asperities and barriers on the seismogenic zone in north chile state of the art after the 2007 mw 7 7 tocopilla earthquake inferred by gps and insar data the mw 7 7 2007 november 14 earthquake had an epicentre located close to the city of tocopilla at the southern end of a known seismic gap in north chile through modelling of global positioning system gps and radar interferometry insar data we show that this event ruptured the deeper part of the seismogenic interface 30 50 km and did not reach the surface the earthquake initiated at the hypocentre and was arrested 150 km south beneath the mejillones peninsula an area already identified as an important structural barrier between two segments of the peru chile subduction zone our preferred models for the tocopilla main shock show slip concentrated in two main asperities consistent with previous inversions of seismological data slip appears to have propagated towards relatively shallow depths at its southern extremity under the mejillones peninsula our analysis of post seismic deformation suggests that small but still significant post seismic slip occurred within the first 10 d after the main shock and that it was mostly concentrated at the southern end of the rupture the post seismic deformation occurring in this period represents 12 19 per cent of the coseismic deformation of which 30 55 per cent has been released aseismically post seismic slip appears to concentrate within regions that exhibit low coseismic slip suggesting that the afterslip distribution during the first month of the post seismic interval complements the coseismic slip the 2007 tocopilla earthquake released only 2 5 per cent of the moment deficit accumulated on the interface during the past 130 yr and may be regarded as a possible precursor of a larger subduction earthquake rupturing partially or completely the 500 km long north chile seismic gap

effect of fault bend on the rupture propagation process of stick slip abstract an experimental study of stick slip is performed to examine the effect of a fault bend on the dynamic rupture propagation process a granite sample used in the experiment has a pre cut fault that is artificially bent by an angle of 5 6 at the center of the fault along strike and accordingly the fault consists of two fault segments the rupture propagation process during stick slip instability is investigated by analyzing the records of shear strain and relative displacement measured with strain gauge sensors together with the hypocenters of ae acoustic emission events detected with piezoelectric transducers the observed rupture propagation process of typical stick slip events is as follows 1 the dynamic rupture started on a fault segment is stopped near the fault bend 2 the rupture propagation is restarted near the bend on the other fault segment 10 8 ms to 3 5 s after the stop of the first rupture the delay time of the second rupture decreases with an increase in the slip amount of the first rupture or a decrease in the normal stress acting on the fault segment where the second rupture started 3 the restarted rupture is not arrested by the presence of a fault bend and slip occurs over the entire fault we theoretically analyze the stress concentration near the fault bend to find that the normal stress produced by the preceding slip near the fault bend plays an important part in controlling the rupture propagation a numerical simulation based on a rate and state dependent friction law is performed to interpret physically the retarded rupture in the experiment the observed time interval of 10 8 ms to 3 5 s between the first rupture and the second is explained by the numerical simulation suggesting that the rate and state dependence of rock friction is a possible mechanism for the retarded rupture on the fault

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

3d simulation of near field strong ground motion based on dynamic modeling abstract we simulate the strong ground motion generated from the earthquake rupture process on a shallow strike slip fault using a 3d finite difference method the faulting process is modeled using a crack model with fixed rupture velocity the variability of peak ground velocity patterns correlated with fault location and source parameters such as stress drop or rupture velocity is investigated our findings suggest that these patterns are strongly affected by rupture directivity and the uppermost depth of the fault or that of the asperity when a fault breaks the ground surface the peak ground velocity and the peak ground acceleration show a narrow region of strong motion when a fault is buried under the ground the high peak ground velocity zone of the fault parallel component is apart from the fault trace by a distance comparable to the fault depth on the other hand the fault normal peak ground velocity is a maximum along the fault trace the fault length or asperity length is not so effective for peak ground velocities the effect of heterogeneity in stress drop and rupture velocity on strong ground motion is also investigated when stress drop is not uniform but increases linearly with depth from zero at the uppermost depth the peak ground velocity is reduced these results help better predict the strong ground motion generated from a potential fault

regional uplift associated with continental large igneous provinces the roles of mantle plumes and the lithosphere the timing and duration of surface uplift associated with large igneous provinces provide important constraints on mantle convection processes here we review geological indicators of surface uplift associated with five continent based magmatic provinces emeishan traps 260 million years ago ma siberian traps 251 ma deccan traps 65 ma north atlantic phase 1 61 ma and phase 2 55 ma and yellowstone 16 ma to recent all five magmatic provinces were associated with surface uplift surface uplift can be measured directly from sedimentary indicators of sea level in the north atlantic and from geomorpholocial indicators of relative uplift and tilting in yellowstone in the other provinces surface uplift is inferred from the record of erosion in the deccan north atlantic and emeishan provinces transient uplift that results from variations in thermal structure of the lithosphere and underlying mantle can be distinguished from permanent uplift that results from the extraction and emplacement of magma transient surface uplift is more useful in constraining mantle convection since models of melt generation and emplacement are not required for its interpretation observations of the spatial and temporal relationships between surface uplift rifting and magmatism are also important in constraining models of lip formation onset of surface uplift preceded magmatism in all five of the provinces biostratigraphic constraints on timing of uplift and erosion are best for the north atlantic and emeishan provinces where the time interval between significant uplift and first magmatism is less than 1 million years and 2 5 million years respectively rifting post dates the earliest magmatism in the case of the north atlantic phase 1 and possibly in the case of siberia the relative age of onset of offshore rifting is not well constrained for the deccan and the importance of rifting in controlling magmatism is disputed in the emeishan and yellowstone provinces in these examples rifting is not a requirement for onset of lip magmatism but melting rates are significantly increased when rifting occurs models that attempt to explain emplacement of these five lips without hot mantle supplied by mantle plumes often have difficulties in explaining the observations of surface uplift rifting and magmatism for example small scale convection related to craton or rift boundaries edge driven convection cannot easily explain widespread 1000 km scale transient surface uplift emeishan deccan north atlantic and upper mantle convection initiated by differential incubation beneath cratons the hotcell

palaeomagnetism and magnetostratigraphy of the permian triassic northwest central siberian trap basalts abstract a detailed palaeomagnetic and magnetostratigraphic study of the permian triassic siberian trap basalts stb in the noril sk and abagalakh regions in northwest central siberia is presented thermal th and alternating field af demagnetisation techniques have been used and yielded characteristic magnetisation directions the natural remanent magnetisation of both surface and subsurface samples is characterised by a single component in most cases occasionally a viscous overprint can be identified which is easily removed by th or af demagnetisation the resulting average mean direction after tectonic correction for the 95 flows sampled in outcrops is d 93 7 i 74 7 with k 19 and 95 3 3 the corresponding pole position is 56 2 n 146 0 e unoriented samples from four boreholes cores in the same regions have also been studied they confirm the reversed normal succession found in outcrops the fact that only one reversal of the earth s magnetic field has been recorded in the traps can be taken as evidence for a rather short time span for the major eruptive episode in this region however there is evidence elsewhere that the whole volcanic activity associated with the emplacement of the stb was much longer and lasted several million years

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

the seismicity geomorphology and structural evolution of the corinth area of greece in the eastern gulf of corinth geological structure is closely reflected in the topography in the 1981 corinth earthquakes ground deformation accentuated existing geomorphological patterns we explore the relationship between seismicity and landforms in space and time the area examined extends beyond the epicentral region of the 1981 events and its evolution is traced over the last 40000 years to understand the relation between deep and superficial structures we discuss processes that occurred in the 1981 earthquakes and go on to propose that surface faulting appears only above linear faults at depth that move in earthquakes with magnitudes m s greater than six where faults at depth intersect or bend the faulting becomes distributed and prim ary faulting does not reach the surface here the surface manifestation of faulting at depth is surface folding and secondary faulting such regions are identified in maps of the eastern gulf of corinth evidence for the evolution of the fault systems is provided by eyewitness accounts of shoreline changes following the recent earthquakes historical and archaeological data pertaining to old sea levels and 14 c dates for molluscs collected from fossil shorelines the results of these studies broadly confirm an earlier view of j a jackson et al earth planet sci lett 57 377 397 1982 that motion has shifted from faulting south of the city of corinth to faulting in the perachora peninsula but the transfer is not complete areas lying between the two fault systems have moved up and down in historical and archaeological times indicating that both systems are still active the evidence for activity of the northern system points to a repeat time of 300 years for earthquakes com parable with those of 1981 the work discussed in this paper suggests that some of the features previously described as m arine terraces are fault controlled continental surfaces furtherm ore beach deposits at a num ber of different levels long regarded as successive shorelines are in fact contemporaneous the critical ages were obtained by radiocarbon dating of shell carbonate a technique which yields dependable results if applied to samples which have been carefully selected and pretreated palaeontological dating of the terraces in contrast is found to be misleading because the faunas are environm entally controlled and consequently diachronous

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

dynamic rupture activation of backthrust fault branching we perform dynamic rupture simulations to investigate the possible reactivation of backthrust branches triggered by ruptures along a main thrust fault simulations with slip weakening fault friction and uniform initial stress show that fast propagation speed or long propagation distance of the main rupture promotes reactivation of backthrust over a range of branch angles the latter condition may occur separately from the former if rupture speed is limited by an increasing slip weakening distance towards the junction direction the results suggest a trade off between the amplitude and duration of the dynamic stress near the main rupture front for backthrust reactivation termination of the main rupture by a barrier can provide enhanced loading amplitude and duration along a backthrust rooted near the barrier facilitating its reactivation especially with a high frictional resistance the free surface and depth dependent initial stress can have several additional effects the sign of the triggered motion along the backthrust can be reversed from thrust to normal if a deeply nucleated main rupture breaks the free surface while it is preserved as thrust if the main rupture is terminated by a barrier at depth the numerical results are discussed in relation to several recent megathrust earthquakes in sumatra chile and japan and related topics such as branch feedbacks to the main fault the dynamic view on backthrust fault branching provided by the study fills a gap not covered by quasi static models or observations a specific examined case of antithetic fault branching may be useful for indicating a barrier like behavior along the main fault

magnetostratigraphy of the lower triassic volcanics from deep drill sg6 in western siberia evidence for long lasting permo triassic volcanic activity summary the deep drill hole sg6 in western siberia 66 n 78 5 e penetrated 1 1 km of lower triassic basalts which are possibly an extension of the central siberian permo triassic flood basalt province about 300 samples of these basalts were progressively demagnetized and measured principal component analysis often shows multiple magnetizations carried by haematite and magnetite the corrected mean inclinations are 77 and 77 for the haematite component a magnetostratigraphic scale was derived and showed a n r n r n succession this is quite diverent from the noril sk and taimyr typical polarity scale r n the basalts found in the sg6 deep drill hole are slightly younger than those of central siberia and taimyr they correspond to middle upper induan age whereas the noril sk and taimyr sections correspond to an uppermost permian and lower induan age altogether they indicate that after a high output rate of volcanic material near the permo triassic boundary this activity slowed down drastically on the siberian platform and taimyr but persisted for several million years in western siberia

delineation of the geometry of nodes in the alps dinarides hinge zone and recognition of seismogenic nodes m 6 we introduce a new method based on the analysis of the topographical alignments and used to delineate the structural boundaries of the nodes which permits the definition of relatively narrow earthquake prone areas by the pattern recognition approach the structurally bounded nodes capable of earthquakes with m 6 0 identified with pattern recognition in fact cover a significantly smaller area of the study region as compared with that defined by gorshkov et al 2004 who used conventional circles the proposed method thus improves the precision in the location of potential large earthquakes

detection of microearthquakes and identification of their causative structures in the eastern offshore region of south korea abstract a matched filter has been applied to continuous seismic records from the eastern offshore region of south korea to identify small earthquakes undetected by routine processing the resulting density of the regional earthquake catalog has increased by a factor of five relative to the detections reported by the korea meteorological administration high precision locations of newly identified microearthquakes and previously located earthquakes cluster into streaks that delineate structures responsible for the seismicity associated with the hupo fault offshore of the southern korean peninsula microearthquakes in the northern and southern segments of the fault zone exhibit different behaviors earthquakes in the northern segment occur at a regular temporal interval while those in the southern segment occur in bursts the identified fault system dips steeply to the west at shallow

crustal heterogeneity in bulk velocity beneath the 2001 bhuj earthquake source zone and its implications in order to resolve an enigmatic issue relating to the existence of fluid related or temperature related anomalies at the mainshock hypocenter of the 2001 bhuj india earthquake m w 7 6 an estimate of the 3d bulk sound velocity structure is made from the inverted high quality p and s arrival times from a total of 368 aftershocks recorded by 12 temporary seismic stations installed following the 2001 bhuj earthquake results reveal strong lateral and vertical heterogeneity in bulk velocity graphic 1 beneath the source zone the 2001 bhuj mainshock and its aftershock source zones are associated with anomalously high bulk sound velocity high graphic 2 indicating high bulk elastic strength of the source rocks at the mainshock hypocenter due to high pore pressures of the fully saturated cracked rocks associated with solute precipitation through the processes of acoustic fluidization and cementation the interpretation of bulk velocity tomograms suggests that the processes of mineral dehydration and permeation of sea surface water through several active quaternary faults down to the deep crust might have contributed to in situ fluid related material heterogeneity in bulk velocity within the fluid filled fractured rock matrix in the paleorift zone at the 2001 bhuj mainshock hypocenter which in turn increased pore pressure lowered the effective stress and brought the system into a brittle failure high graphic 3 in the intersecting fault geometry in the fractured rock matrix at the mainshock hypocenter can be taken as evidence for the strong role of fluids in association with the intraplate earthquake of the indian peninsula 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif

active folding in the algerian earthquake of 10 october 1980 a fold controlling the form of the local topography near el asnam algeria increased in amplitude at the time of the earthquake of 10 october 1980 the deformation occurred rapidly in an elastic brittle manner and not in the gradual ductile fashion in which folds are normally thought to develop

speculations on the geometry of the initiation and termination processes of earthquake rupture and its relation to morphology and geological structure earthquake initiation and termination processes are commonly described in terms of barriers and asperities barriers fall into two classes geometric barriers are associated with places where the orientation of a failure surface changes and relaxation barriers where stress is low because aseismic creep processes outpace tectonic loading geometric barriers fall into conservative and nonconservative subgroups according to whether finite fault motion can proceed without the creation of new structures or whether it demands the creation of new faulting or void space the multiple faulting or fragmentation associated with some nonconservative barriers can disrupt fault planes and form asperities by means of selected examples it is shown that a description in terms of these barriers can help one to visualise the processes of earthquake rupture and its relation to the geological environment

the kinematics of the plate boundary zone through new zealand a comparison of short and long term deformations summary surveys of shear strain rates derived from repeated triangulation cover about one quarter of the area of the plate boundary zone through new zealand and are well distributed within it using a method developed by haines relating shear strains to the total strain and velocity fields the dilatational and rotational strain rates and the velocities within the deformed zone are derived the plate boundary zone is shown to be two dimensional for the most part in that gradients of the velocity along the length of the zone are small or zero the shear strain rates are not uniform however they reach a maximum along a central axis and decrease gradually to zero toward the sides nor are the two independent components of strain one involving shortening or extension perpendicular and the other shear parallel to the zone equally developed everywhere there is a clear geographic separation with shortening developed over the subduction thrust and shear developed behind in a zone of wrench faulting time variations in the strain field in part of the region above the subduction interface are related to changes in the degree of coupling across the interface a velocity field is computed the relative velocity of the two plates from this data agree very well with that derived from seafloor spreading data these strain and velocity fields derived from geodetic studies give the short term kinematics of the plate boundary zone the long term kinematics of the zone are estimated from 1 uplift and subsidence data which are related to changes in crustal thickness and hence to dilatational strain and 2 variation in the declination of primary magnetization in rocks of known age related to the rotational strain the rate of rotational strain has increased in time from about 2 to 3 myr 1 10 myr ago to about 9 myr 1 today the increase can be understood as a secondary effect of a developing compressional component increasing the coupling between the plates so that more of the motion parallel to the zone is accommodated by distributed shear and less by aseismic slip the rates of strain averaged over the last 1 myr or so and at a scale length of a few tens of kilometres are closely similar in distribution and magnitude to the strain rates derived from short term kinematics while therefore at scale lengths of a few hundred metres or so faulting is very important and the deformation is discontinuous with unstrained blocks faulted with large but uncertain slip against adjacent blocks the deformation at these longer scale lengths is continuous and regular the two consequences of this study are that 1 strain from geodetic data can be directly related to the average long term deformation and therefore can be an important tool in the study of deformation in regions of current tectonic activity and 2 at scale lengths of a few tens of kilometres the deformation of a region can be described as the deformation of a continuum and we can ignore the effects of faulting

the parkfield california earthquake prediction experiment five moderate magnitude 6 earthquakes with similar features have occurred on the parkfield section of the san andreas fault in central california since 1857 the next moderate parkfield earthquake is expected to occur before 1993 the parkfield prediction experiment is designed to monitor the details of the final stages of the earthquake preparation process observations and reports of seismicity and aseismic slip associated with the last moderate parkfield earthquake in 1966 constitute much of the basis of the design of the experiment

paleolatitudes determined from paleomagnetic data from vertical cores most of the paleomagnetic data available from oceanic plates consist of measurements of inclination but not declination from azimuthally unoriented vertical cores similarly the basic paleomagnetic data to be analyzed from crustal blocks that have rotated by varying amounts about vertical axes are a set of paleoinclinations a new method is proposed for determining the paleocolatitude of a sampling site and the associated confidence limits paleomagnetic inclinations are first converted to paleocolatitudes and averaged to produce a mean colatitude after showing that this mean is biased we derive a paleocolatitude correction to remove the bias using a model for geomagnetic secular variation based on the latitude dependence of secular variation during the past 5 million years after testing the validity of the model by applying it to paleomagnetic data from quaternary lavas for which both inclination and declination are known we apply the method to inclination only paleomagnetic data from suiko seamount the most complete data set from a drilling site the method is then applied to paleomagnetic data from all deep sea drilling project sites for the pacific plate to obtain for each site an unbiased mean paleocolatitude and its confidence limits these paleocolatitudes and confidence limits are then used as input for a least squares analysis to obtain early and late cretaceous poles for the pacific plate and 95 confidence limits for these poles it is shown that the scatter of individual site paleocolatitudes about the best fit pole is consistent with the confidence limits at each site as determined by the new method of analysis

on the causes of mass extinctions the temporal link between large igneous province lip eruptions and at least half of the major extinctions of the phanerozoic implies that large scale volcanism is the main driver of mass extinction here we review almost twenty biotic crises between the early cambrian and end cretaceous and explore potential causal mechanisms most extinctions are associated with global warming and proximal killers such as marine anoxia including the early middle cambrian the late ordovician the intra silurian intra devonian end permian and early jurassic crises many but not all of these are accompanied by large negative carbon isotope excursions supporting a volcanogenic origin most post silurian biocrises affected both terrestrial and marine biospheres suggesting that atmospheric processes were crucial in driving global extinctions volcanogenic atmospheric kill mechanisms include ocean acidification toxic metal poisoning acid rain and ozone damage and consequent increased uv b radiation volcanic darkness cooling and photosynthetic shutdown each of which has been implicated in numerous events intriguingly some of the most voluminous lips such as the oceanic plateaus of the cretaceous were emplaced with minimal faunal losses and so volume of magma is not the only factor governing lip lethality the missing link might be continental configuration because the best examples of the lip extinction relationship occurred during the time of pangaea many of the proximal kill mechanisms in lip extinction scenarios are also potential effects of bolide impact including cooling warming acidification and ozone destruction however the absence of convincing temporal links between impacts and extinctions other than the chicxulub cretaceous example suggests that impacts are not the main driver of extinctions with numerous competing extinction scenarios and the realisation that some of the purported environmental stresses may once again be driving mass extinction we explore how experimental biology might inform our understanding of ancient extinctions as well as future crises

3d geometry of range front blind ramp and its effects on structural segmentation of the southern longmen shan front eastern tibet abstract a 3d fault morphology model has been constructed from seismic profiles covering the piedmont of the southern longmen shan lms eastern margin of the tibetan plateau it reveals a spatial correlation between an 3 5 km high geometrical bump on the range front blind ramp rfbr and the gap between the 2008 m w 7 9 wenchuan and 2013 m w 6 6 lushan earthquakes sandbox modeling is then used to probe the effects of the geometrical irregularity of the rfbr on fault behaviors and the lms range front deformation sand wedges are designed to thrust over artificial blind ramps analogous to the thrusting of the lms orogenic wedge toward the sichuan basin through the rfbr the experiments reproduce the first order deformation features presented in the southern lms range front confirming that along strike geometrical variations of the rfbr have induced the segmentation of both fault motion and the range front deformation their results also suggest that the gap between the wenchuan and lushan earthquakes is located directly within the structural transition zone originating from the geometrical bump on the rfbr additionally there is a duplex structure occurring in the hanging wall of the geometrical bump which localizes significant shear strain with progressive shortening and represents a fracture zone corresponding to the observed geophysical anomaly low seismic velocity underneath the seismic gap it is likely that this fractured body protected the gap from the ruptures of the wenchuan and lushan earthquakes

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

subsidence of the west siberian basin effects of a mantle plume impact comparison of modeling results with observed subsidence patterns from the west siberian basin provides new insight into the origin of the siberian traps and constrains the temperature size and depth of an impacting mantle plume head during and after the eruption of the siberian traps at the permian triassic boundary 250 ma we compare subsidence patterns from one dimensional conductive heat flow models to observed subsidence from backstripping studies of wells in the basin this results in a best fit scenario with a 50 km thick initial plume head with a temperature of 1500 c situated 50 km below the surface and an initial regional crustal thickness of 34 km in agreement with published values backstripping and modeling results agree very well including a 60 90 m y delay between the rifting phase and the first regional sedimentation regional subsidence patterns indicate that the plume head was present across a minimum area of 2 5 106 km2 these results re emphasize the viability of a mantle plume origin for the siberian traps provide important constraints on the dynamics of mantle plume heads and suggest a thermal control for the subsidence of the west siberian basin

a minimum upb age for siberian flood basalt volcanism abstract establishing an accurate and precise age for siberian flood basalt volcanism is of great importance in evaluating causes for the unequaled mass extinction of flora and fauna at the permian triassic boundary we report a new minimum u pb age obtained from zircon and baddeleyite from the mineralized noril sk i intrusion that cuts the lower third of this rapidly deposited 3500 m thick volcanic sequence near noril sk this 251 2 0 3 2 ma age is within analytical error of the shrimp u pb age for zircon from the permian triassic boundary at meishan south china 251 1 3 6 ma 2 and confirms siberian basaltic volcanism as a possible contributor to the mass extinction

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

complex geometry and segmentation of the surface rupture associated with the 14 november 2001 great kunlun earthquake northern tibet china abstract the 14 november 2001 kunlun china earthquake with a moment magnitude m w 7 8 occurred along the kusai lake kunlun pass fault of the kunlun fault system we document the spatial distribution and geometry of surface rupture zone produced by this earthquake based on high resolution satellite landsat etm aster spot and ikonos images combined with field measurements our results show that the surface rupture zone can be divided into five segments according to the geometry of surface rupture including the sun lake buka daban hongshui river kusai lake hubei peak and kunlun pass segments from west to east these segments each 55 to 130 km long are separated by step overs the sun lake segment extends about 65 km with a strike of n45 75 w between 90 05 e 90 50 e along the previously unrecognized west sun lake fault a gap of about 30 km long exists between the sun lake and buka daban peak where no obvious surface ruptures can be observed either from the satellite images or field observations the buka daban hongshui river kusai lake hubei peak and kunlun pass segments run about 365 km striking n75 85 w along the southern slope of the kunlun mountains between 91 07 e 94 58 e this segmentation of the surface rupture is well correlated with the pattern of slip distribution measured in the field detailed mapping suggest that these five first order segments can be further separated into over 20 second order segments with a length of 10 30 km linked by smaller scale step overs or bends our result also shows that the total coseismic surface rupture length produced by the 2001 kunlun earthquake is about 430 km excluding the 30 km long gap which is the longest coseismic surface rupture for an intracontinental earthquake ever recorded finally we suggest a multiple bilateral rupture propagation model that shows the rupture process of the 2001 m w 7 8 earthquake is complex it consists of westward and eastward rupture propagations and interaction of these bilateral rupture processes

frictional constraints on crustal faulting we consider how variations in fault frictional properties affect the phenomenology of earthquake faulting in particular we propose that lateral variations in fault friction produce the marked heterogeneity of slip observed in large earthquakes we model these variations using a rate and state dependent friction law where we differentiate velocity weakening behavior into two fields the strong seismic field is very velocity weakening and the weak seismic field is slightly velocity weakening similarly we differentiate velocity strengthening behavior into two fields the compliant field is slightly velocity strengthening and the viscous field is very velocity strengthening the strong seismic field comprises the seismic slip concentrations or asperities the two intermediate fields weak seismic and compliant have frictional velocity dependences that are close to velocity neutral these fields modulate both the tectonic loading and the dynamic rupture process during the interseismic period the weak seismic and compliant regions slip aseismically while the strong seismic regions remain locked evolving into stress concentrations that fail only in main shocks the weak seismic areas exhibit most of the interseismic activity and aftershocks but can also creep seismically this mixed frictional behavior can be obtained from a sufficiently heterogeneous distribution of the critical slip distance the model also provides a mechanism for rupture arrest dynamic rupture fronts decelerate as they penetrate into unloaded complaint or weak seismic areas producing broad areas of accelerated afterslip aftershocks occur on both the weak seismic and compliant areas around a fault but most of the stress is diffused through aseismic slip rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area by reloading weak fault areas that slipped in the main shock and then healed we test this frictional model by comparing the seismicity and the coseismic slip for the 1966 parkfield 1979 coyote lake and 1984 morgan hill earthquakes the interevent seismicity and aftershocks appear to occur on fault areas outside the regions of significant slip these regions are interpreted as either weak seismic or compliant depending on whether or not they manifest interevent seismicity

evolution of the west siberian basin the west siberian basin is one of the largest intracratonic basins of the world and an important hydrocarbon province of russia perhaps the most important geologic event in siberia was the emplacement of basalts around 250 ma i e permo triassic boundary covering an area of about 5 10 6 km 2 this volcanism may be responsible for a mass extinction that occurred around permian triassic time the prebasaltic rifting event was limited to the north northeastern sector of the basin initial basin wide subsidence took place in the jurassic as a result of which the western part of siberia became the west siberian basin bounded by uplifts to the east and to the west one of the surprising aspects of the west siberian basin is the abundance of subvertical faults believed to be result of strike slip movement while intraplate inversions and fault reactivation structures have been observed in many cratons subvertical faults observed in the west siberian basin are unique because of their geometries and abundance the differentiation between the effects of tectonics and eustasy in cratonic basins is simple the global eustatic signal is basin wide with regional and local tectonics playing an overprinting role thus the middle jurassic turonian first second and third order cycles in the west siberian basin were primarily driven by eustasy the middle jurassic turonian series can be subdivided into two second order and 16 third order transgressive regressive cycles within dataset extent fourth order cycles appear to be controlled by delta shifting although extensively studied a number of fundamental questions regarding the origin and evolution of the west siberian basin remain unresolved or poorly documented in the literature

localized slip and distributed deformation in oblique settings the example of the denali fault system alaska in most fault systems the direction of the relative plate motion is oblique to the azimuth of the existing faults hence during earthquakes the displacement may be partitioned between several faults that accommodate different components of the total motion here we quantify the effect of the obliquity of the fault system relatively to the plate motion direction on the distribution of the deformation in the fault system during distinct periods of the seismic cycle the 2002 november m w 7 9 denali strike slip earthquake ruptured 341 km of the denali fault the azimuth of the fault varies by more than 50 over the total rupture length making the denali fault an ideal system to test the effect of obliquity from west to east thrust dominates the first part of the rupture while strike slip dominates the central and eastern sections using a kinematic model that considers the obliquity of the plate motion direction relative to the local fault azimuth we explored how much of the far field tectonic loading is accommodated on the main strike slip fault during the earthquake and how much is accommodated by distributed deformation off the main fault on secondary structures using a dataset of 735 focal mechanisms we represent the deformation using strain rosettes and we compare seismological data with model results using the areal strain then we developed the parameter ca the coefficient of accommodation which allows a direct quantification of the efficiency of a fault to accommodate oblique motion using these indicators we show that in oblique setting such as in the denali case the aftershocks and the background seismicity are organized to accommodate a significant part of the deformation that is not taken on the denali strike slip fault during the main earthquakes the westward increase of the obliquity actually increases the amount of such deformation accommodated through distributed thrust faults leading to the westward widening of the alaska range located north of the denali fault therefore the strain partitioning between localized slip on pre established major faults and distributed deformation accommodated through aftershocks and background seismicity on smaller faults highlighted here by the longer term topography seems to be needed during the seismic cycle to accommodate the boundary conditions in such oblique settings

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

determining the geometry of the north anatolian fault east of the marmara sea through integrated stress modeling and remote sensing techniques abstract the 1200 km long north anatolian fault naf is part of an east west trending dextral shear zone naf system along the boundary between the anatolian and eurasian plates that widens to the west this widening zone of deformation complicates potential earthquake rupture paths and highlights the importance of understanding the geometry of active fault systems in the central portion of the naf system just west of the town of bolu the naf splits into two major faults the northern and southern strands these two faults diverge almost converge and then diverge again to border the marmara sea earthquake data from the region where the two faults converge indicate that they may be linked by an active fault we model the active fault geometries with and without the linking fault to explore its impact on the output regional stress field from a finite element model these results are compared to focal mechanism records and lineament analyses to determine which geometry best simulate the stress field in a regional model our results show that a linking fault between the northern and southern strands of the naf system is necessary to best match the primary stress orientations of the model with the maximum paleostress orientations inferred from deformation patterns and observed in earthquake focal mechanisms furthermore the linking fault should be a significant component in future models of the naf system within the region

causative source of mw 6 9 sikkim nepal border earthquake of september 2011 gps baseline observations and strain analysis abstract the recent earthquake of mw 6 9 which occurred on september 18 2011 in sikkim nepal border region epicenter 27 72 n 88 06 e depth 20 7 km 68 km nw of the capital city gangtok is the strongest earthquake in the instrumentally recorded history of the region the fault plane solution of this earthquake indicates a strike slip motion however the seismological and geological studies carried out so far after the earthquake could not confirm the causative fault plane in the present study gps observations are used to ascertain causative source in the generation of earthquake and its correlation with the observed seismic data of the region the co seismic displacements recorded by gps show maximum displacement of 11 mm at phodong and 9 mm at taplejung station near the epicenter a simple rigid cross fault model using gps baseline observations was employed to figure out the causative fault plane and seismological characteristic of the region it is inferred that the movement represents the kinematic adjustment of the subsidiary faults as a result of the displacement along the nw se principal plane strain analysis using gps baseline inferred that the region southeast of epicenter has undergone large deformation in addition a significant part of the measured deformation across the surface fault zone for this earthquake can be attributed to post seismic creep

on the estimation of the true mean inclinations when declinations are unknown paleomagnetists dealing with deep drill samples cannot use the classical fisher statistics when they don t know the declinations of the magnetization of their samples the arithmetical mean of the inclinations gives a strongly biased estimation of the true mean inclination when these inclinations are steep and scattered by fitting cumulative distribution curves we show that we can obtain an unbiased or at least less biased estimation of the true mean inclination and of the k value the method is tested on artificial and real cases

volcanism impact and mass extinctions incredible or credible coincidences massive continental volcanism and or bolide impacts are considered by many authors to have caused three major mass extinction events during the last 300 million years the end permian end cretaceous and end triassic extinctions however reevaluation of the frequency of bolide impacts and plume related flood basalt provinces indicates that both types of event occur much more frequently than mass extinctions and so in isolation may not be responsible for the largest extinctions furthermore the kill mechanisms associated with either flood basalts or impacts do not appear to be sufficiently powerful to cause worldwide collapse of ecosystems leading to the largest mass extinctions contemporaneous flood basalts and bolide impact may be prerequisites for the largest mass extinctions we present a statistical analysis of the probability of coincidence between volcanism and impact and show that three random coincidences of these events in the last 300 m y are likely no causal relationship between impact and volcanism is necessary the lesser mass extinctions on the other hand may not require juxtaposition of two such catastrophic events such coincidences occurring on more than three occasions during the last 300 m y become increasingly unlikely d 2004 elsevier b v all rights reserved

thickness of the seismic slip zone this article reviews geologic and other evidence constraining the thickness of the principal slip zone psz that accommodates the bulk of coseismic shear displacement during an individual rupture event surface deformation from rupturing may occupy swaths tens of meters or more in width but trenches across active faults generally reveal that incremental slip is accommodated by a psz that is tens of centimeters or less in thickness geomorphic evidence coupled with the observations from trenching suggest a psz may stay well localized for distances of several kilometers through many rupture episodes mine exposures and exhumed fault zones demonstrate that pszs separating different lithologies within the fault core although contained within damage zones of variably fractured rock ranging up to hundreds of meters in thickness often comprise just a few centimeters of gouge ultracataclasite that have accommodated large finite displacements 1 km microstructural studies demonstrate incremental slip localized still further down to 1 10 mm as do other fault rock assemblages slickensides and slickenfibers fault veins of pseudotachylyte friction melt intravein septa in hydrothermal fault infills the accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone with extreme localization to less than 1 cm not uncommon however some distributed coseismic shear may also develop especially at rupture irregularities coseismic reduction of shear resistance from friction melting t 1000 c or from transient thermal pressurization of aqueous fluids t 100 c requires slip during moderate to large earthquakes u 1 m to be restricted to narrow zones respectively a few centimeters or tens of centimeters in thickness given the evidence for slip localization the apparent scarcity of pseudotachylyte suggests either that seismic friction melting is a rare phenomenon or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones

segmentation and holocene surface faulting on the median tectonic line southwest japan the median tectonic line mtl active fault system is a 300 km long arc parallel right lateral strike slip fault related to oblique subduction of the philippine sea plate beneath the eurasian plate at the nankai trough southwest japan the fault on shikoku island has a slip rate of 5 10 mm yr one of the highest in onshore japan we identified 12 geometric segments along the mtl separated by discontinuities such as en echelon steps bends changes in strike and gaps in the surface trace a chronology of latest holocene surface faulting on the mtl was constructed based on previously published and new work including trenching geomorphic mapping and acoustic profiling and piston coring of the submarine extension of the fault zone the mtl probably does not rupture along its entire length in a single earthquake but instead consists of multiple earthquake segments that rupture independently of one another the recurrence interval and surficial offset for surface rupturing earthquakes at four individual sites on the mtl in shikoku island are 1000 3000 years and 5 8 m respectively the relatively long recurrence interval and large surficial offset per earthquake suggest large seismic moment release during surface rupturing earthquakes on the mtl as commonly observed for japanese moderate to large intraplate earthquakes because the predicted rupture lengths based on empirical relations between surface displacement and rupture length are considerably larger than those of individual segments large earthquakes on the mtl probably rupture multiple geometrically defined segments the fault was previously thought to be unruptured at least in the past 1000 years based on the absence of historical evidence for destructive earthquakes however trench excavations show that part of the mtl ruptured most recently during or after the 16th century a d with at least 6 9 0 7 m of slip along the main fault trace this rupture may be correlated to the 1596 keicho kinki earthquake but further geological and historical investigations are needed to confirm this hypothesis

control of rupture by fault geometry during the 1966 parkfield earthquake a reanalysis of the available data for the 1966 parkfleld california earthquake mr 5 suggests that although the ground breakage and aftershocks extended about 40 km along the san andreas fault the initial dynamic rupture was only 20 to 25 km in length the foreshocks and the point of initiation of the main event locate at a small bend in the mapped trace of the fault detailed analysis of the p wave first motions from these events at the gold hill station 20 km southeast indicates that the bend in the fault extends to depth and apparently represents a physical discontinuity on the fault plane other evidence suggests that this discontinuity plays an important part in the recurrence of similar magnitude 5 to 6 earthquakes at parkfield analysis of the strong motion records suggests that the rupture stopped at another discontinuity in the fault plane an en echeion offset near gold hill that lies at the boundary on the san andreas fault between the zone of aseismic slip and the locked zone on which the great 1857 earthquake occurred foreshocks to the 1857 earthquake occurred in this area sieh 1978 and the epicenter of the main shock may have coincided with the offset zone if it did a detailed study of the geological and geophysical character of the region might be rewarding in terms of understanding how and why great earthquakes initiate where they do

seismic potential revealed by surface folding 1983 coalinga california earthquake the 2 may 1983 coalinga california earthquake magnitude 6 5 failed to rupture through surface deposits and instead elastically folded the top few kilometers of the crust the subsurface rate of fault slip and the earthquake repeat time are estimated from seismic geodetic and geologic data three larger earthquakes up to magnitude 7 5 during the past 20 years are also shown to have struck on reverse faults concealed beneath active folds

excess 40ar in biotite and hornblende from the noril sk 1 intrusion siberia implications for the age of the siberian traps the siberian traps represent the largest known phanerozoic manifestation of continental flood volcanism the general agreement is now that the volcanism was of short duration 1 m y and was synchronous with the permian triassic boundary discrepancies between different geochronologic results prevent rigorous evaluation of the age and duration of magmatism several alkalic mafic intrusions associated with the siberian traps represent subvolcanic feeders for the trap lavas the noril sk 1 intrusion is intruded into the earliest flows and is chemically and isotopically related to stratigraphically overlying flows biotites from the noril sk 1 intrusion have previously yielded 40ar39ar plateau dates 254 251 ma that are significantly older than seemingly reliable 40ar39ar plateau dates 250 247 ma on plagioclase and whole rock samples from trap basalts that are geologically constrained to be older than the intrusion possible explanations of this discrepancy include 1 plagioclase and whole rock samples are anomalously young due to 40ar loss via alteration or episodic outgassing and or 2 the biotites contain excess 40ar detailed laser heating 40ar39ar analysis of six individual grains of biotite in a total of 214 steps yield data that permit characterization of multiple components of ar through isotope correlation patterns an isochron age of 250 1 1 5 ma 2 and an excess ar component with 40ar36ar 565 39 are obtained by regression of the 115 highest temperature steps step heating of a bulk hornblende sample also reveals excess ar with 40ar36ar 327 10 and an isochron age of 249 3 1 6 ma neglecting uncertainties in the ages of neutron fluence monitors the two dates just overlap at 2 but are distinctly younger than the previous mean plateau date 253 9 1 6 ma for biotite the different initial 40ar36ar for the two phases is interpreted as reflecting the evolution of an initial lower mantle composition towards increasing crustal contamination

models of the complex source of the el asnam earthquake abstract the el asnam earthquake of 10 october 1980 was originated by a thrust across a sw ne oriented fault 36 km long and 15 km wide it is a complex event with a rupture propagating from the sw to the ne fault mapping hypocenter distribution and b factor studies indicate fault branching to the ne a dislocation model is used to explain the branch with normal faulting at beni rached as a consequence of the thrust across a main fault that changes orientation the mechanism of the 1954 earthquake must be similar even though only normal faulting was observed at the surface

active faults and state of stress in the central part of the trans mexican volcanic belt mexico 1 the venta de bravo fault the central part of the trans mexican volcanic belt is being deformed by seismically active west east striking normal faults that cause pronounced scarps structural and seismic along strike discontinuities allow the following segmentation 1 the western segment the area between morelia and the los azufres volcanic center is characterized by 25 km long fault scarps that define the cuitzeo graben and the santa ana maya horst which has a relief 850 m with respect to the cuitzeo graben the faults cut several quaternary scoria cones as well as alluvium 2 the central neotectonic segment extends between maravatio in the west and altamirano volcano in the east the most prominent structure of this segment is the 45 km long venta de bravo fault with a relief 300 m the february 22 1979 mb 5 3 maravatio earthquake occurred on this fault the late quaternary vertical slip rate along the easternmost part of the venta de bravo fault is estimated at 2 mm yr the lateral extension of the segment is defined by the limits of the venta de bravo fault and the eastern termination of the cuitzeo graben 3 the eastern segment is made up of the acambay graben the limit between the central and eastern segments is defined by an extensional jog between the venta de bravo and pastores faults which indicates a left lateral strike slip component the most recent rupture of this segment occurred in the november 19 1912 ms 6 9 acambay earthquake that caused vertical displacements 50 cm along the faults flanking the graben stress determinations based on quaternary scoria cone alignments the focal mechanism of the 1979 earthquake and the inversion of striation measurements indicate a stress field with sv sene snnw the fault striations as well as the focal mechanism indicate a minor but consistent left lateral strike slip component the observed stress and deformation can be explained by the superposition of two sources of stress isostatically compensated surface loads related to the high elevation of the trans mexican volcanic belt probably cause horizontal deviatoric tension and the observed crestal normal faults which strike parallel to the axis of the volcanic belt the observed left lateral strike slip component on the other hand can be explained by compressional far field stresses caused by loads at the boundary between the cocos and north american plates the orientation of the faults with respect to the direction of plate convergence is a prefered orientation for left lateral slip along the observed faults alternatively the observed left lateral strike slip component may accommodate trench parallel motion of crustal blocks in southwestern mexico

fault zone connectivity slip rates on faults in the san francisco bay area california the slip rate of a fault segment is related to the length of the fault zone of which it is part in turn the slip rate of a fault zone is related to its connectivity with adjoining or contiguous fault zones the observed variation in slip rate on fault segments in the san francisco bay area in california is consistent with connectivity between the hayward calaveras and san andreas fault zones slip rates on the southern hayward fault taper northward from a maximum of more than 10 millimeters per year and are sensitive to the active length of the maacama fault

frictional properties and 3 d stress analysis of the southern alpine fault new zealand abstract new zealand s alpine fault af ruptures quasi periodically in large magnitude earthquakes paleoseismological evidence suggests that about half of all recognized af earthquakes terminated at the boundary between the central and south westland sections of the fault there fault geometry and the polarity of uplift change the south westland af exhibits oblique normal fault motion on a structure oriented 052 82 se that for at least 35 km along strike contains saponite rich principal slip zone gouges new hydrothermal friction experiments reveal that the saponite fault gouge is frictionally weak exhibiting friction coefficients between 0 12 and 0 16 for a range of temperatures t 25 210 c and effective normal stresses n 31 2 93 6 mpa the saponite gouge is rate strengthening in all velocity steps performed at velocities between 0 01 and 3 0 m s behavior conducive to aseismic creep a three dimensional stress analysis shows that the south westland af is favorably oriented with respect to the regional stress field for slip within the frictionally weak saponite fault gouge geometrically the fault is severely misoriented for slip in any fault forming materials with friction coefficients exceeding 0 5 the combination of weak gouges prone to aseismic creep strong asperities and low resolved shear stress may impede earthquake rupture propagation along the south westland alpine fault

the timing and extent of the eruption of the siberian traps large igneous province implications for the end permian environmental crisis we present new high precision 40ar 39ar ages on feldspar and biotite separates to establish the age duration and extent of the larger siberian traps volcanic province samples include basalts and gabbros from noril sk the lower tunguska area on the siberian craton the taimyr peninsula the kuznetsk basin vorkuta in the polar urals and from chelyabinsk in the southern urals most of the ages except for those from chelyabinsk are indistinguishable from those found at noril sk cessation of activity at noril sk is constrained by a 40ar 39ar age of 250 3 1 1 ma for the uppermost kumginsky suite the new 40ar 39ar data confirm that the bulk of siberian volcanism occurred at 250 ma during a period of less than 2 ma extending over an area of up to 5 million km2 the resolution of the data allows us to confidently conclude that the main stage of volcanism either immediately predates or is synchronous with the end permian mass extinction further strengthening an association between volcanism and the end permian crisis a sanidine age of 249 25 0 14 ma from bed 28 tuff at the global section and stratotype at meishan china allows us to bracket the p tr boundary to 0 58 0 21 myr and enables a direct comparison between the 40ar 39ar age of the traps and the permo triassic boundary section younger ages 243 ma obtained for basalts from chelyabinsk indicate that volcanism in at least the southern part of the province continued into the triassic

why large earthquakes do not nucleate at shallow depths although by definition tectonic earthquakes may nucleate anywhere within the seismogenic layer in almost all cases those earthquakes that become large nucleate near the base of the seismogenic layer because frictional strength and stress drop should increase with depth and in situ stress measurements suggest that the ambient stress increases with depth we have examined spontaneous rupture models with gradients of both average stress drop and average strength relative to ambient stress to determine whether this explains the observed phenomena we report here that ruptures that are nucleated with in the low stress drop shallow regions of the model are inhibited from propagating but those that are nucleated within the high stress drop regions can propagate over the entire fault plane

linear and planar structure in ordered multivariate data as applied to progressive demagnetization of palaeomagnetic remanence summary consider a sequence of say 10 to 20 vector observations in threedimensional space it is suspected that a few subsets of consecutive observations are made up of collinear points the purpose of this paper is to construct a statistically based algorithm to find such linear segments and to assess their accuracy a similar assessment is made for coplanar sets of points this algorithm is applied here to palaeomagnetic data and is claimed to be superior to previous methods of palaeomagnetic analysis in terms of completeness and balance of analysis treatment of measurement errors and other sources of scatter criteria for identification of linear and planar sets of points and statistical rigour stability spectra with statistically based confidence limits are obtained as a by product 1 palaeomagnetic analysis background to the geometrical problem the natural remanent magnetization nrm in rocks is known in general to have originated in one or more relatively short time intervals during their formation and subsequent history i e during rock forming or metamorphic events during which nrm is frozen in stabilized by falling temperature grain growth etc the nrm acquired during each such event is a single vector magnetization parallel to the then prevailing geomagnetic field and is called a component of nrm rocks which have suffered more than one event of this kind are therefore liable to carry multi component nrm in the laboratory these components can be identified by demagnetizing the rock step by step usually by thermal alternating field or chemical demagnetization which involves the analysis of the distribution of blocking rzmperature coercivity and chemical leaching respectively resistance to these treatments is called stability of remanence and the range of treatment over which a particular component is removed is called the stability range of the component the various discrete

local source tomography applications to italian areas we describe three study cases in which we used local earthquake and shot travel time residuals to investigate the upper crustal structure of three regions in italy we inverted for velocity and hypocentral parameters using a damped least squares technique making use of parameter velocity and hypocentre separation the three studied regions are in italy namely a the vulsinian volcanic complex latium where there is an active geothermal field b the irpinia campania lucania region in the southern appennines site of the strongest earthquake in italy for at least 65 years november 1980 ms 6 9 c the friuli region in northeastern italy where another strong earthquake ms 6 5 occurred in 1976 the computed shallow velocity models generally correspond with surface geological structures for the three studied areas the main results are respectively a a low velocity anomaly detected in the centre of the vulsinian volcanic complex at a depth of 5 8 km probably due to anomalous heat flow caused by a partially molten or cooling intrusive body b the identification of a deep 10 km discontinuity in the crust beneath the irpinia fault zone approximately corresponding with the fault extension at depth c the detection of a wedge of high velocity high density material at seismogenic depth 5 10 km beneath the friuli region interpreted as a buried thrust of the metamorphic basement

the middle palaeolithic site of birzgane tebessa algeria rock magnetic property characterisation and past rainfall reconstruction abstract a new middle palaeolithic site was discovered at birzgane south of the city of tebessa in eastern algeria the archaeological study revealed richness in archaeological artefacts belonging probably to the aterian culture but an absence of pedunculates the aterian archaeological layer was assigned to the end of the middle pleistocene by uranium thorium dating the environmental conditions at the time were assessed by means of magnetic proxy data such as hysteresis parameters magnetic susceptibility and remanent magnetisation the magnetic fraction of the alluvial sediment contains mainly oxidised magnetite and smaller amounts of haematite and goethite indicated by thermal demagnetisation curves of isothermal remanent magnetisation magnetic properties such as enhanced susceptibility anhysteretic remanent magnetisation and frequency dependent susceptibility indicate that the upper part of the section was subjected to pedogenesis after deposition a conceptual magnetic enhancement model was applied to reconstruct past rainfall quantities in the upper part taking into account present day temperatures and rainfall water saturation soil moisture and magnetic susceptibility a precipitation quantity of 560 40 mm was estimated for the transition period from mis 5 to 4 corresponding to the saharan pluvial an extended humid climate period in northern africa between 100 000 and 70 000 years before present

a model of damage mechanics for the deformation of the continental crust 1 we derive a continuum rheology for the deformation of the continental crust using continuum damage mechanics it is hypothesized that when a constant strain rate is applied to a solid material the stress and damage increase until failure occurs which is analogous to an earthquake we further assume that this process is repeated in analogy to the reoccurrence of earthquakes on a fault our model assumes that the continental crust behaves elastically below a yield stress y above this stress the continuum deformations can be modeled as a non newtonian viscous flow with y n where n is constant we derive the modified omori s law for aftershock decay using a viscoelastic version of our model and get good agreement with observations taking n 6 using parameter values appropriate for aftershocks we obtain a continuum crustal rheology that can explain major orogenies such as the indian asian collision

the rupture process of the 1980 irpinia italy earthquake from the inversion of strong motion waveforms abstract the distribution of slip and the behaviour of rupture propagation during the 23rd november 1980 irpinia earthquake ms 6 9 was investigated by analysing strong motion accelerograms the rupture was assumed to develop on a two dimensional purely normal fault whose geometry was constrained by geologic and geodetic data and by the aftershock space distribution theoretical seismograms have been computed using the isochron approach with a spatially variable slip intensity the asymptotic ray theory is used to evaluate the far field green functions the rupture model was updated following a trial and error approach the fit of observed waveforms with synthetic seismograms allowed several peculiarities in the rupture history to be pointed out the source model resulting from the solution of the forward waveform modelling was then used as starting model for the inversion of ground velocities therefore we performed a linearized inversion for slip velocity and rupture times on the fault by iteratively perturbing the assumed starting model the inverse problem is solved by means of a tomographic back projection technique the inferred source model shows a bilateral rupture which does not propagate uniformly away from the hypocentre the rupture velocity and the slip distribution on the fault plane are rather variable the solution confirms the shallow dislocation gap in the central part of the fault suggested by the behaviour of the surface rupture the results indicate that the rupture propagated northwestward along a further fault fragment for which no surface evidence is observed the aftershocks occurred mostly inside of or near to the edges of the source areas of maximum co seismic slip

flow patterns in the siberian traps deduced from magnetic fabric studies summary the siberian traps rank among the largest flood basalt provinces in the world major magmatic activity is restricted to several short periods of less than 1 myr around the permo triassic boundary we measured the anisotropy of magnetic susceptibility ams of 183 basaltic samples from 28 individual lava flows belonging to the northwestern part of the flood basalt province in order to test the reliability of such data in structural interpretation these preliminary ams data show a remarkably consistent pattern of magnetic lineations that likely reflect the primary flow related texture of the basalt our results also emphasize that ams data are consistent with the well documented petrological and geochronological data the inferred flow directions are also consistent with flow directions expected from isopach maps our results suggest that the entire 2 km thick lava pile was fed by fissure eruptions located in the rifted basin that bound the siberian platform and was controlled by topographical features particularly major rift zones

a synthetic seismicity model for the xianshuihe fault southwestern china simulation using a rate and state dependent friction law summary we performed a numerical simulation of seismic activity along the xianshuihe fault a highly active strike slip fault approximately 350 km long located along the eastern margin area of the tibetan plateau southwestern china historical earthquake data over the last 300 yr indicate repeated periods of seismic activity and migration of large earthquakes along the fault during active seismic periods to understand the characteristics of historical seismicity and to obtain insight into seismic potential we performed a numerical simulation of slip behaviour along the fault using a 2 d elastic plate model the friction on the model fault obeys a laboratory derived rate and state dependent friction law while the long term slip rates along the fault are assumed to be consistent with geologically and geodetically estimated slip rates to simulate segmented rupture behaviour we introduced non uniformity into friction parameters along the fault the simulation results indicate that seismic rupture is arrested in regions with frictional properties that are highly velocity strengthening or large values of characteristic slip distance over which frictional stress evolves in the regions where seismic rupture is arrested post seismic sliding occurs causing time dependent stress transfer along the fault post seismic slip histories in highly velocity strengthening regions are well approximated by logarithmic time functions while those in regions with large characteristic slip distances increase more rapidly in the initial stages of post seismic sliding this difference in post seismic sliding produces the difference in time dependent stress transfer and in consequence the statistical characteristics of earthquake recurrence fault interactions near a fault branch point produce complexity in the simulated earthquake sequence simulated rupture commonly triggers additional rupture in a neighbouring segment with a time delay of several years the simulated seismic activity shows good agreement with observational data with respect to the following statistical features 1 successive seismically active periods are separated by periods of relative quiescence of 100 200 yr duration 2 and the duration of active period is a few tens of years strictly speaking neither the time nor slip predictable models are able to describe the simulated local slip history for each fault segment the ratio of the standard deviation to the average value of the recurrence intervals of simulated earthquakes ranges from 0 05 to 0 22 depending on the fault segment the cumulative distribution function of the recurrence intervals of simulated earthquakes at each segment approximately obeys a brownian passage time distribution or a lognormal distribution which is commonly used in the statistical evaluation of earthquake occurrence

synchrony and causal relations between permian triassic boundary crises and siberian flood volcanism the permian triassic boundary records the most severe mass extinctions in earth9s history siberian flood volcanism the most profuse known such subaerial event produced 2 million to 3 million cubic kilometers of volcanic ejecta in approximately 1 million years or less analysis of 40 ar 39 ar data from two tuffs in southern china yielded a date of 250 0 0 2 million years ago for the permian triassic boundary which is comparable to the inception of main stage siberian flood volcanism at 250 0 0 3 million years ago volcanogenic sulfate aerosols and the dynamic effects of the siberian plume likely contributed to environmental extrema that led to the mass extinctions

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

fault geometry and earthquakes in continental interiors abstract although large earthquakes in continental interiors are much less frequent than those along plate boundaries they have been responsible for a disproportionate amount of destruction i present a testable model for strain accumulation and seismicity in the upper crust of continental interiors intersecting faults provide a focus for strain build up resulting in local pockets of high strain accumulation rigid plates typically deform at strain rates 10 10 to 10 9 strain yr 1 but at intersecting fault zones strain accumulates at anomalously high rates of 10 8 to 10 7 strain yr 1 i e the strain rates are comparable with those at plate boundaries the resulting large earthquakes are associated with relatively short return times hundreds of years typically one of the intersecting faults appears to split and to offset the other main fault defined as a fault on which the larger offset occurs forming two parallel strands separated by a jog i also observe a rotation of one leg of the main fault with respect to the other the region of intersection is usually associated with intense fracturing increased microseismicity and uplift

a faulting model for the 1979 imperial valley earthquake by comparing synthetic particle velocities with the near source strong motion data we have constructed by trial and error a faulting model for the 1979 imperial valley earthquake the calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the imperial valley and the spatial variation of the slip rate parameters on the fault plane the independent slip rate parameters are 1 the strike slip rate amplitude 2 the dip slip rate amplitude 3 the duration that slip rate is nonzero the rise time of the slip function and 4 the rupture time which determines when the slip rate is initiated our faulting model has the following principal features 1 faulting occurred on the imperial fault and on the brawley fault rupture on the brawley fault being triggered by rupture on the imperial fault 2 the imperial fault is a plane 35 km long and 13 km wide with a strike of 323 measured clockwise from north and a dip of 80 ne the brawley fault is a 10 km long and 8 km wide plane with a strike of 360 and a dip of 90 3 faulting on the imperial fault is primarily right lateral strike slip with a small component of normal dip slip in the sediments at its northern end the larger strike slip rates are generally confined between depths of 5 and 13 km with maximum values of about 1 0 m s the duration varies on the fault with a maximum of 1 9 s which is considerably shorter than the total time for the rupture to take place 4 the rupture velocity on the imperial fault is highly variable locally it exceeds the shear wave velocity and in one instance the compressional wave velocity the average rupture velocity though is less than the shear wave velocity 5 although the slip on the brawley fault contributes only about 4 of the total moment it greatly affects the ground motion at nearby stations 6 the total seismic moment is 6 7 1018 n m where the imperial fault contributes 6 4 1018 n m and the brawley fault contributes 2 7 1017 n m in the process of trying almost 300 faulting models we found that given the elastic parameters of the medium the synthetic seismograms were most sensitive to the specification of the rupture time although the slip rate amplitudes are linearly related to the data the rupture time and the duration are not the parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

paleomagnetism and magnetostratigraphy of the traps from western taimyr northern siberia and the permo triassic crisis abstract the siberian traps were emplaced near the permo triassic boundary and are among the largest continental igneous provinces a 1750 m thick section of traps from the western taimyr 72 9 n 84 e has been sampled this section is equivalent to the lower and middle part of the total siberian traps section thirty one oriented hand samples were studied and demagnetised by alternating fields and heating cycles a stable characteristic component passes the fold test and is thought to be primary the mean direction is d 84 i 75 with 95 10 n 29 and the corresponding pole is 59 n 150 e the bottom part 660 m is of reversed polarity the middle part 900 m is normal and the uppermost level 150 m is mixed correlations with reference permo triassic magnetostratigraphic timescales are discussed the most probable correlation indicates an age quite close to the permian triassic boundary and a duration for the volcanism of less than 1 m y the data are therefore consistent with the hypothesis that this volcanism triggered the permian triassic crisis

late early triassic climate change insights from carbonate carbon isotopes sedimentary evolution and ammonoid paleobiogeography the late early triassic sedimentary facies evolution and carbonate carbon isotopemarine record 13ccarb of ammonoid rich outer platform settings show striking similarities between the south china block scb and the widely distantnorthern indianmargin nim the studied sections are located within the triassic tethyshimalayan belt losar section himachal pradesh india and the nanpanjiang basin in the south china block jinya section guangxi province respectively carbon isotopes from the studied sections confirm the previously observed carbon cycle perturbations at a time of major paleoceanographic changes in the wake of the end permian biotic crisis this study documents the coincidence between a sharp increase in the carbon isotope composition and the worldwide ammonoid evolutionary turnover extinction followed by a radiation occurring around the smithian spathian boundary based on recent modeling studies on ammonoid paleobiogeography and taxonomic diversity we demonstrate that the late early triassic smithian and spathian was a time of a major climate change more precisely the end smithian climate can be characterized by a warm and equable climate underlined by a flat pole to equator sea surface temperature sst gradient while the steep spathian sst gradient suggests latitudinally differentiated climatic conditions moreover sedimentary evidence suggests a transition froma humid and hot climate during the smithian to a dryer climate fromthe spathian onwards by analogywith comparable carbon isotope perturbations in the latedevonian jurassic andcretaceouswe propose that high atmosphericco2 levels could have been responsible for the observed carbon cycle disturbance at the smithian spathian boundary we suggest that the end smithian ammonoid extinction has been essentially caused by a warm and equable climate related to an increased co2 flux possibly originating froma short eruptive event of the siberian igneous province this increase in atmospheric co2 concentrations could have additionally reduced the marine calcium carbonate oversaturation and weakened the calcification potential of marine organisms including ammonoids in late smithian oceans

the evolution of the gulf of corinth greece an aftershock study of the 1981 earthquakes summary a preliminary study of the aftershocks of three earthquakes that occurred near to corinth greece in 1981 is combined with observations of the morphology and faulting to understand the evolution of the eastern gulf of corinth the well located aftershocks form a zone 60km long and 20km wide they do not lie on the main fault planes and are mostly located between the north dipping faulting on which the first two earthquakes occurred and the south dipping faulting associated with the third event a cluster of aftershocks also lies in the footwall of the eastern end of the south dipping fault of the third event morphologically it is observed that in the evolution of the eastern gulf of corinth antithetic faulting apparently predates the appearance of the main faulting at the surface this evolution can be explained by motion on a deep seated shallow angle aseismic normal fault a model based on such a fault also accounts for the aftershock distribution of the 1981 earthquakes

fault related folding near the wind river thrust wyoming usa reflection profiles across the wind river uplift in wyoming usa show that folding of basement rocks occurs in the footwall of the main fault at depths between 6 and 10km it is shown using elastic modelling that these features are a consequence of uneven fault slippage slip on the fault must be greater at depths between 3 and 18 km but reduced outside this range this is the depth range of catastrophic rupture associated with earthquakes in the continental crust

the evolution of a thrust fault system processes of rupture initiation propagation and termination in the 1980 el asnam algeria earthquake summary we discuss work completed to date on the 1980 algerian earthquake and introduce a description of the earthquake in terms of rupture propagation using the nomenclature of fracture mechanics field and teleseismic studies have shown the earthquake fault to be divided into three major thrust segments rupture began at the sw end of the system and propagated along successive segments geological sections reveal that different fault segments have suffered different amounts of displacement in the past the amount of geological displacement increases systematically from almost zero at the sw end of the fault to several hundred metres further ne faulting at the sw end is very young and appears to be extending the thrust system along strike the aftershock data of ouyed et al reveal that strike slip aftershocks occur beyond the sw end of the thrust fault these are accommodating compression by conjugate strike slip faulting on north and west trending planes this network of conjugate faults plays a crucial role in the initiation of major eathquakes on the thrust system and may be regarded as a plastic zone beyond the end of the thrust fault increasing horizontal stress causes the strike slip system to evolve into a zig zag network of thrusts which is partly controlled by the pre existing strike slip faults finally a through going thrust can develop and leads to catastrophic rupture along the main fault plane to describe the propagation of the main shock we extend aki s concept of geometric barriers and divide these into two types in conservative barriers the slip vector is common to both fault planes whereas in non conservative barriers the slip vectors are different on the two fault planes that meet at the barrier although both types of barrier arrest dynamic rupture only nonconservative barriers need produce aftershocks as off fault deformation is required to accommodate the difference in slip vectors by considering the aftershock zones as areas of distributed deformation we show that fracture toughness in the earth is not a material constant but is related to fault geometry and therefore changes as fault systems evolve the current south westwards growth of the el asnam thrust system can be seen as the latest phase in an evolution consisting of periods of along strike extension alternating with periods of increasing net displacement during which no fault growth occurs these two types of behaviour allow a segmented fault system to be produced

model of earthquake recurrence role of elastic wave radiation relaxation of friction and inhomogeneity we have constructed a dynamical model of seismicity wherein a fault is embedded in an infinite continuous elastic medium therefore the influence of the energy dissipated in seismic wave radiation oil the sequential history of model earthquakes is fully taken into account in this model the drop in friction at rupture takes place gradually thus introducing a relaxation dimension as an example we consider a finite homogeneous fault that is terminated by infinitely strong barriers at the ends the features of the seismicity are dominated by the stresses that are reflected from the unbreakable barriers there is a strong dependence of the patterns of seismicity on the ratio of the relaxation dimension to the distance between the barriers at the ends for large values of this parameter we find that periodicity begins after a short transient interval and a dominance of the statistical distributions by large events that break completely through the fault from end to end for small values of this parameter smaller scale seismicity is interspersed with the large events and no periodicity is observed within the time spanned by the computations we conclude that major unquenched heterogeneities such as those found at barriers which we suppose arise in nature due to the nonuniform geometry of faults are vital ingredients for generating complex seismic histories as well as giving rise to the complex features of individual earthquake source time functions in models of seismicity as a dynamical process

on the geometric complexity of earthquake focal zone and fault systems a statistical study we discuss various methods used to investigate the geometric complexity of earthquakes and earthquake faults based both on a point source representation and the study of interrelations between earthquake focal mechanisms we briefly review the seismic moment tensor formalism and discuss in some detail the representation of double couple dc earthquake sources by normalized quaternions non dc earthquake sources like the clvd focal mechanism are also considered we obtain the characterization of the earthquake complex source caused by summation of disoriented dc sources we show that commonly defined geometrical fault barriers correspond to sources without any clvd component we analyze the cmt global earthquake catalog to examine whether the focal mechanism distribution suggests that the clvd component is likely to be zero in tectonic earthquakes although some indications support this conjecture we need more extensive and significantly more accurate data to answer this question fully

weathered bedrock as a source of sand and gravel aggregate in north eastern new south wales australia the most commonly recognized sources of sand and gravel aggregate are the deposits of coastal fluvial and glacial sedimentary processes it is not commonly recognized that weathered bedrock is also an important source of sand and gravel aggregate in the case of weathered sedimentary bedrock the product may be indistinguishable from modern sedimentary materials and deposits may be misidentified batson s quarry is a major sand and gravel aggregate resource for the rapidly developing region of north eastern new south wales the deposit has previously been assumed to be a young sedimentary deposit but detailed field examination and comparison with surrounding rock types indicates that it has formed from weathered mesozoic sandstone bedrock the extraction of weathered bedrock aggregate deposits has distinctive environmental implications because unlike sedimentary aggregates they are not restricted by the geometry of sedimentary environments and do not necessarily interfere with surface drainage systems this study shows that the recognition of the geological origin of a resource is essential in order to determine its potential geographical extent and thereby maximize its utilization and minimize land use conflict

frictional changes induced by seismic slip on a non planar fault summary we propose a model which describes the formation of a strong asperity on a fault we consider a fault surface which differs slightly from a plane due to a jog like topographic variation the fault is placed in an elastic space and is subject to a uniform stress field the orientation of the fault is such that the normal traction which is compressive is greater on the topographic variation determining a higher static friction and hence an asperity the value of friction on this asperity depends on the magnitude of shear stress for times of seismological interest the increase in shear stress at rates typical of tectonic processes does not produce a sensible increase in friction with respect to the adjacent fault segments a considerable increase in friction and the formation of a strong asperity or even a barrier can occur due to repeated seismic slip episodes on the fault slip results in an elastic medium deformation causing an increase in normal traction on the asperity and hence in friction this process is described with the aid of a tensile somigliana dislocation regions with high friction undergo partial fracturing of the fault face material which can produce fault gouge the tensile dislocation introduces a small non double couple component in the seismic moment of the seismic event the magnitude of this component depending mainly on the relative size of the asperity

palaeomagnetism of flood basalts in the pilbara craton western australia late archaean continental drift and the oldest known reversal of the geomagnetic field 1 a late archaean circa 2775 2715 ma succession of terrestrial continental flood basalts mafic tuffs felsic volcanic rocks and clastic sedimentary rocks in the nullagine synclinorium and meentheena centrocline of the east pilbara basin western australia has been sampled for a palaeomagnetic study over 500 oriented mostly basalt drill cores were collected from the supracrustal succession and associated dykes thermal and alternating field demagnetization revealed two distinct components positive fold conglomerate and reversal tests confirm that the primary natural remanent magnetization nrm is still preserved the secondary component is interpreted as the record of remagnetization during a major thermal event possibly in the early proterozoic analysis of the primary nrm directions results in a magnetostratigraphy and an apparent polar wander path apwp for the 60 myr interval covered by the sampled succession assuming a geocentric axial dipole during this time interval the apwp shows that the pilbara craton was drifting during the late archaean and that drift rates probably varied significantly in particular a mean 27 2 shift in palaeolatitude is recorded across an unconformity that represents a relatively short time period and that marks a significant change in basalt geochemistry this study suggests that continents moved horizontally during the late archaean and that the rates of movement were significantly faster than in the phanerozoic in addition a reversed polarity interval with a positive reversal test is recorded we argue that it documents the oldest known geomagnetic reversals of the geomagnetic field

fault kinematics and surface deformation across a releasing bend during the 2010 mw 7 1 darfield new zealand earthquake revealed by differential lidar and cadastral surveying dextral slip at the western end of the east west striking greendale fault during the 2010 m w 7 1 darfield earthquake transferred onto a northwest trending segment across an apparent transtensional zone here named the waterford releasing bend we used detailed surface mapping differential analysis of pre and postearthquake light detection and ranging lidar and property boundary cadastral resurveying to produce high resolution centimeter scale estimates of coseismic ground surface displacements across the waterford releasing bend our results indicate that the change in orientation on the greendale fault incorporates elements of a large scale releasing bend from the viewpoint of westward motion on the south side of the fault as well as a smaller scale restraining stepover from the viewpoint of southeastward motion on the north side of the fault these factors result in the waterford releasing bend exhibiting a decrease in displacement to near zero at the change in strike and the presence within the overall releasing bend of a nested localized restraining stepover with contractional bulging the exceptional detail of surface deformation and kinematics obtained from this contemporary surface rupture event illustrates the value of multimethod investigations our data provide insights into strike slip fault bend kinematics and into the potentially subtle but important structures that may be present at bends on historic and prehistoric rupture traces

structural analysis of the brigham city weber segment boundary zone wasatch normal fault utah implications for fault growth and structure we investigate the history kinematics principal stress orientations and geometry of deformation at the end of a bent normal fault segment of the wasatch fault zone utah three fault types developed in archean crystalline rocks reflect progressive uplift of fault related footwall rocks chlorite breccias and phyllonites reflect deep level reaction assisted plastic deformation along the north striking part of the segment planar fretted faults which formed by cataclasis cut the phyllonites and breccias and are developed throughout the footwall of the segment youngest faults are hematitecoated extremely narrow polished surfaces slip vectors and kinematic analyses of small faults developed in the footwall indicate oblique normal slip along the north striking portion of the segment slip vectors and fault orientation along the northwest striking portion of the segment reflect complexly oriented slip on faults which strike subparallel and at high angles to the main fault trace yet slip is confined to a broad fault parallel zone small faults at the southernmost tip of the segment indicate a strong influence of the north striking weber segment to the south inversion of fault data for principal stress orientations document complexly oriented principal stresses through the segment boundary zone and suggest that 3 may have reoriented approximately 60 over the life of the segment subsurface structure combined with small fault data indicate the segment boundary is comprised of a southwest plunging bedrock high which is reflected by a sharp bend in the brigham city segment the southern end of the brigham city segment may have started as a straight north striking fault which has bent due to changes in stress orientations and or interaction with the adjacent weber segment

fault geometry at the rupture termination of the 1995 hyogo ken nanbu earthquake the source geometry and slip distribution at rupture termination of the 1995 hyogo ken nanbu earthquake were investigated using waveform inversion on the assumption of fault branching in the northeastern part of the rupture model possible branching of the okamoto fault is suggested both by the static displacement distribution and damage extension east of kobe nishinomiya area to exclude data contaminated by the basin edge diffracted wave in the waveform inversion process we examined the spatio temporal variation of its influence and from a comparison with a flat model we determined windows appropriate for the data three subevents were identified as was reported in previous works the largest was in the shallow part on the awaji side whereas the smaller two occurred at great depths 7km on the kobe side we found a smaller subevent in the deep part of the branch total variance reduction was larger and the abic value was smaller when we assumed the branch than when we did not which shows the superiority of the branching fault model resolution checks showed that the slips on proposed branched portions are physical and not caused by random data noise or systematic errors in green s func tions that arise from misestimation of velocity structures calculation of the relative static displacement between two leveling observation stations near the branching fault also showed the greater utility of the branching fault model the effect of slip on the branched fault has been shown in near source ground motion simulation using the 3d finite difference method iwata et al 1999 the characteristic distribution of ground motion in the near source region indicated by the damage distribution is well reproduced by the modeling of both the source process and wave propagation in the realistic 3d velocity structure slip on the branched fault affected the ground motion in eastern kobe nada and higashi nada wards ashiya and nishinomiya cities but its contribution is not dominant even in those regions about 30 to 50 maximum velocity in the frequency range of 0 1 to 1 0 hz we conclude that branching rupture of the okamoto fault during the hyogo ken nanbu earthquake is the preferable interpretation on the source process of this earth quake this supports the idea of a geometrical barrier suggested by geological ob servations

a reconnaissance 40ar39ar geochronologic study of ore bearing and related rocks siberian russia abstract 40 ar 39 ar age spectra of biotite from a mineralized vein in the ore bearing noril sk i intrusion and from picritic like gabbrodolerite from the weakly mineralized lower talnakh intrusion show that these bodies were emplaced at 249 2 ma which is not significantly different from the age of the permian triassic boundary the ore bearing intrusions postdate the lower third of the flood basalt sequence in the noril sk area and on the basis of geochemistry can best be correlated with lavas slightly younger than those which they cut thus flood basalt was erupted at the time of the permian triassic mass extinction event although its role in this event is as yet ill defined additional new 40 ar 39 ar age data for a group of intrusive and extrusive rocks on the western margin of the siberian craton indicate that mafic magmatism extended over a period of several tens of million years whereas paleomagnetic data suggest that the bulk of the siberian flood basalt sequence near noril sk has been erupted in only a million years or so 40 ar 39 ar ages of plagioclase from early flood basalt flows are about 2 younger than those obtained for biotite from the crosscutting noril sk i intrusion probably because of slight alteration and argon loss from the plagioclase

late permian to early triassic magnetostratigraphy a late permian to early triassic magnetostratigraphic reference section is presented the lower triassic part is based on results from marine limestone sections in south china published earlier 1 2 reliable new permian data are added here which have been collected in the nammal gorge salt range northwest pakistan where marine sediments have been deposited quasi continuously with occasional minor hiatuses during the late palaeozoic to early mesozoic about 50 of the permian samples from the nammal section contain hidden beneath a strong recent or tertiary overprint a characteristic remanent magnetization chrm which is very likely of permian age this component which was imprinted on the southern hemisphere has normal as well as reversed polarity with a normal mean direction decl 289 3 incl 50 3 95 4 3 n 113 which is in close agreement with the palaeofield direction expected for a site belonging to the indian plate as part of gondwanaland during the permian in the lower upper permian several normal polarity zones are recognized this contradicts the current assumption that rocks of this age belong to the long reversely polarized kiaman hyperzone the kiaman interval must end and the illawarra hyperzone of mixed polarity must begin in or prior to the lowermost upper permian the permian triassic boundary at nammal as well as in the chinese sections is situated very close to a transition from a reversed to a normal polarity zone the upper permian at nammal together with the lower triassic south china sections is estimated to cover about 20 ma nearly 30 polarity changes are observed which result in an average reversal frequency very similar to that observed during the early tertiary the reversal rate after the end of the long lasting reversed kiaman hyperchron apparently increases in a manner similar to that after the end of the cretaceous long normal superchron only a few polarity zones are found in the lower upper permian while progressively more frequent reversals follow in the lower triassic

geologic structures related to new madrid earthquakes near memphis tennessee based on gravity and magnetic interpretations new inversions of gravity and magnetic data in the region north of memphis tennessee and south of latitude 36 define boundaries of regional structures and igneous complexes in the upper crust microseismicity patterns near interpreted boundaries suggest that igneous complexes influence the locations of microseismicity a weak seismicity cluster occurs near one intrusion covington pluton at the intersection of the southwest margin of the missouri batholith and the southeast margin of the reelfoot rift a narrow seismicity trend along the reelfoot rift axis becomes diffuse near a second intrusion osceola intrusive complex and changes direction to an area along the northwest flank of the intrusion the axial seismicity trend also contains a tight cluster of earthquakes located just outside the osceola intrusive complex the mechanical explanation of the two seismicity patterns is uncertain but the first cluster may be caused by stress concentration due to the high elastic stiffness and strength of the covington intrusion the spatially changing seismicity pattern near the osceola complex may be caused by the preceding factors plus interaction with faulting along the rift axis the axial seismicity strand itself is one of several connected and interacting active strands that may produce stress concentrations at strand ends and junctions the microseismicity clusters at the peripheries of the two intrusions lead us to conclude that these stress concentrations or stressed volumes may be locations of future moderate to large earthquakes near memphis

influence of fault bends on ruptures data on slip along the san andreas fault have been examined to understand the influence of a bend in the fault system on the extent of slip release a correlation of slip along the fault in the great 1906 and 1857 earthquakes with fault geometry shows that maximum slip occurred near a major change in the fault strike and may be a function of this change the data appear to suggest that in general it takes about 10 years of strain accumulation to negotiate a 1 change in fault strike assuming a slip rate of about 3 cm yr seismic hazard along the san andreas fault may therefore also be a function of fault geometry

3 d 40ar39ar geochronology in the parana continental flood basalt province new 40ar39ar analyses of borehole samples from the parana etendeka continental flood basalt province provide critical evidence of eruption rates in unexposed regions when combined with surface samples the new data clarify the duration of this major volcanic province new ages from both surface and borehole samples confirm a 10 12 million year duration of magmatism which post dates the tithonian mass extinction and provide a unique 3 dimensional picture of the spatial and temporal eruption of the lava pile chemically defined magma types are diachronous and the onset of magmatism occurred 500 1000 km inland migrating southeast towards the incipient south atlantic ocean calculated eruption rates increased from 0 03 km3 yr 1 between 138 and 135 ma through 0 13 km3 yr 1 between 135 and 133 ma to 0 21 km3 yr 1 between 133 and 131 ma supporting the notion that the rate of magmatism increased with time and proximity to the developing south atlantic after 131 ma the continental eruption rates dropped dramatically to 0 01 km3 yr 1 presumably because rifting had occurred and eruption centred in the oceanic rio grande rise with eruption rates of around 0 3 0 5 km3 yr 1 given the available constraints on the potential temperature of the plume thickness of the continental lithosphere and degrees of extension through time predicted melt production rates within the plume seriously underestimate the calculated eruption rates on the continent however the eruption rates can be reconciled if melting occurred by conductive heating of volatile enriched mantle the diachronous nature of the magma types supports the idea that melting occurred over a wide area and that the different magma types reflect different source regions rather than the temporal evolution of magmas from a single source given that 10 million years is appropriate to the timescales for conductive heating above the mantle plume it is suggested that these distinct source regions were located within the lithospheric mantle consistent with geochemical studies

palaeomagnetism of east siberian traps and kimberlites two new poles and palaeogeographic reconstructions at about 360 and 250 ma summary we studied basalt sills and dykes and kimberlite pipes from the eastern part of the siberian platform these are spread out over a few hundred kilometres and are divided into two age groups late permian early triassic mir aikhal and olenyek regions and late devonian early carboniferous viluy and markha basins aikhal region the palaeomagnetic poles determined for each sill or dyke are statistically different from each other but averaging all corresponding directions from these sills and dykes with those from kimberlites of different generations yields results with acceptable statistics this is probably due to the averaging out of secular variation and or changes in magnetic polarity the resulting palaeomagnetic poles allow one to reconstruct the palaeopositions of siberia during the two large flood basalt events at about 360 and 250 ma a significant rotation of the siberian platform during the devonian and carboniferous is suggested the new data are in general agreement with some earlier palaeomagnetic poles for the late permian early triassic traps of the tungusska basin and significantly reduce uncertainties for previous late devonian early carboniferous siberian poles which were very scattered together with geological and absolute age data the palaeomagnetic data support the hypothesis that kimberlite magmatism and trap intrusions were both rapid and relatively close in time the 360 ma event is emerging as a magmatic event with considerable extent over the russian and siberian platforms related to incipient continental break up and triple junction formation possibly at or near the time of the frasnian famennian mass extinction

field evidence of rupture of the qingchuan fault during the 2008 mw7 9 wenchuan earthquake northeastern segment of the longmen shan thrust belt china abstract although many studies of the 2008 mw 7 9 wenchuan earthquake have described the ground deformation features rupture mechanism and structural features of the seismogenic fault zone associated with this event debate remains concerning the total length of the co seismic surface rupture zone and whether the earthquake ruptured the qingchuan fault in the northeastern segment of the longmen shan thrust belt lstb china in this paper we present new field evidence that the qingchuan fault was ruptured by the 2008 wenchuan earthquake and that the total length of the co seismic surface rupture zone is up to 285 300 km field investigations reveal that the earthquake produced a 60 km long surface rupture zone along the pre existing qingchuan fault with the offset being mainly right lateral strike slip and a distinct component of vertical slip co seismic surface ruptures are characterized by faults and extensional cracks field measurements indicate co seismic right lateral strike slip displacements along the qingchuan fault of 0 3 0 6 m and vertical offsets of 0 2 0 5 m which differs to the displacements observed along the central and southwestern segments of the wenchuan surface rupture zone in the displacement amount and sense the change in slip sense from thrust dominated slip in the central and southwestern segments of the lstb to right lateral strike slip dominated displacement along the qingchuan fault northeastern segment of the lstb reflects a change in the orientation of compressive stress along the lstb associated with eastward extrusion of the tibetan plateau as it accommodates the ongoing penetration of the indian plate into the eurasian plate

permo triassic boundary superanoxia and stratified superocean records from lost deep sea pelagic cherts of japan and british columbia canada recorded a long term and worldwide deep sea anoxic oxygen depleted event across the permo triassic or paleozoic and mesozoic boundary 251 2 million years ago the symmetry in lithostratigraphy and redox condition of the boundary sections suggest that the superocean panthalassa became totally stratified for nearly 20 million years across the boundary the timing of onset climax and termination of the oceanic stratification correspond to global biotic events including the end guadalupian decline the end permian extinction and mid triassic recovery