application of high resolution seismic techniques in the evaluation of earthquake site response ottawa valley canada abstract high resolution seismic surveys including p and s wave studies have been conducted in an area of the ottawa river valley located 80 km east of ottawa canada based on dating of paleolandslides the existence of paleoearthquake activity has been postulated in this area the target zone for the seismic survey is characterized by surface disturbance and sediment deformation p wave seismic imaging was used to map the overburden bedrock interface as well as to indicate reflecting boundaries within the overburden the area of surface disturbance was found to overlie a buried bedrock basin 8 km in diameter infilled with a maximum thickness of 180 m of unconsolidated quaternary sediments preliminary results of core logging show the presence of sand overlain by deformed fine sediments within the disturbed area shear refraction studies reveal differences in the velocity depth profiles between the disturbed area and the surrounding undisturbed areas the shear wave reflection method was used to produce a fundamental resonant period map for the area surface sediment disturbance was probably due to a combination of ground motion amplification due to the basin thick soft sediments and the presence of water saturated sand at depth

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

a new magma chamber model based on structural studies in the oman ophiolite abstract structural mapping in the mafic ultramafic transition zone and in the overlying crustal section of the oman ophiolite has revealed the importance of magmatic flow in the formation of layering in the gabbros and the mechanical coupling between this flow and the asthenospheric flow of the underlying peridotites the crustal section near the spreading axis and in particular the magma chamber are fed by two independent melts a dominant gabbroic melt episodically injected from depth and a subordinate wehrlitic crystal mixture produced by compaction of the transition zone layering in the gabbros can be partly produced by tectonic transposition of the gabbroic and wehrlitic mixtures during magmatic flow whatever its origin the layering orientation in the newly created crust does not necessarily reflect its original attitude the final orientation of the layering is determined by the attitude of the magmatic flow plane at the time it was frozen a new magma chamber model is proposed which solves some of the physical difficulties of previous models and accounts for the seismic imaging of magma chambers beneath oceanic ridges

linear zones seismicity and the possibility of a major earthquake in the intraplate western lake ontario area of eastern north america seismic hazard assessments conducted in eastern canada rely on seismological data which are essential but alone inadequate that is because the earthquake record is too short to provide a representative picture of where large earthquakes have occurred in the past consequently seismic hazard may be underestimated in areas such as that encompassing western lake ontario that are devoid of documented large earthquakes to attempt to ascertain the likelihood of a major earthquake occurring in that highly populated and industrialized area three regionally extensive geophysically expressed lineaments were investigated and the results were combined with available seismological information the most conspicuous is the niagara pickering linear zone within which there have been at least two if not three periods of brittle faulting including displacements compatible with the current stress field it also appears to represent the same major structure as the akron magnetic boundary in eastern ohio the site of the mb 4 9 leroy earthquake the second is the georgian bay linear zone which extends from georgian bay to new york state it displays evidence of recent outcrop scale faulting an alignment of earthquakes along its southwestern boundary and a possible spatial relationship to other earthquakes including two of m 5 lastly there is the hamilton lake erie lineament which is parallel and proximal to a possible fault and coincides with a linear array of small to moderate earthquakes all three converge on the western lake ontario area which has a higher frequency of seismicity than the adjacent areas thus the western lake ontario area might have a greater potential to experience a major earthquake than heretofore believed resume les evaluations des risques sismiques dans l est du canada sont fondees sur les donnees sismologiques dont

the presence characteristics and earthquake implications of the st lawrence fault zone within and near lake ontario canada usa abstract questions persist concerning the earthquake potential of the populous and industrial lake ontario canada usa area pertinent to those questions is whether the major fault zone that extends along the st lawrence river valley herein named the st lawrence fault zone continues upstream along the st lawrence river valley at least as far as lake ontario or terminates near cornwall ontario canada massena ny usa new geological studies uncovered paleotectonic bedrock faults that are parallel to and lie within the projection of that northeast oriented fault zone between cornwall and northeastern lake ontario suggesting that the fault zone continues into lake ontario the aforementioned bedrock faults range from meters to tens of kilometers in length and display kinematically incompatible displacements implying that the fault zone was periodically reactivated in the study area beneath lake ontario the hamilton presqu ile fault lines up with the st lawrence fault zone and projects to the southwest where it coincides with the dundas valley ontario canada the dundas valley extends landward from beneath the western end of the lake and is marked by a vertical stratigraphic displacement across its width the alignment of the hamilton presqu ile fault with the st lawrence fault zone strongly suggests that the latter crosses the entire length of lake ontario and continues along the dundas valley the rochester basin an east northeast trending linear trough in the southeastern corner of lake ontario lies along the southern part of the st lawrence fault zone submarine dives in may 1997 revealed inclined layers of glaciolacustrine clay along two different scarps within the basin the inclined layers strike parallel to the long dimension of the basin and dip about 20 to the north northwest suggesting that they are the result of rigid body rotation consequent upon post glacial faulting those post glacial faults are growth faults as demonstrated by the consistently greater thickness unit by unit of unconsolidated sediments on the downthrown northwest side of the faults relative to their counterparts on the upthrown southeast side underneath the western part of lake ontario is a monoclinal warp that displaces the glacial and post glacial sediments and the underlying bedrock sediment interface because of the post glacial growth faults and the monoclinal warp the st lawrence fault zone is inferred to be tectonically active beneath lake ontario furthermore within the lake it crosses at least five major faults and fault zones and coexists with other neotectonic structures those attributes combined with the large earthquakes associated with the st lawrence fault zone well to the northeast of lake ontario suggest that the seismic risk in the area surrounding and including lake ontario is likely much greater than previously believed

new probabilistic strong seismic ground motion maps of canada new probabilistic strong seismic ground motion maps of canada are derived by applying the cornell mcguire method to 32 earthquake source zones in canada and adjacent regions peak horizontal acceleration and peak horizontal velocity are mapped to depict strong ground motion in the frequency ranges near 5 hz and near 1 hz respectively some earthquake source zones are well defined on the basis of both tectonics and average seismicity rates but a lack of understanding of the near field effects of the large earthquakes prohibits accurate estimates of ground motion in their vicinity some source zones have no known large scale crustal features or zones of weakness that can explain the seismicity and must therefore be defined simply as concentrations of seismic activity with no geological or geophysical controls on the boundaries other source zones lack information on low magnitude seismicity that would be representative of longer periods of time a significant source of uncertainty in the ground motion estimates is introduced by the uncertainty in strong ground motion attenuation relations particularly in the near field of large earthquakes and particularly in eastern canada where no strong motion data are available for earthquakes larger than magnitude 5 valid estimates can be made of relative levels of probabilistic strong ground motion on a regional basis at moderate probabilities however the simple peak ground motion parameters are not sufficient for engineering design purposes in the immediate vicinity of large earthquakes a comparison of the new probabilistic ground motion estimates at the canada united states border with equivalent estimates made in the united states reveals that peak acceleration contours match well in the british columbia washington state yukon alaska and lake ontario border regions canadian peak velocities are a factor of two higher near the british columbia washington state border canadian peak accelerations are higher in the border regions of eastern canada influenced by the charlevoix zone and in regions of the alaska panhandle british columbia border influenced by the active queen charlotte and fairweather fault zones the new ground motion estimates are used to produce new peak acceleration and peak velocity zoning maps to replace the 1970 peak acceleration zoning map in the national building code of canada the acceleration and velocity maps provide independent ground motion reference levels for small rigid structures and taller flexible structures respectively compared to the 1970 map with four zones the new maps with seven zones have a finer subdivision of zoning in moderate risk areas and additional zones in the high risk areas a change in probability of exceedence from 0 01 per annum on the 1970 map to 10 per cent in 50 yr on the new maps and the addition of velocity as a zoning parameter have necessitated changes in the seismic design provisions these revisions will be incorporated into the 1985 edition of the code

physical properties of rocks from the upper part of the yaxcopoil 1 drill hole chicxulub crater physical properties were determined in a first step on post impact tertiary limestones from the depth interval of 404 666 m of the yaxcopoil 1 yax 1 scientific well drilled in the chicxulub impact crater mexico thermal conductivity thermal diffusivity density and porosity were measured on 120 dry and water saturated rocks with a core sampling interval of 2 2 5 m nondestructive non contact optical scanning technology was used for thermal property measurements including thermal anisotropy and inhomogeneity supplementary petrophysical properties acoustic velocities formation resisitivity factor internal surface and hydraulic permeability were determined on a selected subgroup of representative samples to derive correlations with the densely measured parameters establishing estimated depth logs to provide calibration values for the interpretation of geophysical data significant short and long scale variations of porosity 1 37 turned out to be the dominant factor influencing thermal acoustic and hydraulic properties of this post impact limestone formation correspondingly large variations of thermal conductivity thermal diffusivity acoustic velocities and hydraulic permeability were found these variations of physical properties allow us to subdivide the formation into several zones a combination of experimental data on thermal conductivity for dry and water saturated rocks and a theoretical model of effective thermal conductivity for heterogeneous media have been used to calculate thermal conductivity of mineral skeleton and pore aspect ratio for every core under study the results on thermal parameters are the necessary basis for the determination of heat flow density demonstrating the necessity of dense sampling in the case of inhomogeneous rock formations

earthquake triggered slumps 1935 timiskaming m6 2 in lake kipawa western quebec seismic zone canada abstract the western quebec seismic zone wqsz of eastern north america is characterised by frequent moderate magnitude intracratonic earthquakes e g 1732 m5 8 1935 m6 2 and 1944 m5 2 the wqsz is centered along the timiskaming and ottawa bonnechere grabens which form part of a complex aulacogen st lawrence rift within the canadian shield the wqsz includes the urban areas of montreal and ottawa but seismic risk analysis is challenged by short instrumental records and long recurrence intervals the m6 2 1935 timiskaming earthquake is the largest recorded to date and was felt over some 1 3 million km 2 of eastern north america with many aftershocks of magnitude 4 to 5 its epicenter lies below the western margin of lake kipawa quebec in the area where a major proterozoic crustal boundary the grenville front tectonic zone crosses the timiskaming graben a high resolution chirp seismic reflection survey of the lateglacial and postglacial sediment infill of lake kipawa reveals a clear record of recent ground shaking that is attributed to the 1935 earthquake widespread large slumps record down slope failure of the lateglacial and postglacial sediment fill indicating that the 1935 temblor was the largest in this area since deglaciation some 8000 years ago systematic mapping of landslides shows that they extend across an area of 600 km 2 around the earthquake s epicenter lakes cover a large area of eastern canada a regional scale survey of lake floors could constrain historic epicenters and postglacial seismic history of the heavily populated wqsz

seismicity and faulting in the charlevoix zone of the st lawrence valley abstract continuous monitoring of the seismically active charlevoix zone since late 1977 has delineated the boundaries of the earthquake zone under the north shore and has enabled an association to be made with surface mapped faults that strike along the st lawrence valley and dip to the southeast within the active zone aseismic volumes are found under parts of the st lawrence river and another elongated zone of activity is found to the southeast on unmapped faults dipping under the river the previous suggestions that the activity is related to old rift faults which have been later weakened by a meteor impact would seem to be upheld

determination of thermal conductivity for deep boreholes two methods for thermal conductivity determinations on rock cores and fragments were tested on a suite of samples from the kontinentales tiefbohrprogramm der bundesrepublik deutschland ktb superdeep drill hole in germany they were also compared with estimates of thermal conductivity using the mineral composition of the rock and physical well logs and with in situ thermal conductivity measurements laboratory methods provide reasonably precise determinations of the thermal conductivities of both solid core 5 and drill cuttings 10 at room temperature and pressure the most common methods presently used for crystalline rocks are the steady state divided bar db technique and the transient half space line source ls sample preparation and measurement times are comparable for the db and ls with sample preparation being more time consuming on average for isotropic rocks there is little to choose from between the two methods which both give reliable values of conductivity in the vertical direction the ls is easier to set up and use in field laboratory situations which renders it the preferred method for field reconnaissance the gneissic crystalline rocks penetrated by the ktb boreholes typically have anisotropy of the order of 10 20 the db provides unambiguous values of conductivity in a given direction so its use is preferable for obtaining both principal conductivities and the vertical component anisotropy can be estimated using ls measurements in many different directions but the potential for large random errors is much greater than with the more straightforward db approach for deep research wells the difficulties of extrapolating laboratory results to in situ conditions particularly temperature present additional obstacles to determining heat flow laboratory measurements of water saturated samples under in situ conditions combined with in situ measurements and judicious use of calculations based on mineralogy and well log derived physical properties can aid in the accurate characterization of thermal conductivity in deep wells the application of different methods helped to link variations of heat flow with depth in the ktb hole to the anisotropy of thermal conductivity or thermal refraction and thus allowed the calculation of background heat flux in this geologically complex area

high resolution seismic reflection profiling of neotectonic faults in lake timiskaming timiskaming graben ontario quebec canada the timiskaming graben is a 400 km long 50 km wide north west trending morphotectonic depression within the canadian shield of eastern north america and experiences frequent intraplate earthquakes the graben extends along the border of ontario and quebec connecting southward with the nipissing and ottawa bonnechere grabens and the st lawrence rift system which includes a similar structure underlying the hudson valley of the eastern usa together they form a complex failed rift system related to regional extension of north american crust during the breakup of rodinia and later pangea the timiskaming graben lies within a belt of heightened seismic activity western quebec seismic zone with frequent moderate magnitude greater than magnitude 5 earthquakes including a magnitude 6 2 in 1935 these events threaten aging urban infrastructure built on soft glacial sediments post glacial landslides along the ottawa valley suggest earthquakes as large as magnitude 7 the inner part of the timiskaming graben is filled by lake timiskaming a large 110 km long post glacial successor to glacial lake barlow that was ponded by the laurentide ice sheet 9500 years ago the effects of frequent ground shaking on lake floor sediments was assessed by collecting more than 1000 line kilometres of high resolution chirp seismic profiles late glacial lake barlow glaciolacustrine and overlying post glacial sediments are extensively deformed by extensional faults that define prominent horsts and grabens multibeam bathymetry data suggest that faults influence the morphology of the modern lake floor despite high sedimentation rates and indicate recent neotectonic deformation the lake timiskaming area provides evidence of post glacial intracratonic faulting related to recurring earthquake activity along a weak spot within the north american plate

late quaternary slumps and debris flows on the scotian slope the scotian slope just west of verrill canyon was surveyed using the sea marc i deep towed sidescan sonar system high resolution seismic reflection profiles and 25 piston cores the generally smooth continental slope has a gradient of 2 5 it is crossed by 2 small valleys that are 1 km wide and 100 m deep much of the sea bed shows evidence of surficial sliding that removed 10 20 m of sediment and the slide scars give the sea bed a steplike morphology from the 600 m isobath to 1 800 m there extend 2 zones of disturbed sediment these disturbed zones have the rough surface and transparent acoustic character previously regarded as characteristic of debris flows but sidescan sonar images and cores suggest that they are principally rotational slide deposits with true debris flows at their distal limits streamlined erosional depressions near the downslope edge of the debris flows cut both the flow and sediment farther down slope these may have been produced by a turbidity current associated with the debris flows sorted coarse sand in piston cores provides further evidence of current activity this widespread sediment failure on relatively low slopes was probably the result of a large earthquake that can be dated from cores as occurring between 5000 and 12000 yr b p

stochastic prediction of ground motion and spectral response parameters at hard rock sites in eastern north america empirical predictions of ground motions from large eastern north american earthquakes are hampered by a lack of data for such events for this reason most prediction techniques have been based at least in part on data from the seismically active and well instrumented western north america concentrating on the prediction of response spectra on hard rock sites we have used a relatively new theoretical technique that does not require western data to make ground motion predictions for eastern north america this method often referred to as the stochastic model has its origins in the work of hanks and mcguire who treat high frequency motions as filtered random gaussian noise for which the filter parameters are determined by a seismological model of both the source and the wave propagation the model has been successfully applied to the predictions of ground motions in the western united states and to short period magnitudes from large to great earthquakes worldwide for our application the essential parameters of the model are estimated by using existing data from small to moderate eastern north american earthquakes a crucial part of the model is the relation between seismic moment and corner frequency the relation proposed in 1983 by nuttli for mid plate earthquakes leads to predictions of ground motions that are lower than available data by a factor of about 4 on the other hand a constant stress parameter of 100 bars gives model predictions in good accord with the data to aid in applications the ground motion predictions are given in the form of regression equations for earthquakes of magnitude 4 5 to 7 5 at distances within 100 km of the source the explanatory variables are hypocentral distance and moment magnitude m because predictions are often required in terms of m g rather than m we have used the theoretical model to establish a relation between the two magnitudes the predicted relation agrees with the sparse data available although the large uncertainties in the observed magnitudes for the larger events as well as the sensitivity of the theoretical magnitude to the attenuation model make it difficult to discriminate between various source scaling models

an analysis of the 1985 nahanni earthquakes abstract two large magnitude earthquakes occurred in 1985 near the north nahanni river in the northeast cordillera northwest territories canada on 5 october m s 6 6 and 23 december m s 6 9 these events were unprecedented for this region of the cordillera and the december event is the largest earthquake ever known in the eastern part of the canadian cordillera this report presents detailed studies of the nahanni earthquakes their source parameters macroseismic effects aftershock sequences triggered rock avalanches their relationship to the geology of the epicentral area and their seismic hazard implications parameters calculated here for these two major events are parentheses indicate other studies the earthquakes occurred within a small relatively undeformed plateau the mackenzie plain in the foreland fold belt created along the northeastern cordillera during the columbian or laramide orogeny that fold belt is now subjected to northeast southwest horizontal compressive stresses possibly very similar to the original laramide stress regime and the fault plane implied by the seismic mechanisms is very similar to the laramide faults in the area however no surface fault break has been found and none of the mapped laramide faults in the epicentral area appears to be involved in the aftershock activity it is thus believed that the nahanni earthquakes occurred on a blind laramide thrust fault under the mackenzie plain the large magnitudes of the nahanni earthquakes show that the present seismic zoning for building code purposes in the eastern cordillera north of 60 n needs reassessment and suggest that the zoning in the eastern cordillera in british columbia and alberta may also need revision the felt areas of the earthquakes show that regional anelastic attenuation in the eastern canadian cordillera is significantly anisotropic and much lower along strike than across strike the felt areas also appear to scale with seismic moment rather than m b magnitude the thrust mechanisms regional stress regime shallow focal depth and high velocity sedimentary rocks in the focal region suggest that the nahanni earthquakes and particularly the near field strong ground motion recorded for the second event are ideal engineering design data for critical facilities in eastern north america

problems of seismic hazard estimation in regions with few large earthquakes examples from eastern canada abstract seismic hazard estimates and seismic zoning maps are based on an assessment of historical and recent seismieity and any correlations with geologic and tectonic features that might define the earthquake potential evidence is accumulating that the large earthquakes in eastern canada m 7 may be associated with the rift systems hat surround or break the integrity of the north american craton the problem for seismic hazard estimation is that the larger historical earthquakes are not uniformly distributed along the paleozoic st lawrence ottawa rift system and are too rare on the mesozoic eastern margin rift to assess the overall seismogenic potential multiple source zone models for hazard estimation could include hypotheses of future m 7 earthquakes at any location along these rift systems but at a moderate probability such as that used in the canadian zoning maps the resultant hazard will be so diluted that it will not result in adequate design against the near source effects of such earthquakes the near source effects of large rare earthquakes can however be accommodated in conservative codes and standards for critical facilities if society is willing to pay the price

new geothermal data from the kola superdeep well sg 3 abstract the kola superdeep well sg 3 reaches a depth of 12 262 m this provides the opportunity to obtain experimental data on thermal properties of deep horizons since 1985 a 8578 m deep borehole with a casing depth of 8278 m has been used as a geolaboratory the determination of the equilibrium temperature gradient and heat flow density hfd is more reliable than as published before to estimate hfd we used measurements of thermal conductivity from more than 8000 core samples below 4000 m rocks schists amphibolites gneisses and plagiogranites are characterized by significant anisotropy 1 17 2 10 this was taken into account when estimating the conductive hfd new experimental data on hfd in the interval of 0 4 0 9 km are in good agreement with previous results from 470 to 1675 m deep holes drilled near the sg 3 the 0 9 2 0 km interval shows abrupt increase in hfd up to an average value of 57 mw m 2 which differs significantly from the previously reported values of hfd from sg 3 from 37 to 44 mw m 2 as reported by different researchers the average hfd value of 63 mw m 2 in the 5 2 7 5 km interval is 17 43 higher than the previously estimated values within the depth interval from 7 6 to 8 2 km hfd shows a gradual decrease from 62 to 51 mw m 2 positive correlation between 1 and is observed only in the intervals of 2 5 4 3 km and 5 0 6 5 km as can be expected for a stationary conductive thermal regime analysis of the temporal variations of during the return of the hole to thermal equilibrium after its completion reveals that this parameter is capable of characterizing the permeability of a rock massif from the analyses of temporal variations of a lower permeability can be attributed to the part of the massif lying in the 3 0 4 5 km depth range it is proposed that the observed vertical variations in hfd are due to movement of fluids in the massif in some cases resulting in non stationary fields in particular the largest geothermal anomaly at 0 2 km depth is caused by a downward movement of meteoric waters in the zone of active water exchange the experimental results can be understood quantitatively if a permeability of 1 to 3 10 13 m 2 over a 1 2 km zone of exogenic fracturing is assumed an abrupt change of conductive hfd in the depth interval 1 7 2 2 km is attributed to a downward movement of fluids of 2 3 cm yr along inclined zones of fracturing at the boundary between igneous and sedimentary sequences this movement of fluids might be caused by a post glacial uplift of the baltic shield and would continue as lateral pressure in deep faults decreases

geothermal characteristics of the ries impact structure summary a new investigation of the thermal conductivity of the drill cores from the research drill hole nordlingen 1973 in the ries impact structure was conducted the 1206 m deep drill hole pen etrated 331 m of post impact lake formations then 275 m of suevitic impact formations with varying amounts of large crystalline basement blocks and then 600 m of fractured displaced basement blocks containing appreciable amounts of dyke breccias the main purpose of the measurements was to see the signature of the shock effects in the thermal properties of the impact formations the use of the new non contact optical scanning instrument allowed mea surements with a resolution of a few centimetres a complicated preparation of the samples was not required thermal conductivity values on dry and on water saturated drill cores and thermal inhomogeneity factors were obtained for samples with a spacing of about 2 m it could be shown that the thermal conductivity is extremely inhomogeneous on various scales and that there is a close relation with the degree of shock and thermal transformation of the target rocks an improved theoretical model for the thermal conductivity of rocks taking into account the form of grains pores and cracks and using measurements on dry and saturated cores yields information on the porous space of the rock samples correlations between the thermal con ductivity and other petrophysical properties determined from well logging data were found they allow other physical properties to be predicted from the conductivity values the new thermal conductivity data together with temperature logging data also gave the possibility of making new estimates of the undisturbed heat flow density in the crater area 90 95 mw m 2 with about 30 per cent higher values than previous estimates a significant increase of the heat flow density in the upper part of the structure indicates fluid migration from deeper parts the absence of thermal anisotropy in crystalline rocks increasing thermal conductivity with depth and increasing heat flow density may be characteristic features of impact structures

thermal conductivity of water saturated rocks from the ktb pilot hole at temperatures of 25 to 300 c the conductivitites of selected gneiss two and amphibolite one core samples have been measured under conditions of elevated temperature and pressure with a needle probe water saturated thermal conductivity measurements spanning temperatures from 25 to 300 c and hydrostatic pressures of 0 1 and 34 mpa confirm the general decrease in conductivity with increasing temperature but deviate significantly from results reported from measurements on dry samples over the same temperature range the thermal conductivity of water saturated amphibolite decreases with temperature at a rate approximately 40 less than the rate for dry amphibolite and the conductivity of water saturated gneiss decreases at a rate approximately 20 less than the rate for dry gneiss the available evidence points to thermal cracking as the primary cause of the more rapid decrease in dry thermal conductivity with temperature the effects of thermal cracking were also observed in the water saturated samples but resulted in a net decrease in room temperature conductivity of less than 3 these results highlight the importance of duplicating in situ conditions when determining thermal conductivity for the deep crust

apatite fission track thermochronology of khibina massif kola peninsula russia implications for post devonian tectonics of the ne fennoscandia abstract the thermal history of the kola peninsula area of ne fennoscandia remains almost fully unknown because of the absence of any thermochronological data such as apatite and or zircon fission track or u th he ages in order to fill this gap and to constrain the post devonian erosion and exhumation history of this region we present the results of apatite fission track aft dating of eleven samples selected from the cores taken from different depths of the northern part of the khibina intrusive massif the rb sr isochron age of this alkaline magmatic complex which is located at the center of kola peninsula is 368 6 ma kramm and kogarko 1994 samples were analyzed from depths between 520 and 950 m and yielded aft ages between 290 and 268 ma with an age uncertainty 1 of between 19 ma 7 and 42 ma 15 mean track lengths mtl lie between 12 5 and 14 4 m inverse time temperature modeling was conducted on the age and track length data from seven samples of the khibina massif thermal histories that best predict the measured data from three samples with the most reliable data show three stages 1 290 250 ma rapid cooling from 110 c to 70 c 50 c for lower upper sample correspondingly 2 250 50 ma a stable temperature stage 3 50 0 ma slightly increased cooling rates down to modern temperatures we propose that the first cooling stage is related to late hercynian orogenesis the second cooling stage may be associated with tectonics accompanying with opening of arctic oceanic basin the obtained data show that geothermal gradient at the center of kola peninsula has remained close to the modern value of 20 c km for at least the last 250 myr aft data show that the khibina massif has been exhumed not more then 5 6 km in the last 290 myr

a re examination of the 1925 charlevoix quebec earthquake the 1 march 1925 charlevoix earthquake is one of the largest earthquakes known to have occurred in southeastern canada because it occurred in one of the most active seismic zones of southeastern canada and near now heavily populated regions understanding this earthquake may have implications for seismic hazard assessments of the region previous attempts have been made to study this earthquake using modern waveform analysis techniques but the source parameters could be only partially constrained due to a lack of good data recently a number of seismograms that had not been previously studied were rediscovered warranting a second look at the earthquake the best overall solution is strike 42 7 dip 53 7 rake 105 10 depth 10 km seismic moment 3 1 2 5 1025 dyne cm mw 6 2 ms 6 2 0 3 mb 6 5 0 4 source duration 5 sec and stress drop 35 bars the focal mechanism is consistent with many recent earthquakes in the charlevoix seismic zone but inconsistent with the regional stress field

twelve years of geophysical research in the charlevoix seismic zone abstract various and extensive geophysical monitoring began in 1974 in the charlevoix seismic zone csz the historical record and a major earthquake in 1925 characterize this zone as the likely site of a future damaging earthquake i e m 5 5 or larger and the aim of the monitoring was to develop the capability of predicting such earthquakes the parameters studied included microseismicity seismic travel times electrical impedance vertical movement horizontal movement tilt gravity change and strain through water well level changes although no clear precursor was detected in the months before the largest seismic event that occurred during the observation period m 5 0 the multiparameter experiment provided new insights into the structure and the mechanics of this active region observations of several hundred well located microearthquakes have permitted the delineation of ancient rift faults that are now being activated by high horizontal compression the geographical extent of the zone is sharply defined by the microseismicity which occurs in an area of 35 km 80 km straddling the st lawrence river observation of p waves from accurately timed explosions and s waves from earthquakes support the hypothesis of extensive dilatancy anisotropy eda involving saturated parallel cracks in the crust the data have permitted an estimate of both crack density and the direction for the principal compressive stress in the region n 30 e changes in electrical parameters with periods of months to years were detected at five of the six magnetotelluric stations installed in the region changes in the polarization angle of the earth s electrical telluric field correlated well for seven years with calculated groundwater accumulation levels at one site electric impedance changes showed no clear correlation from station to station but changes at one station appear to correlate with a seismic p wave travel time change anomaly and with the disappearance of a negative gravity anomaly at the time of an unusual number of earthquakes in the range m 2 to 3 from mid 1976 to mid 1977 it is suggested that these correlated changes could be related to aseismic stress redistribution and fluid flow along one of the ne striking rift faults about two years before the m 5 0 earthquake in 1979 continuous monitoring of tilt surface and borehole and well water levels was carried out at a single site charlevoix geophysical observatory although there were unexplained near surface tilts of the order of the earth tide amplitude within two or three days before some earthquakes they were either not spatially coherent or were related to small unexplained temperature changes in the tiltmeter vault no intermediate term one week to one year precursors were seen against a noise level of 1 3 rad rms for near surface tilt observations and a noise level of 0 2 0 3 rad rms for borehole tilt measurements at a depth of 50 100 m the threshold of detectable tidal tilt admittance changes for the borehole tiltmeters was lowered to 2 but no significant changes were seen four coseismic changes in the levels of water in boreholes were observed all were drops in water level which were much larger than expected on the basis of elastic dislocation theory it is suggested that these could be explained either by the collapse of a dilatant zone around the respective hypocentres or by triggered aseisnuc movement on a nearby active fault borehole water level tides observed from 1980 to 1986 exhibit significant variations in amplitude and phase which are thought to be the result of time varying elastic properties in a nearby structure some constraints can now be placed on the long term deformation of the csz as a whole from tiltmeter levelling and horizontal surveys data from a levelling array observed from 1976 to 1986 puts a limit of 0 54 rad yr on the secular tilt rate at the observatory a further limit of 0 1 rad yr is provided by borehole tilt measurements over the period 1983 1986 a limit of 2 cm is placed on vertical movements northwest of the st lawrence river by levelling surveys in 1965 1978 1980 and 1982 no significant 90 confidence deviatoric strain has been detected across the csz from horizontal control surveys carried out in 1912 1919 1965 1978 and 1983 the maximum allowable long term strain rate across the csz from 1919 to 1983 is 0 16 strain yr

radiogenic heat production in the lithosphere of sulu ultrahigh pressure metamorphic belt abstract the chinese continental scientific drilling ccsd project is located at the sulu ultrahigh pressure metamorphic uhpm belt it offers a unique opportunity for studying the radiogenic heat production of both shallower and deeper rocks based on the concentrations of radiogenic elements u th and k on 349 samples from main hole of ccsd ccsd mh pilot holes and exposures we determined radiogenic heat productions of all major rock types in the sulu uhpm belt results show the mean values of orthogneiss and paragneiss are respectively 1 65 0 81 and 1 24 0 61 w m 3 due to different composition and grade of retrogressive metamorphism the eclogites display significant scatter in radiogenic heat production ranging from 0 01 to 2 85 w m 3 with a mean of 0 44 0 55 w m 3 the radiogenic heat production in ultramafic rocks also varies within a large range of 0 02 to 1 76 w m 3 and the average turns out to be 0 18 0 31 w m 3 based on the measurements and crustal petrologic model the vertical distribution model of heat production in sulu crust is established the resulting mean heat production 0 76 w m 3 contributes 24 mw m 2 to the surface heat flow 1 d thermal model indicates that the temperature at the moho reaches above 750 c and the thermal thickness of the lithosphere is 75 km in good agreement with the geophysical results the high teat flow 75 mw m 2 together with thin lithosphere presents strong support for the extension events during the late cretaceous and cenozoic

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

depth dependence of thermal transport properties for typical crustal rocks abstract thermal conductivity and thermal diffusivity were measured for a collection of granitic samples at high pressures up to 500 mpa and high temperatures up to 750 c the depth dependence was calculated from these results as typical constituents of the lower crust high grade metamorphic rocks of the granulite facies were investigated the thermal diffusivity was measured up to 1 8 gpa and 800 c under quasihydrostatic conditions thermal conductivity was calculated taking into account the temperature dependence of the specific heat from literature data the depth dependence of the thermal transport properties was obtained from the experimental results using a graphical method

the fennoscandian ice sheet during the late weichselian geothermal evidence geothermal estimates of the ground surface temperatures for the last glacial cycle in northern europe have been analysed during the middle and late weichselian 55 12 kyr bp a substantial part of this area was covered by the fennoscandian ice sheet the analysis of geothermal data allows reconstructing the limits of ice sheet extent and its basal thermal state in the late weichselian ground surface temperatures outside the ice sheet were extremely low from 7 to 17 c within the ice sheet there were both thawed and frozen zones the revealed temperature pattern is generally consistent with the modern one for ground surface temperatures in greenland which makes it possible to consider these ice sheets as analogues the anomalous climatically induced surface heat flux and orbital insolation of the earth varied consistently outside the glaciation and independently within the limits of the ice sheet

new heat flow data from the immediate vicinity of the kola super deep borehole vertical variation in heat flow confirmed and attributed to advection abstract we present new heat flow values and other geothermal data in the upper crystalline crust in the immediate vicinity of the 12 4 km deep kola super deep borehole nw russia our results show a systematic vertical increase in geothermal gradient and heat flow density as deep as we could measure 1 6 km our results confirm earlier results on vertical heat flow trends of in the uppermost part of the kola super deep hole and imply that the thermal regime is not in steady state conductive conditions in an area of 3 km 5 km measurements were performed in 1 2 km deep boreholes surrounding the kola super deep hole and on core samples from these holes temperature logs are available from 36 holes core data exists from 23 boreholes with a total length of 11 5 km at a vertical resolution of 10 m we carried out a very detailed study on thermal conductivity with regard to anisotropy inhomogeneity and temperature dependence tensor components of thermal conductivity were determined on 1375 core samples from 21 boreholes in 3400 measurements additionally we measured specific heat capacity heat generation rate density porosity and permeability on selected subsets of core samples heat flow from 19 boreholes varies between 31 and 45 mw m 2 with an average value of 38 mw m 2 in most boreholes the vertical heat flow profiles show a considerable variation with depth this is consistent with observations in the upper part of the kola super deep borehole we conclude that this variation is not caused by technical operations but reflects a natural process it is considered to be due to a combination of advective structural and paleoclimatic effects preliminary 3 d numerical modeling of heat and flow in the study area provides an indication of relative contributions of each of these factors advective heat transfer turns out to have a major influence on the vertical variation of heat flow although transient changes in surface temperature may also cause a significant variation heterogeneity of the rocks in the study area is less important

role of topography in isotherm perturbation apatite u th he and fission track results from the malta tunnel tauern window austria 1 apatite u th he and fission track age determinations of samples from a 20 km long near horizontal tunnel in the hochalm ankogel dome eastern tauern window austria are presented in order to determine the role of paleo topography in perturbing isotherms in the shallow crust apatite fission track ages 26 8 ma show no systematic correlation with distance along the tunnel or elevation two age components in the fission track data indicate cooling through 120 c at approximately 20 ma and 80 c at approximately 6 ma surface and tunnel u th he ages 17 9 ma and 13 5 ma respectively are consistently younger than the equivalent fission track ages u th he ages vary systematically along the tunnel with older ages at the northern and southern tunnel portals and younger ages in the central section geological factors faulting lithology appear to have had little effect on this age distribution the u th he age pattern is inconsistent with rock cooling underneath the present day hochalm ankogel dome topography the age minimum is interpreted to coincide with a paleotopographic maximum in the hochalm ankogel dome and suggests that the 40 60 c isotherms were warped sufficiently to affect apatite u th he ages the tunnel apatite u th he ages match synthetic he ages derived from a two dimensional numerical model of landscape evolution integrating the thermal model results with the data allows the relief development to be constrained and we calculate that the present day hochalm ankogel dome topography was formed at 7 to 10 ma

geothermal characteristics of the vorotilovo deep borehole drilled into the puchezh katunk impact structure abstract the vorotilovo borehole 5374 m in depth was drilled in 1989 1992 in the central part of the large puchezh katunk impact structure which is located in the east european platform lat 57 1 n long 43 6 e the geothermal studies of the borehole section were based on the temperature logging of the entire borehole 1992 1995 on the thermal conductivity measurements for more than 3700 air dry and fluid saturated core samples under normal p t conditions and for 473 samples at a temperature up to 100 c the rock anisotropy was taken into account in these measurements significant local vertical variations 20 30 even within short depth intervals of 100 200 m and a regular increase of conductivity from 0 8 1 2 w m 1 k 1 to 2 5 3 0 w m 1 k 1 with depth were established it was shown that conductivity variations are closely related to the grade of shock thermal metamorphism the thermal conductivity of metamorphic rocks from the basement of the vorotilovo uplift appeared to be substantially lower up to 40 than the conductivity of similar archaean rocks from ukrainian and baltic shields which we have investigated previously after the drilling had been completed the thermal regime of the rock massif was restored significantly faster than was inferred from previous theoretical considerations by september 1995 it was generally stabilized substantial vertical variations were recorded for all geothermal characteristics the section can be subdivided into three segments with distinct heat flow densities the interval down to 1200 m with the least heat flow density 22 31 mw m 2 i e 50 60 of the highest value the 1200 1900 m interval 34 42 mw m 2 i e 75 85 of the highest value and the 1900 5300 m interval with the highest density 40 56 mw m 2 appreciable local variations of the heat flow density obviously are caused by the refraction of heat flow at structural elements of the massif the character of mutual change of geothermal parameters in certain intervals testifies to the non steady thermal regime and fluid filtration the value of terrestrial heat flow density for the drilling site was estimated as 52 58 mw m 2 calculations show that in the depth range of 400 2000 m the effect of palaeoclimate causes a reduction of heat flow density of approximately 25 this cannot exhaustively account of the recorded vertical variation of heat flow density and allows us to suppose an effect of mass transfer or non steady thermal regime in the upper part of the section

subsurface thermal conductivity assessment in calabria southern italy a regional case study determining the suitability of a local area at a regional or local scale for the geothermal application of low enthalpy systems requires the knowledge of rock thermal conductivity values to evaluate the possibility of low enthalpy heat exchange a digital cartographic tool is also needed to synthesize the thermal properties of the underground this tool should be easily accessible and upgradeable and thus suitable for territorial planning and environmental control in order to address these key issues a methodological approach was developed within the framework of the national vigor project dedicated to evaluating the geothermal potential in southern italy in this paper the region of calabria was selected as a case study around 70 samples that were representative of the main geological formations were collected from all over the area thermal property tests were carried out both in dry and wet conditions using a thermal device in accordance with the modified transient plane source method the thermal conductivity values were then compared with data from the international literature in order to consider the influence of the entire stratigraphic sequence on the thermal conductivity parameters a geostatistical analysis of the available lithostratigraphic data was performed using the matlab toolbox modalstrata specially developed for this purpose a comprehensive geothermal subsurface characterization of calabria was thus obtained