relocation and assessment of seismicity in the iran region summary more than 2000 instrumentally recorded earthquakes occurring in the iran region during the period 1918 2004 have been relocated and reassessed with special attention to focal depth using an advanced technique for 1 d earthquake location a careful review of starting depths association of teleseismic depth phases and the effects of reading errors on these phases are made and when necessary waveforms have been examined to better constrain ehb focal depths uncertainties in ehb epicentres are on the order of 10 15 km in the iran region owing to the earth s lateral heterogeneity and uneven station distribution uncertainties of reviewed ehb focal depth estimates are on the order of 10 km as compared to about 4 km for long period p and sh body waveform inversions nevertheless these ehb depth estimates are sufficiently accurate to resolve robust differences in focal depth distribution throughout the iran region and within their errors show patterns that are in agreement with the smaller number of earthquakes whose depths have been confirmed by body wave modelling or local seismic networks the importance of this result is that future earthquakes with apparently anomalous depths can easily be identified and checked if necessary most earthquakes in the iranian continental lithosphere occur in the upper crust with the crustal shortening produced by continental collision accommodated entirely by thickening and distributed deformation in the zagros mountains nearly all earthquakes are confined to the upper crust depths 20 km and there is no evidence for a seismically active subducted slab dipping ne beneath central iran by contrast in southeastern iran where the arabian seafloor is being subducted beneath the makran coast low level earthquake activity occurs in the upper crust as well as to depths of at least 150 km within a northward dipping subducting slab near the oman line a region transitional between the zagros and the makran seismicity extends to depths of up to 30 45 km in the crust consistent with low angle thrusting of arabian basement beneath central iran in north central iran along the alborz mountain belt seismic activity occurs primarily in the upper crust but with some infrequent events in the lower crust particularly in the western part of the belt the talesh where the south caspian basin underthrusts nw iran earthquakes that occur in a band across the central caspian following the apscheron balkhan sill between azerbaijan and turkmenistan have depths in the range 30 100 km deepening northwards these are thought to be connected with either incipient or remnant northeast subduction of the south caspian basin basement beneath the east west trending apscheron balkhan sill curiously in this region of genuine mantle seismicity there is no evidence for earthquakes shallower than 30 km

empirical observations regarding reverse earthquakes blind thrust faults and quaternary deformation are blind thrust faults truly blind active thrust faults pose a significant seismic hazard worldwide many of these faults include blind thrusts where the propagating fault tip does not reach the earth s surface and buried faults where the geomorphic expression of the fault is obscured by subsequent sedimentation and or erosion this raises the issue of whether conventional geologic geomorphic and paleoseismic methods can be used to identify and characterize thrust faults for the assessment of seismic hazards or whether these faults sometimes are truly blind we compiled a data base of 148 worldwide moderate to large magnitude thrust reverse earthquakes to evaluate whether or not the event occurred on a fault that could have been identified prior to the earthquake on the basis of recognizable quaternary surface deformation i e a pre existing fault or fold analysis of the data shows that interplate reverse earthquakes almost always are associated with pre existing quaternary deformation that was or could have been recognized prior to the earthquake in particular most interplate reverse earthquakes are associated with an active reverse fault at the surface and or an active anticline in contrast intraplate reverse earthquakes seldom occur on faults associated with pre existing recognizable surface deformation we conclude that thrust faults can be detected in interplate regions with careful quaternary geologic and geomorphic mapping furthermore the absence of quaternary surface deformation can be used to infer the absence of an underlying active blind thrust fault in interplate tectonic settings however the data show that quaternary geologic mapping techniques alone likely are insufficient to characterize blind thrusts in intraplate regions in these areas inclusion of a floating or random earthquake may be necessary to assess earthquake hazards

active faults in the zagros and central iran abstract active tectonic movements in the northwestern zagros include right lateral slip at the rate of about 10 mm a along the main recent fault which inherits the position of the main thrust now inactive and active thrusting and accompanying folding distributed between several zones southwest of the main recent fault in the southeastern zagros the fars province there are several right lateral faults that extend n s obliquely to the overall trend of the zagros fault and fold belt these may be either branches of the main recent fault or faults accommodating relative broadening of the outer zagros in its southeastern segment the main thrust in the southeastern zagros also remains inactive the ipak north tehran and mosha fault zones and several minor structures in the eastern alborz form the e w trending active fault system with combined reverse and left lateral slip on the ipak and mosha zones lateral movements with the late quaternary mean rate exceeding 1 mm a dominate over vertical fault movements together with right lateral faults stretching northeast of zagros the faults of the alborz may accommodate east directed motion of the iranian microplate

a palaeomagnetic study of jurassic intrusives from southern new south wales further evidence for a pre cenozoic dipole low the results of rock magnetic thermal demagnetization and thellier palaeointensity studies are presented for two high level intrusions from southern new south wales australia the gingenbullen dolerite gb 34 5 s 150 3 e and the gibraltar microsyenite gs 34 5 s 150 4 e were emplaced during the second of three major phases of igneous activity that affected the southern sydney basin and are k ar dated at 172 and 178 ma respectively the magnetic mineralogy of the two intrusions is different the gb is dominated by single domain sd pseudo single domain grains of magnetite whereas the gs has both sd magnetite and haematite components although the haematite component does not record a stable remanence the gb records two opposed components of magnetization above 100 c occupying distinct parts of the blocking temperature spectrum the lower blocking temperature lbt component resides between 150 and 400 c and is of normal polarity having a mean direction of d i 021 79 95 8 k 63 with a corresponding vgp at lat long 54 s 137 e dp 12 dm 13 this component is believed to be a tcrm or tvrm related to the initial opening of the tasman sea at 90 ma the higher blocking temperature hbt chrm component is recognized between 450 and 580 c and is of reverse polarity with a mean direction of d i 174 81 95 11 k 33 and a corresponding vgp at lat long 52 s 153 e dp 17 dm 18 the chrm for the gs resides in the 100 450 c region and although the scatter is high has a similar mean direction d i 167 79 95 24 k 26 to the hbt component of the gb with a pole position at lat long 54 s 158 e dp 30 dm 31 there is no evidence of the gb lbt component in samples from the gs suggesting that this intrusion was magnetically unaffected by the later event which is also seen for other intrusions in the sydney basin the vgps calculated from the chrm directions both plot on the jurassic segment of the australian apwp dunlop et al 1997 providing further palaeomagnetic confirmation for the k ar ages thellier palaeointensity results were of variable quality as expected for rocks of this age the mean vdm values calculated for the chrms of the gb and gs were 1 3 1022 and 4 1 1022 am2 respectively approximately 16 and 51 per cent of the present value on application of a cooling rate correction estimate the gb result falls to a minimum of 0 87 1022 am2 approximately 11 per cent of the present day value representing an overestimate of up to 56 per cent these values arising from a time window previously lacking in thellier estimates provide further confirmation of the existence of a pre cenozoic dipole low the vdm values derived from the overprint in the gb samples yield an average of 4 8 1022 am2 from a range between 44 and 81 per cent of the present day mean vdm and are tentatively attributed to the cretaceous normal superchron cns these results may document evidence for a previously unrecognized low dipole moment during the bulk of the cns a possibility that requires further investigation by performing palaeointensity work on igneous rocks with radiometric ages between 110 and 90 myr that carry unequivocal primary trms

three dimensional kinematic modeling of reversible fault and fold development in the current context of continuous supply of energy the discovery and development of new prospects will rely on our ability to detect reserves in deeper and structurally more complex formations these exploration areas stretch the capabilities of currently available three dimensional 3 d exploration software which cannot accommodate a realistic geometrical description of present day geological structures and the tectonic deformation steps correctly handling the kinematics of structural deformation and evaluating the pressure regime and temperature history at the scale of exploration will remain as challenges for several years to come in this article we focus on geometric aspects using a reversible kinematic approach to deform and restore faulted and folded structures kinematic modeling is a good alternative to the complexity of a mechanical approach and is sufficiently representative of the natural processes involved sedimentation erosion and compaction its reversibility ensures that the basin parameters need to be defined only once for both the restoration and the deformation steps the model describes the incremental development of the basin in space and time it is based on a hexahedral discretization process that is fully adapted and appropriate for thermal and fluid transfer different deformation modes flexural slip and vertical shear are mixed to integrate natural deformation more effectively the algorithm is validated using different geological examples of growing complexity up to curved normal and thrust faults the approach offers various prospects for improvement integrating both kinematic and mechanical constraints considering the challenges that the industry needs to overcome in future exploration the results of this approach are very encouraging and can be considered as a solution for solving the structural part of 3 d basin modeling in complex areas

digital mapping of three dimensional structures of the chimney rock fault system central utah abstract part of the chimney rock fault system located on the northern san rafael swell utah was mapped by integrating air photograph interpretation and differential global positioning system gps location data fault slip slip directions and hanging wall subsidence footwall uplift were digitally recorded in the field along and between the normal faults using trimble pathfinder equipment and software gps was used to record with sub meter precision the location of each measurement as well as the utm coordinates and elevation of stratigraphic markers at the top of the jurassic navajo sandstone and near the base of the overlying carmel formation the fault system as well as the associated deformation of the sedimentary layers within the fault blocks have been precisely characterized using this technique the geographic coordinates and local elevation were transferred to gocad to produce a three dimensional surface representation of a selected resistant limestone layer by interpolating the elevation between the collected data points using imposed constraints such as the dips of the layers and the locations of the major faults separations of the selected horizon from the footwall to the hanging wall were used to calculate the dip slip distribution along the faults the digital field data were compared with the results of numerical modeling based on continuum mechanics to study the mechanical interaction among intersecting normal faults and the effects of this interaction on slip distribution and direction this project illustrates the complete circle from digital mapping to data analysis to numerical modeling to quantitative comparison of theoretical models and field data

calibration and validation of reservoir models the importance of high resolution quantitative outcrop analogues rapidly developing methods of digital acquisition visualization and analysis allow highly detailed outcrop models to be constructed and used as analogues to provide quantitative information about sedimentological and structural architectures from reservoir to subseismic scales of observation terrestrial laser scanning lidar and high precision real time kinematic gps are key survey technologies for data acquisition 3d visualization facilities are used when analysing the outcrop data analysis of laser scan data involves picking of the point cloud to derive interpolated stratigraphic and structural surfaces the resultant data can be used as input for object based models or can be cellularized and upscaled for use in grid based reservoir modelling outcrop data can also be used to calibrate numerical models of geological processes such as the development and growth of folds and the initiation and propagation of fractures

influence of landscape coverage on measuring spatial and length properties of rock fracture networks insights from numerical simulation natural fractures are ubiquitous in the earth s crust and often deeply buried in the subsurface due to the difficulty in accessing to their three dimensional structures the study of fracture network geometry is usually achieved by sampling two dimensional 2d exposures at the earth s surface through outcrop mapping or aerial photograph techniques however the measurement results can be considerably affected by the coverage of forests and other plant species over the exposed fracture patterns we quantitatively study such effects using numerical simulation we consider the scenario of nominally isotropic natural fracture systems and represent them using 2d discrete fracture network models governed by fractal and length scaling parameters the groundcover is modelled as random patches superimposing onto the 2d fracture patterns the effects of localisation and total coverage of landscape patches are further investigated the fractal dimension and length exponent of the covered fracture networks are measured and compared with those of the original non covered patterns the results show that the measured length exponent increases with the reduced localisation and increased coverage of landscape patches which is more evident for networks dominated by very large fractures i e small underlying length exponent however the landscape coverage seems to have a minor impact on the fractal dimension measurement the research findings of this paper have important implications for field survey and statistical analysis of geological systems

paleointensity of the earth s magnetic field in early cretaceous time the parana basalt brazil paleointensity experiments were carried out with the coe and thellier methods on early cretaceous basalt 133 my old from the parana basin in southern brazil paleointensity estimates could be obtained from only six lava flows three of normal and three of reversed polarity of the 71 sampled moreover the quality of the determinations is fairly low with q ratio usually less than 10 mainly as a result of chemical and or physical changes of the magnetic oxides during heating this study strongly underscores the difficulty of finding natural rocks suitable for paleointensity experiments even so the directional results previously obtained were good the most reliable result give an intensity of 28 1 t while the others range from 20 8 t to 37 7 t the corresponding virtual dipole moments vdms range from 4 7 x 10 22 to 7 9 x 10 22 am 2 this dispersion is attributed mainly to inaccurate estimates of the ancient field rather than to secular variation although the number of cooling units for which paleointensity estimates could be obtained is limited the results nevertheless indicate that the early cretaceous vdm was significantly lower than that for the recent field but greater than has been reported for this portion of the mesozoic dipole low period

palaeoseismicity and pottery investigating earthquake and archaeological chronologies on the hajiarab alluvial fan iran for millennia humans have lived in locations that are highly vulnerable to large earthquakes often out of strategic or cultural necessity and or the proximity of these locations to resources necessary for survival despite the often catastrophic effects when large earthquakes occur recent history reveals that human nature is to rebuild rather than relocate implying that seismic activity is not a sufficient deterrent of population growth in tectonically vulnerable areas in order to investigate whether this was the case for ancient civilisations and thus perhaps a fundamental tenet of human behaviour a palaeo earthquake history was developed for the active cheskin and ipak faults in northwestern iran and compared with the well resolved archaeological history of the nearby sagzabad cluster settlements of zagheh 7170 6300 bp ghabristan 6215 4950 bp and sagzabad 4050 2350 bp combining new geologic geomorphic and chronologic datasets revealed the presence of a fault propagated anticline formed by large mw 6 5 7 0 earthquakes on a blind thrust fault that projects to seismogenic depth directly beneath the sagzabad cluster settlement sites large earthquakes with a return period of 90 probability under most faulting scenarios that the energy release from these earthquakes would have been of sufficient magnitude to generate peak horizontal acceleration pha values at the sagzabad cluster in excess of likely threshold values for complete settlement destruction poisson modelling assuming a time displacement repeating model for earthquake recurrence indicates a 66 42 probability of one two earthquakes that would generate pha 0 25 g occurring during occupation of zagheh a 79 55 probability for ghabristan and an 88 65 probability for sagzabad despite the near certainty that the residents of these holocene settlements experienced large destructive earthquakes the near continuous history of occupation at this area suggests that early humans were not apt to relocate in response to earthquake activity environmental e g alluviation stream channel avulsion climate change cultural and or political factors may have been more important drivers of settlement shifts and abandonment at the sagzabad cluster of iran

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

high paleointensities of the geomagnetic field from thermomagnetic studies on rift valley pillow basalts from the mid atlantic ridge nineteen pillow basalts dredged within the rift valley of the mid atlantic ridge at 36 8on were studied by the thellier stepwise heating method in order to determine the paleointensity of the geomagnetic field when they erupted on to the sea floor previously reported fission track ages are 2 000 to 6 000 years for the youngest rocks mainly olivine basalts and 10 000 to 100 000 years for the others mainly plagioclase basalts and pyroxene basalts all but three pillow basalts meet the conditions commonly considered as indicative of quite reliable paleointensity estimates stability of the direction of nrm during its thermal demagnetization constant ratio of nrm trm natural remanent magnetization to thermoremanent magnetization over 50 or more of the original nrm intensity 80 to 94 for 11 specimens and reproducibility of low temperature partial trm ptrm however strong field thermomagnetic measurements indicate that 11 of these 16 samples display a significant increase in curie temperature 15 to 80oc during the paleointensity experiments below 250oc notwithstanding the linearity of the nrm trm plot in this temperature interval this alteration probably due to low temperature oxidation of the specimens seems typical of young pillow basalts and may result in paleointensity estimates which are too high this result shows that excellence of remanence tests nrmtrm linearity and ptrm stability does not ensure the absence of chemical changes during the thellier experiments and therefore the validity of the paleointensity obtained the assumption that reliable paleointensities are obtained when the curie point increase is 10oc or less led to the selection of five of our specimens all from the youngest group their mean paleointensity is 64 2 20 5 xt standard deviation and the corresponding virtual axial dipole moment vadm is 11 5 3 7 x 1022 a m 2 given the variations of the vadm of the earth s magnetic field over the last 6 000 years as established from archeomagnetic studies our paleointensity results suggest that the latest eruptions on the inner floor of the rift valley at 36 8on occurred 1 500 1 000 years ago

unlocking the spatial dimension digital technologies and the future of geoscience fieldwork the development of affordable digital technologies that allow the collection and analysis of georeferenced field data represents one of the most significant changes in field based geoscientific study since the invention of the geological map digital methods make it easier to re use pre existing data e g previous field data geophysical survey satellite images during renewed phases of fieldwork increased spatial accuracy from satellite and laser positioning systems provides access to geostatistical and geospatial analyses that can inform hypothesis testing during fieldwork high resolution geomatic surveys including laser scanning methods allow 3d photorealistic outcrop images to be captured and interpreted using novel visualization and analysis methods in addition better data management on projects is possible using geospatially referenced databases that match agreed international data standards collectively the new techniques allow 3d models of geological architectures to be constructed directly from field data in ways that are more robust compared with the abstract models constructed traditionally by geoscientists this development will permit explicit information on uncertainty to be carried forward from field data to the final product current work is focused upon the development and implementation of a more streamlined digital workflow from the initial data acquisition stage to the final project output

ephemeral stream response to growing folds the response of ephemeral alluvial streams to active tectonics is not as well established as those documented for perennial alluvial streams this study documents the response of ephemeral streams transverse to growing folds along the north fl ank of the san bernardino mountains in southern california the growing folds emerge amid a broad sloping piedmont mantled by north dipping alluvial fans and underlain by coarse angular gravel and sand of mixed provenance the study area contains fans composed of two distinct lithologies that control the expression of the folds sediment transport processes differ among alluvial perennial and ephemeral channels and play a primary role in defi ning the range of responses that ephemeral streams have to an actively rising fold we fi nd that ephemeral streams respond by 1 changing pattern from a single slightly incised channel with well defi ned banks to a braided channel upstream of the fold axis 2 incising across the fold axis preserving a terrace and braid bars and 3 returning to a single thread less incised channel downstream of the fold axis this channel response is documented for both a topographically obvious anticlinal fold the cougar buttes anticline as well as a suspected but not topographically obvious anticline the pitzer buttes anticline variations from this general model appear to be correlated with locations of slow fold growth and or channel alluvium that is fi ne grained and of low cohesion a growing fold such as the cougar buttes anticline provides a laboratory for the investigation of the development of transverse streams with respect to position along strike with the fold axis some streams crossing the cougar buttes anticline are antecedent whereas others are consequent to the growth of the fold these observations lay the foundation for a conceptual model for ephemeral stream response to active tectonics particularly useful in identifying previously unrecognized actively rising folds in this study the fold axis of the cougar buttes anticline is revealed to extend at least 1 km beyond its current obvious topographic expression because ephemeral streams are sensitive to tectonic deformation they can be used locally in paleoseismological investigations regionally to understand the strain partitioning between the big bear and mojave blocks and conceptually to constrain geodynamic models investigating the interaction between surface processes and the geometry of and slip rates on faults responsible for fold growth

implications of earthquake focal mechanism data for the active tectonics of the south caspian basin and surrounding regions summary the south caspian basin is a relatively aseismic block within the alpine himalayan belt but is surrounded by zones of high seismicity we used the focal mechanisms of 16 earthquakes whose source parameters we determined from inversion of body waves and the mechanisms of 15 other earthquakes to determine the style of faulting in the seismic belts surrounding the south caspian basin earthquakes beneath the talesh mountains of north west iran and immediately off shore in the south west caspian sea have shallow thrust mechanisms showing that the continental crust of north west iran is overthrusting the oceanic like crust of the south caspian basin earthquakes south of the caspian sea in northern iran show a mixture of focal mechanisms both high angle reverse faulting and left lateral strike slip faulting mechanisms are observed in the high alborz mountains farther south on the edge of the central iran plateau oblique left lateral reverse mechanisms are observed it appears that the ne direction of shortening between central iran and the south caspian basin is partitioned into pure left lateral strike slip and thrusting in the wnw trending high alborz but is accommodated by oblique faulting in lower elevations earthquakes in the kopet dag mountains east of the caspian sea also show a mixture of high angle reverse and strike slip faulting mechanisms and may be another example of the partitioning of oblique slip into strike slip and thrust motion normal faulting mechanisms at centroid depths of 35 50 km dominate in the belt of seismicity that extends across the central caspian sea the significance of the normal faulting earthquakes is enigmatic it is improbable that these events represent the motion between the southern caspian basin and eurasia for they imply a sense of motion that is incompatible with the observed topography and folding in the sediments two shallow earthquakes at about 12 km depth in this belt one a small event and the other a large second subevent of a multiple earthquake have thrusting mechanisms suggesting that shortening occurs as the continental crust of the northern caspian sea is thrust over the oceanic like crust of the southern caspian basin shortening is also suggested by the orientations of folds in the sedimentary cover south of the central caspian sea seismic belt we suggest that this shortening does indeed represent a nne motion of the caspian sea relative to eurasia but that the motion is slow and has not produced many earthquakes the deeper normal faulting events may be related to bending or down dip extension of the incipient subducted slab if the motion of the caspian sea relative to eurasia is indeed slow then the motion in the alborz between central iran and the south caspian basin will be almost the same as that between iran and eurasia as has previously been assumed the combined effect of the overthrusting of the south caspian basin by the talesh alborz mountains in the south and by the continental crust of the northern caspian sea in the north will lead to the eventual destruction of the south caspian basin and the possible formation of an intermediate depth dipping seismic zone within the continental interior similar to that presently observed in the hindu kush

the bam iran earthquake of december 26 2003 from an engineering and seismological point of view abstract this paper is devoted to studying the destructive bam earthquake from an engineering seismological point of view on december 26 2003 a large earthquake of magnitude 6 7 m s shook the bam district located in southeastern iran about 80 of buildings totally collapsed several dozen villages were destroyed and tens of them were severely damaged more than 45 000 people were killed and 30 000 were injured according to the macroseismic data focal depth of the event was estimated at 7 2 km the event was associated with a 9 km surface rupture of the bam fault the maximum residual strike slip displacement is 5 cm which is left lateral the highest recorded peak ground acceleration is at bam station 0 98 g vertical and 0 87 g horizontal located about 1 5 km from the surface rupture the macroseismic analyses show that the epicenter of the quake is 1 5 km east of bam all of the masonry buildings totally collapsed in the epicentral area many semi engineered structures were heavily damaged and some of them collapsed engineered structures constructed according to the seismic code of iran have shown very good structural behavior without significant damage finally the earthquake intensity at the epicenter is determined as ix on the msk scale which strongly decreases with distance from the surface ruptures

some aspects of magnetic viscosity in subaerial and submarine volcanic rocks summary the magnetic viscosity of 334 upper tertiary and pre bruhnes quaternary volcanic rocks from the massif central france and the steens mountain oregon and of 40 basaltic cores from dsdp leg 37 has been investigated thellier s viscosity index follows a log normal distribution with mean values equal to 6 and 3 5 per cent for subaerial and submarine rocks respectively for subaerial rocks the average intensity of the viscous remanent magnetization vrm acquired in the earth s field since the beginning of the bruhnes polarity epoch t 0 7 myr is estimated to be equal to one quarter of the average intensity of the primary remanence alternating field demagnetization of vrms acquired in low fields for acquisition times t ranging from 2 day to 32 month indicates the resistance to alternating fields is quite different from sample to sample and increases linearly with log t neel s diagnostic parameter of domain structure of the grains involved in magnetic viscosity shows that hard vrm is carried by single domain grains and soft vrm carried by multidomain particles single domain particles carrying hard vrm in subaerial volcanic rocks are almost equant magnetite intergrowths with size near the superparamagnetism threshold resulting from high temperature oxidation of titanomagnetite soft vrm is carried by low curie point homogeneous titanomagnetite unlike his single domain theory neel s multidomain theory of magnetic viscosity does not account quantitatively for the resistance of vrm to alternating fields

some global features of palaeointensity in geological time summary a global palaeointensity data base was constructed from all published data from volcanic rocks in geological time older than 0 03 ma the data base contains a total of 1123 flow mean data retrieved from 83 original papers various features of the earth s dipole moment were examined from the data which are based on thellier and shaw methods long term variation of the earth s dipole moment seems to have existed in the past 300 ma with a broad minimum at 120 180 ma as suggested by prevot et al 1990 however due to limited site distribution we cannot regard this mesozoic dipole low as being completely established precambrian palaeointensity data are still insufficient to conclude any long term variation in this time range although the geodynamo processes of moderate magnitude definitely existed in the early time of the earth s history the 2 test was applied to the distribution of the virtual dipole moment for the past 5 ma in which the transitional data were excluded the results indicate that the distribution of virtual dipole moment is better represented by a log normal distribution rather than a normal distribution and this tendency seems to be true for the past 20 ma the relation of mean palaeointensity versus palaeomagnetic colatitude was examined for the past 10 ma for the data excluding transitions the relation is concordant with a theoretical curve from a geocentric axial dipole this reconfirms that the dipole field was dominant in the past geomagnetic field which is the dipole hypothesis in palaeomagnetism on the other hand the virtual dipole moment is much smaller for transitional palaeomagnetic fields and a virtual geomagnetic pole lower than 45 seems to be a reasonable criterion to be categorized as a transition the mean dipole moment for the pole latitude of 30 n 50 n band is larger than that for 30 s 50 s indicating that there might have been a persistent asymmetry of palaeointensity between normal and reversed states or some kind of geometrical asymmetry between the northern and southern hemispheres

source mechanisms of three moderate california earthquakes of july 1986 abstract we studied the source processes of three moderate size earthquakes in california the m s 6 0 event of july 8 1986 near palm springs the m s 5 8 shock of july 13 1986 offshore of oceanside and the m s 6 2 event of july 21 1986 in the chalfant valley on the east side of the sierra nevada the centroidal source parameters are estimated by inversion of long period p and sh waves recorded at teleseismic distances by seismographs of worldwide networks a more detailed description of the source is then obtained by analyzing broadband seismograms the north palm springs earthquake had a simple rupture process most of the seismic moment was released in the first 3 sec in a single step the strike of the source fault plane follows the average trend of the banning fault and its dip agrees with the dip of the fault plane delineated by the aftershocks the faulting mechanism of the main shock is right lateral strike slip with a sizable reverse component that is consistent with uplift north of the banning fault the earthquake offshore of oceanside had a slightly more complex rupture process the far field source time function consists of two pulses that represent the release of most of the moment in the first 3 sec the source mechanism indicates reverse faulting with the compressional axis trending northeast almost perpendicular to the trend of mapped faults offshore the event does not appear to be associated with major mapped faults in the area but the strike of one of the nodal planes agrees with the trend of the major mapped faults offshore and its mechanism is consistent with the missing component of plate convergence not taken up by the onshore strike slip fault systems and the idea of a weak san andreas fault system the rupture process of the chalfant valley earthquake was yet more complicated the source time function indicates that in a 4 sec time window three asperities were broken the source mechanism indicates right lateral strike slip faulting with a small normal faulting component on a fault that dips approximately 50 southwest earthquake activity suggests that presently the deformation in the northern part of the owens valley which includes the chalfant valley is dominated by conjugate strike slip faults which strike obliquely to the main range bounding normal faults the waveforms indicate the presence of a low velocity zone at a depth of about 20 km in the crust in the chalfant valley a synthesis of information from waveform modeling first motion fault plane solutions and aftershock distributions indicates that the nucleation and or termination of rupture for the north palm springs and the chalfant valley events were controlled by preexisting fault geometry

faulting and folding in quaternary deposits of tehran s piedmont iran abstract tehran lies on the southern flank of the central alborz an active mountain belt characterized by many historical earthquakes some of which have affected tehran itself the border between the alborz mountain and the tehran s piedmont northern part of tehran city is marked by the north tehran fault ntf dividing the eocene rock formation from the alluvial units of different ages early pleistocene to the recent alluvium a detail mapping of the piedmont combined with structural study reveal that two active thrust faults situated south of the ntf are of importance for hazard assessment of the city the geomorphological evidences along the ntf are not in agreement with an active fault indicating that the fault activity may have been shifted southward furthermore differentiation of newly recognized alluvial units and their inferred ages together with the mapped fault pattern permit us to characterize the quaternary deformation the late pleistocene alluvial deposits consist of three alluvial fans among them the youngest one together with the modern alluvial fan defines the holocene deposit the present deformation in the piedmont is accommodated along vertically left lateral strike slip faults and low angle thrust faults trending in range from n070 to n110e

static stress drop associated with brittle slip events on exhumed faults 1 we estimate the static stress drop on small exhumed strike slip faults in the lake edison granodiorite of the central sierra nevada california the subvertical strike slip faults were exhumed from 4 to 15 km depth and were chosen because they are exposed in outcrop along their entire tip to tip lengths of 8 12 m slip nucleated on joints and accumulated by crystal plastic shearing forming quartz mylonites from early quartz vein filling in joints and successive brittle faulting forming epidote bearing cataclasites the occurrence of thin 300 m wide pseudotachylytes along some small faults throughout the study area suggests that some if not all of the brittle slip on the study area faults may have been seismic we suggest that the contribution of brittle cataclastic slip to the total slip along the studied cataclasite bearing small faults may be estimated by the length of epidote filled rhombohedral dilatational jogs rhombochasms distributed quasi periodically along the length of the faults the interpretation that slip recorded by rhombochasms occurred in single events is based on evidence that 1 epidote crystals are randomly oriented and undeformed within the rhombochasm 2 cataclasite in principal slip zones does not include clasts of previous cataclasite and 3 rhombochasm lengths vary systematically along the length of the faults with slip maximum occurring near the fault center tapering to the fault tips we thereby constrain both the rupture length and slip on the basis of these measurements we calculate stress drops ranging over 90 250 mpa i e one to two orders of magnitude larger than typical seismological estimates for earthquakes but similar in magnitude to seismological estimates of small m2 earthquakes from the san andreas fault observatory at depth safod the slip events described in the present study occurred along small deep seated faults and given the calculated stress drops and observations that brittle faults exploited joints sealed by quartz bearing mylonite we conclude that these were strong faults

holocene slip rate on the sabzevar thrust fault ne iran determined using optically stimulated luminescence osl abstract fault slip rates and the recurrence interval between earthquakes can be determined from reliable dating of deformed sediments we report optically stimulated luminescence osl ages of alluvial gravels fine grained sediments and colluvial deposits associated with the sabzevar thrust fault in northeastern iran six samples of the late quaternary deposits were dated by osl using the single aliquot regenerative dose sar protocol the osl ages indicate deposition of alluvial gravels in the study region between 30 and 9 13 ka followed by a period of fluvial incision which is ongoing at the present day the alluvial deposits have been uplifted by 9 5 m relative to the river level indicating a holocene slip rate of 1 mm yr and a rate of convergence across the fault of 0 4 0 6 mm yr assuming a maximum fault dip of 60 the average interval between large earthquakes on the sabzevar fault will be 3000 years if the fault dips 60 and less if the fault dip is less the last earthquake to destroy sabzevar was in 1052 a d

patterns of historical earthquake rupture in the iranian plateau the iranian plateau accommodates the 35 mrn yr convergence rate be tween the eurasian and arabian plates by strike slip and reverse faults with relatively low slip rates in a zone 1000 km across although these faults have only locally been the subject of paleoseismological studies a rich historical and archeological record spans several thousand years long enough to establish recurrence intervals of 1000 to 5000 yr on individual fault segments several clusters of earthquakes provide evidence of interaction among reverse and strike slip faults probably due to adjacent faults being loaded by individual earthquakes the dasht e bayaz sequence of 1936 to 1997 includes earthquakes on left lateral right lateral and reverse faults the neyshabur sequence of four earthquakes between 1209 and 1405 respected the seg ment boundary between the neyshabur and binalud reverse fault systems the two pairs of earthquakes may have ruptured different faults in each segment similar to the 1971 and 1994 san fernando california earthquakes the 1978 tabas reverse fault earthquake was preceded by the 1968 ferdows earthquake part of the dasht e bayaz sequence the north tabriz fault system ruptured from southeast to north west in three earthquakes from 1721 to 1786 a previous cluster may have struck this region in 855 to 958 the mosha fault north of tehran ruptured in three earthquakes in 958 1665 and 1830 five large earthquakes struck the tehran region from 743 to 1177 but only two that large have struck the area since 1177 other earthquakes occurred in pairs in the talesh mountains near the caspian sea 1863 1896 the iran turkey border 1840 1843 and the nayband gowk fault system both 1981 other historical events did not occur as parts of sequences the historic seismic moment release in iran accounts for only a small part of the plate convergence rate which may be due to aseismic slip or to the iranian historical record long as it is being too short to sample long term deformation across the plateau no historic earthquakes of m 8 have struck iran however several long straight strike slip faults doruneh west neh east neh and nayband have not sustained large historical earthquakes raising the possibility that these long faults could produce earthquakes of m 8 thereby removing at least part of the apparent slip deficit an increased understanding of iran s seismic hazard could be obtained by an extensive paleoseismology program and space geodetic arrays supplementing the abundant historical and archaeological record

strike slip fault terminations at seismogenic depths the structure and kinematics of the glacier lakes fault sierra nevada united states 1 structural complexity is common at the terminations of earthquake surface ruptures similar deformation may therefore be expected at the end zones of earthquake ruptures at depth the 8 2 km long glacier lakes fault glf in the sierra nevada is a left lateral strike slip fault with a maximum observed displacement of 125 m within the fault pseudotachylytes crosscut cataclasites showing that displacement on the glf was accommodated at least partly by seismic slip the western termination of the glf is defined by a gradual decrease in the displacement on the main fault accompanied by a 1 4 km wide zone of secondary faulting in the dilational quadrant of the glf the secondary faults splay counterclockwise from the main fault trace forming average angles of 39 with the main fault slip vectors defined by slickenlines plunge more steeply west for these splay faults than for the glf static stress transfer modeling shows that the orientations of the splays and the plunge of displacement on those splays are consistent with displacement on the main fault the glf termination structure shows that structural complexity is present at the terminations of faults at seismogenic depths and therefore ruptures that propagate beyond fault terminations or through step overs between two faults will likely interact with complex secondary fault structures models of dynamic rupture propagation must account for the effect of preexisting structures on the elastic properties of the host rock additionally aftershock distributions and focal mechanisms may be controlled by the geometry and kinematics of structures present at fault terminations

a re assessment of focal depth distributions in southern iran the tien shan and northern india do earthquakes really occur in the continental mantle summary we investigate the depth distribution of earthquakes within the continental lithosphere of southern iran the tien shan and northern india by using synthetic seismograms to analyse p and sh body waveforms in the zagros mountains of southern iran earthquakes are apparently restricted to the upper crust depths of 20 km whereas in the tien shan and northern india they occur throughout the thickness of the continental crust to depths of 40 45 km we find no convincing evidence for earthquakes in the continental mantle of these regions in spite of previous suggestions to the contrary and question whether seismicity in the continental mantle is important in any part of the world in some regions such as iran the aegean tibet and california seismicity is virtually restricted to the upper continental crust whereas in others including parts of east africa the tien shan and northern india the lower crust is also seismically active although usually less so than the upper crust such variations cannot reliably be demonstrated from published catalogue or bulletin locations even from ones in which depth resolution is generally improved in contrast to the oceanic mantle lithosphere in which earthquakes certainly occur the continental mantle lithosphere is we suggest virtually aseismic and may not be significantly stronger than the lower continental crust these variations in continental seismogenic thickness are broadly correlated with variations in effective elastic thickness suggesting that the strength of the continental lithosphere resides in the crust and require some modification to prevalent views of lithosphere rheology

complex fault patterns transtension and structural segmentation of the lofoten ridge norwegian margin using digital mapping to link onshore and offshore geology an integrated onshore offshore study involving regional to outcrop scale fault analysis is used to develop a self consistent structural model for transtension along the lofoten ridge the lofoten vesteralen archipelago lva is a segmented basement high showing distinct lateral variations in trend deformational style and structural complexity this study investigates whether segmentation can be linked to differences in the obliquity of preexisting structures relative to plate movement vectors regional analysis of fault lineament patterns using geographic information systems gis reveals that the lva can be subdivided into a series of distinct lineament domains these domains are closely coincident with changes in ridge trend and variations in structure within offshore models derived from seismic reflection studies digital field mapping and spatial analysis of faulting in the north lofoten reveal that multimodal faulting is dominated by transtensional dip slip and oblique slip movements which are comparable to analogue models where the ridge axis is 30 oblique to regional extension the overall change in fault orientation fault geometry and deformation style are consistent with models for transtension where the ridge bounding structure becomes increasingly oblique to regional extension previously identified transfer zones simply reflect segment domain boundaries and are not reactivating basement structures this model is a possible analogue for other orthogonal and oblique rift structures on the norwegian and other margins

geomagnetic field intensity in early jurassic investigation of the newark supergroup eastern north america abstract a collection of 220 samples from early jurassic newark supergroup volcanic units watchung talcott holyoke hampden and deerfield basalts and intrusive units manitook and palisades sills was studied with the aim of testing the previously suggested occurrence of a low average dipole moment of the earth s magnetic field some 200 ma ago after viscosity tests alternating field demagnetization of all samples and thermal variation studies of saturation magnetization of 74 selected samples we find that only 8 of the entire collection was a priori suitable for paleointensity experiments using the original thellier and thellier method we have obtained 17 reliable paleointensity values of average quality from the palisades sill and the holyoke basalt although these two units recorded substantially different field directions they provide similar estimates of the virtual dipole moment 9 4 1 2 and 11 3 2 2 10 22 a m 2 respectively these values are within the range of secular variation of the recent geomagnetic field

three dimensional reconstruction of geological surfaces an example of growth strata and turbidite systems from the ainsa basin pyrenees spain the external and internal geometry of four turbidite systems outcropping around the buil syncline ainsa basin spanish pyrenees has been reconstructed with reservoir scale resolution in three dimensions 3 d the irregular geometry of the syncline and the resolution required for the reconstruction cannot be resolved with cross sections therefore reconstruction has been carried out with a new methodology that applies a 3 d dip domain geometrical model and 3 d restoration techniques to achieve reservoir scale resolution in kilometric scale reconstructions this methodology is aimed at resolving 3 d geometries in folded areas and regions with variable thickness stratigraphy the 3 d reconstruction of the buil syncline reveals the synsedimentary growth of an intrabasinal anticline and the foreland lithospheric flexure associated with tectonic loading north of the ainsa basin

fault interactions and reactivation within a normal fault network at milne point alaska a normal fault network from milne point alaska is investigated focusing on characterizing geometry displacement strain and different fault interactions the network constrained from three dimensional seismic reflection data comprises two generations of faults cenozoic north northeast trending faults and jurassic west northwest trending faults which highly compartmentalize upper triassic to lower cretaceous reservoirs the west northwest trending faults are influenced by a similarly oriented underlying structural grain this influence is characterized by increases in throw on several faults strain localization reorientation of faults and an increase in linkage maturity reconstructing fault plane geometries and mapping spatial variations in throw identified key characteristic features in their interactions and reactivation of pre existing structures faults are divided into isolated abutting and splaying faults isolated faults exhibit a range of displacement profiles depending on the degree of restriction at fault tips fault splays accommodate step like decreases in throw along larger main faults with a throw maximum at the intersection with the main fault throw profiles of abutting faults are divided into two groups early stage abutting faults with throw minima at both the isolated and abutting tips and developed abutting faults with throw maxima near the abutting tip developed abutting faults accumulate throw after initial abutment locally reactivating and transferring throw onto the pre existing fault two abutting faults can link kinematically by reactivating a segment of the pre existing fault forming a trailing fault the motion sense of the trailing fault can be synthetic or antithetic to the reactivated pre existing fault producing increases or decreases in the throw of the pre existing fault respectively

reverse drag revisited why footwall deformation may be the key to inferring listric fault geometry abstract although reverse drag the down warping of hanging wall strata toward a normal fault is widely accepted as an indicator of listric fault geometry previous studies have shown that similar folding may form in response to slip on faults of finite vertical extent with listric or planar geometry in this study we therefore seek more general criteria for inferring subsurface fault geometry from observations of near surface deformation by directly comparing patterns of displacement stress and strain around planar and listric faults as predicted by elastic boundary element models in agreement with previous work we find that models with finite planar planar detached and listric detached faults all develop hanging wall reverse drag folds all of these model geometries also predict a region of tension and elevated maximum coulomb stress in the hanging wall suggesting that the distribution and orientation of near surface joints and secondary faults may also be of limited utility in predicting subsurface fault geometry the most notable difference between the three models however is the magnitude of footwall uplift footwall uplift decreases slightly with introduction of a detachment and more significantly with the addition of a listric fault shape a parametric investigation of faults with constant slip ranging from nearly planar to strongly listric over depths from 1 to 15 km reveals that footwall fold width is sensitive to fault geometry while hanging wall fold width largely reflects fault depth application of a graphical approach based on these results as well as more complete inverse modeling illustrates how patterns of combined hanging wall and footwall deformation may be used to constrain subsurface fault geometry

scale dependence strain compatibility and heterogeneity of three dimensional deformation during mountain building a discussion plate motion at convergent margins causes crustal shortening and orogenic thickening relative motion that is oblique to the plate margins is an inevitable consequence of plate kinematics on a sphere and results in non coaxial three dimensional deformation that cannot be approximated to simple shear models of mountain building that include a smoothly varying component of pure shear shortening allow strain compatibility to be maintained by deforming the upper free surface of the earth without disrupting the material continuum however such models do not reflect accurately the nature of deformation in many areas of high strain in the upper crust which are characterized by interconnected arrays of kinematically linked faults that can be active on several scales of magnitude simultaneously as brittle deformation increases the coherence of the material continuum is highly reduced in such situations strain compatibility is maintained by partitioning the deformation amongst structures of varying kinematic significance over a wide range of scales and not by smooth variations in strain magnitude acting on a single scale across a material continuum there is a marked tendency for such partitioned domains to be oriented parallel or sub parallel to the orogenic grain alignment of domains in this way represents a strong structural anisotropy which acts as a highly significant boundary condition that controls deformation at subordinate scales finite strain observed within an individual domain at a given scale need not therefore display the same magnitude or orientation as bulk finite strain at the plate scale and consequently data must be collected from as large an area as possible to relate outcrop scale structures to global scale tectonics

intensity of the earth s magnetic field since precambrian from thellier type palaeointensity data and inferences on the thermal history of the core summary we present a compilation of palaeointensity data obtained by the thellier method from magmatic rocks up to 3 5 gyr old no apparent very long term variation occurs from present to early precambrian the overall data are compatible with a gravitationally powered dynamo model in which the inner core is some 4 0 gyr old however palaeointensity data are still too incomplete to dismiss the possibility of a more complex field history with a geodynamo first thermally driven then gravitationally powered despite the limited number of data currently available large differences in the dipole field moment are clearly documented with a time scale of the order of 50 100myr the changes in intensity can be due to repetitive instabilities of the thermal boundary layer at the base of the mantle

long term fault slip rates distributed deformation rates and forecast of seismicity in the iranian plateau in this paper the long term crustal flow of the iranian plateau is computed using a kinematic finite element model neokinema software based on the iterated weighted least squares method the models are fitted to the newest data set of iran including updated fault traces geologic fault offset rates geodetic benchmark velocities principal stress directions and velocity boundary conditions we are successful to find the best kinematic model in which geological slip rates geodetic velocities and interpolated stress directions are fitted at levels of 0 35 1 0 and 1 0 datum standard deviation respectively the best fitted model for the first time provides long term fault slip rates velocity and anelastic strain rate field in the iranian plateau from all available kinematic data in order to verify the model the estimates of fault slip rates are compared to slip rates from merely analyzing geodetic benchmark velocities or paleoseismological studies or published geological rates which have not been used in the model our estimated rates are all in the range of geodetic rates and are even more consistent with geological rates than previous gps based estimates using the selected model long term average seismicity maps and long term moment rates are produced on the basis of the shift hypothesis and previous global calibrations our kinematic model also provides a new constraint on ratio of seismic deformation to total deformation for different seismic zones of iran the resulting slip rates and the proposed seismic fraction of deformation provide the necessary input data for future time dependent hazard studies in iran moreover spatial distribution and total number of strong m 6 and major m 7 earthquakes which dominate the seismic hazard are all compatible with the regional seismic catalog

paleointensity of the earth s magnetic field in the jurassic new results from a thellier study of the lesotho basalt southern africa thellier paleointensity experiments carried out on the jurassic 180 m y old karoo basalt lesotho southern africa provided paleointensity estimates for 40 samples from 10 distinct lava flows with reversed magnetization mean paleointensity was found to be equal to 24 2 11 3 t standard deviation with a minimum of 12 t and a maximum of 41 3 t this corresponds to a mean virtual dipole moment vdm of 4 6 2 0 1022 am2 the between flow dispersion is ascribed to paleosecular variation which thus would approach up to 40 of the mean paleointensity as is observed from the published paleointensity data set covering last 20 m y this result yields further evidence for the period of low geomagnetic field in jurassic to early cretaceous time mesozoic dipole low a symmetrical intensity versus time pattern is suggested for this time interval with a minimum vdm of 3 1022 am2 in late jurassic and substantially higher 4 5 1022 am2 vdms in early to middle jurassic and early cretaceous respectively

response of alluvial rivers to slow active tectonic movement alluvial rivers respond to valley slope deformation caused by active tectonics in various ways depending on the rate and amount of surficial deformation and on the type of river on the basis of experimental results and field examples hypothetical models of river response to anticlinal uplift and synclinal subsidence were developed for different types of alluvial rivers an experimental braided channel responded to anticlinal uplift across the channel with degradation and terrace formation in the central part of the uplift with subsidence aggradation in the central reach was the main response transverse bars developed downstream of the subsidence axis an experimental meandering channel responded to slope steepening with a sinuosity increase bank erosion and point bar growth occurred downstream of the anticlinal axis and upstream of the synclinal axis upstream of the uplift axis and downstream of the subsidence axis where the slope was flattened water flooded over bars local convexity in longitudinal profiles of the middle rio grande new mexico is considered to be formed by a domal uplift local aggradation and degradation could be explained by the effect of uplift the san joaquin river california which is now highly controlled does not show clear adjustment to the rapid subsidence due to ground water withdrawal it shows however a channel pattern adjustment to active tectonic subsidence that has been occurring for a long time the san antonio and guadalupe rivers in texas both increase their sinuosity significantly where monoclinal movements steepen valley slopes

accuracy evaluation of both wallace bott and bem based paleostress inversion methods abstract four decades after their introduction the validity of fault slip inversion methods based on wallace 1951 and bott 1959 hypothesis which states that the slip on each fault surface has the same direction and sense as the maximum resolved shear stress is still a subject of debate according to some authors this hypothesis is questionable since fault mechanical interactions induce slip reorientations as confirmed by geomechanical models this leads us to ask as to what extent the wallace bott simplifications are reliable as a basis hypothesis for stress inversion from fault slip data in this paper we compare two inversion methods the first is based on the wallace bott hypothesis and the second relies on geomechanics and mechanical effects on fault heterogeneous slip distribution in that context a multi parametric stress inversion study covering i the friction coefficients ii the full range of andersonian state of stress and iii slip data sampling along the faults is performed for each tested parameter the results of the mechanical stress inversion and the wallace bott wb based stress inversion for slip are compared in order to understand their respective effects the predicted discrepancy between the solutions of both stress inversion methods based on wb and mechanics will then be used to explain the stress inversions results for the chimney rock case study it is shown that a high solution discrepancy is not always correlated with the misfit angle and can be found under specific configurations r geometry invalidating the wb solutions we conclude that in most cases the mechanical stress inversion and the wb based stress inversion are both valid and complementary depending on the fault friction some exceptions i e low fault friction simple fault geometry and pure regimes that may lead to wrong wb based stress inversion solutions are highlighted

defining folds on three dimensional surfaces we present a new method for the structural analysis of folded surfaces the method requires a generalized definition of a fold as a patch consisting of contiguous points with gaussian curvature and mean curvature of consistent sign four classes of folds result from this definition antiforms and synforms each of synclastic and anticlastic forms this new analysis is illustrated with reference to several examples

transitional geomagnetic field behavior volcanic records from french polynesia here we report the behavior of the earth s magnetic field for transitions recorded on volcanic islands from polynesia in the south central pacific ocean detailed transitional fields are observed on huahine island the data suggest the record of an excursion n n following the kaena event the jaramillo termination and the brunhes onset are recorded in a volcanic sequence from tahiti island the transitional field is mainly characterized by low intensities while the beginning of the transition appears to be consistent with the zonal model of reversal large deviations from a north south planar distribution of the intermediate directions show that non dipolar fields without preferential axisymmetry control the middle of the transition

application of an iterative least squares waveform inversion of strong motion and teleseismic records to the 1978 tabas iran earthquake an iterative least squares technique is used to simultaneously invert the strong motion records and teleseismic p waveforms for the 1978 tabas iran earthquake to deduce the rupture history the method solves for both slip amplitudes and rupture times on a finite fault several inversions of the data are done to determine the best fitting hypocenter average rupture velocity and source time function within the range of our parameter search the effects of using different data sets and different parametrizations of the problem linear versus nonlinear are also considered teleseismic body waves are shown to be essential to obtain a reliable solution due to the sparse coverage of the fault plane by strong motion stations a simple triangular source time function is compared with a modified kostrov source time function for a circular rupture and a constant propagating stress drop although the waveforms used in the inversions can not resolve between these two time functions the kostrov source time function gives a moment estimate and maximum fault displacement more consistent with long period surface waves and field observations the results of the iterative inversion for slip amplitudes and rupture times are compared with the results of a linear inversion for slip amplitudes in which the rupture velocity is fixed flexibility in the sequence of faulting for the linear inversion is obtained by allowing multiple rupture intervals a consensus of all the inversion runs indicates a complex multiple source for the tabas earthquake with four main source regions over a fault length of 90 km and an average rupture velocity of 2 5 km sec

contribution of archaeological data to studies of earthquake history in the iranian plateau we use archaeological evidence to identify ancient earthquakes in the vicinity of large 20th century events in the iranian plateau two large earthquakes on the zagros main recent fault were preceded by historical earthquakes in ad 1008 and ad 1107 and by earthquakes in the intervals ad 224 459 and 1650 1600 bc giving return times of 1800 2100 500 800 and 850 950 years the ad 1962 ms 7 2 bo in zahra earthquake on the ipak fault in north central iran was preceded by an earthquake in 2000 1500 bc recorded at the sagzabad mound a return time of 3500 4000 years if there are no missing events the ad 1990 ms 7 3 rudbar tarom earthquake in the western alborz mountains was preceded by an earthquake in 1000 800 bc recorded at the marlik mound a return time of 2800 3000 years the ad 1948 ms 7 2 kopeh dagh earthquake that destroyed ashkabad capital of turkmenistan was preceded by an earthquake in 10 bc ad 10 recorded at mithradatkert nesa mound and by an earthquake in 2000 bc recorded at ak tapeh mound assuming no missing earthquakes this region has an earthquake return time of about 2000 years in khorasan province which was struck by a sequence of large earthquakes from ad 1936 to 1997 a mosque at qa en was destroyed in the mid 11th century ad probably the historical earthquake of ad1066 in the absence of palaeoseismic investigations archaeology offers the promise of recording earthquakes through more than one seismic cycle in different regions of iran q 2001 elsevier science ltd all rights reserved

variation in slip on intersecting normal faults implications for paleostress inversion numerical models based on linear elasticity theory predict asymmetric slip distribution with a steep slip gradient near the line of intersection of intersecting normal faults they also predict a discrepancy between the direction of slip on the fault plane and the direction of resolved shear stress both variations in slip magnitude and direction are due to mechanical interaction between the faults with intersecting patterns these interactions cause local perturbations of the shear stress field acting on the plane of the adjacent fault field observations from the chimney rock area of central utah show that slickensides on normal faults cutting the navajo sandstone change rake away from the expected downdip direction as the intersection line with adjacent faults is approached the sense and magnitude of this change in orientation are similar to those computed by using the numerical models the good correspondence between field observations and theoretical results from this paper not only provides insight into the mechanics of intersecting faults but suggests that care is required when using standard inverse methods to compute paleostresses from slickenside data the slickenside orientation near intersection lines will generally not be in the direction of the remote maximum shear stress as resolved on the fault plane a parameter study of this change in orientation provides helpful results for evaluating field data prior to a paleostress analysis

slip distributions on intersecting normal faults abstract slip distributions on normal faults often are asymmetric and display multiple local maxima numerically computed slip distributions from elastic models indicate that such irregular slip distributions can be caused by mechanical interaction between intersecting faults that produce local perturbations of the stress field resolved on the faults a three dimensional boundary element model based on the displacement discontinuity method has been used to analyze the mechanical interaction of faults that form y or t shaped intersections slip distributions are asymmetric with a steeper slip gradient toward the line of intersection multiple slip maxima occur depending on the angle between the faults but generally they are not located along the intersections nor at the fault centers examples of intersecting normal faults taken from oil reservoir seismic surveys and sandbox experiments have been used to confirm the application of the theoretical results despite considerable simplifications in terms of geometry and boundary conditions the computed slip distributions capture the characteristics of the observed slip distributions

fracture characterization and modeling from virtual outcrops advances in virtual outcrop technologies and their introduction to fracture characterization allow extraction of fracture data from very large and inaccessible areas the recent development of automated or semiautomated methods for fracture extraction aims to reduce or avoid tedious time consuming and biased manual interpretation of fractures from virtual outcrops we present a benchmarking exercise between a previously proposed automated fracture picking method manual picking and fieldwork methods comparison between the three methods highlighted their relative advantages and limitations the automated fracture picking method provided excellent results in terms of fracture orientation size spatial distribution and density fieldwork is complementary to fracture extraction from virtual outcrops and it should focus on quality control of remote sensing data poorly exposed areas small scale observations diagenesis timing of fracture development building conceptual models and linking fracture stratigraphy to rock properties we propose a best practice for the use and integration of manual and or automated fracture extraction from virtual outcrop and fieldwork data for fracture characterization and modeling from outcrop analogs we consider integration of different methods as the best way to improve the modeling exercise while reducing operational costs and risks

assessment of the precision of smart phones and tablets for measurement of planar orientations a case study abstract although paper and pencil approaches to geological mapping continue digital mapping tools are being increasing implemented in field geology of particular note is the use of an electronic compass inclinometer built into tablets and smartphones for obtaining orientation data where an important question is the reliability of these digital devices relative to conventional analogue compass inclinometers this paper deals with this question through detailed tests of two android devices an honor 3c smartphone and a lenovo b8080 f tablet in order to evaluate potential electronic noise effects the devices were tested in two modes standard and airplane over 14 000 readings from the sensors were collected to evaluate the stability of the sensor s readings and showed that the magnetic sensor in the tablet was unacceptably unstable seven geological compass applications were installed on the honor 3c smartphone and tested against the analogue freiberg geological compass in a field experiment during the experiment 25 fractures varying in azimuth and dip were measured using both devices a high level of disagreement was observed with discrepancies as high as 80 with azimuthal errors dominant analysis of the time series in the data suggest the source of the problem was instability in the magnetic sensor for the smartphone despite the fact the device passed the initial stability test although only two devices were studied these data indicate care must be taken to evaluate compass accuracy on these devices

low intensity of the geomagnetic field in early jurassic time from a large collection of jurassic continental tholeiites cropping out in europe and africa we selected 90 samples for paleointensity determinations the samples were carefully selected to avoid any secondary magnetizations especially viscous magnetization use of the thellier method reveals that magnetic property changes due to heating begin often at quite low temperatures but fortunately without modifying noticeably their natural remanent magnetization thermoremanent magnetization ratio twenty eight well clustered paleointensity estimates were obtained from two european dikes that were emplaced during early jurassic time the kerforne dike at brenterc h in brittany northwestern france and the messejana dike on the iberian peninsula spain and portugal virtual dipole moments calculated from both magmatic units are similar and only about one third of present day values these new data lend support to the recently postulated low dipole moment of the mesozoic geomagnetic field

holocene settlement shifts and palaeoenvironments on the central iranian plateau investigating linked systems for thousands of years humans have inhabited locations that are highly vulnerable to the impacts of climate change earthquakes and floods in order to investigate the extent to which holocene environmental changes may have impacted on cultural evolution we present new geologic geomorphic and chronologic data from the qazvin plain in northwest iran that provides a backdrop of natural environmental changes for the simultaneous cultural dynamics observed on the central iranian plateau well resolved archaeological data from the neighbouring settlements of zagheh 7170 6300 yr bp ghabristan 6215 4950 yr bp and sagzabad 4050 2350 yr bp indicate that holocene occupation of the hajiarab alluvial fan was interrupted by a 900 year settlement hiatus multi proxy climate data from nearby lakes in northwest iran suggest a transition from arid early holocene conditions to more humid middle holocene conditions from ca 7550 6750 yr bp coinciding with the settlement of zagheh and a peak in aridity at ca 4550 yr bp during the settlement hiatus palaeoseismic investigations indicate that large active fault systems in close proximity to the tell sites incurred a series of large mw 7 1 earthquakes with return periods of 500 1000 years during human occupation of the tells mapping and optically stimulated luminescence osl chronology of the alluvial sequences reveals changes in depositional style from coarse grained unconfined sheet flow deposits to proximal channel flow and distally prograding alluvial deposits sometime after ca 8830 yr bp possibly reflecting an increase in moisture following the early holocene arid phase the coincidence of major climate changes earthquake activity and varying sedimentation styles with changing patterns of human occupation on the hajiarab fan indicate links between environmental and anthropogenic systems however temporal coincidence does not necessitate a fundamental causative dependency

structural analysis of the tabaco anticline cerrejon open cast coal mine colombia south america abstract the tabaco anticline is a 15 km long south plunging east vergent anticline in northern colombia close to the transpressional collisional margin between the caribbean and south american plates in the cerrejon open cast coal mine systematic mapping of coal seams in the middle to upper paleocene cerrejon formation has yielded an exceptional dataset consisting of 10 horizontal slices sea level to 90 m elevation regularly spaced at 10 m intervals through the anticline coal seams and fault traces in these slices are used to construct a 3d model of the anticline this 3d model shows tighter folds within lower coal seams nw vergent thrusts and related folds on the gentler western limb and strike slip faults on the steeper eastern limb fault slip tendency analysis is used to infer that these two faulting styles resulted from two different stress fields an earlier one consistent with thrusting and uplift of the perija range and a later one consistent with strike slip faulting oca rancheria and saman faults our preferred interpretation is that the anticline developed its eastern vergence during the early stages late paleocene early eocene of tilting of the santa marta massif later nw vergent thrusting on the western limb early to middle eocene was related to western propagation of the perija thrust system these results contribute to the understanding of the structural evolution of the area they are also a good example of the complex interplay between detachment folding thrusting and strike slip faulting during the growth of a km size fold in a transpressive setting

geomagnetic paleointensities from excursion sequences in lavas on oahu hawaii paleomagnetic data demonstrating three late tertiary excursions in the direction of the geomagnetic field recorded in sequences of basaltic lavas on the island of oahu hawaii were published by r r doell and g b dalrymple in 1973 we have determined geomagnetic paleointensities by the thelliers method for 14 lavas from the three sites during these experiments considerable difficulty was encountered because of the presence of titanomaghemite in many lavas and the contamination of natural remanent magnetization by lightning in many others moreover we often observed the production of spurious high temperature chemical remanent magnetization during the thellier experiments an analysis of this particularly troublesome problem is presented two of the sites showed low paleointensities associated with angular departures of the paleomagnetic field direction from that of a geocentric axial dipole which suggests that these excursions represent aborted reversals or fragments of reversals at the third site however the paleointensity did not become low as the field diverged this excursion may reflect the variation of a large nondipole source near hawaii

an integrated rock magnetic approach to the selection or rejection of ancient basalt samples for palaeointensity experiments abstract the rock magnetic properties of basalts are often useful indicators of suitability for use in palaeointensity experiments the normal approach to sample selection is based on the use of a limited amount of rock magnetic data possibly from only a single rock magnetic technique this approach may result in the exclusion of otherwise suitable samples or the inclusion of unsuitable samples this study stresses the importance of analysing results from a number of rock magnetic techniques before selecting or rejecting samples for use in palaeointensity experiments a new integrated rock magnetic method of sample selection or rejection is proposed which uses the combined results from thermal thermomagnetic and high temperature susceptibility and non thermal low temperature susceptibility hysteresis and alternating field demagnetisation rock magnetic techniques to define sets of rock magnetic behaviour for precambrian basalts with a mixed grain size of pure magnetite the behaviour of all samples in each set during both thellier and shaw palaeointensity experiments is categorised allowing a set of selection or rejection criteria to be defined this new approach to sample selection or rejection for palaeointensity experiments has value for basalts of all ages provided the sample collection is large enough and all available rock magnetic techniques are used

determining the size and shape of blocks from linear sampling for geotechnical rock mass classification and assessment classifying and assessing geotechnical aspects of rock masses involves combining parameters in various ways guided by empirical considerations to derive quantitative geotechnical parameters geological structures and the deformation history of rocks underpin the nature of rock masses the kinematics of a deforming rock mass may occur as sliding along throughgoing discontinuities or as distributed sliding on block faces distributed sliding will tend to disrupt the continuity of planar structures such that data on the size and shape of blocks is needed rather than relying on discontinuity orientation data alone orientation and spacing data can be combined to provide a geometric analysis of block systems from linear samples such as drill core dihedral angles and spacing of sequential pairs of discontinuities provides a sample of the size and shape of blocks that can be interpreted stereologically further detail can be derived by combining neighbouring intersections that enclose or partially enclose individual blocks the shape and size of a block can be represented on a stereograph with the enclosing faces shown as poles and their perpendicular distance from an arbitrary point inside the block shown as a number identifying the size and shape of specific blocks rather than relying on statistical methods is beneficial to critical aspects of design such as analysing keyblocks that would be exposed during excavations the detailed characterization of block size and shape is also a step toward interpreting the kinematics of rock mass deformation and the analysis of rock masses as ultra close packed dilatant granular systems

three dimensional structural modeling of an active fault zone based on complex outcrop and subsurface data the middle durance fault zone inherited from polyphase meso cenozoic tectonics southeastern france the objective of this study was to realize a three dimensional 3 d geological model of the deep basin structure of the middle durance region of folds and faults by integration of geological and geophysical data and to evaluate its fault geometry and tectonic history all of the available geophysical and geological data were compiled in three dimensions using the gocad geomodeler the geological and geophysical data were used to build a 3 d geological model of the middle durance region the data on the 3 d geometry of fault surfaces and stratigraphic horizons and the thickness maps of the main stratigraphic units are supported by the 3 d geological model we show that the middle durance fault cannot be interpreted as a single fault plane that affected the entire meso cenozoic sedimentary layers and the paleozoic basement but as a listric segmented faulting system in sedimentary layers rooted in triassic evaporites and a normal block faulting system in the basement this decoupling level in the triassic layers reveals thin skin deformation formed by strong mechanical decoupling between the mesozoic sedimentary cover and the paleozoic basement this study also confirms that the provence geological structure has resulted mainly from pyrenean deformation which was partly reactivated by alpine deformation we demonstrate that the middle durance fault zone is a transfer fault that accommodates deformation of the sedimentary filling of the south east basin through modified fold geometry over a zone of 7 km to 8 km around the main segment of the fault zone

paleointensity results from the jurassic new constraints from submarine basaltic glasses of odp site 801c 1 tholeiite of the oldest oceanic crust was drilled during odp legs 129 and 185 at hole 801c in the western pacific fresh appearing submarine basaltic glass sbg was recovered from the tholeiites 167 ma which has been shown to be nearly ideal for determining absolute paleointensity paleointensities of the younger off axis alkalic basalts 160 ma overlying the tholeiites had been studied earlier here we report results from the older tholeiitic on axis sequence we subjected a total of 73 specimens from 17 cooling units to absolute paleointensity experiments of these 30 specimens and six cooling unit averages met our strictest reliability criteria yielding an average of 11 9 3 9 t the bulk of evidence suggests a paleolatitude of the site of 14 s with an uncertainty of 10 this translates the intensity to a value for the virtual axial dipole moment of 28 zam2 slightly lower than values determined from the plagioclase crystals in the three cooling units of the younger alkalic basalts overlying the tholeiites tarduno cottrell 2005 our value is low when compared to the long term median value of the field of 42 zam2 our results and those of the published literature therefore support the contention of a low magnetic field strength in the jurassic average of 28 14 zam2 n 138 individual estimates as initially suggested by prevot et al 1990 our interpretation of the body of available data argue for low field strengths for the entire jurassic extending into the early cretaceous

archaeological sediments from settlement mounds of the sagzabad cluster central iran human induced deposition on an arid alluvial plain abstract we outline results of a pilot geoarchaeological study of three settlement mounds tepe in the qazvin plain near tehran ca 7350 to 2450 cal bp conducted as part of a wider investigation of the interaction between prehistoric human communities and their environments in western iran the aim of the geoarchaeological study was to assess the potential of settlement sediments as records of past human practices and to guide future systematic sampling for geoarchaeological analyses here we integrate bulk sediment sediment texture organic matter with thin section based thin section micromorphology sem analyses in order to characterize human inputs in settlement deposits and infer human practices that drove sediment deposition plinth degradation and various kinds of burning byproducts and domestic and manufacturing waste furnished distinctive inputs to settlement sediments different types of fuel wood perhaps tamarix straw dung may reflect diverse domestic and manufacturing contexts of fire use

the 2002 june 22 changureh avaj earthquake in qazvin province northwest iran epicentral relocation source parameters surface deformation and geomorphology summary the m w 6 4 changureh avaj earthquake occurred on 2002 june 22 in qazvin province northwest iran we use observations from seismology field investigation and analysis of satellite imagery and digital topography to suggest that slip on a previously unrecognized thrust fault herein named the abdarreh fault was responsible for the earthquake inversion of longperiod p and sh body wave seismograms shows rupture on a thrust fault dipping 49 to the southwest and with a centroid depth of 10 km multiple event relocation of the main shock and aftershock epicentres and discontinuous surface ruptures observed after the earthquake are compatible with a northwest propagating rupture on a southwest dipping thrust but maximum recorded displacements are much less than expected from seismology suggesting that much of the slip failed to reach the surface and was accommodated as folding at the surface instead long term folding is difficult to see in the topography of the epicentral region as the abdarreh fold is growing through a relict neogene topography anticlinal uplift can however be inferred from drainage disruption and stream incision the 2002 june 22 changureh earthquake shows the importance of being able to interpret diagnostic features of active faulting in the landscape