displacement of surface monuments vertical motion several measurements of vertical ground motion at pinon flat observatory california indicate the overall weakness and instability of the earth s weathered surface with respect to the underlying rock cumulative long period motions of order 0 5 mm per year dominate these records though smaller elastic deformations caused by precipitation loading atmospheric loading and tidal strains are evident at higher frequencies all of these help to characterize the near surface material the long period records suggest that near surface weathering is the dominant influence on monument motion at least at this site on crystalline rock in a semi arid environment rainfall loading gives an average vertical modulus of 2 6 gpa for the material in the uppermost 26 m of the ground compared with 88 gpa for granite under moderate confining stress atmospheric loading gives similar results but indicates the ground is permeable to airflow at periods longer than a few hours earth tide records show poisson s ratio to be 0 09 in contrast to the normative range of 0 2 0 25 establishing that horizontal strains couple only weakly into vertical ones so that vertical strains near the surface are a poor measure of areal strain the form of the ground surface displacement power spectrum indicates that analyses of geodetic surveys would be improved with the inclusion of a monument positioning error budget that increases with time because of ground instability and the generally small rate of crustal tectonic motions deeply emplaced monuments will be needed for observational programs designed to detect short term changes in crustal deformation over baselengths of order 10 km and less

difference information criterion for the analysis of a seismotectonic influence on a radon time series at the ksm site japan summary this research investigates how a difference information criterion combined with a function of observed seismotectonic activity can be used to analyse the influence of seismotectonic activity on the variation in a radon time series observed at the ksm site izu peninsula japan the difference information criterion is used to identify significant variance in the radon time series the seismotectonic activity is represented by an aggregated univariate function of seismic observations a flexible definition of the function is proposed enabling an analysis of various geometrical and energetic relations between the seismotectonic activity and the monitoring site the results are compared with previous results obtained at the same site with a different approach identifying 12 post seismic signals and one pre seismic signal to 23 earthquakes with mw 6 0 and within 1000 km hypocentral distance during the period considered the combination of a difference signal criterion and the introduced aggregation function of seismic observations is more sensitive for identifying seismotectonic related variance in the radon time series than the use of confidence intervals as proposed in former works

restoring proterozoic deformation within the superior craton abstract geometrical patterns of paleoproterozoic dyke swarms in the superior craton north america and paleomagnetic studies of those dykes both indicate relative motion across the kapuskasing structural zone ksz that divides the craton into eastern and western sectors previous work has optimized the amount of vertical axis rotation necessary to bring the dyke trends and paleomagnetic remanence declinations into alignment yet such calculations are not kinematically viable in a plate tectonic framework here we subdivide the superior craton into two internally rigid subplates and calculate euler parameters that optimally group the paleomagnetic remanence data from six dyke swarms with ages between 2470 and 2070 ma our dataset includes 59 sites from the matachewan dykes for which directional results are reported for the first time our preferred restoration of the eastern superior subprovince relative to the western subprovince is around an euler pole at 51 n 85 w with a rotation angle of 14 ccw although we do not include data from the ksz in our rigid subplate calculations we can align its dyke strikes by applying a 23 ccw distributed shear that preserves line length of all dykes pinned to the western margin our model predicts approximately 90 km of dextral transpressional displacement at ca 1900 ma about half of which is accommodated by distributed strain within the ksz and the other half by oblique lateral thrusting with ne vergence across the ivanhoe lake shear zone we produce a combined apparent polar wander path for the early paleoproterozoic superior craton that incorporates data from both western and eastern subplates and that can be rotated to either of the subplates reference frames for the purposes of archean paleoproterozoic supercraton reconstructions

regional gravity setting of the sudbury structure in the vicinity of sudbury ontario canada the boundary between the southern and superior tectonic provinces is overlain by the elliptical sudbury structure on the basis of gravity modeling genesis of the sudbury structure has been attributed to either a magmatic origin having a dense hidden differentiate zone or a meteorite impact origin there being no dense hidden mass the difference between the two gravity models centers on the problem of regional residual separation as shown by numerous previous studies any such separation of components is nonunique this becomes especially problematic when as in sudbury a portion of the near surface geology has a similar orientation and dimension to more deep seated sources in this paper several numerical methods upward continuation downward continuation wavelength filtering trend surface analysis for determining the regional component of the gravity field associated with the sudbury structure have been applied and evaluated of the numerical methods used the upward and downward continuation operators provided the most insight into the deep structural controls of the sudbury basin our preferred interpretation of the regional gravity field invokes a two component structure underlying the southern half of the sudbury structure is a laterally continuous gravity anomaly that is probably associated with a zone of uplifted huronian volcanics the gravity anomaly under the northern portion of the sudbury structure has a more restricted spatial extent the close association between the northern limit of the gravity anomaly and the surface outcrop of the levack gneiss suggests the source of this anomaly is probably a slab of dense levack gneiss this interpretation favors a meteorite impact origin for the sudbury structure

tectonic contraction across los angeles after removal of groundwater pumping effects after the 1987 whittier narrows and 1994 northridge earthquakes revealed that blind thrust faults represent a significant threat to metropolitan los angeles a network of 250 continuously recording global positioning system gps stations was deployed to monitor displacements associated with deep slip on both blind and surface faults here we augment this gps data with interferometric synthetic aperture radar imagery to take into account the deformation associated with groundwater pumping and strike slip faulting after removing these non tectonic signals we are left with 4 4 mm yr 1 of uniaxial contraction across the los angeles basin oriented n 36 degrees e perpendicular to the major strike slip faults in the area this indicates that the contraction is primarily accommodated on thrust faults rather than on the northeast trending strike slip faults we have found that widespread groundwater and oil pumping obscures and in some cases mimics the tectonic signals expected from the blind thrust faults in the 40 km long santa ana basin groundwater withdrawal and re injection produces 12 mm yr 1 of long term subsidence accompanied by an unprecedented seasonal oscillation of 55 mm in the vertical direction and 7 mm horizontally

displacement of surface monuments horizontal motion measurements of tectonic deformation depend on both accurate instrumentation and adequate coupling of the apparatus to the earth s crust existing techniques capable of resolving the signals of interest strain rates of 10 n yr are mainly observatory based the limitation in the baselength of these instruments 1 km results in a requirement that the reference monuments be exceptionally stable 10 tzm yr however records from pition flat observatory california show that the actual horizontal displacements for massive near surface monuments eraplaced in competent weathered granite are of the order of 50 tzm yr the low noise level of the strain measurements at this site indicates that this magnitude of monument displacement is abnormally small until high accuracy geodetic techniques are developed sophisticated monuments or monument monitoring devices will be necessary to record faithfully continuous crustal deformation

the mcewan lake fault gravity evidence for a new structural element of the kapuskasing zone the chapleau block the largest uplifted crustal block within the kapuskasing zone continues after sinistral offset of about 20 km for a further 60 km to the southwest of chapleau this newly discovered extension referred to as the pineal lake block terminates to the west in a north south trending west verging thrust named the mcewan lake fault new gravity data suggest that the fault has a vertical displacement of at least 5 km a dip of about 25 e and a length of at least 30 km it is not known whether the fault crosscuts the kapuskasing structure in which case it may represent a younger thrusting event or represents a southerly extension of the saganash lake fault that bounds the northwestern side of the kapuskasing zone in the chapleau area

tectonic influences on the morphometry of the sudbury impact structure implications for terrestrial cratering and modeling impact structures developed on active terrestrial planets earth and venus are susceptible to pre impact tectonic influences on their formation this means that we cannot expect them to conform to ideal cratering models which are commonly based on the response of a homogeneous target devoid of pre existing flaws in the case of the 1 85 ga sudbury impact structure of ontario canada considerable influence has been exerted on modification stage processes by late archean to early proterozoic basement faults two trends are dominant 1 the nnw striking onaping fault system which is parallel to the 2 47 ga matachewan dyke swarm and 2 the ene striking murray fault system which acted as a major paleoproterozoic suture zone that contributed to the development of the huronian sedimentary basin between 2 45 2 2 ga sudbury has also been affected by syn to post impact regional deformation and metamorphism the 1 9 1 8 ga penokean orogeny which involved nnw directed reverse faulting uplift and transpression at mainly greenschist facies grade and the 1 16 0 99 ga grenville orogeny which overprinted the se sector of the impact structure to yield a polydeformed upper amphibolite facies terrain the pre syn and post impact tectonics of the region have rendered the sudbury structure a complicated feature careful reconstruction is required before its original morphometry can be established this is likely to be true for many impact structures developed on active terrestrial planets based on extensive field work combined with remote sensing and geophysical data four ring systems have been identified at sudbury the inner three rings broadly correlate with pseudotachylyte friction melt rich fault systems the first ring has a diameter of 90 km and defines what is interpreted to be the remains of the central uplift the second ring delimits the collapsed transient cavity diameter at 130 km and broadly corresponds to the original melt sheet diameter the third ring has a diameter of 180 km the fourth ring defines the suggested apparent crater diameter at 260 km this approximates the final rim diameter given that erosion in the north range is 6 km and the ring faults are steeply dipping impact damage beyond ring 4 may occur but has not yet been identified in the field one or more rings within the central uplift ring 1 may also exist this form and concentric structure indicates that sudbury is a peak ring or more probably a multi ring basin these parameters provide the foundation for modeling the formation of thisrelatively large terrestrial impact structure

synopsis of paleomagnetic studies in the kapuskasing structural zone this paper summarizes results from paleomagnetic studies sponsored by lithoprobe on the kapuskasing structural zone ksz data from archean rocks outside the ksz indicate that the wawa subprovince has not been significantly rotated or translated 5 relative to the abitibi subprovince results from the granulites and amphibolites indicate that the ksz underwent several kilometres of uplift at ca 2 51 ga and then 10 5 west northwest tilt with several kilometres of further uplift between 2 04 and 1 88 ga from thrust faulting on the ivanhoe lake fault zone localized chemical remagnetization occurred at 1 1 ga along the west side of the shawmere anorthosite paleomagnetic data from the 2 45 ga matachewan diabase dike swarm indicate that it was emplaced within one reversed to normal polarity interval of less than 5 ma their polarity pattern indicates major north trending faults with several kilometres of dip slip displacement their remanence confirms that the superior province was deformed around th

crustal displacements due to continental water loading the effects of long wavelength 100 km seasonal variability in continental water storage on vertical crustal motions are assessed the modeled vertical displace ments arm have root mean square rms values for 1994 1998 as large as 8 mm with ranges up to 30 mm and are predominantly annual in character regional strains are on the order of 20 nanostrain for tilt and 5 nanostrain for hori zontal deformation we compare arm with observed global positioning system gps heights aro which include ad justments to remove estimated effects of atmospheric pres sure and annual tidal and non tidal ocean loading for 147 globally distributed sites when the aro time series are ad justed by arm their variances are reduced on average by an amount equal to the variance of the arm of the aro time series exhibiting a strong annual signal more than half

paleomagnetism and u pb geochronology of the 2 17 ga biscotasing dyke swarm ontario canada evidence for vertical axis crustal rotation across the kapuskasing zone u pb dates on baddeleyite yield ages of 2167 8 2 2 and 2171 6 1 2 ma on two northeast trending dykes west of the kapuskasing zone in ontario canada these ages identify the dykes as belonging to the biscotasing dyke swarm east of the kapuskasing zone which was previously dated at 2166 7 1 4 ma by u pb on baddeleyite and zircon the new dates show that the biscotasing swarm was emplaced over an area of at least 300 000 km2 much larger than hitherto suspected and in a geologically short period of time of about 5 million years a comparison of paleomagnetic data from biscotasing and 2 45 ga matachewan dykes on either side of the kapuskasing zone suggests that the western half of the superior province has rotated about 10 20 counterclockwise relative to the eastern half across the kapuskasing zone this movement may have been accompanied by rifting farther north which ultimately led to the paleoproterozoic embayment underlying hudson bay that gives the superior province its characteristic butter

a new global mode of earth deformation seasonal cycle detected we have detected a global mode of earth deformation that is predicted by theory precise positioning of global positioning system sites distributed worldwide reveals that during february to march the northern hemisphere compresses and the southern hemisphere expands such that sites near the north pole move downward by 3 0 millimeters and sites near the equator are pulled northward by 1 5 millimeters the opposite pattern of deformation occurs during august to september we identify this pattern as the degree one spherical harmonic response of an elastic earth to increased winter loading of soil moisture snow cover and atmosphere data inversion shows the load moment s trajectory as a great circle traversing the continents peaking at 6 9 1022 kilogram meters near the north pole in winter indicating interhemispheric mass exchange of 1 0 1016 0 2 1016 kilograms

constraints on the nature of the kapuskasing structural zone from the study of proterozoic dyke swarms petrochemical paleomagnetic and structural studies on early proterozoic dyke swarms show that the rocks of the kapuskasing structural zone ksz central superior province were upthrust about 10 15 km along the ivanhoe lake fault after intrusion of 2 04 ga kapuskasing dykes this uplift was part of a more widespread deformation in flanking terranes that involved sinistral motion along north north northwest trending faults dextral displacement along east northeast northeast trending faults and a distortion of the 2 45 ga matachewan swarm to the west and northwest of the ivanhoe lake fault the most spectacular demonstration that the ksz is largely a product of proterozoic deformation is that matachewan dykes change their magnetic polarity on crossing the zone a consequence of remanence acquisition at deep crustal levels being delayed until after a reversal of the earth s magnetic field and prior to uplift of the dykes matachewan and kapuskasing dykes within the amphibolite to granulite grade rocks o

structural correlation within the kapuskasing uplift comparison of progressive deformation and metamorphic history within and between the tectonic domains of the kapuskasing uplift indicates significant variation in age and style of deformation across this large segment of the central superior province multiple stages of tonalite and granitoid intrusion melt generation polyphase diachronous deformation and likely rapid deep burial of supracrustal rocks collectively produced the complex character of this example of archean mid to deep crust at least four archean deformation phases are recognized although not all are of regional extent dated structural chronology suggests that the locus of the earliest recorded deformations migrated to deeper crustal levels with time pre 2680 ma deformation local d d within high level tonalites is correlated with deformation in the michipicoten supracrustal belt the apparent earliest deformational fabrics at deeper crustal levels in the granulite terrane of the kapuskasing structural zone occurred between 2660 and 2640 ma archean third and fourth phase deformation phases 2667 to 2629 ma are present at mid crustal and deeper levels and deform post 2667 ma metaconglomerate these resulted in large scale folding and subhorizontal ductile shear zones which seem to represent an important transitional zone that separated a passive upper crust from continued ductile strain at deeper levels subsequent uplift of the high grade rocks was accomplished in multiple stages initiated prior to 2 45 ga and likely culminated around 1 9 ga although continued movement occurred as late as 1 14 ga the ivanhoe lake fault zone along which much of the uplift must have occurred exhibits some evidence of ductile deep thrust related fabrics but most of the observed structures are brittle to brittle ductile and steeply inclined a broad zone of pervasive cataclasis and brittle ductile shear zones is a characteristic feature of the fault zone throughout its length and both dextral and sinistral offset are locally present clear ground evidence for major transcurrent or thrust displacements however has not been recognized

rb sr biotite and whole rock data from the kapuskasing uplift and their bearing on the cooling and exhumation history rb sr isotopic ratios were measured on biotite and whole rocks from a suite of 21 granitoid rocks from the southern kapuskasing uplift results of 18 of the whole rock analyses fall on an isochron with an age of 2 677 0 057 ga and sri 0 70080 biotite model ages range from 2 50 to 1 93 ga in a general spatial relationship of decreasing age with depth in the structural section as calibrated with the igneous hornblende barometer for tonalitic rocks and garnet pyroxene barometers for granulites near the michipicoten belt in the west biotite ages of 2 ga reflect disturbances also recorded by paleomagnetic and whole rock rb sr systems to the east in a 70 km long northwest southeast transect toward the ivanhoe lake fault zone ages decrease from 2 50 to 1 95 ga in a southern transect ages are in the range 2 30 2 38 ga to within 15 km of the fault reflecting consistent erosion levels corresponding to 0 53 mpa but decrease to 1 93 ga to the east in concert with paleopressures in the 0 7 1 0 gpa ra

heterogeneity and seismic scattering in exploration environments abstract seismic scattering and the corresponding reduction in signal to noise ratio is a severe limitation to seismic exploration in crystalline environments in this paper we summarize recent elastic numerical modeling of scattering regimes and discuss the implications for seismic exploration in shallow hardrock environments the resulting synthetic seismograms range from relatively transparent to highly reflective depending on the ratio of seismic wavelength to heterogeneity scale length we note that the archean canadian shield is characterized by large scale lengths typical for crystalline environments which translates to moderately reflective seismic sections exhibiting scattering features that are coherent over large distances in contrast the highly fractured footwall of the sudbury impact structure in the canadian shield translates to a medium with small to moderate scale lengths resulting in seismic sections that can in places be highly reflective or relatively transparent from the perspective of mineral exploration in sudbury we find that the possible detection of massive sulfide targets is dependent not only on the shape and size of the deposit but on the scattering nature of the background as well with information about the petrophysical properties and the distribution of heterogeneity within an exploration area acquisition parameters such as source frequencies and minimum receiver spacing can be adjusted in order to survey within the scattering regime that will produce the least amount of noise

thermoelastic strain in a half space covered by unconsolidated material an algorithm to predict crustal thermoelastic strain from observed local atmospheric temperature is given and applied to a 24 month crustal strain record of one test strainmeter site located near bouquet reservoir in southern california we use a crustal model that consists of an elastically decoupled layer overlying a uniform elastic half space and a thermal source that is given by a stationary temperature wave whose wavelength is related to local topography and or lateral material heterogeneity the decoupled layer delays attenuates and low pass filters the source temperature field the thermoelastic strain in the underlying half space resulting from the temperature variations at the base of the decoupled layer is calculated using the berger 1975 solution for thermoelastic strain in a uniform half space applying our model to the test data we obtain a good fit between predicted and observed strains if we filter the surface thermal signal through a 63 cm thick decoupled layer much of the remaining strain variations clearly correspond to other environmental sources reservoir loading and rainfall our analysis suggests that the horizontal thermoelastic strain is inversely proportional to the wavelength of local topography and or lateral material heterogeneity thus the horizontal thermoelastic strain will be greater in areas of local topography and or lateral material heterogeneity and smaller in more homogeneous and flat areas an upper layer of loose material natural or artificial acts as a thermoelastic strain insulator burial of strainmeters in places where such a layer exists can reduce the thermoelastic strain noise considerably even for shallow strainmeter emplacements

geology of the giant sudbury polymetallic mining camp ontario canada a new 1 100 000 scale compilation bedrock geology map provided with this issue presents a geologic synthesis of canada s most prolific mining camp the world class sudbury structure with total past production and current reserves of over 1 7 billion tonnes of ni cu co pt pd au ag ore lydon 2007 the polymetallic ore is hosted within one of earth s largest preserved impact craters the new map of the ni cu pge sudbury district after ames et al 2005 is included in a pocket at the back of this issue map 1 and is linked to mineral deposit commodity and geochronology data in tables 1 and 2 of this paper view this table table 1 list of mineral deposits and occurrences of the sudbury map area map 1 view this table table 2 u pb isotope data across the map area since 1891 six compilation maps of the geology of sudbury have been published bell 1891 collins 1937 cooke 1946 card 1969 dressler 1984 ames et al 2005 fig 1 some of the ni cu pge mines have operated for over a century whereas new ore deposits discovered as recently as 2004 are already in production or are in the process of being developed i e advanced prospects in the last 15 years sudbury has been the training ground for 60 postgraduate geoscience students in north america fig 1 from 1903 to 1990 only 23 graduate theses were completed on sudbury related topics eight of them in the 1970s after the discovery of shatter cones dietz 1964 fig 1 number of graduate theses of north american geoscientists trained on sudbury geology per decade showing the minor peak in training after the discovery of shatter cones and the recent education boom with over 50 geoscience graduate theses completed since 1990 the dashed lines represent the regional geologic maps of the sudbury area

petrogenesis of the early proterozoic matachewan dyke swarm canada and implications for magma emplacement and subsequent deformation major minor and rare earth element analyses of fine grained marginal material from 249 dykes of the matachewan giant radiating swarm show that the range in compositions cannot be produced by any simple fractionation model instead a two stage process is required whereby melts were modified by both fractionation and assimilation of lower crustal material before rising and ponding at shallower crustal levels 15 20 km maximum where a combination of fractional crystallization plagioclase phenocryst formation and periodic melt replenishment took place these shallow crustal chambers acted as feeders for the numerous dykes one hypothesis compatible with these observations involves an extensive rising plume that would provide heterogeneous melts over a large area accompanied by stresses that could produce a radial pattern of dykes in a search for indications of lateral magma flow a comparison of longitudinal variations in composition along four sample traverses across the western subswarm showed no t

satellite interferometric observations of displacements associated with seasonal groundwater in the los angeles basin 1 the newport inglewood fault zone nifz displays interferometric synthetic aperture radar sar phase features along most of its length having amplitudes of up to 60 mm however interpretation in terms of right lateral shallow slip along the fault fails to match the range of geologic estimates of slip recently bawden et al 2001 proposed that these phase features as well as a broader deformation pattern in the los angeles basin are due to vertical motion related to annual variations in the elevation of the water table we confirm this hypothesis through the analysis of a longer span of data consisting of 26 sar images collected by the ers 1 and ers 2 spacecraft between june 1992 and june 2000 moreover we use continuous gps measurements from 1995 to the present to establish the amplitude and phase of the vertical deformation the los angeles basin becomes most inflated one quarter of the way through the year which is consistent with water table measurements as well as with the end of the rainy season when the aquifer should be at a maximum the spatial pattern of the amplitude of the annual signal derived from continuous gps measurements is consistent with the shape of the interferometric fringes gps sites both near the nifz and in a 20 by 40 km zone within the basin also show significant n s annual variations that may be related to the differential expansion across the fault since these horizontal signals have peak to trough amplitudes of 6 mm they mask the smaller tectonic signals and need to be taken into account when interpreting gps time series of site position moreover since the groundwater signal appears to have a long term vertical trend which varies in sign depending on location it will be difficult to distinguish interseismic tectonic slip along the nifz and within the affected areas in the basin

the sudbury structure a circular impact crater 1 petrological geochemical and structural evidence supports genesis of the sudbury structure by a meteorite impact the sudbury igneous complex sic represents the ponded melt sheet the primary morphology and size of the sudbury crater remains the subject of extensive discussion a model is presented explaining the transformation of an originally circular crater to the current elliptical form processes involved in the geometrical transformation include a volume reduction through melt sheet crystallization and repeated expulsion of melt into the surrounding footwall b translation and segmentation on multiple southeast dipping thrust surfaces and c relative displacement on steep north northwest trending faults paleomagnetic geochemical and structural evidence supports the concept of periodic melt expulsions into the footwall seismic potential field and paleomagnetic surveys provide evidence in support of multiple thrust surfaces after over 9 km of subsequent erosion only a small volumetric portion of the original sic remains although complete vertical sections through the melt sheet have been preserved none of the crater wall has been preserved thus the contacts between the sic and the footwall on the north and south ranges are interpreted as uplifted crater floor margins

aliased tidal signatures in continuous gps height time series 1 coordinate time series are often derived from continuous gps data processed as discrete 24 hour solutions under this regimen residual semi diurnal and diurnal crustal tide signatures are under sampled resulting in aliased periodic signals in the coordinate time series a secondary aliasing effect well known from satellite altimetry studies but generally ignored in gps analysis arises from the repeat period of the satellite orbits being longer than the nyquist period of the semi diurnal and diurnal tidal signatures this paper derives the theoretical periods for these two aliasing effects for the principal semi diurnal and diurnal tidal constituents the presence of both types of aliased signals in gps time series is then demonstrated using simulated gps data and also considered for time series derived from real gps data it is shown that the beating of the two aliased signals invariably results in spurious signatures in the time series with semi annual and annual periods

geoscience impact a synthesis of studies of the sudbury structure geophysical probing results are synthesized into a three dimensional framework necessary for understanding the genesis of the sudbury structure based primarily on seismic reflection results centred on the sudbury igneous complex remnants of crustal melting from a catastrophic meteorite impact are superimposed on the juxtaposition of mid crustal rocks exhumed during the archean against deformed paleoproterozoic sedimentary rocks sedimentation metamorphism deformation and metasomatic overprints are all part of the post impact history of sudbury and tend to dominate the geophysical response of the structure pre impact deformation although certainly preserved in some aspects of sudbury geology is not clearly expressed in the geophysical data nor are any elements of impact induced deformation geophysical views of the sudbury igneous complex are thus somewhat biased in representing mostly the post impact but pre grenvillian history of the region with the exception of igneous events establishing th

seasonal variations of seismic velocities in the san jacinto fault area observed with ambient seismic noise s u m m a r y we observe seasonal seismic wave speed changes dv v in the san jacinto fault area and investigate several likely source mechanisms velocity variations are obtained from analysis of 6 yr data of vertical component seismic noise recorded by 10 surface and six borehole stations we study the interrelation between dv v records frequency dependent seismic noise properties and nearby environmental data of wind speed rain ground water level barometric pressure and atmospheric temperature the results indicate peak to peak seasonal velocity variations of 0 2 per cent in the 0 5 2 hz frequency range likely associated with genuine changes of rock properties rather than changes in the noise field phase measurements between dv v and the various environmental data imply that the dominant source mechanism in the arid study area is thermoelastic strain induced by atmospheric temperature variations the other considered environmental effects produce secondary variations that are superimposed on the thermal based changes more detailed work with longer data on the response of rocks to various known external loadings can help tracking the evolving stress and effective rheology at depth

paleomagnetism u pb geochronology and geochemistry of lac esprit and other dyke swarms james bay area quebec and implications for paleoproterozoic deformation of the superior province an extensive set of north to northwest trending diabase dykes termed the lac esprit swarm is identified in the superior province east of james bay based on geological mapping and a distinctive paleomagnetic pole 61 7 n 169 1 e dm 7 7 dp 5 5 the lac esprit swarm yields a u pb baddeleyite age of 2069 1 ma similar to that of the 2076 5 4 ma fort frances swarm of the western superior province their paleomagnetic declinations differ by 23 12 after correction to a common reference locality the difference is likely due mainly to counterclockwise rotation about a vertical axis of the fort frances area relative to the lac esprit area differential rotation of 10 20 has been proposed more locally across the kapuskasing structural zone separating the eastern and western superior province in earlier paleomagnetic studies of ca 2450 ma matachewan and 2170 ma biscotasing dyke swarms thus relative rotation may have involved the entire eastern and western superior province perhaps in response

onaping fault system age constraints on deformation of the kapuskasing structural zone and units underlying the sudbury structure the deformation of the matachewan dyke swarm of the superior province which includes a 60 km right lateral offset and moderate uplift localized along the kapuskasing structural zone represents an

effect of annual signals on geodetic velocity 1 our analysis of global positioning system gps site coordinates in a global reference frame shows annual variation with typical amplitudes of 2 mm for horizontal and 4 mm for vertical with some sites at twice these amplitudes power spectrum analysis confirms that gps time series also contain significant power at annual harmonic frequencies with spectral indices 1 2 which indicates the presence of repeating signals van dam et al 2001 showed that a major annual component is induced by hydrological and atmospheric loading unless accounted for we show that annual signals can significantly bias estimation of site velocities intended for high accuracy purposes such as plate tectonics and reference frames for such applications annual and semiannual sinusoidal signals should be estimated simultaneously with site velocity and initial position we have developed a model to calculate the level of bias in published velocities that do not account for annual signals simultaneous estimation might not be necessary beyond 4 5 years as the velocity bias rapidly becomes negligible minimum velocity bias is theoretically predicted at integer plus half years as confirmed by tests with real data below 2 5 years the velocity bias can become unacceptably large and simultaneous estimation does not necessarily improve velocity estimates which rapidly become unstable due to correlated parameters we recommend that 2 5 years be adopted as a standard minimum data span for velocity solutions intended for tectonic interpretation or reference frame production and that we be skeptical of geophysical interpretations of velocities derived using shorter data spans

southern california permanent gps geodetic array spatial filtering of daily positions for estimating coseismic and postseismic displacements induced by the 1992 landers earthquake the june 28 1992 m w 7 3 landers california earthquake was the first earthquake to be surveyed by a continuously operating global positioning system gps array the coordinate time series of seven sites are evaluated for station displacements during an interval of 100 days centered on the day of the earthquake we employ a new spatial filtering technique that removes common mode errors from the coordinate time series this approach provides precise estimates of site specific displacements compared to the cumbersome method of analyzing baselines between pairs of stations all sites indicate significant coseismic horizontal displacements of 5 65 mm with uncertainties of 1 2 mm horizontal displacements are in general agreement with elastic dislocation models in particular for sites closer to the epicenter vertical displacements range from 13 to 7 mm with uncertainties of 2 4 mm the observed vertical displacements in all cases show 5 10 mm more subsidence than expected from geodetic and seismic geologic models significant postseismic horizontal displacements totaling 6 2 mm 10 20 of the coseismic displacement are detected at the three sites closest to the epicenter these displacements are modeled as a short term exponential relaxation with a decay time of 22 10 days superimposed on a longer term linear interseismic trend scaling the observed coseismic and postseismic displacements at one of the sites with the distance to the epicenter provides a measure of site strain which agrees well with the direction and magnitude determined from more precise laser strain meter data the time series do not show any detectable preseismic displacements

observation and modeling of thermoelastic strain in southern california integrated gps network daily position time series 1 we suggest that strain in the elastic part of the earth s crust induced by surface temperature variations is a significant contributor to the seasonal variations observed in the spatially filtered daily position time series of southern california integrated gps network scign stations we compute the predicted thermoelastic strain from the observed local atmospheric temperature record assuming an elastically decoupled layer over a uniform elastic half space and compare the seasonal variations in thermoelastic strain to the horizontal gps position time series we consider three regions palmdale 29 palms and idyllwild each with one temperature station and three to six gps stations the temperature time series is used to compute thermoelastic strain at each station on the basis of its relative location in the temperature field for each region we assume a wavelength for the temperature field that is related to the local topography the depth of the decoupled layer is inferred from the phase delay between the temperature record and the gps time series the relative amplitude of strain variation at each gps station calculated to be on the order of 0 1 strain is related to the relative location of that station in the temperature field the goodness of fit between model and data is evaluated from the relative amplitudes of the seasonal signals as well as the appropriateness of the chosen temperature field wavelength and decoupled layer depth the analysis shows a good fit between the predicted strains and the gps time series this suggests that the model captures the key first order ingredients that determine the thermoelastic strain in a given area the results can be used to improve the signal noise ratio in gps data