tertiary tectonics of the border ranges fault system chugach mountains alaska deformation and uplift in a forearc setting the border ranges fault system brfs locally separates supracrustal upper cretaceous tertiary rocks of the cook inlet matanuska valley forearc basin on the peninsular terrane from metamorphosed cretaceous subduction complex rocks of the chugach terrane to the south this 5 to 10 km wide zone of concentrated deformation along the inboard edge of southern alaska s accretionary prism has suffered a protracted history beginning with its inception as a megathrust by early cretaceous time and continuing into early tertiary time when it was transected by a system of steeply arcward dipping normal and dextral slip faults based on detailed geologic mapping structural analysis metamorphic mineral assemblage data and k ar and fission track geochronology the tertiary history of displacements along a central part of this forearc fault system has been divided into several phases of deformation these include a paleocene phase of regional uplift of the forearc basin together with block faulting along the brfs to rapidly uplift and subaerially expose low grade metamorphic rocks of the subduction complex upper cretaceous valdez group within 15 ma of their inferred underplating at deep structural levels of the accretionary prism continued normal separation faulting along the brfs in late paleocene early eocene time to further uplift the subduction complex was recorded by deposition of a syntectonic alluvial fan system chickaloon formation across the brfs and along the southern margin of the forearc basin a third mid eocene increment of normal separation faulting along the brfs juxtaposed greenschist facies fabrics of early eocene age in the subduction complex against the chickaloon formation this latter uplift event predated intrusion of early late eocene 43 48 ma zircon fission track minimum ages felsic dikes into the present terrane bounding fault and was accompanied by no more than a few tens of kilometers of dextral slip faulting along the brfs a conclusion that does not accord with recent suggestions for thousands of kilometers of displacement along that fault system in early middle tertiary time based on paleomagnetic data field observations in the study area indicate that the great oroclinal bend of southern alaska is postearly eocene and possibly prelate oligocene in age a final period of deformation in middle to late tertiary time was marked by periods of minor north south contraction of the forearc basin and by local reverse slip reactivation of earlier faults fission track age data on apatite indicate rapid cooling and probably uplift of both subduction complex and adjacent parts of the forearc basin in miocene time 17 24 ma episodic uplift of the subduction complex either locally by normal separation faulting along its backstop or by a more regional uplift also affecting the adjacent forearc basin overlapped in time or closely followed discrete pulses of large scale sediment underplating along the gulf of alaska subduction margin this coincidence suggests that major pulses of sediment underplating along southern alaska s convergent margin may have led to isostatic uplift of its critical taper accretionary prism an uplift that was in part accommodated by normal separation faulting along its mechanical backstop

assessment of teleseismically determined source parameters for the april 25 2015 mw 7 9 gorkha nepal earthquake and the may 12 2015 mw 7 2 aftershock on april 25 2015 a major m w 7 9 thrust earthquake ruptured the deeper portion of the seismogenic plate boundary beneath nepal along which india is underthrusting eurasia an m w 7 2 aftershock on may 12 2015 extended the eastern down dip edge of the rupture these destructive events caused about 9000 fatalities and 23 000 injuries the overall rupture zone is about 170 km long and 40 80 km wide this region of the plate boundary previously experienced a large earthquake in 1833 and in 1934 a larger m s 8 0 event located to the east ruptured all the way to the surface the main himalayan thrust mht on which slip occurred in 2015 has a very low dip angle of 6 and the depth of the mainshock slip distribution is very shallow extending from 7 to 18 km the shallow dip and depth present challenges for resolving faulting characteristics using teleseismic data we analyze global teleseismic signals for the mainshock and aftershock to estimate source parameters evaluating the stability of various procedures used for remotely characterizing kinematics of such shallow faulting back projection and finite fault slip inversion are used to assess the spatio temporal rupture history and evidence for frequency dependent radiation along dip slip zone width constraints from near field geodetic observations are imposed on the preferred models to overcome some limitations of purely teleseismic methods radiated energy stress drop and moment rate functions are determined for both events

detailed rupture imaging of the 25 april 2015 nepal earthquake using teleseismic p waves we analyze the rupture process of the 25 april 2015 nepal earthquake with globally recorded teleseismic p waves the rupture propagated east southeast from the hypocenter for about 160 km with a duration of 55 s backprojection of both high frequency hf 0 2 to 3 hz and low frequency lf 0 05 to 0 2 hz p waves suggest a multistage rupture process from the low frequency images we resolve an initial slow downdip northward rupture near the nucleation area for the first 20 s stage 1 followed by two faster updip ruptures 20 to 40 s for stage 2 and 40 to 55 s for stage 3 which released most of the radiated energy northeast of kathmandu the centroid rupture power from lf backprojection agrees well with the global centroid moment tensor solution the spatial resolution of the backprojection images is validated by applying similar analysis to nearby aftershocks the overall rupture pattern agrees well with the aftershock distribution a multiple asperity model could explain the observed multistage rupture and aftershock distribution

three dimensional dynamic simulation of the 1992 landers earthquake the 1992 landers california earthquake magnitude 7 3 was modeled as the propagation of a spontaneous rupture controlled by a realistic prestress distribution with the use of a three dimensional finite difference method the dynamic rupture reproduces the general slip pattern used to compute the initial stress distribution and generates near fault ground motions at the surface similar to observations the simulated rupture propagates on the fault along a complex path with highly variable speed and rise time changing the magnitude and pattern of the stress significantly the method provides the framework to estimate earthquake rupture parameters from recorded seismic and geodetic data

a self consistent mechanism for slow dynamic deformation and tsunami generation for earthquakes in the shallow subduction zone 1 dynamic pore pressure changes in the overriding wedge above a shallow dipping plate interface significantly affect the rupture dynamics of shallow subduction zone earthquakes and their tsunamigenesis for a wedge on the verge of coulomb failure everywhere including the basal fault the dynamic pore pressure increase due to up dip rupture propagation leads to widespread yielding within the wedge which is greatly enhanced by the shallow dip of the fault the widespread yielding reduces the stress drop slip velocity slip and rupture velocity giving rise to prolonged rupture duration thus explaining many anomalous features of shallow subduction zone earthquakes significant inelastic seafloor uplift occurs in the case of a shallow fault dip with the largest uplift located landward from the trench integrating this physical mechanism with existing seismic geodetic and tsunami observations can provide new insights into earthquake dynamics and deformation processes in shallow subduction zones

dynamic modeling of the 2004 mw 6 0 parkfield california earthquake 1 we present two spontaneous rupture models of the 2004 mw 6 0 parkfield earthquake constrained by near source ground motions we start with a stress drop distribution calculated from a kinematic slip distribution using a linear slip weakening friction law we utilize trial and error to obtain both the stress conditions and frictional parameters on the fault that produce synthetics consistent with records the material contrast across the san andreas fault is incorporated using different one dimensional velocity structures on each side of the fault an approximately constant s parameter of 0 3 and a uniform slip weakening distance of 0 15 m are used in the dynamic models in our preferred dynamic model consistent with the ground motion and gps the slip is bounded by seismicity streaks at 5 and 10 km depths confirming a locked zone at depth the stress drop is approximately 10 mpa in the hypocentral region and about 2 mpa elsewhere the material contrast across the fault causes significant normal stress variations 1 mpa leading to a larger strength drop to the southeast than to the northwest the main rupture front propagates at nearly a constant subshear rupture velocity 3 km s in both directions the total radiated energy determined from the preferred dynamic model is 1 1 1013 j seismic moment is 1 0 1018 nm and fracture energy is 3 0 1013 j the limited number of aftershocks in the slipped area suggests the important role of stress on the distribution of seismicity in the locked zone

ubiquitous weakening of faults due to thermal pressurization faults weaken during earthquakes analysis of the amount of energy released during earthquakes globally suggests that heat induced pressurization of pore fluids can weaken faults during earthquakes of all sizes laboratory simulations of earthquakes show that at high slip rates faults can weaken significantly aiding rupture1 2 3 various mechanisms such as thermal pressurization and flash heating have been proposed to cause this weakening during laboratory experiments1 4 5 6 yet the processes that aid fault slip in nature remain unknown measurements of seismic radiation during an earthquake can be used to estimate the frictional work associated with fault weakening known as an event s fracture energy7 8 9 here we compile new and existing8 9 measurements of fracture energy for earthquakes globally that vary in size from borehole microseismicity to great earthquakes we observe a distinct transition in how fracture energy scales with event size which implies that faults weaken differently during small and large earthquakes and earthquakes are not self similar we use an elastodynamic numerical model of earthquake rupture to explore possible mechanisms we find that thermal pressurization of pore fluid by the rapid shear heating of fault gouge can account for the observed scaling of fracture energy in small and large earthquakes over seven orders of fault slip magnitude we conclude that thermal pressurization is a widespread and prominent process for fault weakening

linked 3 d modelling of megathrust earthquake tsunami events from subduction to tsunami run up e h m t u and a a g acknowledge additional support by the german research foundation dfg projects no ga 2465 2 1 ga 2465 3 1 by bacatec project no a4 and baylat by konwihr the bavarian competence network for technical and scientific high performance computing project newwave by kaust crg gast grant no ors 2016 crg5 3027 and fragen grant no ors 2017 crg6 3389 02 by the european union s horizon 2020 research and innovation program exahype grant no 671698 cheese grant no 823844 and tear grant no 852992

geological manifestations of ridge collision evidence from the golfo de penas taitao basin southern chile recent geological and geophysical studies in the southern andes adjacent to the intersection of the chile rise with the peru chile trench ant naz sam triple junction have revealed a number of features and a neogene geologic history that are unique along the pacific margin of south america this history includes 1 development of a tertiary quaternary marine basin with up to 3 km of sediment infill golfo de penas taitao basin gtb 2 disruption of the region by a series of faults with both normal and strike slip movements and 3 localization of silicic near trench volcanism and epizonal plutonism and related hydrothermal activity the northern portion of the gtb began to subside in the late miocene possibly earlier and has subsequently been deformed uplifted and exposed gravity and seismic reflection data suggest that the basin continues offshore where it is still actively subsiding today golfo de penas subsidence and uplift have thus occurred diachronously in the region although it is unclear when subsidence began in the golfo de penas tectonic disruption of the region is likely related to the liquine ofqui fault lof a major ns trending crustal shear zone that curves westward and terminates in the golfo de penas the lof has both down to the west and right lateral offset and separates the main andean cordillera on the east from a large crustal block the chiloe block on the west we hypothesize that the gtb has developed as a pull apart basin in response to northward movement of the chiloe block along the lof we propose a dynamic model whereby a stress gradient that decreases longitudinally away from the chile rise peru chile trench intersection is set up because the youngest most buoyant oceanic lithosphere is being subducted at the triple junction the chile rise is viewed as a type of indenter which is acting to drive the chiloe block northward in front of the northward migrating triple junction this model explains the unique set of geologic features found in the region and suggests that ridge trench interactions may be an important factor in orogenesis at active continental margins

depth varying rupture properties during the 2015 mw 7 8 gorkha nepal earthquake on april 25th 2015 the mw 7 8 gorkha nepal earthquake ruptured a portion of the main himalayan thrust underlying kathmandu and surrounding regions we develop kinematic slip models of the gorkha earthquake using both a regularized multi time window mtw approach and an unsmoothed bayesian formulation constrained by static and high rate gps observations synthetic aperture radar sar offset images interferometric sar insar and teleseismic body wave records these models indicate that kathmandu is located near the updip limit of fault slip and approximately 20 km south of the centroid of fault slip fault slip propagated unilaterally along strike in an ese direction for approximately 140 km with a 60 km cross strike extent the deeper portions of the fault are characterized by a larger ratio of high frequency 0 03 0 2 hz to low frequency slip than the shallower portions from both the mtw and bayesian results we can resolve depth variations in slip characteristics with higher slip roughness higher rupture velocity longer rise time and higher complexity of subfault source time functions in the deeper extents of the rupture the depth varying nature of rupture characteristics suggests that the up dip portions are characterized by relatively continuous rupture while the down dip portions may be better characterized by a cascaded rupture the rupture behavior and the tectonic setting indicate that the earthquake may have ruptured both fully seismically locked and a deeper transitional portions of the collision interface analogous to what has been seen in major subduction zone earthquakes

the mechanism of partial rupture of a locked megathrust the role of fault morphology assessment of seismic hazard relies on estimates of how large an area of a tectonic fault could potentially rupture in a single earthquake vital information for these forecasts includes which areas of a fault are locked and how the fault is segmented much research has focused on exploring downdip limits to fault rupture from chemical and thermal boundaries and along strike barriers from subducted structural features yet we regularly see only partial rupture of fully locked fault patches that could have ruptured as a whole in a larger earthquake here we draw insight into this conundrum from the 25 april 2015 m w 7 8 gorkha nepal earthquake we invert geodetic data with a structural model of the main himalayan thrust in the region of kathmandu nepal showing that this event was generated by rupture of a decollement bounded on all sides by more steeply dipping ramps the morphological bounds explain why the event ruptured only a small piece of a large fully locked seismic gap we then use dynamic earthquake cycle modeling on the same fault geometry to reveal that such events are predicted by the physics depending on the earthquake history and the details of rupture dynamics however great earthquakes that rupture the entire seismogenic zone are also possible these insights from nepal should be applicable to understanding bounds on earthquake size on megathrusts worldwide

miocene magnesian andesites and dacites evia greece adakites associated with subducting slab detachment and extension abstract mid miocene volcanic rocks are rare in the aegean region although early miocene and late miocene quaternary volcanism is widespread at oxylithos island of evia 14 ma dacites form a dome or sub volcanic complex phreatomagmatic eruptions formed nearby rhyolitic pyroclastic surge deposits the calc alkaline dacites contain bronzite mg rich clinopyroxene phlogopite and plagioclase phenocrysts the magma results from mixing of a mg rich andesitic magma similar to that in the nearby island of skyros with more felsic magmas represented by the rhyolitic pyroclastics the dacites are geochemically similar to adakites which are derived by partial melting of eclogitic subducted oceanic crust and have low y and yb and high sr y ratio 87 sr 86 sr 0 7095 is found in both dacite and rhyolite lead isotopic composition from the high mg andesite from skyros with 207 pb 204 pb 15 70 and 208 pb 204 pb 38 90 forms a linear trend with evia dacite and rhyolite with 207 pb 204 pb 15 71 and 208 pb 204 pb 39 05 the high temperatures required to produce such magma resulted from decompression due to extension of the aegean basin at the same time as the initial intrusion of the detached subducted slab in the western aegean that has been imaged by seismic tomography the oxylithos rocks extend the known occurrences of adakite series rocks this series is not restricted to sites with subduction of young oceanic crust

slip weakening distance and energy budget inferred from near fault ground deformation during the 2016 mw7 8 kaikōura earthquake the 2016 m7 8 kaik ura new zealand earthquake struck the east coast of the northern south island resulting in strong ground shaking and large surface fault slip since the earthquake was well recorded by a local strong motion seismic network near fault data may provide direct measurements of dynamic parameters associated with the fault weakening process here we estimate a proxy for slip weakening distance dc defined as double the fault parallel displacement at the time of peak ground velocity from accelerograms recorded at a near fault station three component ground displacements were recovered from the double numerical integration of accelerograms and the corresponding final displacements are validated against coseismic displacement from geodetic data the estimated dc is 4 9 m at seismic station keks located 2 7 km from a segment of the kekerengu fault where large surface fault slip 12 m has been observed the inferred dc is the largest value ever estimated from near fault strong motion data yet it appears to follow the scaling of dc with final slip for several large strike slip earthquakes the energy budget of the m7 8 kaik ura earthquake inferred from the scaling of dc with final slip indicates that a large amount of energy was dissipated by on and off fault inelastic deformation during the propagation of the earthquake rupture resulting in a slower average rupture speed 2 0 km s

slip weakening distance estimated at near fault stations we estimated the slip weakening distance from the seismograms recorded at near fault stations considering the effect of spatio temporal filtering for a continuous propagation of rupture this effect is usually observed at some distance away from the fault we used a green s function for 2 d anti plane rupture propagating with constant rupture velocity and instantaneous slip at the crack tip as a source time function we used a regularized yoffe function which is a kinematically good approximation of dynamic slip weakening behavior by convolving these functions near fault waveforms are computed as a proxy of slip weakening distance d c we used d c which is defined as a slip at the time of peak slip velocity then d c values can be computed as a function of the distance from the fault this procedure is applied to the observation of the 2000 western tottori japan earthquake m w 6 6 as well as the 2002 denali alaska earthquake m w 7 9 we estimated d at about 0 3 m at gsh station 100 m away from the fault for the tottori earthquake and that at about 2 5 m at ps10 station 3 km away from the fault for the denali earthquake we confirmed that both estimates are not affected by the spatio temporal smoothing

effects of seismogenic width and low velocity zones on estimating slip weakening distance from near fault ground deformation fault weakening process controls earthquake rupture propagation and is of great significance to impact the final earthquake size and seismic hazard critical slip weakening distance dc is one of

integrated seismic source model of the 2015 gorkha nepal earthquake we compared spatiotemporal slip rate and high frequency around 1 hz radiation distributions from teleseismic p wave data to infer the seismic rupture process of the 2015 gorkha nepal earthquake for these estimates we applied a novel waveform inversion formulation that mitigates the effect of green s functions uncertainty and a hybrid backprojection method that mitigates contamination by depth phases our model showed that the dynamic rupture front propagated eastward from the hypocenter at 3 0 km s and triggered a large slip event centered about 50 km to the east it also showed that the large slip event included a rapid rupture acceleration event and an irregular deceleration of rupture propagation before the rupture termination heterogeneity of the stress drop or fracture energy in the eastern part of the rupture area where aftershock activity was high inhibited rupture growth high frequency radiation sources tended to be in the deeper part of the large slip area which suggests that heterogeneity of the stress drop or fracture energy there may have contributed to the damage in and around kathmandu

rupture processes of the 2015 mw 7 9 gorkha earthquake and its mw 7 3 aftershock and their implications on the seismic risk abstract the rupture processes of the 2015 april 25 gorkha earthquake and its strongest aftershock occurred on may 12 in nepal are investigated by joint inversion of seismological and geodetic data synthetic test shows that the sedimentary layers in the source region play an important role in the rupture process inversion our optimized model of the mainshock shows that the rupture has a unilateral propagation pattern the dominant mechanism is pure thrust with maximum slip of 5 8 m the rupture scale extends 60 km along dip and 150 km along strike and the largest static stress change is 7 6 mpa the total seismic moment is 7 87 1020 n m equivalent to mw 7 9 most seismic moment was released within 80 s and the majority seismic moment was released at the first 40 s the rupture propagated in main slip asperity with a velocity of 3 0 km s the strong aftershock magnitude is about mw 7 3 and the peak slip is about 5 0 m close to the peak slip of the mainshock moreover the slips of the mainshock and the aftershocks are in good complementary suggesting a triggering relationship between them considering the strain accumulation the gorkha earthquake ruptured only part of the seismic gap alone thus still poses high earthquake risk especially in the west side of the mainshock rupture zone

rupture dynamics with energy loss outside the slip zone 1 energy loss in a fault damage zone outside the slip zone contributes to the fracture energy that determines rupture velocity of an earthquake a nonelastic two dimensional dynamic calculation is done in which the slip zone is modeled as a fault plane and material off the fault is subject to a coulomb yield condition in a mode 2 crack like solution in which an abrupt uniform drop of shear traction on the fault spreads from a point coulomb yielding occurs on the extensional side of the fault plastic strain is distributed with uniform magnitude along the fault and it has a thickness normal to the fault proportional to propagation distance energy loss off the fault is also proportional to propagation distance and it can become much larger than energy loss on the fault specified by the fault constitutive relation the slip velocity function could be produced in an equivalent elastic problem by a slip weakening friction law with breakdown slip dc increasing with distance fracture energy g and equivalent dc will be different in ruptures with different initiation points and stress drops so they are not constitutive properties they are determined by the dynamic solution that arrives at a particular point peak slip velocity is however a property of a fault location nonelastic response can be mimicked by imposing a limit on slip velocity on a fault in an elastic medium

seismic structures of the calico fault zone inferred from local earthquake travel time modelling author posting the authors 2011 this article is posted here by permission of john wiley sons for personal use not for redistribution the definitive version was published in geophysical journal international 186 2011 760 770 doi 10 1111 j 1365 246x 2011 05055 x

earthquake source nucleation as self organization process abstract the theory of an earthquake source nucleation is discussed based on the assumption that self organization of damage process takes place in the zone of an earthquake source nucleation the theory incorporates the damage rheology framework of lyakhovsky et al and the approach of phenomenology theory of second order phase transition namely the free energy governing the process of an earthquake source nucleation depends on two collective variables and in addition to the strain tensor eij the variable quantifies the fracture of the medium and the variable quantifies the interaction effect of cracks the region s is associated with a potential source of an earthquake if the damage variable exceeds the critical value cr 1 inside s the important feature of a potential source is that interaction of fractures causes acceleration of damage process inside the region of potential source and the material should lose stability primarily in this region interaction of fractures results also in occurrence of a residual stress caused by nonuniformity of fracture density the appearance and development of the potential source result in increase of intensity of damage process not only in the region of potential source but also in a certain neighborhood of the last it is compatible with such observed effects as acceleration of seismic energy release and growth of correlation length of weak seismicity before large earthquake transition of potential source to the stage of avalanche unstable fracturing is associated with instability generated by explosive increase of interaction of fractures when the damage variable exceeds the second critical value cr 2 inside s

dynamic rupture simulations with heterogeneous initial stresses inversed from a given slip distribution a case study of the 2017 mw 6 5 jiuzhaigou earthquake abstract heterogeneous initial stresses are extremely important in understanding the physics of earthquake rupture processes we propose a method to estimate heterogeneous initial stresses by comparing the slip from dynamic rupture simulations and the input joint inversion result and apply it to the 2017 mw 6 5 jiuzhaigou earthquake which occurred in the intersection area of the minjiang tazang and huya faults in sichuan province china with the slip distributed on two distinct left lateral strike slip faults as shown in previous geodetic and seismic joint inversion we use the seismic efficiency empirical relation to infer the average stress and the average stress drop is estimated using the static stress drop with the angle of the maximum principal stress and the nucleation fault determined from the relocated aftershocks different principal stresses are calculated with different combinations of average stress and average stress drop the initial normal and residual stresses can be determined using the projection of the principal stresses the initial shear stresses are generated by adding the residual stress and the heterogeneous stress drop which is generated by a set of gaussian random numbers with a given mean and the variance and mapped one by one with the given slip on the fault so that the area with a large slip has a large stress drop by comparing the slip from dynamic rupture simulations and the input joint inversion result we show that the case with a 36 mpa average stress and 2 1 mpa average stress drop provides the best fitting slip snapshots the dynamic coulomb stress change shows that the 2017 mw 6 5 jiuzhaigou earthquake could bring the southeast of the tazang fault and the middle of the minjiang fault closer to failure this work provides a new insight to understand the initial stresses of nature earthquakes

paleogene metamorphism of an accretionary flysch terrane eastern gulf of alaska reconnaissance field studies have identified a regional metamorphic complex at least 200 km long and 25 to 50 km wide in the eastern chugach mountains southern alaska the metamorphic complex was developed within the cretaceous valdez group a flysch sequence that was accreted to the continental margin during the late cretaceous or early tertiary the metamorphic complex shows the progressive development from subgreenschist and green schist facies slate phyllite and semischist that is regionally characteristic of the valdez group to biotite plagioclase quartz schist muscovite cordierite andalusite staurolite garnet and sillimanite in an intermediate zone and amphibolite facies muscovite biotite plagioclase quartz schist and gneiss sillimanite and garnet in a higher grade central zone k feldspar is characteristically absent in the amphibolite facies schists but it is present in migmatitic rocks that are common to the central zone the mineral assemblages and petrographic relations indicate that metamorphism took place under low pressure intermediate facies series conditions partial melting took place at the highest grade of metamorphism melting produced granodioritic magmas in migma titic rocks of the central zone that were emplaced as discrete plutons in both the intermediate zone and peripheral rocks of the complex the timing of metamorphism as indicated by field relations and k ar data is about 50 to 65 m y ago and overlaps or is coeval with the emplacement throughout the gulf of alaska region of early tertiary plutons that are thought to be anatectic in origin the distribution of these plutons suggests that a high temperature low pressure metamorphic belt about 1 800 km long developed along the leading edge of the continental margin in late paleocene to early eocene time

evidence in cerro pampa volcanic rocks for slab melting prior to ridge trench collision in southern south america late miocene approx 12 ma hornblende bearing andesitic to dacitic documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage wasysym pagestyle empty declaremathsizes 10 9 7 6 begin document mathrm 63 to 68 sio 2 1 2 to 1 9 k 2 o end document adakite flows at the small cerro pampa center in patagonia 47 55 s 71 25 have some of the clearest slab melt geochemical signatures yet seen in a phanerozoic center on continental crust these magmas formed in response to melting of the hot thin slab that was subducting beneath south america prior to the collision of the chile rise at approx 6 ma or at approx 10 ma their n morb like 87 sr 86 sr 0 70285 0 70309 and low 206 pb 204 pb 18 44 18 59 ratios show that they could have been generated by

correlation length as an indicator of critical point behavior prior to a large earthquake abstract a large earthquake preparation is often manifested in correlation of seismicity in an area whose characteristic dimension greatly exceeds a dimension of source of main shock zoller et al g zoller s hainzl j kurths observation of growing correlation length as an indicator for critical point behavior prior to large earthquakes j geophys res 106 2001 2167 2176 show the growth of correlation length of earthquakes prior to nine large earthquakes in california according to a power low we argue that the algorithm of correlation length estimation proposed by zoller et al g zoller s hainzl j kurths observation of growing correlation length as an indicator for critical point behavior prior to large earthquakes j geophys res 106 2001 2167 2176 can result in a decrease of correlation length preceding its precursory growth before large earthquakes if the area in which earthquake activity is correlated grows with time during a main shock preparation the correlation length analysis of acoustic emission events recorded in laboratory experiments on destruction of rocks and correlation length analysis of intermediate magnitude earthquakes in the area of large earthquakes preparation on kamchatka and in italy confirms the theoretical argument this effect can be considered as an additional premonitory pattern of large earthquake preparation

dynamics of the 2015 m7 8 nepal earthquake the 2015 m7 8 nepal earthquake ruptured part of the main himalayan thrust beneath kathmandu to study the dynamics of this event we compute p wave spectra of the main shock and of two large aftershocks to estimate stress drop and radiated energy we find that surface reflections depth phases of these shallow earthquakes produce interference that severely biases spectral measurements unless corrections are applied measures of earthquake dynamics for the main shock are within the range of estimates from global and regional earthquakes we explore the azimuthal and temporal variations of radiated energy and highlight unique aspects of the m7 8 rupture the beginning of the earthquake likely experienced a dynamic weakening mechanism immediately followed by an abrupt change in fault geometry correlation of backprojection results with frequency dependent variations in the radiated energy rate and with the suggested geometry of the main himalayan thrust yields new constraints on dynamic ruptures through geometrical barriers

geology and geochemistry of volcanogenic massive sulfide deposits and related igneous rocks prince william sound south central alaska the prince william sound region is located approximately 100 km east southeast of anchorage alaska and contains the geologically diverse late cretaceous to eocene valdez and orca groups which comprise a portion of the accretionary prism complex of south central alaska the rocks host more than 600 known massive sulfide deposits and prospects historically the deposits have been described as epigenetic vein replacement and shear zone hosted ores we define the prince william sound massive sulfide deposits in terms of two genetically related yet geochemically distinct types of deposits both related to submarine volcanism the first type is hosted in submarine pillow basalt massive basalt flows and mafic tuffs and is analogous to cyprus type deposits the second type is hosted in intercalated slate and graywacke and is analogous to besshi type deposits both types are similar morphologically and are characteristically stratiform to strata bound the deposits vary in size from less than 1 million tons to greater than 5 million tons with the majority of the largest deposits forming in sediment dominated besshi type environments the massive sulfide deposits are fe cu zn systems dominated mineralogically by pyrite pyrrhotite chalcopyrite and sphalerite minor phases include cubanite arsenopyrite tetrahedrite and secondary marcasite silicate gangue is comprised predominantly of quartz and chlorite with minor sericite talc and calcite primary sedimentary features preserved within massive sulfide are ubiquitous within the deposits and include planar bedding crossbedding and graded bedding fluid inclusion microthermometry of quartz gangue from the massive sulfide deposits is consistent with hydrothermal fluid temperatures found in genetically related modern seafloor hydrothermal environments minimum trapping temperatures of fluid inclusions in quartz from the stockwork feeder zone of the volcanic hosted deposits generally range from 210 degrees to 260 degrees c fine grained anhedral quartz gangue in massive sulfide layers also contains sparse primary fluid inclusions typically the homogenization temperature is lower in the sediment hosted deposits hydrothermal fluids in the volcanic hosted settings exited the volcanic pile directly into seawater and were rapidly quenched thus fluid inclusions only record high temperature fluid conditions similar hydrothermal fluids in the sediment hosted settings exited the volcanic pile into warm seawater saturated sediments and were cooled more slowly in an environment where lower temperature fluid inclusions were formed and preserved sulfur and oxygen isotope data support a submarine origin for the deposits sulfur isotope values range from delta 34 s gdt 0 8 to 5 9 per mil for volcanic hosted deposits and from 2 7 to 9 2 per mil for sediment hosted deposits the higher values for sediment hosted ores reflect increased amounts of reduced seawater sulfate in the hydrothermal fluid with sulfate reduction occurring in the seawater hydrothermal fluid mixing zone within the sediment pile below the seawater sediment interface oxygen isotope values for quartz gangue associated with massive sulfide also reflect the lower temperature deposition that is characteristic of the sediment hosted deposits delta 18 o quartz 7 0 to 7 8 per mil smow for volcanic hosted deposits and delta 18 o quartz 9 6 to 16 9 per mil for sediment hosted ores whole rock geochemical analyses of the basalts and related igneous rocks from both the valdez and orca groups show that these rocks are consistent with formation in midocean ridge and or seamount environments the geochemistry of the valdez group rocks suggests that sediment contamination of basaltic magma has occurred imparting a primitive arclike signature discrimination diagrams show that the rocks from both groups have normal midocean ridge basalt enriched midocean ridge basalt and low k arc tholeiite affinities and plot along the tholeiitic calc alkaline boundary the fluid inclusion stable isotope and whole rock data collected in this study are all consistent with the hypothesis that the massive sulfide deposits in the prince william sound district are sea floor volcanogenic massive sulfide deposits that formed in both sediment starved and sedimented midocean ridge settings

paleogene history of the kula plate offshore evidence and onshore implications paleocene to middle eocene magnetic anomalies were mapped over oceanic crust that accreted at the kula pacific spreading center and is now obliquely entering the western aleutian trench between 179 e and 168 e the strike of anomalies and the pattern of abyssal hills and fracture zones changed abruptly during 56 55 ma when north south spreading veered to northwest southeast 310 130 kula pacific spreading ceased in 43 ma a 75 km long section of the fossil kula rift axis has avoided subduction although it now intersects the trench axis almost orthogonally near 171 5 e a narrow remnant of the former kula plate northwest of this fossil spreading center is bounded by a fossil kula pacific transform with a high transverse ridge alongside a sediment filled transform valley anomalies on this remnant show that eocene kula pacific spreading was highly asymmetric 2 1 the 56 55 ma change in kula plate rotation inferred from the change in spreading direction coincided with birth of the aleutian subduction zone and was probably a consequence of the resulting change in slab pull stresses on the oceanic lithosphere the change in direction of kula north american motion is a plausible explanation for the detachment of continental terranes from the pacific northwest and their migration around the gulf of alaska and for the early eocene demise of alaska range are volcanism the cessation of kula pacific spreading coincides with a major change in pacific plate rotation and the subsequent direction of convergence of the pacific plate with the aleutian arc was similar to the 55 43 ma direction of kula plate convergence

the geologic history of redoubt volcano alaska abstract redoubt volcano is a composite cone built on continental crust at the northeast end of the aleutian arc magmas erupted at redoubt are medium k calc alkaline basalts andesites and dacites the eruptive history of the volcano can be divided into four parts the early explosive stage early cone building stage late cone building stage and post glacial stage the most silicic products of the volcano were erupted during the early explosive stage about 0 888 ma and include pumiceous pyroclastic flow deposits block and ash flow deposits and a dome or shallow intrusive complex basalt and basaltic andesite lava flows and scoria and ash flows were produced during the early cone building stage which was underway by 0 340 ma during the late cone building stage andesitic lava flows and block and ash flows were emplaced airfall deposits produced during post glacial eruptions are silicic andesite in composition since the early cone building stage magmas have become progressively more silicic but none are as silicic as those in the early explosive stage limited pb and sr isotopic data suggest that redoubt magmas were contaminated by north american continental crust

distributed damage faulting and friction we present a formulation for mechanical modeling of geological processes in the seismogenic crust using damage rheology the seismogenic layer is treated as an elastic medium where distributed damage modifying the elastic stiffness evolves as a function of the deformation history the model damage rheology is based on thermodynamic principles and fundamental observations of rock deformation the theoretical analysis leads to a kinetic equation for damage evolution having two principal coefficients the first is a criterion for the transition between strength degradation and recovering healing and is related to friction the second is a rate coefficient of damage evolution which can have different values or functional forms for positive degradation and negative healing evolution we constrain these coefficients by fitting model predictions to laboratory data including coefficient of friction in sawcut setting intact strength in fracture experiments first yielding in faulting experiments under three dimensional strain onset and evolution of acoustic emission and dynamic instability the model damage rheology accounts for many realistic features of three dimensional deformation fields associated with an earthquake cycle these include aseismic deformation gradual strength degradation development of process zones and branching faults around high damage areas strain localization brittle failure and state dependent friction some properties of the model damage rheology e g cyclic stick slip behavior with possible accompanying creep are illustrated with simplified analytical results the developments of the paper provide an internally consistent framework for simulating long histories of crustal deformation and studying the coupled evolution of regional earthquakes and faults this is done in a follow up work

nonlinear dynamic rupture inversion of the 2000 western tottori japan earthquake 1 we have developed a systematic nonlinear inversion method for estimating rupture propagation and the underlying dynamic parameters for large historical earthquakes the rupture modeling is carried out using a three dimensional finite difference method and the inversion is implemented by a neighbourhood algorithm minimizing the misfit between computed and observed near fault seismograms we test the method by estimating the stress drop within 32 regions on the causative fault for the 2000 magnitude 6 6 western tottori japan earthquake while the dynamic models show both similarities and differences with the conventional kinematic models our method provides an ensemble of physically correct models with plausible rupture propagation for the earthquake

earthquake rupture dependence on hypocentral location along the nicoya peninsula subduction megathrust abstract although interseismic locking distributions have been used in qualitatively evaluating the future earthquake potential quantitatively estimating how an earthquake may rupture through the locked interface is a more useful tool for quantifying both seismic and tsunami hazards here we investigate rupture scenarios from interseismic locking models along the megathrust interface below nicoya peninsula costa rica using spontaneous rupture simulations we first estimate initial stress from locking then initiate spontaneous ruptures at different nucleation points and observe the eventual earthquake magnitudes and slip distribution we find that 40 of nucleations tested develop into large earthquakes of m w 7 2 based on present interseismic locking models of these events those nucleated from deeper depths have a tendency for larger amplitude shallow slip suggesting increased tsunami potential furthermore irrespective of the input locking models we do not observe rupture scenarios of earthquakes with intermediate magnitudes between 6 and 7 a result consistent with observations in nicoya the results of hypocentre dependent earthquake magnitudes and tsunamigenic potential not only pose challenges in estimating rupture extents from locking models but also underscore the significance of quantitatively evaluating seismic and tsunami hazard in subduction zones

implications of a statistical physics approach for earthquake hazard assessment and forecasting there is accumulating evidence that distributed seismicity is a problem in statistical physics seismicity is taken to be a type example of self organized criticality this association has important implications regarding earthquake hazard assessment and forecasting a characteristic of a thermodynamic system is that it exhibits a background noise that is self organized in the case of a dilute gas this self organization is the maxwell boltzmann distribution of molecular velocities in seismicity it is the gutenberg richter frequency magnitude scaling this scaling is fractal observations favor the hypothesis that smaller earthquakes in moderate sized regions occur at rates that are only weakly dependent on time thus the rate of occurrence of smaller earthquakes can be extrapolated to assess the hazard of larger earthquakes in a region we obtain the rate of occurrence of earthquakes with m 4 in 1 1 areas from the neic catalog using only this data we produce global maps of the seismic hazard observations also favor the hypothesis that the stress level at which an earthquake occurs is a second order critical point as a critical point is approached correlations extend over increasingly larger distances in terms of seismicity the approach to a critical point is associated with an increase in the rate of occurrence of intermediate sized earthquakes prior to a large earthquake this precursory activation has been shown to exhibit power law scaling and to occur over a region about ten times larger than the rupture length of the large earthquake analyses of the spinoidal behavior associated with second order critical points predict the power law increase in seismic activity prior to a characteristic earthquake this precursory activation provides the basis for intermediate range earthquake forecasting

eocene volcanism above a depleted mantle slab window in southern alaska the caribou creek volcanic fi eld lies along the continent side edge of forearc basin rocks in south central alaska and consists of over 1000 m of shallow dipping basalt and andesite lavas with minor mafi c pyroclastic deposits dacite and rhyolite lavas along with shallow intrusions form dome complexes with associated pyroclastic deposits that overlie and crosscut the basalt and intermediate lavas the basalts are tholeiitic and strongly depleted in the light rare earth elements la yb 0 18 1 5 with concentrations of high fi eld strength elements e g zr hf ti y similar to mid ocean ridge basalt and with variable enrichment in fl uid mobile elements e g cs ba and pb intermediate and felsic rocks show enrichment in the rare earth elements and fl uid mobile elements plus rb and k but retain low la yb ratios 0 48 3 6 a few andesite and dacite samples are strongly depleted in the heavy rare earth elements and are geochemically similar to adakites e g sr y up to 52 ten 40 ar 39 ar ages for the caribou creek volcanic rocks range from 49 4 2 2 to 35 6 0 2 ma an adakite like tuff beneath the other volcanic rocks yields an age of 59 0 0 4 ma caribou creek basalts were derived from mid ocean ridge like depleted mantle that was emplaced beneath the southern margin of alaska through a slab window following spreading ridge subduction caribou creek volcanism was coeval with oblique subduction oroclinal bending and right lateral strike slip faulting in south central alaska all of which could have induced crustal extension to allow adiabatic melting of the depleted mantle reservoir to form basaltic magmas the basalts then evolved by fractional crystallization with moderate to high degrees of assimilation of jurassic arc basement rocks to form the intermediate and felsic magmas enrichment of the basaltic parent magmas in fl uid mobile elements occurred by contamination from the jurassic arc rocks and or by contamination with metasomatic mantle remnant from preceding subduction high heat fl ow through the slab window induced partial melting of garnet bearing mafi c parts of the jurassic arc basement to form the adakite like rocks the caribou creek volcanic rocks demonstrate that slab windows can directly infl uence magmatism inboard of accretionary prism and forearc basin settings given a suitable deformation regime e g crustal extension and that the infl uence of a slab window on continental margin magmatism can be long lived 20 m y

the 2015 gorkha nepal earthquake sequence i source modeling and deterministic 3d ground shaking to better quantify the relatively long period 0 3 hz shaking experienced during the 2015 gorkha nepal earthquake sequence we study the finite rupture processes and the associated 3d ground motion of the mw7 8 mainshock and the mw7 2 aftershock the 3d synthetics are then used in the broadband ground shaking in kathmandu with a hybrid approach summarized in a companion paper chen and wei 2017 submitted together we determined the coseismic rupture process of the mainshock by joint inversion of insar sar gps static and high rate strong motion and teleseismic waveforms our inversion for the mainshock indicates unilateral rupture towards the ese with an average rupture speed of 3 0 km s and a total duration of 60 s additionally we find that the beginning part of the rupture 5 18 s has about 40 longer rise time than the rest of the rupture as well as slower rupture velocity our model shows two strong asperities occurring 24 s and 36 s after the origin and located 30 km to the northwest and northeast of the kathmandu valley respectively in contrast the mw7 2 aftershock is more compact both in time and space as revealed by joint inversion of teleseismic body waves and insar data the different rupture features between the mainshock and the aftershock could be related to difference in fault zone structure the mainshock and aftershock ground motions in the kathmandu valley recorded by both strong motion and high rate gps stations exhibited strong amplification around 0 2 hz a simplified 3d basin model calibrated by an mw5 2 aftershock can match the observed waveforms reasonably well at 0 3 hz and lower frequency the 3d simulations indicate that the basin structure trapped the wavefield and produced an extensive ground vibration our study suggests that the combination of rupture characteristics and propagational complexity are required to understand the ground shaking produced by hazardous earthquakes such as the gorkha event

stress breakdown time and slip weakening distance inferred from slip velocity functions on earthquake faults we estimate the critical slip weakening distance on earthquake faults by using a new approach which is independent of the estimate of fracture energy or radiated seismic energy the approach is to find a physically based relation between the breakdown time of shear stress tb the time of peak slip velocity tpv and the slip weakening distance dc from the time histories of shear stress slip and slip velocity at each point on the fault which can be obtained from dynamic rupture calculations using a simple slip weakening friction law numerical calculations are carried out for a dynamic shear crack propagating either spontaneously or at a fixed rupture velocity on a vertical fault located in a 3d half space and a more realistic horizontally layered structure with finite difference schemes the results show that tpv is well correlated with tb for faults even with a heterogeneous stress drop dis tribution except at locations near strong barriers and the fault edges we also inves tigate this relation for different types of slip weakening behavior we have applied the method to two recent strike slip earthquakes in western japan the 2000 tottori and the 1995 kobe events we integrated the slip velocity functions on the vertical fault obtained from kinematic waveform inversion of strong motion and teleseismic records from the arrival time of rupture tr to the time of the peak slip velocity tpv and we then corrected the slip obtained at tpv for the errors expected from the dynamic calculations it was found that the slip weakening dis tance d c estimated in the frequency window between 0 05 and 0 5 hz ranges between 40 and 90 cm on the two earthquake faults however if we consider the limited frequency resolution of the observed waveforms probable time errors in the slip velocity functions obtained from kinematic inversion and the uncertainty of the slip weakening behavior the above estimates may be those located between the minimum resolvable limit and the upper bound of their real values the estimated dc values do not necessarily seem to indicate larger values in the shallower part and smaller values in the deeper part of the fault but rather a spatially heterogeneous distribution that appears to be dependent on the local maximum slip this possible dependence might be interpreted by the frictional properties of the fault such as the degree of roughness or the thickness of gouge layers in addition to stress heterogeneities

imaging of seismogenic asperities of the 2016 ml 6 0 amatrice central italy earthquake through dynamic rupture simulations numerical simulations are carried out for the dynamic rupture and wave propagation process of the 24th august 2016 ml 6 0 amatrice italy earthquake using a boundary domain method bdm a hybrid method of boundary integral equation and finite difference methods dynamic rupture parameters of two seismogenic asperities are searched by iterative search through the comparison of the near field ground motions the preferred models indicate two asperities aligned at around 4 5 km depth and separated from each other as well as from the initial rupture point this requires a few supplementary patches connecting them and that are less energetic than the asperities the asperities are characterized by a radius of 2 3 km in the south first to rupture and of 2 4 km in the north second to rupture and the corresponding fracture energies of the asperities are 25 35 0 63 1012 j and 38 05 7 91 1012 j respectively these values are consistent with the scaling relation extrapolated from various analyses of large earthquakes although the parameter space of the search is limited due to the numerical performance of the dynamic rupture simulation the proposed simple characterization of the earthquakes source confirms the scaling relation in fracture energy of the seismogenic asperities which is essential for constructing mechanical earthquake source models

low velocity zones along the san jacinto fault southern california from body waves recorded in dense linear arrays we derive high resolution information on low velocity fault zone fz structures along the san jacinto fault zone sjfz southern california using waveforms of local earthquakes that are recorded at multiple linear cross fault arrays we observe clear across fault delays of direct p and s waves indicating damage zones at different segments of the sjfz we then compute synthetic traveltimes and waveforms using generalized ray theory and perform forward modeling to constrain the fz parameters at the southern section near the trifurcation area the low velocity zone lvz of the clark branch has a width of 200 m 30 45 reduction in vp and 50 reduction in vs from array data across the anza seismic gap we find a lvz with 200 m width and 50 reduction in both vp and vs nearly as prominent as that on the southern section we only find prominent lvzs beneath three out of the five arrays indicating along strike variations of the fault damage fz reflected phases are considerably less clear than those observed above the rupture zone of the 1992 landers earthquake shortly after the event this may reflect partially healed lvzs with less sharp boundaries at the sjfz given the relatively long lapse time from the last large surface rupturing event alternatively the lack of observed fz reflected phases could be partially due to the relatively small aperture of the arrays nevertheless the clear signatures of damage zones at anza and other locations indicate very slow healing process at least in the top few kilometers of the crust

earthquake slip weakening and asperities explained by thermal pressurization for the earth s crust to release accumulated stress in the form of an earthquake a fault must weaken and give way otherwise the movement would quickly grind to a halt due to the surrounding pressure this weakening is not really understood laboratory experiments simply don t match seismologists estimates of the distance a fault must slip before it becomes very weak a new study concludes that the missing ingredient is water geological studies and measurements show the slip zones to be narrow impermeable structures water already in the fault zone can quickly become pressurized by frictional heating as the rocks start to move catalysing large earthquakes from minor movements an earthquake occurs when a fault weakens during the early portion of its slip at a faster rate than the release of tectonic stress driving the fault motion1 2 this slip weakening occurs over a critical distance dc understanding the controls on dc in nature is severely limited however because the physical mechanism of weakening is unconstrained conventional friction experiments typically conducted at slow slip rates and small displacements have obtained dc values that are orders of magnitude lower than values estimated from modelling seismological data for natural earthquakes3 4 5 6 here we present data on fluid transport properties of slip zone rocks and on the slip zone width in the centre of the median tectonic line fault zone japan we show that the discrepancy between laboratory and seismological results can be resolved if thermal pressurization of the pore fluid7 8 9 10 is the slip weakening mechanism our analysis indicates that a planar fault segment with an impermeable and narrow slip zone will become very unstable during slip and is likely to be the site of a seismic asperity

earthquake rupture extents and coseismic slips promoted by damaged fault zones here we investigate the effects of damage fault zones on rupture propagation by conducting a series of 3 d dynamic rupture simulations on a planar vertical strike slip fault we find that damage fault zones can promote rupture extent and increase earthquake potency the waves reflected from the bottom of shallow damage fault zones can increase shear stress on the fault and thus promote rupture propagation in addition the promotional effects increase with the width and depth extent of damage fault zones the overall effects of the waves reflected from the fault parallel side boundaries of damage fault zones are unfavorable for rupture propagation therefore rupture propagation is promoted with the increased width of fault zones due to geometrical spreading effects moreover nonground breaking ruptures may reach the ground surface with the effects of damage fault zones furthermore along strike segmented fault zones as suggested by observations could also promote ruptures and may lead to preferred rupture directions if epicenters are close to fault zones the effects of damage fault zones on rupture propagation hold important implications on assessing earthquake risk

short period energy of the 25 april 2015 mw 7 8 nepal earthquake determined from backprojection using four arrays in europe china japan and australia abstract we apply a backprojection analysis to determine the locations and timing of the sources of short period 0 5 5 s energy generated by the 2015 nepal earthquake we use data from four different arrays at varying azimuths in europe china japan and australia which show generally consistent features for the rupture propagation the sources of strong short period energy are generally distributed east of the epicenter at distances of 10 100 km during the time period of 25 55 s after the initiation the rupture speed was 1 0 km s for the first 20 s then accelerated to 3 0 km s for the remaining 30 40 s the locations of sources of short period energy are close to the down dip edge of the fault and are complementary to the areas of large fault slip that occur further up dip the nepal earthquake might be another example in which regions of large fault slip do not coincide with the source areas of short period energy which are likely associated with the damaging strong ground motions online material animations of backprojections for the 2015 nepal earthquake using four different arrays

the mckinley sequence of granitic rocks a key element in the accretionary history of southern alaska the mckinley sequence of granitic rocks consists of several discrete plutons in the central alaska range most of these plutons crop out south of the denali fault system dfs in the talkeetna quadrangle plutons of the mckinley sequence largely intrude deformed upper meszoic flysch between the dfs and the northern edges of wrangellia and the peninsular terrane which jointly make up the talkeetna superterrane the average k ar age of biotite from nine granites of the mckinley sequence is 57 3 ma rb sr data for whole rock samples indicate that the mckinley sequence cannot be older than 60 ma a selected suite of 20 samples of granite and granodiorite range in sio2 from 65 9 to 77 6 all 20 samples are corundum normative and 18 are moderately peraluminous initial 87sr 86sr ratios range from 0 7054 to 0 7085 the 18o values range from 11 2 to 14 6 these high and variable sr isotopic ratios peraluminous nature rare earth element patterns and high 18o values suggest that granitic rocks of the mckinley sequence crystallized from hybrid magmas produced by assimilation of sedimentary rocks by a mantle derived melt mesozoic flysch is the likely source of the crustal component of the hybrid magmas geologic evidence suggests that the talkeetna superterrane collided with stable alaska after early cretaceous time the flysch basin lying south of stable alaska was closed by northward movement of the talkeetna superterrane maximum age for basin closure and terrane accretion is middle cretaceous cenomanian paleomagnetic evidence indicates that all terranes north of the dfs have been part of stable alaska since the paleocene and that northward movement of wrangellia was completed by 50 ma granitic rocks of the mckinley sequence may be products of terrane accretion the granitic rocks crystallized from hybrid magmas produced during terrane collision and deformation of the flysch basin isotopic ages of the mckinley sequence establish the time of final accretion of the talkeetna superterrane as paleocene

barrier induced supershear ruptures on a slip weakening fault here we investigate the effects of a patch with elevated effective normal stress barrier on two dimensional in plane supershear rupture propagation on a planar fault from numerical experiments our results confirm that the barrier may slow down or stop coseismic ruptures but may also induce supershear ruptures we demonstrate that the supershear rupture may emerge in a region that is delineated by two approximate linear boundaries if the barrier size is below the lower boundary ruptures can overcome the barrier and propagate at subshear speeds if the barrier size is larger than the upper boundary ruptures are always stopped by the barrier furthermore we find that the barrier induced supershear ruptures may eventually slow down into subshear speed depending on the size and the location of the barrier the duration of supershear ruptures increases as the barrier sizes grow from the lower to the upper boundary which are proportional to the reduction in rupture speeds caused by the barrier these results indicate that a barrier on the fault may not stop coseismic ruptures rather the barrier may induce ruptures propagating at supershear speeds that play important roles in near field ground shaking and damage

generation of new cracks accompanied by the dynamic shear rupture propagation of the 2000 tottori japan earthquake the 2000 tottori japan earthquake caused fracture zones of surface rupture at some places away from the trace of the main causative fault in order to explain this observation the 3d dynamic rupture process of the 2000 tottori japan earthquake was simulated the attractive feature of the problem under consideration is the possibility of introducing internal new cracks that propagate under tensile stress as a consequence of the dynamic process of shear slip propagation the discrete element method was used to solve this problem because it can introduce internal tensile cracks for the shear rupture propagation the simple slip weakening model was used as a friction law on the fault the new tensile cracks occur following the classical griffith theory when the critical value of tensile fracture surface energy has been reached the first step to solve the problem was the estimation of the dynamic parameters such as stress drop strength excess and critical slip which were recov ered from the results of waveform inversion in the second step a shear dynamic rupture process was simulated assuming that shear slip occurs only on the pre existing fault and the tensile stress concentration resulting from shear slip causes the new cracks that propagate away from the pre existing fault the results which are consistent with the observations show a free surface rupture caused by the new cracks and the development of a flowerlike structure springing from the borders of the pre existing fault and main asperity

shallow low velocity zone of the san jacinto fault from local earthquake waveform modelling summary we developed a method to determine the depth extent of low velocity zone lvz associated with a fault zone fz using s wave precursors from local earthquakes the precursors are diffracted s waves around the edges of lvz and their relative amplitudes to the direct s waves are sensitive to the lvz depth we applied the method to data recorded by three temporary arrays across three branches of the san jacinto fz the fz dip was constrained by differential traveltimes of p waves between stations at two side of the fz other fz parameters width and velocity contrast were determined by modelling waveforms of direct and fz reflected p and s waves we found that the lvz of the buck ridge fault branch has a width of 150 m with a 30 40 per cent reduction in vp and a 50 60 per cent reduction in vs the fault dips 70 5 to southwest and its lvz extends only to 2 1 km in depth the lvz of the clark valley fault branch has a width of 200 m with 40 per cent reduction in vp and 50 per cent reduction in vs the coyote creek branch is nearly vertical and has a lvz of 150 m in width and of 25 per cent reduction in vp and 50 per cent reduction in vs the lvzs of these three branches are not centred at the surface fault trace but are located to their northeast indicating asymmetric damage during earthquakes

possible manifestations of slab window magmatisms in cretaceous southwest japan abstract the slab window system related to ridge subduction is studied to explain the conspicuous activity and the along arc migration of the magmatisms in the eastern margin of eurasian continent in the late mesozoic the trend of the granite ages is scrutinized with systems approach and analyzed by the statistical method in cretaceous southwest japan a reference field of the eurasian eastern margin the magmatic distribution of simultaneous activity was determined to be the v shape of the slab window excluding dating errors from the located age data the slab window magmatism has the most dominant zone of the acidic rocks at or near the centerline of the window the spreading center of two plates and also has the subdominant zone of the acidic to intermediate rocks on either side of the window as the slab window opens due to the plate motions the upwelling current is adiabatically induced in the asthenosphere to fill the window gap the partial melt is generated in the upwelling flux and transports heat to the lower crust to make greater granitic magma chambers by heat conduction to and assimilation with the crustal matter the younger and hotter slabs outside the window also play a role in partial slab melting and or dehydration to the asthenosphere and generate the subdominant granodioritic and adakitic and or high magnesian andesitic magmatisms as the pre and post activities of the main granite genesis the slab window formed by the subducted ridge between the kula and pacific plates was the strong heat source of the active magmatisms and migrated at the rate of 2 8 cm year from southwest to northeast about 8000 km along the continental margin the growth of the continent associated with the active acidic to intermediate magmatisms including the adakitic and or high magnesian andesitic activities is modeled by the slab window system

mid pleistocene lavas from the seguam volcanic center central aleutian arc closed system fractional crystallization of a basalt to rhyodacite eruptive suite in contrast to adjacent volcanic centers of the modern central aleutian arc seguam island developed on strongly extended arc crust k ar dates indicate that mid pleistocene late pleistocene and holocene eruptive phases constitute seguam this study focuses on the petrology of the mid pleistocene 1 07 07 ma turf point formation tpf which is dominated by an unusual suite of porphyritic basalt and basaltic andesite lavas with subordinate phenocryst poor andesite to rhyodacite lavas increasing whole rock feo mgo from basalt to dacite the anhydrous plag ol cpx opx mt phenocryst assemblage groundmass pigeonite and the reaction ol liq opx preserved in the mafic lavas indicate a tholeiitic affinity thermometry and comparison to published phase equilibria suggests that most tpf basalts crystallized plag ol cpx mt at 1160 c between about 3 5 kb 1 2 h2o andesites crystallized plag cpx opx mt at 1000 c between 3 4 kb with 3 5 h2o and dacites crystallized plag cpx opx mt at 1000 c between 1 2 kb with 2 3 h2o all lavas crystallized at f o 2 close to the nno buffer mineral compositions and textures indicate equilibrium crystallization of the evolved lavas petrographic evidence of open system mixing or assimilation is rare mgo cao al2o3 cr ni and sr abundances decrease and k2o na2o rb ba zr and pb increase with increasing sio2 50 71 lree enrichment ce yb n 1 7 0 2 characterizes most tpf lavas total ree contents increase and eu anomalies become more negative with increasing sio2 relative to other aleutian volcanic centers tpf basalts and basaltic andesites have lower k2o na2o tio2 rb ba sr zr y and lree abundances 87sr 86sr ratios 0 70361 0 70375 and ratios of 206pb 204pb 18 88 18 97 207pb 204pb 15 58 15 62 208pb 204pb 38 46 38 55 are the highest measured for any suite of lavas in the oceanic portion of the aleutian arc conversely end values 5 8 to 6 7 are among the lowest from the aleutians sr nd and pb ratios are virtually constant from basalt through rhyodacite whereas detectable isotopic heterogenity is observed at most other aleutian volcanic centers major and trace element ree and sr nd and pb isotopic compositions are consistent with the basaltic andesitic andesitic dacitic and rhyodacitic liquids evolving from tpf basaltic magma via closed system fractional crystallization alone fractionation models suggest that removal of 80 wt cumulate 61 plag 17 cpx 12 opx 7 ol and 3 mt can produce 20 wt rhyodacitic residual liquid per unit mass of parental basaltic liquid petrologic and physical constraints favor segregation of small batches of basalt from a larger mid crustal reservoir trapped below a low density upper crustal lid in these small magma batches the degree of cooling crystallization and fractionation are functions of the initial mass of basaltic magma segregated the thermal state of the upper crust and the magnitude of extension tholeiitic magmas erupted at seguam evolved by substantially different mechanisms than did calc alkaline lavas erupted at the adjacent volcanic centers of kanaga and adak on unextended arc crust these variable differentiation mechanisms and liquid lines of descent reflect contrasting thermal and mechanical conditions imposed by the different tectonic environments in which these centers grew at seguam intra arc extension promoted eruption of voluminous basalt and its differentiates unmodified by interaction with lower crustal or upper mantle wallrocks

an analysis of the process of acceleration of seismic energy emission in laboratory experiments on destruction of rocks and before strong earthquakes on kamchatka and in italy abstract the time to failure model is a technique in which a failure function is fitted to a time series of accumulated benioff strain before a large earthquake we analyze the relation of the time to failure model to the hypothesis of fractal structure of seismicity a power law failure function varnes 1989 bufe and varnes 1993 and its log periodic generalization sornette and sammis 1995 are discussed the results of application of the log periodic time to failure model to the analysis of the process of acceleration of seismic energy emission in the laboratory experiments on rock destruction and before strong earthquakes on kamchatka and in italy are presented

continuum of earthquake rupture speeds enabled by oblique slip earthquake rupture speed can affect ground shaking and thus seismic hazard seismological observations show that large earthquakes span a continuum of rupture speeds from slower than rayleigh waves up to p wave speed and include speeds that are predicted to be unstable by 2d theory this discrepancy between observations and theory has not yet been reconciled by a quantitative model here we present numerical simulations that show that long ruptures with oblique slip both strike slip and dip slip components can propagate steadily at various speeds including those previously suggested to be unstable the obliqueness of slip and the ratio of fracture energy to static energy release rate primarily control the propagation speed of long ruptures we find that the effects of these controls on rupture speed can be predicted by extending the 3d theory of fracture mechanics to long ruptures with oblique slip we propose that this model provides a quantitative framework to interpret supershear earthquakes to constrain the energy ratio of faults based on observed rupture speed and rake angle and to relate the potential rupture speed and size of future earthquakes to the observed slip deficit along faults

lower edge of locked main himalayan thrust unzipped by the 2015 gorkha earthquake faults are unlocked by earthquakes analysis of seismic data from the 2015 nepal earthquake shows that only part of the main himalayan thrust fault was unzipped by the quake leaving much of the fault locked and ready to slip in a future event

slip weakening distance in dynamic rupture of in slab normal faulting earthquakes we apply the above method to three large in slab normal faulting earthquakes in the mexican subduction zone to do this we calculate the spatial distribution of slip velocity functions and final slip from kinematic waveform inversion of strong motion and teleseismic records and the stress history and final stress change from dynamic rupture calculations by integrating the slip velocity functions obtained from the inversion from the rupture arrival time to the time of peak slip velocity we obtain slip dat t pv and then correct it for dc at t b through dynamic calculations we also estimate the lowest resolvable limit and probable errors of dc from the slip velocity functions and its upper bound from a theoretical constraint between the dynamic stress drop and dc we found that the slip weakening distance dc estimated in the frequency band between 0 05 and 0 5 hz ranges between 40 and 120 cm on the in slab fault of the 1999 oaxaca earthquake mw 7 5 the largest dc is detected in the central fault and in part of the deeper sections and dc in the zone around the hypocentre ranges between 50 and 70 cm the estimated dc values appear to be less depth dependent but are rather more dependent on the local maximum slip this possible slip dependence might be interpreted by the degree of fault roughness in addition to stress heterogeneities the fracture energy g in the central section and in the hypocentral zone are roughly estimated to be of the order of 10 15 and 5 8 mj m 2 respectively both of the estimated dc and g values are somewhat larger than those on the vertical fault of two recent shallow strike slip earthquakes in western japan

constraints on stress and friction from dynamic rupture models of the 1994 northridge california earthquake we have simulated several scenarios of dynamic rupture propagation for the 1994 northridge california earthquake using a three dimensional finite difference method the simulations use a rate and slip weakening friction law starting from a range of initial conditions of stress and frictional parameters a critical balance between initial conditions and friction parameters must be met in order to obtain a moment as well as a final slip distribution in agreement with kinematic slip inversion results we find that the rupture process is strongly controlled by the average stress and connectivity of high stress patches on the fault in particular a strong connectivity of the high stress patches is required in order to promote the rupture propagation from the initial nucleation to the remaining part of the fault moreover we find that a small amount of rate weakening is needed in order to obtain a level of inhomogeneity in the final slip similar to that obtained in the kinematic inversion results however when the amount of rate weakening is increased the overall moment drops dramatically unless the average prestress is raised to unrealistic levels a velocity weakening parameter on the order of 10 cm per second is found to be adequate for an average prestress of about a hundred bars the presence of the free surface and of the uppermost low impedance layers in the model are found to have negligible influence on the rupture dynamics itself because the top of the fault is at a depth of several kilometers the 0 1 0 5 hz radiated waves from the dynamic simulation provides a good fit to strong motion data at sites nwh and ssa underprediction of the recorded peak amplitude at jfp is likely due to omission of near surface low velocity and 3 d basin effects in the simulations

determination of constitutive relations of fault slip based on seismic wave analysis constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields no actual relation during a natural earthquake has been determined the 1995 kobe earthquake is suitable for detailed kinematic analysis and this enables the first evaluation of constitutive relations for a natural earthquake in this study we determine spatiotemporal slip distribution on an assumed fault plane of the 1995 kobe earthquake by waveform inversion and then solve elastodynamic equations using a finite difference method to determine the stress distribution and constitutive relations on the fault plane an inversion method based on bayes theorem is employed to obtain a spatiotemporal slip distribution and enables us to ensure the objective uniqueness of the solution with numerous parameters and smoothing constraints this slip distribution is then used as part of the boundary condition in the finite difference calculation the time histories of slip and shear stress obtained then provide a constitutive relation at each point on the fault plane they show slip weakening relations almost everywhere on the fault plane while slip rate dependency is not clear the slip weakening behavior has a clear depth dependency indicating that the slip weakening rate d du is smaller in the shallow crust than that in the deep crust this may be associated with the paucity of shallow seismicity observed in the source region of this earthquake as reported for many mature fault systems

physical basis for statistical patterns in complex earthquake populations models predictions and tests understanding the physics of earthquakes and the space time patterns they produce is illuminated by the use of coarse grained models and simulations that capture the basic physical processes and that are amenable to analysis we present a summary of ideas that describe the nucleation growth and arrest of earthquakes on individual faults under shear loading we find that faults reside in a metastable state near a classical spinodal that governs the nucleation and growth of slip events the roughness of an associated stress distribution field x t determines whether slip events are confined within the initial high stress patch or break away and grow to become very large we find a critical value of roughness that is associated with a first order order disorder transition we also give a number of predictions examples and applications of these ideas and indicate how they might be tested through systematic observational programs

an experimentally based friction law for high velocity long displacement slip pulse events during earthquakes abstract large earthquakes initiate at small nucleation sites and propagate as rupture fronts along the host fault it is inherently challenging to resolve the complexity of fault rupture at depth and therefore the evolution of frictional strength during earthquakes is commonly analyzed in laboratory experiments we experimentally demonstrate here that this evolution depends simultaneously on all slip kinematic components displacement velocity and acceleration we incorporate these components in shear experiments with slip histories that resemble the theoretical expectations for earthquake slip these experiments led to a new friction law that fits fault behavior during high velocity long displacement slip our numerical simulations of dynamic rupture along a planar fault that obeys this friction law reproduced a range of earthquake source features including slip pulse yoffe function gaussian velocity and spontaneous slip arrest finally we demonstrate that this experimentally based friction law can realistically simulate the propagation and arrest of natural earthquakes

earthquake fracture energy inferred from kinematic rupture models on extended faults 1 we estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms we define the breakdown work wb as the excess of work over some minimum traction level achieved during slip wb is equivalent to seismological fracture energy g in previous investigations our numerical approach uses slip velocity as a boundary condition on the fault we employ a three dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture we estimate wb by calculating the scalar product between dynamic traction and slip velocity vectors this approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity if these vectors are not collinear the inferred breakdown work depends on the initial traction level we show that breakdown work depends on the square of slip the spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution breakdown work density and its integral over the fault breakdown energy scale with seismic moment according to a power law with exponent 0 59 and 1 18 respectively our estimates of breakdown work range between 4 105 and 2 107 j m2 for earthquakes having moment magnitudes between 5 6 and 7 2 we also compare our inferred values with geologic surface energies this comparison might suggest that breakdown work for large earthquakes goes primarily into heat production

rupture process of the mw 7 9 2015 gorkha earthquake nepal insights into himalayan megathrust segmentation we investigate the rupture process of the 25 april 2015 gorkha earthquake mw 7 9 using a kinematic joint inversion of teleseismic waves strong motion data high rate gps static gps and synthetic aperture radar sar data the rupture is found to be simple in terms of coseismic slip and even more in terms of rupture velocity as both inversion results and a complementing back projection analysis show that the main slip patch broke unilaterally at a steady velocity of 3 1 3 3 km s this feature likely contributes to the moderate peak ground acceleration 0 2 g observed in kathmandu the 15 km deep rupture occurs along the base of the coupled portion of the main himalayan thrust and does not break the area ranging from kathmandu to the front the limitation in length and width of the rupture cannot be identified in the preearthquake interseismic coupling distribution and is therefore discussed in light of the structural architecture of the megathrust

structural segmentation controlled the 2015 mw 7 8 gorkha earthquake rupture in nepal the ongoing collision of india with asia is partly accommodated by slip on the main himalayan thrust mht the 25 april 2015 m w 7 8 gorkha earthquake is the most recent major event to rupture the mht which dips gently northward beneath central nepal although the geology of the range has been studied for decades fundamental aspects of its deep structure remain disputed here we develop a structural cross section and a three dimensional geologically informed model of the mht that are consistent with seismic observations from the gorkha earthquake a comparison of our model to a detailed slip inversion data set shows that the slip patch closely matches an ovalshaped gently dipping fault surface bounded on all sides by steeper ramps the gorkha earthquake rupture seems to have been limited by the geometry of that fault segment this is a significant step forward in understanding the deep geometry of the mht and its effect on earthquake nucleation and propagation published models of fault locking do not correlate with the slip patch or our fault model in the vicinity of the earthquake further suggesting that fault geometry was the primary control on this event our result emphasizes the importance of adequately constraining subsurface fault geometry in megathrusts in order to better assess the sizes and locations of future earthquakes

evidence for a supershear transient during the 2002 denali fault earthquake elastodynamic considerations suggest that the acceleration of ruptures to supershear velocities is accompanied by the release of rayleigh waves along the fault from the stress breakdown zone these waves generate a secondary slip pulse trailing the rupture front but manifest almost entirely in ground motion perpendicular to the fault in the near source region we construct a spontaneously propagating rupture model exhibiting these features and use it to explain ground motions recorded during the 2002 denali fault earthquake at pump station 10 located 3 km from the fault we show that the initial pulses on both the fault normal and fault parallel components are due to the supershear stress release on the fault whereas the later arriving fault normal pulses result from the trailing subshear slip pulse on the fault online material mpeg movies of rupture history and ground motion

geometrical effects of a subducted seamount on stopping megathrust ruptures 1 we have numerically simulated dynamic ruptures along a slip weakening megathrust fault with a subducted seamount of realistic geometry demonstrating that seamounts can act as a barrier to earthquake ruptures such barrier effect is calculated to be stronger for increased seamount normal stress relative to the ambient level for larger seamount height to width ratio and for shorter seamount to nucleation distance as the seamount height increases from 0 to 40 of its basal width the required increase in the effective normal stress on the seamount to stop ruptures drops by as much as 20 we further demonstrate that when a seamount is subducted adjacent to the earthquake nucleation zone coseismic ruptures can be stopped even if the seamount has a lower effective normal stress than the ambient level these results indicate that subducted seamounts may stop earthquake ruptures for a wide range of seamount normal stress conditions including the case of the thrust fault being lubricated by seamount top fluid rich sediments as suggested from observations in the japan and sunda trenches

modeling earthquake sequences along the manila subduction zone effects of three dimensional fault geometry abstract to assess the potential of catastrophic megathrust earthquakes m w 8 along the manila trench the eastern boundary of the south china sea we incorporate a 3d non planar fault geometry in the framework of rate state friction to simulate earthquake rupture sequences along the fault segment between 15 n 19 n of northern luzon our simulation results demonstrate that the first order fault geometry heterogeneity the transitional segment possibly related to the subducting scarborough seamount chain connecting the steeper south segment and the flatter north segment controls earthquake rupture behaviors the strong along strike curvature at the transitional segment typically leads to partial ruptures of m w 8 3 and m w 7 8 along the southern and northern segments respectively the entire fault occasionally ruptures in m w 8 8 events when the cumulative stress in the transitional segment is sufficiently high to overcome the geometrical inhibition fault shear stress evolution represented by the s ratio is clearly modulated by the width of seismogenic zone w at a constant plate convergence rate a larger w indicates on average lower interseismic stress loading rate and longer rupture recurrence period and could slow down or sometimes stop ruptures that initiated from a narrower portion moreover the modeled interseismic slip rate before whole fault rupture events is comparable with the coupling state that was inferred from the interplate seismicity distribution suggesting the manila trench could potentially rupture in a m8 earthquake