joints and en echelon cracks in middle eocene chalks near beer sheva israel abstract planar vertical joints and straight en echelon cracks are closely associated in an erosional exposure of middle eocene chalks in a syncline south of beer sheva the two dominant joint sets are oriented 357 n3 w and 031 n31 e and both sets occur in two separate outcrops 400 m apart an en echelon crack array accompanies each joint set the individual en echelon cracks are oriented 337 and 053 respectively radial plumose markings are present on the surfaces of the en echelon cracks they imply that fracture occurred normal to a local tensile stress axis a gradual rotation of the azimuths of the joints and cracks occurs between the two outcrops this rotation implies jointing due to nne ssw compression and en echelon cracking due to unloading of this compression

geology and tectonics of the betic zone se spain abstract the southern margin of the iberian continent comprises a complex geological history which can be traced back into the proterozoic when a gneissic basement was formed a cover of nevado filabride rocks was deposited onto this proterozoic basement during the palaeozoic the permian intrusion of the bedar granite suggests that the palaeozoic sedimentary rocks now exposed in the betic cordilleras have been affected by the hercynian orogeny similar to that of palaeozoic rocks in the adjoining ossa morena zone the hercynian basement was probably covered by alpujarride carbonates in the mesozoic when rifting opened tethys and intruded 140 ma old basic dyke swarms the palaeozoic basement of the betic cordilleras comprises a suture of late cretaceous subduction 80 85 ma b p this can be inferred from hp lt metamorphic facies obducted in coeval thrust slices of nevado filabride rocks the nevado filabride nappes include mesozoic carbonates transformed into marbles macael the suture was probably annnealed after the closure of tethys the mesozoic boundary between africa and europe and the rifting in tethys ceased during the palaeogene when the atlas mountains were formed 36 ma b p subsequently relative movements between africa and europe in the neogene were accommodated by strike slip faults these define the iberian microplate moving eastward by atlantic spreading and possibly subducting under italy neogene deformation of iberia is most intensive in southeastern spain due to emplacement of a mantle diapir under the alboran area this occurred early in the neogene aquitanian and caused nappe spreading involving alpujarride and malaguide rocks the subsequent neogene history has now been studied in great detail and is reviewed here it involves clear examples of calc alkaline volcanism most probably not related to subduction seismic motion along strike slip faults within the iberian microplate and syntectonic deposition in intermontane neogene basins

some considerations concerning seismic geomorphology and paleoseismology abstract seismic geomorphology studies landforms which developed in connection with earthquakes among them two different end members may be distinguished 1 seismo tectonic landforms including surface faults and fractures land uplift and subsidence at different scales surface bulges elongate ridges and any other permanent ground deformations directly related to tectonic stress and 2 seismo gravitational landforms such as landslides deep seated gravitational slope deformations sinkholes and fissures due to sediment compaction or liquefaction and sand blows connected with both seismic shaking and gravitational stress a clear cut distinction between the two categories of landforms is not always easy to make and in many instances not really useful while there are in many cases ground effects that might be and should be considered as simultaneous combinations of seismo tectonic and seismo gravitational processes this applies especially to surface fracturing and faulting which could be the combined result of tectonic stress stress produced by seismic shaking and gravitational stress the objective of this paper is to review selected case histories mainly from italy and the mediterranean region in order to show the importance of a comprehensive study of earthquake generated landforms for understanding the seismicity level of the area under investigation we argue that in earthquake prone areas seismic landforms often constitute typical patterns seismic landscapes whose recognition mapping and paleoseismological analysis may help in the evaluation of seismic hazards

active tectonics and human survival strategies tectonic movements continuously remould the surface of earth in response to plate motion yet such deformation is rarely taken into account when assessing landscape change and its impact on human land use except perhaps as an occasional hazard to human life or a temporary disruption in the longer term parems of human history however active tectonics also create and sustain landscapes that can be beneficial to human survival forming a complex topography of potentially fertile sedimentary basins enclosed by mountain bard that can facilitate the control and exploitation of food resources especially animal prey we discuss the tectonic history of northwest greece and show how the paleolithic sites of the region are located to take advantage of tectonically created features at both a local and a regional scale we suggest that the association of significant concentrations of early paleolithic sites with tectonically active regions is not coincidental and that on the longer time spans of human biological evolution active tectonics has been an importam selective agent contributing to the development of the human species as an intelligent predator

p wave fracture prediction algorithm using data with limited azimuthal distribution many carbonate reservoirs are present in china s tarim basin the storage spaces are mostly secondary and about 99 of the porosity is from fractures and dissolution caves or holes fractures represent both the storage space and migration channels of hydrocarbon fluids therefore predicting fracture development is a challenge that confronts us in this area

crustal structure of the northern margin of the eastern tien shan china and its tectonic implications for the 1906 m 7 7 manas earthquake abstract the tien shan orogenic belt is the most active intracontinental mountain belt in the world we describe an 86 km long n s trending deep seismic reflection profile which passes through the southern junggar basin located on the northeastern tien shan piedmont two distinct anticlines beneath the northern margin of the tien shan are clearly imaged in the seismic section in addition we have imaged two detachment surfaces at depths of 7 and 16 km the detachment surface at 16 km depth corresponds to the main detachment that converges with the steep angle reverse fault the junggar southern marginal fault on which the 1906 m 7 7 manas earthquake occurred a 12 14 km thick sedimentary basin is imaged beneath the southern junggar basin near shihezi the crust beneath the northern margin of the tien shan is 50 55 km thick and decreases beneath the junggar basin to 40 45 km thick the crustal image of the deep seismic reflection profile is consistent with models derived from nearby seismic refraction data and bouguer gravity anomalies in the same region the faulting associated with the 1906 manas earthquake also fits within the structural framework imaged by the seismic reflection profile present day micro seismicity shows a hypocentral depth distribution between 5 and 35 km with a peak at 20 km we hypothesize that the 1906 manas earthquake initiated at a depth of 20 km and propagated upwards causing northward slip on the sub horizontal detachments beneath the southern junggar basin thus in accord with regional geological mapping the current shortening within the eastern tien shan is accommodated both by high angle reverse faulting and detachment faulting that can be clearly imaged at depth in seismic reflection data

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

drainage diversions as evidence of propagating active faults example of the el asnam and thenia faults algeria digital elevation models and aerial photographs provide evidence of past drainage diversions associated with known and inferred active faults in northern algeria the el asnam anticline is a fault bend fold that is growing in response to displacement on the historically active el asnam fault the diversion of the fodda river and a sequence of uplifted palaeovalleys across the anticline formed in response to the active southwestward propagation of the sidi ada el ardja segment of the el asnam anticline deformation associated with the 1980 el asnam earthquake ms 7 3 and its effect on drainage demonstrate the occurrence of coseismic uplift of the el asnam anticline associated with slip on the underlying thrust fault similar geomorphic relations are observed between the isser river and the thenia fault diversions of the isser river and evidence for quaternary uplift indicate that the thenia fault which is close to algiers is tectonically active and should be considered to be a source of potentially damaging earthquakes

horizontal coseismic deformation of the 1999 chi chi earthquake measured from spot satellite images implications for the seismic cycle along the western foothills of central taiwan 1 the 1999 chi chi earthquake mw 7 6 broke a major thrust fault along the western foothills of the central range of taiwan we have measured the horizontal coseismic displacement field by correlating optical satellite images acquired before and after the earthquake these data reveal the fault trace and a clockwise rotation of surface displacements toward the north with much larger displacements and strain in the hanging wall at the surface coseismic slip increases from 5 6 m near the epicenter to 10 11 m to the north in the epicentral area we observe a left lateral strike slip zone trending n125 e and farther north a fault zone trending n s with a right lateral component the data were modeled using elastic dislocations the fault geometry consists of a shallow

test of climate leaf physiognomy regression models their application to two miocene floras from kenya and 40ar 39ar dating of the late miocene kapturo site abstract to test multiple regression models developed to predict seven variables of climate from leaf margin and size characters leaf character data were collected from modern woodland and rainforest plant communities in uganda these localities were chosen for their structural similarity to two fossil sites for which climate values were desired the test indicated that for these communities the model accurately predicts mean annual temperature however the multiple regression models overestimate seasonality of temperature and mean annual and seasonal precipitation amounts for the two modern communities reasons for the models inaccuracies may include no african analog in the non african database on which the model is based too much intraspecific variability in leaf size an important character in precipitation models and relationships between leaf form and climate that may not be well defined by multiple regression mean annual temperatures were reconstructed for two miocene paleobotanical localities from the tugen hills of the eastern rift valley kenya using leaf form data primarily margin characters the results indicate that mean annual temperatures at kabarsero 12 6 ma and kapturo 6 7 7 2 ma were essentially equivalent to temperatures at those localities today and differed little from one another the kapturo paleofloral assemblage is a deciduous woodland interpreted as indicating less available or more seasonal moisture than the kabarsero paleofloral assemblage a wet forest with west african floral affinities laser fusion 40 ar 39 ar dating of volcanic materials at kapturo provides the first control of this paleoflora bracketed by a 7 2 ma trachyte at the base of the sedimentary sequence and an age of 6 7 ma on a reworked tuff overlying the fossiliferous horizon the chronologic data places the paleofloral assemblage in stratigraphic context relative to other tugen hills units containing paleofloras and abundant vertebrate remains including hominoids

the structural evolution of active fault and fold systems in central otago new zealand evidence revealed by drainage patterns abstract central otago in new zealand is an area of active continental shortening in which a peneplain surface cut into schist has been deformed by folds which are developed above buried reverse faults we use the drainage patterns in this region to demonstrate various processes in fold and fault growth and interaction that would be difficult to identify by other means in particular we show 1 how simple asymmetric folds can develop into box folds 2 how apparently continuous ridges were formed by the coalescing of quite separate propagating fold and fault segments 3 evidence for the relative ages or relative uplift rates of adjacent structures and 4 evidence for the propagation direction of folds or faults as they grow the few quantitative estimates we obtain for fault propagation rates suggest an increase in length of 10 50 m per earthquake on faults about 20 km long these estimates are very uncertain but are similar in magnitude to an estimate made in nevada for a normal fault of similar size and are also similar to predicted estimates from theoretical growth models they raise the question of whether fault growth earthquake recurrence rates and climate change can interact to produce semi regular discrete features in an active landscape

co seismic ruptures of the 12 may 2008 ms 8 0 wenchuan earthquake sichuan east west crustal shortening on oblique parallel thrusts along the eastern edge of tibet abstract the m s 8 0 wenchuan earthquake which devastated the mountainous western rim of the sichuan basin in central china produced a surface rupture over 200 km long with oblique thrust dextral slip and maximum scarp heights of 10 m it thus ranks as one of the world s largest continental mega thrust events in the last 150 yrs field investigation shows clear surface breaks along two of the main branches of the ne trending longmen shan thrust fault system the principal rupture on the nw dipping beichuan fault displays nearly equal amounts of thrust and right lateral slip basin ward of this rupture another continuous surface break is observed for over 70 km on the parallel more shallowly nw dipping pengguan fault slip on this latter fault was pure thrusting with a maximum scarp height of 3 5 m this is one of the very few reported instances of crustal scale co seismic slip partitioning on parallel thrusts this out of sequence event with distributed surface breaks on crustal mega thrusts highlights regional ew directed present day crustal shortening oblique to the longmen shan margin of tibet the long rupture and large offsets with strong horizontal shortening that characterize the wenchuan earthquake herald a re evaluation of tectonic models anticipating little or no active shortening of the upper crust along this edge of the plateau and require a re assessment of seismic hazard along potentially under rated active faults across the densely populated western sichuan basin and mountains

mechanics of wedge shaped fault blocks 2 an elastic solution for extensional wedges listric planar low angle and high angle normal faults are common in hanging walls of detachment faults an elastic model has been developed to evaluate the role of basal friction wedge geometry pore fluid pressure within the wedge and boundary conditions applied along the wedge rear in controlling the stress distribution in an extensional fault wedge this model assumes a stress free condition on the top and fractional sliding on the base of the wedge respectively a linear variation of stress components as a function of depth along the wedge rear and a uniform horizontal stress applied on the wedge toe the model predicts that 1 for the surface slope equal to zero a thin wedge favors development of high angle and planar faults whereas a thick wedge favors development of low angle and listric normal faults variation of pore fluid pressures along the basal detachment fault hardly affects the predicted fault geometry pore fluid pressure within the wedge is critical in controlling the state of stress in the wedge higher values of the internal pore fluid pressure promote low angle normal faulting and locally high angle reverse faulting 2 variation of surface slope and the uniform horizontal normal stress applied at the wedge toe does not affect the predicted fault geometry appreciably although the distribution of deviatoric stress magnitude changes for different cases and 3 listric normal faults are predicted in all computations and the fault curvature increases as the vertical gradient of the horizontal normal stress along the wedge rear the wedge angle surface slope dip angle and the internal pore fluid pressure increase the model provides a simple conceptual guide to deciphering the formation of complex fault geometries and cross cutting relationships as a function of mechanical parameters related to geologic processes and settings for example it provides an explanation for why low angle normal faults cut high angle normal faults in hanging walls of some detachment fault systems in the u s cordillera

the coexistence approach a method for quantitative reconstructions of tertiary terrestrial palaeoclimate data using plant fossils abstract the coexistence approach is introduced as a method for quantitative terrestrial palaeoclimate reconstructions in the tertiary it is based on the assumption that tertiary plant taxa have similar climatic requirements to their nearest living relatives the aim of the coexistence approach is to find for a given fossil flora and a given climate parameter the climatic interval in which all nearest living relatives of the fossil flora can coexist for this purpose we have developed a data base climbot containing for over 800 tertiary plant taxa the nearest living relatives and their climatic requirements and an algorithm for analysis climst for all types of fossil floras the coexistence approach thus allows the rapid quantitative reconstruction of 10 different climate parameters including the mean annual temperature temperature of the warmest month temperature of the coldest month mean annual precipitation maximum monthly precipitation minimum monthly precipitation precipitation of the warmest month relative humidity potential evaporation as well as the ratio of mean annual precipitation over potential evaporation the reliability and resolution of the coexistence approach are tested with various techniques and proved to be reasonably good for instance the resolution with respect to the mean annual temperature can be up to 1 c applications to various modern and fossil floras are illustrated and the advantages and disadvantages of the coexistence approach are discussed

role of fluids in surface deformation caused by the 1999 chi chi earthquake in taiwan the 1999 chi chi earthquake significantly altered the landscape of central taiwan surface deformation produced by the earthquake along the trace of the chelungpu thrust can be classified into two styles 1 uplift without significant surface rupture and 2 uplift accompanied by surface rupture here we examine areas that exhibited the first style of deformation e g wufeng seismic stress at the time of the main shock may have been relieved by high pore fluid pressure in a 300 m thick sand and gravel aquifer along the thrust fault frictional heating of these sediments resulted in thermal expansion and an increase in pore fluid pressure high pore fluid pressure damped seismic wave energy and enhanced intergranular slips of unconsolidated sandy and gravel sediments which were possibly assisted by sulphuric acid corrosion leading to a high sulphate content in the groundwater c 70 mg l 1 these changes permitted surface folding and terrace style uplifting to occur without significant rupture in contrast other areas in which the second style of deformation is dominant e g fengyuen shihkang have thin 0 10 m sand and gravel deposits and lower concentrations of sulphate c 30 mg l 1 in groundwater in these areas sediments were heated but not sufficiently to produce significant thermal expansion and increase in pore fluid pressure accumulation of stress in these locations led to rupture at the ground surface with the formation of steep fault scarps the areas exhibiting the first deformation style are characterized by the presence of high pore fluid pressure frictional heat conduction and possibly chemical corrosion related to sulphuric acid attack and formation of sulphate in contrast to those involving significant uplift and surface rupture the areal distribution of these two surface deformation styles suggests that the aforementioned fluid related subsurface processes may have altered the characteristics of sediments and caused diverse responses to the quake copyright 2002 john wiley sons ltd

the 21 may 2003 zemmouri algeria earthquake mw 6 8 relocation and aftershock sequence analysis 1 a strong earthquake mw 6 8 struck the coastal region east of algiers and the tell atlas of algeria on 21 may 2003 and was responsible of severe damage and about 2400 casualties the coastal mainshock was followed by a large number of aftershocks the largest reaching mw 5 8 on 27 may 2003 we study the mainshock first major aftershocks and about 900 events recorded by temporary seismic stations using master event approach and double difference dd methods although the seismic station array has a large gap coverage the dd algorithm provides with an accurate aftershocks location the mainshock hypocenter relocation is determined using three major aftershocks 5 0 mw 5 8 chosen as master events the new mainshock location shifted on the coastline 36 83n 3 65e at 8 10 km depth seismic events extend to about 16 km depth and form a n 55 60 e trending and 45 55 se dipping fault geometry up to now it is the unique among the recently studied seismic events of the tell atlas of algeria mainshock and aftershocks relocation the thrust focal mechanism harvard cmt n 57 44 se dip 71 rake and the seismic moment 2 86 1019 nm infer a 50 km long fault rupture that may appear at the sea bottom at 6 to 12 km offshore north of the coastline the zemmouri earthquake occurred along the complex thrust and fold system of the tell atlas and provides with new constraints on the earthquake hazard evaluation in northern algeria

technique evolvement and improvement for better fracture characterization using prestack p wave seismic data abstract anisotropic migration has become a routine practice for fracture prediction because of its remarkable capability of suppressing effects of geologic structures while preserving anisotropy induced by fractures the quality of input seismic gathers is of the first priority among other factors for fracture prediction azimuth sectored migration loses considerable accuracy and reliability because of its coarse and inappropriate manner in dealing with seismic data a full azimuth anisotropic migration in surface offset domain provides better efficiency in using data information furthermore full azimuth anisotropic migration in local angle domain subsurface angle domain allows for accurate and reliable exploitation of seismic wavefield information finally influences of the above three anisotropic migration methods on fracture prediction are prescribed with a field example in which validations with formation micro imager fmi information demonstrate that full azimuth anisotropic migration in local

a comparison of intuitive and objective interpretations of miocene plant assemblages from north bohemia abstract an extensive corpus of semi quantitatively described geobotanical analyses from the early miocene of north bohemia has been examined by parametrical and non parametrical multivariate statistical methods the results of these analyses have been compared with traditional geobotanical interpretations that are based on uniformitarian assumptions the statistical analyses show that there are patterns of relationships inherent in the raw geobotanical analyses that are very similar to the traditional interpretations but the statistical analyses define seventeen groups where tradition recognises eight the objective picture from the statistical study however throws a fresh perspective on the familiar evidence and implies that montane colline and riparian forest associations often sub divided on edaphic lines can be recognised in addition to the lowland marsh ecologies implicit in a major brown coal deposit the present day ecological patterns recognisable in ecosystems more than twenty million years old suggest that most of the components retained their ecological preferences throughout this time the statistical analyses offer fresh insights into aspects of the processes transporting the specimens to their place of burial the success of the statistical analyses indicates that the methods used are potentially capable of identifying ecological associations in older geological systems

seismotectonics of the el asnam earthquake the mechanism of the el asnam earthquake of 10 october 1980 ms 7 2 the strongest recorded in northwestern africa is compatible with a convergence between the african and european plates the thrust is also consistent with field observations and with long period data from the global network aftershocks cluster around the fault trace with a maximum depth of 12 km maximum vertical displacement is 6 m and there is some left lateral motion the fault trace of the 1954 earthquake at beni rached was also reactivated

low angle normal faults in lower eocene chalks near beer sheva israel abstract forty outcrops of lower eocene chalks mor formation around beer sheva were examined for faulting ten well exposed normal faults with mean dip and strike of 39 6 and 294 n66 w 28 respectively were found in four outcrops the timing of fault movement is partly constrained by unfractured lower eocene chert nodules which follow some of the fault traces hence the faults are interpreted to be the result of dynamic failure due to horizontal nne ssw compression during the early eocene horizontal compression is implied by analogy to descriptions of recent faulting caused by an earthquake in another location local folding in the lower eocene secondary fractures and flat and ramp structures associated with the investigated faults

accretion mass wasting and partitioned strain over the 26 dec 2004 mw9 2 rupture offshore aceh northern sumatra abstract the aceh segment of the sunda arc absorbed the largest slip along the 26 december 2004 mw9 2 subduction earthquake rupture and caused the highest and most disastrous tsunami run ups sea floor disruption marks the frontal active part of the accretionary prism along that segment an rov bathymetric and seismic survey r v natsushima jamstec 2 3 2005 revealed pervasive and deeply rooted fracturing along the upper trench slope grabens and ejecta clasts from fluid escape along the crest of an anticline ridge coupled with mass wasting and erosional scouring on the slope below it specific features of the disruption and its patchy distribution suggest coseismic faulting and folding with gravitational collapse of the steepened anticline forelimb the same ridge 40 km along strike was pristine disruption was also generally undetected by rov on the ache basin side of the forearc ridge suggesting a minor role for shaking only some of the faults in the imbricate and segmented accretionary structure ruptured but together they may account for 2004 sea floor rupture along the aceh segment this hypothesis accounts for unusual thrust aftershocks and suspended sediment along the frontal active part of the prism it can also account for the huge tsunami heights in northern sumatra because faults in the prism are steeper than the megathrust down dip and because slip may be larger in the prism following prior blind ruptures rare but large coseismic deformation of the prism can generally account for the erosional morphology of trench slopes and for al least some tsunami earthquakes on the landward side of the forearc high the west andaman fault borders the aceh basin and branches southward into a fault crossing obliquely the forearc high seismic profiles at the bifurcation image a flower structure with strain partitioning and an active dextral pull apart this fault system however did not release significant strain in 2004

integration of knowledge based seismic inversion and sedimentological investigations for heterogeneous reservoir abstract conventional geological modelling methods are not capable to provide precise and comprehensive model of the subsurface structures when dealing with insufficient data knowledge based methods employing rule bases techniques are found vast applications in geoscience studies these methods are applicable for petroleum reservoir geological modelling and characterizations specifically for geologically complex structures in this study we present a knowledge based seismic acoustic impedance inversion method which employs rule based method for porosity estimation the back propagation algorithm and the fuzzy neural network are also used in the methodology for parameter optimization and definition of nonlinear relationship between seismic attributes and porosity of the reservoir rock the methodology initiates by seismic acoustic impedance inversion followed by conventional porosity estimation subsequently a knowledgebase was designed by investigation on more than 24 published case studies this knowledgebase was used for definition of rules and optimization number of rules and improve efficiency of the inference engine the porosity model obtained by conventional method in previous step would be used for primary evaluation of the rules the extracted rules and optimized number rules then would be used for rule based porosity estimation the methodology was applied on a petroleum field containing two heterogeneous reservoir formations result of application of the proposed approach was evaluated with core analysis thin sections and drilling data consistency of result obtained by the proposed method with geological data has shown its capability to resolve problem of insufficient data in reservoir geological modelling

an aftershock study of the el asnam algeria earthquake of 1980 october 10 summary an array of 28 portable seismic stations was operated in the region of el asnam following the magnitude 7 3 ms thrust earthquake of 1980 october 10 locations of 494 events are presented in this paper and provide an indication of the overall form of the aftershock distribution tests to establish location accuracy particularly depth reduce this set to 277 events which it is argued are well constrained p waves alone are used in this study as a consequence of a debate about the reliability of reading s phases from the reduced set of 277 events 81 events provide well constrained focal mechanisms the locations are presented in the form of maps and cross sections and discussed in relation to information already derived from field mapping of surface breaks and teleseismic studies of the waveforms of the main event the zone of surface faulting including secondary normal faulting extended for 35 km but the aftershock distribution extends for twice this distance along the part of the fault which experienced substantial displacement in the main shock the fault plane itself appears to be devoid of aftershocks although many lie in the footwall beneath the fault at junctions between segments of thrust faulting strike slip motion occurs this is apparent in the aftershock focal mechanisms and in the surface ruptures in one place the large number of aftershocks in the north east area appears to be due to the reactivation of a fan like system of smaller reverse faults associated with surface folding activity at the south west end is considerably less than that in the north east and is not obviously associated with recognizable geological or morphological features

analysis of subsurface flow and formation anisotropy in a fractured aquitard using transient water level data a new methodology is proposed to estimate the actual direction of water flow in a fractured aquitard according to the conceptual model the flow direction in a fractured aquitard is dictated by the azimuth of the fractures since almost no flow occurs within the rock matrix which possesses very low hydraulic conductivity thus while groundwater in reality continues to flow along the fractures calculations based on water level data may incorrectly indicate changes in hydraulic gradients and azimuth of flow the present methodology is based on simultaneous analysis of hydraulic gradients and flow direction as calculated from equipotential surfaces the approach was tested in a fractured chalky aquitard and the calculated direction of principal fractures was found to be in good agreement with subsurface fracture data obtained from a tunnel excavated in the vicinity of the study area

fracture stresses at shallow depths during burial abstract single layer joints in lower eocene chalks near beer sheva israel developed at shallow depths during burial prior to folding and uplift fracturing occurred in two stages initially extensional joints marked by circular fracture surface morphology formed at about 100 m depth when pore pressure p 1 5 mpa horizontal maximum effective stress gs y 1 0 mpa vertical effective stress gs z 1 0 mpa and horizontal minimum effective stress gs x 0 5 mpa subsequently hybrid joints that produced a dihedral angle of 35 and were marked by axial horizontal plumes formed at a burial depth of about 150 m where p 2 0 mpa gs x 0 5 mpa gs y 1 0 mpa and gs z 1 8 mpa fracturing continued during further burial to depths of perhaps 200 400 m

fracture interaction in the gregory rift east africa abstract vertical fracture is important and fracture interaction is quite intensive in the central gregory rift crack branching and non coplanar crack interactions in the rift are characterized for major and minor faults these two manifestations follow theoretical and experimental angular relationships of fracture reasonably well mantle diapirism seems to have been responsible for both tensile probably unstable fracture and block tilting ultimately resulting in fault dips deviating from the vertical

control of rupture by fault geometry during the 1980 el asnam algeria earthquake summary the el asnam earthquake of 1980 october 10 ms 7 3 occurred on a segmented reverse fault in the atlas mountains of algeria this report re examines the teleseismic data for the main shock and major aftershocks in the light of detailed studies of the surface breaks geodetic changes and aftershock distribution the observed thrust fault is split into southern central and northern segments by distinct offsets and changes in trend the southern and central segments are each about 12 km long but the northern segment showed only 3 4 km of surface thrust breaks however widespread tensional faulting on ridges in the north east area together with focal mechanisms of locally recorded aftershocks indicates that a series of imbricate listric thrusts exists to the north of the northern fault segment using isc arrival time lists a relative relocation scheme is applied to the main shock and major aftershocks to improve their locations with respect to the mapped faults the main shock epicentre was at the south west end of the fault system in a zone where the thrust has a zig zag surface trace by contrast most of the major aftershocks were located further north east and were associated with the northern thrust segment and the imbricate thrusts to the north the largest aftershock mb 6 1 which occurred about 3 hr after the main shock was located to the east of the main thrust fault beneath the chelif alluvial basin first motion fault plane solutions are presented for the main shock and largest aftershock the main shock solution indicates a fault plane dipping 54 nw with strike 040 the aftershock solution however has a more e w trend 080 in agreement with the trends of the basin edges near its location the rupture history of the main shock is investigated by forward modelling of the long period p waves four subevents are clearly distinguishable the first three subevents occurred in rapid succession and contributed to the first cycle of the p wave radiation these three subevents represent the successive rupturing of the southern central and northern fault segments in order to match the observed waveforms these three ruptures must have different mechanisms and moments the fault segments have successively shallower dipts from south to north 54 45 and 40 respectively and the central segment had the largest moment release in agreement with the geodetic data of ruegg et al the delay times between the three sources suggest a rupture velocity of about 3 5 km s 1 and their nucleation depths were 7 km the junctions between the fault segments acted as geometric barriers to the rupture propagation but were broken by its passage the fourth subevent of the main shock produced the second cycle of the p wave radiation it began about 18 s after the first i e several seconds after the end of the third rupture nabelek demonstrates that the fourth subevent occurred on a shallow angle 20 thrust plane examination of the locally recorded aftershocks suggests that this plane is a decollement surface underlying the imbricate thrusts of the north east area the total seismic moment found from the body wave modelling is 7 7 1026 dyne cm in good agreement with geodetic and surface wave studies

source mechanisms of twenty six large shallow earthquake ms 6 5 during 1980 from p wave first motion and long period rayleigh wave data source mechanisms of 26 large shallow earthquakes are determined in terms of a double couple point source with a correction for the nondirectional part of source finiteness by using p wave first motions and long period rayleigh wave spectra recorded on wwssn ida and gdsn networks the combined use of both data sets allows us to determine the double couple mechanism uniquely in most cases constrained linear moment tensor inversion m xz m yz 0 correctly determines the strike of the fault but fails to estimate the dip and underestimates the scalar moment all thrust events along the deep sea trenches analyzed in this study show nodal planes which dip perpendicular to the trench axis at an angle shallower than 45 the fit to data of the double couple inversion is comparable to that of the constrained moment tensor inversion using the phase spectra of surface waves we can detect a slow source process with an accuracy of about 10 to 20 sec

tectonic analysis of the dead sea rift region since the late cretaceous based on mesostructures we have measured the orientations of small faults slickensides tectonic stylolites vein with secondary mineralization small folds and dikes in israel and sinai these structures are indicators of paleo stress or strain and provide the pattern of tectonic deformation data were collected at 130 stations most with tens of separate measurements most stations showed consistent deformation stations were located on exposures ranging from precambrian crystalline rocks to pleistocene sediments we have defined two tectonic stress fields each relatively uniform in both time and space one stress field with dominating maximum horizontal compression trending w to wnw in the late cretaceous to eocene rocks in the folds and plateaus west of the dead sea rift the second field with dominating horizontal extension trending e to ene in all rocks inside the rift and proximal thereto the first stress field is called the syrian arc stress and the second is called the dead sea stress a change in style of tectonic deformation which corresponds to the two stress fields is manifested also in the major structures in israel the late cretaceous to neogene deformation is characterized by long wavelength folds and monoclines whereas the neogene to recent deformation is characterized by normal and strike slip faults and volcanic activity

holocene coastal deformation in simeulue and nias indonesia west of sumatra indonesia the islands of nias and simeulue as well as their smaller neighbours display elevated coral reefs and abandoned intertidal platforms faunas from three sections indicate a late cainozoic age for the reefs unaltered mollusc shells from nineteen fossil platforms were dated by first order 14c analysis the localities sampled were 0 5 to 3 5 m above normal high tide apart from one non finite result the ages ranged between modern 300 yrs and 5800 300 yrs b p the resulting average uplift rates are 0 3 1 0 mm yr no simple relationship between sample age and height is apparent but the bulk of the ages fall within three periods 0 800 yrs b p 2000 3400 yrs b p and 4500 5800 yrs b p suggesting that episodes of uplift were separated by periods of quiescence and that they were seismic in origin the pattern of deposition at the key section on nias supports this inference evidence of recent subsidence in eastern simeulue shows that uplift was locally accompanied by tilting the pattern and rate of movement are consistent with the position of the islands on the outer arc ridge of the sunda arc and with the long term uplift rates derived from palaeontological sources the inverse darwin coral reef model proposed here for the development of reefs on the flanks of rising neogene cores may also be applicable elsewhere

preliminary results of a paleoseismological analysis along the sahel fault algeria new evidence for historical seismic events abstract the 60 km long sahel ridge west of algiers tell atlas north algeria is considered as an ene wsw fault propagation fold running along the mediterranean coast and associated with a north west dipping thrust its proximity with algiers makes this structure a potential source of destructive earthquakes that could hit the capital city as occurred in 1365 ad and 1716 ad the first paleoseismologic investigation on the sahel ridge was conducted in order to detect paleo ruptures related to active faulting and to date them from the first investigations in the area a first trench was excavated across bending moment normal faults induced by flexural slip folding in the hanging wall of the sahel anticline thrust ramp paleoseismological analyses recognize eight rupture events affecting colluvial deposits 14c dating indicates that these events are very young six of them being younger than 778 ad the first sedimentary record indicates two ruptures before 1211 ad i e older than the first historical earthquake documented in the region three events have age ranges compatible with the 1365 1673 and 1716 algiers earthquakes whereas three other ones depict very recent ages i e younger than 1700 ad potential of these secondary extrados faults for determining paleoseismic events and thrust behaviour is discussed

field and teleseismic observations of the 1981 golbaf sirch earthquakes in se iran summary in 1981 june and july two large earthquakes occurred on the gowk fault system in south east iran both earthquakes were associated with surface faulting showing a combination of reverse and right lateral strike slip motion on parallel adjacent faults striking north south and dipping both east and west such motion can be seen to have occurred in the recent past and is responsible for the formation of elongated alluvium filled depressions in the footwall region common to both the east and west dipping faults the earthquake of june 11 involved motion along about 15 km of the gowk fault system with a moment of about 1 0 1026 dyne cm the earthquake of july 28 was larger and occurred farther north with movement along at least 65km of the gowk fault system and a moment of about 7 1026 dyne cm surface faulting in both earthquakes was complex and spread over several kilometres width on en echelon fault segments as well as on faults dipping both east and west the long period wwssn seismograms of these two mainshocks are unusually complicated and clearly made up of several individual subevents sensible interpretation of these waveforms without guidance from the surface faulting and the long period sro moment tensor inversion of dziewonski woodhouse would be impossible however a combination of these three data sources allows a geologically plausible interpretation of the rupture processes in these earthquakes to be made although the faulting in both mainshocks was on the same large scale feature the gowk fault the rupture zones of the two earthquakes did not apparently overlap and were separated by a gap of 5 km along strike in which both coseismic and recent geological displacements are very small rupture in both mainshocks appears to have nucleated near this gap and to have propagated away from it other such gaps are visible along the irregular displacement of the northern fault break and may have been the nucleation positions for individual subevents of the july 28 earthquake recognition of such nucleation sites is of obvious importance to earthquake prediction efforts

full azimuth subsurface angle domain wavefield decomposition and imaging part i directional and reflection image gathers we present a new subsurface angle domain seismic imaging systemforgeneratingandextractinghigh resolutioninformation about subsurface angle dependent reflectivity the system enables geophysicists to use all recorded seismic data in a continuousfashiondirectlyinthesubsurfacelocalangledomainlad resulting in two complementary full azimuth common imageangle gather systems directional and reflection the complete setofinformationfrombothtypesofanglegathersleadstoaccurate high resolution reliable velocity model determination and reservoir characterization the directional angle decomposition enables the implementation of specular and diffraction imaging in real 3d isotropic anisotropic geological models leading to simultaneous emphasis on continuous structural surfaces and discontinuous objects such as faults and small scale fractures structural attributes at each subsurface point e g dip azimuth andcontinuity canbederiveddirectlyfromthedirectionalangle gathers the reflection angle gathers display reflectivity as a function of the opening angle and opening azimuth these gathers are most meaningful in the vicinity of actual local reflecting surfaces wherethereflectionanglesaremeasuredwithrespectto the derived background specular direction the reflection angle gathers are used for automatic picking of full azimuth angle domainresidualmoveoutsrmowhich togetherwiththederived background orientations of the subsurface reflection horizons provide a complete set of input data to isotropic anisotropic tomography the full azimuth angle dependent amplitude variations are used for reliable and accurate amplitude versus angle andazimuthavazanalysisandreservoircharacterization the proposed system is most effective for imaging and analysis below complex structures such as subsalt and subbasalt high velocity carbonate rocks shallow low velocity gas pockets and others in addition it enables accurate azimuthal anisotropic imaging and analysis providing optimal solutions for fracture detectionandreservoircharacterization

geomorphology and surface tilting in an active extensional basin sw montana usa the valley and alluvial cone of the antecedent madison river in the missouri flats area of sw montana lie in a half graben bounded by a prominent prehistoric fault scarp footwall sourced alluvial fans and fans derived from a major transfer zone have prograded onto the oldest of a prominent suite of three paired terraces of holocene age which bound the modern braided floodplain of the river the terraces have been cut into the pleistocene alluvial cone and are cut by the prehistoric fault scarp levelling studies on the terrace surfaces in the hangingwall reveal that movement on the fault has caused surface tilting erosion and deposition a suite of terraces present in the footwall of the fault shows backtihing consistent with footwall uplift having occurred

a blind thrust and overlying folding earthquake of the 2016 mw 6 0 hutubi earthquake in the northern tien shan fold and thrust belts china

representative styles of deformation along the chelungpu fault from the 1999 chi chi taiwan earthquake geomorphic characteristics and responses of man made structures the chi chi earthquake provides dramatic evidence of the damaging effects of surface ground deformation to buildings lifelines and other facilities much of the building damage is associated with surface faulting and folding along the chelungpu thrust fault our detailed surveying at representative sites along the fault shows that the rupture commonly is a relatively simple 1 to 4 m high scarp with minor hanging wall deformation and localized but severe uplift folding and graben formation along the scarp crest for individual scarps the width of deformation is about 10 to 20 times the net vertical displacement distributed secondary faulting and folding on the hanging wall occurred as much as 350 m from the primary fault near the northern end of the rupture growth of a pre existing 1 km wide late quaternary anticline produced severe ground rupture along multiple thrusts and backthrusts but only minor tilting between fault strands the pattern of building damage coincides with the pattern of geologic deformation with severe damage along large fault scarps and lesser but still significant damage attributable to distributed secondary surface deformation on the hanging wall rupture related building damage on the footwall occurred next to the prerupture fault trace where the hanging wall bulldozed onto the footwall the width of this damage zone is related to the local horizontal shortening along the fault and generally is less than 10 m building zonation along reverse faults should account for this pattern of surface deformation in addition buildings with massive foundations locally influenced the style and location of near surface deformation producing variations in fault strike or accentuated secondary deformation on the hanging wall manuscript received 15 january 2001

chemical weathering of fractured eocene chalks in the negev israel abstract ba ca fe k mg mn sr and insoluble residue i r contents of eocene chalks and of vein filled derivative matter from the northern negev israel were analyzed the eocene chalk country rock weathered physically and chemically and the eroded material has filled the fault planes and some of the joints two types of filling material were found calcite crystals and soft fine carbonate material the latter as the chalk are sometimes associated with fe and mn oxides i r ca mg ca sr ca and k ca values decrease from the country rock chalk to the fine carbonates and are lower in the calcite minerals the ba ca values are low in the soft fine carbonates and high in the calcite minerals barite was found in places in the chalk fe ca and mn ca values are higher in the soft fine carbonate based on k d values the expected ba ca mg ca and sr ca values in the vein carbonates are lower and the expected fe ca and mn ca are higher than the actual values the analysis of the soft fine carbonates from the various joints and faults shows that chemical precipitation was unaffected by these structures this possibly suggests that the soft fine carbonates are younger and not contemporaneous with the structures

high diversity european palaeoflora favoured by early pliocene warmth new chronological constraints from the ca viettone section nw italy abstract we present new chronological constraints for a reference european palaeoflora based on integrated stratigraphic palaeobotanical palaeomagnetic and micropalaeontological analysis carried out on the pliocene section of ca viettone northwestern italy this site is characterized by rich fossil plant records of high taxonomic diversity good preservation and varied taphonomic mode palaeofloral analysis shows that the ca viettone assemblage reflects a chronologically delimited and distinguishable stage of vegetation development in northern italy called ca viettone florenkomplex palaeomagnetic analyses show a dominant normal polarity that however seems to be the result of a remagnetization process due to secondary oxidation layers with no evidence of oxidation have registered a reverse polarity which likely represents the original magnetization of the sediments these results in combination with biochronological indications suggest that deposition of the succession preceded the gilbert gauss reversal and took place during the final part of the gilbert chron this confirms a late zanclean age for the rich ca viettone palaeoflora and allows us to propose this locality both as reference for a regional florenkomplex and as a representative example of terrestrial vegetation in europe during the early pliocene warm interval

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

paleoclimatic estimates from tertiary leaf assemblages a primary obstacle to evaluating numerical modeling of tertiary nonmarine climates has been the significance and reliability of proxy data sloan barron 1990 lacking direct measurements of paleoclimatic parameters inferred paleoclimatic values are based on substitute proxy sources such as fossils or isotopes are proxy data significant that is have they been calibrated in modern environments and to what level is the calibration this is the problem of accuracy validity in the statistical sense second are the proxy data reliable can two workers or even the same worker consistently arrive at the same estimates using the same data set this is the problem of precision repeatability can these two problems be resolved quaternary palynologists have used the concept of transfer functions a methodology originally developed for foraminifera imbrie kipp 1971 applied in palynology a response surface for each palynomorph taxon is constructed for the environmental variables under consideration these transformations can then be subjected to a number of different kinds of multivariate analyses including ordination methodologies bartlein et al 1986 webb bryson 1972 these transfer functions can work for quaternary and especially the lateand post glacial of the last 20 to 30 thousand years pollen assemblages because in most regions where the methodology has been applied the flora is of known diversity and the equivalency of a given palynomorph species to one or a few extant species can be reasonably assumed even in the late neogene 1 5 to 10 million years ago however this assumption can no longer be made we know that the palynomorph assemblages contain exotic genera mccartan et al 1990 and the presence of exotic and or extinct species

fault displacement gradient folds and the structure at lost hills california u s a abstract geometric models of fault propagation folds require that the underlying fault tip propagate upward across layering however related folds can be generated if the tip remains stationary or even moves back along the ramp as a pre existing fault is reactivated fault propagation folds detachment folds as well as those produced when there is no propagation are generated by a displacement gradient along the underlying fault and as a general class can be called fault displacement gradient folds new geometric equations are derived which relate fold shape to displacement gradient and fault propagation folds are a special case of these more general equations growth sequences associated with these structures have been used to distinguish fault propagation folds from fault bend folds when the underlying structure is obscured a displacement gradient fold in which the fault tip retreats back down the ramp generates a growth sequence that in some cases could be confused with that of a fault bend fold the structure at lost hills in the san joaquin valley of california u s a has been interpreted as a fault bend fold but it may be a displacement gradient fold which formed as a pre existing fault was reactivated during a pliocene change in plate motion

earthquake hazards of active blind thrust faults under the central los angeles basin california we document several blind thrust faults under the los angeles basin that if active and seismogenic are capable of generating large earthquakes m 6 3 to 7 3 pliocene to quaternary growth folds imaged in seismic reflection profiles record the existence size and slip rates of these blind faults the growth structures have shapes characteristic of fault bend folds above blind thrusts as demonstrated by balanced kinematic models geologic cross sections and axial surface maps we interpret the compton los alamitos trend as a growth fold above the compton ramp which extends along strike from west los angeles to at least the santa ana river the compton thrust is part of a larger fault system including a decollement and ramps beneath the elysian park and palos verdes trends the cienegas and coyote hills growth folds overlie additional blind thrusts in the elysian park trend that are not closely linked to the compton ramp analysis of folded pliocene to quaternary strata yields slip rates of 1 4 0 4 mm yr on the compton thrust and 1 7 0 4 mm yr on a ramp beneath the elysian park trend assuming that slip is released in large earthquakes we estimate magnitudes of 6 3 to 6 8 for earthquakes on individual ramp segments based on geometric segment sizes derived from axial surface maps multiple segment ruptures could yield larger earthquakes m 6 9 to 7 3 relations among magnitude coseismic displacement and slip rate yield an average recurrence interval of 380 years for single segment earthquakes and a range of 400 to 1300 years for multiple segment events if these newly documented blind thrust faults are active they will contribute substantially to the seismic hazards in los angeles because of their locations directly beneath the metropolitan area

present day kinematics of the plate boundary zone between africa and europe from the azores to the aegean anticlockwise rotation of africa relative to europe around an euler pole in the eastern atlantic causes plate convergence in the central mediterranean towards n20 w at rate considered a priori to be 5 10 mm yr 1 however previous summaries of the present day deformation sense in the central mediterranean are inconsistent with observations in southern italy recent investigations of italy and adjacent parts of north africa enable local deformation sense observed to be reconciled with sense predicted from relative plate motions suggested angular velocity of the african plate relative to europe is 0 07 myr 1 around a pole near 21 n 21 w this predicts 2 6 mm yr 1 maximum extension rate towards n64 e near the azores consistent with the minimum local accretion of new oceanic crust in the past few millions of years and 4 3 mm yr 1 plate convergence towards n20 w in the central mediterranean at 13 e further east the northern margin of the african plate can be regarded as the gargano seismic zone in the central adriatic sea the northern adriatic sea is a microplate rotating anticlockwise relative to europe at 0 3 myr 1 around a pole in northwestern italy causing northeastward shortening in yugoslavia and up to 4 mm yr 1 extension in central and northern italy the african plate is deforming internally in tunisia and northern libya extending obliquely in direction e10 s at rate up to 5 5 mm yr 1 the resultant velocity relative to europe in the ionian and southern adriatic seas 5 mm yr 1 towards n50 e explains the observed relative velocity across southern italy kinematic consistency requires present day shortening rate east of calabria associated with subduction on the tyrrhenian sea benioff zone and tyrrhenian sea extension rate to be both zero or equal to within 1 mm yr 1

deformations associated with the el asnam earthquake of 10 october 1980 geodetic determination of vertical and horizontal movements the resurvey of both a geodetic network and a leveling net was carried out in june 1981 8 months after the ms 7 3 el asnam earthquake of 10 october 1980 previous seismological and neotectonic studies ouyed et al 1981 yielding et al 1981 indicate that this event results from a northeast trending overthrust complex fault of about 40 km length which shows at least three principal segments with slightly different directions vertical movements evaluated by means of a trigonometric leveling method show an uplift of the northwestern side of the thrust fault of about 5 m and a depression of the southeastern edge of about 1 m these movements are progressively attenuated away from the fault trace horizontal movements have been evaluated by a classical first order triangulation method the resulting mean strain tensors calculated for different triangles of the geodetic network indicate a shortening of about 2 50 m which is consistent with the se nw direction of compression determined from neotectonic evaluations and focal mechanisms dislocation models are used to explain and discuss the observed deformations in light of the seismological data and observed ground breakages five segments are required to explain both horizontal and vertical deformations the magnitude of vertical displacements about 6 m at the junction between the southwest and the central segments of the fault argues for the breaking of this area during the main shock and for a slip vector of about 8 m at least in the central segment

azimuth preserved local angle domain prestack time migration in isotropic vertical transversely isotropic and azimuthally anisotropic media conventional prestack migration does not preserve local directional information of the seismic waves at the image points new attempts such as sectored migration of azimuth limited or common offset vector data only concern source receiver azimuth and offset on the surface which can be poor representation of subsurface wavepath direction moreover they could result in inaccurate imaging because they do not account for the energy propagation between azimuths or offset vectors in the past decade local angle domain seismic imaging has been highly advocated to avoid migration artifacts and to improve velocity estimation in complex media considering prestack time migration pstm is still widely used in seismic imaging and seismic data preconditioning for amplitude variations with offset or incident angle avo ava analysis fracture detection and reservoir characterization we present an azimuth preserved local angle domain kirchhoff pstm approach for such purposes we apply a seismic imaging condition i

chronology and development of the 1980 earthquake at el asnam algeria a postscript abstract radiocarbon dating has now confirmed the alluvial chronology that was used in assessing the extent of deformation during the 1980 el asnam earthquake it also supports the suggestion that earlier movements were related to a hypocentre further to the east