multiple dating approaches applied to the recent sediments in the yangtze river changjiang subaqueous delta the accumulation rate of recent deposits in a delta environment is critical to the study of delta dynamics and their sustainable management the most commonly used dating approach for recent 100

numerical simulation of seismic cycles with a composite rate and state dependent friction law properties of rate and state dependent friction laws are examined through numerical simulations among several versions of the rate and state dependent friction laws we use the slowness law the slip law and the composite law the last was recently proposed by kato and tullis 2001 for better explaining experimental observations of rock friction in the laboratory two kinds of simulations are done one is for cyclic stick slip motion of a single degree of freedom spring block system the other is for seismic cycles at a subduction zone where a 2d model of uniform elastic half space is used assuming the same values of friction parameters we compare the simulation results for the three friction laws from the two kinds of simulations we find that the recurrence interval of simulated earthquakes is the longest and the magnitude of preseismic sliding is the smallest for the composite law

simulation of seismic cycles of buried intersecting reverse faults to understand how reverse fault systems interact 1 perform a numerical simulation of seismic cycles the model fault system in a two dimensional uniform elastic half space consists of a shallowly dipping listric main reverse fault and a subfault with a higher dip angle a fixed slip rate is imposed on deeper parts of the main fault and frictional stress on the remaining parts of the main fault and on the subfault obeys a rate and state dependent friction law the main results of the numerical simulation are as follows 1 because of fault interactions there exists moderate scatter in recurrence intervals of large earthquakes on the main fault and the subfault 2 the cumulative slip amounts on deeper parts of the main fault on shallower parts of the main fault and on the subfault are different from one another their values are such that the stress concentration at the fault intersection is a minimum 3 a large earthquake on the main fault increases shear stress and decreases normal stress on the subfault causing slip on deeper parts of the subfault a subfault earthquake sometimes induces slip on the main fault result 3 is consistent with some seismic observations that two conjugate fault planes were active during an earthquake sequence results 1 and 2 may be important for long term evaluation of seismic potential

reconstruction of holocene foreland progradation using optically stimulated luminescence osl dating an example from dungeness uk roberts helen plater a j 2007 reconstruction of holocene foreland progradation using optically stimulated luminescence osl dating an example from dungeness uk the holocene 17 4 pp 495 505 rae2008

late quaternary river incision rates and rock uplift pattern of the eastern qilian shan mountain china abstract the uplift rate and pattern of the qilian shan mountain which lies in the northeast margin of the tibetan plateau are key to understanding the dynamics of crustal deformation in the northeastern tibetan plateau in this work late quaternary terraces in seven river valley sections in the eastern qilian shan mountain are studied to determine terrace abandonment ages by osl optical simulating luminescence and terrace heights by gps global positioning system surveys river incision rates since 76 ka bp are calculated ranging from 0 37 mm a to 1 49 mm a distribution of river incision rates shows that higher river incision rates 0 85 1 49 mm a are located at the rivers upstream reaches where mean mountain elevation is 4000 m and relatively lower incision rates 0 32 0 62 mm a are located at the mountain front where the mean mountain elevation is

beach ridges and prograded beach deposits as palaeoenvironment records abstract beach ridges are landforms commonly developed on prograded coasts with beach shorelines a sequence of beach ridges coupled with their subsurface deposits can be regarded as a time series of coastal evolution methodological advances in field surveying and chronology applicable to beach ridges have led to detailed palaeoenvironmental reconstructions to be derived from such sequences this paper reconsiders the basic aspects of beach ridges and deposits which need to be properly understood for their comprehensive interpretation in a palaeo environmental context it also reviews case studies in which beach ridge sequences have been used to unveil past sea level history catastrophic events and climate changes proposed formative processes of beach ridges include 1 progradation of sandy beach and berm formations in relation to fairweather waves coupled with aeolian foredune accumulation 2 building of gravel ridges by storm waves 3 welding of longshore bars beach ridge formation through sea level oscillation is thought to be questionable and caution is suggested for this process when undertaking palaeoenvironmental reconstruction beach deposit stratification is known to dip either landwards or seawards but landward dips are uncommon seaward dipping stratification is formed in relation to beachface progradation and is usually dissected in places by erosion surfaces resulting from episodic beach retreat the boundary between the foreshore and the underlying shoreface is well defined only in the case that longshore bars lead to complex bedding structure relative to that of the foreshore reliable chronology of beach ridges can be determined by radiocarbon and optically stimulated luminescence osl dating radiocarbon dating of articulated shells which are considered not to be extensively reworked provides robust results but osl dating is more useful as it enables direct dating of sediment grains it is noted that there are restrictions in chronological resolution and continuity inherent to beach ridge and beach deposits the plan view geomorphic expression of beach ridges typically consists of ridge sets with multi decadal intervals whereas their internal sedimentary structures define shorter time scales records of beach sedimentation and erosion are likely to be reworked by episodic high magnitude beach retreat and the resultant record of the net progradation is likely to be sporadic and discontinuous the height of sandy beach ridges is often variable due to differing degrees of aeolian sand accumulation and they are thus not used as sea level indicators unless purely wave built gravel ridge height is a relatively reliable indicator of sea level but can vary in response to storminess fluctuations subsurface sediment facies boundaries are preferred as sea level indicators and those proposed include boundaries of aeolian beach foreshore shoreface and upper lower shorefaces catastrophic events are expressed in both erosional and depositional records erosion surfaces or scarp imprints revealed in a cross section of beach deposits indicate storm or tsunami events however erosional events are likely to rework previous records of sedimentation and even other erosional events and thus the apparent history decoded from the resultant deposits tends to be biased several attempts for estimating the frequency and intensity of prehistoric cyclones rely on assumed relationships between the level of coarse sand beach ridges and cyclone inundation the formative process of coarse sand ridges remains uncertain and needs to be clarified as it constitutes the fundamental basis of these attempts the growth rates of beach ridge systems are expected to reflect fluctuations in river sediment discharge to the coast and in aeolian sand flux due to onshore winds both of which are affected by climate change assessment of the growth rate is potentially improved by ground penetrating radar survey of subsurface structure and by detailed chronology orientation of beach ridges reflects long term trends in wave direction inferred relationships between beach ridges and cyclic fluctuations of sea level and climate rely on weak assumptions and are not substantiated by rigid chronological evidence and thus remain highly questionable correlation between the inherently decadal signal of beach ridge intervals and possible climate cycles such as sunspot activity is probably coincidental as it lacks causal explanations

late pleistocene coastal evolution of san giovanni di sinis west sardinia western mediterranean abstract the upper pleistocene succession of coastal deposits outcropping at san giovanni di sinis west sardinia has been studied since the 1960s however the absence of consistent radiometric ages has allowed the production of competing stratigraphic subdivisions of these deposits with different isotopic stage ois mis attributions the succession is composed of sandy to gravelly shallow marine coastal aeolian and alluvial fan plain deposits facies analysis and log correlations show the presence of three unconformities t1 t2 t3 always overlain by shallow marine deposits cutting through the substrate alluvial fan or aeolian sediments we have collected three samples for optically stimulated luminescence osl dating at the top of each shallow marine deposit the succession is composed of four unconformity bounded units u1 u2 u3 u4 and the new osl dates indicate the presence of three different sea level highstands the first unit u1 which is composed of shallow marine to aeolian deposits and overlies transgressive surface t1 is related to a marine transgression during ois 7 186 13 ky unit 2 is composed of continental deposits and formed during ois 6 unit 3 represents ois 5 and overlies a transgressive surface t2 more precisely subunit u3a is related to ois 5e 120 10 ky eu tyrrhenian or eemian sensu strictu and is characterized by shallow marine to aeolian deposits developed during both transgressive and highstand phases the following bay deposits of subunit 3b are associated with ois 5c 100 5 ky and record a second transgressive event t3 and highstand phase occurred during the neo tyrrhenian the succession of san giovanni di sinis ends with continental deposits of unit 4 associated to a sea level fall that took place at the beginning of the last glacial phase ois 4

a 2 5d interpretation of the eastern galicia magnetic anomaly northwestern spain geodynamical implications abstract the eastern galicia magnetic anomaly egma shows intensities up to 190 nt and is one of the major features of the magnetic field in northwestern spain taking into account the seismic refraction and surface geological data a 2 5d model of the magnetic properties of the crust in the area of the egma has been carried out models show that the anomaly can be produced by a middle to lower crustal layer a few kilometers thick with magnetic susceptibility of approximately 0 045 si emplaced with a ramp flat like geometry in higher crustal levels and giving rise to horizontal displacements of about 50 km on the basal eastern galicia thrust this structure is in close agreement with surface geology since the culmination of the lugo dome and the extensional viveiro fault can be interpreted in relation with the displacement along the eastern galicia thrust the southern termination of the egma can be related to the termination of the anomalous layer on a lateral hanging wall ramp of this thrust rocks in the magnetic layer are interpreted as mainly lower crust mafic and or ultramafic rocks in the northern sector at least part of the anomaly must be attributed to ultramafic hercynian intrusives cropping out in the vicinity of the viveiro fault

esr dating of megafauna enamel teeth from lagoa uri de cima archaeological site pernambuco northeastern brazil abstract excavations in the lagoa uri de cima archaeological site salgueiro pernambuco brazil revealed considerable pleistocene mammalian fossils and lithics in multiple sedimentary layers of the ancient lake currently dry the site was found in 2010 during the construction of an open air system of canals to connect water sheds of the semi arid regions with the sao francisco river the coexistence of a variety of extinct mammals and archaeological remains suggested the possibility of further light on the question of overlapping occupation of northeastern brazil by megafauna and humans in the late pleistocene electron spin resonance esr dating of tooth enamel of mammal fossils can provide valuable information on the chronology of this site this work presents the esr dating of four teeth of two mammal species toxodon platensis 2 and haplomastodon waringi 2 dose response curves were constructed using t1 b1 and t1 b2 amplitudes of the esr signal of the hydroxyapatite co2 radical measured with a bruker emx 10 x band spectrometer to verify the experimental protocol and the reliability of the exponential fittings for additive doses and esr signal intensities the dose response curve of one toxodon platensis sample was independently obtained with a jeol fa 200 x band spectrometer equivalent dose to age conversions were carried out with the rosy esr dating program with the external dose rate given by the environment and cosmic radiation and the internal dose rate given by probable uranium uptake models the results show ages varying from 12 000 to 19 000 years for the four samples the stratigraphical consistency is sub optimal but can be explained by the overall geomorphology of the site these results place the creation of the lowest sedimentary levels of lagoa uri de cima within the late pleistocene

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

a model for possible crustal deformation prior to a coming large interplate earthquake in the tokai district central japan we perform numerical simulations of a seismic cycle by applying a laboratory derived friction law to evaluate possible crustal deformations prior to the hypothesized tokai earthquake which is expected to occur in the near future along the suruga trough central japan the frictional force obeying a rate and state dependent friction law is assumed to act on the plate interface in a 2d model of the subduction zone we test two versions of the friction law the so called slowness version and the slip version we select model parameters on the basis of historical documents about past large earthquakes in the tokai district and the present coupling state of the plate interface beneath the tokai district estimated by gps observations simulation results for both the slowness and the slip version are as follows 1 the coupling region of the plate interface becomes narrower with time in the interseismic period 2 the inland crust contracts at a nearly constant rate for most of the interseismic period the contraction rate decreases or a change from contraction to extension takes place before the occurrence of a large interplate earthquake 3 significant abnormal crustal deformation precedes the earthquake and maximum amplitudes about one day before the earthquake exceed the noise levels in the case of clear weather of borehole strainmeters installed in the tokai district 4 the spatiotemporal variation of aseismic sliding on the plate interface perturbs the regional stress field around the source volume of the coming earthquake leading possibly to precursory seismic quiescence in the overriding plate and a change in focal mechanisms of small earthquakes in the subducting slab the most significant difference in the results between the slowness version and the slip version of the friction law is that amplitudes of preslip and crustal deformation just before earthquakes are several times larger for the slowness version than for the slip version although some ambiguity remains in the present model mainly because of the incompleteness of the friction law and the deficiency of observational data constraining model parameters the physical model can be improved through the comparison of predicted crustal deformation with observations continuous and concentrated observations of crustal deformation and seismic activity are thus important in the tokai district to understand quantitatively the sliding process preceding a large interplate earthquake there

statistical properties of seismicity of fault zones at different evolutionary stages summary we perform a systematic parameter space study of the seismic response of a large fault with different levels of heterogeneity using a 3 d elastic framework within the continuum limit the fault is governed by rate and state friction and simulations are performed for model realizations with frictional and large scale properties characterized by different ranges of size scales we use a number of seismicity and stress functions to characterize different types of seismic responses and test the correlation between hypocenter locations and the employed distributions of model parameters the simulated hypocenters are found to correlate significantly with small l values of the rate and state friction the final sizes of earthquakes are correlated with physical properties at their nucleation sites the obtained stacked scaling relations are overall self similar and have good correspondence with properties of natural earthquakes

a constitutive law for the shear failure of rock under lithospheric conditions abstract this paper first reviews recent studies on constitutive formulations for shear failure which leads to the conclusion that revealing the constitutive property for not only frictional slip failure but also shear failure of intact rock in the brittle to brittle plastic transition regimes is critical to establish the constitutive law which governs earthquake shear failure that proceeds in the lithosphere to this end a unique high stiffness testing apparatus capable of applying polyaxial stress fields to rectangular rock specimens has been constructed for which a brief description is given the paper then presents new results of laboratory experiments on constitutive properties of shear fracture of intact granite at lithospheric conditions in view of the physical principles and constraints to be imposed on the constitutive law for shear failure the slip dependency is a more fundamental property than the time or rate dependency and hence the constitutive law for shear failure should primarily be slip dependent this slip dependent constitutive law which itself is self consistent can unifyingly and quantitatively treat the entire phases from stable quasistatic ruture growth to unstable dynamic fast speed rupture propagation for shear failure of any type whether it is frictional slip failure along a preexisting fault or shear fracture of intact materials the slip dependent constitutive law includes a scaling parameter dc critical slip displacement explicitly which in turn is scaled by a characteristic length c representing geometrical irregularities of the fault surfaces incorporation of dc or c enables this constitutive law to provide a common interpretation for shear failure of any size scale as an earthquake source from small scale in the laboratory to large scale in the earth the present experiments corroborate the slip dependent constitutive relation and other constitutive properties over the entire process from slip strengthening to slip weakening of intact granite under the conditions that confining pressure is in the range 440 to 500 mpa pore pressure is in the range 30 to 300 mpa temperature is in the range from room temperature to 456 c and strain rate is in the range 10 4 to 10 7 s it is found that some constitutive law parameters are not independent but mutually related the constitutive relation for shear failure and the parameters such as p breakdown stress drop and dc prescribing its relation are affected by ambient conditions such as temperature and strain rate

loess chronostratigraphy in eastern croatia a luminescence dating approach abstract in eastern croatia impressive loess palaeosol successions up to 30 m thick are exposed along the steep cliffs of the danube river between zmajevac and sarengrad the croatian loess record provides an excellent high resolution archive of climate and environmental change providing evidence for the interaction between accumulation and erosion of aeolian and fluvial sediments during the middle and late pleistocene sedimentological and pedological investigations including granulometry carbonate content and total organic carbon content and infrared optically stimulated luminescence irsl dating were carried out on samples collected from the loess sections at zmajevac erdut and sarengrad the loess successions are intercalated by at least four palaeosols or pedocomplexes which very likely correlate with middle and upper pleistocene interstadials and interglacials in all sediment successions investigated alluvial sediments are intercalated in the loess deposits indicating periods of fluvial activity the stratigraphically youngest alluvial sediments are exposed at the erdut section loess sandwiching these alluvial sediments yielded irsl age estimates of 61 5 6 2 and 53 8 5 4 ka the irsl age estimates give evidence for periods of increased accumulation of dust during the middle and late pleniglacial correlating with oxygen isotope stage ois 3 and ois 2 respectively during the penultimate glaciation and at least the antepenultimate glaciation however it is likely that irsl age estimates 60 ka are underestimated

extending resolution of fault slip with geodetic networks through optimal network design geodetic networks consisting of high precision and high rate global navigation satellite systems gnss stations continuously monitor seismically active regions of the world these networks measure surface displacements and the amount of geodetic strain accumulated in the region and give insight into the seismic potential sugar sumatra gps array in sumatra geonet gnss earth observation network system in japan and pbo plate boundary observatory in california are some examples of established networks around the world that are constantly expanding with the addition of new stations to improve the quality of measurements however installing new stations to existing networks is tedious and expensive therefore it is important to choose suitable locations for new stations to increase the precision obtained in measuring the geophysical parameters of interest here we describe a methodology to design optimal geodetic networks that augment the existing system and use it to investigate seismo tectonics at convergent and transform boundaries considering land based and seafloor geodesy the proposed network design optimization would be pivotal to better understand seismic and tsunami hazards around the world land based and seafloor networks can monitor fault slip around subduction zones with significant resolution but transform faults are more challenging to monitor due to their near vertical geometry

a composite rate and state dependent law for rock friction existing constitutive laws of rock friction cannot describe both observed strengthening in the absence of slip and frictional behavior around steady state sliding combining existing rate and state dependent friction laws we propose a new friction law which expresses logarithmically time dependent healing at sliding velocities smaller than a cut off velocity v c and approaches the so called slip law at velocities larger than v c numerical simulations show that the new friction law adequately explains experimental results of velocity stepping tests and slide hold slide tests which have widely been used to examine velocity time and displacement dependent property of rock friction because the new friction law has a simple form and appears appropriate for a wide range of conditions it is useful for application to numerical modeling of seismic cycles

under the hood of the earthquake machine toward predictive modeling of the seismic cycle advances in observational laboratory and modeling techniques open the way to the development of physical models of the seismic cycle with potentially predictive power to explore that possibility we developed an integrative and fully dynamic model of the parkfield segment of the san andreas fault the model succeeds in reproducing a realistic earthquake sequence of irregular moment magnitude m w 6 0 main shocks including events similar to the ones in 1966 and 2004 and provides an excellent match for the detailed interseismic coseismic and postseismic observations collected along this fault during the most recent earthquake cycle such calibrated physical models provide new ways to assess seismic hazards and forecast seismicity response to perturbations of natural or anthropogenic origins

gravity changes from a stress evolution earthquake simulation of california 1 the gravity signal contains information regarding changes in density at all depths and can be used as a proxy for the strain accumulation in fault networks a stress evolution time dependent model was used to create simulated slip histories over the san andreas fault network in california using a linear sum of the gravity signals from each fault segment in the model via coseismic gravity green s functions a time dependent gravity model was created the steady state gravity from the long term plate motion generates a signal over 5 years with magnitudes of 2 gal the current limit of portable instrument observations moderate to large events generate signal magnitudes in the range of 10 to 80 gal well within the range of ground based observations the complex fault network geometry of california significantly affects the spatial extent of the gravity signal from the three events studied

dynamic earthquake ruptures in the presence of lithostatic normal stresses implications for friction models and heat production we simulate dynamic ruptures on a strike slip fault in homogeneous and layered half spaces and on a thrust fault in a layered half space with traditional friction models sliding friction exceeds 50 of the fault normal compressive stress and unless the pore pressures approach the lithostatic stress the rupture characteristics depend strongly on the depth and sliding generates large amounts of heat under application of reasonable stress distributions with depth variation of the effective coefficient of friction with the square root of the shear modulus and the inverse of the depth creates distributions of stress drop and fracture energy that produce realistic rupture behavior this ad hoc friction model results in 1 low sliding friction at all depths and 2 fracture energy that is relatively independent of depth additionally friction models with rate weakening behavior which form pulselike ruptures appear to generate heterogeneity in the distributions of final slip and shear stress more effectively than those without such behavior which form cracklike ruptures for surface rupture on a thrust fault the simple slip weakening friction model which lacks rate weakening behavior accentuates the dynamic interactions between the seismic waves and the rupture and leads to excessively large ground motions on the hanging wall waveforms below the center of the fault which are associated with waves radiated to teleseismic distances indicate that source inversions of thrust events may slightly underestimate the slip at shallow depths

the guitiriz granite variscan belt of northern spain extension controlled emplacement of magma during tectonic escape abstract the ollo de sapo domain of the northern part of the variscan belt of spain contains precambrian and ordovician metamorphic rocks intruded by the guitiriz granite the domain is bounded by two n s transcurrent shear zones detailed structural and anisotropy of magnetic susceptibility studies of the guitiriz pluton reveal a syntectonic emplacement relative to movement on the two n s trending bounding shear zones characterized by 1 development of n s trending structural and magnetic fabrics 2 concordant structures in granites and country rocks and 3 development of shear zones along the east and west granite margins gravity data show two roots trending 110 e extending down to 4 5 km from an otherwise thin

mid late pleistocene osl chronology in western amazonia and implications for the transcontinental amazon pathway abstract the origin of the transcontinental amazon drainage system remains unrevealed sedimentary deposits formed from the neogene in the amazonas and solimoes basins constitute natural archives for reconstructing this event in space and time however paleoenvironmental and chronological analyses focusing on these deposits or even their basic mapping are still scarce to allow such investigation in this context primary interests are fluvial strata related to the lithostratigraphic ica formation mapped over a widespread area in western amazonian lowlands although long regarded as plio pleistocene in age this unit has not yet been dated and its overall depositional setting remains largely undescribed the main goal of the present work is to contribute for improving facies analysis and chronology of these deposits approaching an area in southwestern amazonia and another in northern amazonia which are located more than 1000 km apart despite this great distance the sedimentological and chronological characteristics of deposits from these two areas are analogous hence facies analysis revealed paleoenvironments including active channel abandoned channel point bar crevasse splay and floodplain which are altogether compatible with meandering fluvial systems similarly optically stimulated luminescence osl dating revealed thirty three ages ranging from 65 4 16 9 to 219 6 25 1 ky in addition to three outliners of 54 0 7 6 337 3 36 9 and 346 6 48 6 ky and nine 97 1 9 9 to 254 8 23 8 ky for the areas in southwestern and northern amazonia respectively these data lead to establish that deposits mapped as ica formation over a vast area of western brazilian amazonia have a mid late pleistocene age rather than the previously inferred plio pleistocene age it follows that if plio pleistocene deposits exist in this region they remain to be dated and must be restricted to a narrow belt in western amazonia as well as isolated occurrences underlying the mid late pleistocene strata characterized herein the combination of data from this work with previously published provenance studies supports main andean sediment sources only in the mid late pleistocene it is proposed that before this time the amazon river was restricted to eastern amazonia being separated from western amazonian drainage basins due to the presence of the purus arch erosion and or subsidence of this geological feature would have promoted the connection of these drainage systems ultimately with the expressive record of the transcontinental amazon pathway into the atlantic ocean in the mid late pleistocene

some kinematical patterns leading to the formation of similar folds abstract a new mechanism named heterogeneous rotation shear is defined to explain the development of similar folds it is based on the heterogeneous distribution of a type of deformation in which a line rotates without length change and another maintains constant its direction and length pure rotation shear or undergo a constant stretching through the rock rotation shear with area correction with these constraints a kinematical numerical model of similar folds is developed the mechanism produces a divergent pattern of the major axis directions of the strain ellipses throughout the fold which does not agree with the usual axial plane cleavage of natural similar folds the operation of layer parallel shortening is necessary to solve this problem this shortening agrees with the incompetent character of the rocks where similar folds develop eventually fold flattening can modify the fold shape whilst maintaining the similar geometry the model is applied to explain the development of a natural similar fold indicating that this could be formed by a combination of layer parallel shortening and heterogeneous rotation shear finally three types of similar or sub similar folds have been distinguished a sub similar folds formed by intense flattening of parallel folds b sub similar folds formed by simple shear acting on previous perturbations and c similar folds produce by layer parallel shortening and heterogeneous rotation shear

spectral element simulations of long term fault slip effect of low rigidity layers on earthquake cycle dynamics we develop a spectral element method for the simulation of long term histories of spontaneous seismic and aseismic slip on faults subjected to tectonic loading our approach reproduces all stages of earthquake cycles nucleation and propagation of earthquake rupture postseismic slip and interseismic creep we apply the developed methodology to study the effects of low rigidity layers on the dynamics of the earthquake cycle in 2 d we consider two cases small m 1 earthquakes on a fault surrounded by a damaged fault zone and large m 7 earthquakes on a vertical strike slip fault that cuts through shallow low rigidity layers our results indicate how the source properties of repeating earthquakes are affected by the presence of a damaged fault zone with low rigidity compared to faults in homogeneous media we find 1 reduction in the earthquake nucleation size 2 amplification of slip rates during dynamic rupture propagation 3 larger recurrence interval and 4 smaller amount of aseismic slip based on linear stability analysis we derive a theoretical estimate of the nucleation size as a function of the width and rigidity reduction of the fault zone layer which is in good agreement with simulated nucleation sizes we further examine the effects of vertically stratified layers e g sedimentary basins on the nature of shallow coseismic slip deficit our results suggest that low rigidity shallow layers alone do not lead to coseismic slip deficit while the low rigidity layers result in lower interseismic stress accumulation they also cause dynamic amplification of slip rates with the net effect on slip being nearly zero

nucleation of large earthquakes determined by the seismic aseismic boundary agreement between models and observations abstract using a slip dependent constitutive law we investigate how the seismic aseismic boundary determines the nucleation process of large earthquakes we model the depth variation of the breakdown strength drop and the critical weakening displacement on the basis of several studies by ohnaka and co workers in this model the breakdown strength drop increases linearly with depth in an unstable seismogenic zone and decreases sharply in a seismic aseismic transition at the bottom of the seismogenic zone on the other hand the critical weakening displacement is almost constant in the seismogenic zone and increases sharply with depth in the seismic aseismic transition at the bottom of the seismogenic region as the fracture energy remains constant it has been reported that large intra plate earthquakes appear to initiate at the place where the cut off depth of seismicity changes sharply we examine a case in which there is a steep depth change in the seismic aseismic transition at the bottom of the seismogenic region the results of the simulation show two stages of the accelerating slip slip velocity enhancement widely along the seismic aseismic transition at the bottom of the seismogenic region and subsequent localized accelerated slip in the region of a steep depth change in the seismic aseismic transition at the bottom of the seismogenic region the first stage of the accelerating slip will be important for the intermediate term earthquake prediction we also consider a broad aseismic weak zone in the seismogenic zone in this case first slip velocity is enhanced in a broad weak zone then nucleation starts at lower corner of the surrounding strong region our numerical results can explain the location of rupture initiation of some recent large earthquakes

low p metamorphism following a barrovian type evolution complex tectonic controls for a common transition as deduced in the mondonedo thrust sheet nw iberian massif the mondonedo thrust sheet has been studied to investigate the complex dynamic relationships that may be involved in the development of low and medium p metamorphic domains this unit underwent an initial medium p event during the initial stages of variscan convergence related to crustal thickening subsequently the thrust sheet evolved to a low p baric type of metamorphism related to syn convergence thinning and exhumation its footwall cropping out in two tectonic windows registered a different evolution with a low p history that evolved from low to high t under a high geothermal gradient several different p t paths of the mondon edo thrust sheet and its relative autochthon are traced and interpreted according to the structural evolution of the area following the initial crustal thickening two main syn convergence extensional shear zones developed one of them occurs in the hangingwall whereas the other affects the footwall unit both extensional shear zones were contemporaneous with ductile thrusting in the inner parts of the thrust sheet and their activity is viewed as a consequence of the need for gravitational re equilibration within the orogenic wedge the most commonly accepted models of tectonothermal evolution in regions of thickened continental crust assume that low p metamorphism is essentially a late phenomenon and is linked to late orogenic tectonic activity in the mondon edo thrust sheet our conclusions indicate that low p metamorphism may also develop during convergence and that this may occur in at least two cases one is tectonic denudation of an allochthonous unit during its emplacement and the other thinning and extension at the footwall unit of an advancing thrust sheet as a consequence the low p evolution may show different characteristics in different units of an orogenic nappe pile

breakdown in power law scaling in an analogue model of earthquake rupture and stick slip the gutenberg richter relationship for earthquakes in both global and fault specific seismicity has been interpreted as an indication of self similarity for events of all magnitudes it is observed however that the linear extrapolation of this relationship to high magnitude often fails to predict the frequency of occurrence of large events earthquake hazard cannot generally be predicted solely by examination of microseismicity it has been postulated that this break in power law scaling is due to a change in the rupture mechanism as the size of the rupture becomes larger than the thickness of the seismogenic layer here we examine the scaling of earthquake like failures in an analogue model consisting of an elastic solid confined and driven by a steel stressing apparatus sensors embedded in the solid close to the interface with a rough substrate measure local strain and allow the examination of rupture scaling and moment release the frequency magnitude distribution for events is a power law at low magnitude but exhibits enhancement for high energy events which is consistent with a characteristic earthquake model we show unambiguously that this break in scaling corresponds to ruptures whose diameter is equal to the smaller dimension of the model fault

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

shear band foliation as an indicator of sense of shear field observations in central spain the macizo de nevera a paleozoic basement inlier surrounded by essentially flat lying mesozoic cover rocks of central spain exhibits an extremely consistent system of steep dextral strike slip faults different faults have a variable amount of displacement but their en echelon arrangement and similar sense of displacement imply a cogenetic origin a maximum displacement of 1 0 km corresponding to an averaged angular shear strain of 1 5 and peak values of 6 6 occurs along the central part of the 6 km long truchas ductile shear zone an early axial plane cleavage is locally deflected into the truchas shear zone and superposed by coarse shear band foliation the consistent angular relationship between the new foliation and the shear zone boundary confirms the megascopic sense of shear

spatial distribution of stress and frictional strength along the interplate boundary in northern japan and its correlation to the locations of large earthquakes abstract we investigate spatial distribution of stress along the interplate boundary between pacific and okhotsk plates in tohoku and hokkaido regions northern japan from earthquake focal mechanisms compiled from the national institute for earth science and disaster prevention nied of japan the interplate boundary in this work is inferred as the surface defining the upper boundary of the double seismic zone benioff zone to investigate spatial variation in stress field we divide the interplate boundary into 20 km 20 km subfaults and estimate stress field in each subfault of 10 km thickness we find clear spatial variation in stress state along the subduction zone of the pacific plate in northern japan though most of the study area is characterized by trench normal uniaxial compression in the hidaka collision zone the signature of collision between the kurile and japan arcs is evident in terms of radial compression distribution of the angle between the maximum principal stress direction and the fault normal shows that the large subduction earthquakes have occurred in the region where this angle varies between 30 and 45 however in the case of recent m9 1 2011 tohoku oki earthquake this correlation is not observed we further investigate the frictional strength along the interplate boundary our results suggest 1 the fault segments with between 30 and 45 are frictionally strong with friction coefficients between 0 6 and 0 8 2 the fault segments with between 45 and 62 are intermediately strong with friction coefficients between 0 4 and 0 6 and 3 the fault segments with above 62 are weak with friction coefficients below 0 4

rock friction and its implications for earthquake prediction examined via models of parkfield earthquakes abstract the friction of rocks in the laboratory is a function of time velocity of sliding and displacement although the processes responsible for these dependencies are unknown constitutive equations have been developed that do a reasonable job of describing the laboratory behavior these constitutive laws have been used to create a model of earthquakes at parkfield ca by using boundary conditions appropriate for the section of the fault that slips in magnitude 6 earthquakes every 20 30 years the behavior of this model prior to the earthquakes is investigated to determine whether or not the model earthquakes could be predicted in the real world by using realistic instruments and instrument locations premonitory slip does occur in the model but it is relatively restricted in time and space and detecting it from the surface may be difficult the magnitude of the strain rate at the earth s surface due to this accelerating slip seems lower than the detectability limit of instruments in the presence of earth noise although not specifically modeled microseismicity related to the accelerating creep and to creep events in the model should be detectable in fact the logarithm of the moment rate on the hypocentral cell of the fault due to slip increases linearly with minus the logarithm of the time to the earthquake this could conceivably be used to determine when the earthquake was going to occur an unresolved question is whether this pattern of accelerating slip could be recognized from the microseismicity given the discrete nature of seismic events nevertheless the model results suggest that the most likely solution to earthquake prediction is to look for a pattern of acceleration in microseismicity and thereby identify the microearthquakes as foreshocks

large extensional structures developed during emplacement of a crystalline thrust sheet the mondonedo nappe nw spain the mondonedo nappe is a crystalline thrust sheet characterized by large recumbent folds regional intermediate pressure metamorphism synkinematic intrusion of granitoids during nappe emplacement and an extensional ductile shear zone developed within the nappe during thrusting a large tectonic window permits the study of the footwall unit revealing another extensional shear zone contemporaneous with thrusting and a low pressure metamorphic evolution in contrast to that of the hanging wall unit the two main extensional shear zones produced e w extension parallel to the direction of orogenic shortening and normal to the orogenic structural trend furthermore subordinate n s longitudinal extension was accommodated by normal faults in the footwall and some of these faults were used as lateral ramps in late stages of thrusting the role of the extensional shear zones and faults described is discussed in the context of an evolving orogenic wedge dominated by plate convergence but characterized by large scale rheological heterogeneities within it deep seated viscous flow triggered by heat accumulation seems to account for the horizontal stretching and probable tapering of the orogenic wedge which was induced by gravitational instabilities due to partial melting and underplating by buoyant continental crust

comment on frechen et al late pleistocene fluvial dynamics in the hochrhein valle and in the upper rhine graben chronological frame

challenges involved in obtaining luminescence ages for long records of aridity examples from the arabian peninsula abstract in the last 35 years luminescence dating has provided a large database of ages for the deposition of dunes in desert environments over 380 ages have been generated for dunes from the arabian peninsula and demonstrate episodic dune deposition in the late quaternary but give a less clear pattern prior to 50 ka interpreting databases of luminescence ages faces two issues first the precision of luminescence ages in the last 50 ka is between 5 and 10 but for older ages the uncertainties may be much larger as luminescence signals reach saturation second different luminescence signals from quartz and from feldspar have been used over the last 35 years as the method has developed and expanded these different signals have different saturation limits and different rates at which they are reset by exposure to daylight at deposition approaches which focus on the most light sensitive signals e g quartz osl are better suited to dating recent events while those which show growth of the luminescence signal over the largest dose range e g the thermally transferred osl tt osl signal from quartz and the post infrared infrared stimulated luminescence pir irsl from feldspars have the potential to date much older events

a new method for the geometrical classification of large data sets of folds abstract the classification proposed here for folded layers is based on the use of two parameters p 1 and p 2 modified to p 1 and p 2 which are related to the variation in slope of the curves that describe orthogonal thickness vs dip each fold limb is represented by a point on a p 1 p 2 diagram from p 1 and p 2 it is possible to obtain a one dimensional statistical variable intercept value t 90 which characterizes the geometry of folds and complements the proposed classification the fold classification method suggested is easy to use and it has considerable advantages in the geometrical analysis of large sets of folds in addition it can be applied to the theoretical analysis of fold geometry to the comparative regional studies of fold and to the analysis of geometrical variations in a folded multilayer

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

anatomy of the mondonedo nappe basal shear zone nw spain this paper analyses a major shear zone from the iberian hercynian belt which forms the basal thrust of the mondonedo nappe the shear zone developed by ductile deformation under amphibolite facies metamorphic conditions and later by brittle ductile deformation in greenschists facies folds in the shear zone are asymmetric very tight 1c or similar class and frequently developing sheath geometries the sheath folds originated by non coaxial flow superimposed on earlier irregularities the fabric of quartzitic rocks in the shear zone changes from bottom to top from ultramylonites through blastomylonitic rocks to non mylonitic tectonites c axis fabrics vary across the shear zone but show a dominant monoclinic symmetry the blastomylonitic rocks include the fabrics representing the highest temperatures the main foliation of the schists results from flattening of an earlier foliation recording occasional microfolds the use of different kinematic criteria has allowed an analysis of their validity as well as an assessment of movement direction towards the foreland of the orogen

a theoretical analysis of sliding of rough surfaces 1 i used a model proposed by greenwood and williamson 1966 who analyzed closure between a rough surface and a smooth surface under normal stress to analyze the growth of slip under increasing shear stress normal stress remaining constant the two bodies are elastic half spaces one rough and one smooth and coulomb friction resists slip at sliding contacts the elastic and dissipative components of the constitutive relation in shear depend upon statistical parameters which describe the topography of the rough surface i made a parametric study of the effect of topography on the constitutive relations in shear by comparing a model in which the progress of slip at a contact is continuous with one in which the contact goes discontinuously from stuck to sliding the effect of topography was also studied by assuming that the probability density distribution of the heights of asperities is gaussian or alternatively a negative exponential these variations in topography produced only minor differences in the constitutive behavior this insensitivity of the constitutive behavior to differences in the statistical description of the topography arises in part because only relatively a small range of asperity heights is active in typical experiments work done against friction introduces a dissipative component into the constitutive behavior which i evaluated analytically i show that the components have a simple graphical construction on plots of shear stress versus displacement developed from experimental observations sliding in the reverse sense which occurs when the applied shear stress is relaxed is analyzed resulting in expressions which describe the shape of hysteresis loops formed when shear stress is cycled introducing measurements made on surfaces of specimens of granite and quartzite into the theoretical relations i found reasonable agreement with experimental data

the concept of steady state foliation abstract a steady state foliation is thought of as a foliation with constant orientation and intensity in a rock undergoing steady state flow the problem discussed is whether such straininsensitive foliations exist in rocks and how they might be distinguished from the more familiar strain sensitive foliations steady state foliations would be useful indicators of stress or of strain rate yet misleading if used as indicators of finite strain one requirement for maintenance of steady state foliations is operation of processes that locally weaken grain shape preferred orientation or reduce grain aspect ratios or destroy lithological layering during flow these are the inverses of the processes normally discussed in connection with foliation development many such processes are known though the details of how and when they operate efficiently enough to stabilize a foliation are unknown there is however a tendency for some of them to operate more efficiently at high strains high temperatures and in flow regimes with high vorticity natural and experimental high temperature shear zones are accordingly one environment in which steadystate foliations may be encountered an experiment is described in which a thin specimen of para dichlorobenzene was given a large shearing deformation at 90 of its absolute melting point a steady state foliation was not produced but the technique is a promising one for further microstructural studies where in situ observation of material undergoing large deformations is desirable

secondary cleavages in ductile shear zones abstract secondary cleavages developed at late stages in ductile shear zones show several features that are inconsistent with progressive simple shear in the zone these are the orientation of a single secondary cleavage oblique to the shear zone boundaries conjugate sets with opposite senses of shear and multiple sets with the same sense of shear these features can be explained if the bulk flow is partitioned into slip along discrete failure planes parallel to the primary foliation s coaxial stretching along the foliation and spin

recumbent folds key structural elements in orogenic belts abstract this review has two main parts the first of them presents existing ideas and data related to recumbent folds reviewing aspects such as the physical conditions of the development of these folds the strain inside the folded layers the kinematic mechanisms of their formation the role of gravitational forces the tectonic context of their development and the structures associated with them in the second part the above ideas are discussed and possible mechanisms for the development of these folds are presented it is proposed that initial perturbations of the layers are essential to give rise to the asymmetry of recumbent folds these perturbations may be non planarities of the layering or may be linked to the existence of a core or basement of competent rock that hinders the normal propagation of the deformation this could explain why many large recumbent folds have a root zone deformation with an important component of simple shear is a general condition for the formation of recumbent folds in areas with very low grade metamorphism competent layers often play an active role during the deformation and undergo buckling with the development of an overturned fold limb which can be stretched and thinned to finally produce a pair of recumbent folds separated by a thrust in areas with low or medium metamorphism buckling under a simple shear regime is probably the most important mechanism for producing large folds with gentle or moderately dipping axial surfaces subsequent kinematic amplification by coaxial strain components with vertical maximum shortening is important for the formation of recumbent folds these components involve a sub horizontal stretching that can cause a problem of strain compatibility and give rise to a basal thrust in areas deformed under high p and t conditions recumbent folds can develop by flow perturbations and kinematic amplification of folds this is probably a common mechanism in ductile shear zones

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

geochronological osl and geomorphological investigations at the presumed frankfurt ice marginal position in northeast germany abstract the weichselian frankfurt ice marginal position in northeast germany has been critically discussed in the past owing to weak morphological evidence and a lack of clear sedimentological records this study aims to contribute to this discussion with new geochronological and geomorphological results apart from very few cosmogenic exposure ages the time frame is to date still based on long distance correlation with radiocarbon chronologies we selected a study site in a key position regarding the classic location of the frankfurt ice marginal position and the recently described arcuate ridge structures on the barnim plateau for the first time we present optically stimulated luminescence osl ages of quartz from glaciofluvial deposits for this weichselian phase our results indicate an advance of the scandinavian ice sheet sis at around 34 1 4 6 ka this is in agreement with osl ages from sandur deposits at the brandenburg ice marginal position located farther south and could also be correlated with the klintholm advance in denmark the subsequent meltdown phase lasted until around 26 3 3 7 ka during the meltdown phase a minor oscillation of the sis caused the formation of the recently described arcuate ridges on the barnim till plain recalculated surface exposure ages of glacigenic boulders with an updated global production rate indicate a landscape stabilization phase at around 22 7 1 6 ka which is in agreement with our ages a phase of strong aeolian activity has been dated with osl to 1 0 1 ka this may have been triggered by human activities that are documented in this region for the medieval period

progressive refolding in ductile shear zones abstract the foliation formed in a ductile shear zone can become folded by continuing shear in the zone without the foliation having to enter the shortening sector of the flow field if the foliation lies parallel to the shear plane infinitesimal variations in the rate of shear strain cause compensating rotations that may amplify into folds small increases in the rate cause backward rotations counter to the sense of shear these do not amplify small decreases cause forward rotations that do amplify

space and time in the tectonic evolution of the northwestern iberian massif implications for the variscan belt recent advances in geochemical studies of igneous rocks isotopic age data for magmatism and metamorphism quantitative pressure temperature p t estimates of metamorphic evolution and structural geology in the northwestern iberian massif are integrated into a synthesis of the tectonic evolution that places the autochthonous

new kinematic constraints on the cantabrian orocline a paleomagnetic study from the penalba and truchas synclines nw spain abstract the cantabrian orocline is a large structure that bends the variscan orogen of western europe in nw iberia the extensively studied kinematics of its core the foreland of the orogen indicates that the structure is secondary i e acquired after the formation of the orogenic edifice however the extent of the cantabrian orocline away from its core is under debate in this paper we study the kinematics of the cantabrian orocline beyond the foreland we collected and analyzed samples from the northern and central parts of the truchas syncline which provides new data within the hinterland of the orogen in nw iberia the analysis of 320 samples shows a late carboniferous remagnetization with an e to ne declination and shallow downward inclinations these results suggest a counter clockwise rotation of 60 and peri equatorial but still southern hemisphere latitude for iberia during the uppermost carboniferous early permian this rotation fits with the expected kinematic evolution of the truchas syncline if it indeed was part of the cantabrian orocline

asperity generation and its relationship to seismicity on a planar fault a laboratory simulation author s selvadurai pa glaser sd abstract the authors 2016 published by oxford university press on behalf of the royal astronomical society earthquake faults and all frictional surfaces establish contact through asperities a detailed knowledge of how asperities form will enable a better understanding of the manner in which they communicate during foreshock failure sequences that are observed leading to the larger main shock we present results of experiments where a pressure sensitive film was used to map size and measure the magnitudes of the normal stresses at asperities along a seismogenic section of a laboratory simulated fault we measured seismicity acoustically and foreshocks were found to be the result of localized asperity failure during the nucleation phase of gross fault rupture since surface roughness plays an important role in how asperities are formed two hurst exponents were measured to characterize a highly worn interface using roughness profiles i long wavelength estimates h 0 45 and ii short wavelength estimates h 0 8 1 2 the short wavelength roughness estimates were computed at the scale of single asperity junction points macroscopically the number of asperities and real contact area increased with additional application of normal force while the mean normal stress remained constant the ratio of real to nominal contact area was low ranging from 0 02 l ar a0 l 0 05 predicting that the asperities should be elastically independent of each other results from the pressure sensitive film showed that asperities were closely spaced and could not be treated as mechanically independent larger asperities carried both higher levels of average normal stress and higher levels of normal stress heterogeneity than smaller ones using linear stability theorem the critical slip distance on foreshocking asperities was estimated to be d0 0 65 3 m the critical slip distance d0 was 1 8 11 5 per cent of the premonitory slip needed to initiate gross fault rupture of the interface 20 40 m and the overall slip necessary to initiate gross fault rupture was on the order of the average asperity diameter 52 m foreshocks may be due to a change in the critical slip distance at localized sections of the fault caused by the two distinct roughness profiles measured at short and long length scales

seismicity on a fault controlled by rate and state dependent friction with spatial variations of the critical slip distance 1 we perform systematic simulations of slip using a quasi dynamic continuum model of a two dimensional 2 d strike slip fault governed by rate and state dependent friction the depth dependence of the a b and l frictional parameters are treated in an innovative way that is consistent with available laboratory data and multidisciplinary field observations various realizations of heterogeneous l distributions are used to study effects of structural variations of fault zones on spatiotemporal evolution of slip we demonstrate that such realizations can produce within the continuum class of models realistic features of seismicity and slip distributions on a fault we explore effects of three types of variable l distributions 1 a depth dependent l profile accounting for the variable width of fault zones with depth 2 uncorrelated 2 d random distributions of l with different degrees of heterogeneity and 3 a hybrid distribution combining the depth dependent l profile with the 2 d random l distributions the first type of l distribution with relatively small l over the depth range corresponding to the seismogenic zone and larger l elsewhere generates stick slip events in the seismogenic zone and ongoing creep above and below that region the 2 d heterogeneous parameterizations generate frequency size statistics with event sizes spanning 4 orders of magnitude our results indicate that different degrees of heterogeneity of l distributions control 1 the number of simulated events and 2 the overall stress level and fluctuations other observable trends are 3 the dependency of hypocenter location on l and 4 different nucleation phases for small and large events in heterogeneous distributions

modeling high stress drops scaling interaction and irregularity of repeating earthquake sequences near parkfield repeating earthquake sequences have been actively investigated to clarify many aspects of earthquake physics the two particularly well studied sequences known as the los angeles and san francisco repeaters have several intriguing observations including their long for the seismic moment recurrence times that would suggest stress drops of 300 mpa based on typical assumptions near syncronized timing prior to 2004 and higher than typical inferred stress drops of 25 to 65 mpa up to 90 mpa locally but not as high as the recurrence times suggest here we show that all these observations are self consistent in the sense that they can be reproduced in a single fault model the suitable models build on the standard rate and state fault models with velocity weakening patches imbedded into a velocity strengthening region by adding either enhanced dynamic weakening during seismic slip or elevated normal stress on the patches or both to allow for the higher stress drops such models are able to match the observed average properties of the san francisco and los angeles repeaters as well as the overall nontrivial scaling between the recurrence time and seismic moment exhibited by many repeating sequences as a whole for reasonable parameter choices based on experiments and theoretical studies these models are characterized by the occurrence of substantial and variable aseismic slip at the locations of the repeating sources which explains their atypical relation between recurrence interval and seismic moment induces variability in the repeating source properties as observed and results in their neither slip nor time predictable behavior

a high resolution late quaternary depositional history and chronology for the southern portion of the lake mungo lunette semi arid australia abstract the willandra lakes region sits on the southern margin of australia s arid core and is one of the oldest localities on the continent known to have been occupied by australia s first people the archaeological traces that accumulated in the lake mungo lunette paint a picture of changing land use over the past 50 thousand years ka and some of these are likely to have been responses to changes in palaeoenvironmental conditions this study set out to determine the finest temporal resolution that can be used to study the depositional and palaeoenvironmental history of the lake mungo lunette the investigation focused on the depositional history documented within stratigraphy exposed in an eroding gully in the southern part of the lunette gully 10 a stratigraphic framework was developed using sedimentological and soil micromorphological analysis this framework was then fixed in time by 56 single grain optically stimulated luminescence osl age estimates these data sets were then combined into a bayesian model that indicated three depositional phases 100 ka lu1 65 33 ka lu2 lu3 and from 30 to 16 ka lu4 lu9 with the late pleistocene and holocene samples lu10 11 not being modelled furthermore the redating of thirteen lower and upper mungo osl samples from bowler et al 2003 s study of the southern tip of the lunette yielded younger age estimates for twelve of these bringing them into line with previously published independent age control as well as the ages presented in this study this study provides an approach for future efforts to establish consistency in age estimation and palaeoenvironmental interpretation along the length of the lunette

the role of late pleistocene holocene tectono sedimentary history on the origin of patches of savanna vegetation in the middle madeira river southwest of the amazonian lowlands abstract savanna patches are features of the amazonian landscape that have been long under intense debate but there are still questions about the main factors that have determined their establishment and evolution within the rainforest matrix in particular their geological substrates were poorly documented the aim of this work is to reconstruct the tectono sedimentary history of four savanna patches in the middle madeira river southwest amazonia and discuss its potential control over the development of the savanna communities the approach consisted in the integration of geomorphological sedimentological chronological and floristic data the results revealed that the savanna substrates are sandy deposits aged between 118 9 and 35 6 ky overlain by late pleistocene to holocene muddier successions

nucleation process of magnitude 2 repeating earthquakes on the san andreas fault predicted by rate and state fault models with safod drill core data recent laboratory shear slip experiments conducted on a nominally flat frictional interface reported the intriguing details of a two phase nucleation of stick slip motion that precedes the dynamic rupture propagation this behavior was subsequently reproduced by a physics based model incorporating laboratory derived rate and state friction laws however applying the laboratory and theoretical results to the nucleation of crustal earthquakes remains challenging due to poorly constrained physical and friction properties of fault zone rocks at seismogenic depths here we apply the same physics based model to simulate the nucleation process of crustal earthquakes using unique data acquired during the san andreas fault observatory at depth safod experiment and new and existing measurements of friction properties of safod drill core samples using this well constrained model we predict what the nucleation phase will look like for magnitude 2 repeating earthquakes on segments of the san andreas fault at a 2 8 km depth we find that despite up to three orders of magnitude difference in the physical and friction parameters and stress conditions the behavior of the modeled nucleation is qualitatively similar to that of laboratory earthquakes with the nucleation consisting of two distinct phases our results further suggest that precursory slow slip associated with the earthquake nucleation phase may be observable in the hours before the occurrence of the magnitude 2 earthquakes by strain measurements close a few hundreds meters to the hypocenter in a position reached by the existing borehole

successive development of plane noncylindrical folds in progressive deformation in the history of superposed deformations of the iron formations at the western border of the kolar gold field in s india an important event was the successive growth of broadly coaxial plane noncylindrical folds in course of a progressive deformation concomitant with development of ductile mesoscopic shear zones the noncylindrical folds were initiated as active folds by the creation of a buckling instability at successive stages on newly developed foliation surfaces the nucleation of noncylindrical folds and the subsequent axial plane folding of the tightened mature folds are explained by the mechanical inhomogeneity of the rocks and the heterogeneous character of strain the correlation between increasing tightness and increasing noncylindricity of the folds indicates that the initial curvatures of hinge lines were accentuated by an extension parallel to the subhorizontal stretching lineation from the patterns of deformed lineations over folds of varying tightnesses it is concluded that the passive accentuation of hinge line curvatures was mostly achieved when the folds had already become isoclinal or very tight

quartz fabric and strain partitioning in sheath folds an example from the voltri group western alps italy abstract a mesoscopic sheath fold defined by an almost pure quartzitic level in quartz mica schists of the voltri group southeastern border of the western alps was sampled and studied in detail microstructural analysis was carried out on thin sections from different structural domains in the quartzitic layer with the emphasis to analyse quartz shape fabrics and the crystallographic preferred orientation of the c axes of this mineral quartz was dynamically recrystallized but its degree of preferred orientation is not as high as it would be expected in a high shear strain regime required for the development of sheath folds this may suggest strain partitioning between the quartzitic level and the micaceous matrix crystallographic preferred orientation of c axes and grain shape fabric asymmetry indicate the same sense of shear on both fold limbs in the xz plane this is in agreement with a model of sheath fold development by the passive rotation of material lines clustering of the c axis poles shows a configuration indicative of a different strain state in different domains of the sheath fold and suggests an evolution of the fold characterized by combined simple shear and coaxial progressive deformation

late quaternary aeolian and fluvial aeolian deposits from southwestern pampas of argentina southern south america abstract the central region of argentina southern south america is characterized by an extensive quaternary aeolian record in this context three locations from the southwestern pampas an andean foreland region bearing a rich fossil mammal record that contributed to the south america biostratigraphic scheme were selected to carry out a comprehensive sedimentological analysis of the late quaternary deposits the case studies are located at the transverse valleys of la pampa province chapalco quehue and utracan argentino valleys and exhibit a high resolution of the late quaternary in comparison with others areas of the southwestern pampas the toay locality 36 41 s 64 24 w records aeolian dominant activity since the end of the late pleistocene 30 ka onwards soil formation at some point during the holocene and early mid 20th century reactivation of aeolian process the arroyo quehue locality 37 04 s 64 42 w presents a late pleistocene holocene succession mostly related to an ephemeral endorheic fluvial system with an interval of relative surface stabilization and aeolian aggradation during the late holocene the utracan locality 37 17 s 64 35 w exhibits a prevailing aeolian and fluvial aeolian interaction succession developed in the mid to late holocene in a sand mud flat environment of a shallow saline lake the three studied cases are representative of aeolian aggradation in association with ephemeral fluvial shallow lake and pedogenic processes in a currently subhumid dry region numerical ages indicate sedimentation during the last 30 kyr they allow constraining and evaluating the paleoenvironmental conditions in this inland region of southern south america and provide age constraints for the regional databases of paleoclimatic proxies the results are in agreement with other late quaternary paleoclimatic paleoenvironmental archives of central argentina and show a fragile aeolian landscape that is susceptible to deterioration under extreme conditions including both aeolian reactivation during dry phases and erosion of sandy silty sediments during wet phases

tubular folds and sheath folds definitions and conceptual models for their development with examples from the grapesvare area northern sweden abstract two parameters are used in the classification of highly non cylindrical folds the hinge line angle and the ratio of the length of the cone axis to that of the long axis of the cross section of the structure at the position where the hinge angle was measured if in a non cylindrical fold a cross section can be selected so that the hinge angle w measured where the cross section cuts the cone is less than 90 and the length of the cone axis x is more than a quarter of the length of the long axis y of the cross section the fold is a sheath fold a tight sheath fold with w x y 1 can be termed a tubular fold a tubular fold is thus an extreme type of sheath fold while sheath folds with w 20 but x y 0 25 but tubular folds from the grapesvare area comply to the definition given above and they occur in a structural setting that is consistent with the models described

the partitioning of deformation in flowing rock masses abstract most geological structures owe their development to heterogeneous and or non steady flow flow partitioning refers to the division of the instantaneous velocity field into components related to translation strain and rotation flow partitioning during the development of a geological structure usually changes with time and different histories of flow are involved at different points in the developing structure heterogeneity leads to the development of flow domains with different characteristics notably the degree of non coaxiality of deformation and different partitionings of the rotational component of flow into shear induced vorticity and spin during non steady flow there is often continual repartitioning of vorticity between the spin and shear induced components spin is an important aspect of flow leading to the development of structure this paper discusses the partitioning of deformation in a flowing rock mass coaxial flow tends to occur in isotropic materials in regions near weakly constrained boundaries non coaxial flow is favoured by suitably oriented material anisotropy and or the presence of well defined boundary constraints involving parallel relative displacements a developing anisotropy e g a crystallographic fabric in a shear zone can induce a change from coaxial to non coaxial flow other effects are related to the scale of approximation for example bulk shear induced vorticity can be locally converted to spin flow in the crust and mantle of the earth produces geological structures on all scales and involves many different types of rheological response the factors that affect flow partitioning e g spin versus non coaxial deformation are therefore of interest

structural metamorphic and magmatic history of the mondonedo nappe hercynian belt nw spain abstract the mondonedo nappe is one of the main units in the internal zone of the hercynian belt in the iberian peninsula it consists of low to medium grade metasediments late precambrian and palaeozoic in age folded by large d 1 e verging recumbent structures and thrusted several tens of km towards the east during a d 2 deformation episode at the base of the thrust sheet a shear zone of up to 3 km thick was developed granitoid bodies which were intruded after d 1 and before or during d 2 were deformed in this basal zone the geometry of d 1 and d 2 structures and that of the isograds are described as well as the relationships between metamorphism and deformation a structural evolution is inferred which shows an episode of generalized ductile deformation d 1 followed by another in which the deformation tended to concentrate in a subhorizontal ductile shear zone d 2 and culminated with the thrusting along an important fracture the shear zone originated in a thermally softened level which according to metamorphic data was at temperatures in the range 550 600 c the structural metamorphic and magmatic features of the mondonedo nappe suggest a relationship with a crustal scale overthrusting of the continental mass to which the nappe belongs this could be a consequence of the collision against another continental mass to the west

gem plate boundary simulations for the plate boundary observatory a program for understanding the physics of earthquakes on complex fault networks via observations theory and numerical simulation the last five years have seen unprecedented growth in the amount and quality of geodetic data collected to characterize crustal deformation in earthquake prone areas such as california and japan the installation of the southern california integrated geodetic network scign and the bay area regional deformation bard network are two examples as part of the recently proposed earthscope nsf geo ear mre initiative the plate boundary observatory pbo plans to place more than a thousand gps strainmeters and deformation sensors along the active plate boundary of the western coast of the united states mexico and canada http www earthscope org pbo com html the scientific goals of pbo include understanding how tectonic plates interact together with an emphasis on understanding the physics of earthquakes however the problem of understanding the physics of earthquakes on complex fault networks through observations alone is complicated by our inability to study the problem in a manner familiar to laboratory scientists by means of controlled fully reproducible experiments we have therefore been motivated to construct a numerical simulation technology that will allow us to study earthquake physics via numerical experiments to be considered successful the simulations must not only produce observables that are maximally similar to those seen by the pbo and other observing programs but in addition the simulations must provide dynamical predictions that can be falsified by means of observations on the real fault networks in general the dynamical behavior of earthquakes on complex fault networks is a result of the interplay between the geometric structure of the fault network and the physics of the frictional sliding process in constructing numerical simulations of a complex fault network we will need to solve a variety of problems including the development of analysis techniques also called data mining data assimilation space time pattern definition and analysis and visualization needs using simulations of the network of the major strike slip faults in southern california we present a preliminary description of our methods and results and comment upon the relative roles of fault network geometry and frictional sliding in determining the important dynamical modes of the system

variability of earthquake nucleation in continuum models of rate and state faults and implications for aftershock rates using two continuum models of rate and state faults one with a weaker patch and the other with rheological transition from steady state velocity weakening to velocity strengthening friction we simulate several scenarios of spontaneous earthquake nucleation plausible for natural faults investigate their response to static shear stress steps and infer the corresponding aftershock rates overall nucleation processes at weaker patches behave similarly to theories based on spring slider models with some notable deviations in particular nucleation and aftershock rates are affected by normal stress heterogeneity in the nucleation zone nucleation processes at rheological transitions behave differently producing complex slip velocity histories nonmonotonic responses to static stress changes and aftershock rates with pronounced peaks and seismic quiescence for such processes positive stress steps sometimes delay nucleation of seismic events by inducing aseismic transients that relieve stress and postpone seismic slip superposition of the complex aftershock response for spatially variable stress changes results in omori s law for a period of time followed by seismic quiescence such behavior was observed at the base of the seismogenic zone near the 1984 morgan hill earthquake we show that the computed aftershock rates are linked to unperturbed slip velocity evolution in the nucleation zone and construct simplified analytical scenarios that explain some features of the response the qualitative differences that we find between the two nucleation models indicate that aftershock response of rate and state faults to static stress changes would depend on the conditions under which nucleation occurs on natural faults and may be different from predictions based on spring slider models

foreshocks during the nucleation of stick slip instability 1 we report on laboratory experiments which investigate interactions between aseismic slip stress changes and seismicity on a critically stressed fault during the nucleation of stick slip instability we monitor quasi static and dynamic changes in local shear stress and fault slip with arrays of gages deployed along a simulated strike slip fault 2 m long and 0 4 m deep in a saw cut sample of sierra white granite with 14 piezoelectric sensors we simultaneously monitor seismic signals produced during the nucleation phase and subsequent dynamic rupture we observe localized aseismic fault slip in an approximately meter sized zone in the center of the fault while the ends of the fault remain locked clusters of high frequency foreshocks mw 6 5 to 5 0 can occur in this slowly slipping zone 5 50 ms prior to the initiation of dynamic rupture their occurrence appears to be dependent on the rate at which local shear stress is applied to the fault the meter sized nucleation zone is generally consistent with theoretical estimates but source radii of the foreshocks 2 to 70 mm are 1 to 2 orders of magnitude smaller than the theoretical minimum length scale over which earthquake nucleation can occur we propose that frictional stability and the transition between seismic and aseismic slip are modulated by local stressing rate and that fault sections which would typically slip aseismically may radiate seismic waves if they are rapidly stressed fault behavior of this type may provide physical insight into the mechanics of foreshocks tremor repeating earthquake sequences and a minimum earthquake source dimension

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

frictional behavior and its seismological implications within thrusts in the shallow portion of an accretionary prism abstract the emi group in the boso accretionary complex is reported to have experienced a relatively shallow burial depth approximately 1 4 km below the sea floor at low temperature 50 75 c indicating that the group passed through or around the upper portion of the seismogenic zone two representative thrusts in the group were recognized as products of deformations in the setting frictional experiments using the powder samples from the fault zones showed the frictional behavior of velocity hardening under the wet condition with 20 mpa and 40 mpa normal stresses microstructures within the thrusts exhibited pervasive deformation with composite planer fabrics this results that the shallow portion of the thrust at the base of the accretionary prism is aseismic with stable sliding

scaling of the shear rupture process from nucleation to dynamic propagation implications of geometric irregularity of the rupturing surfaces a series of systematic high resolution laboratory experiments have been performed on the nucleation of propagating slip failure on preexisting faults having different surface roughnesses to demonstrate how the size scale and duration of shear rupture nucleation are affected by geometric irregularity of the rupturing surfaces on the basis of the experimental results it has been discussed theoretically how consistently scale dependent physical quantities inherent in shear rupture are scaled the experiments led to conclusive results that the nucleation process consists of two phases phase i an initial quasi static phase and phase ii a subsequent accelerating phase and that the nucleation process is greatly affected by geometric irregularities on the rupturing surfaces in phase i the rupture grows at a slow steady speed which is independent of the rupture growth length l in contrast during phase ii the rupture develops at accelerating speeds v which increase with an increase in l obeying a power law v vs l c n where vs is the shear wave velocity c is the characteristic length representing the geometric irregularity of the fault surfaces and and n are constants 8 87 10 29 and n 7 31 scale dependency of scale dependent physical quantities including the nucleation zone size and its duration is commonly ascribed to scale dependency of the slip dependent constitutive law parameter dc which is in turn governed by c it has been discussed that a unified comprehension can be provided for shear rupture of any size scale if the constitutive law for shear rupture is formulated as a slip dependent law

the himalayan main central thrust pile and its quartz rich tectonites in central nepal as a consequence of the india asia collision a deeply rooted crustal slice has been moved southwards over the northern boundary of the indian plate at the present level of observation the main central thrust pile a rock pile of several kilometers thickness is affected by shear deformation which imprinted a flat foliation and a constant n s trending lineation these tectonites were deformed under a wide range of metamorphic conditions grading from lower greenschists up to the sillimanite field the m c t shear zone is studied from the view point of the quartz rich rocks over 100 samples helped to define a microstructural zonation roughly parallel to the thermal one 35 samples particularly rich in quartz have been used for the preferred orientation study of their c axes and a few of them for their a axes strong lattice orientations when undisturbed by mainly secondary recrystallization attest to large plastic strains in quartz the c axes are mostly distributed along unequally populated crossed girdles which may evolve into an inclined single girdle the a axes concentrate perpendicular to the more populated girdle concerning quartz the following is suggested 1 1 the deformation has a dominant shear component responsible for the dominant stretching lineation it could be simple shear in case of inclined single girdles 2 2 one set of a axes line up parallel to the shear direction slip on various planes in the a direction may be an important deformation mechanism 3 3 asymmetry in the lattice preferred orientations could be used to predict the sense of shear for the himalayan thrusting in more than 80 of cases

effect of frictional heating on pre seismic sliding a numerical simulation using a rate state and temperature dependent friction law summary using a simple spring block model and a rate and state dependent friction law incorporating the effect of temperature variation i perform a numerical simulation of aseismic sliding prior to unstable seismic faulting i compare the simulation result of pre seismic sliding in the case where the temperature effect due to frictional heating on frictional strength is taken into consideration heated fault with the result in the case where the temperature effect is neglected unheated fault assuming model parameters appropriate for the nucleation site of a large interplate earthquake it is found that an earthquake occurrence time is a little earlier on the heated fault than on the unheated fault this is because the frictional strength is weakened by temperature rise due to frictional heating during pre seismic sliding the amplitude of precursory crustal deformation caused by pre seismic sliding on the heated fault is estimated to be about 20 per cent smaller than that on the unheated fault

discrete characteristics of the aftershock sequence of the 2011 van earthquake an intraplate earthquake of magnitude mw 7 2 occurred on a ne sw trending blind oblique thrust fault in accretionary orogen the van region of eastern anatolia on october 23 2011 the aftershock seismicity in the van earthquake was not continuous but rather highly discrete this shed light on the chaotic nonuniformity of the event distribution and played key roles in determining the seismic coupling between the rupturing process and seismogeneity i analyzed the discrete statistical mechanics of the 2011 van mainshock aftershock sequence with an estimation of the non dimensional tuning parameters consisting of temporal clusters c and the random rn distribution of aftershocks range of size scales ross strength change ed temperature t p value of temporal decay material parameter r value seismic coupling and q value of aftershock distribution i also investigated the frequency size fs temporal t statistics and the sequential characteristics of aftershock dynamics using discrete approach and examined the discrete evolutionary periods of the van earthquake gutenberg richter gr distribution my study revealed that the fs and t statistical properties of aftershock sequence represent the gutenberg richter gr distribution clustered c in time and random rn poisson distribution respectively the overall statistical behavior of the aftershock sequence shows that the van earthquake originated in a discrete structural framework with high seismic coupling under highly variable faulting conditions my analyses relate this larger dip slip event to a discrete seismogenesis with two main components of complex fracturing and branching framework of the ruptured fault and dynamic strengthening and hardening behavior of the earthquake the results indicate two dynamic cases the first is associated with aperiodic nature of aftershock distribution indicating a time independent poissonian event the second is associated with variable slip model varying loading rates and high seismic coupling along the ruptured area this study concludes that the aperiodic statistical behavior of the van aftershock sequence is one of the results of the time independent poissonian seismic deformation in the 2011 van earthquake

seismic signature of variscan and alpine tectonics in nw iberia crustal structure of the cantabrian mountains and duero basin the seismic structure of the crust of the nw iberian peninsula along the cantabrian mountains and their southern foreland the duero basin is investigated from the first data set available from refraction and wide angle reflection profiles the velocity depth distributions obtained along e w and n s transects evidence lateral variations in crustal structure that can be associated to variscan and alpine tectonic episodes the western part of the range toward the variscan hinterland zones as well as the duero basin below the sediments show a crustal structure similar to that of the variscan belt elsewere in europe the total crustal thickness is 30 32 km and three main layers upper middle and lower crust with average velocities 6 0 6 25 and 6 8 km s are resolved some paleozoic structures such as the basal detachment of the cantabrian zone are expressed in the seismic models the crust appears to vary eastward in the external zones the most outstanding feature is a crustal root beneath the highest cantabrian summits where the moho is found at 47 km depth a prominent alpine reworking of the crust in the eastern part of the cantabrian zone is thus revealed and the n s seismic transects delineate a geometry similar to the one found across the central pyrenees in the etude continentale et oceanique par reflexion et refraction sismique ecors profile revealing the importance of the alpine deformations in the northern part of the iberian plate

luminescence dating of quaternary sediments recent advances duller geoffrey 2004 luminescence dating of quaternary sediments recent advances journal of quaternary science 19 2 pp 183 192 rae2008

stress transfer in earthquakes hazard estimation and ensemble forecasting inferences from numerical simulations abstract observations indicate that earthquake faults occur in topologically complex multi scale networks driven by plate tectonic forces we present realistic numerical simulations involving data mining pattern recognition theoretical analyses and ensemble forecasting techniques to understand how the observable space time earthquake patterns are related to the fundamentally inaccessible and unobservable dynamics numerical simulations can also help us to understand how the different scales involved in earthquake physics interact and influence the resulting dynamics our simulations indicate that elastic interactions stress transfer combined with the nonlinearity in the frictional failure threshold law lead to the self organization of the statistical dynamics producing 1 statistical distributions for magnitudes and frequencies of earthquakes that have characteristics similar to those possessed by the gutenberg richter magnitude frequency distributions observed in nature and 2 clear examples of stress transfer among fault activity described by stress shadows in which an earthquake on one group of faults reduces the coulomb failure stress on other faults thereby delaying activity on those faults in this paper we describe the current state of modeling and simulation efforts for virtual california a model for all the major active strike slip faults in california noting that the working group on california earthquake probabilities wgcep uses statistical distributions to produce earthquake forecast probabilities we demonstrate that virtual california provides a powerful tool for testing the applicability and reliability of the wgcep statistical methods furthermore we show how the simulations can be used to develop statistical earthquake forecasting techniques that are complementary to the methods used by the wgcep but improve upon those methods in a number of important ways in doing so we distinguish between the official forecasts of the wgcep and the research quality forecasts that we discuss here finally we provide a brief discussion of future problems and issues related to the development of ensemble earthquake hazard estimation and forecasting techniques

a method for determining absolute ultrasonic velocities and elastic properties of experimental shear zones abstract laboratory experiments are a vital tool for assessing elastic properties of rock and determining the underlying geomechanical processes that inform large scale predictive models in some cases relative values of elastic properties are sufficient but absolute values are necessary when comparing between locations and to address upscaling from lab to field settings however determining absolute values of ultrasonic velocity and elastic parameters in laboratory experiments is often complex and hampered by apparatus design moreover measuring the evolution of elastic properties with shear deformation has proven especially difficult here we describe a method that allows measurements of p and s wave velocity as a function of shear deformation under stresses of 10 s of mpa the approach includes rigorous calibration experiments and accounts for the evolution of impedance contrasts at sample interfaces as a function of strain we describe our method by applying it to sheared layers that represent simulated fault zones composed of clay quartz mixtures and fault rocks recovered from drilling p wave arrival times range from 10 to 20 s and wave speeds are 2 4 km s during shear of layers a few mm in thickness subject to normal stress of 25 mpa and shear strains 30 travel time data for apparatus calibration are fit with rational functions and root mean square error is used to assess uncertainty wave speed varies systematically with shear stress and increases with shear strain due to comminution compaction internal strain localization and shear fabric development

fault interactions and subduction tectonics a re examination of the weber new zealand earthquake sequence of 1990 summary two moderate magnitude mw 6 2 and 6 4 earthquakes in the hikurangi subduction margin north island new zealand occurred 3 months apart in 1990 the epicentres are nearly coincident but the first weber 1 primarily normal faulting occurred within the subducting pacific plate depth about 28 km and the second weber 2 a mix of thrusting and right lateral motion occurred within the overlying australian plate depth about 13 km the plate interface in between the plate interface is interpreted to be locked trenchward se from about the position of these events with a transition to aseismic slip further down dip to the nw several stress interaction questions are examined first to see whether weber 1 triggered weber 2 a range of possible mainshock parameters are used to calculate induced changes in the static coulomb failure stress cfs in most cases the results are consistent with triggering secondly previous work showed that the rate of aftershock occurrence for weber 1 decreased markedly about 35 days before weber 2 recovering afterwards to see whether aseismic pre slip on the weber 2 fault as predicted by rate and state friction could be the cause of the decrease the same fault parameters have been used in reverse the results are ambiguous some fault parameters giving results consistent with the hypothesis and others not the amount of pre slip required for significant inhibition however is about equal to that in the mainshock and distributed over the entire fault plane thirdly observations of episodic aseismic slip down dip from locked sections of other plate interfaces are becoming more common could such slip have triggered both weber events the induced changes in cfs for such slip are uniformly positive on the weber 1 fault plane and mostly positive on the weber 2 fault plane so the answer is yes although there is no independent evidence for aseismic slip prior to the weber sequence this case shows that such slip may trigger events on other nearby faults besides loading the locked section of the plate interface static stress triggering considerations are thus likely to be important in subduction environments

fluvial geomorphology a perspective on current status and methods fluvial geomorphology seeks to study river landform history understand formative processes and predict changes using a combination of field observation experimental studies and numerical models a resurgence in fluvial geomorphology is taking place fostered for example by its interaction with river engineering and the availability of new analytical methods instrumentation and techniques these have enabled development of new applications in river management landscape restoration hazard studies river history and geoarchaeology this paper presents a perspective on recent advances in fluvial geomorphology and introduces a selection of papers presented during the fluvial geomorphology and palaeohydrology session within the sixth international conference on geomorphology held in zaragoza spain in september 2005

on the physical mechanism of silent slip events along the deeper part of the seismogenic zone 1 to investigate the mechanism of recently observed silent slip events we simulated earthquake preparation processes using the dieterich ruina rate and state dependent friction law to ensure realistic modeling of the unstable stable transition we considered small cut off velocity to an evolution effect in the friction law for the transition zone when the cut off velocity to the evolution effect is significantly smaller than that of a direct effect steady state friction behaves as velocity weakening at low slip velocity and velocity strengthening at high slip velocity this frictional behavior was experimentally and theoretically confirmed for the unstable stable transition zone the results of our numerical simulations show that silent slips of which velocity is higher than the velocity of relative plate motion eventually propagates horizontally along the unstable stable transition over a period of several years silent slip events can be interpreted as being caused by the transitional behavior of the fault constitutive law

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