focal mechanisms of three earthquakes in finland and their relation to surface faults abstract focal mechanisms for three recent earthquakes in finland are determined using p wave polarities together with sv p and sh p phase amplitude ratios the events occurred on may 11 2000 in toivakka central finland ml 2 4 on september 15 2000 in kuusamo northeastern finland ml 3 5 and on may 2 2001 in kolari western finnish lapland ml 2 9 in order to obtain reliable estimates of the source parameters one dimensional crust and upper mantle velocity models are derived for the epicenter areas from deep seismic sounding results the starting models are modified by one dimensional ray tracing using the earthquake observations the events are relocated by employing p and s phase arrival times from the nearest seismic stations and the final velocity models synthetic waveforms calculated with the reflectivity method are used to further constrain and verify the source and structural parameters the toivakka earthquake indicates thrust or reverse faulting mechanism at a depth of 5 km after comparison with aeromagnetic and topographic data we suggest the eastward dipping nodal plane 358 42 was the fault plane the best fitting fault plane solution of the kolari earthquake suggests pure thrust faulting at a depth of 5 km the nodal plane striking 035 30 correlates well with surface observations of the postglacial possibly listric fault systems in the source area the kuusamo earthquake focal depth 14 km has a normal faulting mechanism with the nodal planes trending 133 47 or 284 47 preference is given to the sw dipping nodal plane as it seems to coincide with topographic and magnetic lineament directions that have been active after the last ice age the three earthquakes have occurred in old precambrian faults and shear zones which have been reactivated the reactivated faults are favourably oriented in the local stress field

velocity field in asia inferred from quaternary fault slip rates and global positioning system observations we perform a joint inversion of quaternary strain rates and 238 global positioning system gps velocities in asia for a self consistent velocity field the reference frames for all geodetic velocity observations are determined in our inversion procedure india in moves relative to eurasia eu about a pole of rotation at 29 78 n 7 51 e 0 353 myr 1 which yields a velocity along the himalaya within india that is 73 76 of the magnitude of the in eu nuvel 1a velocity and a vector azimuth that is 8 10 clockwise of nuvel 1a in eu vector azimuth relative to eurasia south china moves at 9 11 mm yr in the direction 110 120 with a pole position 64 84 n 156 74 e 0 12 myr 1 amurian block motion has a pole position in a similar location but at a slower rate 64 61 n 158 23 e 0 077 myr 1 and most of the amurian eurasia motion is accommodated by extension across lake baikal tarim basin moves relative to eurasia about a pole of rotation at 39 24 n 98 2 e 0 539 myr 1 and 16 18 mm yr of shortening is accommodated across the west central tien shan there is distributed e w extension throughout both southern and north central tibet within southern tibet between the longitudes of 77 e to 92 e the deformation field accommodates 16 19 mm yr of e w extension we compare predicted seismic moment rates with those observed in this century in asia total observed seismic moment rates within the entire area of central and east asia 2 2 107 km2 in this century are 2 26 0 7 1020 n m yr 1 as compared with a predicted total rate of 2 03 0 066 1020 n m yr 1 comparisons between observed and predicted moment rates within 42 subregions reflect the generally unstable process of inferring long term seismic moment rates from a catalog of limited duration 94 years an observation period of 10 000 years would be required to reduce uncertainties in observed seismic moment rate to the same size as the uncertainties in model tectonic moment rates inferred from the joint inversion of gps and quaternary rates of strain we show that in general a better correlation with model tectonic moment rate is inferred from the seismicity catalog by considering the numbers of earthquakes above a cutoff magnitude mb 5 0 for the period january 1 1965 to january 1 1999

a comparison of strain rates and seismicity for fennoscandia depth dependency of deformation from glacial isostatic adjustment summary we investigate the influence of the glacial isostatic adjustment gia on the deformation at the surface and at seismogenic depths in fennoscandia the surface strain rate field derived from geodetic data is controlled by gia which causes nw se extension of up to 4 10 9 yr 1 in most of mainland fennoscandia surrounded by regions of radial shortening towards the centre of uplift the seismic deformation field derived from a new compilation of focal mechanisms shows consistent nw se compression on the norwegian continental margin and a tendency towards tension in mainland fennoscandia the seismic moment rate is at least two orders of magnitude smaller than the geodetic moment rate we propose that the low level of seismicity and the tendency towards tensional focal mechanisms in mainland fennoscandia may be explained by the destructive interference of the regional stress from ridge push with the flexural stress due to gia

postglacial seismicity offshore mid norway with emphasis on spatio temporal magnitudal variations abstract norway and its continental margin in spite of being located in an intraplate environment is of great interest from a neotectonic perspective influence on neotectonics stems both from the fact that this is a recently deglaciated region in which significant rebound is still occurring and from its proximity both to a rifted continental margin and to failed rift zones passive continental margins and rift related structures are the most seismically active ones within stable continental regions with a number of well documented earthquakes of magnitude 7 and higher as observed around the globe indeed the disparity in seismicity between such regions and plate boundary regions is greater in terms of return times than in terms of maximum magnitude a recent detailed assessment of neotectonics in fennoscandia has shown strong bedrock related evidence for several large magnitude m 7 earthquakes in the northern areas lapland while few if any similar observations have been made farther south a possible explanation for this is that postglacial earthquakes have been occurring on hidden thrusts in the south in fact several major structures have recently been mapped and shown to have capabilities to accommodate m 6 5 7 earthquakes without breaking the surface given that the largest historically known earthquake in fennoscandia is only of the order of m 5 8 it is likely therefore that the potentially largest magnitude in this region may be well above this

the 2003 earthquake swarm in anjalankoski south eastern finland abstract during may 2003 a swarm of 16 earthquakes ml 0 6 2 1 occurred at anjalankoski south eastern finland the activity lasted for three weeks but additional two events were observed at the same location in october 2004 a comparison of the waveforms indicated that the source mechanisms and the hypocentres of the events were nearly identical a relative earthquake location method was applied to better define the geometry of the cluster and to identify the fault plane associated with the earthquakes the relocated earthquakes aligned along an ene wsw trending zone with a lateral extent of about 1 0 km by 0 8 km the relative location and the waveform modelling of depth sensitive surface wave rg and s to p converted body wave sp phases indicated that the events were unusually shallow most likely occurring within the first 2 km of the surface the revised historical earthquake data confirm that shallow swarm type seismicity is characteristic to the area the focal mechanism obtained as a composite solution of the five strongest events corresponds to dip slip motion along a nearly vertical fault plane strike 250 dip 80 rake 90 the dip and strike of this nodal plane as well as the relocated hypocentres coincide with an internal intrusion boundary of the vyborg rapakivi batholith the events occur under a compressive local stress field which is explained by large gravitational potential energy differences and ridge push forces pore pressure changes caused by intrusion of ground water and or radon gas into the fracture zones are suggested to govern the swarm type earthquake activity

research on an automatic roadway formation method in deep mining areas by roof cutting with high strength bolt grouting abstract the excavation of deep mining roadways with traditional mining methods leads to various issues such as the occurrence of large deformations the waste of coal resources complex conditions and the high cost of advanced support measures in this study we examined the roadway damage mechanism of the traditional gob side entry driving method with coal pillars using the suncun coal mine the deepest mine in china as an engineering case study a method for the automatic formation of roadways in deep mining areas by roof cutting with high strength bolt grouting was proposed and several quantitative evaluation indicators namely the roadway deformation control rate anchor cable strength utilization ratio and hydraulic prop strength utilization ratio were established the impacts of controlling the deformation of the surrounding rock were comparatively analysed in consideration of numerous factors such as the mechanical parameters of the surrounding rock roof cutting height roof cutting angle grouting anchor cable length and hydraulic prop spacing on this basis the proposed method was applied in the field the results showed that the automatically formed roadway cross section exhibited decreased convergence deformation moreover the roof deformation was effectively controlled and the passive hydraulic prop supports could be effectively replaced with the active support of grouting anchor cables verifying the effect of the proposed method

seismic activity inferred crustal stresses and seismotectonics in the rana region northern norway abstract the seismotectonic significance of the rana region is known both from the fact that this was the location of the largest known earthquake in fennoscandia in recent times the m s 5 8 6 2 earthquake of august 31 1819 and from its relatively high constant seismic activity also in the 20th century in order to study this region in more detail a local seismic network has been in operation there since july 1997 as part of the neonor neotectonics in norway project the network was primarily designed to detect possible activity on the basmoen fault which runs 50 km subparallel to the rana fjord and which shows signs of likely post glacial activity the results have revealed a quite complex spatio temporal distribution of seismic activity and has also shown no activity on the basmoen fault itself during the first 18 months of operation july 1997 january 1999 the network has detected 373 locatable seismic events of which 267 were local earthquakes most of these earthquakes occurred in five groups in the western parts of the network all five groups had similar nnw esw trends in epicenter locations and all have shallow foci 2 12 km similar to what has also been found earlier for other concentrated earthquake zones in northern norway and the magnitude range is between m l 0 1 and 2 8 earthquake focal mechanism solutions within the network reveal a predominance for normal faulting with the tensional stress axis perpendicular do the coastline implying an unusual coast parallel orientation of the principal horizontal compressive stress the earthquakes occur in a region of maximum post glacial uplift gradients which supports deglaciation flexure as a viable explanation for these earthquakes a certain influence from more local factors however tied in general to crustal in homogeneities cannot be ruled out

investigation on support pattern of a coal mine roadway within soft rocks a case study abstract supporting coal mine roadway within soft rocks is a typical challenge in underground mining practices as the most widely used support structure rock bolt system has been successfully used to support coal mine roadways in various complex geological and geotechnical conditions including roadway in extremely weak rock masses roadways 1000 m below ground open off cut roadways with large section and roadways along the edges of mined out areas with thin pillars or even no pillars however the effectiveness and applicability of rock bolt system for the reinforcement of soft rock masses has not yet been established in this paper we present a case study of rock bolt system as used for ground reinforcement of longwall entries within soft rock masses the study site was the tailgate of the longwall panel 5 2s at the hongmiao coal mine in the pingzhuang coal mining district in china a typical soft rock coal mine of the region since traditional rock bolt system failed to maintain the stability of the tailgate the effectiveness of rock bolt systems for this application remained doubtful the reasons for the failure of the rock bolt system were first examined a discrete element method simulation was then performed to better understand the mechanism of rock bolts in supporting soft rocks an improved rock bolt system was finally proposed that was used to support the tailgate the field monitor showed that the improved rock bolt system successfully suppressed cracking and dilation of the tailgate this case study is useful in enhancing engineering applications of rock bolts to support longwall entries excavated in soft rock masses

a hypothesis for delayed dynamic earthquake triggering 1 it s uncertain whether more near field earthquakes are triggered by static or dynamic stress changes this ratio matters because static earthquake interactions are increasingly incorporated into probabilistic forecasts recent studies were unable to demonstrate all predictions from the static stress change hypothesis particularly seismicity rate reductions however current dynamic stress change hypotheses do not explain delayed earthquake triggering and omori s law here i show numerically that if seismic waves can alter some frictional contacts in neighboring fault zones then dynamic triggering might cause delayed triggering and an omori law response the hypothesis depends on faults following a rate state friction law and on seismic waves changing the mean critical slip distance dc at nucleation zones

seismotectonics of the norwegian continental margin the norwegian continental margin and surrounding areas are seismically less active than some other passive margins worldwide indicating a potential earthquake deficit the adjacent oceanic crust is mostly aseismic except for parts of the lofoten and norway basins which have experienced rapid deposition of glacial sediments the excess load has enhanced the local stress field and in turn the seismic activity the marginal highs along the continent ocean transition and the part of the more and voring basins which experienced crustal extension prior to the early tertiary breakup are practically aseismic this region is also underlain by high velocity lower crust emplaced during breakup suggesting crustal strengthening which also may increase the return periods for the largest events farther landward a spatial correlation of seismic activity and the glacial sediment wedge suggests a causal relationship expressed through preferential rejuvenation of late jurassic early cretaceous faults the locally high seismic activity in the coastal region occurs in areas where the continental crust is relatively thick 25 30 km but still thinner than in the shield area farther east 45 50 km although stress relations are complex we suggest that increased stress due to appreciable postglacial rebound gradients in the coastal region may be a contributing factor while the stress field along the margin complies in general with the ridge push force we infer that regional and local stress enhancement factors are not only present in this region but also necessary for explaining the earthquake activity the relative importance of local stress sources is supported by several cases of 90 stress rotations relative to the ridge push direction the superposition of regional and local stress together with the existence of weakness zones and faults yields potentials for earthquakes primarily through structural reactivation

contemporary horizontal velocity and strain rate fields of the pacific australian plate boundary zone through new zealand we have inverted velocity solutions from nine geodetic networks distributed across new zealand to derive present day continuous horizontal velocity and strain rate fields at the earth s surface throughout the country the nine networks contain a total of 362 global positioning system gps stations that have been observed at least twice and at least a year apart between 1991 and 1998 the model velocity field is expanded as bicubic spline interpolation functions defined within a curvilinear grid that covers the country and extends into the assumed rigid australian and pacific plates to west and east the inversion jointly minimizes the magnitudes of fitted strain rates and the misfit to the observed velocity data the spline technique allows high spatial resolution of strain rate variations especially in regions with spatially dense gps data expansion of the model velocity field on the surface of a sphere allows arbitrarily large areas to be studied previously known aspects of new zealand plate boundary deformation are highlighted with improved resolution including back arc extension in the taupo volcanic zone rotation of the hikurangi forearc away from this zone in the north island and a band of high shear strain rate under the southern alps to the southeast of the alpine fault our results reveal several new features including a region of enhanced shear straining apparently associated with strike slip faults in the southern north island and a band of contractional straining subparallel and well east of the alpine fault that is similar to features found in numerical and sandbox models of continental collision

earthquake swarm in steigen northern norway an unusual example of intraplate seismicity on the first of january 1992 unusual earthquake activity started in steigen northern norway by 31 december 1992 a total of 207 events had been recorded in several pulses among these several events with magnitudes larger than 3 0 mc were also felt by the people the epicentral distribution of these events seems to suggest that they all are concentrated in a small region approximately 10 km in diameter in the brennvika bay 67 8 n 14 9 e between leinesfjorden in the north and nordfolda in the south the distribution of events in time is characteristic of a swarm in which no dear evidence of a mainshock aftershock sequence was observed macroseismic intensity surveys as well as synthetic modelling indicate shallow focal depths in the range 5 8 km based on a composite focal mechanism indicating an oblique slip fault striking ne with a normal component dipping nw combined with an observed ne trend in the epicentres and the focal depths these events correlate with a previously proposed fault zone along nordfolda the ne trend has been dominant in the area throughout geological time starting from the caledonian orogeny to the post caledonian basin developments as well as the post glacial and neotectonic structural features at present the deep seated structural anomaly underneath the lofoten ridge seems to be the major factor controlling the structural trends in the area the activity along the nordfolda fault zone could be related to this large scale structure although the causes of the stresses that would create the seismic activity are not very clear as there are several possible stress generating mechanisms involved such as post glacial uplift of the land masses the ridge push effect from mohn s ridge and vertical stresses generated by the sediment loading in the adjacent basins

the 7 may 2001 induced seismic event in the ekofisk oil field north sea 1 a moderate size seismic event on 7 may 2001 was strongly felt on platforms in the ekofisk oil field in the southern north sea but did not cause damage to platforms or wells we combined near and far field observations to develop a consistent source model and to determine whether the event was induced seismic data placed the epicenter inside the ekofisk field and suggested a shallow source depth based on spectral and moment tensor analysis gps data from the ekofisk platforms displayed permanent vertical and horizontal movement due to the event a topographic bulge in the sea bottom revealed by differential bathymetry data and overpressure in the overburden in the northeastern part of the field detected only after the event had been caused by unintentional water injection that started in 1999 the injection pressure and rate were sufficient to raise the overburden pressure gauge and compaction data ruled out that the event occurred at reservoir level which was further supported by unaffected production rates and absence of well failure we therefore conclude that the event occurred in the overburden at less than 3 km depth initially this appeared unlikely on account of very low shear strength of the overburden clay rich shale and mud rocks the seismic event was induced owing to stress changes caused by water injection the event possibly initiated on the northern flank of the field near the water injector and may have involved flexure of the overburden into the depression bowl in the rest of the field moment tensor analysis is consistent with a pure double couple source we suggest that slip occurred on the near horizontal rather than along the near vertical nodal plane stress drop was low and owing to the low overburden shear strength the event released less energy than a typical stress drop event with similar source dimensions

earthquake strain rates and instantaneous relative motions within central and eastern asia summary we use the spatial distribution of moment tensors of earthquakes in this century to estimate the velocity field in asia within a eurasian reference frame in a least squares inversion strain rates on the surface of the earth are matched with continuous spline functions in order to recover the velocity gradient tensor associated with the seismic moment release in asia earthquakes account for 40 60 per cent of the expected motion of india relative to eurasia with the missing component of strain rate equivalent to about 20 mm yr 1 of n s shortening between siberia and india in this solution south china rotates counterclockwise and moves eastwards relative to siberia using rigid plate constraints we next investigate the characteristics of the complete horizontal strain field in asia that accommodates plate motions our strain rate solutions are analogous to the response of a newtonian thin viscous sheet in which the rate of work done by the straining medium in accommodating the velocity boundary conditions is a minimum in these solutions the euler pole for india relative to eurasia is constrained nuvel 1a demets et al 1994 but in the process of fitting the vlbi velocity at shanghai china ward 1994 heki et al 1995 the euler pole for south china is determined in the inversion a solution that both fits the velocity at shanghai china and yields a strain rate field consistent with the earthquake mechanisms is one where the south china block has a motion relative to siberia described by the pole at 51 n 131 e 0 3 deg myr 1 comparison of the complete strain field that accommodates plate motion with the seismic strains indicates that earthquake moment release rates in this century within mongolia are about a factor of 4 larger than the long term rate within gansu ningxia the earthquake moment rates have been about a factor of 2 higher than the long term rate the strike slip faulting within mongolia gansu ningxia western sichuan and yunnan is possibly a direct result of velocity boundary conditions imposed on the south china block by forces unrelated to continental collision of india and eurasia such as forces associated with subduction along the margins of south eastern asia verification of this requires a better understanding of the role of pre existing zones of weakness within the asian continental lithosphere

gps crustal strain postglacial rebound and seismic hazard in eastern north america the saint lawrence valley example 1 we present global positioning system gps measurements that constrain the amplitude pattern and origin of crustal deformation in the saint lawrence valley quebec one of the most seismically active regions of eastern north america the gps network shows coherent southeastward motion of 0 6 0 2 mm yr 1 relative to north america and uplift of 2 6 0 4 mm yr 1 network average horizontal strain rates are mostly ese wnw shortening at 1 7 1 0 10 9 yr 1 the shortening rate across the charlevoix seismic zone is about twice as big as the regional average these measurements are consistent with both postglacial rebound pgr models and the deformation style indicated by earthquake focal mechanisms although the gps data do not discriminate between various models of crustal deformation they provide important constraints on large earthquake recurrence assuming that the gps strain estimates are representative of seismic moment release they constrain the maximum magnitude of truncated gutenberg richter recurrence statistics in the charlevoix seismic zone to mx 7 8 0 6 one m 7 earthquake per 400 1300 years the remarkable agreement between the gps strain rates seismic catalogue statistics and pgr predictions suggests that in charlevoix most of the pgr driven crustal strain may be released by large m 7 earthquakes in the rest of the saint lawrence valley pgr strain rates are significantly larger than seismic strain rates suggesting either that pgr deformation remains mostly elastic or that large events are more frequent than indicated by small earthquake statistics i e characteristic earthquakes

failure mechanism of surrounding rock with high stress and confined concrete support system abstract surrounding rock control is a big challenge in roadway with high stress in deep underground engineering to address this issue zhaolou coal mine a typical kilometer deep well is taken as engineering background to monitor and analyze the original support scheme the analysis shows that the following main reasons lead to the support failure in roadway with high stress in deep underground coal mine roadway deformation is large and lasts longer with a large extent of damage all anchor bolts are in severely damaged surrounding rock zone without reliable adhesive basis and u shaped steel arch unevenly contacts with surrounding rock without sufficient bearing capacity with summary of support failure mechanisms on site a concept of high strength and integrity support is put forward a support system with square steel confined concrete sqcc is developed and a full scale in door comparative test is conducted on its core component sqcc arch and also on the conventional u29 arch the research shows the bent and damaged legs of u29 arch result in dramatic reduction of bearing capacity of arch however the sqcc arch with similar steel content has a bearing capacity of 2 15 times of that of u29 arch and still has a higher post bearing capacity even after the arch is deformed dramatically quantitative evaluation index is established such as vault displacement control rate and bolt strength utilization rate comparative analysis is made on surrounding rock control mechanism and the mechanical properties of support components under the influence from the four factors arch strength geostress lateral pressure coefficient and surrounding rock mechanical parameters and good control effect on surrounding rock of sqcc support is verified comparative tests are conducted on site the monitoring results show the roadway surrounding rock deformation on the test section of sqcc support is only 21 2 of that on test section of u29 arch support and no yield and damage occurs on the test section of sqcc support therefore the sqcc support system is proved to be effective on surrounding rock control

can deglaciation trigger earthquakes in n america a spherical self gravitating viscoelastic earth model is used to calculate the spatial and temporal evolution of the glacially induced lithospheric stress and fault stability in north america the predicted onset time of a pulse of earthquake activities the mode of failure and the magnitude of instability are investigated for three sites with different distance from the former ice margin it is found that glacial unloading is able to trigger paleo earthquakes within the ice margin near charlevoix 47 5 n 70 1 w and in wabash valley 38 5 n 87 w outside the ice margin however rebound stress decays away from the former ice margin thus glacial unloading is unlikely to have triggered the large m8 earthquakes in new madrid 36 6 n 89 5 w

fennoscandian earthquakes whole crustal rupturing related to postglacial rebound local and regional earthquake locations provide seismic evidence that large shield earthquakes have occurred in northern fennoscandia these paleoearthquakes with fault lengths of up to 160 kilometers and average displacements of up to 15 meters were triggered by nonisostatic compressive stresses caused by the removal of the ice at the end of the last deglaciation the fennoscandian faults were probably formed by single events that ruptured through most of the crust the largest event moment magnitude mw 8 2 was larger than other known stable continent earthquakes outside failed rifts or extended crust

principal oscillation pattern analysis of the 30 to 60 day oscillation in the tropical troposphere the principal oscillation pattern technique is used to derive an index of the 30 to 60 day oscillation in the tropical troposphere in the 200 mb equatorial velocity potential field one dominant pair of pops is found its properties compare very well with the properties of the oscillation identified in previous studies in particular a good correlation between the time evolution of the pop coefficients and area averaged outgoing long wave radiation orl is found the pops are derived from a 2 year subinterval of the whole 5 year data set this leaves independent data for subsequent verification the patterns and their characteristic numbers are almost unchanged if the whole data set is analysed also the analysis is insensitive to changes of the analysis area if the analysis is limited to 90 longitude equatorial sectors the signal is also identified and its patterns are consistent with the patterns derived from the full data set interestingly the signal is best defined in the eastern hemisphere the pops may be used to derive associated correlation patterns of other quantities in winter and summer separately the path of the oscillation has a marked annual cycle in northern winter it migrates from the indian ocean across northern australia into the region of the south pacific convergence zone spcz and in northern summer it moves from the indian ocean across south asia along the intertropical convergence zone itcz to south america the pop coefficient may be seen as a bivariate index of the state phase and strength of the 30 to 60 day oscillation since the pop technique incorporates a prediction equation for the phase of the pop coefficients the pop model allows for the prediction of the complex amplitude of the oscillation in a sequence of forecast experiments of which about two thirds used independent data the pop forecasts were found to be useful in about half of all cases for lead times of several days the correlation and rms skills were calculated for the pop forecast and for persistence the pop forecast appears to be considerably better with respect to both measures the correlation skill scores 60 after 7 days the pop forecast is most skillful in northern winter and if strong signals are present with minima of velocity potential in the eastern hemisphere

to what extent is the present seismicity of norway driven by post glacial rebound abstract the seismicity of scandinavia is low to intermediate in intensity and with magnitudes that rarely exceed 5 5 even so the seismicity is characterized by a great diversity in space and time related to the fact that its driving forces or sources of stress are multiple and also diverse in nature the dominant driving forces range from plate related such as ridge push through regional to local ones such as topography all however are somehow related to lateral inhomogeneities in lithospheric structure whereas it was earlier assumed that the post glacial uplift was the main cause for the seismicity of scandinavia we now conclude that the uplift may at most be playing a minor role along the coastal stretch of northern norway there are still some indications that the seismicity which is often shallow normal faulting and swarm related may be related to the still remaining glacial isostatic adjustment the flexuring that is needed to explain such behaviour could however also be related to erosion and sedimentation processes it will take more work to separate these potential driving forces

an estimate of the stress tensor in sweden using earthquake focal mechanisms abstract an estimate of the state of stress in sweden is made by inversion of the fault plane solutions of naturally occurring earthquakes it is shown that the stress state in southern sweden is significantly different from that in northern sweden in southern sweden the principal compression is in a roughly nw se direction similar to that prevailing in northwest europe as a whole this stress direction is is consistent with the stresses expected on the basis of motions of the major tectonic plates in northern sweden however there is no strongly dominant stress direction this latter observation is consistent with a situation in which processes other than first order plate motions are important the most likely explanation in this case is the effect of the deglaciation of fennoscandia which is producing rates of rebound as high as 9 mm year in northern sweden

dating of late quaternary faulting in northern sweden fault scarps interpreted as post or late glacial in age occur in northern sweden and adjacent parts of finland and norway in the lansjarv area in northern sweden attempts have been made to date fault displacement relative to the glacial and postglacial stratigraphy by trenching across fault scarps it is shown that the faulting occurred soon after the local deglaciation some 9000 years ago with no signs of movements since the faulting appears to have been associated with violent earthquakes because landslides and soil deformation interpreted to be seismically induced and dating from the same period as the faulting are frequently found in the area