holocene fault scarps near tacoma washington usa airborne laser mapping confirms that holocene active faults traverse the puget sound metropolitan area northwestern continental united states the mapping which detects forest floor relief of as little as 15 cm reveals scarps along geophysical lineaments that separate areas of holocene uplift and subsidence along one such line of scarps we found that a fault warped the ground surface between a d 770 and 1160 this reverse fault which projects through tacoma washington bounds the southern and western sides of the seattle uplift the northern flank of the seattle uplift is bounded by a reverse fault beneath seattle that broke in a d 900 930 observations of tectonic scarps along the tacoma fault demonstrate that active faulting with associated surface rupture and ground motions pose a significant hazard in the puget sound region

upper crustal structure in puget lowland washington results from the 1998 seismic hazards investigation in puget sound a new three dimensional 3 d model shows seismic velocities beneath the puget lowland to a depth of 11 kin the model is based on a tomographic inversion of nearly one million first arrival travel times recorded during the 1998 seismic hazards investigation in puget sound ships allowing higher resolution mapping of subsurface structures than previously possible the model allows us to refine the subsurface geometry of previously proposed faults e g seattle hood canal southern whidbey island and devils mountain fault zones as well as to identify structures tacoma lofall and sequim fault zones that warrant additional study the largest and most important of these newly identified structures lies along the northern boundary of the tacoma basin we informally refer to this structure here as the tacoma fault zone although tomography cannot provide information on the recency of motion on any structure holocene earthquake activity on the tacoma fault zone is suggested by seismicity along it and paleoseismic evidence for abrupt uplift of tidal marsh deposits to its north the tomography reveals four large west to northwest trending low velocity basins tacoma seattle everett and port townsend separated by regions of higher velocity ridges that are coincident with fault bounded uplifts of eocene crescent formation basalt and pre tertiary basement the shapes of the basins and uplifts are similar to those observed in gravity data gravity anomalies calculated from the 3 d tomography model are in close agreement with the observed anomalies in velocity cross sections the tacoma and seattle basins are asymmetric the basin floor dips gently toward a steep boundary with the adjacent high velocity uplift locally with a velocity overhang that suggests a basin vetgent thrust fault boundary crustal fault zones grow from minor folds into much larger structures along strike inferred structural relief across the tacoma fault zone increases by several kilometers westward along the fault zone to lynch cove where we interpret it as a zone of south vergent faulting overthrusting tacoma basin in contrast structural relief along the seattle fault zone decreases west of seattle which we interpret as evidence that the n s directed compression is being accommodated by slip transfer between the seattle and tacoma fault zones together the tacoma and seattle fault zones raise the seattle uplift one of a series of east west trending pop up structures underlying puget lowland from the black hills to the san juan islands

fault interaction may generate multiple slip vectors on a single fault surface slip vectors of multiple orientations on a single fault surface may be explained by the interaction of crustal scale faults in response to nearby earthquakes field observations of at least five sets of striae on a single planar fault surface can be reproduced in numerical experiments these experimental results suggest that slip vectors having variable orientations may reflect a highly transient local stress state in an otherwise constant regional stress field our results suggest that stress inversion techniques should be applied with caution to areas with complex regional scale fault patterns

coseismic temporal changes of slip direction the effect of absolute stress on dynamic rupture abstract we investigate the dynamics of rupture at low stress level we show that one main difference between the dynamics of high and low stress events is the amount of coseismic temporal rake rotation occurring at given points on the fault curved striations on exposed fault surfaces and earthquake dislocation models derived from ground motion inversion indicate that the slip direction may change with time at a point on the fault during dynamic rupture we use a 3d boundary integral method to model temporal rake variations during dynamic rupture propagation assuming a slip weakening friction law and isotropic friction the points at which the slip rotates most are characterized by an initial shear stress direction substantially different from the average stress direction over the fault plane we show that for a given value of stress drop the level of initial shear stress i e the fractional stress drop determines the amount of rotation in slip direction we infer that seismic events that show evidence of temporal rake rotations are characterized by a low initial shear stress level with spatially variable direction on the fault possibly due to changes in fault surface geometry and an almost complete stress drop our models motivate a new interpretation of curved and cross cutting striations and put new constraints on their analysis the initial rake is in general collinear with the initial stress at the hypocentral zone supporting the assumptions made in stress tensor inversion from first motion analysis at other points on the fault especially away from the hypocenter the initial slip rake may not be collinear with the initial shear stress contradicting a common assumption of structural geology on the other hand the later part of slip in our models is systematically more aligned with the average stress direction than the early slip our modeling suggests that the length of the straight part of curved striations is usually an upper bound of the slip weakening distance if this parameter is uniform over the fault plane and the direction of the late part of slip of curved striations should have more weight in the estimate of initial stress direction

viscoelastic cycle model of interseismic deformation in the northwestern united states summary we apply a viscoelastic cycle model to a compilation of gps velocity fields in order to address the kinematics of deformation in the northwestern united states a viscoelastic cycle model accounts for time dependent deformation following large crustal earthquakes and is an alternative to block models for explaining the interseismic crustal velocity field building on the approach taken in pollitz et al we construct a deformation model for the entire western united states based on combined fault slip and distributed deformation and focus on the implications for the mendocino triple junction mtj cascadia megathrust and western washington we find significant partitioning between strike slip and dip slip motion near the mtj as the tectonic environment shifts from northwest directed shear along the san andreas fault system to east west convergence along the juan de fuca plate by better accounting for the budget of aseismic and seismic slip along the cascadia subduction interface in conjunction with an assumed rheology we revise a previous model of slip for the m 9 1700 cascadia earthquake in western washington we infer slip rates on a number of strike slip and dip slip faults that accommodate northward convergence of the oregon coast block and northwestward convergence of the juan de fuca plate lateral variations in first order mechanical properties e g mantle viscosity vertically averaged rigidity explain to a large extent crustal strain that cannot be rationalized with cyclic deformation on a laterally homogeneous viscoelastic structure our analysis also shows that present crustal deformation measurements particularly with the addition of the plate boundary observatory can constrain such lateral variations

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

holocene earthquake records from the cascadia subduction zone and northern san andreas fault based on precise dating of offshore turbidites abstract we present preliminary evidence for a 10 000 year earthquake record from two major fault systems based on sediment cores collected along the continental margins of western north america new stratigraphic evidence from cascadia demonstrates that 13 earthquakes ruptured the entire margin from vancouver island to at least the california border since the eruption of the mazama ash 7700 years ago the 13 events above this prominent stratigraphic marker have an average repeat time of 600 years and the youngest event 300 years ago coincides with the coastal record we also extend the record of past earthquakes to the base of the holocene at least 9800 years ago during which 18 events correlate along the same region the sequence of holocene events in cascadia appears to contain a repeating pattern of events a tantalizing first look at what may be the long term behavior of a major fault system the northern california margin cores show a cyclic record of turbidite beds that may represent holoce

tectonic evolution of the cenozoic olympic subduction complex washington state as deduced from fission track ages for detrital zircons

transpressive duplex and flower structure dent fault system nw england abstract revised mapping along the dent fault northwest england has improved the resolution of folds and faults formed during variscan late carboniferous sinistral transpression a nne trending east down monocline comprising the fell end syncline and taythes anticline was forced in carboniferous cover above a reactivated precursor to the dent fault within the lower palaeozoic basement the taythes anticline is periclinal due to interference with earlier acadian folds the steep limb of the monocline was eventually cut by the west dipping dent fault the hangingwall of the dent fault was dissected by sub vertical or east dipping faults together forming a positive flower structure in cross section and a contractional duplex in plan view the footwall to the dent fault preserves evidence of mostly dip slip displacements whereas strike slip was preferentially partitioned into the hangingwall faults this pattern of displacement partitioning may be typical of transpressive structures in general the faults of the taythes duplex formed in a restraining overlap zone between the dent fault and the rawthey fault to the west the orientations of the duplex faults were a response to kinematic boundary conditions rather than to the regional stress field directly kinematic constraints provided by the dent and neighbouring variscan faults yield a nnw sse regional shortening direction in this part of the variscan foreland

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

integration of paleoseismic data from multiple sites to develop an objective earthquake chronology application to the weber segment of the wasatch fault zone utah we present a method to evaluate and integrate paleoseismic data from multiple sites into a single objective measure of earthquake timing and recurrence on discrete segments of active faults we apply this method to the weber segment ws of the wasatch fault zone using data from four fault trench studies completed between 1981 and 2009 after systematically reevaluating the stratigraphic and chro nologic data from each trench site we constructed time stratigraphic oxcal models that yield site probability density functions pdfs of the times of individual earth quakes we next qualitatively correlated the site pdfs into a segment wide earthquake chronology which is supported by overlapping site pdfs large per event displace ments and prominent segment boundaries for each segment wide earthquake we computed the product of the site pdf probabilities in common time bins which emphasizes the overlap in the site earthquake times and gives more weight to the narrowest best defined pdfs the product method yields smaller earthquake timing uncertainties compared to taking the mean of the site pdfs but is best suited to earth quakes constrained by broad overlapping site pdfs we calculated segment wide earthquake recurrence intervals and uncertainties using a monte carlo model five surface faulting earthquakes occurred on the ws at about 5 9 4 5 3 1 1 1 and 0 6 ka with the exception of the 1 1 ka event we used the product method to define the earthquake times the revised ws chronology yields a mean recurrence interval of 1 3 kyr 0 7 1 9 kyr estimated two sigma 2 range based on interevent recurrence these data help clarify the paleoearthquake history of the ws including the important question of the timing and rupture extent of the most recent earthquake and are essential to the improvement of earthquake probability assessments for the wasatch front region

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

ages and stratigraphy of lower and middle tertiary sedimentary and volcanic rocks of the central cascades washington application to the tectonic history of the straight creek fault in the central cascade range of washington three structural blocks of early tertiary sedimentary and volcanic rocks help to define the position and history of the southern segment of the straight creek fault east of the fault in the teanaway river block the early eocene fluviatile feld spathic sandstone of the swauk formation is interbedded with largely dacitic volcanic rocks of the silver pass volcanic member zircon fission track ages on the silver pass are about 52 m y overlying the tightly folded swauk and silver pass is the teanaway formation a gently dipping accumulation of basalt andesite rare dacite and rhyolite that yields middle eocene about 47 m y whole rock k ar ages conformably overlying the teanaway is the roslyn formation a coal bearing fluviatile feld spathic sandstone of probable middle to late eocene age the late eocene and oligocene naches formation exposed west of the straight creek fault in the cabin creek block is rich in fluviatile feldspathic sandstone and rhyolite flows and tuffs in its lower part but grades upward into a sequence dominated by basalt but with some andesite the basal guye sedimentary member of the naches formation underlies and is interbedded with the mount catherine rhyolite member in the snoqualmie pass area on the basis of zircon fission track ages on silicic tuffs and whole rock k ar ages on basalt the basal part of the naches is about 40 to 44 m y old the formation is tightly folded and complexly faulted along the straight creek fault the straight creek fault intersects the olympic wallowa lineament in the strongly deformed manastash river block in this block fluviatile coal bearing feldspathic sandstone of the manastash formation is overlain by principally dacitic volcanic rocks of the taneum formation overlying the taneum is the basalt of frost mountain we correlate this threefold sequence feldspathic sandstone dacite basalt with the sequence in the teanaway river block small patches of rhyolitic ash flow tuff dated at 33 m y late oligocene and interbedded feldspathic sandstone overlie the roslyn and teanaway formations in the teanaway river block and are probably correlative with the late oligocene wenatchee formation exposed in the chiwaukum graben east of the teanaway river block as well as with the late oligocene volcanic rocks 30 m y along the cascade crest to the southwest these latter rocks are little deformed and unconformably overlie the naches formation the ages and depositional record in the three blocks indicate a tertiary history of dominantly vertical movement along the straight creek fault and its southeasterly splays that merge with the olympic wallowa lineament the horst and graben structure of the blocks as well as enechelon fold axes in the swauk formation suggests some post early eocene right lateral shear along the fault although there is no direct evidence of lateral offset vertical movement significant since early eocene swauk deposition followed late eocene naches deposition but tapered off by late oligocene time and ceased by miocene time when the fault was intruded by the 25 m y old snoqualmie batholith and other plutons however structures with olympic wallowa lineament trends appear to have influenced folding of the miocene yakima basalt subgroup

mount mazama eruption calendrical age verified and atmospheric impact assessed geochemical identification of mount mazama ash in the greenland ice sheet project 2 gisp2 ice core gives a calendrical age of 7627 150 cal yr b p 5677 150 b c for the eruption thus providing a more accurate early holocene stratigraphic time line than previously available the gisp2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 mt spread over an 6 yr period following the eruption of mount mazama taking into account the likelihood of some tropospheric aerosol transport to greenland realistic estimates of the resulting atmospheric optical depth range from 0 6 to 1 5 these values may have produced a temperature depression of 0 6 to 0 7 c at mid to high northern latitudes for 1 3 yr after the eruption these results indicate that the 5677 b c eruption of mount mazama was one of the most climatically significant volcanic events of the holocene in the northern hemisphere we also calculate a maximum stratospheric cl release of 8 1 mt by the eruption which may have led to substantial stratospheric ozone depletion

active shortening of the cascadia forearc and implications for seismic hazards of the puget lowland 1 margin parallel shortening of the cascadia forearc is a consequence of oblique subduction of the juan de fuca plate beneath north america strike slip thrust and oblique crustal faults beneath the densely populated puget lowland accommodate much of this north south compression resulting in large crustal earthquakes to better understand this forearc deformation and improve earthquake hazard assessment we here use seismic reflection surveys coastal exposures of pleistocene strata potential field data and airborne laser swath mapping to document and interpret a significant structural boundary near the city of tacoma this boundary is a complex structural zone characterized by two distinct segments the northwest trending eastern segment extending from tacoma to carr inlet is formed by the broad 11 5 km southwest dipping 11 20 rosedale monocline this monocline raises crescent formation basement about 2 5 km resulting in a moderate gravity gradient we interpret the rosedale monocline as a fault bend fold forming above a deep thrust fault within the rosedale monocline inferred quaternary strata thin northward and form a growth triangle that is 4 1 to 6 6 km wide at its base suggesting 2 3 mm yr of slip on the underlying thrust the western section of the 40 km long north dipping tacoma fault extending from hood canal to carr inlet forms the western segment of the tacoma basin margin structural relief on this portion of the basin margin may be several kilometers resulting in steep gravity and aeromagnetic anomalies quaternary structural relief along the tacoma fault is as much as 350 400 m indicating a minimum slip rate of about 0 2 mm yr the inferred eastern section of the tacoma fault east of carr inlet crosses the southern part of the seattle uplift has variable geometry along strike and diminished structural relief the tacoma fault is regarded as a north dipping backthrust to the seattle fault so that slip on a master thrust fault at depth could result in movement on the seattle fault the tacoma fault or both

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

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

finding concealed active faults extending the southern whidbey island fault across the puget lowland washington 1 the southern whidbey island fault zone swif as previously mapped using borehole data potential field anomalies and marine seismic reflection surveys consists of three subparallel northwest trending strands extending 100 km from near vancouver island to the northern puget lowland east of puget sound the swif makes landfall between the cities of seattle and everett but is concealed beneath a thick mantle of young glacial deposits and vegetation a 20 km wide northwest trending swath of subparallel low amplitude aeromagnetic anomalies crosses this region of the puget lowland and is on strike with the swif the most prominent aeromagnetic anomaly the cottage lake lineament extends at least 18 km and lies approximately on strike with the swif on whidbey island subtle scarps and topographic lineaments on pleistocene surfaces visible on high resolution lidar topography at a number of locations along the swif lie on or near these magnetic anomalies in the field scarps exhibit northeast side up and vertical relief of 1 to 5 m excavations across several lidar scarps lying on or near magnetic anomalies show evidence for multiple folding and faulting events since deglaciation most likely above buried reverse oblique faults excavations in areas away from magnetic anomalies do not show evidence of tectonic deformation in total paleoseismological evidence suggests that the swif produced at least four earthquakes since deglaciation about 16 400 years ago the most recent less than 2700 years ago

gps deformation in a region of high crustal seismicity n cascadia forearc we estimate the rate of crustal deformation in the central and northern cascadia forearc based on a combination of existing global positioning system gps velocity data along the cascadia subduction zone gps strain rates and velocities show that the northwestern washington southwestern british columbia region is currently shortening at 3 3 5 mm yr 31 in a n s direction in good agreement with inference from crustal earthquake statistics on the longterm the shortening rate is 5 6 mm yr 31 providing that the subduction related interseismic loading of the margin is purely elastic compared to the velocity of the oregon forearc with respect to north america v 7m m yr 31 this indicates that most of the forearc motion is accommodated in the puget georgia basin area corresponding to the main concentration of crustal seismicity the difference between the current and long term shortening rates may be taken up during subduction megathrust earthquakes thus these events could produce a sudden increase of n s compression in the puget sound region and could trigger major seattle fault type crustal earthquakes published by elsevier science b v

prehistoric rock avalanches in the olympic mountains washington rock avalanches blocked streams in the olympic mountains southwest of puget sound during the past few thousand years limiting radiocarbon ages indicated that three or four of six avalanches occurred from 1000 to 1300 years ago or shortly thereafter most of the dates were from the outer preserved rings of trees drowned behind avalanche dams these three or four avalanches may be coeval not only with one another but also with abrupt tectonic deformation in western washington no rock avalanches in the olympic mountains are known to have resulted from storms or earthquakes during the past century the avalanches strengthen the case that a large prehistoric earthquake occurred in the puget sound region

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

evidence for earthquake induced subsidence about 1100 yr ago in coastal marshes of southern puget sound washington buried forest and high marsh soils indicate abrupt changes in relative sea level at four coastal localities in southern puget sound at little skookum inlet and red salmon creek douglas fir stumps in growth position are buried by salt marsh peat at localities along mcallister creek and the nisqually river high marsh soils are buried by tidal flat mud localized liquefaction coincided with submergence of the high marsh soil at mcallister creek dramatic changes in seed and diatom assemblages across these contacts confirm rapid submergence at little skookum inlet and red salmon creek salt marsh peat immediately above a buried forest soil contains diatoms indicative of low marsh and tidal flat environments at mcallister creek and nisqually river low marsh and tidal flat diatoms are abundant in laminated mud directly over high marsh peat inferences from modern analogs indicate at least 1 m of subsidence at each site and possibly up to 3 m at skookum inlet abrupt burial of lowland soils in southern puget sound is best explained by coseismic subsidence some of the submergence may be the result of coseismic compaction and postearthquake settlement widespread buried soils large amounts of subsidence coeval submergence across a wide area and ground shaking at the time of subsidence all point to a large earthquake between 1150 and 1010 cal yr b p in southern puget sound as the most likely cause of subsidence

deglacial paleoseismicity in sweden the 9663 bp iggesund event abstract the iggeesund event is an example of the high seismicity which occurred in fennoscandia during deglaciation as a function of the high rate of glacial isostatic uplift this event is dated to varve 9663 bp the iggesund hudiksvall area is represented by intensive postglacial fracturing of the bedrock recorded over an area of at least 50 50 km the most remarkable locality is the boda cave system a hill fractured into a field of large detached blocks with a cave system of more than 2 km length in the varve year 9663 bp an extensive turbidite was spread over an area of 210 80 km liquefaction structures are recorded over an area of 80 30 km and can be assigned to the same varve year structures and deposits of a tsunami are recorded over 80 50 km

paleoseismic evidence for late holocene tectonic deformation along the saddle mountain fault zone southeastern olympic peninsula washington abstract trench and wetland coring studies show that northeast striking strands of the saddle mountain fault zone ruptured the ground about 1000 years ago generating prominent scarps three conspicuous subparallel fault scarps can be traced for 15 km on light detection and ranging lidar imagery traversing the foothills of the southeast olympic mountains the saddle mountain east fault the saddle mountain west fault and the newly identified sund creek fault uplift of the saddle mountain east fault scarp impounded stream flow forming price lake and submerging an existing forest thereby leaving drowned stumps still rooted in place stratigraphy mapped in two trenches one across the saddle mountain east fault and the other across the sund creek fault records one and two earthquakes respectively as faulting juxtaposed miocene age bedrock against glacial and postglacial deposits although the stratigraphy demonstrates that reverse motion generated the scarps slip indicators measured on fault surfaces suggest a component of left lateral slip from trench exposures we estimate the postglacial slip rate to be 0 2 mm yr and between 0 7 and 3 2 mm yr during the past 3000 years integrating radiocarbon data from this study with earlier saddle mountain fault studies into an oxcal bayesian statistical chronology model constrains the most recent paleoearthquake age of rupture across all three saddle mountain faults to 1170 970 calibrated years cal b p which overlaps with the nearby m w 7 5 1050 1020 cal b p seattle fault earthquake an earlier earthquake recorded in the sund creek trench exposure dates to around 3500 cal b p the geometry of the saddle mountain faults and their near synchronous rupture to nearby faults 1000 years ago suggest that the saddle mountain fault zone forms a western boundary fault along which the fore arc blocks migrate northward in response to margin parallel shortening across the puget lowland

chemical and ecological evolution of the miocene ries impact crater lake germany a reinterpretation based on the enkingen subo 18 drill core scientific drilling conducted at the inner slope of the miocene central ries impact crater recovered a partial section of crater lake sediments four sequences were recovered composed of suevite derived sandstones thin lignite seams bituminous shales and marlstones to claystones these flooding evaporation sequences reflect the impact of short term climatic fluctuations on a hydrologically closed basin the superimposed trend from sequences rich in bituminous shales in the lower parts of the section to sequences dominated by organic poor claystones and intercalated lignites in the upper parts of the section resembles that of the 300 m thick central crater basin succession which has previously been considered to reflect a climate controlled development from an alkaline saline lake to a freshwater lake with temporary coal swamps in the sediment core of enkingen however the change from bituminous shales to organic poor claystones with intercalated lignites is associated with a general increase in salinity as indicated by 1 palynomorphs 2 increase in 13c of the lipid biomarker archaeol bis o phytanylglycerol and 3 the occurrence of 13c enriched c20 c25 archaeol o phytanyl o sesterterpanylglycerol specific to halophilic archaea in addition the unidirectional trend in 87sr 86sr of carbonates declining from ratios of variscan basement rocks toward marine ratios indicates a change from 1 weathering of crystalline rocks and suevite to 2 ejected jurassic sediments bunte breccia in the catchment area as the major source of ion influx to the lake from that trend a change in lake water composition and a general increase in ion concentrations are inferred these new results can be applied to a reassessment of major parts of the lacustrine succession of the ries crater we use these data to propose a new hypothetical model for the chemical and ecological evolution of the ries crater lake 1 after the establishment of a stratified brackish eutrophic soda lake due to silicate weathering and evaporation the increasing influx of waters from the bunte breccia carbonate and authigenic silicate precipitation led to a mesotrophic halite lake with marine like ion ratios and concentrations 2 further increase in ions among them mg2 and sr2 resulted in hypersaline conditions with gypsum precipitation low primary production and phreatic sr rich dolomitization in marginal carbonates 3 the final sudden change to oligotrophic freshwater conditions is explained by the formation of an outlet late in the lake history we conclude that the chemical and ecological evolution of the ries lake therefore appears to have been mainly controlled by the weathering history of the catchment area with climate fluctuations causing superimposed cycles similarly changes in terrestrial palynomorph associations may at least partly reflect a change in soil types in the catchment area from fertile moist soils on suevite to dry karst soils and soils on bunte breccia these interpretations imply that the initial suevite blanket of the ries crater was much more continuous and widespread than previously assumed

late holocene earthquakes on the toe jam hill fault seattle fault zone bainbridge island washington five trenches across a holocene fault scarp yield the first radiocarbon measured earthquake recurrence intervals for a crustal fault in western washington the scarp the first to be revealed by laser imagery marks the toe jam hill fault a north dipping backthrust to the seattle fault folded and faulted strata liquefaction features and forest soil a horizons buried by hanging wall collapse colluvium record three or possibly four earthquakes between 2500 and 1000 yr ago the most recent earthquake is probably the 1050 1020 cal calibrated yr b p a d 900 930 earthquake that raised marine terraces and triggered a tsunami in puget sound vertical deformation estimated from stratigraphic and surface offsets at trench sites suggests late holocene earthquake magnitudes near m7 corresponding to surface ruptures 36 km long deformation features recording poorly understood latest pleistocene earthquakes suggest that they were smaller than late holocene earthquakes postglacial earthquake recurrence intervals based on 97 radiocarbon ages most on detrital charcoal range from 12 000 yr to as little as a century or less corresponding fault slip rates are 0 2 mm yr for the past 16 000 yr and 2 mm yr for the past 2500 yr because the toe jam hill fault is a backthrust to the seattle fault it may not have ruptured during every earthquake on the seattle fault but the earthquake history of the toe jam hill fault is at least a partial proxy for the history of the rest of the seattle fault zone

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