structural analysis and interpretation of the surface deformations of the el asnam earthquake of october 10 1980 the el asnam earthquake of october 10 1980 represents the major seismotectonic event of these last decades in the west mediterranean area it has induced a large amount of surface breaks this earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of north africa the tectonic analysis of surface rupture shows the complexity of the deformation mechanism the principal mechanism consists of the activation of a nw se trending thrust fault accompanied with a left lateral motion and with an intense deformation of the northwestern overthrusting block an accurate description of these deformations shows that for a large part the breaks geometry depends closely on the substratum structure finally the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation

deformation of the pacific north america plate boundary at queen charlotte fault the possible role of rheology published 2018 this article is a u s government work and is in the public domain in the usa the definitive version was published in journal of geophysical research solid earth 123 2018 4223 4242 doi 10 1002 2017jb014770

structure seismicity and thermal regime of the queen charlotte transform margin 1 this study examines structural seismicity thermal and current deformation constraints on the tectonic regime of the queen charlotte margin located off the northwest coast of canada the margin is primarily a transcurrent boundary between the oceanic pacific plate and the continental north america plate but plate motion models indicate 20 of current oblique convergence that initiated 5 myr the estimated 120 km of convergence has been variously explained as accommodated by underthrusting or by crustal shortening the near vertical queen charlotte transcurrent fault and lack of wadati benioff earthquakes argue against underthrusting however structural models for the margin from receiver function and refraction studies show little evidence of crustal thickening the pattern of landward decreasing heat flow gravity anomalies an accretionary prism landward of the trench or trough down bowing ocean crust and sediments horizons and a variety of other geophysical evidence support underthrusting receiver function analysis on teleseismic data indicates a 10 km thick low velocity layer at 35 km depth dipping 20 to the east which is interpreted as underthrusting oceanic crust the heat flow across the fault zone rapidly decreases landward in agreement with predictions from a finite element thermal model of underthrusting

pacific north america plate boundary reorganization in response to a change in relative plate motion offshore canada 1 the transition from subduction in cascadia to the transform queen charlotte fault along western canada is often drawn as a subduction zone yet recent studies of gps and earthquake data from northern vancouver island are not consistent with that model in this paper we synthesize seismic reflection and gravity interpretations with microseismicity data in order to test models of 1 microplate subduction and 2 reorganization of the preexisting strike slip plate boundary we focus on the critical region of outer queen charlotte sound and the adjacent offshore on much of the continental shelf several million years of subsidence above thin crust are a counterindicator for subduction an undated episode of compression uplifted the southernmost shelf but subsidence patterns offshore show that recent subduction is unlikely to be responsible previously unremarked near vertical faults and a mix of extensional and compressional faults offshore indicate that strike slip faulting has been a significant mode of deformation seismicity in the last 18 years is dominantly strike slip and shows large amounts of moment release on the revere dellwood fault and its overlap with the queen charlotte fault the relative plate motion between the pacific and north american plates rotated clockwise 6 ma and appears to have triggered formation of an evolving array of structures we suggest that the paleo queen charlotte fault which had defined this continental margin retreated northward as offshore distributed shear and the newly formed revere dellwood fault propagated to the northwest

crustal thickness beneath the queen charlotte basin canada results of a seismically constrained gravity inversion a gravity inversion routine was used to calculate crustal thickness variations in the queen charlotte basin western canada first a crustal bouguer anomaly was derived using a digital well constrained depth to basement map and densities determined from well logs and rock samples this anomaly was subsequently inverted for crustal thickness assuming a single density contrast at depth and an average crustal thickness provided by seismic refraction data the results restricted to that portion of the basin for which there are good quality data show crustal thickness variations of the order of 12 km regions of thin crust are located off northern vancouver island 20 km along the axis of hecate strait and in northern queen charlotte sound 24 km thicker crust is associated with central queen charlotte ridge and northeastern hecate strait tests show these trends in crustal thickness prevail for all reasonable ranges of input parameters calculated residual gravity anomalies contain information useful for mapping the distribution of volcanics interbedded with sediments in subbasins and for refining estimates of depth to basement derived from seismic data alone our results are for the most part in excellent agreement with seismically derived estimates of moho depth they show minimum crustal thickness beneath regions of maximum sediment accumulation supporting an extensional origin for the basin they indicate that this extension was quite heterogeneous and yield minimum estimates which vary from 13 in some parts of the basin to as much as 65 in others the results can be used to discriminate between models on the tertiary evolution of the basin the observed trends are not predicted by the lithospheric flexure or simple margin perpendicular extension models but are consistent with a model of crustal thinning by distributed shear in a transtensional regime

plate boundary localization slip rates and rupture segmentation of the queen charlotte fault based on submarine tectonic geomorphology abstract linking fault behavior over many earthquake cycles to individual earthquake behavior is a primary goal in tectonic geomorphology particularly across an entire plate boundary here we examine the 1150 km long right lateral queen charlotte fairweather fault system using comprehensive multibeam bathymetry data acquired along the queen charlotte fault qcf offshore southeastern alaska and western british columbia fine scale analysis of tectonic geomorphology allowed us to identify and reconstruct 184 strike slip piercing points over a 630 km stretch of the qcf age constraints from glacial recession and offshore sedimentation patterns yield a consistent slip rate of 50 57 mm yr since 17 12 ka the fastest rate for a continent ocean strike slip fault on earth these slip rates equal or exceed estimates of pacific north america pa na relative motion from global plate reconstructions indicating that pa na motion is highly localized the qcf cuts the seafloor along a narrow and unusually straight trace for its entire length and multiple fault traces are observed only at local step overs the geometry and behavior of the qcf over many earthquake cycles is simple and typical of mature faults with relatively homogeneous stress fields since the qcf is the primary pa na plate boundary we used the trace of the qcf to define the small circle path for relative plate motion and computed the associated euler pole predicted along strike obliquity variations based on the new pole agree with observed tectonic geomorphology and suggest that previous global plate reconstructions overestimated the degree of oblique convergence along the qcf we also find that subtle long wavelength 75 150 km bends and discrete step overs appear to define the endpoints of m 7 earthquakes suggesting that obliquity and resultant fault geometry may control rupture segmentation and asperity development lastly the agreement between predicted obliquity and tectonic geomorphology along the entire length of qcf compelled a reevaluation of regional tectonic models in the north the eastern yakatat terrane appears to be translating northwest with the pacific plate and slip transferred from the qcf to the fairweather fault results in 20 mm yr of convergence along the southern st elias mountains in the south we predict a reduced rate of convergence along the qcf west of haida gwaii 5 6 mm yr of shortening on average relative to previous studies our results support a model for transpression and strike slip partitioning along the edge of a hot and weak pacific plate leading to crustal thickening and growth of the queen charlotte terrace to the west of haida gwaii

transpression between two warm mafic plates the queen charlotte fault revisited the queen charlotte fault is a transpressive transform plate boundary between the pacific and north american plates offshore western canada previous models for the accommodation of transpression include internal deformation of both plates adjacent to the plate boundary or oblique subduction of the oceanic plate the latter has been the preferred model both plates are warm and mafic and have similar mechanical structures new multichannel seismic reflection data show a near vertical queen charlotte fault down to the first water bottom multiple significant subsidence east of the queen charlotte fault a large melange where the fault is in a compressive left step and faulting which involves oceanic basement gravity modeling of profiles indicates that moho varies fairly smoothly across the plate boundary isostatic anomalies indicate that the pacific plate is flexed downward adjacent to the queen charlotte fault upward flexure of north america along with crust thickened relative to crust in the adjacent basin creates topography known as the queen charlotte islands combined with other regional studies these observations suggest that the plate boundary is a vertical strike slip fault and that transpression is taken up within each plate

seismic velocity structure across the 2013 craig alaska rupture from aftershock tomography implications for seismogenic conditions abstract the 2013 craig alaska mw 7 5 earthquake ruptured along 150 km of the queen charlotte fault qcf a right lateral strike slip plate boundary fault separating the pacific and north american plates regional shear wave analyses suggest that the craig earthquake rupture propagated in the northward direction faster than the s wave supershear theoretical studies suggest that a bimaterial interface such as that along the qcf which separates oceanic and continental crust with differing elastic properties can promote supershear rupture propagation we deployed short period ocean bottom seismometers obs as a part of a rapid response effort less than four months after the craig earthquake mainshock during a 21 day period 1 133 aftershocks were recorded by 8 obs instruments aftershock spatial distribution indicates that the base of the seismogenic zone along the qcf approaches 25 km depth consistent with a thermally controlled fault rheology expected for igneous rocks at oceanic transform faults the spatial distribution also provides supporting evidence for a previously hypothesized active strand of the qcf system within the pacific plate tomographic traveltime inversion for velocity structure indicates a low velocity vp and vs zone on the pacific side of the plate boundary at 5 20 km depths where neogene pacific crust and upper mantle seismic velocities average 3 11 slower than the north american side where the paleozoic north american crust is seismically faster our results suggest that elastic properties along the studied portion of the qcf are different than those of a simple oceanic continental plate boundary fault in our study region velocity structure across the qcf while bimaterial does not support faster material on the west side of the fault which has been proposed as one possible explanation for northward supershear propagation during the craig earthquake instead we image low velocity material on the west side of the fault explanations could include that part of the rupture was subshear or that fault damage zone properties or fault smoothness are more important controls on supershear rupture than a bimaterial contrast

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

an abrupt transition in the mechanical response of the upper crust to transpression along the queen charlotte fault the queen charlotte fault qcf is a major strike slip fault that forms the boundary between the pacific and north american plates from 51 to 58 n near 53 2 n the angle of oblique convergence predicted by the mid ocean ridge velocity morvel interplate pole of rotation decreases from 15 in the south to 15 in the north south of 53 2 n the convergent component of plate motion results in the formation of a 40 km wide terrace on the pacific plate west of qcf and earthquakes with thrust mechanisms including the 2012 haida gwaii earthquake sequence are observed north of 53 2 n in the primary rupture zone of the m 8 1 strike slip earthquake of 1949 the linear terrace disappears and topography of the continental slope west of the qcf is characterized by a complex pattern of ridges and basins that trend obliquely to the primary trace of the qcf deformation within the pacific plate appears to occur primarily through strike slip faulting with a minor thrust component on secondary synthetic faults the orientations of these secondary faults as determined from seismic reflection and bathymetric data are consistent with the reactivation of faults originally formed as ridge parallel normal faults and as thrust faults formed parallel to the qcf south of the bend at 53 2 n and subsequently translated to the north we suggest that an oblique convergence angle of 15 represents a critical threshold separating distinct crustal responses to transpression this result is consistent with theoretical and analog strain models of transpressive plate boundaries the sharpness of this transition along the qcf in contrast to purely continental transform boundaries may be facilitated by the relatively simple structure of oceanic crust and the presence of pre existing optimally oriented faults in the young pacific plate

genesis of the xiaolonghe quartz vein type sn deposit sw china insights from cathodoluminescence textures and trace elements of quartz fluid inclusions and oxygen isotopes abstract quartz textures revealed by scanning electron microscope cathodoluminescence sem cl images suggest that quartz in the xiaolonghe sn deposit formed in at least three fluid episodes quartz q1 in the pre ore silicification zone has homogeneous texture high cl intensity and high ti content 19 53 ppm fluid inclusions hosted in q1 are vapor rich v1 type and homogenized as supercritical fluid at 570 c quartz q2 in the syn ore topaz cassiterite quartz veins has lower cl intensity and is characterized by euhedral growth zones with lower ti content 1 3 12 ppm fluid inclusions hosted in q2 topaz and cassiterite are liquid rich fluid inclusions of moderate salinity 15 wt nacl equiv l1 type which homogenized at 423 c the post ore quartz q3 closely associated with sericitization of topaz generally crosscuts q2 and has dark cl intensity and much lower ti concentration the upper limits of t p conditions of pre ore and syn ore stage are constrained by the intersection of nacl h2o fluid inclusion isochores and ti in quartz isopleths and the lower limits are based on microthermometry results of fluid inclusions combined with the 18ofluid value 8 3 of q1 it indicates that the pre ore supercritical fluid was directly exsolved from a granitic magma at t 570 600 c and p 0 70 0 77 kbars corresponding to a maximum depth of 2 8 km under lithostatic pressure the syn ore subcritical fluid 8 0 18ofluid 6 3 mixed with some meteoric water was under 423 450 c 0 32 0 45 kbars the transition from the pre ore supercritical fluid to the syn ore subcritical fluid indicates boiling condition probably at 512 c 0 62 kbars which was likely caused by hydraulic fracturing under high pressure both the fluid boiling and fluid mixing contribute to the cassiterite precipitation in xiaolonghe sn deposit in the post ore stage the coexisting s type and v2 type fluid inclusions in q3 indicates a second fluid boiling at 269 c 0 05 kbars which was probably caused by decompression due to rapid denudation of the overlain strata the low salinity 5 5 wt nacl equiv l2 type fluid inclusions hosted in fluorite homogenized at 199 c and

surface faulting accompanying the borah peak earthquake central idaho the ms 7 3 borah peak earthquake that struck central idaho on october 28 1983 was one of the strongest historic earthquakes in the intermountain seismic belt much of the 34 km long northwest trending zone of fault scarps and surface ruptures that formed during the earthquake follows holocene and upper pleistocene scarps of the lost river fault throw along the new fault scarps averages 0 8 m exceeds 1 0 m along 43 of their length and attains a maximum of 2 7 m along the broad and complex zone of deformation in the southern section the net slip was normal sinistral averaging 17 cm lateral slip for 100 cm of dip slip the preferred nodal plane from the focal mechanism strikes n22 w dips 59 sw and suggests a much larger component of strike slip than do the geologic data

shortening within underplated oceanic crust beneath the central california margin structures within a tectonically underplated layer of early miocene age oceanic crust indicate that the lower crust of offshore central california has been deformed under compression prior to the inception of the san andreas transform system along the continental margin shortening in the lower crust is inferred from the geometry of two structures the santa lucia monocline and the santa maria antiform delineated by an integrated interpretation of multichannel and wide angle seismic reflection data in conjunction with regional gravity data and teleseismic receiver functions the 700 km of multichannel seismic data and 300 km of wide angle seismic data from the 1986 pacific gas and electric edge seismic experiment form the primary data base used to establish the northwesterly trend and extent of the monocline and the wnw trend of the antiform in cross sectional view the santa lucia monocline is a 30 kink in the oceanic crust while the santa maria antiform is characterized by local thickening of the oceanic crust these structures are probably the result of convergence between the monterey and arguello microplates that took place as subduction along the margin waned the multichannel seismic reflection data image two miocene age shelf basins the santa lucia and offshore santa maria basins that formed within a transtensional stress regime the offshore santa maria basin directly overlies the santa maria antiform suggesting that either the upper and lower crustal stress regimes were completely decoupled in miocene time or that the two features formed in different places differential slip between the upper crust and lower crust may have been accommodated along a detachment zone located above oceanic crust convergence within the oceanic crust and apparent differential motion between upper and lower crust are indicative of the processes that can affect the transition from subduction to an oceanic continental transform zone

queen charlotte area cenozoic tectonics and volcanism and their association with relative plate motions along the northeastern pacific margin cenozoic relative plate interactions along the queen charlotte margin based on published models for the north america and northeast pacific plates are related to the tectonic and igneous history of the region plate motion models indicate convergence and subduction prior to the eocene since that time there has been transcurrent motion with varying small amounts of oblique extension or compression assuming that the pacific america farallon triple junction was to the south of the region a late miocene or early pliocene about 4 ma to present period of oblique convergence is well resolved the present queen charlotte fault zone along the west coast of the islands may have initiated more recently within the cenozoic transcurrent regime a period of oblique extension in the mid tertiary 36 20 ma in one model is supported by a variety of volcanic and tectonic evidence a small plate motion change at about 20 ma may have resulted in the transfer of the yakutat terrane from the north america plate to the pacific plate and the resulting motion of the terrane northwestward to its present position along the margin of alaska the onset of tertiary masset volcanism that is extensive on the queen charlotte islands corresponds within a few million years to the time of major plate reorganization at 43 ma that has tectonic expression around the entire pacific basin the period of most extensive masset volcanism and plutonism appears to correlate with the model oblique extension in the mid tertiary for one model the geochemistry and physical volcanology of the masset volcanic s are indicative of an extension regime the main syntectonic deposition in the queen charlotte basin skonun formation as inferred from seismic reflection and well data also appears temporally correlated with this time interval of oblique extension a variety of data including plate models dikes normal faults basin subsidence crustal thickness from seismic refraction and present and paleo heat flow indicate mid tertiary crustal extension of at least 20 in the queen charlotte region with up to 150 up to 2 5 in the main queen charlotte basin posttectonic basin subsidence and deposition may correlate with the model time interval of general transcurrent or oblique convergence motion from 20 to 4 ma more recent shortening deformation observed in outcrop and seismic sections of the northern parts of the basin may correlate with plate model oblique convergence from 4 ma to the present the latter convergence is associated with underthrusting that formed a trough or trench and an accretionary sedimentary prism off the west coast of the queen charlotte islands and with inferred uplift and erosion of the western part of the islands

shear wave velocity structure in the vicinity of the 2012 mw 7 8 haida gwaii earthquake from receiver function inversion abstract the thrust mechanism of the 2012 m w 7 8 haida gwaii earthquake suggests convergence across the transpressive pacific north america plate boundary in the region is accommodated by underthrusting with important consequences for seismic and tsunami hazard analysis this article investigates the crustal structure and extent of subduction beneath haida gwaii by nonlinear inversion of receiver function data processed from teleseismic recordings at five land based seismograph stations three of these stations were deployed since the 2012 earthquake to extend coverage to the southeast and have not been analyzed previously the inversions provide estimates of the shear wave velocity structure beneath much of moresby island results indicate a positive velocity contrast at approximately 18 26 km depth interpreted as a shallow continental moho a 12 17 km thick low shear wave velocity zone is also identified which increases in depth from 25 to 42 km along the direction of plate convergence which is interpreted as subducting oceanic material these results provide the first evidence that the subducting oceanic plate extends beneath the entirety of moresby island

lithoprobe southern vancouver island cenozoic subduction complex imaged by deep seismic reflections reply the lithoprobe seismic reflection project on vancouver island was designed to study the large scale structure of several accreted terranes exposed on the island and to determine the geometry and structural characteristics of the subducting juan de fuca plate in this paper we interpret two lithoprobe profiles from southernmost vancouver island that were shot across three important terrane bounding faults leech river san juan and survey mountain to determine their subsurface geometry and relationship to deeper structures associated with modem subduction the structure beneath the island can be divided into an upper crustal region consisting of several accreted terranes and a deeper region that represents a landward extension of the modern offshore subduction complex in the upper region the survey mountain and leech river faults are imaged as northeast dipping thrusts that separate wrangellia a large mesozoic paleozoic terrane from two smaller accreted terranes the leech river schist mesozoic rock

tectonic history of the queen charlotte islands and adjacent areas a model the region including queen charlotte islands hecate strait and queen charlotte sound is underlain by two allochthonous terranes wrangellia and the alexander terrane the suture between them occurs in central graham island and central hecate strait and is coincident with the traces of the sandspit and rennell sound fault zones each of which developed in response to crustal rifting in queen charlotte sound during mid tertiary time the stratigraphic succession comprises four tectonic assemblages 1 the allochthonous assemblages comprise paleozoic rocks of the alexander terrane and upper triassic and jurassic rocks of wrangellia which on the basis of paleomagnetic and biogeographical data are clearly exotic the distribution of these terranes beneath queen charlotte sound and hecate strait is supported by geophysical information and subsurface data obtained from offshore wells 2 the suture assemblage is represented by extremely coarse conglomerates massive graywackes and turbidites of early cretac

basement and regional structure along strike of the queen charlotte fault in the context of modern and historical earthquake ruptures the queen charlotte fault qcf is a dextral transform system located offshore of southeastern alaska and western canada accommodating 4 4 cm yr of relative motion between the pacific and north american plates oblique convergence along the fault increases southward and how this convergence is accommodated is still debated using seismic reflection data we interpret offshore basement structure faulting and stratigraphy to provide a geological context for two recent earthquakes an m w 7 5 strike slip event near craig alaska and an m w 7 8 thrust event near haida gwaii canada we map downwarped pacific oceanic crust near 54 n between the two rupture zones observed downwarping decreases north and south of 54 n parallel to the strike of the qcf bending of the pacific plate here may have initiated with increased convergence rates due to a plate motion change at 6 ma tectonic reconstruction implies convergence driven pacific plate flexure beginning at 6 ma south of a 10 bend the qcf which is currently at 53 2 n and lasting until the plate translated past the bend by 2 ma normal faulted approximately late miocene sediment above the deep flexural depression at 54 n topped by relatively undeformed pleistocene and younger sediment supports this model aftershocks of the haida gwaii event indicate a normal faulting stress regime suggesting present day plate flexure and underthrusting which is also consistent with reconstruction of past conditions we thus favor a pacific plate underthrusting model to initiate flexure and accommodation space for sediment loading in addition mapped structures indicate two possible fault segment boundaries along the qcf at 53 2 n and at 56 n

lithospheric structure in northwestern canada from lithoprobe seismic refraction and related studies a synthesis the snorcle refraction wide angle reflection r war experiment snore 97 included four individual lines along the three transect corridors a combination of snore 97 results with those from earlier studies permits generation of a 2000 km long lithospheric velocity model that extends from the archean slave craton to the present pacific basin using this model and coincident near vertical incidence nvi reflection data and geological information an interpreted cross section that exemplifies 4 ga of lithospheric development is generated the velocity structural models correlate well with the reflection sections and provide additional structural compositional and thermal constraints geological structures and some faults are defined in the upper crust at a larger scale the seismic data identify a variety of orogenic styles ranging from thin to thick skinned accretion in the cordillera and crustal scale tectonic wedging associated with both paleoproterozoic and mesozoic collisions models of poisson

fracture related hydrothermal alteration of metagranitic rock and associated changes in mineralogy geochemistry and degree of oxidation a case study at forsmark central sweden red staining of rocks due to fluid rock interaction during hydrothermal circulation in fractures is a common feature in crystalline sequences in this study red stained metagranitic rock adjacent to fractures in forsmark central sweden has been studied with emphasis on the mineral reactions and associated element mobility occurring during the alteration the main mineral reactions associated with the hydrothermal alteration are an almost complete saussuritization of plagioclase accompanied by total chloritization of biotite magnetite has been partly replaced by hematite whereas quartz and k feldspar were relatively unaffected by the hydrothermal alteration we show that redistribution of elements on the whole rock scale was very limited and is mainly manifested by enrichment of na2o and volatiles and depletion of cao feo and sio2 in the red stained rock however on the microscale element redistribution was more extensive with both intragranular and intergranular migration of e g ca k na al si fe ba cs rb sr ti and rees the altered rock shows a shift towards higher total oxidation factors but the change is smaller than 1 and the red staining of the rock is due to hematite dissemination rather than a significant oxidation of the rock an increase in the connected porosity is also observed in the altered rock

acidity salinity diagrams application to greisen and porphyry deposits to a first approximation alteration minerals in greisen and related fluorine rich porphyry deposits lie in the system k 2 o al 2 o 3 sio 2 h 2 o f 2 o sub 1 equilibria in this model system can be depicted on quartz and fluid saturated chemical potential diagrams whose axes are mu hf acidity where mu hf mu hcl mu sub fcl sub 1 and mu kf salinity where mu kf mu nacl mu sub kna sub 1 mu sub fcl sub 1 advantages of this approach are that it reflects the fact that the anion f unlike cl is incorporated in greisen minerals mainly topaz fluorite and micas and that mineral stabilities can be correlated with possible ore forming processes the most important of these processes is probably vapor phase separation from an aqueous brine or magma first or second boiling fluid inclusion studies have shown that boiling occurs in all porphyry and many but not all greisen deposits vapor phase separation from a magma pneumatolysis must similarly be responsible for the formation of greisenlike mineral assemblages in miarolitic topaz rhyolite lava flows and is presumably also responsible for the formation of gem pockets in more deeply seated pegmatites and granites the result of boiling is an increase in mu hf and a decrease in mu kf in the vapor phase and the opposite in the residual brine or magma in deep greisen veins the muscovite stability field is encountered between the k feldspar and topaz fields whereas in f rich relatively shallow porphyry deposits such as henderson colorado boiling causes aqueous fluids to pass directly from the k feldspar ore zone to the overlying topaz magnetite zone muscovite or f bearing mn fe garnet is only encountered farther out as the fluids are condensed neutralized and diluted by cooler meteoric waters when ca fe mn be w o 2 s 2 and co 2 are added to the greisen model system scheelite is shown to transform to wolframite with increasing mu hf and beryl to phenakite with increasing mu hf or mu kf biotite transforms to magnetite hematite siderite pyrite chlorite or fayalite beyond the k feldspar field its stability is enhanced by high mu hf and chlorite cordierite or mn fe garnet transform to an mn fe carbonate oxide or sulfide or biotite beyond the al silicate field the ca content of plagioclase coexisting with fluorite decreases with an increase in either mu hf or mu kf and thus provides an indicator of total fluorine in both acid and neutral species

constraints on the frequency magnitude relation and maximum magnitudes in the uk from observed seismicity and glacio isostatic recovery rates summary earthquake populations have recently been shown to have many similarities with critical point phenomena with fractal scaling of source sizes energy or seismic moment corresponding to the observed gutenberg richter g r frequency magnitude law holding at low magnitudes at high magnitudes the form of the distribution depends on the seismic moment release rate mand the maximum magnitude m max the g r law requires a sharp truncation at an absolute maximum magnitude for finite m i n contrast the gamma distribution has an exponential tail which allows a soft or credible maximum to be determined by negligible contribution to the total seismic moment release here we apply both distributions to seismic hazard in the mainland uk and its immediate continental shelf constrained by a mixture of instrumental historical and neotectonic data tectonic moment release rates for the seismogenic part of the lithosphere are calculated from a flexural plate model for glacio isostatic recovery constrained by vertical deformation rates from tide gauge and geomorphological data earthquake focal mechanisms in the uk show near vertical strike slip faulting with implied directions of maximum compressive stress approximately in the nnw sse direction consistent with the tectonic model maximum magnitudes are found to be in the range 6 3 7 5 for the g r law or 7 0 8 2 m l for the gamma distribution which compare with a maximum observed in the time period of interest of 6 1 m l the upper bounds are conservative estimates based on 100 per cent seismic release of the observed vertical neotectonic deformation glacio isostatic recovery is predominantly an elastic rather than a seismic process so the true value of m max is likely to be nearer the lower end of the quoted range

distribution of the pacific north america motion in the queen charlotte islands s alaska plate boundary zone 1 we present gps data that constrain the distribution of the relative pacific north america motion across the queen charlotte islands alaska panhandle margin nw north america velocities from a network of 22 campaign and permanent sites indicate that the pacific north america transpressive motion is mostly accommodated along the locked queen charlotte fairweather fault a significant portion 6 7 mm yr of the relative plate motion is taken up by distributed dextral shear across a 200 km wide region of the margin two models have been proposed to describe how the pacific north america convergence is accommodated off the queen charlotte islands internal shortening vs underthrusting of the pacific plate although the gps data cannot discriminate between the models they provide strong constraints on the convergence distribution the significant non transient motion of gps sites along the central british columbia southern alaska margin has implications for seismic hazard and tectonic evolution models of the canadian cordillera

the october 28 2012 mw 7 8 haida gwaii underthrusting earthquake and tsunami slip partitioning along the queen charlotte fault transpressional plate boundary the pacific north american plate boundary is undergoing predominantly right lateral strike slip motion along the queen charlotte and fairweather transform faults the queen charlotte fault qcf hosted the largest historical earthquake in canada the 1949 m s 8 1 strike slip earthquake which ruptured from offshore northern haida gwaii several hundred kilometers northwestward on january 5 2013 an m w 7 5 strike slip faulting event occurred near the northern end of the 1949 rupture zone along central and southern haida gwaii the relative plate motion has 20 oblique convergence across the left stepping plate boundary there had been uncertainty in how the compressional component of plate motion is accommodated the october 28 2012 m w 7 8 haida gwaii earthquake involved slightly 20 oblique thrust faulting on a shallow 18 5 northeast dipping fault plane with strike 320 parallel to the qcf consistent with prior inferences of pacific plate underthrusting beneath haida gwaii the rupture extended to shallow depth offshore of moresby island beneath a 25 30 km wide terrace of sediments that has accumulated in a wedge seaward of the qcf the shallow thrusting caused seafloor uplift that generated substantial localized tsunami run up and a modest far field tsunami that spread across the northern pacific prompting a tsunami warning beach closure and coastal evacuation in hawaii although ultimately tide gauges showed less than 0 8 m of water level increase the mainshock rupture appears to have spread with a 2 3 km s rupture velocity over a length of 150 km with slip averaging 3 3 m concentrated beneath the sedimentary wedge the event was followed by a substantial aftershock sequence in which almost all of the larger events involve distributed intraplate normal faulting extending 50 km oceanward from the qcf the highly oblique slip partitioning in southern haida gwaii is distinctive in that the local plate boundary parallel motion on the qcf may be accommodated either by infrequent large strike slip ruptures or by aseismic creep as seems to be the case for deeper oblique relative plate motion beneath haida gwaii while the sedimentary terrace accumulates plate boundary perpendicular compressional strain that releases in almost pure thrust faulting earthquakes seaward of the qcf

slip behavior of the queen charlotte plate boundary before and after the 2012 mw 7 8 haida gwaii earthquake evidence from repeating earthquakes the queen charlotte plate boundary near haida gwaii b c includes the dextral strike slip queen charlotte fault qcf and the subduction interface between the downgoing pacific and overriding north american plates in this study we present a comprehensive repeating earthquake catalogue that represents an effective slip meter for both structures the catalogue comprises 712 individual earthquakes 0 3 mw 3 5 arranged into 224 repeating earthquake families on the basis of waveform similarity and source separation estimates from coda wave interferometry we employ and extend existing relationships for repeating earthquake magnitudes and slips to provide cumulative slip histories for the qcf and subduction interface in 6 adjacent zones within the study area between 52 3 n and 53 8 n we find evidence for creep on both faults however creep rates are significantly less than plate motion rates which suggests partial locking of both faults the qcf exhibits the highest degrees of locking south of 52 8 n which indicates that the seismic hazard for a major strike slip earthquake is highest in the southern part of the study area the october 28 2012 mw 7 8 haida gwaii thrust earthquake occurred in our study area and altered the slip dynamics of the plate boundary the qcf is observed to undergo accelerated right lateral slip for 1 2 months following the earthquake the subduction interface exhibits afterslip thrust motion that persists for the duration of the study period i e 3 years and 2 months after the haida gwaii earthquake afterslip is greatest 5 7 8 4 cm yr on the periphery of the main rupture zone of the haida gwaii event

geology mineralization and fluid inclusion characteristics of the lermontovskoe reduced type tungsten cu au bi skarn deposit sikhote alin russia abstract the lermontovskoe deposit 48 kt wo 3 average 2 6 wo 3 0 24 cu 0 23 g t au is situated in a w sn au metallogenic belt that formed in a collisional tectonic environment this tungsten skarn deposit has a w au as bi te sb signature that suggests an affinity with reduced intrusion related au deposits the deposit is associated with an intrusion that is part of the ilmenite series high k peraluminous granitoid granodiorite to granite suite these rocks formed via mantle magma induced melting of crustal sources the deposit comprises reduced type pyroxene dominated prograde and retrograde skarns followed by hydrosilicate amphibole chlorite pyrrhotite scheelite quartz and phyllic muscovite sericite carbonate albite quartz scheelite sulfide with abundant apatite alteration assemblages fluid inclusions from the skarn assemblages indicate high temperature 500 c high pressure 1400 1500 bars and high salinity 53 60 wt nacl equiv magmatic hydrothermal fluids they were post dated by high carbonic methane dominate low salinity fluid at the hydrosilicate alteration stage these fluids boiled at 360 380 c and 1300 1400 bars the subsequent phyllic alteration started again with a high temperature 450 c high pressure 1000 1100 bars and high salinity 42 47 wt nacl equiv fluid with further incursion of high carbonic methane dominated low salinity fluid that boiled at 390 420 c and 1150 1200 bars the latest phyllic alteration included the lower temperature 340 360 c lower pressure 370 400 bars high carbonic methane dominated but with higher co 2 fraction low salinity fluid and then the low temperature 250 300 c h 2 o co 2 ch 4 nacl fluid with both fluids boiled at the deposit level the high salinity aqueous fluids are interpreted to have come from crystallizing granitoid magma whereas the reduced high carbonic fluids probably came from a deeper mafic magma source both of these fluids potentially contributed to the w au as bi te sb metal budget decreasing temperatures coupled with high aca 2 and fluid boiling promoted scheelite deposition at all post skarn hydrothermal stages the deposit is characterized by limited downdip extent of mineralized zones and abundant coarse grained muscovite quartz apatite scheelite aggregates that formed at the phyllic alteration stage together with presence of high temperature high pressure and high salinity fluids directly exsolving from crystallizing magma this suggests a root level of the mineralized magmatic hydrothermal system of reduced w skarn deposits

late quaternary faulting and thermoluminescence dating of the east cache fault zone north central utah the east cache fault zone ecfz the southernmost of five en echelon quaternary normal faults between the wasatch and teton faults displays evidence of two large paleoearthquakes in the last 15 000 years 15 ka stratigraphic data from a trench on the central segment of the ecfz are augmented with one radiocarbon date the regional radiocarbon chronology and 14 thermoluminescence tl age estimates of the 14 tl analyses performed by alpha analytic inc only 8 satisfied our criteria for statistical acceptability 20 per cent coefficient of variation 50 per cent extrapolation to residual tl level the tl age estimates broadly bracket the earlier faulting event at between 8 7 1 0 and 17 4 3 0 ka and the later event at between 2 5 0 5 and 8 7 1 0 ka one radiocarbon age further constrains the earlier event to be younger than 15 540 130 yr bp correlation of local quaternary deposits to the regional radiocarbon chronology provides indirect but more tightly limiting age constraints of ca 4 to ca 7 ka for the later event and ca 13 ka to 15 540 130 yr bp for the earlier event both events had small vertical displacements at the trench site 0 8 to 1 8 m but the cumulative net vertical tectonic displacement elsewhere is up to 4 2 m suggesrive of m s 6 9 to 7 1 paleoearthquakes single event displacements and the extent of fault scarps suggest that these two paleoearthquake ruptures were probably limited to the 20 kin long central segment of the east cache fault zone near logan utah the elapsed time since the most recent event on the central segment ca 4 to ca 7 ka is somewhat less than the estimated recurrence interval between the latest two paleoearthquake 8 6 3 0 ka however comparison of only a single poorly constrained recurrence interval with the elapsed time does not result in a confident assessment of future earthquake potential

tectonics and structure of the queen charlotte fault zone haida gwaii and large thrust earthquakes abstract this article provides a summary of the structure and tectonic history of the queen charlotte transform fault zone off western canada as background to understanding the 2012 m w 7 8 thrust earthquake off haida gwaii there was margin subduction prior to the eocene the fault zone then became the mainly transcurrent pacific north america boundary there was mid tertiary oblique extension then 15 20 oblique convergence from 6 ma to the present that resulted in underthrusting and subduction initiation the total underthrusting has been too small for benioff wadati seismicity or arc volcanics but is indicated by 1 a trench the queen charlotte trough into which the oceanic plate bows downward and an offshore flexural bulge the oshawa rise 2 the queen charlotte terrace an accretionary sedimentary prism 3 seismic receiver function delineation of the underthrusting pacific plate 4 heat flow decreasing landward as predicted for underthrusting 5 low gravity offshore and high onshore consistent with underthrusting and 6 late tertiary uplift and erosion of the west coast of the islands oblique convergence is partitioned into nearly margin normal underthrusting i e m w 7 8 event relative to the terrace which is moving along the margin and margin parallel on the queen charlotte strike slip fault just off the coast that produced the 1949 m s 8 1 earthquake landward on the mainland global positioning system data suggest slow coast parallel shear with no historical seismicity the convergence rate decreases to the north of haida gwaii off dixon entrance but large thrust earthquakes are possible to the south underthrusting of the winona basin margin also could generate large earthquakes

coarse muscovite veins and alteration in porphyry systems abstract coarse muscovite veins and alteration occur in porphyry copper and porphyry molybdenum copper systems within the laramide arc in arizona as well as at the yerington district in nevada this work describes coarse muscovite in veins and altered wall rock in porphyry systems in this region and documents mineral assemblages mineral compositions spatial and temporal relationships and hydrogen isotopic compositions coarse hydrothermal muscovite is documented in the roots of porphyry cu mo systems as well as in and above the ore bodies in porphyry mo cu systems and it is compared to coarse hydrothermal muscovite greisen in lode sn w mo systems basin and range extension has exposed coarse hydrothermal muscovite in several laramide and jurassic porphyry cu mo systems at paleodepths of 3 to 12 km miami inspiration sierrita esperanza copper basin crown king granite mountain roots of the ray porphyry system gunnison texas canyon stock grayback kelvin riverside district sycamore canyon the new cornelia mine ajo district and two systems in the yerington district muscovite is the dominant mica in these coarse muscovite veins and associated alteration with common k feldspar and albite an00 06 common accessory hematite rutile pyrite and apatite and rare accessory chalcopyrite fluorite molybdenite wolframite and scheelite coarse hydrothermal muscovite yields d compositions that suggest formation from fluids that are dominantly magmatic hydrothermal in origin whole rock compositions of coarse hydrothermal muscovite show common gains in k and loss of ca na coarse muscovite veins and alteration in porphyry copper systems postdate mineralized potassic veins and form too deeply to overlap with shallower acidic forms of alteration sericitic advanced argillic variation in mineral assemblage mineral compositions and mineralization of coarse hydrothermal muscovite correlate with the composition of laramide stocks porphyry mo cu systems contain coarse muscovite alteration assemblages with the highest mineral diversity and trace element enrichment coarse muscovite veins and alteration in porphyry mo cu systems related to stocks ranging from quartz monzonite to granite in composition form at shallower paleodepths and occur within and above the associated orebodies in contrast coarse muscovite veins and alteration associated with subalkaline porphyry copper systems occur at deeper levels in some cases overlapping with the bottom of potassic alteration and the ore body but extending well into the roots of the system in the underlying granitoid cupola in these latter systems zones of coarse muscovite alteration typically are poorly mineralized and mineral assemblages are less varied these characteristics suggest that coarse muscovite forming fluids are predominately of magmatic hydrothermal origin and exsolved from late stage fractionated magmas of the larger pluton that sourced porphyry stocks and dikes responsible for porphyry copper mineralization in some instances however the exposed coarse muscovite alteration is associated with a petrologically unrelated commonly more felsic later intrusion rather than being related to late exsolution of fluid from the same crystallizing stock or batholith

statistical relations among earthquake magnitude surface rupture length and surface fault displacement abstract in order to refine correlations of surface wave magnitude fault rupture length at the ground surface and fault displacement at the surface by including the uncertainties in these variables the existing data were critically reviewed and a new data base was compiled earthquake magnitudes were redetermined as necessary to make them as consistent as possible with the gutenberg methods and results which make up much of the data base measurement errors were estimated for the three variables for 58 moderate to large shallow focus earthquakes regression analyses were then made utilizing the estimated measurement errors the regression analysis demonstrates that the relations among the variables magnitude length and displacement are stochastic in nature the stochastic variance introduced in part by incomplete surface expression of seismogenic faulting variation in shear modulus and regional factors dominates the estimated measurement errors thus it is appropriate to use ordinary least squares for the regression models rather than regression models based upon an underlying deterministic relation in which the variance results primarily from measurement errors significant differences exist in correlations of certain combinations of length displacement and magnitude when events are grouped by fault type or by region including attenuation regions delineated by evernden and others estimates of the magnitude and the standard deviation of the magnitude of a prehistoric or future earthquake associated with a fault can be made by correlating m s with the logarithms of rupture length fault displacement or the product of length and displacement fault rupture area could be reliably estimated for about 20 of the events in the data set regression of m s on rupture area did not result in a marked improvement over regressions that did not involve rupture area because no subduction zone earthquakes are included in this study the reported results do not apply to such zones

seismotectonics of the explorer region 1 the explorer region offshore western canada is a tectonically complex area surrounded by the pacific north america and juan de fuca plates existing tectonic models for the region differ fundamentally proposed plate configurations range from multiple independent plate fragments to an explorer plate now fused to north america along the continental margin and cut by pacific north america transform faults in the west we present new seismological data constraining the region s current tectonics we use three component regional waveforms to determine the source parameters of 84 earthquakes with magnitude greater than 4 combined with 34 harvard centroid moment tensor solutions they represent the region s largest earthquake source parameter data set obtained by robust waveform modeling techniques in addition we perform joint epicenter determination to relocate larger earthquakes recorded since 1918 the source parameters and improved locations provide a consistent tectonic picture earthquake slip vector azimuths along the pacific plate boundary change smoothly and are significantly less northerly oriented than the pacific north america plate motion direction requiring an independent explorer plate the present day pacific explorer boundary is formed by transform faults subparallel to the revere dellwood wilson fault plate motion vectors indicate that the winona block is part of the explorer plate current explorer motion is more northerly than indicated by magnetic anomalies prior to 2 ma implying a recent change possibly coinciding with a northwestward ridge jump near explorer plate s northern end transferring the winona block from the pacific to the explorer plate in response to these plate motion changes the region north of the western sovanco fracture zone was assimilated into the pacific plate the region around the eastern sovanco fracture zone characterized by broadly distributed seismicity is composed of well defined sets of conjugate faults bounding rotating crustal blocks earthquake fault strikes agree with the dominant northwest southeast fault sets however the conjugate sets must be also active to fully accommodate present day explorer plate motion the sw portion of the strike slip nootka fault zone the explorer juan de fuca plate boundary is well defined by focused seismicity however its full extent under nootka island remains unresolved the explorer north america boundary shows sporadic low magnitude seismicity our explorer north america rotation pole predicts convergence varying from negligible at the boundary s northwest end to 2 cm yr at the se end this convergence can be accommodated either by subduction or by crustal thickening extending to the north american continent we favor subduction based on low deformation rates observed by onshore gps sites the present explorer plate system configuration is a result of stepwise reorientation of the explorer ridge system each step successively reducing the subduction rate relative to north america

queen charlotte fault zone microearthquakes from a temporary array of land stations and ocean bottom seismographs a temporary array of land and ocean bottom seismograph stations was used to accurately locate microearthquakes on the queen charlotte fault zone which occurs along the continental margin of wester

subsidence and thermal history of queen charlotte basin a tectonic model for the formation subsidence and thermal history of queen charlotte basin is developed based upon regional geological and geophysical data subsidence data from offshore wells in hecate strait and queen charlotte sound and thermal criteria derived from present heat flow and vitrinite reflectance information queen charlotte basin is seen to have resulted from two distinct mechanisms 1 during a period of broad regional uplift rifting and crustal extension occurred in queen charlotte sound up to about 17 ma ago and the queen charlotte islands were displaced northwards toward their present position by transcurrent motion along the louscoone inlet sandspit fault system the rifting generated a significant thermal anomaly and a restricted deep basin as a consequence of crustal thinning and subsequent thermal cooling 2 beginning about 6 ma ago oblique underthrusting commenced along the margin resulting in flexural uplift of the western part of the queen charlotte islands and comp

hydrothermal fluids responsible for the formation of precious minerals in the nigerian younger granite province preliminary investigations in the younger granite province of nigeria have revealed that precious and semi precious minerals like rubies sapphires emeralds aquamarine zircon and fluorite can be found in the region the gem minerals are shown to have been produced either by direct deposition along fissures veins and greisens by hydrothermal fluids or as a result of hydrothermal fluids reacting with wall rocks these wall rocks are either biotite granites from which the hydrothermal fluids originated or basement rocks or any other rocks which the biotite granites intrude and their residual hydrothermal fluids have invaded the hydrothermal fluids appear to have been rich in alkalis na k etc rare elements be zr f ree etc and siliceous as these fluids rose through fractures and channel ways through the rocks they either deposited the gem minerals in the fractures at the appropriate stability conditions or reacted with the wall rocks producing the gem minerals at the expense of elements like ca and a1 in the minerals of these rocks

contemporary movements and tectonics on canada s west coast a discussion abstract evidence from published tidal records and geodetic relevelling data in british columbia indicates that there is a consistent pattern of contemporary uplift on the outer coast 2 mm yr and subsidence on the inner coast 1 2 mm yr the zero uplift contour or hinge line runs through hecate strait georgia strait and victoria this pattern continues southwards into washington state but is interrupted to the north by considerable uplift in southeastern alaska although glacio isostatic recovery has dominated vertical movements in the region over the last 10 000 years the distribution and trend of the observed contemporary movements are not compatible with the pattern to be expected from this source and are most probably tectonic in origin there is however no clear distinction between the movements seen opposite the queen charlotte transform margin and the vancouver island convergent margin comparison with movements observed at other active plate margins show that the pattern is essentially similar to that seen in association with subduction and convergence the paradox that the vertical movement rates are much too great to explain observed geology and topography may be soluble by assuming that discontinuous lateral shifts of the movement pattern occur on a scale of hundreds of thousands of years

continental drift and a theory of convection early geologists considered that the earth s surface is rigid and unchanging they assumed that the whole earth is static except for enough sub surface contraction to build mountains after seismology developed most geophysicists agreed a few scientists notably wegener favoured a more mobile earth about 1965 fresh evidence showed that both theories were too simple this evidence explained why neither theory had been able to relate the whole earth s behaviour to laws of physics hence different aspects of geology had only been solved separately which had fragmented earth science this paper proposes a compromise it is that the rigid lithosphere fractures according to navier s law of brittle failure which explains the properties and provides methods for classifying faults plate boundaries and mountains and that the ductile mantle convects by laws of fluid flow in patterns partly controlled by lithospheric fractures these dual interacting influences explain tectonic behaviour the pattern of currents is hidden at any one time upwelling beneath continents only affects a few limited areas today some are in southwestern united states central asia botswana antarctica and rifts in east africa europe and siberia nevertheless recognition of upwelling currents may revolutionize geology because their cumulative effects have been great and neglected

relationships between earthquake magnitude source geometry and slip mechanism abstract the empirical relationships between source area source length source width and magnitude m s are investigated for globally distributed earthquakes of different slip mechanism types a total of nearly 400 events having magnitudes approximately between 4 5 and 8 5 were considered the analyses of specially selected events outlined that the regional setting has no influence on the relationships between m s and source dimensions as well as between rupture length and width instead they depend on the slip mechanism type strike slip reverse and normal oblique slip as mechanisms change from strike slip to oblique slip and further from oblique slip to reverse and normal slip sources of similar length size exhibit increasing magnitudes in steps of 0 8 1 6 in the overall mentioned spectrum of the mechanism types whereas sources of similar areas correspond to the different slip type events with magnitudes increasing in steps of 0 5 0 8 source widths increase by about three times for earthquakes of equal rupture length when the mechanism changes from strike slip to reverse and normal slip therefore it can be concluded that sources of equal length have different areas and length width ratios for various types of mechanism accordingly stress drop may be larger for strike slip sources than for sources with prevailing vertical displacement the regressions of rupture dimensions on surface wave magnitude for different single slip mechanism types restricted in most cases to the magnitude range between 5 5 and 8 0 are strongly correlated having standard deviations of 0 15 0 25 magnitude units corresponding regression coefficients are different at 95 level of significance for different slip mechanism types of each pair of correlated parameters the single slip type regressions have smaller standard deviations and higher correlation coefficients than the all slip type regressions this observation validates the conclusion about strong dependencies of source dimensions and surface wave magnitudes on slip mechanism type the results can be used to evaluate the event magnitude source area length width and mechanism type when any two of these parameters are known

non pegmatitic deposits of beryllium mineralogy geology phase equilibria and origin non pegmatitic occurrences of be minerals constitute a diverse set of geologic environments of considerable mineralogical and petrological interest they currently provide the majority of the world s be ore and emeralds and they contain the greatest resource of these commodities of the approximately 100 be minerals known see chapter 1 by grew appendix a most occur in hydrothermal deposits or non pegmatitic igneous rocks where their distribution varies systematically with the setting and origin table 1 fig 1 view this table table 1 beryllium minerals in non pegmatitic deposits formulas use and occurrence 1 figure 1 chemography of the principal solid phases in the beo al2o3 sio2 h2o f2o 1 bash system with the projected positions of helvite group and alkali be silicates also shown are generalized fields for some of the major types natural of occurrences cf table 1 fig 4 see text for discussion beryllium minerals are best known from geologic systems associated with felsic magmatism they also occur in a variety of settings that lack evident igneous associations environments range from the surface to the deep crust and host rocks range from feldspathic to carbonate to ultramafic in composition genetically related igneous rocks are felsic and share low calcium and high f contents but are diverse in composition setting and origin compositions range from strongly peraluminous to peralkaline and can be silica undersaturated beryllium minerals also occur in metamorphic and basinal environments and are redistributed by surface processes table 2 summarizes the types and significance of major groups of occurrences by their lithologic associations figure 2 shows the global distribution of some important examples and regional belts for most types at least one example has been described in some detail and can be used to help evaluate general patterns however

plate boundary adjustments of the southernmost queen charlotte fault abstract a revision of the plate boundary configuration offshore southern haida gwaii which is the locus of the 2012 m w 7 8 thrust earthquake is based on a re evaluation of regional geophysical data and leads to recognition of fault segments critical for seismic hazard analysis off western canada the strike slip queen charlotte fault qcf and revere dellwood fault rdf constitute the transpressive plate boundary between the pacific and north american plates the southernmost 80 km of the qcf strikes at the highest angle 20 to the relative plate motion yet geomorphology adjacent to the fault is the most subdued synthesizing geomorphology seismicity sidescan sonar gravity and seismic reflection profiles indicates that the plate boundary is evolving to a less transpressive configuration than previously interpreted the rdf is 100 km longer than previously mapped it has propagated northward and overlaps the qcf by 120 km propagation is defined by strike slip earthquakes 3 9 m w m w 7 8 and the 1949 m 8 1 earthquakes

transition from oceanic to continental crustal structure seismic and gravity models at the queen charlotte transform margin seismic refraction data have been interpreted along a line crossing the queen charlotte transform just north of the triple junction where the explorer ridge intersects the continental margin these data observed at three onshore sites help to define the structure of the continental crust beneath the queen charlotte sedimentary basin sediment thicknesses of up to 4 km were determined from a coincident multichannel reflection line beneath the sediments velocities increase from about 5 5 to 6 3 km s 1 at 8 km depth then increase from 6 5 to 6 7 km s 1 at 18 km depth below this depth the lower crust is partly constrained by moho wide angle reflections at the three receiving sites which indicate a lower crust velocity of 6 8 6 9 km s 1 and a moho depth of 26 28 km the crustal velocity structure is generally similar to that in southern queen charlotte sound it is in contrast to the velocity structure across hecate strait to the north where a prominent mid crust interface at 15 km depth was observe

evidence for underthrusting beneath the queen charlotte margin british columbia from teleseismic receiver function analysis summary the queen charlotte fault zone is the transpressive boundary between the north america and pacific plates along the northwestern margin of british columbia two models have been suggested for the accommodation of the 20 mm yr 1 of convergence along the fault boundary 1 underthrusting 2 internal crustal deformation strong evidence supporting an underthrusting model is provided by a detailed teleseismic receiver function analysis that defines the underthrusting slab forward and inverse modelling techniques were applied to receiver function data calculated at two permanent and four temporary seismic stations within the queen charlotte islands the modelling reveals a 10 km thick low velocity zone dipping eastward at 28 interpreted to be underthrusting oceanic crust the oceanic crust is located beneath a thin 28 km eastward thickening 10 continental crust

structure beneath queen charlotte sound from seismic refraction and gravity interpretations a combined multichannel seismic reflection and refraction survey was carried out in july 1988 to study the tertiary sedimentary basin architecture and formation and to define the crustal structure and associated plate interactions in the queen charlotte islands region simultaneously with the collection of the multichannel reflection data refractions and wide angle reflections from the airgun array shots were recorded on single channel seismographs distributed on land around hecate strait and queen charlotte sound for this paper a subset of the resulting data set was chosen to study the crustal structure in queen charlotte sound and the nearby subduction zone two dimensional ray tracing and synthetic seismogram modelling produced a velocity structure model in queen charlotte sound on a margin parallel line moho depth was modelled at 27 km off southern moresby island but only 23 km north of vancouver island excluding the approximately 5 km of the tertiary sediments the crust in the latter area is onl

integrated crustal structure across the south central california margin santa lucia escarpment to the san andreas fault the continental margin of south central california has undergone different styles of deformation over the past 30 m y as the north america pacific plate boundary has evolved from subduction to transform tectonics results presented here identify strike slip and compressional structures in the lower crust that probably developed during this period of tectonic transition an integrated model of crustal structure along deep seismic line pg e 3 crosses the entire continental margin west of the san andreas fault near the latitude of san luis obispo a compressional wave velocity model was developed using coincident marine multi channel seismic and onshore offshore wide angle reflection refraction seismic data and was tested independently with gravity modeling a high velocity layer 6 8 7 0 km s about 6 km thick in the lower crust that extends east possibly as far as the san andreas fault is interpreted as tectonically underplated oceanic crust the upper and middle crust of the patton and sur obispo franciscan terranes extends to depths of 14 to 20 km the velocity and density modeling indicate lower average velocities and densities for the patton terrane supporting earlier interpretations that it is a distinct terrane within the franciscan complex abrupt crustal thickening associated with broken and downdropped oceanic crust beneath the santa lucia escarpment probably results from active transform faulting that occurred along the continental slope from about 22 to 16 ma following the subduction of the pacific arguello ridge an imbrication within the oceanic crust centered beneath the coast is evidence for about 15 km of shortening within the oceanic crust convergence between the monterey and arguello microplates during the final stages of farallon subduction about 24 to 16 ma probably caused the imbrication

an overview of the 28 october 2012 m w 7 7 earthquake in haida gwaii canada a tsunamigenic thrust event along a predominantly strike slip margin the boundary between the pacific and north america plates along canada s west coast is one of the most seismically active regions of canada and is where canada s two largest instrumentally recorded earthquakes have occurred although this is a predominantly strike slip transform fault boundary there is a component of oblique convergence between the pacific and north america plates off haida gwaii the 2012 mw 7 7 haida gwaii earthquake was a thrust event that generated a tsunami with significant run up of over 7 m in several inlets on the west coast of moresby island several over 6 m with a maximum of 13 m damage from this earthquake and tsunami was minor due to the lack of population and vulnerable structures on this coast

a comparison of mechanical thickness estimates from trough and seamount loading in the southeastern gulf of alaska the southern portion of the kodiak bowie seamount chain in the southeastern gulf of alaska presents a unique opportunity to investigate loading on young oceanic lithosphere oceanic lithosphere younger than 25 ma is loaded both by sediments in a deep offshore trough and by seamounts 100 200 km offshore free air gravity anomaly values associated with the trough range from 90 mgal over the trough to 25 mgal over the offshore flexural high whereas values associated with the volcanic loading range from 80 mgal over the seamounts to 10 mgal over their associated moats these anomalies are modeled first using elastic beam theory gravity anomalies associated with the trough are modeled in terms of elastic bending of a sediment filled trench elastic thicknesses associated with the trough range from 12 to 22 km with an estimated uncertainty of 5 km seamounts are approximated as a series of stacked finite cylinders gravity highs over the seamounts are used to model density while gravity patterns associated with the moat and peripheral bulge are used to model the elastic thickness along the seamount chain elastic thicknesses along the seamount chain range from 2 to 5 km estimated uncertainty range 0 to 7 and 0 to 10 km respectively to investigate differences in elastic thickness estimates between the trough and seamount models we incorporate the effects of finite yield strength curvatures implied by the elastic beam models are used to calculate mechanical bending stresses bending moments calculated from elastic beam models and yield envelope models agree for flexure models at the queen charlotte trough and most seamounts the mechanical thickness corresponds to the depth to the 700 c isotherm assuming a dry olivine rheology and a simple cooling model for oceanic lithosphere our results imply that the strength of the lithosphere calculated for both seamount and trench loading corresponds to the same isotherm

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

seismotectonics of the guinean earthquake of december 22 1983 field geological and seismological investigations conducted after the guinean earth quake on december 22 1983 show a shallow dextral strike slip fault with a large normal component the nw se horizontal compressive stress deduced from this event is consistent with measurements made at other places in this region old fissures some of them reactivated during this earthquake show that this intraplate area cons titutes a localized weakness zone in the crust

the seismic structure across an active oceanic continental transform fault zone a seismic structural section across the southern queen charlotte transform fault zone which separates the oceanic pacific plate from the continental america plate off western canada has been determined from an offshore onshore refraction experiment two explosion profiles one parallel and one perpendicular to the fault strike were recorded on three ocean bottom seismographs obs and seven land based seismographs lbs assuming lateral homogeneity along the parallel profile recorded over oceanic crust at one obs one dimensional amplitude modeling produced a velocity model with the characteristics of standard ocean crust the partially reversed perpendicular profile recorded at two obs s and one good quality lbs extended across the fault zone which in bathymetric cross section shows two linear fault escarpments separated by a flat terrace an initial velocity structure provided by time term analysis of the complete data set was modified by ray tracing until the travel time data for the three stations were satisfied by one seismic structural section this model shows three distinctive crustal blocks the oceanic terrace and continental blocks separated by two major crustally pervasive faults the outer and inner queen charlotte faults the rock units composing the terrace block have lower velocities at equivalent depths than those of the blocks on either side this may have resulted from deformation associated with oblique convergence and or the effects of a jump in the position of the active queen charlotte fault from its outer to inner positions about 1 0 5 ma ago depth to the base of the crustal section increases from 12 to 18 km below sea level across the terrace transition zone representing an eastward dip of about 20 the seismic model after conversion to a density model agrees well with the gravity anomaly along the profile the interpreted structural section is consistent with recent tectonic models that require a component of convergence along the transform fault zone

determination of magnitudes of ancient earthquakes from dimensions of observed seismodislocations abstract equations to estimate the magnitude of ancient earthquakes where seismotectonic crustal deformations normal faults strike slip faults etc have been preserved in the epicentral region are presented the equations are based on the results of over one hundred earthquakes including 96 recent continental earthquakes in the magnitude range 5 2 8 7

surface faulting in the southern italian campania basilicata earthquake of 23 november 1980 the campania basilicata earthquake of 23 november 1980 was the largest ms 6 9 and most destructive earthquake that has occurred in this region of southern italy for over 100 years killing more than 3 000 people the consensus among seismologists geologists and earthquake engineers who have studied1 10 this event is in keeping with previous italian earthquakes that it did not produce faulting at the surface this has led to the establishment of a number of models2 3 11 13 requiring an unusual tectonic setting for the southern apennines however on a recent visit to the epicentral region of the earthquake may 1984 we discovered more than 10 km of surface faulting that is consistent with focal mechanisms for this event based on first motion polarities2 4 5 12 and long period waveform studies14 16 which show that it involved normal faulting with one nodal plane dipping at 60 towards the north east our observations of this the first well documented earthquake fault break to be reported in italy suggest that the deformation associated with earthquakes in the southern apennines takes place in the upper 10 15 km of the earth s crust on steep planar normal faults which break the surface as is widely observed in other areas of active extension outside italy

the queen charlotte islands refraction project part i the queen charlotte fault zone the active margin between the continental north american plate and oceanic pacific plate west of the queen charlotte islands was the site of an extensive onshore offshore seismic refraction project

seismicity and rates of relative motion on the plate boundaries of western north america summary the consistency of earthquake data and plate tectonic models and other estimates of fault slip may be tested by estimating rates of motion from the earthquakes using the concept of seismic moment the contribution of individual events may simply be summed but a generally better estimate of long term average slip rate is obtained by integration over magnitudefrequency of occurrence relations estimates of fault motion rates associated with earthquakes are possible within about a factor of 2 using this approach if the major sources of uncertainty are given careful consideration e g incompleteness and inaccuracies in the earthquake data empirical moment magnitude relations and the effect of their stochasticity fault widths or depth extents the recurrence relations maximum magnitudes and the form of truncation at the maximum magnitude a formulation for the recommended magnitude density truncation is developed application of the latter method to the earthquake data of the offshore transform faults of the juan de fuca ridge system the queen charlotte fault zone and the northern vancouver island area in each case gives good agreement with rates from plate tectonic models for the southern san andreas fault and gulf of california area there is also good agreement with previous estimates obtained by summing the contributions of individual events however the displacement rate in the margin convergence zone of southern british columbia washington and oregon computed from the seismicity is at least a factor of 10 lower than from plate models and from other convergence estimates and primarily aseismic slip is suggested the fault motions as a function of time computed from the seismicity records have also been plotted and compared to the longterm average rates the plots permit estimates of the minimum present accumulated elastic strain and show if there are any temporal relations among earthquake displacements on different fault zones

source characteristics of the 2012 haida gwaii earthquake sequence abstract all the significant m l 4 events in the 2012 haida gwaii earthquake sequence are systematically relocated and their moment tensor solutions are determined from waveform inversion the focal mechanism of the mainshock shows low angle thrust faulting along a shallowly dipping plane with a strike parallel to the queen charlotte fault qcf consistent with the inference of pacific plate underthrusting beneath the overriding north american plate the epicenter of the mainshock is located 5 km landward northeast of the surface trace of the qcf suggesting the nucleation of the rupture was near the bottom of the seismogenic locked interface significant aftershocks appear to cluster on the periphery of the main rupture zone with most events located immediately seaward of the deformation front the majority of these events show normal faulting mechanisms that are probably associated with the bending stress within the pacific plate near the deformation front several normal and strike slip events at greater depths within the subducted pacific slab show a consistent pattern of t axis in the down dip direction implying the subducted plate is under a stress regime of down dip extension only a few strike slip events were observed along or near the qcf the limited size and distribution of these events suggest that most of the elastic strain accumulated along the qcf was not released during the 2012 haida gwaii sequence major strike slip earthquakes are likely to occur along the southernmost part of the qcf system in the future

seismic structure across the active subduction zone of western canada the vancouver island seismic project was conducted in 1980 to study the structure of the subducting oceanic juan de fuca plate and the overriding continental america plate the principal seismic refraction line line i was a 350 km onshore offshore profile perpendicular to the continental margin an array of 32 receivers was located on the america plate on the mainland and across vancouver island and extended offshore with three ocean bottom seismometers obs s two shots were fired at the eastern end of the line and 17 shots were located along the westernmost 100 km of the profile control for the interpretation of the onshore offshore profile was provided by a reversed refraction profile along the length of vancouver island and by a marine refraction profile recorded on the obs s modeling of the seismic structure of this complex region utilized an iterative inversion method for travel times from explosions in which shots at several locations are recorded on the same set of receivers and utilized an algorithim based on asymptotic ray theory for the calculation of synthetic seismograms through two dimensional media the major features of the refraction structural model are that 1 the oceanic lithosphere dips at 3 or less beneath the continental slope so the bend in the subducting slab occurs landward of the foot of the slope 2 the oceanic lithosphere dips at 14 16 beneath the continental shelf until it passes beneath the continental moho at 37 km depth below western vancouver island 3 an upper mantle reflector may correspond to the base of the subducting lithosphere and 4 a segment of high velocity material above the downgoing crust with velocity 7 7 km s and depth range 20 25 km may represent a remnant of subducted lithosphere perhaps detached when the subduction zone jumped westward to its present position

queen charlotte fault zone heat flow measurements the heat flow pattern from the deep sea across the queen charlotte terrace to the west coast of the queen charlotte islands has been determined through 20 marine heat flow measurements and by 11 borehole measurements at one land site there is a continuous transition from very high deep sea heat flow through intermediate values on the terrace to low continental heat flow the deep sea values are scattered probably reflecting hydrothermal circulation in the crust but their mean is in agreement with the theoretical value for the 7 ma deep sea oceanic crust the mean heat flow at the land site of 47 mw m 2 is similar to the average for the coast insular belt to the south and east the measurements on the 30 km wide 2 km deep terrace are less scattered and much lower than those on the deep sea floor the main thermal contrast is at the seaward edge of the terrace rather than near the coast where the earthquakes of the main plate boundary are located numerical models suggest that no reasonable steady stat