metamorphic records for subduction erosion and subsequent underplating processes revealed by garnet staurolite muscovite schists in central qiangtang tibet subduction erosion is confirmed as a crucial geodynamic process of crustal recycling based on geological geochemical and geophysical observations at modern convergent plate margins so far not a single metamorphic record has been used for constraining a general tectonic evolution for subduction erosion here we first revealed metamorphic records for a subduction erosion process based on our study of the late paleozoic garnet staurolite muscovite schists in the central qiangtang block tibet provenance analyses suggest that the protoliths of garnet staurolite muscovite schists have the northern qiangtang affinity and were deposited in an active continental margin setting mineral inclusion data show that the early metamorphic stage m1 recorded blueschist facies pressure temperature p t conditions of 0 8 1 1 gpa and 402 441 c indicating that a part of the material from the overriding plate had been abraded into the subduction channel and undergone high pressure low temperature metamorphism the peak metamorphic stage m2 recorded amphibolite facies p t conditions of 0 3 0 5 gpa and 470 520 c the 40ar 39ar cooling ages 263 259 ma yielded from muscovite suggest the amphibolite facies metamorphism 263 ma occurred at oceanic subduction stage the distinctly staged metamorphism defines a clockwise and warming decompression p t t path which reveals an underplating process following the early subduction erosion during the tectonic process the eroded low density material escaped from the cold subduction channel and rise upward into the warm middle lower crust of the upper plate undergoing amphibolite facies metamorphism our new results revealed a complete evolutional process from the early subduction erosion to the subsequent underplating during the northward subduction of the paleo tethys ocean

tectonic erosion of the peruvian forearc lima basin by subduction and nazca ridge collision 1 subsidence of lima basin part of the peruvian forearc is controlled by tectonic erosion by the subducting nazca plate multichannel seismic reflection data coupled with age and paleowater depth constraints derived from ocean drilling program odp coring now allow the rates of erosion to be reconstructed through time in trenchward locations the forearc has experienced limited recent relative uplift 700 850 m likely due to preferential basal erosion under the center of lima basin long term subsidence driven by basal tectonic erosion dominates and is fastest closest to the trench since 47 ma eocene up to 148 km of the plate margin have been lost at an average rate of up to 3 1 km myr 1 appoximately 110 km of that total appears to be lost since 11 ma implying much faster average rates of trench retreat 10 km myr 1 since collision of the nazca ridge with the lima basin at 11 ma although there is no clear subsidence event at odp site 679 during the time at which nazca ridge was subducting beneath this part of the forearc 4 11 ma the more trenchward odp sites 682 and 688 show significant deepening after 11 ma indicating that subduction of the ridge accelerates tectonic erosion long term rates of crustal erosion in the region of lima basin are greater than estimates of regional arc magmatic productivity implying that such margins are net sinks of continental crust

runaway slip to the trench due to rupture of highly pressurized megathrust beneath the middle trench slope the tsunamigenesis of the 2011 tohoku earthquake off the east coast of northern japan abstract the gigantic 2011 march 11 mw 9 tohoku earthquake is examined from the viewpoint of the pre seismic forearc structure the seismic reflection properties of a megathrust around the usual up dip limit of the seismogenic zone the thermal state of a shallow subduction zone and the dehydration of underthrust sediments at the japan trench the pacific plate is subducting westward beneath northeast japan at a dip angle of 4 6 the middle and lower slopes of the landward side dip eastward at angles of 2 5 and 8 0 respectively the forearc prism beneath the middle and lower slopes is inferred to be in extensionally and compressively critical states respectively based on the presence of clear internal deformation features and on the occurrence of aftershock earthquakes the rapid uplift of the forearc that caused the 2011 tohoku tsunami may have been associated with this internal deformation of the prism the critical state of the prism indicates that the effective basal friction b of the plate boundary megathrust is 0 08 for the lower prism the megathrust especially under the middle slope is characterized by a prominent reflector with negative polarity one of multiple possible explanations is that the megathrust hosts highly pressurized fluids underthrust sediments in this part of the japan trench are dominated by pelagic and siliceous vitric diatomaceous silt with clay the dehydration kinetics of opal a to quartz the clay transformation of smectite illite and the thermal structure of the japan trench suggest that maximum dehydration of the sediments would take place at 50 60 km horizontally from the deformation front where the temperature along the megathrust is 100 120 c the zone of maximum dehydration coincides with the prominent seismic reflector that has negative polarity we hypothesize a possible free slip along this portion of the megathrust during the 2011 tohoku earthquake caused by anomalously high fluid pressure resulting from fluid accumulation over centuries

structure and tectonics of the erosional convergent margin off antofagasta north chile 23 30 s subduction erosion has dominated the evolution of the north chile convergent continental margin since at least the mesozoic we investigate the structure of the antofagasta 23 s sector of this margin along a transect using coincident wide angle and near vertical seismic profiling and gravity data a 2 d velocity field of the overriding and subducting plates was obtained using joint refraction and reflection travel time tomography a velocity derived density distribution was used to model marine gravity data and substantiate the velocity model the gravity and velocity models imply that the overriding plate is mainly made of arc type igneous basement the upper plate is constructed of two main rock bodies separated by a subhorizontal layer defined by a velocity inversion the top coincident with a reflection in near vertical seismic images the seismic boundary is interpreted as a detachment separating an upper extended domain with large scale normal faulting from a lower domain apparently undergoing a different type of deformation velocity derived porosity indicates that the front of the margin is probably fluid saturated and disaggregated by fracturation as a consequence of frontal subduction erosion fluids carried into the subduction channel within slope debris filling underthrusting grabens reduce basal friction and probably induce hydrofracturing and basal erosion along the underside of the overriding plate at depths greater than 20 km porosity and density values imply that most fluids have been exhausted and the lower part of the upper plate is structurally coherent and little fractured the change in physical properties leads to increased mechanical coupling along the plate boundary and occurs at the updip limit of the distribution of aftershocks of the 1995 antofagasta earthquake m w 8 0 defining the seismogenic zone

the 2007 m7 7 tocopilla northern chile earthquake sequence implications for along strike and downdip rupture segmentation and megathrust frictional behavior 1 in 2007 a m7 7 earthquake occurred near the town of tocopilla within the northern chile seismic gap main shock slip derived from coseismic surface deformation was confined to the depth range between 30 and 55 km we relocated 1100 events during six months before and one week after the main shock aftershock seismicity is first congruent to the main shock slip and then it spreads offshore west and northwest of mejillones peninsula mp waveform modeling for 38 aftershocks reveals source mechanisms that are in the majority similar to the main shock however a few events appear to occur in the upper plate some with extensional mechanisms juxtaposing the tocopilla aftershocks with those following the neighboring 1995 antofagasta earthquake produces a striking symmetry across an ew axis in the center of mp events seem to skirt around mp probably due to a shallower moho there we suggest that the seismogenic coupling zone in northern chile changes its frictional behavior in the downdip direction from unstable to mostly conditionally stable for both earthquake sequences aftershocks agglomerate in the conditionally stable region whereas maximum inter seismic slip deficit and co seismic slip occurs in the unstable region the boundary between the unstable and conditionally stable zones parallels the coastline we identify a similar segmentation for other earthquakes in chile and peru where the offshore segments break in great m 8 earthquakes and the onshore segments in smaller m 8 earthquakes using critical taper analysis we demonstrate a causal relationship between varying slip behavior on the interface and forearc wedge anatomy that can be attributed to spatial variations in the rate dependency of friction

crustal dynamics and active fault mechanics during subduction erosion application of frictional wedge analysis on to the north chilean forearc abstract the forearc region of the non accreting south american plate margin in northern chile is characterised by subduction erosion and regional uplift neotectonic deformation structures reflect simultaneous extensional and contractional fault kinematics in the outer forearc where the brittle crust directly overlies the subducting nazca plate the stress regime changes from extension in the upper part to compression at the base of the forearc wedge as seen in neotectonic surface structures and seismic data in the inner forearc surface structures indicate a compressional stress regime also affecting the western rim of the magmatic arc this stress regime is limited to a brittle crustal wedge segment which overlies the ductile part of the inner forearc lithosphere the shape of the two brittle forearc wedges at the leading edge of the south american plate is controlled by exogenetic surface processes internal deformation processes contemporaneous basal tectonic erosion and underplating mechanical parameter sets controlling and reflecting the recent tectonic processes and geometrical wedge segmentation within the forearc system are evaluated and applied to general frictional wedge models the states of stress within the crustal wedges are controlled by spatial variations of the basal mechanical parameters in the down dip direction of the forearc wedge base the new models illustrate the fundamental kinematics and dynamic processes of coulomb type basal tectonic erosion and mass transfer modes along active non accretive convergent margins the frictional wedge models explain the dynamics of the simultaneous and contrary deformation processes affecting the forearc crust at the north chilean convergent margin shaped by active basal tectonic erosion

tsunami earthquakes possibly widespread manifestations of frictional conditional stability 1 tsunami earthquakes shallow events that produce larger tsunamis than expected given their surface wave magnitudes ms typically have long durations and a source spectrum depleted in short period energy seven cases of underthrusting tsunami earthquakes provide information on the rupture processes but little constraint on geographic distribution or frequency we compare their rupture characteristics with smaller magnitude earthquakes on circum pacific interplate thrust faults comparable moment release time histories are found for large tsunami earthquakes and for many smaller shallow subduction zone earthquakes with significantly longer durations and additional source complexity than for events deeper than 15 km thus very shallow interplate earthquake ruptures are scale invariant with variable frictional properties on the plate interface controlling the depth dependent rupture process widespread occurrence of small shallow interplate earthquakes with long durations suggests that many subduction faults have frictional properties that may enable large tsunami generating earthquakes to occur fortunately large shallow ruptures are infrequent

noncohesive critical coulomb wedges an exact solution active fold and thrust belts or submarine accretionary complexes can be modeled as critically tapered wedges of material on the verge of coulomb failure everywhere overlying a basal decollement where frictional sliding is occurring ignoring cohesion the four strength parameters needed to describe a critical coulomb wedge are its internal and basal coefficients of friction and b and its internal and basal hubbert rubey fluid pressure ratios and b an exact relation between surface slope and basal dip of a noncohesive critical wedge with uniform properties is derived the state of stress within such a wedge has the same orientation everywhere and is constant if is and vice versa a coefficient of internal friction 1 1 is consistent with the known surface slope basal dip and pore fluid pressures in the active fold and thrust belt of western taiwan assuming that byerlee s law b 0 85 is valid on the base the wide variety of tectonic styles observed to occur along convergent margins including subduction erosion active accretion subduction without accretion and even extension and normal faulting may be controlled by relatively small spatial or temporal variations in either b or b

geological record of fluid flow and seismogenesis along an erosive subducting plate boundary a fossil erosive subduction channel the shear zone marking the plate boundary preserved in the northern apennines of italy is identified the fossil zone records the presence of two decollements which seem to have been simultaneously active at the top and base of the subduction channel in modern subduction zones the onset of seismic activity is believed to occur at 150 c however in the fossil channel the onset seems to have occurred at colder temperatures tectonic erosion of the overriding plate by the downgoing slab is believed to occur at half the earth s subduction zones1 2 in situ investigation of the geological processes at active erosive margins is extremely difficult owing to the deep marine environment and the net loss of forearc crust to deeper levels in the subduction zone until now a fossil erosive subduction channel the shear zone marking the plate boundary3 has not been recognized in the field so that seismic observations have provided the only information on plate boundary processes at erosive margins here we show that a fossil erosive margin is preserved in the northern apennines of italy it formed during the tertiary transition from oceanic subduction to continental collision and was preserved by the late deactivation and fossilization of the plate boundary the outcropping erosive subduction channel is 500 m thick it is representative of the first 5 km of depth with its deeper portions reaching 150 c the fossil zone records several surprises two decollements were simultaneously active at the top and base of the subduction channel both deeper basal erosion and near surface frontal erosion occurred at shallow depths extension was a key deformation component within this erosive convergent plate boundary and slip occurred without an observable fluid pressure cycle at depths greater than about 3 km a fluid cycle is clearly shown by the development of veins and the alternation of fast co seismic and slow inter seismic slip in the deepest portions of the outcropping subduction channel extension is finally overprinted by compressional structures in modern subduction zones the onset of seismic activity is believed to occur at 150 c but in the fossil channel the onset occurred at cooler palaeo temperatures

accretionary prisms in subduction earthquake cycles the theory of dynamic coulomb wedge 1 we expand the theory of critically tapered coulomb wedge for accretionary prisms by considering stress changes in subduction earthquake cycles building on the coulomb plasticity of the classical theory we assume an elastic perfectly coulomb plastic rheology and derive exact stress solutions for stable and critical wedges the new theory postulates that the actively deforming most seaward part of an accretionary prism the outer wedge overlies the updip velocity strengthening part of the subduction fault and the less deformed inner wedge overlies the velocity weakening part the seismogenic zone during great earthquakes the outer wedge is pushed into a compressively critical state with an increase in basal and internal stresses and pore fluid pressure after the earthquake the outer wedge returns to a stable state the outer wedge geometry is controlled by the peak stress of the updip velocity strengthening part of the subduction fault achieved in largest earthquakes the inner wedge generally stays in the stable regime throughout earthquake cycles acting as an apparent backstop and providing a stable environment for the formation of forearc basins the new theory has important implications for the studies of the updip limit of the seismogenic zone the evolution of accretionary prisms and forearc basins activation of splay faults and tsunami generation evolution of the fluid regime and mechanics of frontal prisms at margins dominated by tectonic erosion

effects of frictional behavior and geometry of subduction fault on coseismic seafloor deformation abstract the seismogenic zone of subduction faults appears to have an updip limit seaward of which the fault exhibits velocity strengthening behavior we use a two dimensional finite element model including a frictional subduction fault to explore how coseismic strengthening of the updip segment affects seafloor deformation for a stress drop of a few mpa along the seismogenic zone strengthening of the updip segment by a comparable amount can prevent the rupture from breaking the trench the resultant seafloor uplift is much larger than that predicted by a model of equal seismic moment or maximum fault slip in which the seismogenic zone extends to the trench with a curved fault geometry although a lower degree of coseismic strengthening of the updip segment leads to greater slip in the shallowest part of the fault it produces smaller seafloor uplift contrary to a popular belief given the paucity of direct observations of the coseismic behavior of the updip segment the models yield important information for understanding rupture mechanics of subduction faults and tsunami generation we also illustrate how the results may be used to guide fault slip parameterization in analytical dislocation models

structure of the kuril trench from seismic reflection records three multichannel seismic reflection records across the kuril convergent margin provide the first deep data in this area the records are located across the southern tip of kamchatka the central kuril arc and the northern extension of hokkaido island platform which show three distinct tectonic regimes the lower slope contains a wedge shaped buttress surrounded by low velocity sediments underplating sediment uplifts the buttress as indicated by faults that displace its upper surface the middle slope is a block of acoustic basement which has a rough surface with significant arcward dipping faults the middle slope is separated from the upper slope along a steep arcward dipping reflection the middle slope boundary the upper slope structure off kamchatka is different from that off hokkaido off kamchatka a regular stratified sediment section has been uplifted tilted and dips seaward off hokkaido stronger uplift has tilted regional blocks seaward and arcward along the southern line north of hokkaido well studied nonthrust earthquakes with lateral motions occur beneath the middle slope boundary and on the boundary of the subducting plate thrust earthquakes occur under the middle and upper slope whereas tsunami earthquakes occur under the lower slope high amplitude reflections along the lower boundary of the wedge shaped buttress and along the active decollement indicate high fluid concentrations which reduce the friction along the tectonic units so that through the weak coupling slow rupture may extend up to the seafloor from a tsunami earthquake

origin of a crustal splay fault and its relation to the seismogenic zone and underplating at the erosional north ecuador south colombia oceanic margin 1 splay faults within accretionary complexes are commonly associated with the updip limit of the seismogenic zone prestack depth migration of a multichannel seismic line across the north ecuador south colombia oceanic margin images a crustal splay fault that correlates with the seaward limit of the rupture zone of the 1958 mw 7 7 tsunamogenic subduction earthquake the splay fault separates 5 6 6 km s velocity inner wedge basement rocks which belong to the accreted gorgona oceanic terrane from 4 to 5 km s velocity outer wedge rocks the outer wedge is dominated by basal tectonic erosion despite a 3 km thick trench fill subduction of 2 km high seamount prevented tectonic accretion and promotes basal tectonic erosion the low velocity and poorly reflective subduction channel that underlies the outer wedge is associated with the aseismic decollement thrust subduction channel fluids are expected to migrate upward along splay faults and alter outer wedge rocks conversely duplexes are interpreted to form from and above subducting sediment at 14 to 15 km depths between the overlapping seismogenic part of the splay fault and the underlying aseismic decollement coeval basal erosion of the outer wedge and underplating beneath the apex of inner wedge control the margin mass budget which comes out negative intraoceanic basement fossil listric normal faults and a rift zone inverted in a flower structure reflect the evolution of the gorgona terrane from cretaceous extension to likely eocene oblique compression the splay faults could have resulted from tectonic inversion of listric normal faults thus showing how inherited structures may promote fluid flow across margin basement and control seismogenesis

asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of antofagasta chile in our study we show that the locations of largest coseismic slip asperities on the fault plane of the m w 8 0 1995 antofagasta earthquake in northern chile can be mapped by the spatial distribution of the seismic b value obtained from the aftershock sequence of the megathrust earthquake these areas of high seismic moment release and concurrent high b values are congruent with anomalies of the gravity isostatic residual ir field in the antofagasta region they are superimposed on the seismogenic part of the north chilean subduction zone where the strongest coupling of the upper and lower plate is expected the ir anomalies are interpreted to be caused by large jurassic early cretaceous batholiths which intruded into the upper crust the observed positive correlations between high seismic b values ir anomalies and geologic structures enable us to propose a mechanical model for the generation of the asperities in the antofagasta region we suggest that the batholiths in conjunction with buoyant forces acting on the subducted slab of the nazca plate are responsible for locking the interface where the asperities are located this implies long term conditions for the existence of the asperity generating tectonic situation concequently the asperities around antofagasta could be stationary features at least for several seismic cycles hence we propose that the ir anomalies along the north chilean convergent margin can be used as an indicator for high moment release and slip in future large earthquakes

interplate patchiness and subduction erosion mechanisms evidence from depth migrated seismic images at the central ecuador convergent margin prestack depth migrated seismic lines provide accurate images of the convergent ecuadorian margin where the southern flank of the carnegie ridge subducts the margin is fronted by a 5 7 km wide compressional sediment prism beneath the slope margin thinning is accomplished by gradual thinning of the lower part of the basement accompanied by pervasive seaward dipping normal faulting indicating basal subduction erosion at a low friction plate interface along the plate boundary a thin subduction channel locally thickens to form low velocity 600 m thick lenses of underthrusted fluid rich sediment supplied by slope mass wasting the contrast between the fluid rich sediment and the surrounding thinner and drier sections of the subduction channel creates a three dimensional patchiness across the plate boundary implying variations in mechanical interplate coupling the subduction channel patchiness modulates subduction erosion processes by alternately favoring margin basement weakening and material removal basement weakening would occur 1 at the base of the upper plate where enhanced reflectivity indicates basement damage by overpressured fluids from the subduction channel and 2 at the basement apex where basement breakup is caused by superposition of compressional and extensional fault systems resulting from time variable interplate mechanical coupling the detachment of rock debris in the higher coupled sections and the subsequent dragging of the fragments into the subduction channel cause tectonic erosion deeper in the subduction the subduction channel patchiness may influence processes like earthquake nucleation and rupture propagation and material recycling in the mantle

tsunamigenic earthquake simulations using experimentally derived friction laws abstract seismological tsunami and geodetic observations have shown that subduction zones are complex systems where the properties of earthquake rupture vary with depth as a result of different pre stress and frictional conditions a wealth of earthquakes of different sizes and different source features e g rupture duration can be generated in subduction zones including tsunami earthquakes some of which can produce extreme tsunamigenic events here we offer a geological perspective principally accounting for depth dependent frictional conditions while adopting a simplified distribution of on fault tectonic pre stress we combine a lithology controlled depth dependent experimental friction law with 2d elastodynamic rupture simulations for a tohoku like subduction zone cross section subduction zone fault rocks are dominantly incohesive and clay rich near the surface transitioning to cohesive and more crystalline at depth by randomly shifting along fault dip the location of the high shear stress regions asperities moderate to great thrust earthquakes and tsunami earthquakes are produced that are quite consistent with seismological geodetic and tsunami observations as an effect of depth dependent friction in our model slip is confined to the high stress asperity at depth near the surface rupture is impeded by the rock clay transition constraining slip to the clay rich layer however when the high stress asperity is located in the clay to crystalline rock transition great thrust earthquakes can be generated similar to the mw 9 tohoku 2011 earthquake

subduction erosion crustal structure and an evolutionary model of the northern yap subduction zone new observations from the latest geophysical survey the yap subduction zone is a distinctive erosive margin with an extremely slow convergence rate the high relief of the subducting plate generated by horst and graben structures and seamounts leads to attenuation of the crust in this study we present the latest geophysical data collected by the chinese research vessel kexue to investigate subduction erosion at the yap subduction zone and develop subduction models for yap subduction zone structures we show an anomalous distance between the yap trench and the adjacent volcanic arc the steep slope of the trench arcward a frontal prism and rare sediment in the trench all typical features of erosive margins we propose that the high relief subducting plate has led to erosion of the overlying plate and that different subduction processes controlled locally by the topography of the subducting plate have modified the yap subduction zone numerous normal faults increase the relief of the seafloor entering the trench and an anomalously large slope angle along the trench reflects uplift of the fore arc high via seamount subduction in addition the thin crust of the subducted horst and graben structures along with the normal faults might have eroded the fore arc crust and subsequently eroded the yap arc crust during subduction these subduction erosional processes at the yap trench provide one of the best cases of an erosive margin in the world particularly for a subduction zone with an extremely slow convergence rate

measuring the onset of locking in the peru chile trench with gps and acoustic measurements the subduction zone off the west coast of south america marks the convergence of the oceanic nazca plate and the continental south america plate nazca south america convergence over the past 23 million years has created the 6 km deep peru chile trench 150 km offshore high pressure between the plates creates a locked zone leading to deformation of the overriding plate the surface area of this locked zone is thought to control the magnitude of co seismic release and is limited by pressure temperature sediment type and fluid content1 here we present seafloor deformation data from the submerged south america plate obtained from a combination of global positioning system gps receivers and acoustic transponders we estimate that the measured horizontal surface motion perpendicular to the trench is consistent with a model having no slip along the thrust fault between 2 and 40 km depth a tsunami in 1996 200 km north of our site was interpreted as being the result of an anomalously shallow interplate earthquake2 seismic coupling at shallow depths such as we observe may explain why co seismic events in the peruvian subduction zone create large tsunamis

nonlinear variations of the physical properties along the southern ecuador subduction channel results from depth migrated seismic data abstract we use two high quality pre stack depth migrated multichannel seismic profiles acquired to quantify physical properties variations of underthrust sediments along the first 30 km of subduction off the erosional southern ecuadorian margin seismic data show three zones along the subduction channel referred to as zones i ii and iii characterized by distinct velocity and velocity derived physical properties which are in agreement with values estimated from experimental results of deformation in granular media these three zones result from transformational changes of underthrust sediments governed by fundamentally different physical processes that control their mechanical behavior at increasing confining pressures based on our observations and its comparison with experimental results we argue that the transformations undergone by underthrust sediments as they dip into the subduction zone are the following within zone i progressively increasing velocity and decreasing velocity derived porosity indicates continuous sediment compaction which must be accompanied by effective fluid drainage along the decollement and or across the accretionary wedge the underthrust material is here unconsolidated from a mechanical point of view laboratory experiments indicate that the dominant processes at this range of pressures are grain rolling particle rotation and frictional slip at grain contacts within zone ii velocity and porosity remains constant for 16 km sis 72 and 12 km sis 18 this suggests undrained conditions resulting in growing fluid overpressure at the subduction channel grain deformation is similar to zone i within zone iii velocity increases and porosity falls rapidly indicating sediment compaction and subsequent release of over pressured fluids where grain deformation is likely to be elastic this might be the dominant process until the grains attain their crushing strength resulting in granular cataclasis and eventually in the collapse of the system we suggest that over pressured fluid release may induce hydrofracturation and it is likely to increase inter plate coupling down from zone iii

updip limit of the seismogenic zone beneath the accretionary prism of southwest japan an effect of diagenetic to low grade metamorphic processes and increasing effective stress off southwest japan the seaward limit of coseismic displacement or updip limit of the seismogenic zone of the 1946 mw 8 3 thrust earthquake reaches to 4 km depth and 40 km landward of the trench this limit coincides with the estimated location of the 150 c isotherm and has been linked to changes in physical properties associated with the smectite to illite clay mineral transition here we show that this limit correlates with a suite of diagenetic to low grade metamorphic processes characterized by 1 declining fluid production and decreasing fluid pressure ratio and 2 active clay carbonate and zeolite cementation and the transition to pressure solution and quartz cementation these diagenetic to low grade metamorphic changes cause the onset of velocity weakening during thrust faulting an increase in effective stress and strengthening of the hanging wall which together combine to produce recordable earthquakes

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

the java convergent margin structure seismogenesis and subduction processes the java margin is characterized by a distinct variation in lower to upper plate material transfer and recurring catastrophic tsunamogenic earthquakes both processes are closely linked to the subduction of oceanic basement relief resulting in varying degrees of fore arc deformation tomographic models of refraction seismic profiles and reflection seismic lines in combination with high resolution multibeam bathymetric data reveal the variability in the deep structure and deformation of the java fore arc shallow subduction processes are governed by the sediment supply in the trench as well as by the nature and fabric of the oceanic lithosphere the deep structure of the fore arc reveals a shallow upper plate crust mantle transition present along the entire java margin section the serpentinized fore arc mantle wedge governs the depth extent of the seismogenic zone here which is narrower compared to its sumatran analogue in addition offshore central java high relief oceanic basement features potentially act as asperities as well as barriers to seismic rupture limiting the possible magnitude of subduction thrust earthquakes however the potential for geohazards in particular tsunamis is high along the entire margin this results from tsunamogenic earthquakes ubiquitous splay faults and potentially tsunamogenic landslides which further increase the risk of future tsunamis

interplate earthquakes as a driver of shallow subduction erosion basal erosion is a prevalent process at subduction zones and plays an important role in the mass balance of global plate tectonics in contradiction with the theoretical expectation that basal erosion requires high basal friction and hence compression in the upper plate extensional faulting is commonly observed in submarine wedges that undergo such erosion here we propose a model to explain this apparent paradox in terms of stress fl uctuations during earthquake cycles in this model basal erosion occurs during large earthquakes when the shallow rate strengthening part of the plate interface strengthens and its overlying wedge weakens but extension occurs during interseismic relaxation of wedge stress the mechanics of basal erosion provide important information on the nature of the updip limit of the megathrust seismogenic zone in margins dominated by basal erosion

bar morphology of dissipative beaches an empirical model this study of 150 examples of nearshore bar morphology along the highly dissipative beaches 33 of the southeast mediterranean shoreline employs 32 years of aerial photography and wave data aided by detailed short term field studies three major bar types were delineated non rhythmic parallel meandering bars inner single crescentic bars and double crescentic bars each of these bar families includes variations the bars were related to daily ship and shore wave data including wave spectra from the day of observation back to 60 days prior to the observation the increase in total bar occurrence during summer is related to crossing of a major wave energy threshold in the spring when significant wave heights 1 m sharply increase to 70 85 in april may the bar morphology wave comparisons further indicate that as the significant wave heights decrease and remain below 1 m non rhythmic bars form within 7 10 days single crescentic bars require 15 days and double crescentic bars require 20 30 days this adjustment period of the bars to wave power causes a delayed response which accounts for lack of coincidence between wave energy and bar occurrence the formation of the initial double crescentic bar and its transformation to the mature double crescentic type requires a short pulse of wave energy 0 5 h13 1 5 m some bar families occur throughout the year the aseasonal occurrence is best shown by the mature double crescentic type which apparently is the final stage in the crescenticbar development sequence however other bar families show a tendency for a seasonal distribution which reflects their sensitivity to wave energy inner single crescentic and initial double crescentic bars are largely restricted to the calmest wave months of may april to october november there is an antiphase relationship between the frequencies of non rhythmic and crescentic bars

tectonic structure across the accretionary and erosional parts of the japan trench margin structure sections across the japan trench from prestack depth migrated seismic data define the accretionary prism a wedge shaped seaward end of the continental framework and a tectonized middle slope between them the 10 km wide accretionary prism is underthrust by sediment remaining with the subducted oceanic crust structure beneath the steep middle slope more nearly resembles the adjacent continental margin than the accreted mass this deformed middle slope domain forms a buffer between the compliant accretionary wedge and a more rigid older continental framework along the plate boundary subducted strata thicken beneath the middle and upper slopes and where last imaged are four times the input thickness beneath the accretionary prism this interplate stratified layer appears to control interplate friction because the layer is imaged 45 km landward from the trench axis to 12 km depth and in that expanse few upper plate earthquakes are recorded erosion of the base of the upper plate beneath the middle continental slope is indicated by margin subsidence and material flux this erosion is concurrent with accretion at the front of the margin

coseismic strengthening of the shallow portion of the subduction fault and its effects on wedge taper 1 according to the dynamic coulomb wedge model coseismic strengthening of the shallowest part of the subduction interface can cause permanent deformation of the overlying outer wedge so that the cumulative effects of great interplate earthquakes control the geometry of the wedge in this work we use a numerical model which is a hybrid of the frictional contact model and the classical crack model to study how stress is coseismically transferred from the seismogenic zone to the strengthening updip zone to cause wedge deformation in this static model the critical strengthening required to prevent the rupture from breaking the trench depends on the force drop of the seismogenic zone defined as the product of the average shear stress drop and the area of the seismogenic zone in a simple model of uniform material properties with a few megapascals average stress drop over a seismogenic zone of 120 km downdip width the critical strengthening for a 30 km wide updip zone is an increase in the effective friction coefficient by about 0 05 using the coulomb wedge theory we demonstrate that this level of strengthening can readily push the overlying wedge into a critical state of failure with much greater strengthening the rupture is able to extend into the updip zone only slightly causing localized wedge compression in the area of slip termination we examined wedge geometry of 22 subduction zones in the light of the model results we found that the surface slope of these wedges is generally too high to be explained using the classical wedge theory but can be explained using the dynamic coulomb wedge model including coseismic strengthening of the shallow portion of the megathrust

crustal structure of the peruvian continental margin from wide angle seismic studies keine zusammenfassung in englischer sprache vorhanden no summary in english language