thrust fault growth and segment linkage in the active ostler fault zone new zealand abstract thrust faulting is a fundamental mode of crustal deformation yet many of the key geometrical attributes of thrust faults and the controls on fault rupture growth and linkage remain poorly resolved numerous surface rupturing thrust faults cut through upper quaternary glacial outwash terraces within the ostler fault zone an active thrust system in the southern alps new zealand we use these deformed marker surfaces to define the three dimensional deformation field associated with their surface expression and to map displacement and length on 40 fault segments displacement transfer across two fault segment arrays occurs in distinctly different styles in one displacement is transferred between en echelon fault segments to produce a smooth linear displacement gradient in the other large scale folding and a population of small faults transfer displacement between two non overlapping fault segments with a residual displacement minimum within the transfer zone size distribution of fault segment length and maximum displacement follow a power law scaling relationship maximum displacement d max scales linearly with and represents 1 of segment trace length l d max l data from the segments of the ostler fault zone display similar scaling to a global fault dataset this similarity is surprising given that the observed displacements along the ostler fault represent only 20 ky of slip on fault segments that are likely to be many times older

the topology of evolving rift fault networks single phase vs multi phase rifts rift fault networks can be complex particularly those developed by multiple periods of non coaxial extension comprising non colinear faults with many interactions thus topology rather than simple geometry is required to characterise such networks as it provides a way to describe the arrangement of individual faults in the network topology is analysed here in terms of nodes isolated i nodes or connected y or x nodes and branches i i i c c c branches in map view the relative proportions of these parameters vary in natural single and multi phase rift fault networks and in scaled physical models at different stages of development and strain interactions in single phase rifting are limited to fault splays and along strike fault linkage i node and i i or i c branch dominated networks whereas in multi phase rifting the topology evolves towards y node and c c branch dominated networks with the degree of connectivity increasing with greater strain the changes in topology and network connectivity have significant implications for fluid flow and reservoir compartmentalisation studies furthermore topology helps to distinguish single and multiple phase extension i e tectonic histories and thus provide constraints on the geodynamic context of sedimentary basins

the importance of small scale faulting in regional extension a recurring observation in many studies of extensional basins has been that the amount of extension visible on normal faults for example on seismic reflection profiles is significantly less than the amount of extension indicated by crustal thickness and thermal subsidence1 5 one mechanism suggested to account for this discrepancy is small scale faulting with offsets too small to be resolved seismically6 7 but earthquake studies8 10 indicate that small faults are responsible for only a small fraction of the total seismic moment in an active area scholz and cowie11 have recently attempted to extend this approach to the total strain at the end of a finite deformation interval by combining scaling laws describing the distributions of fault lengths and displacements here we present fault displacement data that directly conflict with scholz and cowie s conclusions and imply that up to 40 of the extension may be missed by summing fault offsets on basin profiles the fault population at the end of a long deformation interval may differ substantially from that responsible for the earthquake population at any one time

the gutenberg richter or characteristic earthquake distribution which is it abstract paleoearthquake and fault slip rate data are combined with the cit usgs catalog for the period 1944 to 1992 to examine the shape of the magnitude frequency distribution along the major strike slip faults of southern california the resulting distributions for the newport inglewood elsinore garlock and san andreas faults are in accord with the characteristic earthquake model of fault behavior the distribution observed along the san jacinto fault satisfies the gutenberg richter relationship if attention is limited to segments of the san jacinto that are marked by the rupture zones of large historical earthquakes or distinct steps in fault trace the observed distribution along each segment is consistent with the characteristic earthquake model the gutenberg richter distribution observed for the entirety of the san jacinto may reflect the sum of seismicity along a number of distinct fault segments each of which displays a characteristic earthquake distribution the limited period of instrumental recording is insufficient to disprove the hypothesis that all faults will display a gutenberg richter distribution when averaged over the course of a complete earthquake cycle but given that 1 the last 5 decades of seismicity are the best indicators of the expected level of small to moderate size earthquakes in the next 50 years and 2 it is generally about this period of time that is of interest in seismic hazard and engineering analysis the answer to the question posed in the title of the article at least when concerned with practical implementation of seismic hazard analysis at sites along these major faults appears to be the characteristic earthquake distribution

structure of lower carboniferous basins of nw ireland and its implications for structural inheritance and cenozoic faulting abstract the geometry of lower carboniferous basins across the northern part of ireland is characterised by a gradual change in polarity of structure from a predominantly southward dipping fault system in northern ireland through the lough allen basin and into a mainly northward dipping fault system of connemara in the southwest this polarity change is reflected in the emergence of northward facing uplifted footwall blocks such as at croagh patrick and the ox mountains in the southwest with southward facing blocks in the northeast despite these structural changes there is a great degree of along strike continuity of lower carboniferous structure strain and displacement with the system forming a link between comparable sized and coeval basins in northern england and scotland to the east and the canadian maritime provinces to the west the spatial distribution of carboniferous normal faults suggests that caledonian structure such as the fair head clew bay line plays an important role in the localisation of post caledonian strain although the reactivation of individual caledonian structures may be less common the terrain of the west of ireland is strongly influenced by major carboniferous faults offsetting the base carboniferous unconformity as opposed to previously suggested cenozoic normal faulting of a tertiary peneplain

variability in fault size scaling due to rock strength heterogeneity a finite element investigation abstract practical application of fault size scaling relationships usually involves extrapolation of a limited data set over a scale range beyond that observed or into adjacent unstudied areas here we investigate the validity of such extrapolations by considering the variability in the size frequency distributions of fault populations that develop under identical tectonic conditions using a numerical model to generate conjugate normal fault populations in cross section the deforming material is modelled using a strain softening von mises rheology with gaussian heterogeneity in yield strength distributed randomly throughout the mesh we present eight deformation experiments that differ only in the random spatial pattern of yield strengths we observe power law size frequency scaling i e n ax c where n is the cumulative number of faults and x is a measure of fault size but with a range of values of c the ensemble average value of c decreases with increasing percentage extension however for individual model runs the dependence of c on total strain shows significant variability that we can relate to small but important differences in fault growth and strain localisation at any particular strain the range of values of c is 10 times greater than the error estimate derived from least squares regression of the cumulative frequency data our results suggest therefore that large uncertainties should be associated with extrapolating fault population data from one scale or region to another even if the lithology and tectonic history are similar

mesoscale characteristics of monsoonal convection and associated stratiform precipitation abstract observations undertaken on 12 january 1990 at darwin australia 12 s 130 e are used to document the structure of a monsoonal rainband in a low cape low shear tropical environment dual doppler radar analyses are employed to investigate the structure and kinematics of the convective and stratiform regions a system with the characteristics of a relatively short lived squall line in which warm rain processes play a significant role in the production of precipitation is evident planetary boundary layer cold pool production is important in the organization and motion of the system a trailing stratiform region is evident with a mean updraft downdraft circulation but is composed of in situ decaying convective cells a storm relative mesoscale cyclonic circulation is also observed within the stratiform cloud this vortex was maintained by thermodynamically induced midlevel convergence convectively generated storm scale circulations and their interaction with the background monsoon now

the late oligocene to early miocene early evolution of rifting in the southwestern part of the roer valley graben the roer valley graben is a mesozoic continental rift basin that was reactivated during the late oligocene the study area is located in the graben area of the southwestern part of the roer valley graben rifting initiated in the study area with the development of a large number of faults in the prerift strata some of these faults were rooted in preexisting zones of weakness in the mesozoic strata early in the late oligocene several faults died out in the study area as strain became focused upon others some of which were able to link into several kilometer long systems within the late oligocene to early miocene northwestward prograding shallow marine syn rift deposits the number of active faults further decreased with time a relatively strong decrease was observed around the oligocene miocene boundary and represents a further focus of strain onto the long fault systems miocene extensional strain was not accommodated by further growth but predominantly by displacements along the long fault systems since the oligocene miocene boundary coincides with a radical change in the european intraplate stress field the latter might have contributed significantly to the simultaneous change of fault kinematics in the study area

a numerical study of the stratiform region of a fast moving squall line part ii relationship between mass pressure and momentum fields abstract in a companion paper a two dimensional simulation of a fast moving tropical squall line was successfully compared to observations performed during the copt81 experiment over west africa the full ice phase parameterization is shown to be crucial in the simulation of trailing anvil precipitation different diagnostic tools are applied to the simulated fields to further our understanding of the scale interactions within a squall line type mesoscale convective system the pressure organization is characterized by two marked features important for explaining the inner circulation first a front to rear midlevel pressure gradient and second the surface pressure mesohigh extending from the gust front to the rear of the most active part of the trailing stratiform region based on the hydrostatic approximation an original method of decomposition of the pressure field is proposed whereby dynamical and buoyant contributions depend only on the horizontal and vertical respectively the mean pressure i

circulations associated with a mature to decaying midlatitude mesoscale convective system part i surface features heat bursts and mesolow development abstract this study examines surface features associated with a mature to dissipating midlatitude mesoscale convective system that occurred on 23 24 june 1985 during the oklahoma kansas preliminary regional experiment for storm central the primary data sources include a 400 500 km surface mesonetwork on a 50 km grid rawinsonde observations from 12 supplementary sites in kansas and oklahoma and radar measurements from conventional as well as dual doppler networks the mesoscale convective system under investigation developed in an environment with weak vertical shear and had a lifetime of 9 12 h it consisted in its mature stage of a southward moving arc shaped line of deep convective cells with a trailing stratiform precipitation region to the north thirty three percent of the surface rain in the portion of the mesonetwork experiencing storm passage was from the stratiform region an intense mesoscale downdraft developed beneath the stratiform cloud with a strong mesohigh at the surface a wake low w

earthquake frequency distribution and the mechanics of faulting the level of intraplate seismicity in japan generally shows a positive correlation with the density of quaternary faulting in southwest japan where intraplate seismicity is concentrated on land rates of seismic moment release m 0 are similar when calculated from either the 400 year historical record of seismicity or geologically determined slip rates of quaternary faults a data set of 18 earthquakes with seismic moments m0 ranging from 0 01 to 3 1027 dyn cm shows a relationship between rupture lengthl and m0 log m0 23 5 1 94 log l when seismic moment on each quaternary fault is assumed to occur in discrete events every t m0 m 0g years where m0 is estimated for a rupture extended over the entire fault length and m 0g is proportional to the slip rate of each quaternary fault the moment frequency distribution of earthquakes log n a b log m0 predicted from the geologic record is virtually identical to that seen with the 400 year record of seismicity in contrast if it is assumed that earthquakes on each fault occur according to the gutenberg richter relation we obtain poor agreement with the observed seismicity thus while regional seismicity satisfies the relation log n a b log m0 or equivalently log n a b log m where m is magnitude it appears that seismicity on individual faults does not this further implies that the primary factor that leads to the magnitude frequency distribution in regional seismicity studies is the relative distribution of the slip rates and lengths of preexisting faults

kinematic analysis of faults in a physical model of growth faulting above a viscous salt analogue abstract syn sedimentary faults overlying an extended ductile layer within a sand model provide an analogue for studying some aspects of the geometry and kinematics of basin scale extensional listric faults associated with salt rollers the displacement analysis techniques used to examine displacement variations over fault surfaces within the sand model show that displacement varies in a regular and predictable manner deviations from simple fault displacement patterns are due to transfers of displacement onto adjacent synthetic faults aggregation of the displacements on adjacent synthetic faults produces more regular patterns of displacement distribution and demonstrates the geometric coherence of the aggregated faults rapid upward decreases in displacement on the model faults are due to fault growth during sedimentation elsewhere in the model post sedimentary faulting is associated with very low upward displacement gradients and pre and syn faulting sedimentation are readily distinguished on cross sectional fault traces in three dimensions a non horizontal line separating the pre faulting and syn faulting sequences tracks the lateral extent of a fault through time backstripping of fault displacements by subtracting the fault displacement of a sedimentary horizon from the displacements of underlying horizons gives the displacement distribution on a fault surface at the time of deposition of the backstripped horizon backstripped fault displacement distributions also allow examination of the general fault structure through time backstripping of fault displacements on one of the larger faults within the model and on an associated hanging wall synthetic splay shows that the two structures originated as a relay zone which was breached by lateral propagation of one of the overlapping faults which form the relay zone the backstripping technique allows determination of the geometrical changes during growth of a fault system

a numerical study of the genesis of extratropical convective mesovortices part i evolution and dynamics abstract the purpose of this study is to understand the genesis of extratropical convective mesovortices and the large scale environmental features that influence the vortex formation a hypothesis is proposed that mesovortices form in the stratiform rain regions of mesoscale convective systems mcss due to the reduction of static stability that reduces the effective local rossby radius in such regions a conceptual model of the mesoscale convective cyclogenesis is introduced which describes the three stages of the mesovortex formation a modified version of the pennsylvania state university national center for atmospheric research three dimensional hydrostatic mesoscale model is used to simulate mesovortex genesis in analytically generated pre mcs large scale environments the model simultaneously incorporates parameterized convection and a grid resolvable convective scheme containing the effects of hydrostatic water loading condensation evaporation freezing melting and sublimation a control si

numerical simulation of an intense squall line during 10 11 june 1985 pre storm part ii rear inflow surface pressure perturbations and stratiform precipitation abstract an intense rear inflow jet surface pressure perturbations and stratiform precipitation associated with a squall line during 10 11 june 1985 are examined using a three dimensional mesoscale nested grid model it is found that the large scale baroclinity provides favorable and deep rear to front flow within the upper half of the troposphere and the mesoscale response to convective forcing helps enhance the trailing extensive rear inflow however latent cooling and water loading are directly responsible for the generation of the descending portion of the rear inflow the role of the rear inflow is generally to produce convergence ahead and divergence behind the system and thus assist the rapid acceleration of the leading convection when the prestorm environment is convectively favorable and the rapid dissipation of the convection when encountering unfavorable conditions in this case study the rear inflow jet appears to have caused the splitting of the surface wake low as well as the organized

progressive localisation of strain during the evolution of a normal fault population abstract the evolution of a syn sedimentary normal fault population has been established from the analysis of a high quality 3d seismic reflection survey from the timor sea offshore nw australia growth of the fault population which initiated ca 6 ma ago occurred in three distinct but temporally overlapping stages the initial stage of fault population evolution was characterised by rapid growth of fault length in the first 1 2 ma of extension displacement rates of individual faults were established during this stage and were constant throughout subsequent fault growth the second stage involved amplification of fault displacements on existing fault traces with minimal fault propagation during the third stage shortening of the traces of active faults and high mortality rates for small faults resulted in a net decrease in fault trace length on successively younger horizons this stage was accompanied by a declining extension rate fault throw populations have constant slopes on each syn faulting horizon however an up sequence shallowing of the slope of length and geometric moment populations demonstrates a progressive concentration of strain onto fewer and larger faults through time if extension were to continue beyond the present value of 4 5 this strain localisation might culminate in the formation of a single active through going fault

a sublimation initiated mesoscale downdraft and its relation to the wind field below a precipitating anvil cloud abstract a simple one dimensional model is developed to examine the potential for a sublimation initiated mesoscale downdraft to influence the dynamics of the subanvil region by advecting horizontal momentum from a high level precipitating anvil cloud downward into the middle or lower troposphere model results suggest that this vertical advection can occur on a time scale of several hours or less although it is found to be highly dependent upon the snow mixing ratio within the overlying anvil cloud and lapse rates in the environment below the study is motivated by an examination of data from a 50 mhz radar wind profiler on 24 june 1985 that suggests downward momentum advection from anvil base may have produced unbalanced flow in midlevels owing to strong flow within the anvil and weak midlevel geostrophic winds for this situation we hypothesize that as the anvil cloud both dissipated and was advected horizontally away from the profiler site by the strong upper level winds the downdraft weakened a

lithospheric strength and rift migration controls on synrift stratigraphy and breakup unconformities at rifted margins examples from numerical models the atlantic and south china sea margins synrift stratigraphy and the distribution of breakup related erosional unconformities vary vastly between passive margins and cannot be explained by classical rifting models here we use numerical modeling to predict their spatiotemporal distribution we show that synrift stratigraphy mimics rift architecture which is controlled by lithospheric strength basinward rift migration during extension produces 1 oceanward younging syntectonic and posttectonic sequences 2 rift migration unconformities rmus predating breakup and 3 a breakup unconformity bu that only extends over the outermost margins since breakup is not linked with a sudden stress drop with small synrift sedimentation the rmus and bu laterally merge to form a margin wide unconformity in symmetric wide conjugate margins which arise for weak lithospheres such as the south china sea a long phase of distributed deformation with little subsidence results in early synrift sediment over most of the margins rmus merge into a single event that marks the subsequent focusing of deformation into a narrow breakup area which experiences short lived intense thinning and subsidence in asymmetric conjugate margins lateral rift migration transports shallowly deposited early synrift sediments from the narrow to the wide hyperextended margin leading to a condensed syntectonic sequence and a single bu in the narrow margin and a series of rmus in the wide one for very weak lower crusts lateral rift migration generates large synrift sag basins in the wide margin as in angola and congo margins our models resemble the observed margins tectonic diversity and may be used as templates for interpreting their distal unexplored areas

occurrence and development of folding related to normal faulting within a mechanically heterogeneous sedimentary sequence a case study from inner moray firth uk folds associated with normal faults are potential hydrocarbon traps and may impact the connectivity of faulted reservoirs well calibrated seismic reflection data that image a normal fault system from the inner moray firth basin offshore scotland show that folding was preferentially localized within the mechanically incompetent lower middle jurassic pre rift interval comprising interbedded shales and sandstones and within upper jurassic syn rift shales upward propagation of fault tips was initially inhibited by these weak lithologies generating fault propagation folds with amplitudes of c 50 m folds were also generated or amplified by translation of the hanging wall over curved convex upward fault planes these fault bends resulted from vertical fault segmentation and linkage within mechanically incompetent layers the relative contributions of fault propagation and fault bend folding to the final fold amplitude may vary significantly along the strike of a single fault array in areas where opposite dipping conjugate normal faults intersect the displacement maxima are skewed upwards towards the base of the syn rift sequence i e the free surface at the time of fault initiation and significant fault propagation folding did not occur these observations can be explained by high compressive stresses generated in the vicinity of conjugate fault intersections which result in asymmetric displacement distributions skewed towards the upper tip with high throw gradients enhancing upward fault propagation our observations suggest that mechanical interaction between faults in addition to mechanical stratigraphy is a key influence on the occurrence of normal fault related folding and controls kinematic parameters such as fault propagation slip ratios and displacement rates

fault orientation variations along the strike of active normal fault systems in italy and greece implications for predicting the orientations of subseismic resolution faults in hydrocarbon reservoirs the orientations of subseismic scale faults vary systematically along the strike of basin bounding active normal faults in italy and greece a total of 16 272 outcrop measurements of the strike and dip of fault planes and their associated slip vectors indicate oblique slip near the lateral fault tips of the normal faults subseismic faults vary in orientation to accommodate this slip if viewed in map view from the footwall looking toward the hanging wall right lateral slip occurs at the left end of the faults with left lateral slip at the right end overall slip vectors converge toward the hanging wall with intersection lines for faults accommodating this slip parallel to the slip vector if the same faulting style applies elsewhere the empirical relationships presented herein can be used to calibrate results from mechanical fault models and provide a pragmatic guide to the orientations of normal fault bound compartments of rock in subsurface hydrocarbon reservoirs given that the offsets across such faults may be below seismic resolution and not amenable to direct measurement

pseudo gamma ray volume from extended elastic impedance inversion for gas exploration the unayzah formation has been an exploration target in saudi arabia for more than a decade with oil and gas production from the unit now well established however exploration in the unayzah in central saudi arabia remains technically challenging this is due in large part to its complex interplay of continental clastic depositional environments that include braided stream wadi fill playa lake interfluve alluvial fan and eolian dune systems

a mechanism to explain rift basin subsidence and stratigraphic patterns through fault array evolution rift basin stratigraphy commonly records an early stage of slow subsidence followed by an abrupt increase in subsidence rate the physical basis for this transition is not well understood although an increase in extension rate is commonly implied here a numerical fault growth model is used to investigate the influence of segment linkage on fault displacement rate patterns along an evolving normal fault array the linkage process we describe is controlled by a stress feedback mechanism which leads to enhanced growth of optimally positioned faults model results indicate that even with constant extension rates slow displacement rates prevail during an initial phase of distributed extension followed by an increase in displacement rates as strain becomes localized on linked fault arrays this is due to the dynamics of fault interactions rather than mechanical weakening comparison of model simulations with rift basin subsidence and stratigraphic patterns in the gulf of suez and north sea suggests that the occurrence and timing of rapid basin deepening can be explained by the mechanics of fault zone evolution without invoking a change in regional extension rates

scaling of fault displacements and implications for the estimation of sub seismic strain fault displacement populations have been shown to follow a power law scaling relationship characterized by an exponent d this relationship can be used to make predictions of the sub seismic fault population from data derived from seismic surveys although fault populations exist in three dimensions the use of section data is recommended d values derived from sections can be applied directly to several problems and are also related to the d value for the fault set in higher dimensions accurate determination of d requires proper consideration of the scale range and sample size limitations of available data the most common technique of using a cumulative frequency graph often leads to an upwards bias an iterative correction procedure is proposed discrete frequency methods avoid this bias but as a standard linear interval graph has other associated problems a log interval graph method is preferred simulations of these methods applied to random computer generated samples from power law distributions have been made to examine the accuracy of d values derived from typical data equations to estimate the confidence intervals for these d values have been derived from a synthesis of the results the application of the techniques is shown using fault data measured on seismic sections from the southern north sea and the inner moray firth where local differences in d are shown to be significant there is usually a marked change in structural style fault data are used to make improved estimates of crustal extension b by extrapolating the derived powerlaw relationship a value of 13 1 20 is calculated for the inner moray firth applications predicting the intersection of horizontal wells with large sub seismic faults and quality control of fault interpretation on seismic sections are also described

crustal deformation processes and the stability of the gutenberg richter relationship abstract global and regional surveys of earthquakes show that empirically determined b values of the gutenberg richter distribution are remarkably stable generally limited to values of 1 0 2 here i interpret observations from california new zealand and japan to suggest that the stability of the b value is a manifestation of a physical process specifically the tendency of crustal strains to organize along relatively discrete zones given a portion of the earth9s crust subject to a displacement field displacement is accommodated by a system of fault lengths that obey a power law distribution with continued displacement longer faults develop at the expense of shorter faults and take up an increasingly greater portion of the displacement budget shifts in regional displacement directions lead to reversals of these trends the changes in the ratio of long faults to short faults in a region is thus accompanied by changes in the relationship between fault length and fault slip rate because the recurrence of earthquakes on faults is a function of both fault length and fault slip rate the deformation process may result in a system of feedback that inhibits changes in the b value as fault populations change a corollary to the idea is that the magnitude frequency statistics of seismicity may be attributed to the same physical processes that are responsible for the development of plate tectonic boundaries and the gross spatial distribution of seismicity around the globe

the role of environmental shear and thermodynamic conditions in determining the structure and evolution of mesoscale convective systems during toga coare abstract a collection of case studies is used to elucidate the influence of environmental soundings on the structure and evolution of the convection in the mesoscale convective systems sampled by the turboprop aircraft in the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare the soundings were constructed primarily from aircraft data below 5 6 km and primarily from radiosonde data at higher altitudes the well documented role of the vertical shear of the horizontal wind in determining the mesoscale structure of tropical convection is confirmed and extended as noted by earlier investigators nearly all convective bands occurring in environments with appreciable shear below a low level wind maximum are oriented nearly normal to the shear beneath the wind maximum and propagate in the direction of the low level shear at a speed close to the wind maximum when there is appreciable shear at middle levels 800 400 mb convective bands form parallel to the shear with

fault slip accumulation in an active rift over thousands to millions of years and the importance of paleoearthquake sampling abstract the catastrophic earthquakes that recently september 4th 2010 and february 22nd 2011 hit christchurch new zealand show that active faults capable of generating large magnitude earthquakes can be hidden beneath the earth s surface in this article we combine near surface paleoseismic data with deep 1 ma timescales in the taranaki rift new zealand our analysis shows that the integration of different timescale datasets provides a basis for identifying active faults not observed at the ground surface estimating maximum fault rupture lengths inferring maximum short term displacement rates and improving earthquake hazard assessment we find that fault displacement rates become increasingly irregular both faster and slower on shorter timescales leading to incomplete sampling of the active fault population surface traces have been recognised for

fractal analysis of three dimensional spatial distributions of earthquakes with a percolation interpretation although many studies have shown that faults and fractures are self similar over a large range of scales none have tested the fault structure for self similarity in three dimensions in this study earthquake hypocentral locations in central and southern california were used to illuminate three dimensional 3 d fault structures for which we measured the fractal capacity dimension d0 3 d hypocentral distributions from the joshua tree big bear and upland aftershock sequences as well as background seismicity at parkfield were found to be fractal where d0 3 d increased with increasing event density asymptotically approaching a stable value the joshua tree data set stabilized at d0 3 d 1 92 0 02 the parkfield data set asymptotically approached d0 3 d 1 82 and the big bear data set approached d0 3 d 2 01 as a test of the effects of location errors upon the measured value of d0 3 d the upland aftershock data were located with both the southern california hadley and kanamori 1977 h k velocity model and the more accurate hauksson and jones 1991 h j velocity model events located with the h k model asymptotically approached d0 3 d 2 07 and events located with the h j model approached d0 3 d 1 79 suggesting that improved hypocentral locations may decrease the measured fractal dimension one interpretation of our results of d0 3 d 2 0 for all of the hypocentral data is that earthquakes only occur on the percolation backbone of a fault network i e the active part of the network that accommodates finite strain deformation sahimi et al 1993 we show that a percolation model that allows for healing of previously broken bonds is consistent with this interpretation

the oklahoma kansas mesoscale convective system of 10 11 june 1985 precipitation structure and single doppler radar analysis abstract the 10 11 june mesoscale convective system observed in kansas during pre storm is studied using a variety of observations including conventional radar satellite and single doppler radar this storm at maturity consisted of a strong line of convection trailed by a broad region of stratiform rain the pre storm doppler radar observations show that the general airflow pattern is similar to that seen in previously analyzed cases however since the doppler observations were quite extensive in time and space they permit several details of the airflow to be revealed for the first time a rear inflow jet front to rear flow aloft and a mesoscale updraft and downdraft were all present the mesoscale downdraft commenced at the top of the slanted rear inflow jet sublimation and evaporation of hydrometeors in this flow apparently generated the necessary cooling to drive the mesoscale downdraft circulation the intensity and slope of the rear inflow jet varied with location in the storm which apparen

evolution of a salt related listric growth fault near the d 1 well block 5605 danish north sea displacement history and salt kinematics abstract the top chalk surface and the tertiary sediments of the danish north sea are cut by only a few major faults which are often related to or controlled by the mobile zechstein salt a single listric growth fault the d 1 fault and its adjacent area have been mapped in detail in order to unravel the fault geometry and kinematics the spatial distribution of displacements and lateral dimensions of the fault are used to examine the interaction between salt movements and the evolution of the fault the displacement distribution on the fault is systematic with contours of equal displacement forming concentric semi ellipses centred on the point of maximum displacement with displacement decreasing upwards and laterally approaching the displacement configuration for the upper part of an ideal simple blind fault furthermore within the volume surrounding the fault vertical displacement shows similar contour patterns for the hangingwall and footwall respectively the lateral displacement variation during fault growth and reconstructed displacement geometries indicate that footwall uplift was mainly a result of salt flow despite the complicated nature of salt dynamics the evolution of the d 1 fault resulted in a systematic fault displacement geometry within the rock volume surrounding the fault

the development of a regional scale intraplate strike slip fault system alpine deformation in the north of ireland abstract a paucity of displacement markers can make constraining the kinematics and interaction of regional scale strike slip faults difficult in this study a high resolution aeromagnetic survey allows quantitative analysis of kilometre scale paleogene faulting in the north of ireland mapping offset dykes and igneous centres reveals the presence of two orientations of cenozoic strike slip faults attributed to broadly n s alpine shortening arising from the convergence of africa and europe reactivated ne sw striking faults accommodated up to 2 3 km of sinistral displacement mainly during the paleocene following tectonic quiescence up to 2 5 km of oligocene aged dextral movement was accommodated on newly formed nnw sse striking faults displacement analysis suggests that the faults were kinematically linked and experienced a switch in polarity of the predominantly active fault orientation during the paleogene forming an apparent conjugate system with asymmetric displacement distributions the switch in fault polarity is attributed to a rotation in the regional maximum horizontal stress orientation and the locus of deformation moving from pre existing reactivated structures to newly formed faults the analysis also illustrates that despite low strain rates the interaction of the principal components of the fault system controlled the formation of sedimentary basins and defined the present day geography of the region far from an active plate boundary

rapid spatiotemporal variations in rift structure during development of the corinth rift central greece the corinth rift central greece enables analysis of early rift development as it is young 5 ma and highly active and its full history is recorded at high resolution by sedimentary systems a complete compilation of marine geophysical data complemented by onshore data is used to develop a high resolution chronostratigraphy and detailed fault history for the offshore corinth rift integrating interpretations and reconciling previous discrepancies rift migration and localization of deformation have been significant within the rift since inception over the last circa 2 myr the rift transitioned from a spatially complex rift to a uniform asymmetric rift but this transition did not occur synchronously along strike isochore maps at circa 100 kyr intervals illustrate a change in fault polarity within the short interval circa 620 340 ka characterized by progressive transfer of activity from major south dipping faults to north dipping faults and southward migration of discrete depocenters at 30 m kyr since circa 340 ka there has been localization and linkage of the dominant north dipping border fault system along the southern rift margin demonstrated by lateral growth of discrete depocenters at 40 m kyr a single central depocenter formed by circa 130 ka indicating full fault linkage these results indicate that rift localization is progressive not instantaneous and can be synchronous once a rift border fault system is established this study illustrates that development processes within young rifts occur at 100 kyr timescales including rapid changes in rift symmetry and growth and linkage of major rift faults

growth folds above propagating normal faults abstract growth folds above the upper tips of normal faults are ubiquitous in extensional settings especially during the early phases of extension and in salt rich basins as slip accumulates on the underlying normal fault the geometry and size of the fold changes these changes reflect the dip throw displacement and propagation rate of the underlying normal fault as well as the thickness and rheology of the overlying cover these changes also have a marked impact on the architecture and distribution of synkinematic sediments as well as the styles of secondary deformation accommodating strain within the growing fold here we analyse a large dataset of natural and physically and numerically modelled growth folds to i characterise their diagnostic features ii investigate the controls on their geometry size and differences and iii describe how they grow with increasing extensional strain we demonstrate that larger fault throws and a thicker and weaker cover are associated with larger growth folds in contrast small fault throws as well as thin and strong brittle cover are associated with smaller growth folds we show that the geometry and size of growth folds vary through time the width and thus the wavelength of the fold is established relatively early during fold growth whereas fold amplitude increases gradually with increasing fault throw fold width and amplitude become increasingly similar during fold evolution until the fold is breached by the underlying normal fault we also derive a number of preliminary empirical relationships between readily observable structural and stratigraphic parameters in our dataset that may help estimate the geometry and size of poorly exposed i e in the field or imaged i e in the subsurface growth folds in addition we discuss how fault growth models i e constant length vs propagating may impact the three dimensional evolution of growth folds finally our work shows that growth folds are likely more common than previously thought for example although they are well documented in areas characterised by weak ductile cover strata and low strain rates our dataset illustrates that growth folds may also occur in brittle relatively strong rocks and in regions with high strain rates however the underlying controls on fold occurrence remain elusive

localized vs distributed deformation associated with the linkage history of an active normal fault whakatane graben new zealand abstract the deformation associated with an active normal fault is investigated at a high temporal resolution c 10 4 yr the rangitaiki fault whakatane graben new zealand and its adjacent faults accommodated an overall extension of 0 83 oriented at n324 e over the past 17 kyr this is consistent along strike but the pattern of faulting that accommodates this strain defines two different spatial domains to the sw one domain is characterized by a few large faults with 80 of strain localized onto geometrically and kinematically linked segments of the main fault this produces marked heterogeneity in the spatial distribution of strain across the graben in contrast to the ne a domain of distributed faulting is characterized by numerous small faults contributing to the overall deformation with only 35 of strain localized onto the rangitaiki fault the transition from distributed to localized deformation is attributed to an increase in linkage maturity of the rangitaiki fault progressive strain localization has been ongoing within the network over the last 17 kyr with localization of fault activity increasing by 12 indicating this process occurs over kyr time periods that only reflect a few earthquake events

a mesovortex within a near equatorial mesoscale convective system during toga coare abstract airborne doppler radar observations are used to investigate the internal structure of a midlevel mesovortex that developed within the rear part of the stratiform precipitation region of a mature to decaying mesoscale convective system this system composed of several convective elements occurred on 13 december 1992 on the eastern side of the intensive flux array of the tropical ocean global atmosphere coupled ocean atmosphere response experiment near the equator 2 s the mesovortex contained several features that were previously observed in other tropical and midlatitude systems radar observations show that the closed wind circulation at midlevels had a horizontal dimension of 150 km and was coincident with a marked rear inflow at the central rear of the stratiform region where a notch pattern clearly identified the rear dry air intrusion it was associated with positive vertical vorticity anticyclonic for the southern hemisphere and could be classified as a cooling induced vortex maxi

predictive permeability model of extensional faults in crystalline and metamorphic rocks verification by pre grouting in two sub sea tunnels norway abstract this paper link quantitative fault zone descriptions qualitative fracture and fault rock properties and engineering data in the study of the permeability structure of fault zones datasets include scan lines drill cores and cement pre grouting from two sub sea tunnels in gneissic and granitic rocks from which systematic pre grouting volumes can be used to analyse the in site relative permeability both in host rocks and fault zones major extensional faults intersected by the tunnels reveal common fault rocks surrounding intensively fractured rock lenses in the core fracture frequencies in these lenses can reach 100 fractures metre f m in the bounding damage zones networks of fracture sets make up an inner zone of fairly high frequency 20 30 f m of fault parallel long fractures connected by shorter fractures an outer zone has lower frequencies tunnel scale injection of cement reveals patterns that can be ascribed to the impact of faulting there is an increase in cement injection in fault zones compared to areas with background fracturing away from faults in detail there is an innate division of the rock volume into sub zones characterized by distinct structural style and permeability with a background level and three fault related sub zones fault core inner damage zone and outer damage zone injection data shows that the background sub zone commonly can be injected with less than 0 05 m3 cement per metre tunnel commonly not injected whereas the fault core has permeability characteristics nearly as low as the outer damage zone represented by 0 1 0 2 m3 cement per metre tunnel with occasional peaks towards 0 5 m3 the maximum of cement injection lies in the inner damage zone marginal to the fault core with 0 3 0 7 m3 cement per metre tunnel locally exceeding 1 m3 this gives a relative relationship for cement injection of approximately 1 2 1 between fault core inner damage zone and outer damage zone of extensional fault zones in crystalline and metamorphic rocks

sequential faulting explains the asymmetry and extension discrepancy of conjugate margins rifted continental margins are the sites that record the thinning and break up of continents to form new oceans cesar ranero and marta perez gussinye use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this to crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy in which crustal thinning appears to be greater than the extension caused by brittle faulting by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins these authors use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this with crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy where crustal thinning seems to be greater than the extension caused by brittle faulting during early extension cold continental lithosphere thins and subsides creating rift basins if extension continues to final break up the split and greatly thinned plates subside deep below sea level to form a conjugate pair of rifted margins although basins and margins are ubiquitous structures the deformation processes leading from moderately extended basins to highly stretched margins are unclear as studies consistently report that crustal thinning is greater than extension caused by brittle faulting1 2 3 4 this extension discrepancy might arise from differential stretching of brittle and ductile crustal layers2 but that does not readily explain the typical asymmetric structure of conjugate margins5 6 in cross section one margin displays gradual thinning accompanied by large faults and the conjugate margin displays abrupt thinning but smaller scale faulting5 whole crust detachments active from early in the rifting could in theory create both thinning and asymmetry1 but are mechanically problematical furthermore the extension discrepancy occurs at both conjugate margins leading to the apparent contradiction that both seem to be upper plates to a detachment fault7 8 alternative models propose that much brittle extension is undetected because of seismic imaging limitations caused either by subseismic resolution faulting9 invisible deformation along top basement 100 km scale detachments8 or the structural complexity of cross cutting arrays of faults3 here we use depth migrated seismic images to accurately measure fault extension and compare it with crustal thinning the observations are used to create a balanced kinematic model of rifting that resolves the extension discrepancy by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins contrary to current wisdom the observations support the idea that thinning is to a first degree explained by simple andersonian faulting that is unambiguously visible in seismic data

rifted margin architecture and crustal rheology reviewing iberia newfoundland central south atlantic and south china sea abstract crustal rheology controls the style of rifting and ultimately the architecture of rifted margins here we review the formation of three magma poor margin pairs iberia newfoundland the central segment of the south atlantic rift and the south china sea by integrating observational data into a numerical forward modelling framework we utilise a 2d version of the finite element code slim3d which includes nonlinear temperature and stress dependent elasto visco plastic rheology and is able to reproduce a wide range of rift related deformation processes such as flexure lower crustal flow and faulting extension in cold strong or thin crust is accommodated by brittle faults and ductile shear zones that facilitate narrow rifts with asymmetric fault geometries hot weak or thick continental crust is dominated by ductile deformation and often extends symmetrically into a wide rift system this simple recipe provides the standard framework to understand initial rift geometry however it is insufficient to account for the dynamics of intermediate and late rift stages that shape the final margin architecture asymmetric conjugate margins where one side is wide and the other narrow can be formed via both wide and narrow rift styles which we reproduce with weak and strong crustal rheologies respectively exemplified by the iberia newfoundland conjugates and the central south atlantic we define three characteristic rift phases an initial phase of simultaneous faulting an intermediate phase of rift migration that involves sequential fault activity and finally the breakup phase crustal rheology plays an overarching role in governing the dynamics of these asymmetric margins we illustrate that weak rheologies generally prolong the phase of simultaneous faulting while rift migration is enabled by initial fault asymmetry as well as relatively weak crust formation of the predominantly symmetric and wide margins of the south china sea was controlled by extraordinarily weak crust that extended the phase of simultaneous faulting until breakup the weak crustal rheology of this region relates to the south china sea s pre rift history where plate convergence lead to crustal thickening and magmatic additions in a back arc regime shortly before the onset of rifting

estimates of strain due to brittle faulting sampling of fault populations abstract the geometry of sampling domains is a first order consideration in the characterization of brittle fault populations in most cases descriptions of fault size distributions based on map cross section traverse or borehole data systematically underestimate the number of small faults present in a volume the geometry of sampling domains may be accounted for using an empirical proportionality between fault displacement and trace length estimates of strain in which the sampling geometry is considered suggest that small faults accommodate a significant portion of the total strain due to the brittle faulting process

controls on strain localization in a two dimensional elastoplastic layer insights into size frequency scaling of extensional fault populations 1 we use a two dimensional 2 d finite element code to investigate how mechanical properties and boundary conditions influence progressive strain localization during extension of a 2 d elastoplastic layer the deforming medium is modeled using a strain softening von mises rheology with a gaussian heterogeneity in yield strength distributed randomly in space specifically we examine the effects of changing 1 the thickness of the deforming layer 2 the basal boundary condition 3 the range of strengths in the deforming layer 4 the strength loss on failure and 5 the total accommodated strain discrete zones of plastic shear strain are observed to nucleate and grow progressively during each experiment in order to quantify and thus discriminate between the deformation patterns produced under differing conditions we calculate the size frequency distributions of the shear band populations size is defined as the total plastic strain represented by each discrete structure a wide range of size frequency distributions is observed including both power law and exponential as well as distributions that show breaks in scaling with a transition from power law at small sizes to exponential at large sizes we show that these variations in population statistics are directly reflecting a change in strain localization in space and time caused by changing model parameters furthermore by making an analogy between the model shear bands and tectonic faults we provide insights into key features of fault size frequency distributions that have been measured in continental and oceanic extensional settings and also observed in analogue experiments

growth of a normal fault system observations from the lake malawi basin of the east african rift abstract we have studied the growth history of the usisya normal fault system which bounds the west side of the lake malawi basin one of the largest rift basins in the east african rift system the lake malawi rift basin is a complex of intrabasins and intrabasin highs formed by three major fault segments each about 100 km in length the basin has been actively subsiding since the late miocene and has a maximum depth of about 3 km unlike the majority of previous studies of fault systems we are able to define the temporal evolution of this fault system using the patterns of sediment infill this is due almost exclusively to the availability of a high density seismic reflection network in combination with several clearly identifiable temporal marker beds an analysis of the seismic reflection data reveals that growth of the basin bounding faults occurred in the following sequence 1 in the early stages of rifting starting about 8 6 ma the northern fault was the most active 2 then extension shifted to the southernmost fault segment and lasted until about 2 5 ma 3 during the interval between about 2 3 ma and 1 6 ma the central segment was most active prior to the last interval the central segment accrued the least total displacement of the three segments this contradicts the common notion that the location of maximum displacement remains at a fixed location from fault inception or that the largest fault in any population of faults always maintained the highest displacement rate consistent with observations on smaller faults there is a marked increase in the displacement gradient on individual faults in the regions of overlapping segments although there is an observable asymmetry in individual segment displacement profiles there is a clear evolution toward a flattened bell shaped total displacement profile for the fault system that is consistent with the shape and scaling relationships of displacement vs length that are observed on a wide range of individual normal faults this suggests that the irregularities in the shape and scaling relationships observed in complex fault systems will eventually smooth out moreover the observed growth pattern suggests that the profile of the fault system will progress toward that of isolated faults provided the system is allowed sufficient time to evolve this in turn describes a process for maintaining a self similar scaling observed in large populations of faults which span several orders of magnitude in fault length

circulations associated with a mature to decaying midlatitude mesoscale convective system part ii upper level features abstract the vertical structure of a midtropospheric mesovortex that developed during the decay of a midlatitude mesoscale convective system over kansas and oklahoma on 23 24 june 1985 is documented surface rawinsonde wind profiler and dual doppler data are used to define its structure as has been observed in other midlatitude and tropical cases the mesovortex occurred within the trailing stratiform precipitation region of a squall line system it was associated with a preexisting synoptic scale short wave trough and as the circulation developed it deformed the back edge of the stratiform precipitation region into a hooklike pattern the 100 200 km mesovortex was confined to the midtroposphere 3 8 km with a maximum amplitude just above the 0 c level the vortex axis sloped toward the northeast but its orientation changed hour by hour over the 2 h period of dual doppler coverage overall the mesovortex was warm core although its thermal structure was complex and apparently significantly infl

midlevel cyclonic vortices generated by mesoseale convective systems abstract despite the large number of convective systems that occur over the central united states every year there are typically only a few well defined midlevel vortices apparent in satellite imagery after the overlying anvil debris from some convective complexes has dissipated or advected away a climatology of mesoscale convectively generated vortex mcv events for 1981 1988 is presented and the synoptic setting in which the circulation becomes apparent is discussed proximity sounding data from numerous cases are used to examine features of the kinematic and thermodynamic setting of mcvs at various lifelycle stages defined by satellite imagery features ofthe large scale environment that appear conducive to the formation and longevity of mcvs include weak flow weak vertical shear weak background relative vorticity and intense horizontal and vertical moisture gradients the rapid mesovortex generation observed can be explained by the stretching term of the vorticity equation most mcvs emerge fro

fault size distributions are they really power law abstract power law fault size throw distributions spanning ca seven orders of magnitude are analysed using sample lines from seismic coal mine plan and outcrop data sets outcrop data sets generally have lower power law exponent values than seismic data sets consistent with a general decrease in exponent value with decrease in fault size if such a relationship does exist then probably it cannot be accounted for by sampling bias alone we suggest that either i fault size populations are not power law over a large scale range or ii they are power law but at smaller scales show a greater range of exponent values due to spatial clustering

mesoscale downdraft influences on vertical vorticity in a mature mesoscale convective system abstract the vorticity dynamics of a lower tropospheric mesovortex within a mature mesoscale convective system mcs is investigated with observations from a special sounding network and with dual doppler radar measurements the data show that the vorticity distribution and tendency were dictated by the mesoscale downdraft which formed within the storm s trailing stratiform region and not by the mesoscale updraft at midlevels preexisting vertical vorticity was amplified by convergence as environmental air overtook the storm from the rear and funneled into the evaporatively cooled mesoscale downdraft vertical vorticity within the stratiform region also increased by the twisting of horizontal vorticity associated with a backing wind the horizontal vorticity vector pointed opposite the velocity vector and tipped into positive vertical vorticity when the row encountered the mesoscale downdraft at lower middle storm levels the twisted vorticity was subsequently amplified by convergence along with preexi

contrasting origins of breached relay zone geometries abstract relay zones accommodate transfer of displacement between pairs of adjacent segments of a fault array that become linked to form a through going fault as displacement increases 3d geometric and kinematic analysis of two vertically aligned relay zones that form a complex boundary between two fault segments generally support this model of relay zone growth but they also highlight some departures from this scheme the two seismically mapped relay zones although separated vertically by 100 m were synchronously active over most of their development history a causal relationship between them is proposed with the geometric complexity arising from the formation of the lower relay zone triggering the formation of the upper the lower relay zone is now breached but originally formed a hole within the fault surface up to throws of ca 50 m the upper relay zone displays both breached and intact relay zone geometries at different structural levels demonstrating that relay zone breaching is a protracted rather than geologically instantaneous process geometrically the lower part of this structure resembles a breached relay zone but it formed by propagation of a splay fault from a pre existing bend to enclose an intervening and steepening ramp a growth scheme which is the opposite of conventional relay zone models

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

fault growth by linkage observations and implications from analogue models abstract using time sequence analyses of extensional fault models we demonstrate the pivotal role played by fault segmentation in the accumulation of displacement and length during the growth of faults experiments are described in which incremental steps during the development of individual faults have been reconstructed from time lapse photographs taken during model deformation these records confirm the composite segment hierarchy of fault structure a pattern that is frequently recognised in many natural arrays they reveal the progressive enlargement of individual faults to be the product of a repetitive cycle of tip line propagation overlap and linkage between nearest neighbours by contrasting the displacement patterns of successive increments during growth convincing evidence is also presented to suggest that individual segments of faults may remain kinematically independent once they are physically linked this behaviour is shown to be responsible for the characteristic saw tooth patterns often recognised in strike parallel fault displacement profiles such patterns are believed to arise where relict segment boundaries remain preserved as asperities to slip so that displacement is confined to discrete parts of a fault plane surface growth in this way also causes the maximum displacement d and surface length l of faults to continually change by different proportions incremental displacement records presented here corroborate field evidence which shows that linkage between fault segments during growth is responsible for a significant component of the spread of values often recorded in d versus l compilations finally we speculate that linkage between fault segments also accounts for transient irregularities recorded in the frequency distribution of the fault length populations of each model

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

a comparison of historical and paleoseismicity in a newly formed fault zone and a mature fault zone north canterbury new zealand the timing of large holocene prehistoric earthquakes is determined by dated surface ruptures and landslides at the edge of the australia pacific plate boundary zone in north canterbury new zealand collectively these data indicate two large m 7 earthquakes during the last circa 2500 years within a newly formed zone of hybrid strike slip and thrust faulting herein described as the porter s pass to amberley fault zone ppafz two earlier events during the holocene are also recognized but the data prior to 2500 years are presumed to be incomplete a return period of 1300 2000 years between large earthquakes in the ppafz is consistent with a late holocene slip rate of 3 4 mm yr if each displacement is in the range 4 8 m historical seismicity in the ppafz is characterized by frequent small and moderate magnitude earthquakes and a seismicity rate that is identical to a region surrounding the structurally mature hope fault of the marlborough fault system farther north this is despite an order of magnitude difference in slip rate between the respective fault zones and considerable differences in the recurrence rate of large earthquakes the magnitude frequency distribution in the hope fault region is in accord with the characteristic earthquake model whereas the rate of large earthquakes in the ppafz is approximated but over predicted by the gutenberg richter model the comparison of these two fault zones demonstrates the importance of the structural maturity of the fault zone in relation to seismicity rates inferred from recent historical and paleoseismic data

connecting seismically active normal faults with quaternary geological structures in a complex extensional environment the colfiorito 1997 case history northern apennines italy 1 the northern apennines of italy are characterized by a complex tertiary tectonic history where superposed compressional and extensional deformation occurred in such regions characterized by low active extensional strain rate the coseismic surface ruptures are rare and often a matter of much debate resulting in a difficult connection between geological faults i e faults which can be mapped at the surface and seismological faults i e faults which actually generate earthquakes the availability of detailed geological mapping and high resolution seismological data for the colfiorito area struck in 1997 by a sequence of six 5 mw 6 normal faulting earthquakes allow us to compare and verify the existence of geometric and kinematic correspondence between the mapped geological quaternary faults and the activated structures in map view the earthquakes distribution reflects the fault pattern mapped at the surface the length of activated and mapped faults is quite similar 7 10 km the coseismic subsided region imaged by interferometric synthetic aperture radar data is located in the hanging wall of the mapped normal faults that bound the quaternary basins in section view there is a geometric connection between mapped normal faults and the aftershock alignments used to image fault geometry at depth comparison of striated fault planes and aftershock focal mechanism solutions show a strong kinematic consistency this study points out that the quaternary tectonosedimentary evolution and the present day geological and geomorphologic setting of the colfiorito area can be interpreted as the result of repeated extensional earthquakes similar to the 1997 events occurring on nw se trending normal faults our data also show that the main shocks of the colfiorito sequence nucleated close to the intersections between the normal faults and the preexisting compressional transpressional structures which in 1997 acted as lateral barriers to rupture propagation and consequently constrained the fault size

the growth and propagation of synsedimentary faults abstract offset of each syn fault horizon across a synsedimentary i e growth fault records the throw subsequent to its deposition allowing successive growth stages of a fault to be determined this technique has been applied to synsedimentary faults mapped on 3d seismic datasets to distinguish between faults which propagated laterally during growth faults which did not propagate laterally for significant growth periods and faults in which the lateral dimensions of the active surface decreased during their growth these different fault tip line behaviours result in characteristic lateral and dip parallel fault displacement variations fault propagation rates have been measured for 10 fault tips the maximum propagation rate is 15 km my for gravity driven faults and 3 km my for tectonically driven faults rates of fault propagation decrease with elapsed time from the initiation of faulting with tip line stasis and retreat becoming dominant in the later stages of fault growth static and retreating lateral tip lines are associated with overlap of the fault strain field with that of a neighbouring fault most often with the formation of a fault relay zone

a healing reloading feedback control on the growth rate of seismogenic faults spatial and temporal variations in the growth rates of faults are explained in terms of a stress feedback mechanism operating in the seismogenic upper crust it is based on the idea that seismic rupture of a fault perturbs the surrounding stress field advancing the occurrence of future earthquakes on some faults that are optimally oriented while relaxing stress levels on others if post slip healing is geologically rapid then the earthquakes that are thus induced will contribute to reloading along the earlier rupture zone because of the symmetry of the optimal geometry a positive feedback is set up so that even in areas that are undergoing uniform tectonic straining some faults develop higher displacement rates and grow more rapidly while others experience reduced rates or become inactive using a thin plate elastic model for lithospheric scale faulting it is shown that this healing reloading feedback mechanism drives rapid localisation and the formation of major through going faults moving at plate boundary velocities enhanced displacement rates compared to an isolated fault develop shortly after the onset of deformation along those faults which are optimally positioned in the overall fault population thus the formation of a new plate boundary fault zone is predetermined and is a consequence of rather than the precursor of preferentially high displacement rates also fault segments located at points of rupture symmetry e g the central portion of a fault zone are reloaded more frequently and develop higher displacement rates and consequently have longer segment lengths and or larger displacement to length ratios episodic fault movement through time is a general feature of the model these predictions are consistent with available field observations over a wide range of scales thus elastic brittle failure and healing appear to be important rheological components of the lithosphere on long time scales 104 106 y as well as on the time scale of earthquake recurrence

a mesoscale vortex couplet observed in the trailing anvil of a multicellular convective complex abstract observations collected during the oklahoma kansas pre storm experiment are used to document the evolution and structure of a mesoscale vortex couplet that developed in the mesoscale convective system that occurred on 16 17 june 1985 the evolution of the circulations was captured by dual doppler radar observations for 1 4 hours this allowed an evaluation of the various terms of the vertical vorticity equation which give insight into the mechanisms that are important in the generation of the circulations the primary mechanism responsible for the formation of the observed vortices was the interaction of the larger scale flow with low level momentum transported to higher levels by multiple convective updrafts as a consequence vertical shear of the horizontal wind was important to initial vorticity production the vorticity generated in this manner was subsequently increased in strength due to middle level convergence when the convection weakened and dissipated the primary source of vorticity w

strain localisation and population changes during fault system growth within the inner moray firth northern north sea abstract the evolution of fault populations is established for an area within the late jurassic inner moray firth sub basin of the north sea sedimentation rates outstripped fault displacement rates resulting in the blanketing of fault scarps and the preservation of fault displacement histories displacement backstripping is used to establish the growth history of the fault system fault system evolution is characterised by early generation of the main fault pattern and progressive localisation of strain onto larger faults this localisation is accompanied by the death of smaller faults and an associated change in the active fault population from power law to scale bound fault length populations evolve from a power law frequency distribution containing all faults to a power law distribution with a marked non power law tail containing the largest faults this change in population character is synchronous with the development of a fully connected fault system extending across the mapped area and the accommodation of displacements almost exclusively on the largest faults strain localisation onto fewer and better connected faults represents the most efficient means of accommodating fault related deformation and is considered to be a fundamental characteristic of the spatio temporal evolution of fault systems progressive strain localisation requires complementary changes in the characteristics of associated earthquake populations

analysis of the relationships between strain polarity and population slope for normal fault systems abstract the evolution of normal fault populations and their synthetic and antithetic sub populations has been studied for a number of fault systems imaged from seismic reflection data relationships between fault strain and polarity and the slope of fault throw populations have been investigated by backstripping a fault system in the inner moray firth north sea and by comparison between throw populations for pre faulting horizons from an additional 11 fault systems with variable extensional strains fault population slopes decrease with increasing strain reflecting strain localisation onto progressively fewer and larger faults synthetic and antithetic sub populations also show an inverse relationship between slope and the strain they accommodate but the slopes of antithetic sub populations are independent of the total strain on the fault system the slopes of antithetic sub populations are higher than those of synthetic sub populations from the same area and the difference in slope correlates with the polarity of the fault system i e the proportion of the total strain accommodated by the two sub populations the data are consistent with progressive decrease in the slopes of sub populations until the antithetic fault sets become inactive the absence of a correlation between strain and polarity is attributed to the effects of fault system reactivation

kinematic and thermodynamic characteristics of the flow over the western pacific warm pool during toga coare abstract rawinsonde and satellite infrared radiation ir data from the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare are used to investigate mean and transient behavior and horizontal variability of the atmosphere over the western pacific warm pool infrared data for the 4 mo intensive observing period iop and vertical motion fields indicate that the intensity of convection height of maximum upward motion and sst all increased from west 140 e to east across the coare domain iop mean ir data show a double itcz intertropical convergence zone structure north and south of the intensive flux array ifa centered at 2 s 156 e although marked variability in the patterns occurred on a month to month basis three prominent westerly wind bursts occurred over the ifa during the 4 mo iop in association with the intraseasonal oscillations isos strong upward motion usually occurred 1 3 weeks prior to the peak low level westerlies subsidence dominated when

an alternative model for the growth of faults conventional growth models suggest that faults become larger due to systematic increases in both maximum displacement and length we propose an alternative growth model where fault lengths are near constant from an early stage and growth is achieved mainly by increase in cumulative displacement the model reconciles the scaling properties of faults and earthquakes and predicts a progressive increase in fault displacement to length ratios as a fault system matures this growth scheme is directly applicable to reactivated fault systems in which fault lengths were inherited from underlying structure and established rapidly the model may also apply to some non reactivated fault systems near constant fault lengths during subsequent growth are attributed to retardation of lateral propagation by interaction between fault tips the model is validated using kinematic constraints from growth strata which are displaced by a system of reactivated normal faults in the timor sea nw australia

quantitative analysis of populations of small faults abstract tectonic strain includes contributions from small faults with length less than the thickness of the brittle upper crust this study derives algebra to determine the strain associated with small faults that follow a power law i e fractal distribution independent of assumptions concerning how they relate to large faults in the same region and discusses how to apply this algebra for a range of small fault sample types the method is illustrated using as case studies the jurassic extension in the north sea the miocene and younger extension in the gulf of suez and the hercynian strike slip faulting the badajoz cordoba fault zone in southern spain my preferred estimates for the strain accommodated on small normal faults with length

effective crustal permeability controls fault evolution an integrated structural mineralogical and isotopic study in granitic gneiss monte rosa northern italy two dextral faults within granitic gneiss in the monte rosa nappe northern italy reveal key differences in their evolution controlled by evolving permeability and water rock reactions the comparison reveals that identical host rock lithologies develop radically different mineralogies within the fault zones resulting in fundamentally different deformation histories oxygen and hydrogen isotope analyses coupled to microstructural characterisation show that infiltration of meteoric water occurred into both fault zones the smaller virgin fault shows evidence of periodic closed system behaviour which promoted the growth of hydrothermal k feldspar whilst the more open system behaviour of the adjacent ciao ciao fault generated a weaker muscovite rich fault core which promoted a step change in fault evolution effective crustal permeability is a vital control on fault evolution and coupled to the temperature i e depth at which key mineral transformations occur is probably a more significant factor than host rock strength in controlling fault development the study suggests that whether a fault in granitic basement grows into a large structure may be largely controlled by the initial hydrological properties of the host rocks small faults exposed at the surface may therefore be evolutionary dead ends that typically do not represent the early stages in the development of larger faults

multiscale variability of deep convection in relation to large scale circulation in toga coare deep convection over the indo pacific oceanic warm pool in the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare occurred in cloud clusters which grouped together in regions favoring their occurrence these large groups of cloud clusters produced large scale regions of satellite observed cold cloud top temperature this paper investigates the manner in which the cloud clusters were organized on time and space scales ranging from the seasonal mean pattern over the whole warm pool region to the scale of individual cloud clusters and their relationship to the large scale circulation and sea surface temperature sst the dominant convective variability was associated with the intraseasonal oscillation iso a large eastward propagating ensemble of cloud clusters marked the iso s progress the meridional structure of the iso was strongly affected by the seasonal cycle with a southward shift from the northern hemisphere in october november to the southern hemisphere in january february the sst had an intraseasonal signal in lagged quadrature with the cold cloudiness and rainfall in coare the sst increased decreased during the convectively suppressed active phases of the iso enhanced low level westerly winds occurred toward the later stages of the enhanced convection periods of the iso though not always centered at the equator the strongest westerlies tended to be located between two synoptic scale cyclonic gyres which were often not symmetric about the equator in the low level wind field this asymmetry in the anomalous equatorial low level westerlies may have different implications for the oceanic response in the coupled atmosphere ocean system than those centered on the equator the cyclonic gyres contained highly concentrated deep convection and in four cases the gyres developed into tropical cyclones within the envelope marking the convectively active phase of the iso cloud clusters were frequently concentrated into westward propagating disturbances with a local periodicity of similar to 2 days these 2 day disturbances have been identified in earlier spectral studies and appear to be related to westward propagating inertio gravity waves in coare they typically contained numerous cloud clusters which underwent a distinct diurnal cycle most of the cloud clusters embedded in the 2 day disturbances moved westward though some were stationary and a few moved eastward a cloud duster tracking program identified groups of clusters lime dusters that exhibited continuity in time and space in the most convectively active period of the iso the tracking program identified almost the entire iso cloud ensemble as a long lasting trackable superconvective system this observation indicates the lack of a distinct scale separation between convection and large scale disturbances during the most intense convective periods in coare

seismic hazard scenarios from the longest geologically constrained active fault of the aegean abstract several seismic hazard scenarios are examined concerning the seismic potential of the north aegean basin nab based for the first time purely on geological data detailed analysis of the bathymetry incorporated by seismic reflection profiling has recently revealed the neotectonic structure of the nab and demonstrates that the dominant structure is a 160 km long ne sw trending fault comprising of four major segments this is the longest geologically constrained active fault in the aegean sea following deterministic fault specific analyses six major seismic sources are identified firstly a 55 km oblique normal fault segment towards the southwestern end of the basin that can accommodate a m 7 1 event such an event could produce a maximum vertical offset up to 3 4 m posing also a tsunami threat based on geological data a minimum throw rate of 1 2 0 2 mm yr is estimated for this segment implying a recurrence interval of 1100 350 yrs secondly a sub vertical 70 km long e w dextral trending shear zone northwards the southwestern corner of the n aegean basin that can generate a m 7 2 strike slip event sources 3 and 4 towards the central and eastern segment of the fault are expected to produce seismic strike slip events of m 7 1 whereas the fifth source suggests the simultaneous activation of sources 3 and 4 producing a 105 km long rupture and a m 7 4 event finally the sixth source implies a multi segment rupture involving the entire 160 km long south marginal fault producing a m max 7 6 which represents the worst case scenario this value limits all uncertainties posed on the maximum expected magnitude by other published estimates ranging from m 7 2 up to 8 5 that are based solely on seismological and or geodetic approaches

displacement rates of normal faults previous estimates of displacement rates on individual faults have been limited to neotectonic faults and averaged over time intervals of about 200 kyr or less1 2 3 4 5 these estimates have been highly variable which has led to a belief that longer term displacement rates on individual faults are likely to be variable as well here we report estimates of long term normal fault displacement rates averaged over time intervals ranging from 1 to 40 myr and based on observed decreases in displacement of progressively younger horizons intersected by syn sedimentary faults we find that displacement rates are remarkably stable over these longer time periods and within a given fault system the rates are strongly dependent on the relative size of the fault as measured by cumulative vertical displacement taken together these results indicate that faults become large relative to nearby faults by having higher displacement rates even when small rather than as a consequence of having been active for longer our analyses also show that high regional strain rates tend to be accommodated by high fault displacement rates rather than high fault densities

evolution and structure of the 6 7 may 1985 mesoscale convective system and associated vortex abstract observations collected during the oklahoma kansas pre storm experiment are used to document the evolution and structure of the mesoscale convective system mcs that occurred on 6 7 may 1985 the storm began when a short squall line developed in an area of preexisting thunderstorm activity thunderstorm updrafts along the squall line lifted warm moist air with its southerly momentum to the upper troposphere a broad region of convective outflow and a meso scale updraft region with a mean vertical velocity in excess of 15 10 3 mb s 1 were created a stratiform rain area with an embedded mesovortex formed behind the squall line the vortex resided beneath the deepest upper level outflow the mesovortex altered the wind field and consequently became the principal organizational feature within the mcs a descending current from the storm s rear that depending on location extended from 1 km to the upper troposphere was intensified and focused by the vortex the descending rear inflow had a peak

geometrically coherent continuous deformation in the volume surrounding a seismically imaged normal fault array abstract we calculated an apparent dip attribute which was used to ascertain the spatial distribution of fault related continuous deformation the vertical component of displacement calculated from the continuous deformation acts to fill in missing displacement in the fault throw profile this result shows that apparently complex 3d patterns of continuous strain in the volumes surrounding the fault array developed as part of a single geometrically coherent fault array however if this component of continuous deformation was not added to the throw profile the fault array could have been misinterpreted as a series of isolated fault segments with coincidental overlaps this technique permits the analysis of continuous deformation structures which are up to an order of magnitude smaller than previously described in the study area these structures are interpreted as small fault propagation folds forming in a shale dominated cover sequence the fault propagation folds above the upper tip line of the mapped fault array bifurcate upwards from the fault surface into three coherent lobes and resemble secondary fault segments the near constant along strike length of the region of continuous deformation throughout the syn rift sequence implies that the length of the fault array was established at an early stage in its growth prior to the establishment of a seismically visible fault surface

3 d numerical modelling of the influence of pre existing faults and boundary conditions on the distribution of deformation example of north western ghana abstract high strain zones bound and separate the high grade tectono metamorphic terranes from low grade greenstone belts in the north western parts of ghana these belts are bounded by granitoid domains characterized by two main episodic pulses of magmatic intrusive events which occurred between 2213 ma and 2086 ma high strain zones are thought to play a significant role in creating fluid pathways particularly for partially molten material from lower crustal sources to the upper crust in this study a three dimensional thermo mechanical model has been used to explore the evolution of high strain zones and relief under compressional and simple shear boundary conditions different orientations of a system of branched strike slip faults were tested the effects of the frictional angle and density contrast on the evolution of relief were also compared in this study the resulting model indicates domains of tensile vs compressional strain as well as shear zones this shows that the internal fault zones as well as the host rock in between the faults behave as relatively weaker domains than the external regions under both applied compressive and simple shear boundary conditions these weakened domains constitute preferential zones of tensile and shear strain accommodations in the upper crust which may favour infilling by deeper partially molten rocks this processes is suggested by the authors as the most likely processes to have occurred in pre existing branched shear zones systems in north western ghana during the eburnean orogeny around 2 20 2 10 ga the orientations of faults in these models play an important role in controlling the evolution of relief and localized deformation in particular greatest the largest relief is obtained when faults dip parallel to each other and when they are inclined at depth as they thus facilitate strain rotation and material transfer from depth the host rock density does not play a primary role in producing relief compared to variations in friction angle at crustal scale of our model relief increases by 200 300 m when the host rock density is increased by 200 kg m3 whereas relief reduces by about 1200 m when decreasing the host rock friction from 20 to 10 this study suggests a model for interpreting the evolution and locus of exhumation of partially molten rocks in north western ghana

growth of faults by accumulation of seismic slip the accommodation of large strains in the upper crust is largely achieved by the accumulation of displacement on faults observation shows that as a fault accumulates displacement it grows in size i e its surface area and its length increase here we address the question for an increase in the amount of displacement on a fault by how much would the length of the fault change it is argued by cowie and scholz 1992a that the displacement on a fault is linearly related to the length of the fault this simple result is expanded upon in this paper by assuming that a fault accumulates displacement by repeated earthquakes two different approaches are presented the first approach considers the balance that must be achieved between the energy available for deformation and the work involved in creating new fault surface area as the fault grows the available energy is provided by changes in strain energy when the fault slips the second approach is to construct a geometrical model for fault growth using the scaling relationship between the slip during a single earthquake and the length of the rupture the total displacement on a fault is the sum of the slips contributed by many earthquakes the usefulness of these two approaches is that the growth of a fault over geologic time can be described by parameters that can be obtained from earthquake and fault data the models presented here predict that 1 the maximum amount a fault can grow in a single earthquake that ruptures the entire fault is of the order of 1 of its previous length and 2 the work of faulting may account for 10 of the total energy available during an earthquake the energy lost from the system is accounted for by work done against friction and seismic radiation consequences of fault growth for the segmentation and thus seismogenic potential of a fault over geologic time are discussed using predictions of the theory

stochastic inversion by matching to large numbers of pseudo wells abstractwe have developed a 1d stochastic algorithm for estimating reservoir properties based on matching large numbers of pseudo wells to seismic angle stacks the pseudo wells are part deterministic and part stochastic 1d stratigraphic profiles with consistent elastic and reservoir properties pseudo wells are sampled from a prior distribution defined by the geological interpretation a rock physics model and a model for the vertical statistics that provides close control of the lithofacies proportions a new set of pseudo wells typically 103 104 tied to the local stratigraphy is constructed for each seismic trace synthetics derived from the pseudo wells using extended elastic impedance are matched to either one or two seismic angle stacks and the best matches are selected and averaged to provide a joint estimate of reservoir properties and impedances and the associated uncertainties the algorithm has been tested on a number of data sets and validated by blind well ties the algorithm is 1d with