite element model for postseismic deformation of the great 1960 chile earthquake 2 5 10 19 pa s for the continental upper mantle the model well explains the gps observations numerical tests suggest that the continental mantle viscosity value is reasonably well constrained the model shows the prolonged postseismic seaward motion of the inland area to be a unique feature of earthquakes with very long rupture along strike and large coseismic fault slip for short rupture and small coseismic slip the motion will stop very quickly after the earthquake explaining why this phenomenon is not more commonly observed with an oceanic mantle viscosity of 10 20 pa s the model also provides an explanation for tide gauge constrained postseismic uplift 200 km from the trench that had previously been explained using a model of prolonged afterslip of a deep segment of the chile subduction fault index terms 1236 geodesy and gravity rheology of the lithosphere and mantle 8160 1242 geodesy and gravity seismic deformations 7205 3230 mathematical geophysics numerical solutions 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling keywords postseismic deformation viscoelastic stress relaxation gps finite element modeling chile subduction zone upper mantle viscosity

comparison of postseismic afterslip models with aftershock seismicity for three subduction zone earthquakes nias 2005 maule 2010 and tohoku 2011 we focus on the relation between seismic and total postseismic afterslip following the maule mw 8 8 earthquake on 2010 february 27 in central chile first we calculate the cumulative slip released by aftershock seismicity we do this by summing up the aftershock regions and slip estimated from scaling relations comparing the cumulative seismic slip with afterslip models we show that seismic slip of individual aftershocks exceeds locally the inverted afterslip model from geodetic constraints as the afterslip model implicitly contains the displacements from the aftershocks this reflects the tendency of afterslip models to smear out the actual slip pattern however it also suggests that locally slip for a number of the larger aftershocks exceeds the aseismic slip in spite of the fact that the total equivalent moment of the afterslip exceeds the cumulative moment of aftershocks by a large factor this effect seen weakly for the maule 2010 and also for the tohoku 2011 earthquake can be explained by taking into account the uncertainties of the seismicity and afterslip models in spite of uncertainties the hypocentral region of the nias 2005 earthquake is suggested to release a large fraction of moment almost purely seismically therefore these aftershocks are not driven solely by the afterslip but instead their slip areas have probably been stressed by interseismic loading and the mainshock rupture in a second step we divide the megathrust of the maule 2010 rupture into discrete cells and count the number of aftershocks that occur within 50 km of the centre of each cell as a function of time we then compare this number to a time dependent afterslip model by defining the afterslip to aftershock ratio asar for each cell as the slope of the best fitting line when the afterslip at time t is plotted against aftershock count although we find a linear relation between afterslip and aftershocks for most cells there is significant variability in asar in both the downdip and along strike directions of the megathrust we compare the spatial distribution of asar with the spatial distribution of seismic coupling coseismic slip and bouguer gravity anomaly and in each case we find no significant correlation

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

space geodetic observations and models of postseismic deformation due to the 2005 m7 6 kashmir pakistan earthquake we use the l band advanced land observing satellite alos and c band envisat interferometric synthetic aperture data and campaign gps observations to study the postseismic deformation due to the 2005 magnitude 7 6 kashmir pakistan earthquake that occurred in the northwestern himalaya envisat data are available from both the descending and ascending orbits and span a time period of 4 5 years immediately following the earthquake 2005 2010 with nearly monthly acquisitions however the envisat data are highly decorrelated due to high topography and snow cover alos data are available from the ascending orbit and span a time period of 2 5 years between 2007 and 2009 over which they remain reasonably well correlated we derive the mean line of sight los postseismic velocity maps in the epicentral area of the kashmir earthquake using persistent scatterer method for envisat data and selective stacking for alos data los velocities from all data sets indicate an uplift decrease in radar range primarily in the hanging wall of the earthquake rupture over the entire period of synthetic aperture radar observations 2005 2010 models of poroelastic relaxation predict uplift of both the footwall and the hanging wall while models of viscoelastic relaxation below the brittle ductile transition predict subsidence increase in radar range in both the footwall and the hanging wall therefore the observed pattern of surface velocities indicates that the early several years of postseismic deformation were dominated by afterslip on the fault plane possibly with a minor contribution from poroelastic rebound kinematic inversions of interferometric synthetic aperture radar and gps data confirm that the observed deformation is consistent with afterslip primarily downdip of the seismic asperity to place constraints on the effective viscosity of the ductile substrate in the study area we subtract the surface deformation predicted by stress driven afterslip model from the mean los velocities and compare the residuals to models of viscoelastic relaxation for a range of assumed viscosities we show that in order to prevent surface subsidence the effective viscosity has to be greater than 1019 pa s

postseismic relocking of the subduction megathrust following the 2007 pisco peru earthquake characterizing the time evolution of slip over different phases of the seismic cycle is crucial to a better understanding of the factors controlling the occurrence of large earthquakes in this study we take advantage of interferometric synthetic aperture radar data and 3 5 years of continuous global positioning system gps measurements to determine interseismic coseismic and postseismic slip distributions in the region of the 2007 mw 8 0 pisco earthquake peru using the same fault geometry and inversion method our interseismic model based on pre 2007 campaign gps data suggests that the 2007 pisco seismic slip occurred in a region strongly coupled before the earthquake while afterslip occurred in low coupled regions large afterslip occurred in the peripheral area of coseismic rupture in agreement with the notion that afterslip is mainly induced by coseismic stress changes the temporal evolution of the region of maximum afterslip characterized by a relaxation time of about 2 3 years is located in the region where the nazca ridge is subducting consistent with rate strengthening friction promoting aseismic slip we estimate a return period for the pisco earthquake of about 230 years with an estimated aseismic slip that might account for about 50 of the slip budget in this region over the 0 50 km seismogenic depth range a major result of this study is that the main asperity that ruptured during the 2007 pisco earthquake relocked soon after this event

afterslip following the 2007 mw 8 4 bengkulu earthquake in sumatra loaded the 2010 mw 7 8 mentawai tsunami earthquake rupture zone the 12 september 2007 mw 8 4 bengkulu earthquake in sumatra marked the first in a modern series of large earthquakes along the mentawai section of the sunda megathrust understanding the spatial distribution of coseismic slip and ensuing afterslip is important for assessing seismic hazard in neighboring unruptured regions of the megathrust we re estimate the spatial distribution of coseismic slip during this earthquake with improved coseismic offsets from the sumatran gps array sugar and estimate afterslip following this earthquake with sugar postseismic time series spanning 6 3 years after the earthquake we invert for the spatio temporal distribution of afterslip with the principal component analysis based inversion method pcaim and we take into account viscoelastic deformation by incorporating into the inversion the estimation of strain within ductile deforming blocks located at asthenospheric depths our results suggest cumulative afterslip concentrated within updip and downdip of the 2007 coseismic rupture area and shallow afterslip that borders and overlaps the 2010 mw 7 8 mentawai earthquake rupture zone the cumulative contribution of stress changes due to the coseismic event and the ensuing afterslip likely increased strain rates in the shallow portion of the megathrust adjacent to the mentawai earthquake rupture area potentially promoting its rupture in 2010

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 new look at the midlatitude mjo teleconnection in the northern hemisphere winter the midlatitude to madden julian mjo teleconnection in the northern hemisphere wintertime was investigated using twenty years of outgoing long wave radiation and national center for atmospheric research national centers for environmental prediction re analysis data it is revealed through empirical orthogonal functions and regression analyses that the tropical upper level divergence convergence associated with enhanced reduced tropical convection has a subtropical counterpart of upper level convergence divergence as the convective region of mjo moves eastward from the indian ocean to the western pacific the divergent circulation connecting the tropics and subtropics moves eastward from an analysis of vertical motion diagnosed by the generalized omega equation it was revealed that the position of the subtropical rossby gyres of the mjo with respect to the asian pacific jet was the most important factor affecting the existence of the localized divergence convergence and associated lower level vertical motion in the subtropics as the subtropical rossby gyres pass by the longitudinal position of the asian pacific jet vertical motion occurs to meet the balance required by quasi geostrophic theory since this anomalous vertical motion is large enough to cause convection at that region the diabatic heating process reinforces the vertical motion furthermore other dynamical processes neglected in quasi geostrophic theory are activated and contribute to the vertical motion balancing the diabatic heating as a result of the vertical motion near the jet entrance region in the subtropics the vorticity advection by vertical wind and the tilting of vorticity become important since these two terms are similar in shape and magnitude they reinforce each other during the development phase of the midlatitude mjo teleconnection combining these two terms we define the baroclinic jet source bjs in order to evaluate the bjs as a source for the midlatitude mjo teleconnection a numerical experiment is carried out the linear barotropic model is forced by only two terms yet the model captured clearly the main feature of the midlatitude mjo teleconnection copyright 2006 royal meteorological society

seismic and aseismic slip on the central peru megathrust slip on a subduction megathrust can be seismic or aseismic with the two modes of slip complementing each other in time and space to accommodate the long term plate motions although slip is almost purely aseismic at depths greater than about 40 km heterogeneous surface strain suggests that both modes of slip occur at shallower depths with aseismic slip resulting from steady or transient creep in the interseismic and postseismic periods thus active faults seem to comprise areas that slip mostly during earthquakes and areas that mostly slip aseismically the size location and frequency of earthquakes that a megathrust can generate thus depend on where and when aseismic creep is taking place and what fraction of the long term slip rate it accounts for here we address this issue by focusing on the central peru megathrust we show that the pisco earthquake with moment magnitude m w 8 0 ruptured two asperities within a patch that had remained locked in the interseismic period and triggered aseismic frictional afterslip on two adjacent patches the most prominent patch of afterslip coincides with the subducting nazca ridge an area also characterized by low interseismic coupling which seems to have repeatedly acted as a barrier to seismic rupture propagation in the past the seismogenic portion of the megathrust thus appears to be composed of interfingering rate weakening and rate strengthening patches the rate strengthening patches contribute to a high proportion of aseismic slip and determine the extent and frequency of large interplate earthquakes aseismic slip accounts for as much as 50 70 of the slip budget on the seismogenic portion of the megathrust in central peru and the return period of earthquakes with m w 8 0 in the pisco area is estimated to be 250 years

links between tropical convection and variations of the extratropical circulation during toga coare abstract data from the intensive observation period of the tropical ocean global atmosphere coupled ocean atmosphere response experiment november 1992 february 1993 have been used to investigate the links between intraseasonal variations in tropical convection and those in forcing of upper tropospheric rossby waves in the extratropics the primary databases are geostationary meteorological satellite imagery and tropical wind analyses from the bureau of meteorology australia a number of 5 day periods showing convection in different locations were chosen for each period mean fields of divergence cloud top temperature and upper tropospheric rossby wave source are presented vorticity budgets are used to demonstrate the processes responsible for the rossby wave source patterns the approach follows earlier studies of links between interannual variations of tropical convection associated with the southern oscillation and variations of the extratropical circulation it is shown that the regions of tropi

viscoelastic relaxation following subduction earthquakes and its effects on afterslip determination afterslip is commonly thought to be the controlling process in postseismic deformation immediately following a great megathrust earthquake and is usually inferred from geodetic observations using purely elastic models however observed motion reversal of the near trench area right after the 2011 mw 9 tohoku oki earthquake demonstrates the dominance of viscoelastic relaxation of coseismically induced stresses to understand the importance of incorporating viscoelasticity in afterslip determination we employ biviscous burgers mantle rheology and use finite element models to explore how viscoelastic relaxation in short term postseismic deformation is controlled by various geometrical and rheological factors our results indicate that immediately after large megathrust earthquakes mw 8 0 viscoelastic deformation should always cause opposing motion of inland and trench areas and subsidence around landward termination of the rupture although the rate of such postseismic motion depends on local conditions such as the age and hence thickness of the slab and transient mantle viscosity values while elastic models may be adequate for afterslip estimation for earthquakes of mw 7 5 neglect of viscoelasticity for larger events leads to overestimate of afterslip downdip of the rupture and underestimate of afterslip at shallower depths reassessing shallow afterslip following the 2005 mw 8 7 nias earthquake using 2 d viscoelastic models suggests that the actual afterslip may be greater than that estimated using an elastic model by more than 50 similarly interpreting trenchward motion of some seafloor gps sites following the tohoku oki earthquake using a viscoelastic model suggests large shallow afterslip outside of the main rupture area

afterslip and viscoelastic relaxation following the 2011 tohoku oki earthquake mw9 0 inferred from inland gps and seafloor gps acoustic data we simultaneously estimate 2 5 years of afterslip and viscoelastic relaxation as well as coseismic slip for the 2011 tohoku oki earthquake displacements at inland gps and seafloor gps acoustic stations are inverted using viscoelastic green s functions for a model with an upper elastic layer and lower viscoelastic substrate the result shows that afterslip is isolated from the rupture area and possibly asperities of historical earthquakes and has almost decayed by 10 september 2013 2 5 years after the main shock the inversion result also suggests that observed landward postseismic displacements at the seafloor gps acoustic stations are caused by the viscoelastic relaxation whereas trenchward displacements at inland stations are mainly an elastic response to afterslip

a pole to pole west pacific atmospheric teleconnection during august 1 an observational analysis is presented that reveals an august teleconnection involving both the northern hemisphere nh and the southern hemisphere sh the teleconnection includes three primary anomalies in the monthly average surface pressure field 1 a high southern latitude component including wilkes land antarctica the nearby southern ocean and the ross sea 2 a sh midlatitude component near australia and new zealand and 3 a nh subtropical component over the extreme western pacific ocean surface pressure for the sh high latitude anomaly is negatively correlated to the other two primary anomalies the sh midlatitude and nh subtropical component are positively correlated furthermore the teleconnection is correlated to surface pressure near the aleutian islands the teleconnection anomalies result from tropical convection on intraseasonal timescales monsoon rainfall over east asia during august is correlated to the teleconnection furthermore august precipitation at several other locations in the nh and sh is modulated by the teleconnection two different sets of numerical experiments with the national center for atmospheric research ncar community climate model version 2 ccm2 show a similar appearing teleconnection during late boreal summer the modeled teleconnection however is forced from high southern latitudes

the updip and downdip limits to great subduction earthquakes thermal and structural models of cascadia south alaska sw japan and chile this study examines thermal and structural controls of the updip and downdip rupture limits of great subduction thrust earthquakes data on past great earthquake seismic limits have been compiled for four continental subduction zones cascadia sw japan south alaska and chile these limits have then been compared to the predictions of several models for what constrains great earthquake rupture temperatures on the subduction thrusts have been estimated by finite element numerical models the landward limits of the observed updip aseismic zones correspond to the position where the thrust temperature reaches about 100 c that is depths of about 2 to 10 km for the subduction zones studied this temperature agrees with the dehydration of stable sliding smectite clays to illite chlorite the temperatures in this region are controlled mainly by the thickness of sediment on the incoming crust and by the crustal age and thus heat flow the downdip limits correspond to the depth on the thrust where either 1 the temperature reaches about 350 c which corresponds to thermally activated stable sliding behavior for crustal rocks with a transition to 450 c or 2 about 40 km depth if 350 c is reached at greater depth depths of about 40 km approximately correspond to the intersection of the thrust with the continental forearc moho and this downdip limit may be a consequence of stable sliding serpentinite or talc and other hydrated forearc mantle rocks the primary temperature controls on the downdip region are the age of the subducting oceanic plate and the thrust dip profile secondary control comes from the thickness of incoming sediment the convergence rate and the radioactive heat generation in the overlying forearc the 100 c updip limit occurs near the trench for young subducting plates with a thick sediment section such as cascadia 6 8 ma and up to 80 km landward for older oceanic crust such as south alaska 50 ma the 350 c downdip thermal limit is applicable for young oceanic plates e g cascadia and nankai whereas the forearc mantle limit applies for older plates e g south alaska and chile except near the chile rise for the margins studied that have experienced great earthquakes there is generally good agreement between the postulated thermal and moho limits and the rupture or seismogenic zone as defined by the distribution of aftershocks and by waveform tsunami and dislocation modeling the downdip limit of the interseismic locked zone from dislocation modeling is also in agreement with these limits

the effect of boreal late autumn snow cover over western and central china on the northern hemisphere wintertime blocking frequency abstractthe impact of snow cover in western and central china during late autumn on wintertime blocking occurrence is investigated using reanalysis data the study results show that wintertime atmospheric circulations affected by late autumn snow cover anomalies form favorable conditions for increased blocking frequency bf especially in the north pacific and north atlantic evidence is also presented that the stratosphere troposphere interactions are the key mechanism of the lag response of wintertime north pacific and north atlantic bfs to the late autumn snow cover that is positive anomalous snow cover can induce a dipole anomaly in the geopotential height field over the lower stratosphere due to the decrease of the 300 1000 hpa thickness and the concurrent variation between the east asian plateau jet and the polar front jet the associated positive geopotential height anomalies are located over northwestern eurasia meanwhile western and central china features remarkably negative geopotential he

role of lower crust in the postseismic deformation of the 2010 maule earthquake insights from a model with power law rheology the surface deformation associated with the 2010 mw 8 8 maule earthquake in chile was recorded in great detail before during and after the event the high data quality of the continuous gps cgps observations has facilitated a number of studies that model the postseismic deformation signal with a combination of relocking afterslip and viscoelastic relaxation using linear rheology for the upper mantle here we investigate the impact of using linear maxwell or power law rheology with a 2d geomechanical numerical model to better understand the relative importance of the different processes that control the postseismic deformation signal our model results reveal that in particular the modeled cumulative vertical postseismic deformation pattern in the near field 50 km depth as suggested in previous studies the explanation for this difference is that in the model with power law rheology the relaxation of coseismically imposed differential stresses occurs mainly in the lower crust however even though the model with power law rheology probably has more potential to explain the vertical postseismic signal in the near field the uncertainty of the applied temperature field is substantial and this needs further investigations and improvements

blocking over the south pacific and rossby wave propagation abstract atmospheric blocking events over the south pacific are investigated using a 39 yr record of 500 hpa height fields from the ncep ncar reanalysis dataset the analysis extends earlier work using a 16 yr record and confirms that the occurrence of blocking over the southeast pacific is strongly modulated by the enso cycle during austral spring and summer comparison of results at 500 hpa with the 300 hpa meridional wind component showed that blocking events are associated with large scale wave trains lying across the south pacific from the region of australia to southern south america similar wave trains are evident in both hemispheres in singular value decomposition analyses between 300 hpa meridional wind components and tropical pacific outgoing longwave radiation olr anomalies the hypothesis that the divergence associated with tropical olr anomalies forces an extratropical wave response that results in enhanced blocking over the southeast pacific was tested using a linearized barotropic vorti

grain size evolution and the rheology of ductile shear zones from laboratory experiments to postseismic creep abstract geologic experimental and geodetic studies indicate that ductile shear zones do not deform in steady state we present a theoretical model for an elastically loaded ductile shear zone deforming by combined dislocation and diffusion creep in which grain size is allowed to evolve toward its equilibrium recrystallized value several grain size evolution laws are considered simulations of laboratory experiments show that grain size evolution can lead to changes in the dominant deformation mechanism that are accompanied by transient strain weakening or strain strengthening episodes reminiscent of laboratory observations ductile shear zones can also produce postseismic creep as observed in geodetic data following large earthquakes non steady state ductile creep is difficult to differentiate from frictional sliding with velocity strengthening friction hence ductile creep may play a role in the transition from velocity weakening to velocity strengthening friction with increasing temperature

dependency of the north pacific winter storm tracks on the zonal distribution of mjo convection 1 we investigate the effects of the tropical madden julian oscillation mjo convection on the zonal location and intensity of storm activity during the boreal cool season nov 1 to feb 28 120 days over the pacific ocean as tropical convection shifts eastward from the eastern indian ocean to the western north pacific mjo induced local hadley circulation leads to an eastward displacement of extratropical rossby wave source rws consequently this influence leads to an eastward shift of the peak area of the storm track the storm track is strongest with the mjo convection over the eastern indian ocean phase 3 and it experiences the suppression when mjo convection is located over the maritime continents phase 4 and it increases again when the mjo propagates to the western pacific phase 5 after which it weakens again phase 6 the intensity of the storm track particularly over the western north pacific 120 e 180 is determined by the integrated effects of three factors the midlatitude convective forcing mcf the jet stream and rws these factors are associated with the locations of mjo convections it is estimated that mjo induced suppression accounts for only 2 5 of the total observed midwinter suppression mws however the pattern generated by the mjo is remarkably similar to the observed meridional displacement of north pacific storm track associated with sub seasonal variation we conclude that the spatial distribution of mjo affects the variation of the pacific storm track but is not a cause of the mws

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

controls on early diagenetic overprinting in icehouse carbonates insights from modeling hydrological zone residence times using carb3d abstract icehouse carbonate diagenesis is complex with carbonate sequences being exposed to multiple meteoric hydrozones vadose zone freshwater lens mixing zone on multiple occasions a forward modeling approach using carb3d has enabled quantitative exploration of the nature of this diagenetic overprinting by explicit simulation of meteoric hydrozone residence times during evolution of an isolated carbonate platform a sensitivity analysis was performed encompassing the fundamental controls on hydrozone residence time frequency and magnitude of sea level variation subsidence rate and climate the latter via its effect on freshwater lens thickness and rate of dissolutional lowering of the land surface residence time within all meteoric hydrozones is characterized by a high degree of lateral continuity vertical continuity is much more limited with significant variations on a fourth order sequence scale across the platform below sequence boundaries prolonged exposure to the vadose zone results from multiple missed beats when the platform remains exposed at relative sea level maxima overprinting gives total meteoric residence times significantly in excess of the duration of exposure of the overlying sequence boundary there is a hierarchy of eustatically driven overprint cycles with higher frequency cyclicity modifying the primary signal generated by lower frequency cycles fifth order cycles thus have only a minor impact on hydrozone residence times whilst third order seismic scale cycles are a critical control and could be used as a first order approximation of the amount of diagenetic overprinting subsidence has a strong control on residence time with greater overprinting at lower subsidence rates but in high subsidence regimes sediment packages move below the zone of meteoric water influence sufficiently rapidly that residence time can be minimal high land surface dissolution rates which result from a wetter climate remove a large proportion of the subaerially exposed sediment and reduce vadose zone residence time higher effective recharge can increase the thickness of freshwater lens and mixing zones which increases residence times significantly residence times in the vadose zone can be directly linked to a sequence stratigraphic framework but for the freshwater lens and the mixing zone this is possible only with a well constrained relative sea level history

poroelastic stress triggering of the 2005 m8 7 nias earthquake by the 2004 m9 2 sumatra andaman earthquake abstract the m9 2 sumatra andaman earthquake sae occurred three months prior to the m8 7 nias earthquake ne we propose that the ne was mechanically triggered by the sae and that poroelastic effects were a major component of this triggering this study uses 3d finite element models fems of the sumatra andaman subduction zone sasz to predict the deformation stress and pore pressure fields of the sae the coseismic slip distribution for the sae is calibrated to near field gps data using fem generated green s functions and linear inverse methods the calibrated fem is then used to predict the postseismic poroelastic contribution to stress triggering along the rupture surface of the ne which is adjacent to the southern margin of the sae the coseismic deformation of the sae combined with the rheologic configuration of the sasz produces two transient fluid flow regimes having separate time constants sae coseismic pore pressures in the relatively shallow forearc and volcanic arc regions within a few km depth dissipate within one month after the sae however pore pressures in the oceanic crust of the down going slab persist several months after the sae predictions suggest that the sae initially induced mpa scale negative pore pressure near the hypocenter of the ne this pore pressure slowly recovered increased during the three month interval separating the sae and ne due to lateral migration of pore fluids driven by coseismic pressure gradients within the subducting oceanic crust because pore pressure is a fundamental component of coulomb stress the mpa scale increase in pore pressure significantly decreased stability of the ne fault during the three month interval after the sae and prior to rupture of the ne a complete analysis of stress triggering due to the sae must include a poroelastic component failure to include poroelastic mechanics will lead to an incomplete model that cannot account for the time interval between the sae and ne our transient poroelastic model explains both the spatial and temporal characteristics of triggering of the ne by the sae