obducted nappe sequence in the san juan islands northwest cascades thrust system washington and british columbia the san juan islands northwest cascades thrust system in washington and british columbia is composed of previously accreted terranes now assembled as four broadly defined composite nappes stacked on a continental footwall of wrangellia and the coast plutonic complex emplacement ages of the nappe sequence are interpreted from zircon ages field relations and lithlogies to young upward the basal nappe was emplaced prior to early turonian time 93 ma indicated by the occurrence of age distinctive zircons from this nappe in the sidney island formation of the nanaimo group the emplacement age of the highest nappe in the thrust system postdates 87 ma detrital zircons within the nappe the nappes bear high pressure low temperature hp lt mineral assemblages indicative of deep burial in a thrust wedge however several features indicate that metamorphism occurred prior to nappe assembly metamorphic discontinuities at nappe boundaries absence of hp lt assemblages in the footwall to the nappe pile and absence of significant unroofing detritus in the nanaimo group a synorogenic relationship of the thrust system to the nanaimo group is evident from mutually overlapping ages and by conglomerates of nanaimo affinity that lie within the nappe pile from the foregoing relations and broader cordilleran geology the tectonic history of the nappe terranes is interpreted to involve initial accretion and subduction zone metamorphism south of the present locality uplift and exhumation orogen parallel northward transport of the nappes as part of a forearc sliver and finally obduction at the present site over the truncated south end of wrangellia and the coast plutonic complex

linked thrust and strike slip faulting during late cretaceous terrane accretion in the san juan thrust system northwest cascades orogen washington the san juan thrust system makes up the western elements of the late cretaceous northwest cascades orogen of washington a stack of metamorphic nappes with terranes ranging in age from early paleozoic to middle cretaceous the tectonic development of the nappes is an unresolved issue important to understanding plate convergent processes operating in the north american cordillera in the creta ceous as well as at other times two terrane bounding fault zones were studied in this project the lopez and the rosario fault zones the fault zone rocks were affected by two cataclastic plastic late cretaceous deformational events d1 and d2 that included accretion and lateral motion during blueschist facies metamorphic conditions d1 produced upright folds and a subvertical axial planar s1 foliation fabric in the lopez fault zone and southwest vergent folds and gently northeast dipping axial planar s1 foliation in the rosario fault zone in the lopez fault zone d2 produced northwest striking and subvertical strike slip shear zones s2 with dominant sinistral displacements whereas in the rosario fault zone d2 generated low angle s2 shear zones and various slip crenulation fabrics formed by northwest directed thrust motion the d1 fabrics are inferred to be related to initiation of subduction related accretion of the nappes by orogen normal southwest northeast shortening and accretionary tectonics the subsequent d2 fabrics developed as temporally overlapping subduction related low angle thrusts in the rosario fault zone and high angle sinistral strike slip faults in the lopez fault zone in an overall transpressive setting due to oblique convergence this model suggests that the high angle lopez fault zone d2 was located above a gently northeast dipping thrust detachment s2 expressed by the rosario fault zone that allowed the accreted nappes to move parallel to the orogen the kinematic model cannot validate regional scale dextral terrane translation of the san juan thrust system as inferred by paleomagnetic data elsewhere in the western united states but addresses important tectonic processes caused by oblique subduction and changing plate conditions

fracture cleat analysis of coals from zonguldak basin northwestern turkey relative to the potential of coalbed methane production abstract in this study the fracture structure of three coals sulu k 1 acilik k 2 and cay dogu ayak from two different seams in the zonguldak basin located on the black sea coast of turkey have been analyzed in relation to coalbed methane recovery x ray computerized tomography ct light microscopy image analysis and scanning electron microscopy sem analysis have been performed on mine coal samples to have a better understanding of distribution of minerals fracture morphology and apertures and matrix fracture interactions via examination of fracture surfaces results show that the acilik and sulu coals seem to be structurally more prone to be commercially productive these coals show a high degree of fracturing and cleat development as evidenced by x ray ct and light microscopy examination of polished surfaces although the cay dogu ayak coal shows a high fracture density the cleat surface morphology and smaller fracture apertures may make this coal unfavorable for gas flow

regional p wave velocity structure of the northern cascadia subduction zone 1 this paper presents the first regional three dimensional p wave velocity model for the northern cascadia subduction zone sw british columbia and nw washington state constructed through tomographic inversion of first arrival traveltime data from active source experiments together with earthquake traveltime data recorded at permanent stations the velocity model images the structure of the subducting juan de fuca plate megathrust and the fore arc crust and upper mantle beneath southern vancouver island the megathrust above the juan de fuca plate is characterized by a broad zone 25 35 km depth having relatively low velocities of 6 4 6 6 km s this relative low velocity zone coincides with the location of most of the episodic tremors recently mapped beneath vancouver island and its low velocity may also partially reflect the presence of trapped fluids and sheared lower crustal rocks the rocks of the olympic subduction complex are inferred to deform aseismically as evidenced by the lack of earthquakes within the low velocity rocks the fore arc upper mantle beneath the strait of georgia and puget sound is characterized by velocities of 7 2 7 6 km s such low velocities represent regional serpentinization of the upper fore arc mantle and provide evidence for slab dewatering and densification tertiary sedimentary basins in the strait of georgia and puget lowland imaged by the velocity model lie above the inferred region of slab dewatering and densification and may therefore partly result from a higher rate of slab sinking in contrast sedimentary basins in the strait of juan de fuca lie in a synclinal depression in the crescent terrane the correlation of in slab earthquake hypocenters m 4 with p wave velocities greater than 7 8 km s at the hypocenters suggests that they originate near the oceanic moho of the subducting juan de fuca plate

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

characteristics and origins of coal cleat a review abstract cleats are natural opening mode fractures in coal beds they account for most of the permeability and much of the porosity of coalbed gas reservoirs and can have a significant effect on the success of engineering procedures such as cavity stimulations because permeability and stimulation success are commonly limiting factors in gas well performance knowledge of cleat characteristics and origins is essential for successful exploration and production although the coal cleat literature spans at least 160 years mining issues have been the principal focus and quantitative data are almost exclusively limited to orientation and spacing information few data are available on apertures heights lengths connectivity and the relation of cleat formation to diagenesis characteristics that are critical to permeability moreover recent studies of cleat orientation patterns and fracture style suggest that new investigations of even these well studied parameters can yield insight into coal permeability more effective predictions of cleat patterns will come from advances in understanding cleat origins although cleat formation has been speculatively attributed to diagenetic and or tectonic processes a viable mechanical process for creating cleats has yet to be demonstrated progress in this area may come from recent developments in fracture mechanics and in coal geochemistry

mineral matter in coals cleat minerals and their origin in some coals from the english midlands abstract in four coal seam profiles from the cannock coalfield west midlands the cleat joint frequency is a function of lithotype greatest in vitarin and is inversely related to bed thickness the cleat minerals were studied 1 under the microscope optical and electron 2 by x ray diffraction and 3 chemically the minerals present are pyrite marcasite sphalerite galena sulphides quartz kaolinite silicates ankerite calcite carbonates and apatite this sequence has features in common with diagenetic sequences recorded in other rock types and it is concluded that the cleat minerals in coal form in response to pore fluid evolution and movement during burial diagenesis the elements are thought to originate from both the coal and the associated sediments mainly mudrocks similarities in diagenetic sequences are in part a reflection of the importance of organic maturation reactions in all the rock types in the sequence whereas differences are attributed to the dominance of these reactions in the coal itself

modelling of gas generation in coals of the zonguldak basin northwestern turkey abstract the generation of gas in selected coal seams of the zonguldak basin northwestern turkey has been modelled by incorporating laboratory derived non isothermal reactions kinetics into the geothermal histories of the coal bearing strata kinetic parameters have been determined by programmed temperature open system pyrolysis of a low maturity 0 5 r 0 coal at three linnear heating rates of 0 1 0 7 and 5 0 k min the mathematical analysis of the bulk hydrocarbon evolution profiles assuming 25 first order reactions with activation energies regularly spaced between 46 and 70 kcal mol and a single pre exponential factor a yielded a value of a 3 17 10 16 min 1 and a rather broad hydrocarbon potential vs activation energy distribution with a maximum at 55 kcal mol geological time temperature relationships have been reconstructed by use of the basin modelling technique depending on the location within the basin of the wells studied and on the geological history of the coal bearing sediments the simulation procedure resulted in a predicted gas generation of up to 40 mg per g of coal

high resolution temporal and stratigraphic record of siletzia s accretion and triple junction migration from nonmarine sedimentary basins in central and western washington the presence of early eocene near trench magmatism in western washington and southern british columbia has led to speculation that this area experienced ridge trench interaction during that time however the effects of this process as they are preserved in other parts of the geologic record are poorly known we present high precision u pb zircon geochronology from paleogene nonmarine sedimentary and volcanic sequences in central and western washington that preserve a record of tectonic events between ca 60 and 45 ma the data reveal that the swauk chuckanut and manastash formations formed a nonmarine sedimentary basin along the north american margin between 59 9 and 51 3 ma this basin experienced significant disruption that culminated in basinwide deformation uplift and partial erosion during accretion of the siletzia terrane between 51 3 and 49 9 ma immediately following accretion dextral strike slip faulting began or accelerated on the darrington devil s mountain entiat leavenworth eagle creek and straight creek fraser fault zones between 50 and 46 ma during this time the chumstick formation was deposited in a strike slip basin coeval with near trench magmatism faulting continued on the entiat eagle creek and leavenworth faults until a regional sedimentary basin was reestablished 45 9 ma and may have continued on the straight creek fraser fault until 35 30 ma this record of basin disruption volcanism and strike slip faulting is consistent with ridge trench interaction and supports the presence of an oceanic spreading ridge at this latitude along the north american margin during the early eocene

remagnetization during cretaceous normal superchron in eastern san juan islands wa implications for tectonic history abstract the eastern san juan islands expose an island arc ophiolite sequence and one or more ocean floor terranes cover rocks of the former including red radiolarian tuff and arc derived sandstone have no penetrative fabric and lack high pressure minerals in contrast pillow basalts and ribbon cherts of the latter are strongly deformed and the overlying metagraywacke is folded with a penetrative axial plane cleavage all ocean floor rocks have aragonite in veins indicative of higher pressure conditions than experienced by the island arc rocks a downward magnetization is common to the ocean floor rocks consistent with widespread remagnetization during the cretaceous normal superchron this magnetization is carried by magnetite and in red rocks by hematite fluid flow during or after deformation and high p metamorphism likely facilitated remagnetization at low temperature the magnetic directions are somewhat scattered but most are moderately to steeply down to the southeast they are far from directions expected with or without northward transport of baja bc rotation of observed directions into agreement with those expected for either present or more southerly locations also rotate structural elements in the host rocks three alternative rotation histories explored here all produce structural reconstructions that differ considerably from the present structure a tectonic history of the eastern san juan islands based on any of these reconstructions would be superior to one based on present attitudes of structures this is because at least a constraint that the restored paleomagnetic directions match a paleomagnetic field direction is satisfied choices among alternative reconstructions would become clearer with better understanding of relative ages of specific structures and their magnetizations improved geologic understanding of the regional setting where the rocks could have been deformed and remagnetized would also help

mineral matter in triassic and tertiary low rank coals from south australia abstract the minerals and non mineral inorganic constituents in triassic and tertiary low rank coals from various coal deposits in south australia were studied using selective chemical leaching and oxygen plasma ashing techniques although gypsum may be present in some samples most of the sodium calcium and magnesium as well as part of the sulphur appears to occur as a combination of dissolved ions in pore water and exchangeable ions attached to carboxylate groups significant concentrations of iron and aluminium occur in acid soluble form probably as organometallic complexes within the hydrocarbon structure quartz is the dominant mineral in the tertiary coal samples it appears to be mainly detrital but doubly terminated euhedral crystals suggest an authigenic origin in one of the deposits well crystallized kaolinite is common in the triassic coals while poorly crystallized kaolinite occurs in the tertiary samples siderite calcite and possibly collophane occur in the triassic coals sparse pyrite is present in both the tertiary and the triassic samples the differences in minerals and other inorganic constituents between the tertiary and triassic deposits can be explained partly by variations in the composition of the pore waters permeating the strata and partly by mobility of silica and alumina from different sources within the peat deposit the relative mobility of the different inorganic constituents is also significant in beneficiation of the coal for use in combustion processes

geochemistry and tectonic setting of the ophiolitic ingalls complex north cascades washington implications for correlations of jurassic cordilleran ophiolites abstract this study synthesizes new and existing chemical data to interpret the tectonic setting of the late jurassic ingalls complex of the northwest cascades washington and to compare it with other cordilleran ophiolites of similar age mafic rocks of the ingalls complex represent a spectrum of magma types including normal type and enriched mid ocean ridge basalt within plate basalt and island arc basalt based on mafic magma chemistry compositions of cr spinels in associated peridotite and field relations the ingalls complex is a suprasubduction zone ophiolite formed in a back arc basin cut by an oceanic fracture zone regional tectonic relations also support this hypothesis our synthesis of available chronologic geochemical and stratigraphic data for all jurassic cordilleran ophiolites shows that the ingalls complex has similarities and differences with each the most compelling likeness is between the ingalls complex and josephine ophiolite both of which exhibit a wide range of magmatic af

the wallula fault and tectonic framework of south central washington as interpreted from magnetic and gravity anomalies abstract the yakima fold and thrust belt yftb in central washington has accommodated regional mostly north directed deformation of the cascadia backarc since prior to emplacement of miocene flood basalt of the columbia river basalt group crbg the yftb consists of two structural domains northern folds of the yftb strike eastward and terminate at the western margin of a 20 mgal negative gravity anomaly the pasco gravity low straddling the north american continental margin southern folds of the yftb strike southeastward form part of the olympic wallowa lineament owl and pass south of the pasco gravity low as the wallula fault zone an upper crustal model based on gravity and magnetic anomalies suggests that the pasco gravity low is caused in part by an 8 km deep tertiary basin the pasco sub basin abutting the continental margin and concealed beneath crbg the pasco sub basin is crossed by north northwest striking magnetic anomalies caused by dikes of the 8 5 ma ice harbor member of the crbg at their northern end dikes connect with the eastern terminus of the saddle mountains thrust of the yftb at their southern end dikes are disrupted by the wallula fault zone the episode of ne sw extension that promoted ice harbor dike injection apparently involved strike slip displacement on the saddle mountains and wallula faults the amount of lateral shear on the owl impacts the level of seismic hazard in the cascadia region ice harbor dikes as mapped with aeromagnetic data are dextrally offset by the wallula fault zone a total of 6 9 km assuming that dike offsets are tectonic in origin the wallula fault zone has experienced an average dextral shear of 0 8 mm y since dike emplacement 8 5 ma consistent with right lateral stream offsets observed at other locations along the owl southeastward the wallula fault transfers strain to the north striking hite fault the possible location of the m 5 7 milton freewater earthquake in 1936

arc parallel extension and fluid flow in an ancient accretionary wedge the san juan islands washington structural analysis of the lopez structural complex a major late cretaceous terrane bounding fault zone in the san juan thrust system reveals a sequence of events that provides insight into accretionary wedge mechanics and regional tectonics after formation of regional ductile flattening and shear related fabrics the area was crosscut by brittle structures including 1 southwest vergent thrusts 2 extension veins and normal faults related to northwest southeast extension and 3 conjugate strike slip structures that record northwest southeast extension and northeast southwest shortening aragonite bearing veins are associated with thrust and normal faults but only rarely with strike slip faults high pressure low temperature hp lt minerals constrain the conditions for brittle deformation to 20 km and

late mesozoic and possible early tertiary accretion in western washington state the helena haystack melange and the darrington devils mountain fault zone the helena haystack melange hh melange and coincident darrington devils mountain fault zone ddmfz in northwestern washington separate two terranes the northwest cascade system nwcs and the western and eastern melange belts wemb the two terranes of paleozoic and mesozoic rocks superficially resemble each other but record considerable differences in structural and metamorphic history the hh melange is a serpentinite matrix melange containing blocks of adjacent terranes but also exotic blocks of schistose metavolcanic rocks and jurassic tonalite and associated amphibolite the hh melange must have formed between early cretaceous and late middle eocene time because it contains tectonic clasts of early cretaceous shuksan greenschist and is overlain by late middle eocene sedimentary and volcanic rocks less certain constraints on its age are a tectonic clast of metarhyolite that yields 90 ma metamorphic ages and the presumption that the melange was emplaced before the outboard olympic terrane arrived at about 50 ma the apparent continuity of the hh melange and the decatur terrane of the san juan islands suggests that the melange is the strongly tectonized equivalent of the fidalgo ophiolite the out crop pattern suggests that the hh melange overlies rocks of the nwcs and it may have formed when the wemb terranes were thrust over rocks of the nwcs much of the exposed belt of the hh melange is overlain by late middle eocene feldspathic sandstone and volcanic rocks of the barlow pass volcanics of vance 1957a which are cut by numerous faults of the ddmfz paralleling the melange the barlow pass volcanics appear to overlie the straight creek fault without large offset but a displaced exotic block of amphibolite with attached early or early middle eocene sandstone in the melange suggests that strike slip movement along the ddmfz was synchronous with movement on the straight creek fault and stretched cobbles in the conglomerates of the barlow pass volcanics suggest post straight creek movement the possible continuation of the ddmfz to the northwest as the san juan and the west coast faults on vancouver island suggests that the structure has had a major role in the emplacement of all the westernmost terranes in the pacific northwest this major suture is strongly bowed to the northeast opposite the great oroclinal bend of the olympic terrane suggesting that the emplacement of that terrane may have deformed a once straighter strike slip zone

crustal structure and relocated earthquakes in the puget lowland washington from high resolution seismic tomography 1 the availability of regional earthquake data from the pacific northwest seismograph network pnsn together with active source data from the seismic hazards investigation in puget sound ships seismic experiments has allowed us to construct a new high resolution 3 d p wave velocity model of the crust to a depth of about 30 km in the central puget lowland in our method earthquake hypocenters and velocity model are jointly coupled in a fully nonlinear tomographic inversion active source data constrain the upper 10 15 km of the model and earthquakes constrain the deepest portion of the model a number of sedimentary basins are imaged including the previously unrecognized muckleshoot basin and the previously incompletely defined possession and sequim basins various features of the shallow crust are imaged in detail and their structural transitions to the mid and lower crust are revealed these include the tacoma basin and fault zone the seattle basin and fault zone the seattle and port ludlow velocity highs the port townsend basin the kingston arch and the crescent basement which is arched beneath the lowland from its surface exposure in the eastern olympics strong lateral velocity gradients consistent with the existence of previously inferred faults are observed bounding the southern port townsend basin the western edge of the seattle basin beneath dabob bay and portions of the port ludlow velocity high and the tacoma basin significant velocity gradients are not observed across the southern whidbey island fault the lofall fault or along most of the inferred location of the hood canal fault using improved earthquake locations resulting from our inversion we determined focal mechanisms for a number of the best recorded earthquakes in the data set revealing a complex pattern of deformation dominated by general arc parallel regional tectonic compression most earthquakes occur in the basement rocks inferred to be the lower tertiary crescent formation the sedimentary basins and the eastern part of the olympic subduction complex are largely devoid of earthquakes clear association of hypocenters and focal mechanisms with previously mapped or proposed faults is difficult however seismicity structure and focal mechanisms associated with the seattle fault zone suggest a possible high angle mode of deformation with the north side up we suggest that this deformation may be driven by isostatic readjustment of the seattle basin

evidence for late holocene earthquakes on the utsalady point fault northern puget lowland washington trenches across the utsalady point fault in the northern puget lowland of washington reveal evidence of at least one and probably two late holocene earthquakes the teeka and duffers trenches were located along a 1 4 km long 1 to 4 m high northwest trending southwest facing topographic scarp recognized from airborne laser swath mapping glaciomarine drift exposed in the trenches reveals evidence of about 95 to 150 cm of vertical and 200 to 220 cm of left lateral slip in the teeka trench radiocarbon ages from a buried soil a horizon and overlying slope colluvium along with the historical record of earthquakes suggest that this faulting occurred 100 to 400 calendar years b p a d 1550 to 1850 in the duffers trench 370 to 450 cm of vertical separation is accommodated by faulting 210 cm and folding 160 to 240 cm with probable but undetermined amounts of lateral slip stratigraphic relations and radiocarbon ages from buried soil colluvium and fissure fill in the hanging wall suggest the deformation at duffers is most likely from two earthquakes that occurred between 100 to 500 and 1100 to 2200 calendar years b p but deformation during a single earthquake is also possible for the two earthquake hypothesis deformation at teeka trench in the first event involved folding but not faulting regional relations suggest that the earthquake s were m 6 7 and that offshore rupture may have produced tsunamis based on this investigation and related recent studies the maximum recurrence interval for large ground rupturing crustal fault earthquakes in the puget lowland is about 400 to 600 years or less

crustal structure along the west flank of the cascades western washington knowledge of the crustal structure of the washington cascades and adjacent puget lowland is important to both earthquake hazards studies and geologic studies of the evolution of this tectonically active region we present a model for crustal velocity structure derived from analysis of seismic refraction wide angle reflection data collected in 1991 in western washington the 280 km long north south transect skirts the west flank of the cascades as it crosses three tectonic provinces including the northwest cascades thrust system nwcs the puget lowland and the volcanic arc of the southern cascades within the nwcs upper crustal velocities range from 4 2 to 5 7 km s 1 and are consistent with the presence of a diverse suite of mesozoic and paleozoic metasediments and metavolcanics in the upper 2 3 km of the puget lowland velocities drop to 1 7 3 5 km s 1 and reflect the occurrence of oligocene to recent sediments within the basin in the southern washington cascades upper crustal velocities range from 4 0 to 5 5 km s 1 and are consistent with a large volume of tertiary sediments and volcanics a sharp change in velocity gradient at 5 10 km marks the division between the upper and middle crust from approximately 10 to 35 km depth the velocity field is characterized by a velocity increase from 6 0 to 7 2 km s 1 these high velocities do not support the presence of marine sedimentary rocks at depths of 10 20 km beneath the cascades as previously proposed on the basis of magnetotelluric data crustal thickness ranges from 42 to 47 km along the profile the lowermost crust consists of a 2 to 8 km thick transitional layer with velocities of 7 3 7 4 km s 1 the upper mantle velocity appears to be an unusually low 7 6 7 8 km s 1 when compared to velocity models from other regions this model most closely resembles those found in active continental arcs distinct seismicity patterns can be associated with individual tectonic provinces along the seismic transect in the nwcs and puget lowland most of the seismicity occurs below the base of the upper crust as defined by a seismic boundary at 5 10 km depth and continues to 20 30 km depth the region of transition between the nwcs and the puget lowland appears as a gap in seismicity with notably less seismic activity north of the boundary between the two earthquakes within the cascades are generally shallower 0 20 km and are dominated by events associated with the rainier seismic zone

revisiting the baranof leech river hypothesis for early tertiary coastwise transport of the chugach prince william terrane abstract according to the baranof leech river hypothesis originally proposed in 1982 1 schists on southern baranof island in southeastern alaska were contiguous with the leech river schist on southern vancouver island until 40 ma and 2 both rock units were part of the 2200 km long chugach prince william terrane which was displaced northward about 1100 km after 40 ma isotopic data obtained since 1982 show that the syn magmatic metamorphism that produced the baranof and leech river schists occurred at 50 ma not at 40 ma large magnitude coastwise slip of the terrane is therefore post 50 ma igneous rocks in the baranof and leech river units are part of the sanak baranof magmatic belt of forearc magmatism which has been ascribed to the early tertiary subduction of an oceanic ridge the slab window also gave rise to early eocene near trench plutonic and volcanic rocks on north american basement in the north cascades of washington state and probably to coeval igneous rocks on the western coast of vancouver island these igneous suites in the forearc fix the location of the intersection of the ridge with the continental margin 50 myr ago at latitude ca 48 49 n present day coordinates paleomagnetic data obtained since 1982 imply that before 50 ma the parts of the chugach prince william terrane that were to become the baranof and leech river schists were south of 48 49 n from 61 to 50 ma the northward movement of the terrane relative to north america can be reconciled with the southward migration of forearc magmatism in the chugach prince william terrane if the ridge trench intersection was fixed at 48 n present day coordinates the border ranges fault system is the on land structure that most likely accommodated hundreds of kilometers of post early eocene displacement

polyphase brittle and ductile deformation of late jurassic ophiolitic basalt argillite matrix melange and stratigraphic overlap sequence northwestern washington state abstract a belt of jurassic to cretaceous ophiolitic rocks borders the western margin of the u s cordillera and stretches from central california to northwestern washington state the northern end of this belt lies between the san juan islands and the northwest cascades within this region ophiolitic rocks consist of a succession of oceanic and arc affinity igneous and sedimentary rocks which form a sedimentary melange and sedimentary overlap sequence which is imbricated during the mid cretaceous the melange contains blocks and olistoliths of peridotite plagiogranite chert basalt and volcanoclastic conglomerate which range in size from a meter to over 1 km and are contained within a matrix of argillite and volcanoclastic breccia and conglomerate peridotites were exposed to the sub aqueous surface along serpentinized shear zones prior to their incorporation into the melange and the sedimentary matrix of the melange underwent brittle deformation during the earliest stages of its structural history melange rocks are overlain in angular unconformity by a jura cretaceous arc sourced sedimentary succession which is at least 500 meters thick and passes upward from a basal breccia containing clasts of plagiogranite gabbro tonalite chert and basalt into argillite containing late jurassic radiolarians the argillite is overlain by poorly sorted greywacke and conglomerate with clast populations similar to those of the basal breccia the conglomerate fines upward into a massive to bedded feldspathic lithic arenite and greywacke that yields mid cretaceous detrital zircons the overlap succession and the melange are deformed by two generations of highly penetrative structures d1a and d1b which produced north to east vergent tight to isoclinal folds and axial planar pressure solution cleavages all units are further deformed by three generations of penetrative structures the successively younger nne to nw ne and e w to wnw trending folds have foliations that cross cut the earlier structural fabrics and faults formation of the melange required differential elevations during the time of deposition and the presence of rocks which are sourced from both arc and oceanic crust extension within the forearc provides a mechanism to exhume peridotites and generate differential topography for arc and oceanic affinity rocks to erode and be incorporated into the melange as part of olistostromal deposits

structural variation along the devil s mountain fault zone northwestern washington the eastern juan de fuca strait is subject to long term north south oriented shortening the observed deformation is interpreted to result from the northward motion of the oregon block which is being driven north by oblique subduction of the oceanic juan de fuca plate seismic data acquired during the seismic hazards investigation in puget sound survey are used with coincident first arrival tomographic velocities to interpret structural variation along the devil s mountain fault zone in the eastern juan de fuca strait the primary fault of the devil s mountain fault zone developed at the northern boundary of the everett basin during north south oriented tertiary compression interpretation of seismic reflection data suggests that based on their similar geometry including the large magnitude of pre tertiary basement offset the primary fault of the devil s mountain fault west of 122 95 w and the utsalady point fault represent the main fault of the tertiary devil s mountain fault zone the tertiary

depositional history of the southeastern outcrop belt of the chuckanut formation implications for the darrington devil s mountain and straight creek fault zones washington u s a the southeastern outcrop belt of the eocene chuckanut formation contains the erosional remnants of a larger depositional system in the study area the chuckanut formation can be split into four units based upon differences in age lithology sedimentology paleocurrents and provenance relationships the coal mountain unit early eocene represents a southwest flowing fluvial system that shows no evidence for fault control of drainage the overlying higgins mountain unit early middle eocene represents a northeast flowing fluvial system east of the devil s mountain fault zone dmfz with lithologies derived from western source areas the sperry peak unit early middle eocene represents a fluvial system with a wide dispersion of paleocurrent azimuths and a possible mixture of sediment source areas we believe the sperry peak unit was deposited in a fault wedge graben at the junction of the dmfz and straight creek fault zone scfz with sediment sources from both east and west the grade creek unit ag

mid cretaceous thrusting in the southern coast belt british columbia and washington after strike slip fault reconstruction a major thrust system of mid cretaceous age is present along much of the coast belt of northwestern north america thrusting was concurrent and spatially coincided with emplacement of a great volume of arc intrusives and minor local strike slip faulting in the southern coast belt 52 to 47 n thrusting was followed by major dextral slip faulting which resulted in significant translational shuffling of the thrust system in this paper we restore the displacements on major dextral slip faults of the southern coast belt and then analyze the mid cretaceous thrust system two reconstructions were made that use dextral faulting on the yalakom fault 115 km castle pass and ross lake faults 10 km and fraser fault 100 km the reconstructions differ in the amount of dextral offset on the straight creek fault 160 and 100 km and how much the ne part of the cascades crystalline core expanded 30 km and 0 km during eocene extension reconstruction a produces the best match of lithotectonic units and thrust systems our synthesis shows that the southern coast belt thrust system was 250 180 km wide after thrusting the thrust system was mainly southwest vergent but had a belt of northeast vergent back thrusts on the northeast side associated with the tyaughton methow basin which may indicate large scale tectonic wedging thrust faults are commonly low to moderate angle but high angle faults also occur especially as late stage out of sequence structures involving plutons the amount of thrust displacement across the system is unknown but must be at least 100 km and may be many hundreds of kilometers most thrusting occurred from 100 to 80 ma and did not migrate systematically until after 90 ma when thrusting and magmatism shifted to the northeast for a few million years widespread thrusting occurred both near plutons and where there are no or small plutons which strongly suggests that thrust faulting was caused by regional to plate scale forces such as rapid plate convergence and or arc continent collision

the devils mountain fault zone an active cascadia upper plate zone of deformation pacific northwest of north america abstract the devils mountain fault zone dmfz extends east to west from washington state to just south of victoria british columbia in the northern strait of juan de fuca of canada and the usa recently collected geophysical data were used to map this fault zone in detail which show the main fault trace and associated primary and secondary conjugate strands and extensive northeast southwest oriented folding that occurs within a 6 km wide deformation zone the fault zone has been active in the holocene as seen in the offset and disrupted upper quaternary strata seafloor displacement and deformation within sediment cores taken close to the seafloor expression of the faults data suggest that the present dmfz and the re activated leech river fault may be part of the same fault system based on the length and previously estimated slip rates of the fault zone in washington state the dmfz appears to have the potential of producing a strong earthquake perhaps as large as magnitude 7 5 or greater within 2 km of the city of victoria

resistivity structure of the olympic mountains and puget lowlands magnetotellurics has been used to study of the geo electric structure of the olympic mountains and puget lowland data were collected along an west east line extending from the pacific ocean to the cascade mountains the smoothest resistivity model consistent with the data suggests that subduction of the olympic mountains accretionary complex core rocks has been prevented by a 30 km thick sequence of volcanic rocks this may effectively couple the juan de fuca and north american plates and may explain the concentration of crustal earthquakes beneath the puget lowland

effect of the emperor seamounts on trans oceanic propagation of the 2006 kuril island earthquake tsunami 1 the effect of tsunami wave scattering by the emperor seamounts on the propagation of the 2006 kuril island earthquake tsunami is demonstrated using the finite difference method the model results indicate that the contribution of the emperor seamounts on the maximum tsunami energy along the pacific coast of japan is found to be as much as 50 or more also analysis of the spectral evolution of observed tsunami records in japan suggests that the scattering waves from the emperor seamounts possibly dominate the wave components at periods of 4 to 17 minutes