three dimensional splay fault geometry and implications for tsunami generation megasplay faults very long thrust faults that rise from the subduction plate boundary megathrust and intersect the sea floor at the landward edge of the accretionary prism are thought to play a role in tsunami genesis we imaged a megasplay thrust system along the nankai trough in three dimensions which allowed us to map the splay fault geometry and its lateral continuity the megasplay is continuous from the main plate interface fault upwards to the sea floor where it cuts older thrust slices of the frontal accretionary prism the thrust geometry and evidence of large scale slumping of surficial sediments show that the fault is active and that the activity has evolved toward the landward direction with time contrary to the usual seaward progression of accretionary thrusts the megasplay fault has progressively steepened substantially increasing the potential for vertical uplift of the sea floor with slip we conclude that slip on the megasplay fault most likely contributed to generating devastating historic tsunamis such as the 1944 moment magnitude 8 1 tonankai event and it is this geometry that makes this margin and others like it particularly prone to tsunami genesis

comparison of smectite and illite rich gouge frictional properties application to the updip limit of the seismogenic zone along subduction megathrusts along plate boundary subduction thrusts the transformation of smectite to illite within fault gouge at temperatures of 150 c is one of the key mineralogical changes thought to control the updip limit of seismicity if correct this hypothesis requires illite rich gouges to exhibit frictionally unstable velocity weakening behavior here we report on laboratory experiments designed to investigate the frictional behavior of natural and synthetic clay rich gouges we sheared 5 mm thick layers of commercially obtained pure ca smectite a suite of smectite quartz mixtures and natural illite shale grain size ranging from 2 to 500 m in the double direct shear geometry to shear strains of 7 30 at room humidity and temperature xrd analyses show that the illite shale contains dominantly clay minerals and quartz within the clay sized fraction 40 mpa our data specifically the velocity strengthening behavior of illite shale under a wide range of conditions do not support the hypothesis that the smectite illite transition is responsible for the seismic aseismic transition in subduction zones we suggest that other depth and temperature dependent processes such as cementation consolidation and slip localization with increased shearing may play an important role in changing the frictional properties of subduction zone faults and that these processes in addition to clay mineralogy should be the focus of future investigation

displacement and dynamic weakening processes in smectite rich gouge from the central deforming zone of the san andreas fault the strength of clay rich gouge from the central deforming zone cdz of the san andreas fault saf was measured using a high speed rotary shear apparatus to evaluate the potential for unstable slip along the creeping segment of the saf wet and dry gouge was sheared at 0 1 1 3 m s 0 5 1 5 mpa normal stress and 1 20 m displacement cdz gouge is weaker wet than dry and exhibits displacement strengthening to peak friction followed by weakening to steady state strength that decreases with increasing velocity a clay foliation unit 2 develops from the initial microstructure unit 1 during the first 1 5 m of slip coincident with increasing strength subsequent weakening occurs during shear within unit 2 and subsequently with development of a localized foliated slip zone unit 4 and fluidized material unit 3 displacement and dynamic weakening result from slip along clay foliation assisted by shear heating pressurization of pore fluid in wet gouge and additional grain size reduction and possible clay dehydration in dry gouge peak strength is proportional to normal stress but steady state strength is insensitive to normal stress probably because pore pressure approaches the normal stress as such cdz gouge is weak at coseismic rates relative to interseismic creep strength the potential for sustaining rupture propagation into the cdz from an adjacent seismic segment is sensitive to the relationship used to extrapolate the critical weakening displacement from experimental to in situ conditions rupture propagation from a microseismic patch within the cdz is unlikely but sustained propagation from a large earthquake e g parkfield event may be possible

variations in exhumation level and uplift rate along the obliqu slip alpine fault central southern alps new zealand we use geophysical and geological data from the southern alps to explore the relationship between plate motions and crustal structure on the geomorphology exhumation state and deformation style of rocks uplifted along amajor oblique slip fault a 50 km long segment of the southern alps has a higher uplift rate more relief deeper exhumation and a narrower width than surrounding regions there the delaminated east tilted crust of the pacific plate yields the youngest late cenozoic thermochronometric ages contours for fission track ar ar and k ar ages on several different minerals define an asymmetrically nested pattern of ages that increase away from the western side of the central southern alps eleven new 4 0 ar 3 9 ar samples of hornblende from the hanging wall of the alpine fault indicate that lower crustal rocks exhumed from 500 c in the late cenozoic are confined to a 20 km long culmination at the southern end of the central southern alps ages as low as 3 5 ma imply time integrated vertical exhumation rates as high as 6 9 mm yr this is the only part of this 5 8 ma range that may have achieved exhumational steady state remnant plugs of the original crustal hanging wall ramp are apparently preserved outside the central alps implying 70 km of fault convergence there 4 0 ar 3 9 ar age trends for hornblende near the alpine fault suggest that horizontal surfaces in the lower crust in the pacific plate have been overturned by reverse slip ductile shearing across a zone of distributed deformation that extends 2 km beyond the 1 km thick basal mylonite zone at the broadest orogen scale higher uplift rates throughout the central southern alps may be related to a rheologically controlled increase in the convergent velocity of points to the east of the alpine fault associated with a strengthening of the pacific crust at a more local scale maximum rates of uplift are inferred to occur near franz josef and fox glaciers because the alpine fault steepens at depth structural data suggests that its footwall ramp is curved and that the fault s dip steepens by 15 20 relative to its attitude farther to the south this 10 20 km long restraining bend may enhance local rates of rock uplift near franz josef and fox glaciers contemporary normal stress and shear resistance may also be increased on this part of the alpine fault helping to explain the central region s quiet historic seismicity and apparently strongly locked nature

large displacement hydrothermal frictional properties of dfdp 1 fault rocks alpine fault new zealand implications for deep rupture propagation the alpine fault new zealand is a major plate bounding fault that accommodates 65 75 of the total relative motion between the australian and pacific plates here we present data on the hydrothermal frictional properties of alpine fault rocks that surround the principal slip zones psz of the alpine fault and those comprising the psz itself the samples were retrieved from relatively shallow depths during phase 1 of the deep fault drilling project dfdp 1 at gaunt creek simulated fault gouges were sheared at temperatures of 25 150 300 450 and 600 c in order to determine the friction coefficient as well as the velocity dependence of friction friction remains more or less constant with changes in temperature but a transition from velocity strengthening behavior to velocity weakening behavior occurs at a temperature of t 150 c the transition depends on the absolute value of sliding velocity as well as temperature with the velocity weakening region restricted to higher velocity for higher temperatures friction was substantially lower for low velocity shearing v 0 3 m s at 600 c but no transition to normal stress independence was observed in the framework of rate and state friction earthquake nucleation is most likely at an intermediate temperature of t 300 c the velocity strengthening nature of the alpine fault rocks at higher temperatures may pose a barrier for rupture propagation to deeper levels limiting the possible depth extent of large earthquakes our results highlight the importance of strain rate in controlling frictional behavior under conditions spanning the classical brittle plastic transition for quartzofeldspathic compositions

very high strains recorded in mylonites along the alpine fault new zealand implications for the deep structure of plate boundary faults abstract oblique displacement on the alpine fault which forms the principal structure along the australian pacific plate boundary in south island new zealand has resulted in exhumation of a kilometre wide mylonite zone in the hanging wall adjacent to the current brittle fault trace the mylonites formed under amphibolite facies conditions at depths of ca 25 km and have been uplifted during the past 5 ma a suite of 65 70 ma pegmatite veins in the hanging wall alpine schists has been progressively deformed within the mylonite zone and sheared out over a strike length of ca 100 km measurements of the thickness distribution of the pegmatite veins within the non mylonitised schists and at three localities within the progressively strained mylonites have been used to estimate strain values within the mylonites the thicknesses approximate a log normal distribution with a mean value that is progressively reduced through the protomylonites mylonites and ultramylonites by assuming that the thickness distribution currently observed in the schists was the same for the pegmatites within the mylonites before strain a model of deformation incorporating simple shear and simultaneous pure shear is used to strain the undeformed veins until a fit is obtained with the strained distributions shear strains calculated range from 12 to 22 for the protomylonites 120 to 200 for the mylonites and 180 to 300 for the ultramylonites corresponding to pure shear values of 1 3 in each case these values are compatible with the strains predicted if most of the surface displacement on the fault over the past 5 ma were accommodated within a 1 2 km wide mylonite zone through the middle and lower crusts the results suggest that processes such as erosional focussing of deformation and thermal weakening may cause intense strain localisation within the lower crust with plate boundary deformation restricted to narrow zones rather than becoming increasingly distributed over a widening shear zone with depth

anatomy structural evolution and slip rate of a plate boundary thrust the alpine fault at gaunt creek westland new zealand minimum slip rates calculated for plate vector parallel slickenside trends in cataclasite on the sole of the alpine fault at gaunt creek westland new zealand range from 18 to 24 mm yr between half and two thirds of the total relative motion between the pacific and australian plates is being accommodated by movement on a single structure the alpine fault during the past 14 ka the leading edge of the alpine fault has changed from a moderately southeast dipping oblique reverse fault to a shallowly dipping thrust the hanging wall pacific plate is composed of a gradational sequence from basal gouge through pseudotachylite bearing cataclasite to progressively more coherent schist derived mylonite which has been faulted against subhorizontally bedded fluvio glacial gravel in the footwall australian plate during uplift the hanging wall sequence has been internally sheared and imbricated producing duplex structures and retrogressively veined and altered by pervasive hydrothermal fluid flow erosion of the exhumed fault zone produced angular cataclasite and mylonite derived talus fan breccias building a west dipping apron beneath the fault scarp wood fragments from near the base off the talus breccias have been 14 c dated at 12 650 90 yr b p progressive tectonic shortening resulted in 180 m of overthrusting of a schist derived nappe across an irregular talus fan surface composed of its own erosional debris the structural history of the alpine fault at gaunt creek illustrates the importance of the interaction between fault induced topography and erosion and the control these processes exert on the continued tectonic geometric and geomorphic evolution of the fault zone

production of nanoparticles during experimental deformation of smectite and implications for seismic slip abstract nanoparticles and amorphous materials are common constituents of the shallow sections of active faults understanding the conditions at which nanoparticles are produced and their effects on friction can further improve our understanding of fault mechanics and earthquake energy budgets here we present the results of 59 rotary shear experiments conducted at room humidity conditions on gouge consisting of mixtures of smectite ca montmorillonite and quartz experiments with 60 50 25 0 wt ca montmorillonite were performed to investigate the influence of variable clay content on nanoparticle production and their influence on frictional processes all experiments were performed at a normal stress of 5 mpa slip rate of 0 0003 v 1 5 ms 1 and at a displacement of 3 m to monitor the development of fabric and the mineralogical changes during the experiments we investigated the deformed gouges using scanning and transmission electron microscopy combined with x ray powder diffraction quantitative phase analysis this integrated analytical approach reveals that at all slip rates and compositions the nanoparticles grain size of 10 50 nm are partly amorphous and result from cataclasis wear and mechanical solid state amorphization of smectite the maximum production of amorphous nanoparticle occurs in the intermediate slip rate range 0 0003 v 0 1 ms 1 at the highest frictional work and is associated to diffuse deformation and slip strengthening behavior instead the lowest production of amorphous nanoparticles occurs at co seismic slip rates v 1 3 ms 1 at the highest frictional power and is associated with strain and heat localization and slip weakening behavior our findings suggest that independently of the amount of smectite nanoparticles they produce fault weakening only when typical co seismic slip rates 0 1 ms 1 are achieved this implies that estimates of the fracture surface energy dissipated during earthquakes in natural faults might be extremely difficult to constrain

some thermal and mechanical consequences of rapid uplift an example from the southern alps new zealand abstract the thermal evolution of continental crust during active collision is modeled through numerical solutions of the two dimensional heat conduction equation for a rapidly moving medium the boundary conditions used in the modeling are derived from geological and geophysical observations from the active collision zone in the south island of new zealand the problem domain over which the solutions are obtained consists of a 40 km horizontal by 25 km vertical spatial plane with a vertical discontinuity at 10 km from the western boundary to the east of this discontinuity vertical uplift rates of up to 10 mm a occur over a timespan of up to 4 ma temperature distributions are calculated at 10 ka intervals over the 4 ma duration a two dimensional high temperature region is established upon initiation of uplift of the eastern block due to the advective component carrying heat upwards more rapidly than it can be dissipated laterally from the problem domain temperatures within the upper 5 km are greater than 400 c after 2 25 ma with geothermal gradients of up to 200 c km attained within the upper 3 km at times greater than 2 5 ma the vertical temperature distribution changes little while the anomalously high temperatures spread laterally into the stationary crust using rheological equations to describe the brittle behaviour of a water saturated upper crust and the ductile behaviour of a quartz dominated lower crust together with the thermal distribution of the conduction models the mechanical evolution of a collision zone is investigated in addition to high crustal temperatures and associated high heat flow rapid uplift produces a weakening of the crust by raising of the depth of transition from brittle to ductile behaviour within the zone of most rapid uplift the brittle ductile transition rises from 13 km to less than 5 km after 1 5 ma of uplift further uplift reduces the brittle layer to 3 km thickness and causes lateral spreading of the low strength zone the reductions in crustal strength caused by the thermal weakening produce a high strain zone within the region of maximum uplift which is incapable of sustaining large differential stresses this causes horizontal and vertical stress transfer and results in shallow seismicity increases in the adjacent crust as well as in intermediate depth seismicity within the high strength upper mantle because the thermal and mechanical anomalies discussed are a function of rapid uplift all regions of active continental collision may be expected to exhibit similar behaviour some mechanical and thermal characteristics of the himalayan collision zone are briefly examined in light of the numerical modeling

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

crystallographic controls on the frictional behavior of dry and water saturated sheet structure minerals 1 we compare the frictional strengths of 17 sheet structure mineral powders measured under dry and water saturated conditions to identify the factors that cause many of them to be relatively weak the dry coefficient of friction ranges upward from 0 2 for graphite leveling off at 0 8 for margarite clintonite gibbsite kaolinite and lizardite the values of dry correlate directly with calculated 001 interlayer bond strengths of the minerals this correlation occurs because shear becomes localized along boundary and riedel shears and the platy minerals in them rotate into alignment with the shear planes for those gouges with dry 0 8 shear occurs by breaking the interlayer bonds to form new cleavage surfaces where dry 0 8 consistent with byerlee s law the interlayer bonds are sufficiently strong that other frictional processes dominate the transition in dry friction mechanisms corresponds to calculated surface energies of 2 3 j m2 adding water causes to decrease for every mineral tested except graphite if the minerals are separated into groups with similar crystal structures wet increases with increasing interlayer bond strength within each group this relationship also holds for the swelling clay montmorillonite whose water saturated strength is consistent with the strengths of nonswelling clays of similar crystal structure water in the saturated gouges forms thin structured films between the plate surfaces the polar water molecules are bonded to the plate surfaces in proportion to the mineral s surface energy and wet reflects the stresses required to shear through the water films

frictional strength rate dependence and healing in dfdp 1 borehole samples from the alpine fault new zealand abstract the alpine fault in southern new zealand is a major plate boundary fault zone that according to various lines of evidence may be nearing the end of its seismic cycle and approaching earthquake failure in order to better characterize this fault and obtain a better understanding of its seismic potential two pilot boreholes have been completed as part of a larger drilling project samples representative of the major lithologic subdivisions of the fault zone at shallow 100 m depths were recovered and investigated in laboratory friction experiments we show here that materials from within and very near the principal slip zone psz tend to exhibit velocity strengthening frictional behavior and restrengthen heal rapidly compared to samples of the wall rock recovered near the psz fluid saturation causes the psz to be noticeably weaker than the surrounding cataclasites 0 45 and eliminates the velocity weakening behavior in these cataclasites that is observed in dry tests our results indicate that the psz has the ability to regain its strength in a manner required for repeated rupture but its ability to nucleate a seismic event is limited by its velocity strengthening nature we suggest that seismogenic behavior at depth would require alteration of the psz material to become velocity weakening or that earthquake nucleation occurs either within the wall rock or at the interface between the wall rock and the psz coseismic ruptures which propagate to the surface have been inferred for previous earthquakes on the alpine fault and may be facilitated by the slightly weaker psz material and or high rates of healing in the psz which support fault locking and eventual stress drops

frictional properties of exhumed fault gouges in dfdp 1 cores alpine fault new zealand principal slip zone gouges recovered during the deep fault drilling project dfdp 1 alpine fault new zealand were deformed in triaxial friction experiments at temperatures t of up to 350 c effective normal stresses n of up to 156 mpa and velocities between 0 01 and 3 m s chlorite white mica bearing dfdp 1a blue gouge 90 62 m sample depth is frictionally strong friction coefficient 0 61 0 76 across all experimental conditions tested t 70 350 c n 31 2 156 mpa it undergoes a transition from positive to negative rate dependence as t increases past 210 c the friction coefficient of smectite bearing dfdp 1b brown gouge 128 42 m sample depth increases from 0 49 to 0 74 with increasing temperature and pressure t 70 210 c n 31 2 93 6 mpa the positive to negative rate dependence transition occurs as t increases past 140 c these measurements indicate that in the absence of elevated pore fluid pressures dfdp 1 gouges are frictionally strong under conditions representative of the seismogenic crust

frictional behavior of materials in the 3d safod volume 1 we report on frictional properties of rocks within the 3 d crustal volume surrounding the san andreas fault observatory at depth safod samples include lithologies adjacent to the san andreas fault saf in the subsurface safod borehole rocks and synthetic fault gouge composed of talc serpentinite and quartz granodiorite arkosic sandstone and siltstone samples from the safod borehole are frictionally strong 0 56 0 66 sand and clay rich lithologies from outcrop exhibit friction in the range 0 56 0 68 natural serpentinite thought to abut the saf at depth exhibits low friction 0 18 0 26 our results indicate that 1 serpentinite exhibits low strength but is not weak enough to completely satisfy weak fault models 2 all other samples are consistent with a strong fault and crust and 3 if the saf is weak 0 2 due to the presence of serpentinite or talc these minerals would likely need to constitute over 50 by weight of the shear zone

ultrafine spherical quartz formation during seismic fault slip natural and experimental evidence and its implications abstract in recent works on the determination of pseudotachylyte within the principal slip zone psz of the chelungpu fault taiwan we demonstrated that frictional melting occurred at shallow depths during the 1999 mw 7 6 chi chi earthquake thus the characteristics of melts are of paramount importance to investigate processes controlling dynamic fault mechanics during seismic slips we conducted rock friction experiments on siltstone recovered from the taiwan chelungpu fault drilling project tcdp at a slip rate of 1 3 m s and a normal stress of 1 mpa here we not only target to characterize experimental pseudotachylyte and evaluate the associated frictional behavior but also compare it with natural frictional melts of tcdp our results show that 1 initial shear stress drop was related to the generation of low viscosity melt patches 2 the evolution of shear stress in the postmelting regime was congruent with frictional melt rheology and 3 the slip strengthening presumably resulted from the extremely low content of water of the frictional melt in particular the state of art of in situ synchrotron analyses x ray diffraction and transmission x ray microscope determine the presence of ultrafine spherical quartz usq grains 10 nm to 50 nm in the glassy matrices presumably produced at high temperature our observations confirm that the usq grains formed in rock friction experiments do occur in natural faults we surmise the usq is the result of frictional melting on siltstone and represents the latest slip zones of the chelungpu fault and further infer that the viscous melts may terminate seismic slips at shallow crustal conditions

a plate boundary earthquake record from a wetland adjacent to the alpine fault in new zealand refines hazard estimates abstract discovery and investigation of millennial scale geological records of past large earthquakes improve understanding of earthquake frequency recurrence behaviour and likelihood of future rupture of major active faults here we present a 2000 year long seven event earthquake record from john o groats wetland adjacent to the alpine fault in new zealand one of the most active strike slip faults in the world we linked this record with the 7000 year long 22 event earthquake record from hokuri creek 20 km along strike to the north to refine estimates of earthquake frequency and recurrence behaviour for the south westland section of the plate boundary fault eight cores from john o groats wetland revealed a sequence that alternated between organic dominated and clastic dominated sediment packages transitions from a thick organic unit to a thick clastic unit that were sharp involved a significant change in depositional environment and were basin wide were interpreted as evidence of past surface rupturing earthquakes radiocarbon dates of short lived organic fractions either side of these transitions were modelled to provide estimates for earthquake ages of the seven events recognised at the john o groats site three post date the most recent event at hokuri creek two match events at hokuri creek and two events at john o groats occurred in a long interval during which the hokuri creek site may not have been recording earthquakes clearly the preferred john o groats hokuri creek earthquake record consists of 27 events since 6000 bc for which we calculate a mean recurrence interval of 291 23 years shorter than previously estimated for the south westland section of the fault and shorter than the current interseismic period the revised 50 year conditional probability of a surface rupturing earthquake on this fault section is 29 the coefficient of variation is estimated at 0 41 we suggest the low recurrence variability is likely to be a feature of other strike slip plate boundary faults similar to the alpine fault

contemporary horizontal velocity and strain rate fields of the pacific australian plate boundary zone through new zealand we have inverted velocity solutions from nine geodetic networks distributed across new zealand to derive present day continuous horizontal velocity and strain rate fields at the earth s surface throughout the country the nine networks contain a total of 362 global positioning system gps stations that have been observed at least twice and at least a year apart between 1991 and 1998 the model velocity field is expanded as bicubic spline interpolation functions defined within a curvilinear grid that covers the country and extends into the assumed rigid australian and pacific plates to west and east the inversion jointly minimizes the magnitudes of fitted strain rates and the misfit to the observed velocity data the spline technique allows high spatial resolution of strain rate variations especially in regions with spatially dense gps data expansion of the model velocity field on the surface of a sphere allows arbitrarily large areas to be studied previously known aspects of new zealand plate boundary deformation are highlighted with improved resolution including back arc extension in the taupo volcanic zone rotation of the hikurangi forearc away from this zone in the north island and a band of high shear strain rate under the southern alps to the southeast of the alpine fault our results reveal several new features including a region of enhanced shear straining apparently associated with strike slip faults in the southern north island and a band of contractional straining subparallel and well east of the alpine fault that is similar to features found in numerical and sandbox models of continental collision

physical properties of surface outcrop cataclastic fault rocks alpine fault new zealand 1 we present a unified analysis of physical properties of cataclastic fault rocks collected from surface exposures of the central alpine fault at gaunt creek and waikukupa river new zealand friction experiments on fault gouge and intact samples of cataclasite were conducted at 30 33 mpa effective normal stress n using a double direct shear configuration and controlled pore fluid pressure in a true triaxial pressure vessel samples from a scarp outcrop on the southwest bank of gaunt creek display 1 an increase in fault normal permeability k 7 45 10 20 m2 to k 1 15 10 16 m2 2 a transition from frictionally weak 0 44 fault gouge to frictionally strong 0 50 0 55 cataclasite 3 a change in friction rate dependence a b from solely velocity strengthening to velocity strengthening and weakening and 4 an increase in the rate of frictional healing with increasing distance from the footwall fluvioglacial gravels contact at gaunt creek alteration of the primary clay minerals chlorite and illite muscovite to smectite kaolinite and goethite accompanies an increase in friction coefficient 0 31 to 0 44 and fault perpendicular permeability k 3 10 10 20 m2 to k 7 45 10 20 m2 comminution of frictionally strong 0 51 0 57 cataclasites forms weaker 0 31 0 50 foliated cataclasites and fault gouges with behaviors associated with aseismic creep at low strain rates combined with published evidence of large magnitude mw 8 surface ruptures on the alpine fault petrological observations indicate that shear failure involved frictional sliding within previously formed velocity strengthening fault gouge

major earthquakes occur regularly on an isolated plate boundary fault the scarcity of long geological records of major earthquakes on different types of faults makes testing hypotheses of regular versus random or clustered earthquake recurrence behavior difficult we provide a fault proximal major earthquake record spanning 8000 years on the strike slip alpine fault in new zealand cyclic stratigraphy at hokuri creek suggests that the fault ruptured to the surface 24 times and event ages yield a 0 33 coefficient of variation in recurrence interval we associate this near regular earthquake recurrence with a geometrically simple strike slip fault with high slip rate accommodating a high proportion of plate boundary motion that works in isolation from other faults we propose that it is valid to apply time dependent earthquake recurrence models for seismic hazard estimation to similar faults worldwide

palynology of eastern indonesian marine piston cores a late quaternary vegetational and climatic record for australasia abstract pollen analyses of late quaternary sediments from nine marine piston cores reveal a continuous vegetation and environmental record for eastern indonesia and northern australia on the island of halmahera a montane oak forest largely replaced the tropical lowland vegetation during the last glacial period while fern cover was strongly reduced during its maximum 18 000 yr b p climate was cooler and slightly drier than today around 10 000 yr b p mangrove vegetation expanded following the rising sea level in our western new guinea record at 14 000 yr b p climate grew warmer and slightly wetter until it stabilised around 10 000 yr b p at that time the mid to upper montane forests expanded to their full altitudinal range and fern cover increased while montane oak forest grassland and woodland areas had contracted in our marine pollen records during the last glacial the climate of northern australia was distinctly drier than today grassland vegetation with sedges increased considerably at 38 000 and 24 000 yr b p replacing eucalypt forest and culminating in a maximum grassland cover at the height of the last glaciation 18 000 yr b p the rapid sea level rise allowed the expansion of mangrove forests and salt bush marshes which had become established on the large tidal flats of the drowning sahul shelf around 12 000 yr b p one piston core g6 4 extends to 300 000 yr b p and shows that glacial periods are characterized by high pollen concentrations in marine sediments recording expanding grassland vegetation during interglacial woodland and fern cover increased while pollen concentrations in the sediments were low after 190 000 yr b p a more open vegetation suggests that conditions were in general much more arid than before repeated mangrove vegetation expansions suggest major rises in sea level at around 244 000 220 000 and 130 000 yr b p

earthquake rupture propagation inferred from the spatial distribution of fault rock frictional properties abstract the frictional properties of fault rocks that rupture during earthquakes are expected to affect the nucleation and propagation of seismic slip but these properties and their variation under in situ earthquake conditions are typically unknown here we present experimental results on the variation of frictional properties of fault rocks from the alhama de murcia fault amf in se spain which ruptured in the 2011 lorca earthquake in the epicentral area the fault zone is characterized by the presence of abundant phyllosilicate rich gouges that surround more competent fractured lenses of the phyllitic basement measurements of lineaments and orientations of r shears in the gouges are consistent with cmt solutions of the 2011 lorca earthquake suggesting that the bulk of displacement on the amf was accommodated within similar gouges at depth in order to evaluate the frictional properties of the fault rocks of the amf we performed rotary shear experiments under hydrothermal conditions of samples obtained from surface outcrops of the amf zone progressively simulating deeper levels in the crust by stepping temperature effective normal stress and fluid pressure a negative velocity dependence of friction expressed as a negative value of the rate and state friction rsf parameter a b and which is a prerequisite for the nucleation of an instability was observed only for samples derived from competent lenses under hydrothermal conditions gouge derived samples exhibited only velocity strengthening properties i e positive values of a b which increase with deeper conditions in particular with increasing effective normal stress combined with our outcrop observation of the anastomosing nature of gouges surrounding more competent lenses of fractured protolith our results suggest that the 2011 lorca earthquake nucleated in the competent lenses followed by propagation of slip into the frictionally weaker gouges the inferred upward propagation direction of the 2011 lorca earthquake is consistent with propagation of the rupture into the velocity strengthening gouges which at shallower levels provide a smaller barrier to seismic slip due to lower values of effective normal stress and a b our results suggest that the spatial variation of the frictional properties along the amf was an important factor controlling the nucleation and propagation of seismic slip which together with the shallow hypocenter close to the city of lorca led to serious damage we infer that understanding of such variations in frictional properties may significantly improve seismic hazard evaluations in tectonically active regions

the role of sea surface temperature as a control on carbonate platform development in the western coral sea the derivation of a detailed sea surface paleotemperature curve for the middle miocene holocene 10 0 ma from odp site 811 on the queensland plateau northeast australia has clarified the role of sea surface temperature fluctuations as a control on the initiation and development of the extensive carbonate platforms of this region this curve was derived from isotopic analyses of the planktonic foraminifer globigerinoides ruber and converted to temperature using the surface water paleotemperature equation accounting for variations in global ice volume the accuracy of these data were confirmed by derivation of paleotemperatures using the water column isotopic gradient 13o corrected for salinity and variations in seafloor water mass temperature results indicate that during this period surface water temperatures were on average greater than the minimum required for tropical reef growth 20 c veron 1986 with the exception of the late miocene and earliest early pliocene 10 4 9 ma when there were repeated intervals of temperatures between 18 20 c tropical reef growth on the queensland plateau was extensive from the early to early middle miocene 21 13 ma after which reef development began to decline a lowstand near 11 ma probably exposed shallower portions of the plateau after re immersion near 7 ma the areal extent of reef development was greatly reduced 50 paleotemperature data from site 811 indicate that decreased sea surface temperatures were likely to have been instrumental in reducing the area of active reef growth on the queensland plateau reduced reefal growth rates continued until the late pliocene or quaternary despite the increase of average sea surface paleotemperatures to 22 23 c studies on modern corals show that when sea surface temperatures are below 24 c as they were from the late miocene to the pleistocene off northeast australia corals are stressed and growth rates are greatly reduced consequently when temperatures are in this range corals have difficulty keeping pace with subsidence and changing environmental factors in the late pliocene sedimentation rates increased due to increases in non reefal carbonate production and falling sea levels it was not until the mid quaternary 0 6 0 7 ma that sea surface paleotemperatures increased above 24 c as a result of the formation of a western coral sea warm water pool because of age discrepancies it is unclear exactly when an effective barrier developed on the central great barrier reef the formation of the warm water pool was likely to have either assisted the formation of this barrier and or permitted increased coral growth rates fluctuations in sea surface temperature can account for much of the observed spatial and temporal variations of reef growth and carbonate platform distribution off northeast australia and therefore we conclude that paleotemperature variations are a critical control on the development of carbonate platforms and must be considered an important cause of ancient platform drowning

influence of exhumation on the structural evolution of transpressional plate boundaries an example from the southern alps new zealand concentration of erosional activity along transpressional plate boundaries can significantly alter the pattern of mechanical behavior through the influence of exhumation on crustal strength three dimensional numerical modeling of an obliquely convergent orogen shows that a single oblique plate bounding structure is stable if asymmetric erosion patterns such as those observed in orographic mountain belts pertain and if earth9s crust has a strong on weak rheology in early stages of oblique convergence of an initially laterally homogeneous material lateral boundary parallel strain is accommodated along a near vertical structure and convergent boundary normal strain is concentrated on structures dipping at moderate angles into the orogen exhumation of deep crustal material along the convergent structure results in thermal weakening along this dipping structure when the upper crust beneath the orogen is significantly weakened by exhumation lateral strain abandons the vertical structure and shifts to the dipping structure combining with the convergent strain to form a single oblique fault that accommodates the plate motion in the upper crust as is the case along the alpine fault new zealand the process of thermal thinning is controlled by advection and occurs on time frames of 1 2 m y the two components of strain remain separate in the lower crust during active convergence exhumation of lower crustal material occurs only along those structures accommodating convergent strain consequently material exhumed from lower regions of ductile deformation as is the case along the alpine fault contains lineations that indicate a greater component of convergence than predicted from the total plate motion postorogenic exhumation of the roots of an oblique plate boundary will expose two parallel shear zones one dominantly convergent and one dominantly strike slip widely reported orogen parallel transport in the late stages of ancient oblique convergence may represent not a change in plate vector but the exhumation of the lateral transport zone

a record of fire vegetation and climate through the last three glacial cycles from lombok ridge core g6 4 eastern indian ocean indonesia abstract charcoal elemental carbon and clastic particle analyses have been undertaken on tropical marine core g6 4 collected from the eastern indian ocean between the lesser sunda islands of indonesia and northwestern australia to help interpret an existing pollen record in addition a new oxygen isotope record has been constructed and several radiocarbon dates produced to allow a refinement of the chronology of the core the record covers the last 300 000 years with three clear glacial interglacial cycles however the new oxygen isotope record and radiocarbon dates suggest a hiatus and it appears that most isotope stage 3 is missing interglacials are characterised by higher values of mangrove fern and rainforest pollen indicating wetter conditions than intervening glacials which have higher cyperaceae and chenopodiaceae values gramineae percentages are also generally higher during glacials but there is a sustained increase in grasses relative to eucalyptus about 185 000 years ago originally interpreted as a change to drier conditions an increase in burning from about 200 000 years ago from charcoal evidence suggests that fire may have been an important contributing factor this and subsequent increases in charcoal may reflect anthropogenic burning and are considered in relation to archaeological evidence for possible times of arrival of people within australia the elemental carbon record shows major differences to that from charcoal and further research is needed to interpret its meaning little consistent evidence for changes in climate or vegetation disturbance is provided by clastic particle influx which may well reveal a record of volcanicity within the region

slip localization on the southern alpine fault new zealand 1 results of a detailed field study of the southern onshore portion of new zealand s alpine fault reveal that for 75 km along strike dextral normal slip on this long lived structure is highly localized in phyllosilicate rich fault core gouges and along their contact with more competent rocks at three localities martyr river mckenzie creek and hokuri creek we document complete cross sections through the fault new 40ar 39ar dates on mylonites combined with microstructural and mechanical data on phyllosilicate rich fault core gouges show that modern slip is localized onto a single steeply dipping 1 to 12 m thick fault core composed of impermeable k 10 20 to 10 22 m2 frictionally weak s 0 12 0 37 velocity strengthening illite chlorite and saponite chlorite lizardite fault gouges fault core materials are 1 comparable to those of other major weak cored faults e g san andreas fault and 2 most compatible with fault creep despite paleoseismic evidence of quasiperiodic large magnitude earthquakes mw 7 on this portion of the alpine fault we conclude that frictional properties of gouges at the surface do not characterize the overall seismogenic behavior of the southern alpine fault

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

the 2011 tohoku oki earthquake displacement reaching the trench axis we detected and measured coseismic displacement caused by the 11 march 2011 tohoku oki earthquake moment magnitude mw 9 0 by using multibeam bathymetric surveys the difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the japan trench suggesting that the fault rupture reached the trench axis the sea floor on the outermost landward area moved about 50 meters horizontally east southeast and 10 meters upward the large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement

early human occupation at devil s lair southwestern australia 50 000 years ago abstract new dating confirms that people occupied the australian continent before the earliest time inferred from conventional radiocarbon analysis many of the new ages were obtained by accelerator mass spectrometry 14c dating after an acid base acid pretreatment with bulk combustion aba bc or after a newly developed acid base wet oxidation pretreatment with stepped combustion abox sc the samples charcoal came from the earliest occupation levels of the devil s lair site in southwestern western australia initial occupation of this site was previously dated 35 000 14c yr b p whereas the aba bc ages are indistinguishable from background beyond 42 000 14c yr b p the abox sc ages are in stratigraphic order to 55 000 14c yr b p the abox sc chronology suggests that people were in the area by 48 000 cal yr b p optically stimulated luminescence osl electron spin resonance esr ages u series dating of flowstones and 14c dating of emu eggshell carbonate are in agreement with the abox sc 14c chronology these results based on four independent techniques reinforce arguments for early colonization of the australian continent

effects of temperature and sliding rate on frictional strength of granite layers of artificial granite gouge have been deformed on saw cut granite surfaces inclined 30 to the sample axes samples were deformed at a constant confining pressure of 250 mpa and temperatures of 22 to 845 c the velocity dependence of the steady state coefficient of friction ss was determined by comparing sliding strengths at different sliding rates the results of these measurements are consistent with those reported bysolberg andbyerlee 1984 at room temperature andstesky 1975 between 300 and 400 c stesky found that the slip rate dependence of ss increased above 400 c in the present study however the velocity dependence of ss was nearly independent of temperature

hydraulic and acoustic properties of the active alpine fault new zealand laboratory measurements on dfdp 1 drill core abstract we report on laboratory measurements of permeability and elastic wavespeed for a suite of samples obtained by drilling across the active alpine fault on the south island of new zealand as part of the first phase of the deep fault drilling project dfdp 1 we find that clay rich cataclasite and principal slip zone psz samples exhibit low permeabilities 10 18 m 2 and that the permeability of hanging wall cataclasites increases from c 10 18 m 2 to 10 15 m 2 with distance from the fault additionally the psz exhibits a markedly lower p wave velocity and young s modulus relative to the wall rocks our laboratory data are in good agreement with in situ wireline logging measurements and are consistent with the identification of an alteration zone surrounding the psz defined by observations of core samples the properties of this zone and the low permeability of the psz likely govern transient hydrologic processes during earthquake slip including thermal pressurization and dilatancy strengthening

crustal deformation during 1994 1998 due to oblique continental collision in the central southern alps new zealand and implications for seismic potential of the alpine fault the positions of 115 ground marks in a 150 100 km area of oblique continental collision in the central southern alps new zealand have been measured by global positioning system gps two to four times between 1994 and 1998 contemporary velocity and strain rate fields derived from these observations are largely invariant along the northeasterly strike of the mountains and alpine fault across strike more than 60 of the strain occurs within a band from 5 km nw to 20 km se of the alpine fault but significant strain continues at least a further 60 km se to near the edge of the southern alps foothills projections of the fault parallel and fault normal components of velocity onto an alpine faultnormal profile show that about 85 of the nuvel 1a model relative plate motion is observed within the gps network the surface displacements in the high strain rate region are well fit by a model in which stable slip or shearing is occurring at 50 70 of the relative plate rate in a region deeper than about 5 8 km on the down dip extension of the se dipping alpine fault material shallower than this is behaving elastically and thus storing elastic strain in the region of the alpine fault the longer wavelength displacements can be modeled either as distributed deformation beneath the southern alps or by localization of elastic strain around the upper end of a discrete nw dipping fault or shear zone that is slipping stably below about 30 km depth and would outcrop near the se boundary of the mountains if extrapolated to the surface strain determined from a small scale survey network crossing the alpine fault indicates no significant near surface aseismic fault slip on the central alpine fault over the past 25 years our results are consistent with independent geological evidence that the central section of the alpine fault is capable of producing large to great earthquakes

frictional slip of granite at hydrothermal conditions sliding on faults in much of the continental crust likely occurs at hydrothermal conditions i e at elevated temperature and elevated pressure of aqueous pore fluids yet there have been few relevant laboratory studies to measure the strength sliding behavior and friction constitutive properties of faults at hydrothermal conditions we slid laboratory granite faults containing a layer of granite powder simulated gouge velocity stepping experiments were performed at temperatures of 23 to 600 c pore fluid pressures ph2o of 0 dry and 100 mpa wet effective normal stress of 400 mpa and sliding velocities v of 0 01 to 1 m s 0 32 to 32 m yr conditions were similar to those in earlier tests on dry granite to 845 c by lockner et al 1986 the mechanical results define two regimes the first regime includes dry granite up to at least 845 and wet granite below 250 c in this regime the coefficient of friction is high 0 7 to 0 8 and depends only modestly on temperature slip rate and ph2o the second regime includes wet granite above 350 c in this regime friction decreases considerably with increasing temperature temperature weakening and with decreasing slip rate velocity strengthening these regimes correspond well to those identified in sliding tests on ultrafine quartz we infer that one or more fluid assisted deformation mechanisms are activated in the second hydrothermal regime and operate concurrently with cataclastic flow slip in the first cool and or dry regime is characterized by pervasive shearing and particle size reduction slip in the second hot and wet regime is localized primarily onto narrow shear bands adjacent to the gouge rock interfaces weakness of these boundary shears may result either from an abundance of phyllosilicates preferentially aligned for easy dislocation glide or from a dependence of strength on gouge particle size major features of the granite data set can be fit reasonably well by a rate and temperature dependent three regime friction constitutive model chester this issue we extrapolate the experimental data and model fit in order to estimate steady state shear strength versus depth along natural slipping faults for sliding rates as low as 31 mm yr we do this for two end member cases in the first case pore pressure is assumed hydrostatic at all depths shallow crustal strength in this case is similar to that calculated in previous work from room temperature friction data while at depths below about 9 13 km depending on slip rate strength becomes less sensitive to depth but sensitive to slip rate in the second case pore pressure is assumed to be near lithostatic at depths below 5 km strength is low at all depths in this case 20 mpa in agreement with observations of weak faults such as the san andreas the predicted depth of transition from velocity weakening to velocity strengthening lies at about 13 km depth for a slip rate of 31 mm yr in rough agreement with the seismic aseismic transition depth observed on mature continental faults these results highlight the importance of fluid assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry large displacements higher concentrations of phyllosilicates and time dependent fault healing

late interseismic state of a continental plate bounding fault petrophysical results from dfdp 1 wireline logging and core analysis alpine fault new zealand 1 we present a geophysical characterization at 0 1 100 m scales of a major plate bounding continental fault in a late interseismic state the alpine fault produces mw 8 earthquakes every 200 400 years and last ruptured in 1717 ad wireline geophysical logs and rock cores extending from one side of the alpine fault to the other were acquired in two boreholes drilled in 2011 at gaunt creek during the first phase of the deep fault drilling project dfdp 1 these data document ambient conditions under which the next alpine fault earthquake will occur principal component analysis of the wireline logging data reveals that 80 of the variance is accounted for by electrical acoustic and natural gamma properties and preliminary multivariate classification enables the lithologies of sections of missing core to be reconstructed from geophysical measurements the fault zone exhibits systematic variations in properties consistent with common processes of progressive alteration and comminution near the principal slip zone superimposed on different protolith compositions our observations imply that the fault zone has the opposite sense of elastic asymmetry at 0 1 100 m scales to that of the crustal scale orogen imaged by remote geophysical methods on the basis of the fault zone scale asymmetry the bimaterial interface model of preferred earthquake rupture directions implies a northeastward direction of preferred alpine fault rupture on going characterization of the structural and hydraulic architecture of the alpine fault will improve our understanding of the relationship between in situ conditions earthquake rupture processes and the hazards posed by future earthquakes

influence of subduction zone conditions and gouge composition on frictional slip stability of megathrust faults to understand the temperature depth distribution of destructive earthquakes in subduction megathrusts and the mechanisms of nucleation of these events data on the frictional behaviour of phyllosilicate quartz rich megathrust fault gouges under in situ conditions are needed we performed rotary shear friction experiments at effective normal stresses of 25 200 mpa pore fluid pressures of 50 200 mpa at 140 600 c and sliding velocities of 1 100 m s using gouge mixtures with an illite quartz ratio between 65 35 and zero experiments on 65 35 mixtures deformed at an effective normal stress neff of 170 mpa a pore fluid pressure pf of 100 mpa and 150 500 c provided a reference dataset this showed three temperature dependent slip stability regimes with potentially unstable velocity weakening behaviour at 250 400 c and velocity strengthening at lower and higher temperatures the velocity weakening regime was found to shift towards higher temperatures with decreasing neff being located at 350 600 c at 50 mpa increasing quartz content and decreasing sliding velocity also displaced the velocity weakening regime towards lower temperatures increasing pf increased a b at all temperatures narrowing the temperature extent of the velocity weakening regime we explain our results qualitatively in terms of a microphysical model in which changes in friction coefficient and a b with velocity and temperature are brought about by changes in the relative importance of deformation of the clast phase by thermally activated stress corrosion cracking and pressure solution versus athermal granular flow of the mixture accompanied by dilatation our results imply that the depth extent of the seismogenic zone on subduction megathrusts depends not only on temperature and that to predict its location it is essential to have well constrained depth profiles for pore fluid pressure and effective normal stress

sub crustal earthquakes within the australia pacific plate boundary zone beneath the southern alps new zealand abstract sub crustal earthquakes have been observed sporadically for 40 years in the central south island of new zealand we report on 20 events recorded between december 2008 and february 2012 near the alpine fault in the continental collision zone between the australian and pacific plates a subset of 18 events at depths of 47 74 km occurs south of mt cook and together with recently reported tremor locations indicates along strike variations in deformation behaviour along the plate boundary the sub crustal earthquakes south of mt cook increase in depth frequency and size southwards towards the puysegur subduction zone focal mechanisms could be determined for 14 earthquakes and exhibit predominantly strike slip and reverse faulting solutions stress inversion analysis of the focal mechanisms yields a stress field favouring oblique reverse faulting we interpret the geographic and vertical distributions of these sub crustal events in relation to a previously proposed tectonic model of a remnant passive margin that formed south of new zealand in the eocene and was overridden when dextral strike slip motion initiated on the alpine fault we infer that sub crustal earthquakes occur along the leading edge of this structure which is attached to the continental australian crust

constraints on the stress state of the san andreas fault with analysis based on core and cuttings from san andreas fault observatory at depth safod drilling phases 1 and 2 1 analysis of field data has led different investigators to conclude that the san andreas fault saf has either anomalously low frictional sliding strength 0 6 arguments for the apparent weakness of the saf generally hinge on conceptual models involving intrinsically weak gouge or elevated pore pressure within the fault zone some models assert that weak gouge and or high pore pressure exist under static conditions while others consider strength loss or fluid pressure increase due to rapid coseismic fault slip the present paper is composed of three parts first we develop generalized equations based on and consistent with the rice 1992 fault zone model to relate stress orientation and magnitude to depth dependent coefficient of friction and pore pressure second we present temperature and pressure dependent friction measurements from wet illite rich fault gouge extracted from san andreas fault observatory at depth safod phase 1 core samples and from weak minerals associated with the san andreas fault third we reevaluate the state of stress on the san andreas fault in light of new constraints imposed by safod borehole data pure talc 0 1 had the lowest strength considered and was sufficiently weak to satisfy weak fault heat flow and stress orientation constraints with hydrostatic pore pressure other fault gouges showed a systematic increase in strength with increasing temperature and pressure in this case heat flow and stress orientation constraints would require elevated pore pressure and in some cases fault zone pore pressure in excess of vertical stress

late quaternary slip rates and slip partitioning on the alpine fault new zealand abstract published geological data on late quaternary offsets on the alpine fault new zealand have been assembled into a common format and analysed with respect to uncertainties uncertainties arise mainly from measurement of offset features relating apparent offsets to actual fault slip and dating the offset features despite the considerable uncertainties the data form a coherent set consistent with a relatively constant rate of strike slip of 27 5 mm year between milford sound and hokitika this rate represents 70 75 of the fault parallel interplate motion north of the confluence with the hope fault the rate drops substantially dip slip rates on the other hand show considerable variation along strike rising to a maximum of more than 10 mm year in the central section and decreasing to zero at the southern end partitioning of c 25 of the interplate slip on to structures east of the alpine fault occurs in the central section consistent with predictions from critical wedge models the partitioning of all the fault normal component of displacement on to other structures in the south may be related in part to a doubling in width of the deforming wedge to the east most probably however the fault normal displacement is mainly accommodated by underthrusting of the australian plate offshore due to a change in the nature of the crust from continental to oceanic

a 400 000 year record of vegetational and climatic changes from a volcanic basin leizhou peninsula southern china abstract the tianyang lake in leizhou peninsula is an enclosed crater formed during the early to middle pleistocene over 200 m of diatomaceous mud and clay were deposited in the last 400 000 years providing a continuous middle and late quaternary lacustrine sequence for paleoenvironmental studies the pollen record spans the last four glacial interglacial cycles equivalent to oxygen isotope stages ois 10 to 1 during most of the glacial phases fagaceous monsoon forest was replaced by altitudinal vegetation indicating a regional landscape transformation on the peninsula the montane forest reached down to the lowland by at least 600 m during the ois 6 and 8 in a cool and relatively wet condition with temperature estimated to be more than 4 c lower than present a further lowering of the montane forest belts by about 800 1000 m occurred in the ois 4 2 as implied by the appearance of many temperate elements during the last glacial maximum this mixed forest subsequently gave way to the poaceae grassland a savanna vegetation type favored by drier and cooler climatic conditions this drastic change implies a more significant drop in temperature and precipitation than the previous three glacial periods ois 10 8 and 6 it is thus inferred that the weakening of summer monsoon was more significant towards the end of the late pleistocene particularly during the last glacial maximum lgm

late quaternary milankovitch scale climatic change and variability and its impact on monsoonal australasia four pollen and charcoal records derived from marine cores around the northern perimeter of australia are examined to provide a regional picture of patterns causes and impacts of climate change over the last 100 300 ka the availability of radiocarbon dates and oxygen isotope records for the cores provides primary chronological control spectral analysis of components of these records demonstrates an overall importance of milankovitch frequencies with clear glacial interglacial cyclicity dominated by variation in precipitation in addition a number of pollen taxa as well as charcoal particles exhibit a 30 ka frequency that is considered from its relationship with biomass burning and with results of past modelling to reflect changes in the intensity of el nino southern oscillation enso variability pollen components of all records show a decline frequently stepwise in more fire sensitive vegetation and its replacement with more fire tolerant vegetation there is some evidence that this trend is linked to an onset or general increase in enso activity and perhaps also to variation in monsoon activity dating from about 300 ka bp that was caused by changes to oceanic circulation within the indonesian region the trend may have accelerated within the last 45 ka due to burning by indigenous people c 2003 elsevier b v all rights reserved

dynamic weakening of smectite bearing faults at intermediate velocities implications for subduction zone earthquakes the hydrous clay mineral smectite which is pervasive in sediments on subducting oceanic plates is thought to weaken and stabilize subduction thrust faults however these frictional properties of smectite alone cannot explain the large coseismic slip in the vicinity of a trench here we performed friction experiments to demonstrate the rate dependence of friction at slip rates from 30 m s to 1 3 m s for water saturated smectite quartz mixtures with various smectite contents so as to shed light on the frictional response of smectite bearing faults at intermediate to high slip rates at slip rates of 30 to 150 m s the friction coefficients decreased gradually from 0 5 0 6 to 0 1 with an increase in smectite content from 20 to 50 wt in contrast at slip rates higher than 1 3 mm s friction exhibited marked slip weakening resulting in low friction coefficients of 0 1 0 05 even for low smectite contents roughly 30 wt drastic slip weakening occurred at smectite contents of 10 30 wt at slip rates of 10 mm s which is 1 to 2 orders of magnitude lower than the slip rate at which slip weakening was observed in previous experiments on various rock types the intermediate velocity weakening could be attributed to a rise in pore pressure caused by both shear enhanced compaction and microscopic thermal pressurization of pore fluids this process could weaken the fault even below seismic slip rates leading to an acceleration of fault motion and potentially facilitating large coseismic slip and a stress drop in the vicinity of a trench

seabed dynamics of the inner amazon continental shelf temporal and spatial variability of surficial strata the continental shelf southeast and northwest of the amazon river mouth is overlain by a sediment layer of about a meter in thickness characterized by 210pb profiles consisting of one or more segments with nearly uniform excess activity uniform 210pb activity profiles in shelf environments commonly are a result of intense biological reworking of sediments however biological activity is minimal in this area hence this surficial layer sl is a result either of physical reworking of the sediments or of rapid possibly episodic deposition of sediment factors controlling the formation of the sl were examined during the amasseds project between august 1989 and october 1991 primarily using 210pb t1 2 22 3 yr activity profiles and x radiography the thickness and character of the sl were assessed at four locations reoccupied during four seasonal periods corresponding to various riverine and oceanographic conditions e g discharge stage wind stress one of these stations was reoccupied during semidiurnal and fortnightly periods additionally replicate sediment cores were obtained at stations in order to assess small scale spatial variability of geochemical and sedimentological characteristics in the seabed the sl thicknesses in replicate sediment cores obtained at each site were found to vary within 5 cm normalized thickness of the sl decreased by an average of 17 cm between august 1989 and february 1990 a period of increasing wind stress during falling to rising river discharge the sl thickness subsequently increased slightly 8 cm from february to may 1990 and increased again 27 cm between may 1990 and october 1991 the maximum sl thicknesses were observed in october a period of low wind stress and minimal river input suggesting that the observed seasonal changes are dictated by oceanographic conditions as well as by sediment discharge variations in sl thickness are reflected by changes in suspended sediment mostly as fluid muds as the highest suspended sediment inventories and most extensive fluid muds are observed during the period when sl thickness is at a minimum although a significant sl was present during all of the sampling periods changes in the character of 210pb profiles at two of the stations suggest that substantial perhaps complete removal and redeposition of the sl occurred some time between february and may preserved strata i e below the sl is characterized by greater evidence of bioturbation and increased sand content but otherwise is similar to that of the sl long term preservation of strata is thought to occur through episodic suspension and redeposition of the sl with net accumulation of decimeter thick hiatus bounded layers

on the transient response of serpentine antigorite gouge to stepwise changes in slip velocity under high temperature conditions 1 shear sliding tests were conducted on serpentine antigorite gouge to understand the rheology of serpentine bearing faults the experiments were carried out using a constant confining pressure 100 mpa a constant pore water pressure 30 mpa and a range of temperatures from room temperature to 600 c the transient response in frictional behavior following stepwise changes in the slip velocity were documented at each temperature slip rates varied between 0 0115 and 11 5 m s both the general level of frictional strength and the transient responses changed drastically at around 450 c as the temperature increased from 400 c to 450 c the strength of antigorite rose sharply the transient response also indicated a change in the mode of deformation from flow type behavior at temperatures below 400 c to frictional behavior stick slip at temperatures above 450 c 500 c although only a limited volume of serpentine was involved in the dehydration reaction x ray diffraction analyses and scanning electron microscopy observations showed that forsterite had nucleated in the experimental products at the higher temperatures that were associated with frictional behavior submicron sized streaky forsterite masses in shear localized zones may be evidence of shear induced dehydration that caused strengthening and embrittlement of the gouge although antigorite rheology is complicated the subsequent change in friction coefficient per order of magnitude change in sliding velocity increased with both increasing temperature and decreasing velocity implying that a possible flow mechanism of intragranular deformation became activated

microseismicity and stress in the vicinity of the alpine fault central southern alps new zealand 1 we investigate present day microseismicity associated with the central alpine fault and the zone of active deformation and uplift in the central southern alps using 14 months of data robust hypocenter locations have been obtained for 1800 earthquakes of magnitudes between 0 3 and 4 2 we derived a magnitude scale with a frequency dependent attenuation factor f 0f where 0 1 89 0 02 10 3 s km that enables magnitudes to be calculated consistently for earthquakes of different sizes and frequency contents the maximum depth of the seismicity varies systematically with distance from the alpine fault from 10 2 km near the fault to 8 2 km within 20 km and 15 2 km further southeast this distribution correlates with lateral variations in crustal resistivity earthquake hypocenters are concentrated in areas of strong resistivity gradients and restricted to depths of resistivities 100 m rocks at greater depth are too hot too fluid saturated or too weak to produce detectable earthquakes focal mechanism solutions computed for 211 earthquakes ml 0 44 exhibit predominantly strike slip mechanisms we obtain a maximum horizontal compressive stress direction of 115 10 from focal mechanism inversion this azimuth is consistent with findings from elsewhere in the central and northern south island and indicates a uniform crustal stress field despite pronounced variations in crustal structure and topographic relief our stress estimates suggest that the alpine fault with a mean strike of 055 is poorly oriented in an andersonian sense but that individual thrust and strike slip segments of the fault s surface trace have close to optimal orientations

shear zones in clay rich fault gouge a laboratory study of fabric development and evolution abstract clay rich fault rocks have long been recognized to host distinctive fabric elements and fault rock fabric is increasingly thought to play a fundamental role in fault mechanical behaviour in the brittle regime although the geometries of fabric elements in fault gouges have been described for almost a century the genesis and evolution of these elements during shear and their links to bulk mechanical properties remain poorly understood we characterize the development and evolution of fabric elements with increasing shear in a variety of clay rich experimental gouges over shear strains of 20 and at normal stresses of 2 150 mpa in the double direct shear configuration in addition to sem observations of experiment products at a variety of shear strains we quantified clay fabric intensity and the degree of grain size reduction using x ray texture goniometry xtg and particle size distribution psd measurements we also measured p and s wave velocities during shear to further probe the evolution of shear fabric and gouge properties we find that clay fabric elements develop in a systematic manner regardless of the gouge material riedel shears in the r1 orientation and boundary parallel shears are the dominant fabric elements riedel shears nucleate at layer margins and propagate into the layer shortly after reaching yield stress clay particles rotate into the p orientation shortly after riedels propagate through the layer the riedel shears are through going but are 10 thinner than similar zones observed in coarser granular materials our results suggest that the weakness of clay rich fault gouge may be less a function of anisotropic crystal structure as has been suggested previously and more a consequence of very thin shear surfaces permitting deformation in clay rich materials with minimal dilation or cataclasis the very thin shear surfaces are a function of the fine grain size of the materials and possibly polymodal psd s

thermal modeling of the southern alps new zealand finite element modeling of the thermal regime across the southern alps of new zealand has been carried out along two profiles situated near the franz josef and haast valleys the modeling involves viscous deformation beneath the southern alps including both uplift and erosion and crustal lithospheric thickening as a result of crustal shortening extending to 20 mm y of a 25 km thick crust published uplift rates and crustal thickness variations along the two profiles are used to constrain the modeled advection of crustal material and results are compared with the recent heat flow determinations 190 50 mw m2 in the franz josef valley and 90 25 mw m2 in the haast valley comparisons of the model with published k ar and fission track ages show that the observed heat flow in the franz josef valley is consistent with observed zircon fission track ages of around 1 ma if the present day uplift rate is close to 10 mm y major thermal differences between the franz josef and haast profiles appear to be due to different uplift and erosion rates there is weak evidence that frictional heating close to the alpine fault zone is not significant the modeling provides explanations for the distribution of seismicity beneath the southern alps and predicts a low surface heat flow over the eastern foothills due to the dominant thermal effect of crustal thickening beneath this region predicted temperatures at mid crustal depth beneath the zone of maximum uplift rate are 50 100 c cooler than those indicated in previously published models which implies that thermal weakening of the crust may not be the main factor causing the aseismicity of the central southern alps the results of the modeling demonstrate that the different types of reset age data in the region within 25 km of the alpine fault are critical for constraining models of the deformation and the thermal regime beneath the southern alps

frictional strength of cuttings and core from safod drillhole phases 1 and 2 1 we investigated the frictional properties of drill cuttings and core obtained from 1 85 3 1 km true vertical depth in the safod scientific borehole in central california triaxial frictional sliding experiments were conducted on samples from primary lithologic units and significant shear zones including the inferred active trace of the san andreas fault the samples were deformed at room temperature under constant effective normal stresses of 10 40 and 80 mpa with axial shortening rates of 0 01 1 0 m s 1 the weakest samples were from shale claystone and siltstone units with friction coefficient 0 4 0 55 stronger samples were from quartzo feldspathic rocks with 0 6 materials tested from two shear zones at 2560 and 3067 m measured depth had 0 4 0 55 and velocity strengthening behavior consistent with fault creep at depths 4 km the coefficient of friction for bulk samples from the inferred trace of the san andreas fault was 0 6

micromechanisms of creep in clay rich gouge from the central deforming zone of the san andreas fault we report the strength and constitutive behavior of gouge sampled from the central deforming zone cdz of the san andreas fault layers of flaked cdz gouge were sheared in the triaxial saw cut configuration using the stress relaxation technique to measure the gouge strength over 4 orders of magnitude in shear strain rate and at rates as low as 5 10 10s 1 and within an order of magnitude of in situ rates deformation conditions correspond to the in situ effective normal stress 100 mpa and temperature 65 to 120 c at the sampling depth of 2 7 km gouge was sheared dry and with brine pore fluid at 25 mpa pore pressure dry gouge is stronger and more rate strengthening than brine saturated gouge brine saturated cdz gouge strengthens with increasing strain rate and decreasing temperature and the dependencies of strength on strain rate and temperature increase at rates below 5 10 9s 1 at strain rates greater than 5 10 9s 1 the rate dependence is consistent with previous studies on the cdz gouge conducted at even higher rates the increase in rate dependence below 5 10 9s 1 indicates a change in the rate controlling deformation mechanism the magnitude of the friction rate dependence parameter a and the temperature sensitivity of a are consistent with crystal plasticity of the phyllosilicates we hypothesize a micromechanical model for the cdz gouge whereby a transition from fracture and delamination accommodated frictional flow to crystal plasticity accommodated frictional flow occurs with decreasing strain rate

late pleistocene paleoclimatology of the central equatorial pacific sea surface response to the southeast trade winds proxy indicators of sea surface temperature and equatorial divergence based on radiolarian assemblage data and of trade wind intensity based on eolian grain size data show similar aspects of variability during the late pleistocene all indicators fluctuate at higher frequencies than the 100 000 year glacial interglacial cycle display reduced amplitude variations since 300 000 years ago exhibit a change in the record character at about 300 000 years ago the mid brunhes climatic event and have higher amplitude variations in sediments 300 000 850 000 years old time series analyses were conducted to determine the spectral character of each record 18o of planktonic foraminifer sea surface temperature values equatorial divergence indicators and wind intensity indicators and to quantify interrecord coherence and phase relationships the record was divided at the 300 000 year clear change in climatic variability nonstationarity the 18o based time scale is better lower in the core so our spectral analyses concentrated on the interval from 402 000 774 000 years the 18o spectra show 100 000 and 41 000 year power in the younger portion 0 300 000 years and 100 000 41 000 and 23 000 year power in the older interval all highly coherent and in phase with the specmap average stacked isotope record unlike the isotope record the dominant period in both the eolian grain size and equatorial divergence indicators is 31 000 years this period is also important in the sea surface temperature signal where the dominant spectral peak is 100 000 years the 31 000 year spectral component is coherent and in phase between the eolian and divergence records confirming the link between atmospheric and ocean surface circulation for the first time in the paleoclimate record since the 31 000 year power appears in independent data sets within this core and also appears in other equatorial records j imbrie personal communication 1987 we assume it to be real and representative of both a nonlinear response to orbital forcing possibly a combination of orbital tilt and eccentricity and some resonance phenomenon required to amplify the response at this period so that it appears as a dominant frequency component the mid brunhes climatic event is an important aspect of these records but its cause remains unknown

comparison of frictional strength and velocity dependence between fault zones in the nankai accretionary complex accretionary complexes host a variety of fault zones that accommodate plate convergence and internal prism deformation including the decollement imbricate thrusts and out of sequence thrusts or splays these faults especially the decollement and major splay faults are considered to be candidates for hosting slow slip events and large magnitude earthquakes but it is not clear what modes of slip should be expected at shallow levels or how they are related to fault rock frictional properties we conducted laboratory experiments to measure the frictional properties of fault and wall rock from three distinct fault zone systems sampled during integrated ocean drilling program expedition 316 and ocean drilling program leg 190 to the nankai trough offshore japan these are 1 a major out of sequence thrust fault termed the megasplay site c0004 2 the frontal thrust zone a region of diffuse thrust faulting near the trench site c0007 and 3 the decollement zone sampled 2 km from the trench site 1174 at 25 mpa effective normal stress at slip rates of 0 03 100 m s and in the presence of brine as a pore fluid we observe low friction 0 46 for all of the materials we tested however the weakest samples 0 30 are from the decollement zone material from the megasplay fault is significantly weaker than the surrounding wall rocks a pattern not observed in the frontal thrust and decollement all samples exhibit primarily velocity strengthening frictional behavior suggesting that earthquakes should not nucleate at these depths a consistent minimum in the friction rate parameter a b at sliding velocities of 1 3 m s 0 1 0 3 m d is observed at all three sites suggesting that these shallow fault zones may be likely to host slow slip events

shear behavior of dfdp 1 borehole samples from the alpine fault new zealand under a wide range of experimental conditions the alpine fault is a major plate boundary fault zone that poses a major seismic hazard in southern new zealand the initial stage of the deep fault drilling project has provided sample material from the major lithological constituents of the alpine fault from two pilot boreholes we use laboratory shearing experiments to show that the friction coefficient of fault related rocks and their precursors varies between 0 38 and 0 80 depending on the lithology presence of pore fluid effective normal stress and temperature under conditions appropriate for several kilometers depth on the alpine fault 100 mpa 160 c fluid saturated a gouge sample located very near to the principal slip zone exhibits 0 67 which is high compared with other major fault zones targeted by scientific drilling and suggests the capacity for large shear stresses at depth a consistent observation is that every major lithological unit tested exhibits positive and negative values of friction velocity dependence critical nucleation patch lengths estimated using representative values of the friction velocity dependent parameter a b and the critical slip distance d c combined with previously documented elastic properties of the wall rock may be as low as 3 m this small value consistent with a seismic moment m o 4 1010 for an m w 1 earthquake suggests that events of this size or larger are expected to occur as ordinary earthquakes and that slow or transient slip events are unlikely in the approximate depth range of 3 7 km

new on fault evidence for a great earthquake in a d 1717 central alpine fault new zealand the dextral reverse alpine fault is the major onshore plate boundary structure between the australian and pacific plates in new zealand no previous study of the central portion of the 200 km long central segment has provided on fault evidence for the most recent event mre using lidar light detection and ranging data coupled with field mapping we recognized the main trace of the alpine fault north of gaunt creek south island as a north striking fault scarp we enhanced a natural exposure that revealed evidence for repeated late holocene thrust fault movement the north northwest striking fault zone is characterized by a distinct 5 50 cm thick clay fault gouge layer juxtaposing hanging wall bedrock mylonites and cataclasites over unconsolidated late holocene footwall colluvium the bedrock is cut by a strath terrace and overlain by mid holocene ca 5400 calibrated 14 c yr b p alluvial terrace which has been faulted repeatedly and is conformably overlain by undeformed late holocene colluvium and alluvium an unfaulted peat at the base of the scarp is buried by post mre alluvium and yields a calibrated 2 radiocarbon age of a d 1710 1930 which dates the mre as post 1709 our data are consistent with sparse on fault data and validate earlier off fault records that suggest an a d 1717 mre the 1717 event had a moment magnitude of m w 8 1 0 1 based on the 380 km long surface rupture because the fault has not ruptured for 300 yr it is likely approaching the end of its seismic cycle and poses a significant seismic hazard to new zealand

frictional properties and slip stability of active faults within carbonate evaporite sequences the role of dolomite and anhydrite seismological observations show that many destructive earthquakes nucleate within or propagate through thick sequences of carbonates and evaporites for example along the apennines range italy carbonate and evaporite sequences are present at hypocentral depths for recent major earthquakes 5 0 mw 6 3 however little is known about the frictional properties of these rocks which are dominated by dolomite and anhydrite and differ from typical quartzofeldspathic rocks here we report on laboratory experiments designed to illuminate friction constitutive properties and associated microstructures of anhydrite and dolomite fault rocks we performed frictional sliding experiments on powdered samples for a range of normal stresses n from 10 to 150 mpa and sliding velocities from 1 to 300 m s experiments employed the double direct shear configuration and were conducted both dry at room temperature and water saturated at 75 c under true triaxial stresses at 25 c sliding friction is 0 65 for all samples and conditions studied at 75 c samples develop cohesive strength and sliding friction ranges from 0 4 to 0 5 for n from 10 to 35 mpa velocity step tests were used to assess rate state frictional behavior at 25 c the slip behavior is velocity strengthening neutral for all samples microstructural observations indicate localized deformation on r1 riedel and incipient y shear planes with marked grain size reduction at 75 c and larger strain we find that rate state friction behavior correlates with velocity dependent layer dilation and compaction and this is associated with the development of through going y shear planes we conclude that elevated temperature strain and the presence of pore fluids enhance shear localization into continuous y shear planes which could promote frictional instability at seismogenic depth within dolomite anhydrite sequences

the effects of sliding velocity on the frictional and physical properties of heated fault gouge the frictional properties of a crushed granite gouge and of gouges rich in montmorillonite illite and serpentine minerals have been investigated at temperatures as high as 600 c confining pressures as high as 2 5 kbar a pore pressure of 30 bar and sliding velocities of 4 8 and 4 8 10 2 m sec the gouges showed nearly identical strength behaviors at the two sliding velocities all four gouges however showed a greater tendency to stick slip movement and somewhat higher stress drops in the experiments at 4 8 10 2 m sec varying the sliding velocity also had an effect on the mineral assemblages and deformation textures developed in the heated gouges the principal mineralogical difference was that at 400 c and 1 kbar confining pressure a serpentine breakdown reaction occurred in the experiments at 4 8 10 2 m sec but not in those at 4 8 m sec the textures developed in the gouge layers were in part functions of the gouge type and the temperature but changes in the sliding velocity affected among other features the degree of mineral deformation and the orientation of some fractures

erosional control on the structural evolution of a transpressional thrust complex on the alpine fault new zealand abstract the waikukupa thrust is a 4 km long oblique thrust segment of the new zealand alpine fault that has developed over the last 65 000 years emplacing mylonite and cataclasite over fluvioglacial gravel during the last 20 000 years or so a 2 km long out of sequence imbricate the hare mare thrust has formed on the east side of the waikukupa river valley the average rate of slip on the two thrusts is estimated at 22 30 mm year analysis of the fault structure in terms of critical wedge theory is consistent with imbrication resulting from a reduction in wedge taper below the critical value due to rapid river erosion the internal structure of the waikukupa thrust sheet consists of reverse faults and angular folds forming duplex like systems associated with minor strike slip faults within the limits of uncertainty the structures are consistent with strain accumulating during internal transpressional shear of the thrust sheet while the taper of the latter was subcritical prior to the transfer of fault displacement to the hare mare imbricate the thrust complex forms part of a serrated range front fault system consisting of oblique thrust sections linked by strike slip faults we introduce the term serial partitioning for this type of partitioned transpressional fault system its development is linked to the erosional processes at the range front an alternative system consisting of parallel thrust and strike slip faults we here term parallel partitioning while angle of obliquity is an important parameter in determining which partitioning model develops we suggest that erosion rate is also an influential factor

compositional and fluid pressure controls on the state of stress on the nankai subduction thrust a weak plate boundary abstract we show that both fault mineralogy and regional excess fluid pressure contribute to low resolved shear stresses on the nankai subduction plate boundary off southwest japan ring and direct shear tests indicate that saturated clay minerals in the fault possess intrinsically low residual friction coefficients r at stress levels between 1 0 and 40 mpa the direct shear r values for purified smectite are 0 14 0 02 for illite 0 25 0 01 and for chlorite 0 26 0 02 for point load velocities of 0 0001 mm s these clay minerals dominate the nankai subduction decollement zone illite plus quartz is mechanically important in the altered incoming muroto section and the predicted decollement r should lie between 0 2 and 0 32 this low residual strength together with elevated fluid pressure limits shear stresses to below 4 mpa within the frontal 50 km of the subduction system consistent with the low wedge taper in this region a higher wedge taper off the ashizuri peninsula indicates basal shear stresses rise slightly along strike towards this region our analysis indicates lower fluid pressures must predominantly be responsible because only small second order along strike variations in r are predicted to occur as a result of variations in smectite and total clay content these variations should be further reduced at depth under the wedge as smectite is diagenetically altered to illite however our data suggest the low r values of the clay rich decollement still limit shear stresses to between 17 and 29 mpa within the frontal 50 km of the wedge consistent with other estimates of plate boundary weakness indeed we propose that it should be expected that subduction plate boundaries like nankai will be weak because of the intrinsic presence of clay rich faults and moderate fluid overpressures our data do not support the hypothesis that the smectite to illite reaction directly controls the onset of seismogenic behavior deep in the nankai system because there is already a mechanical dominance of illite rather than smectite in the shallow decollement zone and we find all the clay phases tend to velocity strengthen however temperature activated clay diagenesis and dehydration may cause secondary changes in the fault properties and state of stress across the up dip limit of the seismogenic zone

new constraints on megathrust slip stability under subduction zone p t conditions abstract to understand and model subduction zone seismogenesis data are needed on the frictional properties of meta pelitic subduction zone materials under in situ megathrust conditions here we report the results of rotary shear friction experiments on simulated illite quartz fault gouge at an effective normal stress of 170 mpa a pore fluid pressure of 100 mpa at 150 500 c and sliding velocities of 1 100 m s the results show three temperature dependent regimes characterized by velocity strengthening at 150 250 c velocity weakening at 250 400 c and velocity strengthening at 400 500 c the regimes are defined by a decrease in the rate and state friction rsf parameter a b at 150 300 c followed by an increase at 300 500 c these trends correlate with systematic changes in other rsf parameters as well as an increase in friction coefficient above 300 c we explain the effects of increasing temperature in terms of a transition from frictional granular flow 150 250 c through granular flow whereby dilatation is balanced by thermally activated compaction involving stress corrosion cracking scc of quartz clasts 250 400 c to non dilatant slip on the phyllosilicates with accommodation at quartz clasts by scc 400 500 c taking into account the effects of sliding velocity the observed velocity weakening regime broadly explains the extent of the seismogenic zone within subduction megathrusts

effects of temperature on the frictional behavior of material from the alpine fault zone new zealand abstract temperature is widely believed to act as a primary control on fault rheology and therefore on the distribution of seismicity along plate boundary faults however there are few detailed measurements of the frictional strength and stability of natural fault gouges at elevated temperatures here we report on a suite of shearing experiments designed to investigate the frictional behavior of fault rocks sampled from depths of 111 5 142 9 m along the alpine fault in new zealand obtained by the international continental scientific drilling program icdp deep fault drilling project dfdp we tested five samples from the dfdp 1b pilot hole two hanging wall chloritic cataclasites two footwall granitic cataclasites and a fault gouge from the principal slip zone psz 1 each sample was sheared at a range of temperatures from 23 to 500 c and at an effective normal stress of 80 mpa the wall rock cataclasites exhibit an increase in the friction coefficient with temperature from 0 45 0 64 at 23 c to 0 87 at 500 c the psz 1 gouge exhibits lower friction coefficient values than the wall rock at temperatures 180 c 0 35 0 46 vs 0 45 0 65 but comparable values 0 87 0 90 at 500 c the variation in frictional strength is accompanied by a transition from velocity strengthening to velocity weakening behavior at temperatures 180 c for all materials extrapolation of the experimentally defined rheological critical stiffness of the fault material and the estimated in situ stiffness of the surrounding crust suggests upper and lower stability boundaries at 1 8 2 5 km and 8 5 8 8 km depth respectively the upper stability boundary is also consistent with the observed depth frequency distribution of earthquakes

balancing the plate motion budget in the south island new zealand using gps geological and seismological data summary the landmass of new zealand exists as a consequence of transpressional collision between the australian and pacific plates providing an excellent opportunity to quantify the kinematics of deformation at this type of tectonic boundary we interpret gps geological and seismological data describing the active deformation in the south island new zealand by using an elastic rotating block approach that automatically balances the pacific australia relative plate motion budget the data in new zealand are fit to within uncertainty when inverted simultaneously for angular velocities of rotating tectonic blocks and the degree of coupling on faults bounding the blocks we find that most of the plate motion budget has been accounted for in previous geological studies although we suggest that the porter s pass amberley fault zone in north canterbury and a zone of faults in the foothills of the southern alps may have slip rates about twice that of the geological estimates up to 5 mm yr 1 of active deformation on faults distributed within the southern alps 100 km to the east of the alpine fault is possible the role of tectonic block rotations in partitioning plate boundary deformation is less pronounced in the south island compared to the north island vertical axis rotation rates of tectonic blocks in the south island are similar to that of the pacific plate suggesting that edge forces dominate the block kinematics there the southward migrating chatham rise exerts a major influence on the evolution of the new zealand plate boundary we discuss a model for the development of the marlborough fault system and hikurangi subduction zone in the context of this migration

thermal regime in the central alpine fault zone new zealand constraints from microstructures biotite chemistry and fluid inclusion data abstract the thermal state within plate boundary fault zones is likely to influence the dimensions of large co seismic fault ruptures and strain localisation in underlying mylonitic shear zones vein microstructures biotite chemistry and fluid inclusion data offer new insights into the thermal structure of the mylonitic shear zone down dip of the alpine fault the main pacific australian plate boundary structure through southern new zealand quartz veins within the fault rocks were formed and deformed at temperatures ranging from 500 c to immediately above that of the brittle viscous transition 325 c illustrating that fluids are present throughout the fault zone microthermometric data from primary mixed co 2 h 2 o fluid inclusions in boudin neck quartz carbonate veins indicate that these inclusions were trapped at temperatures of 325 15 c and pressures of c 40 mpa vein microstructures indicate that fluid temperatures were equal to rock temperatures assuming hydrostatic fluid pressure the veins were trapped at depths of 2 o co 2 fluids in the shallower crust of 500 kg m 3 biotite grains in the mylonites are a mixture of porphyroclastic grains with high r ti mg inherited from the parent alpine schist and smaller low r grains that recrystallised during mylonitisation particularly those that are found within syn mylonitic shear bands assuming a simple step function model approximating diffusive equilibration the changes in biotite chemistry indicate t during mylonitic deformation of 340 c according to the ti in biotite thermometer of henry et al 2005 a best fit uplift p t path to existing data and these new results indicate that the uplift path p t gradient of fault zone rocks above the brittle viscous transition is of the order of 40 c km 1 below the brittle viscous transition the uplift path p t gradient is 10 c km 1 the p t profile within the fault rocks is comparable to that in the immediate hanging wall alpine schist indicating there is no peak in the crustal isotherms in the fault hanging wall as was indicated by previous numerical models and analyses that did not consider data from the fault rocks themselves

rate and state frictional and healing behavior of carbonate fault gouge explained using microphysical model classical rate and state friction rsf laws are widely applied in modeling earthquake dynamics but generally using empirically determined parameters with little or no knowledge of or quantitative account for the controlling physical mechanisms here a mechanism based microphysical model is developed for describing the frictional behavior of carbonate fault gouge assuming that the frictional behavior seen in lab experiments is controlled by competing processes of rate strengthening intergranular sliding versus contact creep by pressure solution by solving the controlling equations derived from kinematic and energy entropy balance considerations and employing a microphysical model for rate strengthening grain boundary friction plus standard creep equations for pressure solution we simulate typical lab frictional tests namely velocity stepping and slide hold slide test sequences for velocity histories and environmental conditions employed in previous experiments the modeling results capture all of the main features and trends seen in the experimental results including both steady state and transient aspects of the observed behavior with reasonable quantitative agreement to our knowledge ours is the first mechanism based model that can reproduce rsf like behavior in terms of microstructurally verifiable processes and state variables since it is microphysically based we believe that our modeling approach can provide an improved framework for extrapolating friction data to natural conditions

a focused look at the alpine fault new zealand seismicity focal mechanisms and stress observations the alpine fault is the pacific australian plate boundary in the south island of new zealand this study analyzes 195 earthquakes recorded during the 6 month duration of the southern alps passive seismic experiment sapse in 1995 1996 and two mr 5 0 earthquakes and aftershocks in 1997 which occurred close to the central part of the alpine fault precise earthquake locations are derived by simultaneous inversion for hypocenter parameters a one dimensional velocity model and station corrections together with focal mechanisms calculated using a first motion and amplitude ratio method these results provide a picture of the seismotectonics in the central south island over a 6 month period moment tensor inversions of three earthquakes provide an independent means of comparison to the focal mechanisms derived using the amplitude first motion method to validate our observations over time we compare the sapse seismicity with the seismicity recorded by the new zealand national seismic network nznsn and a local network at lake pukaki east of the southern alps 6 months versus 8 years our study indicates that the alpine fault releases elastic strain seismically from the surface down to 10 12 km depth between milford sound in the south and the hope fault in the north the seismicity rate of the alpine fault is low but comparable to locked sections of the san andreas fault with large earthquakes expected seismicity decreases north of bruce bay at the alpine fault and within a triangular region along the alpine fault located between the hope and porters pass fault zones we interpret this as the result of deformation distributed on the alpine fault and the hope and porters pass fault zones the base of the seismogenic zone is fairly uniform at 12 km 2km over large parts of the south island the high alps region has a shallower base of the seismogenic zone indicating localized elevated temperatures east of the alpine fault most of the study region deforms under a uniform stress field with a maximum principal horizontal shortening direction of 110o 120 o similar to geodetic observations and plate motions this confirms that the region is not undergoing strain partitioning the earthquake data show that the deformation away from the alpine fault is distributed on mainly nne trending thrust faults and strike slip transfer faults with a maximum seismogenic depth of 12km

biomass burning in indonesia and papua new guinea natural and human induced fire events in the fossil record abstract microscopic charcoal preserved in sediments from ten wetlands in the indonesian and papua new guinea region provide a proxy record of regional fire events during the last 20 000 years two periods of high regional charcoal frequency are encountered during the last glacial transition 17 000 9000 years b p and the middle to late holocene 5000 years b p to the present despite the presence of humans in the region throughout the last 20 000 years there is no suggestion that on a regional spatial scale fire frequencies were solely related to changing subsistence patterns of the human population pollen data from these same sites suggest that during times of high charcoal the rate at which vegetation changes represented by the fossil pollen spectra also increases high climate variability may promote a greater community turnover rate and in turn a more fire susceptible forest community rapid climate change and high variability during the last glacial transition and intensification of el nino related climate variability during the middle to late holocene may have been important mechanisms for promoting fire in rainforest environments and maintaining diversity of tropical rain forests

frictional properties of jfast core samples and implications for slow earthquakes at the tohoku subduction zone slow earthquakes occur in the shallow 20 km deep part of the tohoku subduction zone to understand how frictional properties of the plate boundary fault affect the generation of these slow earthquakes we conducted friction experiments using borehole samples retrieved from the plate boundary decollement and footwall during integrated ocean drilling program expedition 343 japan trench fast drilling project jfast the plate boundary fault material exhibits a transition from velocity strengthening to velocity weakening behavior at temperatures between 50 and 150 c which in the framework of rate and state friction laws is a necessary condition for the generation of slow earthquakes whereas the footwall sample mainly shows velocity strengthening behavior except at temperatures of 50 c the downdip temperature limit of slow earthquakes in the japan trench also lies between 100 and 150 c our results suggest that the frictional properties of the plate boundary fault may play a key role in controlling the locations of observed slow earthquakes

a microphysical model for strong velocity weakening in phyllosilicate bearing fault gouges 1 previous rotary shear experiments performed on a halite muscovite fault gouge analogue system have shown that the presence of phyllosilicates under conditions favoring the operation of cataclasis and pressure solution in the matrix phase can have major effects on the frictional behavior of gouges while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behavior the strength of mixtures containing 10 30 muscovite is both normal stress and sliding velocity dependent at high sliding velocities 1 m s 1 such mixtures show unusually marked velocity weakening along with the development of a structureless cataclastic microstructure in the present paper a micromechanical model is developed in an attempt to explain this behavior the model assumes a granular flow process involving competition between intergranular dilatation and compaction by pressure solution the predictions of the model agree favorably with the experimental results extension of the model to quartz mica systems implies that the presence of phyllosilicates plus the operation of pressure solution can strongly promote unstable velocity weakening behavior at rapid slip rates on natural faults under midcrustal conditions static stress drop predictions based on the model agree reasonably well with estimates from seismic observations our results may help explain the discrepancy between laboratory derived rate and state friction parameter values obtained for dry low strain and or single phase rock systems and the values for natural fault rocks inferred from seismological data