long term behaviour of australian stable continental region scr faults abstract australia boasts arguably the richest late neogene to quaternary faulting record in stable continental region scr crust anywhere in the world variation in fault scarp length vertical displacement proximity to other faults and relationship to topography permits division of the continent according to fault character six onshore neotectonic domains are recognised with an additional offshore domain proposed by analogy with the eastern united states each domain relates to a distinct underlying crustal type and architecture broadly considered to represent cratonic non cratonic and extended environments in general greater topographic expression associated with faults occurring in extended crust relative to non extended crust suggests a higher rate of seismic activity in the former setting consistent with observations worldwide using the same reasoning non cratonic crust might be expected to have a higher rate of seismic activity than cratonic crust this distinction together with the variation in fault character between domains should be recognised in attempts to identify analogous systems worldwide a common characteristic of morphogenic earthquake occurrence in australia appears to be temporal clustering periods of earthquake activity comprising a finite number of large events are separated by much longer periods of seismic quiescence at the scale of a single fault and of proximal faults in several instances there is evidence for deformation at scales of several hundred kilometres switching on and off over the last several million years what is not clear from the limited palaeoseismological data available is whether successive active periods are comparable in terms of slip number of events magnitude of events etc regardless this apparent bimodal recurrence behaviour poses challenges for probabilistic seismic hazard assessment psha these rely on the simplifying assumption that large earthquake recurrence for long return periods is not random i e poissonian presently our ability to incorporate such time dependent models is limited by available data

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

late quaternary slip rates across the central tien shan kyrgyzstan central asia 1 slip rates across active faults and folds show that late quaternary faulting is distributed across the central tien shan not concentrated at its margins nearly every intermontane basin contains neogene and quaternary syntectonic strata deformed by holocene north south shortening on thrust or reverse faults in a region that spans two thirds of the north south width of the central tien shan slip rates on eight faults in five basins range from 0 1 to 3 mm yr fault slip rates are derived from faulted and folded river terraces and from trenches radiocarbon optically stimulated luminescence and thermoluminescence ages limit ages of terraces and aid in their regional correlation monte carlo simulations that sample from normally distributed and discrete probability distributions for each variable in the slip rate calculations generate most likely slip rate values and 95 confidence limits faults in basins appear to merge at relatively shallow depths with crustal scale ramps that underlie mountain ranges composed of pre cenozoic rocks the sum and overall pattern of late quaternary rates of shortening are similar to current rates of north south shortening measured using global positioning system geodesy this similarity suggests that deformation is concentrated along major fault zones near range basin margins such faults separated by rigid blocks accommodate most of the shortening in the upper crust index terms 8107 tectonophysics continental neotectonics 9320 information related to geographic region asia 8010 structural geology fractures and faults

block rotation by strike slip faulting structural and paleomagnetic evidence geometric analysis shows that motion of sets of strike slip faults should cause block rotation otherwise the distorted fault domain would not fit with its surrounding the sense of the block rotation depends on the sense of fault slip and the spacing and orientation of the faults all of which can be obtained from structural data the predictions of the geometric model can then be independently tested by paleomagnetic measurements the model was tested in northern israel structural data reveal several domains of contemporaneous right and left lateral strike slip faults paleomagnetic measurements show that in a domain of nnw trending left lateral faults blocks rotated 23 3 8 2 clockwise and in a domain of right lateral faults blocks rotated 22 4 9 0 anticlockwise these results are in agreement with the prediction of the geometric analysis of the structure the combined results of the heterogenous deformation of the area resembles a pure shear which allows n s extension by about 1 3 in other domains rotations of 34 6 9 1 and 53 1 11 0 were found in their original orientation the left and right lateral faults intersected at angles of 60 70 enclosing the principal axis of shortening in accordance with theories of brittle failure as a result of block rotations this angle is now larger and may reach 110 the results demonstrate large block rotations in different senses in domains of strike slip faults the independent structural and paleomagnetic data can be interpreted within the framework of a simple geometric model northern israel is considered to be a good model for this efficient mechanism of intraplate deformation which is expected to occur in similar tectonic settings elsewhere

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

structural framework of a major intracontinental orogenic termination zone the easternmost tien shan china the barkol tagh and karlik tagh ranges of the easternmost tien shan are a natural laboratory for studying the fault architecture of an active termination zone of a major intracontinental mountain range barkol and karlik tagh and lesser ranges to the north are bounded by active thrust faults that locally deform quaternary sediments major thrusts in karlik tagh connect along strike to the east with the left lateral gobi tien shan fault system in sw mongolia from a mongolian perspective karlik tagh represents a large restraining bend for this regional strike slip fault system and the entire system of thrusts and strike slip faults in the karlik tagh region defines a horsetail splay fault geometry regionally there appears to be a kinematic transition from thrust dominated deformation in the central tien shan to left lateral transpressional deformation in the easternmost tien shan this transition correlates with a general eastward decrease in mountain belt width and average elevation and a change in the angular relationship between the nne directed maximum horizontal stress in the region and the pre existing basement structural grain which is northwesterly in the central tien shan orthogonal to sh max but more east west in the eastern tien shan acute angular relationship with sh max ar ar ages indicate that major range bounding thrusts in barkol and karlik tagh are latest permian triassic ductile thrust zones that underwent brittle reactivation in the late cenozoic it is estimated that the modern mountain ranges of the extreme easternmost tien shan could have been constructed by only 10 15 km of late cenozoic horizontal shortening

the continuity of active fault systems in greece summary evidence from geomorphology the distribution of large earthquakes and geodetic measurements suggests that the active faulting in mainland greece and the north aegean sea is concentrated into a small number of discrete linear zones that bound relatively rigid blocks on land the zones are most clearly identified where the faulting is associated with large escarpments particularly in hard footwall rocks the zones can become indistinct and diffuse near their ends sometimes because they enter high unstable topography where landsliding obscures the fault morphology but mostly because the extension rates decrease along strike as a consequence of the relative rotation of the blocks they bound the main graben systems of chalkidiki southern thessaly and the north gulf of evia all seem to connect with the strike slip faulting in the offshore aegean and to die out in the west a configuration related to clockwise rotations in east central greece by contrast the gulf of corinth which is the fastest opening graben system in greece opens more rapidly in the west than the east both these features of the gulf of corinth are consequences of the motion of the south aegean and peloponnese as a single block late pliocene and quaternary geology and geomorphology indicate that the boundaries of the rigid blocks in central greece have changed over that time with faulting migrating into the hanging walls sometimes changing in orientation these changes are probably related to the way faulting in the seismogenic layer adapts to block rotation so as to maintain the general features of a velocity field that is controlled by larger scale effects such as buoyancy forces and the seaward migration of the subducting slab beneath crete the image of greece as a mosaic of rigid blocks whose boundaries change with time is a useful framework for seismic hazard evaluation but we emphasize that some moderate sized earthquakes do occur away from the main fault zones within the relatively rigid blocks and especially near their diffuse ends

the dzhungarian fault late quaternary tectonics and slip rate of a major right lateral strike slip fault in the northern tien shan region the dzhungarian strike slip fault of central asia is one of a series of long nw se right lateral strike slip faults that are characteristic of the northern tien shan region and extends over 300 km from the high mountains into the kazakh platform our field based and satellite observations reveal that the dzhungarian fault can be characterized by three 100 km long sections based on variation in strike direction through morphological analysis of offset streams and alluvial fans and through optically stimulated luminescence dating we find that the dzhungarian fault has a minimum average late quaternary slip rate of 2 2 0 8 mm yr and accommodates n s shortening related to the india eurasia collision this shortening may also be partly accommodated by counterclockwise rotation about a vertical axis evidence for a possible paleo earthquake rupture indicates that earthquakes up to at least mw 7 can be associated with just the partitioned component of reverse slip on segments of the central section of the fault up to 30 km long an event rupturing longer sections of the dzhungarian fault has the potential to generate greater magnitude earthquakes mw 8 however long time periods e g thousands of years are expected in order to accumulate enough strain to generate such earthquakes

geomorphology and geochronology of sackung features uphill facing scarps in the central spanish pyrenees abstract the paper analyses uphill facing scarps and associated troughs developed in the oversteepened slopes of two neighbouring glacial valleys in the central spanish pyrenees previous studies of sackung landforms in the pyrenees have argued for deglacial unloading as the genetic mechanism but this causal and temporal relationship has not been proved due to the lack of chronological data the antislope scarps in the two studied locations vallibierna and estos are developed in palaeozoic metasedimentary rocks parallel to the contour lines and the structural grain occur in the intermediate sector of the hillslope and are up to 0 5 km long and several meters high a trench was excavated in a sackung trough fill in each of the valleys in order to gain information about their chronology and genesis charcoal from the lowermost unit in vallibierna provided an age of 5 9 cal ka for the sackung and extrapolation of the three dates obtained in estos indicates that the trough formed ca 7 6 7 8 cal ka deglaciation of the studied sectors of the valleys occurred between 16 and 13 ka the time lag of 5 ka suggests that glacial erosion and the subsequent debutressing of the oversteepened valley walls created slopes predisposed to sackung development but did not initiate the movement seismic shaking is proposed as a probable triggering factor this hypothesis although supported by the sudden deformation event recorded by a failure plane exposed in vallibierna trench and by the seismic and neotectonic activity of the area cannot be proved due to the lack of chronological information about paleoearthquakes

plateau pop up in the great 1897 assam earthquake the great assam earthquake of 12 june 1897 reduced to rubble all masonry buildings within a region of northeastern india roughly the size of england and was felt over an area exceeding that of the great 1755 lisbon earthquake1 hitherto it was believed that rupture occurred on a north dipping himalayan thrust fault propagating south of bhutan2 3 4 5 but here we show that the northern edge of the shillong plateau rose violently by at least 11 m during the assam earthquake and that this was due to the rupture of a buried reverse fault approximately 110 km in length and dipping steeply away from the himalaya the stress drop implied by the rupture geometry and the prodigious fault slip of 18 7 m explains epicentral accelerations observed to exceed 1g vertically and surface velocities exceeding 3 m s 1 ref 1 this quantitative observation of active deformation of a pop up structure confirms that faults bounding such structures can penetrate the whole crust plateau uplift in the past 2 5 million years has caused the indian plate to contract locally by 4 2 mm yr 1 reducing seismic risk in bhutan but increasing the risk in northern bangladesh

earthquake scaling fault segmentation and structural maturity abstract slip and length measurements on earthquakes suggest large stress drop variability we analyze an extended set of slip length measurements for large earthquakes m 6 to seek for the possible origin s of this apparent variability we propose that such variability arises from earthquakes breaking a variable number of major fault segments that number depends on the strength of the inter segment zones which itself depends on the structural maturity of the faults we propose new d max l parameterizations based on that idea of multiple segment ruptures in such parameterizations each broken segment roughly scales as a crack while the total multi segment rupture does not stress drop on individual segments is roughly constant only varying between 3 5 to 9 mpa the slight variation that is still observed depends on fault structural maturity more mature faults have lower stress drops than immature ones the new d max l functions that we propose reduce uncertainties with respect to available relationships they thus provide a more solid basis to estimate seismic hazard by integrating fault properties revealed by geological studies

a block model of distributed deformation by faulting it is clear from palaeomagnetic evidence that large and hitherto unexpected rotations about a vertical axis are common in regions of distributed continental deformation we propose a simple two dimensional model to illustrate how fault movement and block rotation within a zone of distributed deformation may be related to the relative motion of the rigid plates that bound the zone one surprizing feature of this model is that the component of strike slip motion on the faults within the deforming zone is in the opposite sense to the strike slip component across the zone as a whole thus slip vectors within the zone are not the same as that between the bounding rigid plates in contrast to deformation at oceanic plate boundaries examples of active fault geometries similar to those of our model can be seen in greece iran and the western usa

great earthquakes in low strain rate continental interiors an example from se kazakhstan the lepsy fault of the northern tien shan se kazakhstan extends e w 120 km from the high mountains of the dzhungarian ala tau a subrange of the northern tien shan into the low lying kazakh platform it is an example of an active structure that connects a more rapidly deforming mountain region with an apparently stable continental region and follows a known palaeozoic structure field based and satellite observations reveal an 10 m vertical offset exceptionally preserved along the entire length of the fault geomorphic analysis and age control from radiocarbon and optically stimulated luminescence dating methods indicate that the scarp formed in the holocene and was generated by at least two substantial earthquakes the most recent event dated to sometime after 400 years b p is likely to have ruptured the entire 120 km fault length in a m w 7 5 8 2 earthquake the lepsy fault kinematics were characterized using digital elevation models and high resolution satellite imagery which indicate that the predominant sense of motion is reverse right lateral with a fault strike dip and slip vector azimuth of 110 50 s and 317 343 respectively which is consistent with predominant n s shortening related to the india eurasia collision in light of these observations and because the activity of the lepsy fault would have been hard to ascertain if it had not ruptured in the recent past we note that the absence of known active faults within low relief and low strain rate continental interiors does not always imply an absence of seismic hazard

teleseismic investigation of the january 22 1988 tennant creek australia earthquakes the three january 22 1988 earthquakes are the largest to occur within the australian continent in 20 years and produced two colinear but discontinuous wnw trending scarps enclosing a shorter ene trending scarp teleseismic long period p and sh and short period p waves are used to constrain the locations and source parameters for the three events the third earthquake has a seismic moment 1019nm equal to that of the 1968 meckering event and most likely ruptured the southern of the wnw trending faults relative relocations suggest that the two smaller earthquakes initiated north or nw of the third event centroid depths are less than 6 km but most likely 3 to 4 km and source durations are 4 to 6s so it is probable that each event broke the surface all three earthquakes have predominantly thrust mechanisms and nodal planes that strike west to wnw consistent with faults dipping southward at 30 to 40 only the first has a nodal plane that could support a north dip for the ene trending fault as proposed by other researchers on the basis of ground deformation and preliminary aftershock locations however source directivity evident in the short period p waves and relocations are interpreted better if this event like the others ruptured a sw dipping fault plane the ene trending scarp is interpreted to be a tear fault in the hanging wall that may have acted as a barrier to slip on a single continuous sw dipping fault resulting in this unusual at least for australia sequence of three large similar earthquakes

active faulting in apparently stable peninsular india rift inversion and a holocene age great earthquake on the tapti fault we present observations of active faulting within peninsular india far from the surrounding plate boundaries offset alluvial fan surfaces indicate one or more magnitude 7 6 8 4 thrust faulting earthquakes on the tapti fault maharashtra western india during the holocene the high ratio of fault displacement to length on the alluvial fan offsets implies high stress drop faulting as has been observed elsewhere in the peninsula the along strike extent of the fan offsets is similar to the thickness of the seismogenic layer suggesting a roughly equidimensional fault rupture the subsiding footwall of the fault is likely to have been responsible for altering the continental scale drainage pattern in central india and creating the large west flowing catchment of the tapti river a preexisting sedimentary basin in the uplifting hanging wall implies that the tapti fault was active as a normal fault during the mesozoic and has been reactivated as a thrust highlighting the role of preexisting structures in determining the rheology and deformation of the lithosphere the slip sense of faults and earthquakes in india suggests that deformation south of the ganges foreland basin is driven by the compressive force transmitted between india and the tibetan plateau the along strike continuation of faulting to the east of the holocene ruptures we have studied represents a significant seismic hazard in central india

active tectonics and late cenozoic strain distribution in central and eastern iran 1 right lateral shear between central iran and afghanistan is accommodated on n s right lateral strike slip faults surrounding the aseismic dasht e lut north of 34 n the right lateral shear is accommodated on left lateral faults that rotate clockwise about vertical axes little is known of the late tertiary and younger offsets and slip rates on the active fault systems results that are important for understanding the regional tectonics we use observations from satellite imagery to identify displaced geological and geomorphological markers which we use in conjunction with the overall morphology and orientation of the active fault systems to estimate the total cumulative right lateral shear estimates of cumulative fault movements from offset features and inferred vertical axis rotation of fault bounded blocks suggest that the late cenozoic strain is concentrated toward the eastern margin of iran along the sistan shear zone where bedrock offsets of at least 70 km are observed across the active faults the geomorphology of the deh shir anar and great kavir strike slip faults in central iran suggest that although little shortening is accommodated across this region they might still be active and hence capable of producing earthquakes present day activity on these faults in central iran would not be expected from distributions of instrumental and historical earthquakes although speculative the late tertiary strain distribution described in this paper is consistent with what we know of the present day rates of shear in eastern iran and provides a framework to which later more detailed work can be added

inherited strike slip faults as an origin for basement cored uplifts example of the kungey and zailiskey ranges northern tian shan 1 basement cored uplifts bounded by steeply dipping reverse faults are mechanically difficult to explain reactivation of strike slip faults that aid the formation of new high angle reverse faults in the surrounding crust may provide one origin for these structures this hypothesis is explored by examining the late miocene to quaternary evolution of the kungey and zailiskey ranges in the northern tian shan these ranges are cored by the kemin chilik fault kcf an inherited paleozoic structure with sinistral separation of basement terranes range growth in response to northward propagation of the tian shan has taken place along a network of steeply dipping reverse and oblique slip faults surrounding the kcf deformation of a low relief unconformity separating neogene strata from paleozoic basement records structural growth in response to fault slip deformed river terraces surrounding the ranges are correlated to a well preserved chronosequence in the southern kungey range cosmogenic10be dating of this chronosequence combined with offset measurements yields slip rates ranging from 0 07 to 0 37 mm yr for dip slip faults and 1 1 to 1 5 mm yr for strike slip faults late quaternary activity in the kungey zailiskey ranges is consistent with the longer term outward stepping pattern of range growth based on cross sections constrained from the folded unconformity surface deformed neogene strata and quaternary terraces faults building the kungey range are inferred to steepen at depth and emanate from a shear zone co located with the reactivated kcf this geometry is consistent with a slip partitioned system developed by an obliquely slipping reactivated fault at depth

coseismic displacement bilateral rupture and structural characteristics at the southern end of the 1999 chi chi earthquake rupture central taiwan 1 the 1999 chi chi earthquake mw 7 6 was due to slip along the chelungpu fault a major n striking thrust fault in the fold thrust belt of western taiwan the surface rupture extends over 100 km in a n s trend with nw trending horizontal displacement increasing from 2 to 10 m from south to north the central segment of the chelungpu fault is characterized by bedding slip along the pliocene chinshui shale which has resulted in the development of a monoclinal structure on the hanging wall at the southern end of the chi chi earthquake rupture however the chelungpu fault connects with the ne striking tachienshan fault and cuts into miocene strata with complex structures on the hanging wall in this study we use digital cadastral data to calculate coseismic horizontal displacement around the chushan area results show the amount and direction of horizontal displacement to be ca 1 2 to 2 6 m and ca 220 to 260 respectively on the hanging wall and ca 1 4 m and 105 respectively on the footwall coseismic displacement and seismological data pertaining to the hanging wall at the southern end of the chi chi earthquake rupture indicate the existence of three distinct blocks horizontal displacement indicates the chushan block s movement trended sw this result reflects the chushiang and luliao faults being reactivated with different faulting mechanisms and slip azimuths this study considers a complex coseismic displacement field resulting from a bilateral rupture process whereby a southward rupture with sw trending movement results in right lateral strike slip faulting of the tachienshan fault and thrusting with a right lateral component on the ns strike of the chelungpu fault the northward rupture is associated with nw trending movement that results in activation of the luliao and chushiang faults

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

gps velocity field for the tien shan and surrounding regions 1 measurements at 400 campaign style gps points and another 14 continuously recording stations in central asia define variations in their velocities both along and across the kyrgyz and neighboring parts of tien shan they show that at the longitude of kyrgyzstan the tarim basin converges with eurasia at 20 2 mm yr nearly two thirds of the total convergence rate between india and eurasia at this longitude this high rate suggests that the tien shan has grown into a major mountain range only late in the evolution of the india eurasia collision most of the convergence between tarim and eurasia within the upper crust of the tien shan presumably occurs by slip on faults on the edges of and within the belt but 1 3 mm yr of convergence is absorbed farther north at the dzungarian alatau and at a lower rate with the kazakh platform to the west the tarim basin is thrust beneath the tien shan at 4 7 mm yr with respect to eurasia the ferghana valley rotates counterclockwise at 0 7 myr 1 about an axis at the southwest end of the valley thus gps data place a bound of 4 mm yr on the rate of crustal shortening across the chatkal and neighboring ranges on the northwest margin of the ferghana valley and they limit the present day slip rate on the right lateral talas ferghana fault to less than 2 mm yr gps measurements corroborate geologic evidence indicating that the northern margin of the pamir overthrusts the alay valley and require a rate of at least 10 and possibly 15 mm yr

yangzhumingite and phlogopite from the kvaloya lamproite north norway structure composition and origin abstract this study reports a petrographic and crystal chemical analysis of three types of micas yangzhumingite light brown phlogopite and dark brown phlogopite found in a lamproitic dyke at the kvaloya island north norway the study was carried out integrating different analytical techniques electron microprobe single crystal x ray diffraction inductively coupled plasma mass spectrometry mossbauer and micro fourier transform infrared spectroscopy kvaloya yangzhumingite second occurrence in nature was characterized for the first time in detail via single crystal x ray diffraction the different mica types are distinguishable on the basis of the vi fe and mg versus si content yangzhumingite composition is intermediate between those of kmg 2 75 si 3 5 al 0 5 o 10 f 2 and kmg 2 50 si 4 o 10 f 2 synthetic compounds reported in the literature light and possibly dark brown phlogopite is a mg rich fluorotetraferriphlogopite the latter having a greater fe content the infrared spectra of yangzhumingite and the light brown phlogopite show the occurrence of oh absorption bands respectively at 3586 cm 1 which correlates well with the measured f content 3707 cm 1 and 3686 cm 1 assigned mainly to 3mg 2 k oh phlogopitic environment structural analyses performed only on yangzhumingite and light brown phlogopite show that both samples are 1 m polytypes with the expected space group c 2 m crystal chemical details are compatible with the following major substitution mechanisms 2 xii k vi 2 xii vi r 2 where r 2 mg fe oh f for yangzhumingite and 2 vi r 2 vi ti 4 vi ti vacancy oh f for light brown phlogopite all three types of micas formed at relatively constant low pressure but over a large temperature range in equilibrium with a grain boundary fluid that underwent significant changes in composition during reaction progress light brown phlogopite cores and dark brown phlogopite rims formed during crystallization from the lamproitic magma while yangzhumingite formed as a result of reactions between the already formed phlogopite and the highly reactive fluid that was derived from the volatile rich lamproite magma

the 1993 killari earthquake in central india a new fault in mesozoic basalt flows the mw 6 1 1993 killari earthquake in central india was one of the deadliest earthquakes to occur in a stable continental area it had a centroid 2 6 km deep and ruptured to the surface a good fit of teleseismic waveforms is obtained with a simple 4 2 s long pulse that releases a moment mo 1 8 1018 nm from a reverse fault rupture with strike dip and rake of 126 46 and 100 respectively a 10 km wide meizoseismal area is tightly defined by relative casualty count in the center of this area aftershock hypocenters baumbach et al 1994 outline a southwest dipping rupture that extends 5 5 8 km along strike and from the surface 8 10 km along dip these dimensions correspond with an average displacement of 1 5 0 8 m and a stress drop of 10 4 5 mpa respectively we mapped a 1 km long zone of compressional scarps which are spatially correlated with the rupture outlined by hypocenter in the central portion of this zone the scarps are multiple and face in opposite directions deformation features indicate north northeast directed shortening of at least 0 5 m a leveling profile of an irrigation canal about 3 km northwest of the scarps displays a one wavelength warp about 1 km long and 1 3 m in peak to peak amplitude that may reflect deformation associated with the rupture two trenches across the scarps exposed faults that offset the soil rock interface as much as 50 cm we found no convincing evidence suggesting that these faults existed prior to the earthquake in the basalt these faults reactivated exfoliation fractures in shear but were not associated with a zone of preexisting breccia and mineralization the hypothesis that the 1993 rupture is a new fault in the deccan traps is consistent with lack of geomorphic evidence of prior faulting and with the lack of accumulated deformation or tilting in basalt layers exposed as close as few tens of meters from the scarp no convincing clues about a seismogenic fault have yet been detected from either historic seismicity or geology in the 1993 source area but a burst of seismicity 1 year before the mainshock and 2 5 years after the first impounding of a nearby reservoir was interpreted by some as a possible precursor to a larger earthquake before the 1993 mainshock precursory seismicity and artificial effects that cause significant mechanical changes in the crust may provide an indication of future potentially damaging earthquakes in stable continental areas

active faulting in the walker lane 1 deformation across the san andreas and walker lane fault systems accounts for most relative pacific north american transform plate motion the walker lane is composed of discontinuous sets of right slip faults that are located to the east and strike approximately parallel to the san andreas fault system mapping of active faults in the central walker lane shows that right lateral shear is locally accommodated by rotation of crustal blocks bounded by steep dipping east striking left slip faults the left slip and clockwise rotation of crustal blocks bounded by the east striking faults has produced major basins in the area including rattlesnake and garfield flats teels columbus and rhodes salt marshes and queen valley the benton springs and petrified springs faults are the major northwest striking structures currently accommodating transform motion in the central walker lane right lateral offsets of late pleistocene surfaces along the two faults point to slip rates of at least 1 mm yr the northern limit of northwest trending strike slip faults in the central walker lane is abrupt and reflects transfer of strike slip to dip slip deformation in the western basin and range and transformation of right slip into rotation of crustal blocks to the north the transfer of strike slip in the central walker lane to dip slip in the western basin and range correlates to a northward broadening of the modern strain field suggested by geodesy and appears to be a long lived feature of the deformation field the complexity of faulting and apparent rotation of crustal blocks within the walker lane is consistent with the concept of a partially detached and elastic brittle crust that is being transported on a continuously deforming layer below the regional pattern of faulting within the walker lane is more complex than observed along the san andreas fault system to the west the difference is attributed to the relatively less cumulative slip that has occurred across the walker lane and that oblique components of displacement are of opposite sense along the walker lane extension and san andreas contraction respectively despite the gross differences in fault pattern the walker lane and san andreas also share similarities in deformation style including clockwise rotations of crustal blocks leading to development of structural basins and the partitioning of oblique components of slip onto subparallel strike slip and dip slip faults

fault mechanics and the kinematics of block rotations in many strike slip tectonic settings large rotations up to 100 of crustal blocks have been inferred from paleomagnetic data these blocks are bounded by sets of parallel faults which accommodate the relative motion between the blocks as regional deformation progresses simple geometrical considerations require that the faults must also rotate in this paper we show that on the basis of mechanical considerations the amount of fault rotation permissible under a stationary stress field is limited to 20 to 45 consequently block rotations that are larger than 40 or 45 require more than one set of accompanying faults to accommodate the block rotation examples of such multiple sets with 40 to 45 between them as predicted by the model were recognized in sistan iran in yerington the lake mead area nevada and in southern california

field examples of strike slip fault terminations in mongolia and their tectonic significance deformation at the ends of large intracontinental strike slip faults that do not simply link other major structures often involves rotations about a vertical axis we use earthquake slip vectors surface rupture in earthquakes and geomorphology to examine the ends of three major strike slip faults in mongolia in these places a simple pattern is seen consisting of a thrust fault on one side with a displacement that decreases away from the strike slip fault consistent with local rotational deformation strike slip faults that terminate in this way allow the style of faulting to change spatially within a deforming area for example from dominantly strike slip to dominantly dip slip while still accommodating the overall deformation required by larger scale regional motions such a change in fault style should also be accompanied by a change in the rotation rate about a vertical axis which may be detected paleomagnetically the kind of strike slip fault termination described here may have consequences for how large strike slip fxaults evolve and grow and for the variation in displacement along their length

comparison of hypocentre parameters of earthquakes in the aegean region abstract the aegean sea is one of the more seismically active areas in the euro mediterranean region the seismic activity in the aegean sea is monitored by a number of local agencies that contribute their data to the international seismological centre isc consequently the isc bulletin may serve as a reliable reference for assessing the capabilities of local agencies to monitor moderate and low magnitude earthquakes we have compared bulletins of the kandilli observatory and earthquake research institute koeri and the isc for the period 1976 2003 that comprises the most complete data sets for both koeri and isc the selected study area is the east aegean sea and west turkey bounded by latitude 35 41 n and by longitude 24 29 e the total number of events known to occur in this area during 1976 2003 is about 41 638 seventy two percent of those earthquakes were located by isc and 75 were located by koeri as expected epicentre location discrepancy between isc and koeri solutions are larger as we move away from the koeri seismic network out of the 22 066 earthquakes located by both isc and koeri only 4 show a difference of 50 km or more about 140 earthquakes show a discrepancy of more than 100 km focal depth determinations differ mainly in the subduction zone along the hellenic arc less than 2 of the events differ in their focal depth by more than 25 km yet the location solutions of about 30 events differ by more than 100 km almost a quarter of the events listed in the isc bulletin are missed by koeri most of them occurring off the coast of turkey in the east aegean based on the frequency magnitude distributions the koeri bulletin is complete for earthquakes with duration magnitudes md 2 7 both located and assigned magnitudes where as the threshold magnitude for events with location and magnitude determinations by isc is mb 4 0 koeri magnitudes seem to be poorly correlated with isc magnitudes suggesting relatively high uncertainty in the magnitude determinations it is apparent that koeri like other agencies in the region will greatly benefit from a much improved regional cooperation