present day stress field changes along the baikal rift and tectonic implications intraplate extension in a frame of a global compressional stress field seems linked to local lithospheric perturbations lithospheric thinning or thickening able to modify the resulting state of stress zoback 1992 the baikal rift zone brz siberia is located north of the india asia collision zone and exhibits no direct communication with any oceanic domain it can thus be fully considered as an area of continental extension dominated by the global compressional intraplate stress field resulting from plate driving forces in order to address the problem of its dynamics and kinematics and their links with the india asia collision a comprehensive stress tensor analysis is presented based on 319 focal mechanisms of earthquakes located along the whole baikal rift the stress field is varying at different scales of observation when looking at central asia several thousands kilometers the maximum horizontal stress shmax directions remain rather constant with a fan shape geometry when the tectonic regime goes from compressional himalayas to extensional baikal when observing the baikal rift about 1000 km long clear variations of the stress regime are observed from an extensional regime in the central part of the rift to wrench ones in its northern and southern ends finally at the scale of 100 km systematic shmax reorientations occur close to major rift faults we thus infer that the interaction between collisional processes and inherited structures may have a strong influence on rift dynamics we then use computed stress tensors to predict slip vectors on major rift faults deformation patterns show two distinct parts of the rift the south baikal rift sbr is characterized by a constant trending around n100 e slip vector meanwhile the north baikal rift nbr exhibits a complex block rotation behavior involving at least three crustal blocks we propose to interpret these surficial structures and motions as the result of an interaction between the regional compression coming from the india asia collision and the geometry of the hardly deformable siberian platform this particular setting can explain most of the surficial deformation patterns which suggest a large scale cracking of the lithosphere in the baikal region other possible sources of stress could also be considered like deep mantellic upwelling or trench suction linked to the pacific subduction

evidence and causes of the two stage development of the baikal rift abstract the data on the geological and deep seated structures of the baikal rift zone are briefly summarized based on the analysis of the composition of the sedimentary infill in rift basins two stages of the zone development have been recognized 1 1 slow rifting 2 2 fast rifting as a consequence of the study of the deep seated structure and construction of the thermal model of the lithosphere it was assumed that the first stage is associated with a slow uprise of the surface of the asthenospheric upwelling and the second stage connected with sideways flows of the substance involved in this upwelling after the crustal base was reached

geometry and kinematics of recent deformation in the mondy tunka area south westernmost baikal rift zone mongolia siberia we used satellite imagery and field data to investigate the south westernmost baikal rift zone we focus our study in the mondy and ikhe ukhgun valleys site of an mw 6 9 seismic event in 1950 surface deformations are observed along the e w trending mondy strike slip fault and along the ikhe ukhgun thrust the mondy fault system is 80 km long and is composed of four segments 10 15 km long these segments are characterized by subvertical planes with left lateral movements the ikhe ukhgun thrust is 20 km long dips 40 to the south and shows reverse movement with a left lateral component these observations are consistent with the present day regional nne ssw compression and with the focal mechanism of the 1950 mondy earthquake that was recently re evaluated these features like those observed in the tunka basin demonstrate a recent change of regional strain regime from transtension to transpression that we place before the late pleistocene

soft sediment deformation structures induced by strong earthquakes in southern siberia and their paleoseismic significance abstract liquefaction induced soft sediment deformation structures ssds formed by earthquakes in southern siberia that were historically mentioned or monitored by instruments are described and analyzed clastic dikes are the most common among all ssds in the epicentral areas of the investigated seismic events they are also the most reliable paleoseismic indicators in regions where cryogenic processes are intense we suggest seven criteria that may be useful to distinguish the seismogenic clastic dikes from non seismogenic ssds in a single outcrop 1 pushed up sedimentary blocks within the dike body 2 regular distorted contacts of a dike with host sediments reflecting cyclic loading during propagation of seismic waves 3 turned up layers of host deposits on contacts with a dike 4 displacement along dike contacts usually in the form of a normal fault caused by subsidence that compensates for the removed sediment 5 a dike structure similar to a diapir 6 filling of a clasic dike with coarser materials than the host sediments and 7 a sediment layer extruded on the surface or between strata similar in composition to the dike in the extruded sandy gravel pebble layer rock fragments show normal grading from large to small clasts in addition to these indicators fractures may indirectly indicate the seismogenic genesis of liquefaction induced ssds due to the close spatial relationship of dikes with the fault structures of the investigated areas they can be used to identify seismogenic fault and the characteristics of dikes lateral gradual changes in the frequency size and type of the deformations can help to determine the epicenter magnitude and the local intensity of the associated earthquakes

a numerical method for determining the state of stress using focal mechanisms of earthquake populations application to tibetan teleseisms and microseismicity of southern peru the numerical method described in this paper enables the study in terms of stress of the kinematics of seismic faults provided by focal mechanisms this method assumes a mean state of stress in the source region and is based on the simple mechanical model used for fault population analysis which supposes slip in the direction of the resolved shear stress acting on the fault plane the proposed algorithm first defines compressional and tensional zones resulting from superimposition of the compressional and tensional quadrants limited by the nodal planes this enables one to test the data homogeneity furthermore this restricts the space where the principal stress axes have to be searched then for each principal stress reference whose location is constrained by above confined zones the r value chosen equal to 2 1 3 1 is computed which fits the slip vector on each nodal plane this permits one to select a set of preferred seismic fault planes from a set of auxiliary planes finally a state of stress is computed from the preferred seismic fault plane set using the non linear simplex method already applied to fault populations this algorithm is constructed so as to avoid two major difficulties misleading estimation of the deviatoric stress tensor which may result from excessive emphasis by minimizing the residuals by a least squares method if some of the data are wrong and a lengthy prospection of the stress references over all the space of directions this calculation does not take into account possible changes of the strike and dip of the nodal planes however we use rotations of nodal planes in agreement with the first arrival data to test the compatibility of these data with the computed state of stress tibetan teleseisms and southern peruvian microseisms are analyzed and results are compared with kinematics of superficial recent and active faults measured in field in the same regions this suggests that major seismic events may give a good evaluation of the regional mean state of stress focal mechanisms of the small events are also modelled by a mean stress deviator but this differs significantly from the regional state of stress in southern peru deduced from quaternary faulting this may be due to imprecise location of the small events however some movements are strongly different from those predicted by the computed mean stress deviator this suggests that small fault kinematics surely depend on the regional state of stress but that local effects may control the small deformations

cryoturbation versus tectonic deformation along the southern edge of the tunka basin baikal rift system siberia new insights from an integrated morphotectonic and stratigraphic study the tunka basin is a broad emerging basin situated between the baikal lake to the east and the the hovsgol lake to the west the basin is bounded to the north and to the south by the tunka and the khamar daban mountain ranges respectively the tunka normal fault located at the southern foothills of the tunka mountain range is the main structure that controlled the development of the tunka basin during the neogene paleoearthquake surface ruptures attest of its present activity and show that its western and eastern terminations are undergoing a tectonic inversion characterized by left lateral reverse deformations the southern edge of the tunka basin is classically interpreted as being tectonically controlled in this paper we present the results of a geomorphological and stratigraphic analysis within its southwestern and southeastern parts suggesting that there is no active fault affecting the foothills of the khamar daban mountain range the different features observed in the quaternary deposits are interpreted to be the result of periglacial processes induced by alternating episodes of permafrost aggradation and degradation during the holocene our study concludes that the khamar daban range and the tunka basin are uplifting together and that the tunka and mondy faults are the two main triggers of regional earthquakes

asthenospheric imprints on the lithosphere in central mongolia and southern siberia from a joint inversion of gravity and seismology mobal experiment summary we present a joint inversion of gravity and teleseismic data to enlighten the lithospheric structures of the baikal mongolia region an area characterized by high topographic contrasts sporadic cenozoic volcanism extension and large transcurrent faulting in the vicinity of the baikal rift central asia the study uses a 1000 km long seismic transect that cross cuts the main tectonic structures from north to south namely the siberian platform tunka basin hangay dome and gobi altai belt the siberian platform depicts a high velocity lithosphere down to about 150 km we evidence strong velocity contrasts within the crust below the hangay dome and the tunka depression interpreted as a thickened crust a low velocity density region is located at various depths below the hangay dome thanks to the dense spatial coverage of gravity data we are able to define the 3 d geometry of this particular low velocity density anomaly the hangay dome anomalous body extends from 60 to 225 km depth at his largest point and slightly thins to no more than 40 km at its easternmost end a deep low velocity zone below 150 km with only a weak negative density contrast is observed on the eastern part of the transect we propose that the late cenozoic uplift of the whole mongolian plateau and associated rifting magmatism high heat flow and lithospheric thinning are not externally driven by the india asia collision but results from the interaction of two mantle plumes with the overlying lithosphere conversely recent faulting may be the major expression of the india asia collision in this region as well as n s striking rift basins that connect and interact with major strike slip faults such as the bolnai fault the comparison between time residuals of this experiment and the baikal rift seismic data shows an undeniable disproportion for the hangay anomaly the hangay time residuals are far more positive than through the baikal arguing for an asthenospheric signature that is not seen beneath the baikal rift furthermore the southern edge of the thick siberian cratonic lithosphere may favour the rise of a sublithospheric mantle flow at the contact with the baikal mongolia lithosphere

quantification of the spatial distribution of mineral phases and grains in rock using a 2 d multiple area density map technique abstract the most widely used method for quantitative analyses of the spatial distribution of grains in a rock body is the nearest neighbor method a position based method which recognizes the grain center as the position of the grain without consideration of grain size or shape however the spatial distribution of grains is influenced by their size and shape as well as their position here we propose a multiple area density map madm method to quantify the spatial distribution of phases or grains the method is based on image analysis and simultaneously considers the position size shape and proportion of grains the madm constructed by overlaying density maps of grain areas with a set of template size produces a normalized standard deviation nsd value of phase area density which represents the degree to which it is spatially clustered the nsd value is used to quantify the distribution of the phase without considering individual grains to identify the spatial distribution of individual grains the method employs the clustering index ci which is calculated from the ratio of nsd to the reciprocal of the number of grains in a log log plot

gps measurements of crustal deformation in the baikal mongolia area 1994 2002 implications for current kinematics of asia 1 we present new geodetic results of crustal velocities over a large part of northern asia based on gps measurements in the baikal rift zone and mongolia spanning the 1994 2002 period we combine our results with the gps velocity field for china of wang et al 2001 and derive a consistent velocity field for most of asia we find contrasted kinematic and strain regimes in mongolia with northward velocities and n s shortening in westernmost mongolia but eastward to southeastward motion and left lateral shear for central and eastern mongolia this eastward to southeastward motion of central and eastern mongolia is accommodated by left lateral slip on the e w trending tunka bolnay and gobi altay faults 2 1 2 mm yr 1 2 6 1 0 mm yr 1 and 1 2 mm yr 1 respectively and by about 4 mm yr 1 of extension across the baikal rift zone consequently 15 of the india eurasia convergence is accommodated north of the tien shan by n s shortening combined with dextral shear in the mongolian altay and by eastward displacements along major left lateral strike slip faults in central and eastern mongolia we find a counterclockwise rotation of north and south china as a quasi rigid block around a pole north of the stanovoy belt which rules out the existence of an amurian plate as previously defined and implies 2 mm yr 1 of left lateral slip on the qinling shan fault zone

seismicity of the baikal rift system from regional network observations abstract in the paper we report the state of the art of seismicity study in the baikal rift system and the general results obtained at present the regional earthquake catalog for fifty years of the permanent instrumental observations consists of over 185 000 events the spatial distribution of the epicenters which either gather along well delineated belts or in discrete swarms is considered in detail for different areas of the rift system at the same time the hypocenters are poorly constrained making it difficult to identify the fault geometry clustered events like aftershock sequences or earthquake swarms are typical patterns in the region moreover aftershocks of m 4 7 earthquakes make up a quarter of the whole catalog the maximum magnitude of earthquakes recorded instrumentally is mlh7 6 for a strike slip event in the ne part of the baikal rift system and mlh6 8 for a normal fault earthquake in the central part of the rift system lake baikal basin predominant movement type is normal faulting on ne striking faults with a left lateral strike slip component on w e planes in conclusion some shortcomings of the seismic network and data processing are pointed out

characterizing the present day activity of the tunka and sayan faults within their relay zone western baikal rift system russia the sayan and tunka faults are located at the boundary between the northernmost mountain belt of central asia the sayan baikal ranges and the siberian platform these prominent crustal structures were involved in the opening of the southern baikal rift system since the beginning of the cenozoic and define large scale sharp morphotectonic features despite low instrumental seismic activity late pleistocene holocene morphotectonic features along the two faults indicate that the faults are active and have the capacity to produce strong earthquakes a careful mapping of the most recent trace of activity within the southeastern parts of the two faults where they merge within a relay zone demonstrates that they correspond now to left lateral reverse faults suggesting a recent inversion of their vertical component we also show that the two faults are now structurally connected via a young surface rupture and that no obvious post last glacial maximum ruptures are observed along the central part of the sayan fault beyond its junction zone with the tunka fault this suggests that the left lateral strike slip deformation is transferred from the eastern sayan fault to the tunka fault a detailed morphotectonic study along the southeastern sayan fault allows estimating a left lateral slip rate between 1 3 min and 3 9 mm year max finally a critical review of russian paleoseismic data combined with our paleoseismological investigations allows us to propose that the mean recurrence time along the two faults is on the order of 4 kyr and that they may have either ruptured together or during seismic clusters

the amurian plate motion and current plate kinematics in eastern asia we use global positioning system gps velocity data to model eastern asian plate kinematics out of 15 stations in korea russia china and japan studied here three sites considered to be on the stable interior of the hypothetical amurian plate showed eastward velocities as fast as 9 10 mm yr with respect to the eurasian plate they were stationary relative to each other to within 1 mm yr and these velocity vectors together with those of a few additional sites were used to accurately determine the instantaneous angular velocity euler vector of the amurian plate the predicted movement between the amurian and the north american plates is consistent with slip vectors along the eastern margin of the japan sea and sakhalin which reduces the necessity to postulate the existence of the okhotsk plate the euler vector of the amurian plate predicts left lateral movement along its boundary with the south china block consistent with neotectonic estimates of the displacement at the qinling fault possibly the southern boundary of the amurian plate the amurian plate offers a platform for models of interseismic strain buildup in southwest japan by the philippine sea plate subduction at the nankai trough slip vectors along the baikal rift the boundary between the amurian and the eurasian plates are largely inconsistent with the gps based euler vector suggesting an intrinsic difficulty in using earthquake slip vectors in continental rift zones for such studies

fault interaction and stress triggering of twentieth century earthquakes in mongolia 1 a cluster of exceptionally large earthquakes in the interior of asia occurred from 1905 to 1967 the 1905 m7 9 tsetserleg and m8 4 bolnai earthquakes the 1931 m8 0 fu yun earthquake the 1957 m8 1 gobi altai earthquake and the 1967 m7 1 mogod earthquake sequence each of the larger m 8 earthquakes involved strike slip faulting averaging more than 5 m and rupture lengths of several hundred kilometers available geologic data indicate that recurrence intervals on the major source faults are several thousands of years and distances of about 400 km separate the respective rupture areas we propose that the occurrences of these and many smaller earthquakes are related and controlled to a large extent by stress changes generated by the compounded static deformation of the preceding earthquakes and subsequent viscoelastic relaxation of the lower crust and upper mantle beneath mongolia we employ a spherically layered viscoelastic model constrained by the 1994 2002 gps velocity field in western mongolia vergnolle et al 2003 using the succession of twentieth century earthquakes as sources of deformation we then analyze the time dependent change in coulomb failure stress f at remote interaction distances static f values are small however modeled postseismic stress changes typically accumulate to several tenths of a bar over time intervals of decades almost all significant twentieth century regional earthquakes m 6 with well constrained fault geometry lie in positive f lobes of magnitude about 0 5 bar our results suggest that significant stress transfer is possible among continental faults separated by hundreds of kilometers and on timescales of decades

terrestrial 14c age of the antarctic shergottite eeta 79001 abstract the terrestrial age of the elephant moraine shergottite eeta 79001 lithology a has been determined from measurement of its cosmogenic 14 c content as 12 2 kyr the results on saturated and blank samples of l g or less are also discussed the age calculated for eeta 79001 is compared to exposure and terrestrial ages of other shergottites in the light of possible origins of these meteorites on mars

style of active intraplate deformation from gravity and seismicity data the baikal rift asia to better understand how active deformation localizes within a continental plate in response to extensional and transtensional tectonics a combined analysis of high quality gravity bouguer anomaly and seismicity data is presented consisting of about 35000 earthquakes recorded in the baikal rift zone this approach allows imaging of deformation patterns from the surface down to the moho a comparison is made with heat flow variations in order to assess the importance of lithospheric rheology in the style of extensional deformation three different rift sectors can be identified the southwestern rift sector is characterized by strong gravity and topography contrasts marked by two major crustal faults and diffuse seismicity heat flow shows locally elevated values correlated with recent volcanism and negative seismic p velocity anomalies based on earthquake fault plane solutions and on previous stress field inversions it is proposed that strain decoupling may occur in this area in response to wrench compressional stress regime imposed by the india asia collision the central sector is characterized by two major seismic belts the southernmost one corresponds to a single steeply dipping fault accommodating oblique extension in the centre of lake baikal a second seismic belt is associated with several dip slip faults and subcrustal thinning at the rift axis in response to orthogonal extension the northern rift sector is characterized by a wide low bouguer anomaly which corresponds to a broad high topographic dome and seismic belts and swarms this topography can be explained by lithospheric buoyancy forces possibly linked to anomalous upper mantle at a more detailed scale no clear correlation appears between the surficial fault pattern and the gravity signal as in other continental rifts it appears that the lithospheric rheology influences extensional basins morphology however in the baikal rift the inherited structural fabric combined with stress field variations results in oblique rifting tectonics which seem to control the geometry of southern and northeastern rift basins

a double seismic zone in the subducting juan fernandez ridge of the nazca plate 32 s central chile 1 the region of central chile offers a unique opportunity to study the links between the subducting juan fernandez ridge the flat slab the double seismic zone dsz and the absence of modern volcanism here we report the presence and characteristics of the first observed dsz within the intermediate depth nazca slab using two temporary seismic catalogs ovalle 1999 and chile argentina seismological measurement experiment the lower plane of seismicity lp is located 20 25 km below the upper plane begins at 50 km depth and merges with the lower plane at 120 km depth where the slab becomes horizontal focal mechanism analysis and stress tensor calculations indicate that the slab s state of stress is dominantly controlled by plate convergence and overriding crust thickness above 60 70 km depth the slab is in horizontal compression and below it is in horizontal extension parallel to plate convergence which can be accounted for by vertical loading of the overriding lithosphere focal mechanisms below 60 70 km depth are strongly correlated with offshore outer rise bend faults suggesting the reactivation of preexisting faults below this depth the large interplane distances for all nazca dszs can be related to the slab s unusually cold thermal structure with respect to its age since lps globally seem to mimic mantle mineral dehydration paths we suggest that fluid migration and dehydration embrittlement provide the mechanism necessary to weaken the rock and that the stress field determines the direction of rupture

late cenozoic transpression in southwestern mongolia and the gobi altai tien shan connection the gobi altai region of southwestern mongolia is a natural laboratory for studying processes of active transpressional intracontinental mountain building at different stages of development the region is structurally dominated by several major e w left lateral strike slip fault systems the north gobi altai fault system is a seismically active right stepping left lateral strike slip fault system that can be traced along the surface for over 350 km the eastern two thirds of the fault system ruptured during a major earthquake m 8 3 in 1957 whereas degraded fault scarps cutting alluvial deposits along the western third of the system indicate that this segment did not rupture during the 1957 event but has been active during the quaternary the highest mountains in the gobi altai are restraining bend uplifts along the length of the fault system detailed transects across two of the restraining bends indicate that they have asymmetric flower structure cross sectional geometries with thrust faults rooting into oblique slip and strike slip master faults continued ne directed convergence across the fault system coupled with left lateral strike slip displacements will lead to growth and coalescence of the restraining bends into a continuous sublinear range possibly obscuring the original strike slip fault system this may be a common mountain building process the largely unknown gobi tien shan fault system is a major left lateral strike slip fault system 1200 km long that links the southern ranges of the gobi altai with the barkol tagh and bogda shan of the easternmost tien shan in china active scarps cutting alluvial deposits are visible on satellite imagery along much of its central section indicating quaternary activity the total displacement is unknown but small parallel splays have apparent offsets of 20 km suggesting that the main fault zone has experienced significantly more displacement field investigations conducted at two locations in southwestern mongolia indicate that late cenozoic transpressional uplift is still active along the fault system the spatial relationship between topography and active faults in the barkol tagh and bogda shan strongly suggests that these ranges are large coalescing restraining bends that have accommodated the fault s left lateral motion by thrusting oblique slip displacement and uplift thus from a mongolian perspective the easternmost tien shan formed where it is because it lies at the western termination zone of the gobi tien shan fault system the gobi tien shan fault system is one of the longest fault systems in central asia and together with the north gobi altai and other smaller subparallel fault systems is accommodating the eastward translation of south mongolia relative to the hangay dome and siberia these displacements are interpreted to be due to eastward viscous flow of uppermost mantle material in the topographically low e w trending corridor between the northern edge of the tibetan plateau and the hangay dome presumably in response to the indo eurasian collision 2500 km to the south

source history of the 1905 great mongolian earthquakes tsetserleg bolnay summary two great mongolian earthquakes tsetserleg and bolnay occurred on 1905 july 9 and 23 we determined the source history of these events using body waveform inversion the tsetserleg rupture azimuth n60 correspond to a n60 oriented branch of the long ew oriented bolnay fault historical seismograms recorded by wiechert instruments are digitized and corrected for the geometrical deformation due to the recording system we use predictive filters to recover the signals lost at the minute marks the total rupture length for the tsetserleg earthquake may reach up to 190 km in order to explain the width of the recorded body waves this implies adding 60 km to the previously mapped fault the rupture propagation is mainly eastward it starts at the southwest of the central subsegment showing a left lateral strike slip with a reverse component the total duration of the modelled source function is 65 s the seismic moment deduced from the inversion is 1021 n m giving a magnitude mw 8 the nucleation of the bolnay earthquake was at the intersection between the main fault 375 km left lateral strike slip and the teregtiin fault n160 80 km long right lateral strike slip with a vertical component near the main fault the rupture was bilateral along the main fault 100 km to the west and 275 km to east it also propagated 80 km to the southeast along the teregtiin fault the source duration was 115 s the moment magnitude mw varies between 8 3 and 8 5 the nucleation and rupture depths remain uncertain we tested three cases 1 nucleation and rupture depth limited to the seismogenic zone 2 nucleation in the seismogenic zone and rupture propagation going to the base of the crust and 3 nucleation within the crust upper mantle interface and rupture propagation within the upper mantle

new constraints on current deformation in asia from continuous gps measurements at ulan baatar mongolia on the basis of 3 years of continuous gps measurements 1995 1998 show a velocity of 6 4 1 6 mm yr in a n125 30 azimuth with respect to eurasia at a permanent site in ulan baatar mongolia together with recent gps results in asia this result indicates motion of the amurian north china block at 6 10 mm yr to the east to southeast relative to eurasia 0 to 5mm yr slower than south china 10 11 mm yr eastward the small differential motion between these two blocks is in agreement with deformation models of asia where crustal thickening dominates lateral extrusion the fact that the velocity of the amurian north china block is significantly faster than the predictions of models based on the hypothesis that deformation in asia is enterely driven by the india eurasia collision suggests that other mechanisms such as far field effects of subduction processes and gravitational forces could significantly contribute to intracontinental deformation

the 2016 mihoub north central algeria earthquake sequence seismological and tectonic aspects abstract on 28 may 2016 at 23 54 utc an mw5 4 earthquake occurred in mihoub village algeria 60 km southeast of algiers this earthquake was the largest event in a sequence recorded from 10 april to 15 july 2016 in addition to the permanent national network a temporary network was installed in the epicentral region after this shock recorded event locations allow us to give a general overview of the sequence and reveal the existence of two main fault segments the first segment on which the first event in the sequence was located is near vertical and trends e w the second fault plane on which the largest event of the sequence was located dips to the southeast and strikes ne sw a total of 46 well constrained focal mechanisms were calculated the events located on the e w striking fault segment show mainly right lateral strike slip strike n70 e dip 77 to the sse rake 150 the events located on the ne sw striking segment show mainly reverse faulting strike n60 e dip 70 to the se rake 130 we calculated the static stress change caused by the first event md4 9 of the sequence the result shows that the fault plane of the largest event in the sequence mw5 4 and most of the aftershocks occurred within an area of increased coulomb stress moreover using the focal mechanisms calculated in this work we estimated the orientations of the main axes of the local stress tensor ellipsoid the results confirm previous findings that the general stress field in this area shows orientations aligned nnw sse to nw se the 2016 mihoub earthquake sequence study thus improves our understanding of seismic hazard in north central algeria

earthquake depth distributions in central asia and their relations with lithosphere thickness shortening and extension this paper examines the relationship between seismogenic thickness lithosphere structure and rheology in central and northeastern asia we accurately determine earthquake depth distributions which reveal important rheological variations in the lower crust these variations exert a fundamental control on the active tectonics and the morphological evolution of the continents we consider 323 earthquakes across the tibetan plateau the tien shan and their forelands as well as the baikal rift ne siberia and the laptev sea and present the source parameters of 94 of these here for the first time these parameters have been determined through body wave inversion the identification of depth phases or the modelling of regional waveforms lower crustal earthquakes are found to be restricted to the forelands in areas undergoing shortening and to locations where rifting coincides with abrupt changes in lithosphere thickness such as the ne baikal rift and w laptev sea the lower crust in these areas is seismogenic at temperatures that may be as high as 600 c suggesting that it is anhydrous and is likely to have great long term strength lower crustal earthquakes are therefore a useful proxy indicating strong lithosphere in places that are too small in areal extent for this to be confirmed independently by estimating effective elastic thickness from gravity topography relations the variation in crustal rheology indicated by the distribution of lower crustal earthquakes has many implications ranging from the support of mountain belts and the formation of steep mountain fronts to the localization and orientation of rifting in combination these processes can also be responsible for the separation of the front of the thin skinned mountain belts from their hinterlands when continents separate

quantitative textural analysis of packings of elongate crystals the spatial distribution of grains in a solidifying igneous rock controls the physical properties of the crystal mush and in turn is controlled by the rate of crystal growth and accumulation a predominant non spherical habit for igneous minerals brings into question the use of spherical particles in reference packings used for quantification of spatial distribution furthermore variations of crystal clustering ordering with length scale require spatial statistics which take into account the distribution of particles beyond nearest neighbours using random close packings of spherocylinders we demonstrate the importance of aspect ratio for the aggregation index usually known as r and show that packings of spherical particles have more structure than packings of rods the spatial distribution functions demonstrate that the plagioclase grains in the colonnade from the holyoke basalt are clustered on a length scale of 0 5 mm understanding the controls on grain spatial distribution in igneous rocks will depend on the application of these techniques to well understood environments

upper mantle flow beneath and around the hangay dome central mongolia mongolia represents the northernmost area affected by the india asia collision and it is actively deformed along transpressive belts closely associated with large scale strike slip faults the active and past mantle flow beneath this region is however poorly known in order to investigate deep mantle deformation beneath central mongolia and its relation with the surrounding major structures such as the siberian craton the gobi altay belt and the baikal rift a ns trending profile of broadband seismic stations has been deployed in the summer 2003 from the southern siberian craton to the gobi altay range crossing the entire hangay dome mantle flow is deduced from the splitting of teleseismic shear waves such as sks phases in eastern mongolia the permanent station uln in ulaanbaatar reveals the presence of two anisotropic layers the upper one being oriented ne sw close to the trend of lithospheric structures and the lower one nw se close to the trend of eurasia absolute plate motion along the ns profile in central mongolia seismic anisotropy deduced from sks splitting reveals a homogeneous nw se trending structure fully consistent with the observations made in the altay sayan in western mongolia the observed delay times of 1 5 to more than 2 0 s favor consistent mantle flow over large mantle thicknesses since the lithosphere is less than 100 km thick beneath central mongolia and since the observed fast directions are parallel to the trend of the lithospheric structures but also close to the trend of the absolute plate motion we propose that both the lithosphere and the asthenosphere may join their anisotropic effects beneath central mongolia to explain the large delay times although gps vectors represent the instantaneous displacement of the earth s surface and sks splitting the time and vertical integration of finite strain at depth we use the opportunity of the dense geodetic measurements available in this region to discuss the anisotropy pattern in term of present day deformation in the eurasia fixed reference frame gps and sks both depict a similar trend beneath central mongolia suggesting a lithospheric block escaping toward the east that could orient olivine a axes in the upper mantle within a transpressive tectonic regime a different behaviour is observed in western mongolia the gps vectors trend ns close to the regional compression direction whereas the fast sks directions trend ew suggesting a tectonic regime close to a mode of axial shortening generating the development of an ew trending foliation at depth we therefore propose that mongolia is a place where active and frozen lithospheric deformation may add their effects together with the sublithospheric flow in the three sources of anisotropy inferred a fundamental role is played by the siberian craton that acted as an undeformable core of the continent through time the frozen paleozoic and mesozoic structures wrap around the craton building up the fast anisotropic direction pattern the present day sublithospheric flow induced by the plate motion is likely deflecting around its deep roots finally the present day tectonic regime appears to be controlled by the presence of the craton to the north

a reappraisal of the 1950 mw 6 9 mondy earthquake siberia and its relationship to the strain pattern at the south western end of the baikal rift zone the precise nature of the transition between the present day compressional tectonics in central mongolia and extensional deformation in the central baikal rift has still to be determined for that purpose we have built a comprehensive earthquake focal mechanism data base for the mongolia southern siberia area from which we map the variations of the stress field we focus our detailed investigations on the largest seismic event in the transition zone the 1950 mw 6 9 mondy earthquake for which several discordant focal mechanisms have been proposed using a new approach in source inversion we resolve the focal mechanism left lateral strike slip type on a steep south dipping fault and depth 14 3 km of the mondy earthquake with a satisfactory accuracy this seismological information combined with the geological observations allows us to decipher the connections between the 1950 mainshock the local stress tensor and the active faults which strongly suggest a partitioning of the deformation between two faults namely the mondy and ikhe ukghun faults

palaeostress reconstructions and geodynamics of the baikal region central asia part i palaeozoic and mesozoic pre rift evolution abstract this paper presents the first palaeostress results obtained for the basement of the baikal rift system in southern siberia russia large scale structural analysis and palaeostress reconstructions show that the palaeozoic mesozoic kinematic history precursor of the baikal cenozoic rifting is characterized by the succession of six regional palaeostress stages stress inversion of fault slip data and earthquake focal mechanisms is performed using an improved right dieder method followed by rotational optimization d delvaux tensor program the results are interpreted in the light of recent developments in the investigation of regional intraplate stress field and used as additional constraints for palaeogeodynamic reconstruction of central asia after the final palaeozoic closure of the palaeo asian ocean on the southern margin of the siberian platform the marginal suture with the sayan baikal caledonian belt was repeatedly and preferentially reactivated during the subsequent palaeozoic and mesozoic history this suture zone also controlled the opening of the baikal rift system in the cenozoic the progressive closure of the palaeo asian and mongol okhotsk oceans generated successive continental collisions which were recorded in the baikal area by brittle ductile and brittle deformations the first two palaeostress stages correspond to the successive collage of precambrian microcontinents and caledonian terranes along the southern margin of the siberian platform 1 late cambrian early ordovician n s compression and 2 late silurian early devonian nw se compression the next two stages are related to the remote effects of the complex evolution of the western palaeo asian ocean southwest of the siberian continent 3 late devonian early carboniferous n s compression recorded only in the altai region and 4 late carboniferous early permian e w compression recorded both in the altai and baikal regions the last stages are the consequences of the mongol okhotsk oceanic closure 5 late permian triassic nw se extension with development of cordilleran type metamorphic core complexes and volcanism along the active margin of the mongol okhotsk ocean 6 initial development of early middle jurassic 10 15 km wide molassic basins in trans baikal and large foredeeps along the southern margin of the siberian platform in probable extensional context but for which no palaeostress data are available and 7 final closure of the mongol okhotsk ocean in the cretaceous this last event results from the collision between the mongol china and the siberian plates and is evidenced by the inversion of the middle mesozoic basins and by late jurassic early cretaceous coal bearing sedimentation in trans baikal this long tectonic history yielded a highly heterogeneous basement in the baikal area precursor of the cenozoic rifting

the tadjena earthquake mw 5 0 of december 16 2006 in the cheliff region northern algeria waveform modelling regional stresses and relation with the boukadir fault the cheliff region has experienced some significant earthquakes in the last century 1937 1954 and 1980 the most destructive one is that of el asnam on october 10 1980 ms 7 3 io ix which destroyed the chlef city formerly el asnam and its surrounding villages on december 16 2006 a moderate earthquake mw 5 0 hit the cheliff region the maximum observed intensity io v msk scale was observed at abou el hassen benaria bouzghaia and tadjena no damages or human losses were recorded nevertheless minor cracks on walls of the old school at tadjena were observed the point source focal mechanism of the event was determined by inverting the waveforms of three regional broadband stations of the adsn algerian digital seismic network it corresponds to thrust reverse faulting with a strike slip component the stress tensor obtained by the inversion of the 15 focal mechanisms available in the cheliff region exhibits a well constrained compression axis 1 horizontal and trending n145 the nw dipping nodal plane indicating a ne sw thrust fault with a right lateral component strike dip rake 249 38 137 is more compatible with the regional stress tensor than the steep dipping nne ssw nodal plane showing reverse faulting with a left lateral component strike dip rake 15 65 60 accordingly the tadjena moderate size earthquake can be related to the boukadir active fault bordering the lower cheliff basin to the north a situation similar to that of the el asnam fault bordering the middle cheliff basin to the north

full aftershock sequence of the m w 6 9 2003 boumerdes earthquake algeria space time distribution local tomography and seismotectonic implications we present a detailed analysis of the aftershocks of the may 21 2003 boumerdes earthquake m w 6 9 recorded by 35 seismological stations and 2 obs deployed in the epicentral area this network recorded the aftershock activity for about 1 year and resulted in locating about 2500 events the five main aftershocks 4 7 m 5 8 display thrust faulting consistent with the main shock except for the second event m5 8 29 05 2003 which depicts a strike slip focal solution at the western tip of the rupture zone most aftershocks are clustered near the main rupture plane in the footwall or at the westernmost tip of the 2003 boumerdes rupture area many aftershocks last over the whole seismic crisis ahead north of the main rupture zone forming a diffuse low angle surface within the footwall where the coseismic static stress change is predicted to increase at the sw tip of the rupture short lived clusters locate at intersections of faults near the contact between the inner kabylia and outer tell zones the tomographic inversion depicts high velocity p and s wave anomalies coinciding with miocene magmatic intrusive bodies in the upper crust partially hidden by surrounding basins the area of the main shock is associated with a large low velocity body subdivided into sub domains including neogene basins on land and offshore our results support a rupture model strongly controlled by geological inhomogeneities and extending as ramp flat ramp systems upward favoring heterogeneous slip and segmentation in the fault plane with strong afterslip toward the surface the diffuse aftershock activity in the footwall evidences an inherited discontinuity at mid crustal depth that we interpret as the contact of kabylian and african tethyan continental crusts that were stacked during the upper miocene collision

a new statistical description of the spatial distribution of minerals in rocks we propose a new method to describe quantitatively rock textures with a special emphasis on the spatial distributions of minerals the method employs a statistical approach and examines probabilities for particular mineral pairs to occur for variable interpoint distances the probability is measured by counting the number of point pairs on digitized images of rock textures that are obtained with a computer aided digital image processor several problems in obtaining textural images and processing the data that were encountered in the actual procedures are reviewed the method is applied to two rock samples granite and contact metamorphic hornfels the method is useful in examining the extent of homogeneity and randomness of mineral distributions and spatial correlations among minerals of different kinds

stress tensor and fault plane solutions for a population of earthquakes an algorithm for the simultaneous estimation of the orientation and shape of the stress tensor and the individual fault plane solutions for a population of earthquakes is studied it corresponds to a synthesis of the methods used by brillinger et al 1980 to obtain focal mechanisms and by armijo and cisternas 1978 for stress tensor analysis in microtectonics the input data are the polarities of the p arrival and take off angles for the set of source station pairs the method distinguishes in general which one of the nodal planes corresponds to the fault and gives the direction of the slip the application to the aftershock sequence of the 1980 arudy earthquake western pyrenees shows that the observations may be explained by a single stress tensor producing a n32 e extension with a likelihood of 95 per cent

constraints on the viscosity of the continental crust and mantle from gps measurements and postseismic deformation models in western mongolia 1 we use gps measurements and models of postseismic deformation caused by seven m6 8 to 8 4 earthquakes that occurred in the past 100 years in mongolia to assess the viscosity of the lower crust and upper mantle we find an upper mantle viscosity between 1 1018 and 4 1018 pa s the presence of such a weak mantle is consistent with results from independent seismological and petrological studies that show an abnormally hot upper mantle beneath mongolia the viscosity of the lower crust is less well constrained but a weak lower crust 3 1016 to 2 1017 pa s is preferred by the data using our best fit upper mantle and lower crust viscosities we find that the postseismic effects of viscoelastic relaxation on present day horizontal gps velocities are small 2 mm yr 1 but still persist 100 years after the 1905 m8 4 bolnay earthquake this study shows that the gps velocity field in the baikal mongolia area can be modeled as the sum of 1 a rigid translation and rotation of the whole network 2 a 3 5 mm yr 1 simple shear velocity gradient between the siberian platform to the north and northern china to the south and 3 the contribution of postseismic deformation mostly caused by the 1905 bolnay tsetserleg sequence and by the smaller but more recent 1957 bogd earthquake

are post seismic effects of the m 8 4 bolnay earthquake 1905 july 23 still influencing gps velocities in the mongolia baikal area summary gps measurement campaigns in the mongolia baikal area show that 1 the baikal rift zone is currently opening at 4 5 mm yr 1 in a nw se direction and 2 the western part of the amurian north china block is moving eastward relative to eurasia at 5 7 mm yr 1 these results are consistent with recent geodetic studies in asia and indicate that crustal motions in mongolia and north china derived from geodetic measurements are significantly faster than those proposed by most deformation models of asia using a numerical model we test whether post seismic deformation caused by viscoelastic relaxation in the lower crust following the tsetserleg bolnay earthquake sequence mw 7 9 and 8 4 1905 july can explain this discrepancy we find that surface velocities at the gps sites presented here for the 1997 2000 time period can reach 4 mm yr 1 depending on the earthquake source parameters and the rheology used in the models using a model based on our best current knowledge of lithospheric structure and rheology in the mongolia baikal area we find that the contribution of post seismic effects to the gps velocities presented here is less than 2 mm yr 1 for the mongolian sites and less than 1 mm yr 1 for the baikal sites we therefore conclude that the post seismic effects of the mw 8 4 1905 bolnay earthquake cannot explain why the gps derived crustal motions in mongolia and the baikal rift zone are significantly larger than those proposed by deformation models of asia this discrepancy must therefore be sought in processes not accounted for in most of these deformation models such as the farfield contribution of the pacific subduction zones and or the effect of gravitational forces on intracontinental deformation

faulting within the eastern baikal rift as characterized by earthquake studies earthquake relocations focal mechanism determinations waveform modeling and stress analyses using focal mechanism information are used to examine the faulting processes within the western baikal rift 95 to 108 5 results of the study show that high angle dip 70 faulting is most likely to occur in the more youthful parts of the rift and is most likely to be associated with m 4 5 events like the eastern rift nearly all earthquakes occurred on faults dipping 30 suggesting that in no part of the rift is significant deformation occurring on low angle structures focal mechanism information does not indicate there is a sharp boundary to the western rift as observed in the eastern rift less normal faulting rakes 60 to 120 occurs in the western rift than the eastern rift waveform modeling of the two largest earthquakes 1950 mondy and 1959 srednebaikal in the western rift gives focal depths of 10 to 15 km the 1959 event appears to have occurred along the eastern boundary fault on lake baikal just to the north of proval bay a feature created a m 7 1 earthquake in 1862 the 1950 event may have occurred along the southern boundary fault of the tunka depression stress orientation information indicates a near horizontal nw se to wnw ese striking 3 in the eastern part of the western rift

focal mechanism determination and identification of the fault plane of earthquakes using only one or two near source seismic recordings a waveform inversion scheme was developed in order to explore the resolving power of one or two seismic recordings at short epicentral distance for the determination of focal mechanisms and the identification of the fault plane of earthquakes two key features are used to constrain the fault parameters with a reduced number of stations 1 a simple finite dimension source model and 2 the modeling of the complete displacement field including the near field waves the identification of the fault plane should be possible even with a single station as soon as the seismograms produced by the two nodal planes of a same focal mechanism are significantly different which is the general case when waveforms are controlled by source finiteness seven parameters including the strike dip rake and dislocation are explored with a grid search and the minima of the misfit error between the observed and calculated seismograms are mapped with such an approach it is possible to conclude about the uniqueness or nonuniqueness of the solutions the method is tested with three earthquakes of moderate to large size for which the fault plane is well established and for which strong motion records are available at maximum distances of a few tens of kilometers test events are the 1994 northridge m w 6 7 california the 1996 copala m w 7 3 mexico and the 1996 pinotepa nacional m w 5 4 mexico earthquakes in the case of inversions with two stations we find a unique solution or a group of similar solutions with a good estimation of the focal mechanism and the proper selection of the fault plane our results also show that in some cases a single station may be enough to recover the fault parameters the inversion scheme presented here may be systematically applied to future earthquakes especially to those recorded by few stations it should be particularly useful in the case of blind faults for which the fault plane may not be identified with the help of other data

historical earthquakes studies in eastern siberia state of the art and plans for future abstract many problems in investigating historical seismicity of east siberia remain unsolved a list of these problems may refer particularly to the quality and reliability of data sources completeness of parametric earthquake catalogues and precision and transparency of estimates for the main parameters of historical earthquakes the main purpose of this paper is to highlight the current status of the studies of historical seismicity in eastern siberia as well as analysis of existing macroseismic and parametric earthquake catalogues we also made an attempt to identify the main shortcomings of existing catalogues and to clarify the reasons for their appearance in the light of the history of seismic observations in eastern siberia contentious issues in the catalogues of earthquakes are considered by the example of three strong historical earthquakes important for assessing seismic hazard in the region in particular it was found that due to technical error the parameters of large m 7 7 earthquakes of 1742 were transferred from the regional catalogue to the worldwide database with incorrect epicenter coordinates the way some stereotypes concerning active tectonics influences on the localization of the epicenter is shown by the example of a strong 6 4 earthquake of 1814 effect of insufficient use of the primary data source on completeness of earthquake catalogues is illustrated by the example of a strong m 7 0 event of 1859 analysis of the state of the art of historical earthquakes studies in eastern siberia allows us to propose the following activities in the near future 1 database compilation including initial descriptions of macroseismic effects with reference to their place and time of occurrence 2 parameterization of the maximum possible magnitude unlimited number of historical earthquakes on the basis of all the data available 3 compilation of an improved version of the parametric historical earthquake catalogue for east siberia with detailed consideration of each event and distinct logic schemes for data interpretation thus we can make the conclusion regarding the necessity of a large scale revision in historical earthquakes catalogues for the area of study

morphotectonic analysis and 10 be dating of the kyngarga river terraces southwestern flank of the baikal rift system south siberia the formation of the baikal rift system basins is controlled by active faults separating each basin from the adjacent horsts the kinematics of these faults is mainly explored through investigation of complex sequences of the fault intersecting river terraces that record both tectonic and climatic events this study focuses on the northern margin of the major tunka basin that develops south west of lake baikal the development of the basin is controlled by the segmented tunka fault we performed a detailed mapping of the kyngarga river terraces the best preserved terraces staircase in baikal rift system at their intersection with the tunka fault in order to decipher the chronology of seismic events and the slip rates along that segment of the fault key terraces were dated using in situ produced cosmogenic 10be we demonstrate that the formation of the terrace staircase occurred entirely during mis1 mis2 the obtained data allowed us to estimate the rate of incision at different stages of the terrace staircase formation and the relationship between the vertical and horizontal slip rates along this sub latitudinal segment of the tunka fault making respectively 0 8 and 1 12 mm yr 1 over the past 12 5 ka analysis of the paleoseismology and paleoclimate data together with terrace dating provided the possibility to estimate the influence of tectonic and climatic factors on the terrace formation our proposed model of the kyngarga river terrace development shows that the incisions into terraces t3 and t6 were induced by the abrupt climatic warming episodes gi 1 and gi 2 respectively whereas terraces t5 t4 and t2 were abandoned due to the vertical tectonic displacement along the tunka fault caused by coseismic ruptures

recurrent holocene movement on the susitna glacier thrust fault the structure that initiated the mw 7 9 denali fault earthquake central alaska abstract we conducted a trench investigation and analyzed pre and postearthquake topography to determine the timing and size of prehistoric surface ruptures on the susitna glacier fault sgf the thrust fault that initiated the 2002 m w 7 9 denali fault earthquake sequence in central alaska in two of our three hand excavated trenches we found clear evidence for a single pre 2002 earthquake penultimate earthquake pe and determined an age of 2210 420 cal b p 2 for this event we used structure from motion software to create a pre 2002 earthquake digital surface model dsm from 1 62 800 scale aerial photography taken in 1980 and compared this dsm with postearthquake 5 m pixel interferometric synthetic aperature radar topography taken in 2010 topographic profiles measured from the pre earthquake dsm show features that we interpret as fault and fold scarps these landforms were about the same size as those formed in 2002 so we infer that the pe was similar in size to the initial m w 7 2 subevent of the 2002 sequence a recurrence interval of 2270 yrs and dip slip of 4 8 m yield a single interval slip rate of 1 8 mm yr the lack of evidence for pre pe deformation indicates probable episodic clustering behavior on the sgf that may be related to strain migration among other similarly oriented thrust faults that together accommodate shortening south of the denali fault we suspect that slip partitioned thrust triggered earthquakes may be a common occurrence on the denali fault system but documenting the frequency of such events will be very difficult given the lack of long term paleoseismic records the number of potential thrust earthquake sources and the pervasive glacial erosion in the region electronic supplement oxcal code and figures of topographic profiles across fault scarps reactivated during the 2002 denali fault earthquake oxcal models of published age constraints on tephra exposed at the wetfan trench site and map showing locations and data used to measure near surface dips of susanna glacier fault in the vicinity of the wetfan trench site

lithosphere rheology and active tectonics in mongolia relations between earthquake source parameters gravity and gps measurements in this paper we use observations of earthquake source parameters and gravity to investigate the mechanical properties and the active faulting of the lithosphere in mongolia well determined earthquake centroid depths including 10 from inversions of p and sh waveforms that are presented here for the first time show that the seismogenic thickness ts within mongolia itself is less than 20 km however to both the east in parts of the lake baikal rift system and the west adjacent to the junggar basin and kazakhstan platform the seismogenic thickness is considerably greater and includes essentially the whole crust from the admittance between the free air gravity and the topography and also from profiles across a flexural foreland basin we determine the effective elastic thickness te in central mongolia to be 30 km in both mongolia and its surroundings te is comparable with ts and where it is well determined te ts these data are consistent with the view that the strength of the continental lithosphere resides in its seismogenic part which in mongolia is the upper crust but to both the east and west appears to be the whole crust the earthquake source parameters also allow us to ask how the active faulting in mongolia accommodates the velocity field revealed by gps measurements it is likely that the entire mongolian altay range in the west rotates counter clockwise relative to stable asia and is responsible for the distributed e w left lateral shear seen further east in central mongolia the admittance observations show no evidence at the present day for convective mantle support or a hotspot responsible for the elevated region of the hangay dome in central mongolia even though the geochemical data from nodules in late cenozoic basalts and seismic tomography studies suggest elevated temperatures at shallow depths 125 km and probably thinned lithosphere

shape size spatial distribution and composition of garnet crystals in highly deformed gneiss of the otter lake area quebec and a model for garnet crystallization garnet biotite sillimanite gneiss 700 c 7 kbar of the otter lake area in the western grenville province canadian shield occurs as granitic gneiss group 4 that forms a large part of the otter complex and as widely distributed more heterogenous metasedimentary gneiss group 2 in one sample of group 4 gneiss qtz25 pl34 kfs28 bt10 grt2 5 sil1 the true diameter determined by serial grinding of subhedral garnet crystals ranges from 0 2 to 3 0 mm with a mode at 1 0 mm nearest neighbour measurements in this sample and in surfaces of nine additional samples all 5 garnet confirm that garnet crystals are distributed mainly at random slight clustering was detected in two samples in one sample of group 4 gneiss microprobe analyses on sections through crystal centres obtained by serial slicing reveal that small crystals and margins to large crystals contain more fe and mn and less mg than the broad central regions of large crystals based on these and previous results together with theoretical considerations a crystallization model is proposed in which i garnet was produced by the continuous reaction ms bt qtz grt kfs h2o ii nucleation occurred by the random selection of randomly distributed ms bt qtz triple junctions iii the rate of linear growth remained constant and iv as temperature increased the rate of nucleation first increased slowly then remained nearly constant and finally declined within population compositional homogenization was followed on cooling by local fe mg mn exchange with biotite

wavelet transform a future of rock fabric analysis abstract although twenty years ago fabric was defined as the complete spatial and geometrical configuration of all those components that make up a deformed rock fabric was mainly synonymous with lattice preferred orientation very little attention has been paid to the multi scale geometrical and spatial relationships of the rock components fabric quantification in terms of size shape orientation and location at all scales is now performed in two dimensions using anisotropic wavelets as a first example the wavelets are applied to the famous colour plate of sander and the results compared to his axial distribution analysis applied to the k feldspars of a rock section from the sidobre granite pluton montagne noire france the wavelet analysis shows i alignment of grains resulting from mechanical interactions between grains and shows that shearing occurred within the crystalline frame ii preferred grain orientation the classical grain shape fabric parallel to the overall mineral lineation and iii small tensional domains elongate perpendicular to the lineation infilled by the residual melt just before total crystallisation attesting to the stretching nature of the mineral lineation the future of rock fabric analysis will come from new steps in understanding the processes acting during fabric development along with a further development of wavelet analysis using high resolution three dimensional fabric data

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

seismicity structure and rheology of the lithosphere in the lake baikal region this paper combines observations of seismicity gravity topography and thermal and velocity structures to investigate the rheological properties of the lithosphere in the lake baikal region we examine the seismogenic thickness ts using 25 earthquakes of mw 5 1 7 1 whose full source parameters have been determined by inversion of teleseismic waveforms 13 of which are presented here for the first time these 25 events plus six others mw 5 0 5 8 whose depths are well constrained show that moderate earthquakes occur at depths up to 30 km in the northeast baikal rift based on the teleseismic waveform modelling results and published relocations of microearthquakes using regional networks we conclude that the mantle is not a significant source of seismicity in the baikal region using the admittance between free air gravity and topography we estimate the effective elastic thickness te in the region to be between 5 and 20 km nowhere do the data require that te ts consistent with the simple interpretation that the long term strength of the lithosphere resides in its seismogenic layer a weak mantle in the baikal region can be explained by its high temperature which we estimate by combining local geotherm estimates with the regional upper mantle velocity structure obtained from fundamental and higher mode surface waves geotherms are fitted to pressure and temperature estimates from mantle nodules at four sites both within and outside the siberian shield in order to constrain the temperatures at the moho we estimated crustal thicknesses using teleseismic receiver functions moho temperatures are estimated to exceed 550 c beneath the siberian shield and are higher in the more recently deformed mountain belts to the south based on a reassessment of oceanic geotherms and seismicity it seems likely therefore that the mantle in the baikal region is too hot to be a source of long term strength this is consistent with the recent suggestion that the distribution of mantle seismicity in both the oceans and the continents is dependent on temperature alone finally we note that results from s wave tomography studies combined with the observed locations of rift related earthquakes lead us to suspect that the frequently published position of the edge to the siberian shield at the surface provides a poor description of that same boundary at depth

the beni ilmane algeria seismic sequence of may 2010 seismic sources and stress tensor calculations a moderate earthquake with a moment magnitude of mw 5 5 struck the sub bibanique region of eastern algeria on 14 may 2010 killing three people injuring hundreds of others and causing moderate damages in the epicentral area mainly in the villages of beni ilmane and samma the focal mechanism of the seismic source for the first shock obtained by near field waveform modelling exhibits left lateral strike slip faulting with the first nodal plane oriented at n345 and right lateral strike slip faulting with the second nodal plane oriented at n254 a second earthquake that struck the region on 16 may 2010 with a moment magnitude of mw 5 1 was located 9 km sw of the first earthquake the focal mechanism obtained by waveform modelling showed reverse faulting with nodal planes oriented ne sw n25 and n250 a third earthquake that struck the region on 23 may 2010 with a moment magnitude of mw 5 2 was located 7 km s of the first shock the obtained focal mechanism showed a left lateral strike slip plane oriented at n12 and a right lateral strike slip plane oriented at n257 field investigations combined with geological and seismotectonic analyses indicate that the three earthquake shocks were generated by activity on three distinct faults the second and third shocks were generated on faults oriented wsw ene and nne ssw respectively the regional stress tensor calculated in the region gives an orientation of n340 for the maximum compressive stress direction 1 which is close to the horizontal with a stress shape factor indicating either a compressional or a strike slip regime