a comparison of eastern north american seismic strain rates to glacial rebound strain rates glacial rebound strain rates computed using a simple laurentide glacial loading model are of the order of 10 9 per year within the region of glaciation and extending several hundred kilometers beyond the horizontal strain rates receive approximately equal contributions from horizontal and vertical velocities a consequence of the spherical geometry adopted for the earth model in the eastern united states and southeastern canada the computed strain rates are 1 3 orders of magnitude greater than an estimate of the average seismic strain rate anderson 1986 and 1 order of magnitude greater than predicted erosional strain rates the predicted glacial rebound strain rates are not in general oriented in such a way as to augment the observed state of deviatoric stress possibly explaining why the seismic strain rates are much smaller than the glacial rebound strain rates an exception to this may be seismically active regions in the st lawrence valley

crustal thickness and vp vs variations in the grenville orogen ontario canada from analysis of teleseismic receiver functions abstract we have developed a simple semblance weighted stacking technique to estimate crustal thickness and average vp vs ratio using teleseismic receiver functions we have applied our method to data from 32 broadband seismograph stations that cover a 700 400 km2 region of the grenville orogen a 1 2 0 98 ga himalayan scale collisional belt in eastern north america our seismograph network partly overlaps with l ithoprobe and other crustal refraction surveys in 8 out of 9 cases where a crustal refraction profile passes within 30 km of a seismograph station the two independent crustal thickness estimates agree to within 7 our regional crustal thickness model constructed using both teleseismic and refraction observations ranges between 34 0 and 52 4 km crustal thickness trends show a strong correlation with geological belts but do not correlate with surface topography and are far in excess of relief required to maintain local isostatic equilibrium the thickest crust 52 4 1 7 km was found at a station located within the 1 1 ga mid continent failed rift the central gneiss belt which contains rocks exhumed from deep levels of the crust is characterized by vp vs ranging from 1 78 to 1 85 in other parts of the grenville orogen vp vs is found to be generally less than 1 80 the thinnest crust 34 5 37 0 km occurs northeast of the 0 7 ga ottawa bonnechere graben and correlates with areas of high intraplate seismicity

the lithoprobe abitibi grenville transect two billion years of crust formation and recycling in the precambrian shield of canada we summarize the results of lithoprobe studies in the neoarchean southeastern superior province and the mesoproterozoic grenville province in the southeastern precambrian shield of canada through two composite cross sections based on seismic reflection data which define dramatically different styles of crust formation and tectonic accretion in the neoarchean and mesoproterozoic in the neoarchean the structures at the surface are steep with discontinuous and flatter structures at depth much of the crust appears to be juvenile and the predominant process of crustal growth is inferred to have been subduction accretion of primitive crust in a prograding arc system in the mesoproterozoic surface structures are shallow and the seismic character of the crust is continuous over the entire cross section archean parautochthonous rocks and reworked archean crust comprise a very significant proportion of the preserved crust in the mesoproterozoic and provided the backstop to the grenvillian orogeny result

tectonic implications of seismic activity recorded by the northern ontario seismograph network the northern ontario seismograph network which has operated under the canadian nuclear fuel waste management program since 1982 has provided valuable data to supplement those recorded by the canadian national networks on earthquake activity rockburst activity the distribution of regional seismic velocities and the contemporary stress field in northern ontario the combined networks recorded the largest earthquake known in northwestern ontario m 3 9 near sioux lookout on february 11 1984 and many smaller earthquakes in northeastern ontario focal mechanism solutions of these and older events showed high horizontal stress and thrust faulting to be the dominant features of the contemporary tectonics of northern ontario the zone of more intense earthquake activity in western quebec appeared to extend northwestward into the kapuskasing area of northeastern ontario where an area of persistent microearthquake activity had been identified by a seismograph station near kapuskasing controlled explosions o

anatomy of a small intraplate earthquake a dissection of its rupture characteristics using regional data summary the magnitude mblg 5 0 mont laurier earthquake of 1990 october 19 in quebec canada was one of the largest to have occurred in eastern north america during the past decade high frequency ground motions recorded on regional network instruments exceeded values anticipated for an event of its size by a factor of 3 a commonly favoured explanation for the discrepancy is that the source was a rare high stress event in this paper detailed fault slip models are derived to fit waveform and spectral characteristics of the regional data the results establish that the effective rupture stress was normal about 100 bars that the fault rupture developed asymmetrically and that the average slip time for points inside the rupture area approx 0 1 s was significantly less than that associated with the standard brune 1970 source spectral model the rupture area developed in at least four distinct episodes each extending the previously ruptured area taken together with similar results for the mblg 6 5 saguenay earthquake of 1988 november the results indicate that a widely used assumption in hazard analyses that earthquake spectra are adequately represented by the standard brune spectral model is unreliable for the interpretation and prediction of strong ground motion

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

intraplate seismicity of a recently deglaciated shield terrane a case study from northern ontario canada the economy of northern ontario canada is heavily dependent on mining so accurate knowledge of seismicity is important for the safe design and op eration of mines and other critical facilities including a proposed underground repos itory for nuclear waste in this study we analyzed 537 cataloged earthquakes that occurred from 1980 to 2006 seismicity is mainly concentrated in topographically elevated archean terranes northwest of lake superior and in the james bay and ka puskasing regions we analyzed waveforms to determine the focal depth for 331 re corded events using the regional depth phase modeling rdpm method coupled with surface wave relative amplitude analysis the majority of events are shallow 350 m although in the east ern part this pattern breaks down and some deeper earthquakes 12 km are ob served based on a moving window event counting technique we show that distinct spatial clusters of seismicity can be delineated that are statistically significant relative to background seismicity levels a particularly active cluster is located within james bay where focal depths range from a few kilometers to more than 20 km another cluster near kapuskasing contains deep focus events and may occur along a hot spot track that runs through western quebec near dryden a shallow 1 km earthquake swarm concentrated in a 1 1 km region commenced in may 2002 faded and then started up again in february 2003 shallow mining induced events are also common around sudbury a major world center for nickel mining the overall pattern of seis micity appears to correlate with upper mantle p wave velocity anomalies suggesting that lateral variations in mantle rheology may play a significant role in controlling intraplate seismicity of shield areas it is also likely that crustal stresses caused by glacial isostatic adjustment are an important factor although the correlation of seis micity with uplift rate is not as clear online material focal depth solutions for earthquakes in northern ontario canada

postglacial induced surface motion and gravity in laurentia for uniform mantle with power law rheology and ambient tectonic stress abstract previous investigations of postglacial sea levels around laurentia in a non linear earth without ambient stress found that non linear uniform mantle models cannot explain the relative sea level data around the ice margin in this study a 3d finite element model of postglacial readjustment is used to calculate the earth s response due to realistic ice and eustatic water loads on stratified mantle with non linear rheology and ambient tectonic shear stress by varying the creep parameter a and the ambient stress level in a uniform mantle it is found that the combination a around 3 10 35 pa 3 s 1 and ambient stress level around 10 mpa is able to explain the sea level data both outside and inside the laurentian ice margin although for certain sites inside a slightly thicker ice is required to improve the fit to the data other geophysical and geodetic observables namely uplift rate horizontal velocity free air gravity and the rate of change of gravity have also been calculated for this model

small scale distribution of deep sea demersal nekton and other megafauna in the charlie gibbs fracture zone of the mid atlantic ridge abstract videotapes from manned submersibles diving in the area of the charlie gibbs fracture zone of the mid atlantic ridge were used to investigate the distribution of fishes large crustaceans epifaunal and sessile organisms and environmental features along a series of transects submersibles mir 1 and mir 2 conducted paired dives in an area of mixed sediment and rock beginning depth ca 3000 m and on a large pocket of abyssal like sediments depth ca 4000 m in the shallower area the submersibles passed over extremely heterogeneous terrain with a diversity of nekton epifaunal forms and sessile forms in the first pair of dives mir 1 rose along the mid atlantic ridge from 3000 to 1700 m while mir 2 remained near the 3000 m isobath nekton seen in these relatively shallow dives included large and small macrourids genus coryphaenoides shrimp infraorder penaeidea halosauropsis macrochir aldrovandia sp antimora rostrata and alepocephalids the last two were more characteristic of the upper areas of the slope reached by mir 1 as it rose along the mid atlantic ridge to depths less than 3000 m distributions of some forms seemed associated with depth and or the presence of hard substrate sessile organisms such as sponges and large cnidaria were more likely to be found in rocky areas the second pair of dives occurred in an abyssal area and the submersibles passed over sediment covered plains with little relief and many fewer countable organisms and features the most evident of these were holes mounds small cerianthid anemones small macrourids and the holothurian benthodytes sp a few large macrourids and shrimp also were seen in these deeper dives as well as squat lobsters munidopsis sp sponges and larger cnidaria were mostly associated with a few small areas of rocky substrate holes and mounds showed distributions suggesting large scale patterning over all dives most sessile and epifaunal forms showed clumped distributions however large holothurians and large nekton often had distributions not significantly different from random

hotspot tracks and the early rifting of the atlantic abstract many hotspot tracks appear to become the locus of later rifting as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines examples are the west coast of greenland east coast of labrador madeira hotspot the south coast of mexico north coast of honduras guyana hotspot and the south coast of west africa north coast of brazil st helena hotspot a modern day analog of a possible future rift is the snake river plain where the north american continent is being pre weakened by the yellowstone hotspot track this conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years the relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots however once the motion of this one plate is chosen the motions of all the other plates are prescribed by the relative motion constraints in addition to the correlation between the predicted tracks and sites of later continental breakup exposed continental shields correlate with the tracks their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover

glacio seismotectonics ice sheets crustal deformation and seismicity abstract the last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity this growth has been driven largely by the emergence of postglacial rebound models pgm constrained by new field observations that incorporate increasingly realistic rheological mechanical and glacial parameters in this paper we highlight some of these recent field based investigations and new pgms and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation the emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern canada and fennoscandia however many of these models neglect important parameters such as topography lateral variations in lithospheric strength and tectonic strain built up during glaciation in glaciated mountainous terrains glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields in general the short term response to ice fluctuations is similar to the earth s response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre existing stress state when the ice fluctuations occur on the spatial scale and magnitude of the late pleistocene glaciation and deglaciation however the viscoelastic response of the earth especially the mantle causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex the regions of greatest ice thickness and the regions marginal to the late pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting the mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused and continues to cause measureable crustal deformation at hundreds of kilometres from the ice margins for both tectonically active and cratonic regions palaeoseismic investigations of late pleistocene and holocene faults are an important tool in evaluating earthquake hazard the predicted response of the earth over this time however is very dependent on the model assumed for most regions far more carefully designed field observations are needed to constrain the existing rheological and ice models

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

western quebec seismic zone canada clustered midcrustal seismicity along a mesozoic hot spot track 1 the western quebec seismic zone wqsz is a 160 km wide band of intraplate seismicity extending 500 km from the adirondack highlands united states to the laurentian uplands canada previous authors have proposed that the wqsz is localized over the mesozoic track of the great meteor hot spot here we explore this hypothesis further by investigating regional seismicity characteristics focal mechanisms for wqsz earthquakes including a new mechanism for a moderate mn 4 5 earthquake reveal a pattern of reverse sense faulting with sw trending p axes changing to e w in the southern part of the zone we introduce a simple box counting method to delineate spatial clusters based on exceedance of random seismicity density combining this approach with focal depths from regional depth phase analysis we find that seismicity with shallow focus 0 7 km is characterized by a random spatial distribution whereas earthquakes with an intermediate focal depth 8 18 km are strongly clustered along a diffuse linear band trending n50 w earthquakes deeper than 18 km are confined to a few distinct clusters these clusters are characterized by differing b values and for at least one cluster repeating events projection of hypocenters onto a deep seismic profile and comparison with preexisting crustal structures suggest that local reactivation of precambrian structural features may have occurred however the great meteor hot spot track remains the only compelling explanation for the overall distribution of earthquakes proximity of seismicity clusters to historic and prehistoric earthquakes lends support to the hypothesis that modern seismicity may represent exceptionally long lived aftershocks of large past events

geodynamic processes of taiwan arc continent collision and comparison with analogs in timor papua new guinea urals and corsica abstract the taiwan arc continent collision involves four geodynamic processes intra oceanic subduction initial arc continent collision advanced arc continent collision and arc collapse subduction these processes now occur simultaneously in 19 24 30 n but have operated sequentially southward since the late miocene although the geological and geophysical features appear to change progressively from north to south across the island they are distinct within individual tectonic regimes using the present scenario as a basis for comparison it is suggested that timor is at the initial arc continent collision stage while papua new guinea and urals proceeded to the advanced arc continent collision stage however corsica represents an even more advanced stage than in taiwan where a previously accreted arc has collapsed and been totally removed

depth of faulting during the 1968 meckering australia earthquake sequence determined from waveform analysis of local seismograms waveforms for 11 foreshocks and 48 aftershocks of the ms 6 8 meckering earthquake recorded at the world wide standard seismograph network station mundaring are analyzed to determine the depth distribtion of faulting during this unusual intraplate earthquake sequence clear depth phases including sp and rg are seen in the local seismograms at distances of 60 95 km and are studied using synthetic seismograms computed using generalized ray theory and wave number integration techniques large rg s ratios seen on the vertical component short period data for many events imply source depths less than 2 km the short period p waveform contains the best depth estimator in the form of sp so that depth can be estimated to within an uncertainty of about 1 km for most events the foreshocks cluster at less than 2 km depth and most aftershocks occur within 1 km of the surface a few aftershocks occur as deep as 7 km these results are consistent with a previous teleseismic waveform study in which faulting was inferred to start near the surface at 1 5 km depth with rupture proceeding downward and not exceeding 6 km depth these results coupled with previous stress studies in the australian shield and models of crustal strength show that faulting in a cold shield area is a near surface phenomenon and implies that most of the crust is too strong to be fractured

a generalized omori s law for earthquake aftershock decay 1 earthquake aftershock sequences have been found to approximately satisfy three empirical scaling relations i the gutenberg richter frequency magnitude scaling ii bath s law for the difference in the magnitude of a mainshock and its largest aftershock and iii the modified omori s law for the temporal decay of aftershock rates the three laws are incorporated to give a generalized omori s law for aftershock decay rates that depend on several parameters specific for each given seismogenic region it is shown that the characteristic time c first introduced in the modified omori s law is no longer a constant but scales with a lower magnitude cutoff and a mainshock magnitude the generalized omori s law is tested against earthquake catalogs for the aftershock sequences of the landers northridge hector mine and san simeon earthquakes

focal depths for small to moderate earthquakes mn 2 8 in western quebec southern ontario and northern new york regional depth phase modeling is a useful technique to constrain earthquake focal depths for events within sparse networks we demonstrate how regional depth phases can be used to obtain focal depths for hundreds of earthquakes with m n 2 8 that occurred from 1980 to 2004 in southern ontario western quebec and northern new york state we discuss the development of regional depth phases with distance their use in focal depth determinations by matching waveforms to synthetics and possible sources of error in general focal depths can be determined to within about 3 km when there is at least one record at regional distances with clearly identifiable depth phases such as spmp or spg in southwestern ontario and northern new york focal depths range from 2 to 15 km in areas of western quebec and along the ottawa river valley in ontario focal depths range from 2 to 25 km more than half of the earthquakes in a cluster of activity near maniwaki in western quebec are deeper than 20 km all earthquakes deeper than 20 km occurred north of about 45 3 n there is an intriguing tendency for earthquake depths to cluster near 8 km 12 km 15 km and 22 km another interesting observation is that there are several earthquake pairs or small groups with very similar epicenters but quite different depths the most active regions in western quebec and along the ottawa river valley tend to exhibit a relatively wide range of focal depths along broad zones that trend roughly northwest suggesting that seismicity is occurring along diffuse northwest trending faults throughout the crust the wide range of focal depths may indicate the potential for a larger maximum scale of fault rupture and serve as a contemporary marker of locations where large events have occurred in the recent geologic past

seismicity analysis through point process modeling a review the occurrence times of earthquakes can be considered to be a point process and suitable modeling of the conditional intensity function of a point process is useful for the investigation of various statistical features of seismic activity this manuscript summarizes likelihood based methods of analysis of point processes and reviews useful models for particular analyses of seismicity most of the analyses can be implemented by the computer programs published by the author and collaborators

will earthquake activity in eastern canada increase in the next few thousand years knowledge of whether earthquake activity will increase in the next few thousand years is important for the planning of nuclear waste repositories assuming that fault instability portends earthquak

postglacial faulting in eastern canada nature origin and seismic hazard implications abstract at more than 70 locations in southeastern canada and the adjacent united states tiny bedrock faults displace glacial striations that are about 10 000 years old these reverse faults mostly of small displacement occur in a broad arc from western ontario to newfoundland the faults lie near the margin of the laurentian ice sheet strike generally tangential to it and imply compression nearly normal to the ene directed contemporary regional stress these observations and some age relationships suggest that the faults formed very soon after deglaciation perhaps in the first few thousand years after ice melting in each place and probably represent the release of stresses caused by flexural deformation of the upper crust although the individual offsets are small the faults are believed to be pervasive and individual outcrops reflect amounts of stress relief consistent with stresses implied by the postglacial tilt of nearby lake shorelines

intraplate earthquakes and a seismically defined lateral transition in the upper mantle we show that the lateral transition in the upper mantle between the cratonic central eastern and the tectonically active western regions of north america is narrow and deep reaching by travel time analysis of early rise explosion seismic data a concentration of enigmatic intraplate earthquakes coincides with the transition differential potential energy from density changes across the transition may generate a high compressional stress level which locally exceeds the shear strength of the lithosphere the resultant deformation is ductile in most parts of the lithosphere but in the brittle upper crust it explains the enigmatic intraplate earthquakes around the lateral transition in the upper mantle