air sea interactions during an arctic storm 1 the impacts of increased open water in the beaufort sea were investigated for a summer arctic storm in 2008 using a coupled atmosphere ice ocean model the storm originated in northern siberia and slowly moved into the beaufort sea along the ice edge in late july the maximum wind associated with the storm occurred when it was located over the open water near the beaufort sea coast after it had moved over the chukchi and beaufort seas the coupled model system is shown to simulate the storm track intensity maximum wind speed and the ice cover well the model simulations suggest that the lack of ice cover in the beaufort sea during the 2008 storm results in increased local surface wind and surface air temperature compared to enhanced ice cover extents such as occurred in past decades in addition due to this increase of open water the surface latent and sensible heat fluxes into the atmosphere are significantly increased however there were no significant impacts on the storm track the expanded open water and the loss of the sea ice results in increases in the surface air temperature by as much as 8 c although the atmospheric warming mostly occurs in the boundary layer there is increased atmospheric boundary turbulence and downward kinetic energy transport that reach to mid levels of the troposphere and beyond these changes result in enhanced surface winds by as much as 4 m s during the 2008 storm compared to higher ice concentration conditions typical of past decades the dominant sea surface temperature response to the storm occurs over open water storm generated mixing in the upper ocean results in sea surface cooling of up to 2 c along the southern beaufort sea coastal waters the ekman divergence associated with the storm caused a decrease in the fresh water content in the central beaufort sea by about 11 cm

active tectonics of the seattle fault and central puget sound washington implications for earthquake hazards we use an extensive network of marine high resolution and conventional industry seismic reflection data to constrain the location shallow structure and displacement rates of the seattle fault zone and crosscutting high angle faults in the puget lowland of western washington analysis of seismic profiles extending 50 km across the puget lowland from lake washington to hood canal indicates that the west trending seattle fault comprises a broad 4 6 km zone of three or more south dipping reverse faults quaternary sediment has been folded and faulted along all faults in the zone but is clearly most pronounced along fault a the northernmost fault which forms the boundary between the seattle uplift and seattle basin analysis of growth strata deposited across fault a indicate minimum quaternary slip rates of about 0 6 mm yr slip rates across the entire zone are estimated to be 0 7 1 1 mm yr the seattle fault is cut into two main segments by an active north trending high angle strike slip fault zone with cumulative dextral displacement of about 2 4 km faults in this zone truncate and warp reflections in tertiary and quaternary strata and locally coincide with bathymetric lineaments cumulative slip rates on these faults may exceed 0 2 mm yr assuming no other crosscutting faults this north trending fault zone divides the seattle fault into 30 40 km long western and eastern segments although this geometry could limit the area ruptured in some seattle fault earthquakes a large event ca a d 900 appears to have involved both segments regional seismic hazard assessments must 1 incorporate new information on fault length geometry and displacement rates on the seattle fault and 2 consider the hazard presented by the previously unrecognized north trending fault zone

holocene subaqueous paleoseismology of lake tahoe gravity flow deposits recovered in a suite of sediment cores in lake tahoe were examined to determine if the event deposits were triggered by strong shaking from earthquakes on active faults within and in close proximity to the lake tahoe basin the acoustic character and distribution of individual lacustrine deposits as well as potential source regions were constrained by high resolution seismic chirp reflection and multibeam bathymetric data between 14 and 17 holocene event deposits have been identified in lake tahoe and examination of their source areas suggests they originated from different initiation points along the steep margin with some being synchronous around the basin as opposed to flood related deposits lithologic characteristics magnetic susceptibility carbon and nitrogen isotopic signatures opal content and 14 c dating indicate that these event deposits are reworked lacustrine material radiocarbon dates indicate that the emplacement of these event deposit sediments correlates well with the late holocene paleoseismic earthquake record developed for the tahoe basin when taken alone the causality of these events may appear ambiguous but when the evidence is examined comprehensively it suggests that strong shaking may likely have been the primary trigger for many of the event deposits observed in the lake throughout the holocene for example four event deposits are assigned to tahoe basin faults the most recent earthquakes occurred on the incline village fault between 630 and 120 cal yr b p the southern segment of the west tahoe fault between 4510 and 4070 cal yr b p on the central and northern segments of the west tahoe fault 5600 5330 cal yr b p and on the west tahoe fault between 7890 and 7190 cal yr b p the oldest of the four associated tahoe basin events coincides with the beginning of an extended period when lake tahoe was likely not spilling or spilling intermittently and this suggests that active faulting and footwall uplift cut off the outlet at this time exaggerating drought conditions downstream likewise the event between 5600 and 5330 cal yr b p on the west tahoe fault may have exaggerated a smaller drought reflected downstream in pyramid lake this event may also be the most recent event mre on the largest segment of the west tahoe fault if correct the period since the last rupture is approximately twice the estimated average recurrence interval for the rubicon segment of the west tahoe fault a more complete holocene record of strong shaking greatly extends the paleoseismic record in the region and indicates a combined recurrence interval of between 750 and 800 yr for all faults in the region

pollen and lignin records of late quaternary vegetation lake washington analyses of lignin oxidation products and pollen for an 11 meter core from lake washington provide independent but similar reconstructions of the late quaternary vegetation in the puget lowland an exception is in sediments of the late pleistocene where pollen percentages and influx values suggest conifer forest whereas lignin compositions suggest a treeless source region this dissimilarity appears to result from different major provenances eolian transport of pollen to the lake from adjacent or downstream drainage basins as opposed to fluvial transport of lignified plant debris only from the lake washington drainage basin

laboratory and field determinations of small strain shear modulus for a structured champlain clay values of small strain shear modulus gmax for a champlain sea clay deposit were obtained both under an embankment built 18 years ago and outside of the area influenced by this embankment the sma

location structure and seismicity of the seattle fault zone washington evidence from aeromagnetic anomalies geologic mapping and seismic reflection data a high resolution aeromagnetic survey of the puget lowland shows details of the seattle fault zone an active but largely concealed east trending zone of reverse faulting at the southern margin of the seattle basin three elongate east trending magnetic anomalies are associated with north dipping tertiary strata exposed in the hanging wall the magnetic anomalies indicate where these strata continue beneath glacial deposits the northernmost anomaly a narrow elongate magnetic high precisely correlates with magnetic miocene volcanic conglomerate the middle anomaly a broad magnetic low correlates with thick nonmagnetic eocene and oligocene marine and fluvial strata the southern anomaly a broad complex magnetic high correlates with eocene volcanic and sedimentary rocks this tripartite package of anomalies is especially clear over bainbridge island west of seattle and over the region east of lake washington although attenuated in the intervening region the pattern can be correlated with the mapped strike of beds following a northwest striking anticline beneath seattle the aeromagnetic and geologic data define three main strands of the seattle fault zone identified in marine seismic reflection profiles to be subparallel to mapped bedrock trends over a distance of 50 km the locus of faulting coincides with a diffuse zone of shallow crustal seismicity and the region of uplift produced by the m 7 seattle earthquake of a d 900 930

seismic reflection images beneath puget sound western washington state the puget lowland thrust sheet hypothesis seismic reflection data show that the densely populated puget lowland of western washington state is underlain by subhorizontal paleogene and neogene sedimentary rocks deformed by west and northwest trending faults and folds from south to north beneath the lowland features seen on the seismic data include the horizontally stratified 3 5 km thick tacoma sedimentary basin the seattle uplift with south dipping 20 strata on its south flank and steeply 50 to 90 north dipping strata and the west trending seattle fault on its north flank the 7 5 km thick northward thinning seattle sedimentary basin the antiformal kingston arch and the northwest trending transpressional southern whidbey island fault zone swif interpreting the uplifts as fault bend and fault propagation folds leads to the hypothesis that the puget lowland lies on a north directed thrust sheet the base of the thrust sheet may lie at 14 to 20 km depth within or at the base of a thick block of basaltic crescent formation its edges may be right lateral strike slip faults along the base of the cascade range on the east and the olympic mountains on the west our model suggests that the seattle fault has a long term slip rate of about 0 25 mm year and is large enough to generate a m7 6 to 7 7 earthquake

the importance of earthquake induced landslides to long term slope erosion and slope failure hazards in seismically active regions abstract this paper describes a general method for determining the amount of earthquake induced landsliding that occurs in a seismically active region over time this determination can be used as a quantitative measure of the long term hazard from seismically triggered landslides as well as a measure of the importance of this process to regional slope erosion rates and landscape evolution the method uses data from historical earthquakes to relate total volume of landslide material dislodged by an earthquake to the magnitude m and seismic moment m0 of the earthquake from worldwide data a linear regression relation between landslide volume v and m0 is determined as v m0 1018 9 0 13 where v is measured in m3 and m0 is in dyn cm to determine the amount of earthquake generated landsliding over time this relation is combined with data on seismic moment release for a particular region which may be derived from either earthquake history or fault slip data the form of the m0 v relation allows the rate of production of earthquake induced landslides over time to be determined from total rate of seismic moment release without regard to the distribution of individual events thus simplifying and generalizing the determination application of the method to twelve seismically active regions with areas ranging from 13 275 to 2 308 000 km2 shows that erosion rates from earthquake induced landslides vary significantly from region to region of the regions studied the highest rates were determined for the island of hawaii new zealand western new guinea and the san francisco bay region of california significantly lower rates were determined for iran tibet the sierra nevada great basin region of california and central japan for the time period from 715 ad to the present intermediate rates were determined for peru southern california onshore california turkey and central japan for the time period from 1586 ad to the present to determine the relative long term importance of seismically triggered landslides these erosion rates are compared to erosion rates calculated for other slope processes and to rates calculated from fluvial sediment discharge comparisons with other slope processes indicate that earthquake induced landslides are the predominant agents of slope erosion on the island of hawaii in the san francisco bay region and in western new guinea for hawaii the san francisco bay region and sierra nevada great basin region of california the erosion rates calculated for earthquake induced landslides also exceed the regional erosion rates calculated from fluvial sediment discharge

tree ring correlation between prehistoric landslides and abrupt tectonic events in seattle washington radiocarbon ages of submerged trees on landslide deposits in lake washington seattle indicate that the most recent slides in three separate areas may have occurred simultaneously about 1000 years ago tree ring crossdating shows that seven bark bearing trees from one of these recent slides and a tree 23 kilometers to the northwest in a probable tsunami deposit on the shore of puget sound died in the same season of the same year the close coincidence among the most recent lake landslides a probable tsunami abrupt subsidence and other possible seismic events gives evidence for a strong prehistoric earthquake in the seattle region

slope failures associated with the 1988 saguenay earthquake quebec canada nine case records of slope failure during the saguenay earthquake are documented including five in granular embankments two in natural slopes in granular material with small embankments at the top and two in sensitive clay the bedrock motion during the earthquake is well documented each failure is related to the most probable bedrock motion at the site 0 05 to 0 15 g for the seven cases of failure in granular slopes the reserve of stability under static conditions was relatively low before the earthquake and only a small additional undrained loading was necessary to develop failure two slope failures occurred in extrasensitive clay deposits containing no visible lens or layer of silt or sand silty or sandy materials have been identified only at the clay till contact it is believed that in at least one of the sites a portion of the failure surface developed at the inclined clay till contact key words slope failure earthquake sensitive clays embankment fill stability granular material

origin and evolution of the seattle fault and seattle basin washington analysis of seismic reflection data reveals that the seattle basin washington is markedly asymmetric and consists of 9 10 km of eocene and younger deposits the basin began as a discrete geologic element in the late eocene 40 ma the result of a reorganization in regional fault geometry and kinematics in this reorganization dextral offset on the puget fault south east of seattle stepped eastward and the seattle fault began as a restraining transfer zone north vergent reverse or thrust faulting on the seattle fault forced flexural subsidence in the seattle basin to the north offset on the seattle fault and subsidence of the seattle basin have continued to the present

a tsunami about 1000 years ago in puget sound washington water surged from puget sound sometime between 1000 and 1100 years ago overrunning tidal marshes and mantling them with centimeters of sand one overrun site is 10 kilometers northwest of downtown seattle another is on whidbey island some 30 kilometers farther north neither site has been widely mantled with sand at any other time in the past 2000 years deposition of the sand coincided to the year or less with abrupt probably tectonic subsidence at the seattle site and with landsliding into nearby lake washington these findings show that a tsunami was generated in puget sound and they tend to confirm that a large shallow earthquake occurred in the seattle area about 1000 years ago

high temperature memory in calcic amphiboles and constraints on compositional control of their 40ar 39ar ages well characterized calcic amphiboles from an incompletely mixed magmatic rock association of mainly intermediate dioritic composition were studied by incremental heating experiments of 40 ar 39 ar the rocks in question were thermally overprinted by late hercynian granites microprobe and scanning electron microscopy analyses show that the amphibole grains consist of two different calcic hornblende varieties 1 a si and mg rich variety and 2 a variety enriched in al ti fe k and na the mg si rich hornblende can be further characterized by its higher cao k 2 o ratios 30 50 compared to the al ti fe k na rich hornblende 12 15 three hornblende separates that previously had yielded conventional k ar ages of 320 317 and 302 ma have been dated by the 40 ar 39 ar step heating technique the low and medium temperature parts of the 40 ar 39 ar age spectrum show discordant ar systematics with single step ages generally younger than 325 ma the gas released at the highest temperature steps preserves an exceptional record of old and remarkably similar integrated ages 342 346 and 344 ma the high temperature ages correspond to phases with higher apparent cao k 2 o ratios 30 45 and are interpreted to result from ar release from mg si hornblende domains that are assumed to have been very resistent to ar loss during the late hercynian thermal events the results of this study suggest that ar retentivity differs among calcic amphiboles and mg si rich hornblendes are more ar retentive than their al ti fe k na rich counterparts

paleoearthquakes in the puget sound region recorded in sediments from lake washington u s a holocene sediments in lake washington contain a series of turbidites that were episodically deposited throughout the lake the magnetic signatures of these terrigenous layers are temporally and areally correlatable large earthquakes appear to have triggered slumping on the steep basin walls and landslides in the drainage area resulting in turbidite deposition one prominent turbidite appears to have been deposited about 1100 years ago as the result of a large earthquake downcore susceptibility patterns suggest that near simultaneous slumping occurred in at least three separate locations two of which now contain submerged forests several other large earthquakes may have occurred in the last 3000 years

tree ring evidence for an a d 1700 cascadia earthquake in washington and northern oregon geologic evidence and radiocarbon dating indicate that a subduction earthquake or series of earthquakes occurred about 300 yr ago along the pacific northwest coast of the united states some radiocarbon dates come from remnants of the myriad trees drowned by coincident subsidence at several coastal lowland locations in washington and northern oregon we located two or more trees that survived partial submergence and lived to the 1990s many of them were damaged by shaking and or inundation some survivors recorded the event s by anomalous changes in ring width or anatomy of their annual rings the disturbance initiating the changes can be dated to between the growing seasons of a d 1699 and 1700 one killed tree has a last ring of a d 1699 tree ring dated evidence of disturbance extends along about 100 km of coastal washington and northern oregon these results support the inference that a great m w 8 earthquake or larger at the cascadia subduction zone generated the historical tsunami that struck japan in january 1700

optical dating of tsunami laid sands abstract the ages of some tsunami deposits can be determined by optical dating a key requirement being that the deposits are derived from sediment that was reworked and exposed to daylight by tidal currents waves wind or bioturbation during the last years before the tsunami measurements have been made using 1 4 ev infrared excitation of k feldspar grains separated from samples of prehistoric tsunami sand sheets and modern analogs of tsunami source sediments at four sites in washington state and british columbia source sands gave equivalent doses indicative of recent exposure to daylight tsunami sand at cultus bay washington yielded an optical age of 1285 95 yr calendric years before a d 1995 1 at 2 this age overlaps the range of from 1030 to 1100 yr determined through a combination of high precision radiocarbon dating and stratigraphic correlation tsunami sands at three sites near tofino and port alberni on vancouver island british columbia have optical ages of 260 20 325 25 and 335 45 yr historical records and radiocarbon dating show that the sand at each of the three sites is between 150 and 400 yr old these optical ages support the hypothesis that the vancouver island sands were deposited by a tsunami generated by a large earthquake on the cascadia subduction zone about 300 yr ago

proprietes caracteristiques des argiles de l est du canada the compilation of numerous geotechnical data has allowed the definition of the main physical mechanical and hydraulic properties of marine and lacustrine clays of eastern canada as well as the establishment of correlations between some of these properties the possible uses of these correlations are described this study shows that the clays of eastern canada exhibit a behaviour similar to that of other clays but that they are characterized by a higher degree of structuration keywords physical properties mechanical properties hydraulic properties clays canada correlations journal translation

stratigraphic and microfossil evidence for late holocene tsunamis at swantown marsh whidbey island washington abstract four muddy sand sheets occur within a tidal marsh peat at swantown on the west coast of whidbey island washington the two largest sand sheets pinch out about 100 m inland and became thinner and finer grained landward all four sand sheets contain marine microfossils and have internal stratification they record repeated inundation of the marsh over a short time period by distinct pulses of sediment laden ocean water consistent with deposition by a tsunami wave train the layers have been radiocarbon dated to 1160 1350 1400 1700 1810 2060 and 1830 2120 cal yr b p the overlap in age between the two youngest layers and inferred great earthquake events at the cascadia plate boundary some 250 km to the west suggests they were emplaced by tsunamis from this source area the two older layers do not correlate with plate boundary events they may be products of tsunamis caused by earthquakes on local faults in the strait of juan de fuca or by submarine landslides in this area

glaciofluvial infilling and scour of the puget lowland washington during ice sheet glaciation the puget lobe the southwesternmost extension of the cordilleran ice sheet last advanced into the puget lowland of western washington at about 15 ka the advancing ice sheet deposited voluminous sediment on a prograding proglacial outwash plain that extended from the olympic mountains to the cascade range herein recognized as the great lowland fill subsequent overrunning by the ice sheet excavated deep linear troughs now occupied by the large lakes and marine waters of puget sound excavation of these troughs and valleys of the puget lowland required the net transport of about 1000 km3 of sediment almost entirely during ice occupation and primarily by subglacial water these landforms of glaciofluvial deposition and erosion define the modern landscape here emphasizing the importance of these processes in the region s geomorphology

abrupt uplift within the past 1700 years at southern puget sound washington shorelines rose as much as 7 meters along southern puget sound and hood canal between 500 and 1700 years ago evidence for this uplift consists of elevated wave cut shore platforms near seattle and emerged peat covered tidal flats as much as 60 kilometers to the southwest the uplift was too rapid for waves to leave intermediate shorelines on even the best preserved platform the tidal flats also emerged abruptly they changed into freshwater swamps and meadows without first becoming tidal marshes where uplift was greatest it adjoined an inferred fault that crosses puget sound at seattle and it probably accompanied reverse slip on that fault 1000 to 1100 years ago the uplift and probable fault slip show that the crust of the north america plate contains potential sources of damaging earthquakes in the puget sound region

the southern whidbey island fault an active structure in the puget lowland washington information from seismic reflection profiles outcrops boreholes and potential field surveys is used to interpret the structure and history of the southern whidbey island fault in the puget lowland of western washington this northwest trending fault comprises a broad as wide as 6 11 km steep northeast dipping zone that includes several splays with inferred strike slip reverse and thrust displacement transpressional deformation along the southern whidbey island fault is indicated by along strike variations in structural style and geometry positive flower structure local unconformities out of plane displacements and juxtaposition of correlative sedimentary units with different histories the southern whidbey island fault represents a segment of a boundary between two major crustal blocks the cascade block to the northeast is floored by diverse assemblages of pre tertiary rocks the coast range block to the southwest is floored by lower eocene marine basaltic rocks of the crescent formation the fault probably originated during the early eocene as a dextral strike slip fault along the eastern side of a continental margin rift bending of the fault and transpressional deformation began during the late middle eocene and continues to the present oblique convergence and clockwise rotation along the continental margin are the inferred driving forces for ongoing deformation evidence for quaternary movement on the southern whidbey island fault includes 1 offset and disrupted upper quaternary strata imaged on seismic reflection profiles 2 borehole data that suggests as much as 420 m of structural relief on the tertiary quaternary boundary in the fault zone 3 several meters of displacement along exposed faults in upper quaternary sediments 4 late quaternary folds with limb dips of as much as 9 5 large scale liquefaction features in upper quaternary sediments within the fault zone and 6 minor historical seismicity the southern whidbey island fault should be considered capable of generating large earthquakes m s 7 and represents a potential seismic hazard to residents of the puget lowland

holocene landslides and a 3500 year record of pacific northwest earthquakes from sediments in lake washington lake washington which forms the eastern boundary of seattle is located in a tectonically active area containing several strands of the seattle fault high resolution seismic reflection profiling sidescan swath imagery and sediment coring were used to define deformation of holocene lake sediments and the distribution geometry age and causes of submarine landslides numerous large block slides sediment slumps and debris flows are present throughout the lake and large landslides obscure the surficial structure of seattle fault strands as they pass through the lake in addition most bays along the lake margin are the headwalls of large submarine slides submerged forests show evidence of deep seated block failures that have exposed glacial sediments and tertiary rocks the massive submarine block slides and retrogressive submarine slope failures were triggered most likely by large m b 7 earthquakes on the seattle fault and or large to great m b 8 temblors occurring elsewhere in cascadia buried landslides suggest that submarine slope failures and mass wasting occurred more than once in the last 11 000 yr sediments in lake washington preserve a record of episodic deposition of turbidites possibly caused by seismically induced submarine landslides magnetic susceptibility profiles on 36 gravity cores show a characteristic series of magnetic peaks that can be traced throughout the lake x radiography and grain size analyses suggest that the magnetic peaks represent anomalous detrital layers that in some cases are turbidites the areal extent and magnetic signatures of many of the deposits suggest multiple sources which is consistent with numerous local landslides caused by large earthquakes radiocarbon dating and correlation of the downcore magnetic profiles establish a sediment record in which episodic sedimentary disturbances occurred seven times in the last 3500 yr if these deposits are seismically induced turbidites seismites then large earthquakes have occurred about every 300 500 yr in the puget sound region

the general and congruent effects of structure in natural soils and weak rocks the engineering properties of naturally occurring sedimentary and residual deposits which are usually treated in geotechnical engineering as soils are reviewed and it is shown that usually they have characteristics due to bonded structure which are similar to those of porous weak rock while this structure can arise from many causes its effects follow a simple general pattern that involves stiff behaviour followed by yield this yield can be described in a similar way to that occurring due to overconsolidation although it is a separate phenomenon the effects of structure are as important in determining engineering behaviour as are the effects of initial porosity and stress history which are the basic concepts of soil mechanics as it can be described in a general way it is concluded that structure and its effects should be treated as a further basic concept of equal importance l article passe en revue les proprietes des depots sedimentaires et residuels naturels qui sont nor malement traites comm

geologic evidence of earthquakes at the snohomish delta washington in the past 1200 yr exposed channel banks along distributaries of the lower snohomish delta in the puget lowland of washington reveal evidence of at least three episodes of liquefaction at least one event of abrupt subsidence and at least one tsunami since ca a d 800 the 45 measured stratigraphic sections consist mostly of 2 4 m of olivegray intertidal mud containing abundant marsh plant rhizomes the most distinctive stratigraphic unit is a couplet comprising a 0 523 cm thick laminated fining upward tsunami laid sand bed overlain by 2210 cm of gray clay we correlated the couplet which is generally 2 m below the modern marsh surface across an 20 km2 area sand dikes and sand filled cracks to 1 m wide which terminate upward at the couplet and sand volcanoes preserved at the level of the sand bed record liquefaction at the same time as couplet deposition differences in the type and abundance of marsh plant rhizomes across the couplet horizon as well as the gray clay layer suggest that compaction during this liquefaction led to abrupt local lowering of the marsh surface by as much as 50 75 cm radiocarbon ages show that the tsunami and liquefaction date from ca a d 800 to 980 similar to the age of a large earthquake on the seattle fault 50 km to the south we have found evidence for at least two and possibly as many as five other earthquakes in the measured sections at two or more stratigraphic levels above the couplet sand dikes locally feed sand volcanoes radiocarbon ages and stratigraphic position gov suggest that one set of these dikes formed ca a d 910 990 radiocarbon ages on a younger set indicate a limiting maximum age of a d 1400 1640 we also interpret a sharp lithologic change from olive gray rhizome rich mud to grayer rhizome poor mud 1 m above the couplet to indicate a second abrupt lowering of the marsh surface during an earthquake ca a d 1040 1400 but no conclusive liquefaction structures have been identified at this horizon two distinctive coarse sand laminae 30 80 cm below the couplet may record tsunamis older than a d 800 thus study shows that in the past 1200 yr this part of washington s puget lowland has been subjected to stronger ground shaking than in historic times since ca 1870

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

experimental and numerical investigation of the saint adelphe landslide after the 1988 saguenay earthquake on 25 november 1988 after the saguenay earthquake a landslide occurred in the municipality of saint adelphe the soil profile indicated that the deposit was composed of a stiff clay crustal layer

a history of pacific northwest earthquakes recorded in holocene sediments from lake washington large earthquakes can trigger slumping of the steep walls of lake basins and landslides in the drainage area resulting in turbidite deposition in the lake and increased detrital flux from inlets holocene sediments in piston cores from lake washington contain a series of terrigenous layers that were episodically deposited in the lake sedimentological geochemical and paleomagnetic analyses on nine piston cores show that the detrital layers are temporally and areally correlatable indicating basinwide disruptions these layers are opaque on x radiographs are coincident with magnetic susceptibility peaks have abundant aluminosilicate minerals are relatively coarse grained and have low organic carbon and biogenic silica contents the thicknesses and geographic distributions of the layers suggest that they are not due to floods or delta destabilization side scan swath imagery and subbottom profiling show that large slumps subaqueous landslides and debris flows are common along the margins of the lake a detailed chronology established from 21 radiocarbon ages on five cores show that a prominent turbidite was deposited about 1000 1100 years ago this turbidite apparently was triggered by a large earthquake that probably occurred on the seattle fault other depositional events in the sediment record at 1500 1700 2400 2500 and 2800 3200 years ago coincide with periods of landsliding that have been previously inferred from the dating of drowned trees in the lake more than 30 depositional events have occurred in the last 12 000 years and 21 disturbances have occurred since the deposition of the mazama ash about 7 600 years ago if all the events are due to earthquakes the puget sound region has been subject to major shaking every 300 to 400 years the strong intensities needed to trigger subaqueous slides may not be generated by just local sources such as the seattle fault but could also be caused by great subduction earthquakes occurring along the coast

shear modulus and damping ratio of sensitive eastern canada clays the shear modulus and equivalent viscous damping ratio of three sensitive clays from the sediments of the champlain sea were investigated using a combined triaxial simple shear apparatus the tests

time and size of a giant earthquake in cascadia inferred from japanese tsunami records of january 1700 geological evidence shows that great earthquakes have occurred in the recent prehistoric past in the cascadia subduction zone off the pacific coast of north america the most recent event or series of events is dated at about 300 years ago1 4 but the precise date and magnitude have not been determined geological investigations have not been able to distinguish a single giant earthquake from a series of great earthquakes occurring over a timespan of a decade or two4 although this information is important for the assessment of future hazard5 we have found several tsunami records in japan from ad 1700 with no indication of a local cause historical earthquake records and palaeoseismic evidence indicate the absence of a large earthquake in 1700 in south america alaska or kamchatka leaving cascadia as the most likely source of this tsunami the estimated time of the earthquake is the evening about 21 00 local time of 26 january 1700 the magnitude is estimated as 9 from the tsunami heights in which case the earthquake ruptured the entire length of the cascadia subduction zone2 these estimates are consistent with native american legends that an earthquake occurred on a winter night6

the 25 november 1988 saguenay quebec earthquake source parameters and the attenuation of strong ground motion the saguenay earthquake of 25 november 1988 occurred close to the southern margin of the saguenay graben in southern quebec it was caused by almost purely dip slip faulting centered at a depth of 26 km with a p axis oriented northeast southwest this faulting mechanism is similar to those of the larger historical earthquakes in eastern north america but the focal depth is substantially greater than all but one of these events the seismic moment estimated from regional pni waves and teleseismic long period body waves is 5 10 24 dyne cm corresponding to a moment magnitude of 5 8 the source duration of the earthquake is estimated to be 1 8 sec corresponding to a stress drop of 160 bars which is not significantly higher than the average stress drop of 120 bars estimated from previous large earthquakes in eastern north america in order to simultaneously match the recorded ground motion amplitudes of strong motion acceleration strong motion velocity and teleseismic short period and long period body waves it is necessary to use a source function having a complex shape that implies the presence of asperities and larger local stress drops the large set of strong motion recordings of the saguenay earthquake has been used to validate a procedure for estimating strong ground motion attenuation based on a simple wave propagation model the most important feature of the recorded strong motions is that their peak amplitudes do not decay significantly with distance inside 120 km but then decay abruptly beyond 120 km profiles of recorded accelerograms with absolute times indicate that at distances beyond 64 km the peak ground motions are due to strong postcritical reflections from velocity gradients in the lower crust the principal shear wave arrivals and the variation of their peak amplitudes with distance were reproduced in synthetic seismograms generated using a regional crustal structure model the critical distances for the postcritical reflections were short because of the deep focal depth of the event causing the elevation of ground motion amplitudes out to 120 km similar studies of earthquakes in other regions of eastern north america indicate that the strength of the postcritical reflections and the distance ranges over which they are dominant are controlled by the focal depth and crustal structure regional variations in crustal structure thus give rise to predictable regional variations in strong ground motion attenuation