constraining continental margin seismicity by extending on shore seismograph stations to critical off shore sites the westernmost north american plate margin in central california includes major faults with both onshore and offshore segments prior to deployment during 1997 and 1998 of a suite of ocean bottom seismometers within monterey bay the distribution and focal mechanisms of offshore earthquakes were poorly constrained the use of ocean bottom seismic stations improves the accuracy of locations for events in monterey bay especially for those far offshore and permits more robust focal mechanism solutions by reducing uncertainties in strike dip and rake these initial results using u s geological survey crustal velocity models and location parameters reduce the apparent scatter of seismic events and focal mechanisms and the more consistent solutions provide valuable information on fault characteristics for the san gregorio fault sgf and monterey bay fault zone mbfz most seismic events are relocated to the northern section of the sgf defining a zone of compressional deformation and relatively high microseismicity the mbfz is the source for fewer but important and well located events surprisingly no events were observed on the southern sgf offshore of carmel and pebble beach despite the well defined trace of the san gregorio along carmel canyon

seismic reflection imaging of the juan de fuca plate from ridge to trench new constraints on the distribution of faulting and evolution of the crust prior to subduction we present prestack time migrated multichannel seismic images along two cross plate transects from the juan de fuca jdf ridge to the cascadia deformation front df offshore oregon and washington from which we characterize crustal structure distribution and extent of faults across the plate interior as the crust ages and near the df in response to subduction bending within the plate interior we observe numerous small offset faults in the sediment section beginning 50 70 km from the ridge axis with sparse fault plane reflections confined to the upper crust plate bending due to sediment loading and subduction initiates at 120 150 km and 65 80 km seaward of the df respectively and is accompanied by increase in sediment fault offsets and enhancement of deeper fault plane reflectivity most bend faulting deformation occurs within 40 km from the df on the oregon transect bright fault plane reflections that extend through the crust and 6 7 km into the mantle are observed if attributed to serpentinization 0 12 0 92 wt water within the uppermost 6 km of the mantle is estimated on the washington transect bending faults are confined to the sediment section and upper middle crust the regional difference in subduction bend faulting and potential hydration of the jdf plate is inconsistent with the spatial distribution of intermediate depth intraslab seismicity at cascadia a series of distinctive ridgeward dipping 20 40 lower crustal reflections are imaged in 6 8 ma crust along both transects and are interpreted as ductile shear zones formed within the ridge s accretionary zone in response to temporal variations in mantle upwelling possibly associated with previously recognized plate reorganizations at 8 5 ma and 5 9 ma

seismicity at the cascadia plate boundary beneath the oregon continental shelf since 2003 39 small earthquakes have been detected off the coast of central oregon in the nominally locked part of the cascadia subduction zone where very little seismic activity has been recorded in spite of a paleoseismic record of great subduction events although the regional earthquake bulletin reports depths of 29 and 28 km for the two largest events m w 4 9 and m w 4 7 which occurred in 2004 analysis by trehu et al 2008 indicates that they were low angle thrust events that occurred on the plate boundary at depths of 9 11 and 16 km respectively because of sparse onshore station coverage most of the smaller events have large location uncertainties double difference relative location of 30 of these earthquakes reveals two tight clusters approximately 30 km apart each cluster is associated with one of the two larger events within each cluster relocation reduces the hypocenter depth spread from 15 km to 3 km with uncertainties on the order of 0 1 km the relocations combined with independent absolute hypocenter locations for two 2008 events using a deployment of land and ocean bottom seismometers suggest that the seismicity occurred at plate boundary depths possibly on the cascadia megathrust this concentrated activity in the seismogenic zone may represent patches on the fault plane with anomalous frictional characteristics possibly caused by subducted topographic features which can affect the propagation of a large megathrust rupture

tsunami history of an oregon coastal lake reveals a 4600 yr record of great earthquakes on the cascadia subduction zone bradley lake on the southern oregon coastal plain records local tsunamis and seismic shaking on the cascadia subduction zone over the last 7000 yr thirteen marine incursions delivered landward thinning sheets of sand to the lake from nearshore beach and dune environments to the west following each incursion a slug of marine water near the bottom of the freshwater lake instigated a few year to several decade period of a brackish 4 salinity lake four additional disturbances without marine incursions destabilized sideslopes and bottom sediment producing a suspension deposit that blanketed the lake bottom considering the magnitude and duration of the disturbances necessary to produce bradley lake s marine incursions a local tsunami generated by a great earthquake on the cascadia subduction zone is the only accountable mechanism extreme ocean levels must have been at least 5 8 m above sea level and the cumulative duration of each marine incursion must have been at least 10 min disturbances without marine incursions require seismic shaking as well over the 4600 yr period when bradley lake was an optimum tsunami recorder tsunamis from cascadia plate boundary earthquakes came in clusters between 4600 and 2800 cal yr b p tsunamis occurred at the average frequency of 3 4 every 1000 yr then starting 2800 cal yr b p there was a 930 1260 yr interval with no tsunamis that gap was followed by a 1000 yr period with 4 tsunamis in the last millennium a 670 750 yr gap preceded the a d 1700 earthquake and tsunami the a d 1700 earthquake may be the fi rst of a new cluster of plate boundary earthquakes and accompanying tsunamis local tsunamis entered bradley lake an average of every 390 yr whereas the portion of the cascadia plate boundary that underlies bradley lake ruptured in a great earthquake less frequently about once every 500 yr therefore the entire length of the subduction zone does not rupture in every earthquake and bradley lake has recorded earthquakes caused by rupture along the entire length of the cascadia plate boundary as well as earthquakes caused by rupture of shorter segments of the boundary the tsunami record from bradley lake indicates that at times most recently 1700 yr b p overlapping or adjoining segments of the cascadia plate boundary ruptured within decades of each other

seismotectonics of the san andreas fault system between point arena and cape mendocino in northern california implications for the development and evolution of a young transform the northernmost and relatively youthful segment of the san andreas fault system is situated within a 100 km wide zone of northwest trending strike slip faults that includes from west to east the san andreas maacama and bartlett springs faults although the san andreas fault is the principal strike slip fault in this system it has been virtually aseismic since the 1906 earthquake moderate levels of seismicity locate to the east along the maacama fault and to a lesser extent the bartlett springs fault at focal depths typical of other strike slip faults within the san andreas fault system in central california north of the san andreas fault system within the cape mendocino area earthquakes occur at depths of up to 40 km and primarily reflect internal deformation of the subducting gorda slab and slip along the mendocino fracture zone seismicity along the maacama and bartlett springs faults is dominated by right lateral to oblique reverse slip along fault planes that dip 50 75 to the northeast the northern extent of seismicity along these faults terminates near the surface projection of the southern edge of the gorda slab the onset of seismicity along these faults may be related to the abrupt change in the elastic thickness of the north american plate as it enters the asthenospheric window the maacama and bartlett springs faults are strike parallel with active reverse faults within the forearc region of the cascadia subduction zone this preexisting structural fabric of northwest trending reverse faults in the forearc area appears to have strongly influenced the initial slip and complexity of these faults continuation of the moderately dipping maacama fault to the southeast along the steeply dipping healdsburg and rodgers creek fault zones and the near vertical hayward and calaveras fault zones in the san francisco bay area suggests that these faults evolve toward a more vertical dip to minimize the shear stresses that tend to resist plate motion

thermoluminescence dating of a 10 m loess profile in pakistan abstract thermoluminescence tl dates are reported for a 10 m section of loess in northern pakistan age determinations were contrasted using the additive dose n beta i 0 and signal regeneration methods tl dates increase monotonically with depth down the profile with the n beta i 0 approach up to a value of 135 ka for the deepest sample ages assessed by regeneration after optical bleaching tend towards a limiting age of 72 ka the failure of the regenerative approach appears to result from a sensitivity change on bleaching which is proportional to the natural tl signal this effect is modelled in terms of changes in tl efficiency

the complete synthesis of seismic crustal phases at regional distances using a new method to evaluate green s functions for elastic layered media we compute complete synthetic seismograms at regional distances for an earthquake in the earth crust we choose as source parameters the ones inferred for an earthquake in central france and compare the computed seismograms to the ones recorded at several short period stations of the french seismic network the major features of the records including complexity and duration are well reproduced by the synthetics lg waves which are the prominant phase are shown to be guided waves made up of sh and sv waves incident on the moho at angles of incidence more grazing than the critical angle and multiply reflected within the crust the length of the computed lg wave coda extends between group velocities of 3 5 and 2 8 km s and is in good agreement with the data

watching the hayward fault the hayward fault located on the east side of the san francisco bay represents a natural laboratory for seismologists because it does not sleep silently between major earthquakes in his perspective simpson discusses the study by ba rgmann et al who have used powerful new techniques to study the fault the results indicate that major earthquakes cannot originate in the northern part of the fault however surface rupturing earthquakes have occurred in the area suggesting that they originated to the north or south of the segment studied by ba rgmann et al fundamental questions remain regarding the mechanism by which plate tectonic stresses are transferred to the hayward fault

slip along the hayward fault california estimated from space based synthetic aperture radar interferometry for 3 5 years following the 1989 m 7 1 loma prieta earthquake creep along the southern hayward fault california slowed or ceased slip apparently resumed pre earthquake rates by 1994 except for a locked 3 km long segment at the southern fault tip which had consistently slipped at 9 mm yr before 1989 we use repeated interferometric synthetic aperture radar intsar measurements to map active deformation along the hayward fault while slip rates recovered between 1992 and 1995 if pure strike slip is assumed then the slip rates estimated from intsar range changes between 1992 and 1995 are generally consistent with creepmeter and alignment array measurements along much of the fault and confirm the temporary locking of the southernmost fault segment however along 6 km of the fremont segment intsar slip estimates appear to be at least twice those measured in the field transient vertical slip northeast side up of 2 3 mm yr near the southern tip of the creep patch could explain this observation first order boundary element models of a vertical frictionless fault in an elastic half space predict some but not all of the inferred vertical slip

interplate quasi static slip off sanriku ne japan estimated from repeating earthquakes 1 space time distribution of quasi static slip on the plate boundary off sanriku northeastern ne japan was estimated by using small repeating earthquakes we found 2509 repeating earthquakes occurring on the plate boundary for the last 17 years based on the interpretation that these events are caused by repeating slips of small asperities surrounded by stable sliding area we regarded these repeating events as creepmeters embedded on the plate boundary the results show that deeper portions of the plate boundary are sliding almost stably and earthquakes with magnitudes more than 6 are accompanied by quasi static slips in the surrounding areas

geochronology of middle and upper pleistocene loess sections in hungary abstract the application of both thermoluminescence and infrared stimulated luminescence dating to the extensively studied classical hungarian loess paleosol sequences from basaharc mende and paks provides a reliable chronological framework and climatostratigraphic reconstruction for the last interglacial glacial cycle based on this combined luminescence dating study a new chronology is proposed for the young loess in hungary luminescence dating suggests that the loess below the mf2 horizon formed during the penultimate glaciation the mf1 horizon probably formed during an interstade within oxygen isotope stage 3 for the youngest loess overlying mf1 a very high accumulation rate was determined large time gaps occur above mf2 and mf1 indicating that most of the record of the last glaciation is missing in the standard sections at basaharc mende and paks either large discontinuities or a very low accumulation rate occurred in all three type sections during the soil forming periods high resolution studies of climatic proxies using this combined luminescence dating approach provide a reliable chronological framework for loess and loess derivatives of the last glacial cycle in hungary although a precise and complete chronostratigraphic reconstruction cannot be achieved from the incomplete records found at these sites

detection of a locked zone at depth on the parkfield california segment of the san andreas fault the parkfield california segment of the san andreas fault is transitional in character between the creeping segment of the fault to the northwest and the locked carrizo plain segment to the southeast the rate of shallow fault slip decreases from 25 30 mm yr northwest of the epicenter of the 1966 parkfield earthquake to zero at the southeastern end of the 1966 rupture zone data from a network of trilateration lines spanning the san andreas fault near parkfield and extending to the pacific coast near san luis obispo shed light on the rate of fault slip at depth since the 1966 earthquake in this study average rates of line length change and shallow fault slip were inverted to determine the slip rate at depth on the parkfield fault segment the fault is taken to be a vertical surface with unknown distribution of strike slip displacement in an elastic half space a striking result of the inversions is that all solutions providing acceptable fits to the data exhibit a locked zone essentially coincident with the rupture surface of the 1966 parkfield earthquake the data require that the locked zone extend nearly as far north as the 1966 epicenter however the vertical extent of the locked zone is not well resolved over much of the parkfield segment the fault is slipping faster at the earth s surface than it is at seismogenic depths in order to fit the trilateration measurements it is necessary to include a component of contraction normal to the trend of the san andreas the inversion results suggest a spatially uniform normal strain of 0 06 strain yr the orientation of the contraction is compatible with geologic and seismic evidence of active folding and reverse faulting in the region the magnitude of the contraction is consistent with convergence rates inferred from global plate motion models

thermoluminescence dating of sediments older than 100 ka abstract for several years attempts have been made to establish reliable procedures for thermoluminescence tl dating of sediments older than 100 ka disagreement persists among tl workers about which procedures are reliable for which sediments two recent reports have demonstrated that tl ages up to 800 ka for polymineral fine silt loess and up to 600 ka for quartz from beach dune sands agree well with expected ages several factors that apparently have influeneed negatively the accuracy of other results are use of ultraviolet tl emissions use of the regeneration tl procedures for feldspar bearing samples use of a single preheating procedure and use of a peak integration procedure rather than an equivalent dose plateau test consideration of published data suggests that more attention should be paid to the variable emissions intensity glow curve shapes signal lifetimes from discrete grains within subsamples the effects of such variability would probably account for the failure of peak integration and single preheating procedures to yield expected equivalent dose values single grain or micro tl studies of feldspar and quartz tl both spectral emission and glow curve measurements are recommended as aids to further understanding of current tl sediment dating practices

great earthquakes on canada s west coast a review this article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent geological survey of canada contribution 20090196 the first lithoprobe transect in 1984 across vancouver island had primary objectives to define the structure associated with subduction and constraints on the potential for great thrust earthquakes

the upper pleistocene loess record at harmignies belgium high resolution terrestrial archive of climate forcing abstract the loess palaeosol sequence in a section at harmignies in belgium is one of the most important upper pleistocene sites in northwest europe an extensive luminescence dating study was carried out to get a reliable chronological framework and to understand the climate forcing in an area where continuous permafrost dominated during most of the last glaciations twenty eight samples were investigated by infrared optically stimulated luminescence irsl and thermoluminescence tl methods resulting in more than 100 luminescence age estimates the dating results on colluvial sediments are in good agreement with landscape destabilisation phases during ois 5 during the last glacial four major periods of loess accumulation were likely to have occurred in europe at the harmignies section the oldest loess was deposited between 67 000 to 60 000 yr the second one from 60 000 to 50 000 yr the third one from 50 000 to 40 000 yr and the youngest loess accumulation period started most likely after the heinrich 3 event and lasted until the heinrich 2 event 25 000 20 000 yr two main periods of permafrost occurred at approximately 60 000 and 28 000 yr bp

test of thermoluminescence dating of loess from new zealand and alaska abstract the accuracy of thermoluminescence tl ages for loess and sediments in general greater than 100 ka is disputed we tested the accuracy of three common tl sediment dating techniques applied to 4 11 m sized polymineral grains from known age loess using 16 samples from north island and south island new zealand and 2 samples from central alaska estimated sample ages range from 20 26 to 800 ka we varied the optical bleaching spectrum the selected window of the emission spectra ultraviolet or uv blue and green wavelengths the pre readout heat treatment and the tl equivalent dose measurement technique most of the 20 26 ka samples gave tl age underestimates of 3 6 ka that may be attributed to post burial open system behavior for the older samples the partial bleach tl method gave expected ages up to 300 ka and the total bleach tl method produced expected ages above 100 ka the partial bleach regeneration tl method gave significant age underestimates for samples older than 100 ka with a maximum tl age of 250 ka for samples having expected ages up to 350 ka two 300 360 ka samples which gave total bleach age underestimates with use of uv tl and green tl gave expected ages with use of blue tl these results demonstrate that reliable tl ages for loess from new zealand and alaska up to 800 ka can be obtained if uv and green emissions and the various regeneration methods are avoided this age range is well above the former putative 80 100 ka upper age limit for tl dating of loess from other regions which was thought to be a global limit application of our successful procedures to such loess is encouraged

tl analysis of loess samples from achenheim abstract we have investigated four loess samples from achenheim sample j2a and l1 were collected above and below a horizon with a supposed age of 30 ka sample o1 was collected below the last interglacial soil and t1 below the next interglacial soil for the determination of eds the additive dose and regeneration techniques were applied using different filters the additive dose technique was complicated by the observation that the dose response could not be described by a single saturation function we have applied two saturation functions and used only the values below the intercept dose for ed determination nearly all calculated ages are younger than expected given the uncertainties there is not a significant difference between results obtained by the additive dose and the regeneration methods the use of the bg12 and ug11 filters seem to give slightly lower results than the 5 58 filter we have calculated mean lives for the tl signals of samples l1 o2 and t1 assuming the youngest possible estimates 30 130 and 240 ka our measurements imply that the thermal stability of the recorded signals is somewhere in the 100 200 ka region for the 5 58 filter and around 100 ka for the other filters due to the uncertainty of the geological age estimates these values are more likely upper limits of the thermal stability

the 1993 klamath falls oregon earthquake sequence source mechanisms from regional data we use regional broadband seismograms to obtain seismic moment tensor solutions of the two september 20 1993 mw 6 klamath falls oregon earthquakes their foreshock and largest aftershocks my 3 5 several sub groups with internally consistent solutions indicate activity on several fault segments and faults from the estimated moment tensors and depths of the main shocks and from the aftershock distribution we deduce that both main shocks occurred on an east dipping normal fault pos sibly related to the lake of the woods fault system rotation of t axes between the two main shocks is consistent with the two dominant trends of the aftershocks and mapped faults we pro pose that a change in fault strike acted as temporary barrier sepa rating the rupture of the main shocks empirical green s function analysis shows that the first main event had a longer rupture du ration half duration 1 7 s than the second 1 2 s in december vigorous shallow activity commenced near klamath lake s west ern shore 5 10 km east of the primary aftershock zone it ap pears a mw 5 5 aftershock occurring the day before though within the primary aftershock zone triggered the activity

the cape mendocino california earthquakes of april 1992 subduction at the triple junction the 25 april 1992 magnitude 7 1 cape mendocino thrust earthquake demonstrated that the north america gorda plate boundary is seismogenic and illustrated hazards that could result from much larger earthquakes forecast for the cascadia region the shock occurred just north of the mendocino triple junction and caused strong ground motion and moderate damage in the immediate area rupture initiated onshore at a depth of 10 5 kilometers and propagated up dip and seaward slip on steep faults in the gorda plate generated two magnitude 6 6 aftershocks on 26 april the main shock did not produce surface rupture on land but caused coastal uplift and a tsunami the emerging picture of seismicity and faulting at the triple junction suggests that the region is likely to continue experiencing significant seismicity

seismicity in cascadia abstract we examine spatio geometric patterns in the density of seismicity within the cascadia forearc to gain insight into controls on seismogenesis tremor epicenters exhibit the most regular distribution defining a 40 80 km wide band extending along almost the entire convergent margin from the southern terminus of gorda plate subduction in northern california to the central explorer plate below northern vancouver island based on prior characterization of constituent low frequency earthquakes the up and down dip limits of tremor are assumed to represent slab isodepth contours at nominal values of 28 and 45 km between which fluids at near lithostatic overpressures are trapped within the subducting slab epicenters of earthquakes within the north american crust are anticorrelated with those of tremor and concentrated in washington and northern california where they are sandwiched between tremor and the cascade volcanic arc seismicity within the subducting plate possesses the most limited epicentral distribution seismicity is confined to shallow depths off vancouver island and in northern california and projects to greater depths beneath washington and southern british columbia comparison of seismicity patterns with long wavelength slab geometry and thermo petrologic constraints suggests that seismicity occurrence in cascadia is governed by an interplay between slab strain metamorphic dehydration within the subducting oceanic plate and a plate boundary seal that controls where fluids enter the overriding plate the inferred fluid evolution model harbors interesting implications for mantle wedge hydrology forearc crustal composition and volcanism in cascadia and other warm subduction zones

landscape instability at the end of mis 3 in western central europe evidence from a multi proxy study on a loess palaeosol sequence from the eastern lower rhine embayment germany abstract the lower rhine embayment hosts important loess palaeosol sequences lps within the western european loess belt yielding valuable information on landscape evolution and palaeoclimatic dynamics the study focusses on the palaeoenvironmental development based on a lps from the eastern shoulder of the lower rhine embayment dusseldorf grafenberg the palaeoenvironmental development within the study area is presented and discussed based on high resolution grain size analyses selected environmental magnetic parameters and geochemical analyses complemented by luminescence age estimates differences in grain size distribution gsd as well as the u ratio clearly reflect main stratigraphical units within the lps in addition the centered log ratio transformation of gsd gsd clr which is sensitive to post depositional grain size variations traces units of intensified soil formation despite no magnetic enhancement can be observed within the grafenberg lps environmental magnetic parameters combined with selected geochemical analyses sr rb provide direct information on the modification of silicates and magnetic minerals in the course of pedogenesis and diagenesis overall the grafenberg lps contributes to the understanding of environmental conditions within the lower rhine embayment particularly for the late mis 3 and the transition to mis 2 the lps reflects major shifts in the geomorphic system which are compared to palaeoenvironmental records from different archives and different geographic regions in north western europe indicating a direct relation to north atlantic climate oscillations during the last glacial period it is shown that the hesbaye unconformity at the mis 3 2 boundary is bound to an erosional event which can be traced over wide areas within the northern european loess belt

tl dating of partially bleached sediments by the regeneration method abstract thermoluminescence dating of sediments in the warsaw laboratory is based on blue to green emission the partial bleach regeneration method is proposed for dating sediments which have not been completely bleached at the time of burial correct tl ages are reported for sediments covering organic deposits of the eemian interglacial and also for glacial sediments of wurm and riss age we obtained good results for dating till using the partial bleach regeneration method the tl zeroing in till is explained by the rubbing or compression of grains beneath the glacier and by the freeze thaw activity occurring during glacial transport and deglaciation

crustal structure beneath the central oregon convergent margin from potential field modeling evidence for a buried basement ridge in local contact with a seaward dipping backstop models of magnetic and gravity anomalies along two e w transects offshore central oregon one of which is coincident with a detailed velocity model provide quantitative limits on the structure of the subducting oceanic crust and the crystalline backstop the models indicate that the backstop forming western edge of the siletz terrane an oceanic plateau that was accreted to north america 50 million years ago has a seaward dip of less than 60o3 seismic magnetic and gravity data are compatible with no more than 2 km of subducted sediments between the siletz terrane and the underlying crystalline crust of the juan de fuca plate the data also suggest the presence of a n s trending 200 km long basaltic ridge buried beneath the accretionary com plex from about 43on to 45on although the height and width of this ridge probably vary along strike it may be up to 4 km high and several kilometers wide in places and appears to be locally in contact with the siletz terrane beneath heceta bank several models for the origin of this ridge are discussed these include a sliver of siletz terrane detached from the main siletz terrane dur ing a late eocene episode of strike slip faulting imbrication and thickening of subducted oceanic crust in place an aseismic ridge rafted in on the subducting oceanic crust during the past 1 2 mil lion years and a series of ridges and or seamounts rafted in over a longer period of time and trans ferred from the subducting plate to the overlying plate the last model is the most consistent with the complicated history of local uplift subsidence and slope instability recorded in the ridges basins and banks of this part of the margin we speculate that the massive seaward dip ping western edge of the siletz terrane in this region inhibits subduction of seamounts and sedi ments resulting in fomation of buried ridge as the accumulated flotsam and jetsom of subduction this process may also be responsible for thickening of lower accretionary complex material over steepening of slopes leading to massive slumping and north south extension through strike slip faulting in the accretionary complex to the west of the buried ridge regardless of its origin the ridge may currently be acting as an asperity inhibiting subduction

crustal structure of the northwestern vizcaino block and gorda escarpment offshore northern california and implications for postsubduction deformation of a paleoaccretionary margin the vizcaino block is an anomalously shallow region of the western u s continental margin located southwest of the mendocino triple junction it originated as part of the accretionary prism of the north america plate and was transferred to the pacific plate in the miocene as the pacific north america plate boundary migrated 130 km eastward forming the gorda escarpment at its northern boundary we present hybrid crustal models for the northwestern part of the vizcaino block derived from marine seismic and gravity data the velocity and density structure of the northwestern vizcaino block are compatible with paleoaccretionary complex material similar to san simeon patton terrane overlying oceanic crust or a mafic layer the most significant result of our modeling is an abrupt increase in moho dip from 5 to 20 30 beneath the western edge of the oconostota ridge along the northwestern margin of the vizcaino block this moho dip is steeper than observed anywhere along the cascadia subduction zone indicating postsubduction deformation we suggest that the paleotrench was deformed by compression which reactivated preexisting thrust faults in the upper crust and thickened the crust within this apparent weak zone at least part of the deformation predates late pliocene pacific north america plate convergence and may result mainly from north south compression between the pacific juan de fuca plates across the mendocino transform fault north south compression continues today and may dynamically support the uplifted northern margin of the vizcaino block although the primary locus of deformation shifted to the relatively weak gorda plate sometime prior to 3 ma

recent large earthquakes near cape mendocino and in the gorda plate broadband source time functions fault orientations and rupture complexities the northward migration of the mendocino triple junction is associated with complex faulting within the gorda plate and in the convergent zone between the gorda and north american plates this region has experienced substantial recent large earthquake activity and quantification of these faulting processes is essential for understanding the evolution of the triple junction using an empirical green function deconvolution method for teleseismic and regional surface waves and body waves we obtain relative source time functions for the april 25 1992 cape mendocino thrust earthquake m w 7 2 its two large strike slip aftershocks on april 26 1992 m w 6 5 6 6 and two large strike slip events in the gorda plate that occurred july 13 1991 m w 6 8 and august 17 1991 m w 7 1 the removal of propagation effects using empirical green functions provides unusually detailed source rupture information and indicates that all the ruptures are less than 16 s in duration analyzing the directivity effects observed in the source time functions we resolve rupture directions and corresponding fault orientations for the four largest events and place some constraints on the smaller aftershock significant differences in the rupture duration and stress drop are observed between the cape mendocino mainshock and its two largest aftershocks the mainshock which ruptured westward on a shallow dipping plane either on or paralleling the interplate contact between the gorda and north american plates had a smooth 9 s long rupture with a 0 9 4 6 mpa static stress drop the two largest aftershocks occurred within the uppermost mantle of the gorda plate and have more complex ruptures with total durations of 14 15 s and static stress drops of less than 0 3 mpa perhaps reflecting a difference between mantle and crustal earthquakes in this region the aftershocks appear to have ruptured conjugate strike slip faults accounting for differences in their damage patterns the august 17 1991 gorda plate event ruptured a southwest striking fault while the july 13 1991 event ruptured a southeast striking fault with both events relieving north south compression within the deforming gorda plate the existence of multiple active faults in the region constitutes a significant earthquake hazard associated with the complex stress environment of the migrating triple junction

rupture characteristics of the three m 4 7 1992 1994 parkfield earthquakes slip on the san andreas fault was determined for three m 4 7 earthquakes using a tomographic inverse system beroza and spudich 1988 to invert seismic source time functions stfs from s waves stfs were obtained by deconvolving mainshock accelerograms by those from collocated smaller earthquakes accelerograms were from the u s geological survey parkfield small aperture array upsar and from a distributed array of digital accelerometer stations at parkfield eight or nine stfs are used in each of the three inversions stfs are typically symmetrical pulses with a duration of about 0 3 0 5 s in the inversion mainshock rise time was set to 0 05 s and we allowed the rupture time to vary slightly from a constant rupture velocity of approximately 0 85 rupture for all three events which are located in or close to the middle mountain preparation zone or box mmb quickly reaches a local maximum in slip and then propagates outward to peaks ridges or plateaus in the slip distribution slip for the october 20 1992 event located just inside the southern edge of the mmb propagates from an initial spike north and updip along a curving ridge for about 2 km the initial spike continued to grow in the november 14 1993 event located north of the october 20 1992 event just beneath the hypocenter of the 1966 parkfield earthquake which shows little directivity although there is a smaller patch of slip updip and to the south in contrast rupture for the december 20 1994 event located just south of the october 20 1992 event propagated north and slightly updip creating a rough plateau in slip a few kilometers wide on a side directivity for this event also is to the north directivity for all three events points in the approximate direction of the 1966 hypocenter small pulses which comprise a coda are found on the stfs for several seconds after the initial impulsive event several tests based on the assumption that the average of all stfs from upsar for each event is an estimate of the true slip at the source suggest that the codas in the stfs are s waves from a long duration source rather than uncorrected site response an initiation phase is found on the array average for the november 14 1993 and december 20 1994 events these precursory phases are the result of a spike in slip at the hypocenter a value of 2 4 4 mm is obtained for d c the slip weakening distance by interpreting the initial spike as a critical patch the few aftershocks for the october 20 1992 event are distributed to the north and updip of the mainshock but the november 14 1993 event had a strong burst of aftershock activity that propagated to the north of its hypocenter at roughly the same depth aftershocks of the december 20 1994 event are mostly updip the november 14 1993 event had the simplest slip distribution appeared to be the most impulsive and had the most active aftershock sequence and the greatest depth if the eventual parkfield earthquake initiates near the 1966 hypocenter then the directivity of the three events studied here will have pointed to it however it is certainly possible that both the initiation of characteristic parkfield shocks and the directivity of smaller events are controlled by fault properties on a larger scale such as by fault bends or jogs

an earthquake model with interacting asperities summary a model is presented that treats an earthquake as the failure of asperities in a manner consistent with modern concepts of sliding friction the mathematical description of the model includes results for elliptical and circular asperities oblique tectonic slip static and dynamic solutions for slip on the fault stress intensity factors strain energy and second order moment tensor the equations that control interaction of asperities are derived and solved both in a quasi static tectonic mode when none of the asperities are in the process of failing and a dynamic failure mode when asperities are failing and sending out slip pulses that can trigger failure of additional asperities the model produces moment rate functions for each asperity failure so that given an appropriate green function the radiation of elastic waves is a straightforward calculation the model explains an observed scaling relationship between repeat time and seismic moment for repeating seismic events and is consistent with the properties of pseudo tachylites treated as fossil asperities properties of the model are explored with simulations of seismic activity that results when a section of the fault containing a spatial distribution of asperities is subjected to tectonic slip the simulations show that the failure of a group of strongly interacting asperities satisfies the same scaling relationship as the failure of individual asperities and that realistic distributions of asperities on a fault plane lead to seismic activity consistent with probability estimates for the interaction of asperities and predicted values of the gutenberg richter a and b values general features of the model are the exterior crack solution as a theoretical foundation a heterogeneous state of stress and strength on the fault dynamic effects controlled by propagating slip pulses and radiated elastic waves with a broad frequency band

high pore fluid pressure may cause silent slip in the nankai trough silent slip events have been detected at several subduction zones but the cause of these events is unknown using seismic imaging we detected a cause of the tokai silent slip which occurred at a presumed fault zone of a great earthquake the seismic image that we obtained shows a zone of high pore fluid pressure in the subducted oceanic crust located down dip of a subducted ridge we propose that these structures effectively extend a region of conditionally stable slips and consequently generate the silent slip

identifying low frequency earthquakes in central cascadia using cross station correlation abstract we use stations in the willamette valley and oregon coast ranges to identify low frequency earthquakes that occurred during the august september 2009 episodic tremor and slip event while autocorrelation techniques are often successful at identifying lfe templates in central cascadia this technique systematically fails due to the lack of densely spaced high quality stations instead we use cross station methods that have been successful at identifying lfes in northern cascadia to register initial candidate templates network cross correlation to register additional lfe detections and stacking to refine the identified templates using this procedure we detect nearly 16 thousand events comprising a total of 18 lfe families located in central oregon between 30 and 40 km depth either at or near the plate boundary the time history of detections between families is consistent with the slip front in the 2009 sse migrating from north to south at a velocity of 5 km day the templates we identify have more complicated waveforms than those previously identified in northern cascadia these differences in waveform character likely a consequence of the small number of contributing stations

three dimensional crustal structure of the mendocino triple junction region from local earthquake travel times the large scale three dimensional geometry of the mendocino triple junction at cape mendocino california was investigated by inverting nearly 19 000 p wave arrival times from over 1400 local earthquakes to estimate the three dimensional velocity structure and hypocentral parameters a velocity grid 175 km n s by 125 km e w centered near garberville california was constructed with 25 km horizontal and 5 fan vertical node spacing the model was well resolved near cape mendocino where the earthquakes and stations are concentrated at about 40 6 n latitude a high velocity gradient between 6 5 and 7 5 km s dips gently to the south and east from about 15 km depth near the coast relocated hypocenters concentrate below this high gradient which we interpret as the oceanic crust of the subducted gorda plate therefore the depth to the top of the gorda plate near cape mendocino is interpreted to be 15 km the gorda plate appears intact and dipping 8 eastward due to subduction and flexing downward 6 12 to the south both hypocenters and velocity structure suggest that the southern edge of the plate intersects the coastline at 40 3 n latitude and maintains a linear trend 15 south of east to at least 123 w longitude the top of a large low velocity region at 20 30 km depth extends about 50 km n s and 75 km e w roughly between garberville and covelo and is located above and south of the southern edge of the gorda plate we interpret this low velocity area to be locally thickened crust 8 10 km due to either local compressional forces associated with north south compression caused by the northward impingement of the rigid pacific plate or by underthrusting of the base of the accretionary subduction complex at the southern terminous of the cascadia subduction zone south of cape mendocino and southwest of the garberville fault high velocities indicative of oceanic crust are detected at 15 km depth we interpret this evidence as tectonic underplating of the pacific oceanic crust beneath the coastal franciscan complex similar to the situation seismically imaged in central coastal california page and brocher 1994 this geometry indicates that the westernmost portion of the slab window has been filled by tectonic underplating and crustal thickening while deep seated mantle upwelling is confined to an area centered about 75 km north of clear lake benz et al 1992 zandt et al 1992

tidal triggering of earthquakes in the northeast pacific ocean summary there have been many searches for evidence of tidal triggering in earthquake catalogues with the exception of volcanically active regions the more rigorous studies in continental settings tend to find no correlation or only a very weak correlation in the oceans the effect of loading by the ocean tides can increase tidal stresses by about an order of magnitude over continental settings in recent years several studies have reported evidence of tidal triggering in oceanic regions and such observations can represent a useful constraint on models of earthquake rupture in this paper i systematically search for a link between ocean tide height and the incidence of earthquakes in the northeast pacific ocean a region of high amplitude open ocean tides the focal mechanisms of most of the earthquakes in these catalogues are unknown but it can be shown that tidal stresses will in most instances promote failure at low tides i investigate three declustered data sets comprising 1 earthquakes from 1980 to 2007 on the juan de fuca plate and in the queen charlotte fault region from land based catalogues 2 earthquakes from 1992 to 2001 on the juan de fuca plate located with the us navy s sound surveillance system sosus hydrophone array and 3 earthquakes from 1980 to 2001 south of alaska and the aleutians located with land based networks i look at the distributions of earthquakes with ocean tide phase height and tidal range and apply schuster and binomial tests and monte carlo simulations to determine if they deviate significantly from random the results show no evidence of triggering during intervals of increased tidal range but all three data sets show a significant increase in earthquake incidence at low tides the signal is particularly strong in the land based catalogue for the juan de fuca plate and queen charlotte fault regions where there is a 15 per cent increase in the rate of seismicity within 15 of the lowest tides the signal is weakest in the sosus data set which may reflect the lower average tidal range at epicentres in this data set or an analysis that is influenced by gaps in the catalogue the triggering signal in the alaska aleutian may be partially obscured by earthquakes in the aleutians where the total tidal stresses can be significantly out of phase with the ocean tide height the increase in the rates of seismicity i observe at low tides is less than observed by local networks on mid ocean ridges similar to the prediction from an analysis of global thrust earthquakes and greater than inferred by extrapolating laboratory simulations of fault failure under tidal loading

seismological studies at parkfield iv variations in controlled source waveform parameters and their correlation with seismicity 1987 to 1995 since june 1987 at parkfield california the 10 station borehole network of three component sensors has been illuminated 52 times using a shear wave vibrator in three orientations at up to eight source points in a search for temporal changes in elastic wave p and s velocities anisotropy or attenuation the monitoring interval includes the beginning and end of a severe 3 yr drought and four earthquake sequences two of which produced the only a level alerts to date in the parkfield prediction experiment a comprehensive study of the entire data set reveals a progressive travel time advance in the coda of s waves propagating in a localized region southeast of middle mountain the anomalous wave field exhibits high apparent velocities suggesting deep penetration of the fault zone although similar changes are not seen in waveforms from repeating similar microearthquakes accompanying the changes in travel time were systematic variations in spectral content and polarization of the same segments of the wave field these variations correlate well in time and space with significant features of seismicity fault creep and water levels at parkfield a preferred mechanism for the phenomenon is changing hydrologic conditions along the affected stretch of the fault zone possibly deformation induced that perturb the shallow propagating s coda in the upper few hundred meters of section

slow slip phenomena in cascadia from 2007 and beyond a review recent technological advances combined with more detailed analyses of seismologic and geodetic observations have fundamentally changed our understanding of the ways in which tectonic stresses arising from plate motions are accommodated by slip on faults the traditional view that relative plate motions are accommodated by a simple cycle of stress accumulation and release on locked plate boundary faults has been revolutionized by the serendipitous discovery and recognition of the significance of slow slip phenomena mostly in the deeper reaches of subduction zones the cascadia subduction zone located in the pacific northwest of the conterminous united states and adjacent canada is an archetype of exploration and learning about slow slip phenomena these phenomena are manifest as geodetically observed aseismic transient deformations accompanied by a previously unrecognized class of seismic signals although secondary failure processes may be involved in generating the seismic signals the primary origins of both aseismic and seismic phenomena appear to be episodic fault slip probably facilitated by fluids on a plate interface that is critically stressed or weakened in cascadia this transient slip evolves more slowly and over more prolonged durations relative to the slip in earthquakes and it occurs between the 30 and 40 km depth contours of the plate interface where information was previously elusive although there is some underlying organization that relaxes nearly all the accrued plate motion stresses along the entirety of cascadia we now infer that slow slip evolves in complex patterns indicative of propagating stress fronts our new understanding provides key constraints not only on the region where the slow slip originates but also on the probable characteristics of future megathrust earthquakes in cascadia herein we review the most significant scientific issues and progress related to understanding slow slip phenomena in cascadia and highlight some of their societal implications we provide a comprehensive review from the big picture as inferred from studies of regional scale monitoring data to the details revealed by innovative focused experiments and new instrumentation we focus on what has been learned largely since 2007 when several major investments in monitoring and temporary deployments dramatically increased the quality and quantity of available data

interseismic uplift rates for western oregon and along strike variation in locking on the cascadia subduction zone 1 we quantify the spatial pattern of uplift rate in western oregon and northernmost california using tidal and leveling records to better understand the pattern of interseismic locking on the cascadia subduction zone we extend relative sea level time series of the six primary noaa tide gauges to include all observations from 1925 to 2006 previously unidentified bench mark instability biases portions of tidal records by 1 6 mm a 1 before correction we determine precise relative uplift rates at the six tidal sites with an adjustment that includes rates of differenced time series as additional constraints our analysis of national geodetic survey leveling data between tide gauges corrects errors in 1941 leveling and 184 secondary ties double the number of highest quality uplift rate estimates relative uplift rates from leveling are adjusted to the tidal rates accounting for uncertainties in both data types tidal and leveling uplift rates agree within error for all but one of the coastal segments where we infer systematic leveling error affects the 1988 line uplift rates are made absolute using an interval and location specific geocentric sea level rise rate of 2 3 0 2 mm a 1 total propagated one sigma errors for the absolute uplift rates of bench marks are 0 4 mm a 1 along strike changes in uplift rate near 45 n and 42 8 n require two distinct changes in locking depth as inferred from elastic dislocation modeling the along strike changes in locking on this portion of the cascadia subduction zone interface correlate to the western and southern extent of the mafic siletzia block in the fore arc

a comparison of different tl techniques on loess samples from rheindahlen f r g abstract 9 tl samples of the loess profile rheindahlen lower rhine area germany covering the time span of the last 300 ka were studied systematic investigation was carried out using different filters and preheating procedures ed determinations were done by the additive dose and the regeneration method the annual dose was determined by aas alpha counting naa and gamma spectrometry in the laboratory and in the field the results show that the weichselian loess is datable whereas no tl age differentiation between loesses of stage 6 and stage 8 is possible if the accumulated dose ed is in the 600 gy region every apparent tl age between 100 and 300 ka can be obtained this leads to the conclusion that in rheindahlen no reliable tl ages are available for loess deposits underneath the eemian soil stage 5e

seismicity of the gorda plate structure of the continental margin and an eastward jump of the mendocino triple junction analysis of 9 years of data from the humboldt bay seismic network sheds new light on the structure and evolution of the gorda plate and mendocino triple junction significant findings include the buttressing effect of the pacific plate which demonstrates that there is no underthrusting of the gorda plate along the mendocino fault and the pattern of left lateral northeast trending faults which demonstrates how the gorda plate accommodates n s shortening without such underthrusting focal mechanisms are consistent with northward compression of the gorda plate by the pacific plate until the gorda plate passes the triple junction beyond which the n s compressive stress is effectively removed and the focal mechanisms show a change from strike slip to normal faulting with downslab tension another significant feature is the shallow benioff zone 10 40 km which shows a double seismogenic layer unlike most other double seismic layers in deep subduction zones this one appears to be due to underplating with a new subduction zone being developed east of the former one a corner of continental margin material has been partially subducted we attribute this double seismic zone to reactivation of both the old and new subduction boundaries under n s compression produced by pacific gorda plate interaction at the triple junction because the geometry of this triple junction indicates that it is unstable and because there is evidence that as part of its evolution the san andreas fault has migrated eastward we have constructed a model that accounts for both the eastward migration of the san andreas fault and the doubling of the seismic zone in the gorda plate this can be done by assuming that at the time of the last eastward jump of the fault the overriding continental margin north of the triple junction was broken and underthrust producing a new subduction zone that is collinear with the san andreas fault other scenarios for the evolution of the mendocino triple junction do not require that the subduction zone migrate eastward however the position and dip of the double zone indicate that an eastward jump of 100 km some 5 my ago could have taken place this is consistent with other evidence for an eastward jump of the san andreas fault

subducted seamounts and recent earthquakes beneath the central cascadia forearc bathymetry and magnetic anomalies indicate that a seamount on the juan de fuca plate has been subducted beneath the central cascadia accretionary complex and is now located 45 km landward of the deformation front passage of this seamount through the accretionary complex has resulted in a pattern of uplift followed by subsidence that has had a profound influence on slope morphology gas hydrate stability and sedimentation based on potential field data and a new three dimensional seismic velocity model we infer that this is the most recent of several seamounts subducted over the past several million years beneath this segment of cascadia more deeply subducted seamounts may be responsible for recent earthquake activity on the plate boundary in this region and for along strike variations in the thickness of the subduction channel which may affect coupling across the plate boundary

thermoluminescence dating of the malan loess at zhaitang china although the widespread loess deposits of north china have been well described there has been limited information on the absolute age of the various layers loess a wind carried deposit exposed to sunlight and subsequently buried should be amenable to dating by thermoluminescence through use of the fine grain technique ages from 18 to 84 ka have been obtained for a sequence in the malan loess exposed in the zhaitang section near beijing the dates are consistent with the evidence from geology and magnetostratigraphy and provide a chronology for the zhaitang section

implications of geochemical fronts in the notch peak contact metamorphic aureole utah usa abstract the geochemistry of the notch peak contact metamorphic aureole was examined to determine the dominant source of fluid attendant on metamorphism and to estimate fluid fluxes progressive metamorphism of calc silicate rocks is defined by phlogopite diopside and wollastonite isograds mineral assemblages at wollastonite and diopside grades indicate water rich conditions during decarbonation reactions near the intrusion the rocks are highly fractured in both the horizontal and the vertical direction the 18o values of most unmetamorphosed through diopside grade rocks range from 16 3 to 20 2 whereas in the wollastonite zone and near a pre intrusion fault the values approach the 9 5 value of the granitic stock coincident with the zone of18o depletion are zones of ba and zn enrichment consideration of solubilities of these elements in magmatic fluids and of published mineral water distribution coefficients indicates that these elements were advected from the magma model 18o profiles for up temperature flow of formation water assuming variable damko hler numbers and both static and variable thermal gradients fit poorly most data and do not reproduce the broadened front in the observed profile in contrast model profiles for radial one dimensional flow of magmatic water with variable damko hler number under static or variable thermal gradients fit the data well although the model isotopic front remains less distended that the one observed the integrated radial flux of magmatic water indicated by the position of the isotopic front is 1 8 107 mol m 2 additional broadening of the observed front and the scatter of the data suggest diffusion or hydrodynamic dispersion of oxygen regression of the data indicates an effective porosity of 12 in the inner aureole during fluid flow the porosity was largely fracture controlled and resulted from decarbonation sustained exsolution of water from the magma and up to 30 reaction produced volume loss in the high grade rocks the coincidence of the ba zn and 18o fronts suggests that bulk of the magmatic water flow was confined to the wollastontie zone the exception is the proximity of the fault where fluids emanating from an underlying part of the intrusion may also have flowed upward through lower grade rocks

systematic thermoluminescence dating of two loess profiles from the middle rhine area f r g abstract systematic investigation of 104 loess samples from the well studied loess sequences at ariendorf and toenchesberg middle rhine area f r g was carried out to study the reliability of tl ages of the last 150 ka the samples were investigated by the additive dose regeneration and partial bleach methods using integral and plateau ranges for determination of accumulated dose the results show that in ariendorf all the loess deposits of the last glaciation are contaminated with reworked loesses from older glaciations at toenchesberg the tl ages are in good agreement with the stratigraphy up to about 90 ka but no tl age over 110 ka was obtained underneath the interglacial soil at toenchesberg

automated detection and location of tectonic tremor along the entire cascadia margin from 2005 to 2011 abstract we have constructed an automated routine to identify prominent bursts of tectonic tremor and locate their source region during time periods of raised amplitude in the tremor passband this approach characterizes 62 episodes of tectonic tremor between 2005 and 2011 with tremor epicenters forming a narrow band spanning the entire length of the cascadia subduction zone we find a range of along strike lengths in individual episodes but the length appears proportional to both duration and geodetic moment consistent with proposed scaling laws for slow earthquake phenomena examination of individual episodes in detail reveals intriguing updip downdip migration patterns including slow updip migration during initiation and repetitive downdip migration between different episodes the broader catalog of tremor episodes refines the inferences from earlier work that episodic tremor and slip are segmented along strike and correlated with apparent seismogenic zone segmentation in most cases the overall band of tremor is offset 50 km from the downdip edge of interseismic coupling along the central and northern parts of the subduction zone along the southern part of the subduction zone it is adjacent to this boundary suggesting that the locked and transition zones may be more closely linked in southern cascadia

seismological studies at parkfield vi moment release rates and estimates of source parameters for small repeating earthquakes abstract waveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the parkfield segment of the san andreas fault saf analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeating sequences quasiperiodic sequences of earthquakes that are essentially identical in terms of waveform size and location scalar seismic moments have been estimated for 53 of these repeating sequences and combined with equivalent estimates from 8 similar but larger event sequences from the stone canyon section of the fault and the main parkfield sequence these estimates show that seismic moment is being released as a function of time in a very regular manner measurements of the moment release rate combined with an assumed tectonic loading rate lead to estimates of the seismic parameters source area slip and recurrence interval such parameters exhibit a systematic dependence upon source size over a range of 10 10 in seismic moment that can be described by three simple scaling relationships several implications of these scaling relationships are explored including the repeat time of earthquakes average stress drop strength of the fault and heat generated by earthquakes what emerges from this analysis of moment release rates is a quantitative description of an earthquake process that is controlled by small strong asperities that occupy less than 1 of the fault area this means that the fault is highly heterogeneous with respect to stress strength and heat generation such heterogeneity helps to explain many of the apparent contradictions that are encountered in the study of earthquakes such as why faults appear weak why significant heat flow is not observed how significant high frequencies can be generated by large earthquakes and how various geologic features such as pseudotachylytes might form

seimological studies at parkfield v characteristic microearthquake sequences as fault zone drilling targets studies at very high resolution of microearthquakes at parkfield california since 1987 reveal a systematic organization in space and time dominated by clustering of nearly identical regularly occurring microearthquakes characteristic events on 10 to 20 m wide patches within the fault zone more than half of the 4000 events in our 1987 to 1996 catalog exhibit this trait in general recurrence intervals 0 5 to 2 yr scale with the magnitude of the repeating events for the on scale range mw 0 2 to 1 3 in this study the similar waveforms superimposed locations quasi periodic recurrence and uniform size of these characteristic events permit relative hypocenter location accuracy of meters and predictable occurrence times within windows of a few months clustered characteristic events occur at depths as shallow as about 3 km and these are feasible targets for deep scientific drilling and observation at the focus of a subsequent small earthquake within an active plate boundary fault zone at parkfield the achievable location accuracy to which a hypocenter can be specified as well as the predictability of its occurrence time appear to be uniquely favorable for in situ fault zone measurements

location and source parameters of the 19 june 1994 mw 5 0 offshore petrolia california earthquake the mw 5 0 19 june 1994 offshore petrolia california earthquake was well recorded by nine ocean bottom hydrophones obh and seismometers obs providing an opportunity to precisely locate an earthquake in the tectonically active mendocino triple junction region adding the offshore data improves the azimuthal station coverage and essentially removes the epicenter s sensitivity to the choice of inversion parameters and velocity models the hypocentral parameters assuming an oceanic upper mantle velocity of 7 9 km sec are 10 39 33 2 utc for origin time 40 376 n latitude 124 441 w longitude and a depth of 18 8 km the moment tensor solution obtained by modeling of low frequency regional waveforms indicates predominantly strike slip faulting with a north south trending p axis as is typical for gorda plate earthquakes and confirms the depth estimate from the p wave travel time data

test of the partial bleach methodology as applied to the infra red stimulated luminescence of an alluvial sediment from the danube abstract a sample of fine grained distal sediment deposited by the river danube in romania was selected for luminescence measurements using infra red diodes for stimulation to obtain the equivalent dose ed a partial bleach approach was applied using a restricted spectrum in an attempt to replicate bleaching conditions underwater the results and those of the thermoluminescence measurements gave an age in agreement with the archaeological evidence suggesting that this sample was well bleached at deposition a more rigorous test was devised using a simulation experiment and the results suggested that the partial bleach method may not be able to date correctly sediments that have had only part of their infra red stimulated luminescence irsl signal removed at deposition additional types of measurement are required to detect incomplete resetting of the irsl signal at deposition

probable low angle thrust earthquakes on the juan de fuca north america plate boundary in 2004 two clusters of earthquakes occurred in the central part of the cascadia forearc which displays several characteristics indicative of along strike and downdip variations in plate coupling moment tensor analysis for the main shock in each cluster indicates that both events which had magnitudes of 4 9 and 4 8 were compatible with low angle thrust motion on fault planes dipping 6 15 to the east consistent with the plate boundary dip of 12 by tracing rays through a high resolution two dimensional crustal velocity model to match arrival times of secondary arrivals pp and pmp we estimate that the source depth was 9 11 km for the m4 9 event and 15 17 km for the m4 8 event we conclude that these earthquakes probably represent seismogenic thrust motion on the nominally locked or transitional part of the cascadia megathrust updip of where episodic tremor and slip ets have been documented continued high resolution observations of seismicity and improved crustal models are needed to confirm whether apparent temporal correlations between ets and continued seismic activity in these clusters indicate stress transfer along the megathrust

shocks in a box an analogue model of subduction earthquake cycles with application to seismotectonic forearc evolution 1 we introduce and test an experimental approach to simulate elastoplastic megathrust earthquake cycles using an analogue model and apply it to study the seismotectonic evolution of subduction zones the quasi two dimensional analogue model features rate and state dependent elastic frictional plastic and viscoelastic material properties and is scaled for gravity inertia elasticity friction and viscosity the experiments are monitored with a high resolution strain analysis tool based on digital image correlation particle imaging velocimetry piv providing deformation time series comparable to seismologic geodetic and geologic observations in order to separate elastic and nonelastic effects inherent the experimental deformation patterns we integrate elastic dislocation modeling edm into a hybrid approach we use the analogue earthquake slip and interseismic locking distribution as edm dislocation input and forward model the coseismic and interseismic elastic response the residual which remains when the edm prediction is subtracted from the experimental deformation pattern highlights the accumulation of permanent deformation in the model the setup generates analogue earthquake sequences with realistic source mechanisms and elastic forearc response and recurrence patterns and reproduces principal earthquake scaling relations by applying the model to an accretionary type plate margin we demonstrate how strain localization at the rupture peripheries may lead to a seismotectonically segmented forearc including a tectonically stable shelf and coastal high 20 plate convergence accommodated by internal shortening overlying the area of large megathrust earthquake slip fifty to 75 of plate convergence is accommodated by internal shortening in the slope region where earthquake slip tapers out toward the trench the inner forearc region remains undeformed and represents a basin

thermoluminescence dating of loess deposits at paudorf austria abstract the fine grain thermoluminescence tl dating method was applied to an upper palaeosol from a loess deposit in paudorf lower austria this site is of special interest as there is some controversy about the time of formation of this soil horizon the results of the present study strongly indicate that the soil formed during the wurm i ii interstadial deep sea 18 o isotope stage 3 although age underestimation due to a long term instability of luminescence centres in general cannot be ruled out arguments are given for the presented tl age which is also corroborated by the radiocarbon age of charcoal from the top part of the correlated palaeosol in aigen lower austria

reflection signature of seismic and aseismic slip on the northern cascadia subduction interface at the northern cascadia margin the juan de fuca plate is underthrusting north america at about 45 mm yr 1 ref 1 resulting in the potential for destructive great earthquakes2 3 the downdip extent of coupling between the two plates is difficult to determine because the most recent such earthquake thought to have been in 1700 4 occurred before instrumental recording thermal and deformation studies5 indicate that off southern vancouver island the interplate interface is presently fully locked for a distance of 60 km downdip from the deformation front great thrust earthquakes on this section of the interface with magnitudes of up to 9 4 5 have been estimated to occur at an average interval of about 590 yr ref 3 further downdip there is a transition from fully locked behaviour to aseismic sliding where high temperatures allow ductile deformation with the deep aseismic zone exhibiting slow slip thrust events6 here we show that there is a change in the reflection character on seismic images from a thin sharp reflection where the subduction thrust is inferred to be locked to a broad reflection band at greater depth where aseismic slip is thought to be occurring this change in reflection character may provide a new technique to map the landward extent of rupture in great earthquakes and improve the characterization of seismic hazards in subduction zones

do subducting seamounts generate or stop large earthquakes seamount subduction is a common process in subduction zone tectonics contradicting a widely held expectation that subducting seamounts generate large earthquakes seamounts subduct largely aseismically producing numerous small earthquakes on rare occasions when they do produce relatively large events the ruptures tend to be complex suggesting multiple rupture patches or faults we explain that the seismogenic behavior of these seamounts is controlled by the development and evolution of an adjacent fracture network during subduction and cannot be described using the frictional behavior of a single fault the complex structure and heterogeneous stresses of this network provide a favorable condition for aseismic creep and small earthquakes but an unfavorable condition for the generation and propagation of large ruptures

deconvolution of teleseismic body waves for enhancing structure beneath a seismometer array abstract we discuss three stacking deconvolution techniques for enhancing signal of earth structure contained in the seismograms of teleseismic body waves recorded by a seismometer array the goal of the deconvolution is to remove from the seismograms the complications due to the source for three component data the removal of the source can be efficiently achieved by deconvolving one component from another as in the receiver function analysis in the case of an array if the structure beneath individual stations varies the source wavelet can be estimated and removed from the seismograms by stacking this allows structural analysis in the situations when only single component seismometers are used or when a particular component can provide additional independent information here we compare the efficacy of conventional time domain stacking cepstral averaging and autocorrelation stacking the latter is a new approach developed here for cepstral averaging we present conditions that stabilize the convergence examples are presented using synthetics and real data from a broadband seismic array experiment conducted in the cascadia subduction zone oregon in 1993 to 1994 data from subduction zones are particularly well suited because of the spatially rapidly varying structure we find that all three methods work well for low frequencies which are not sensitive to the time alignment of the seismic traces the latter two methods do not require precisely aligned seismograms and their advantage becomes evident at higher frequencies where the appropriate time alignment is harder to achieve at high frequencies time domain stacking is likely to fail

cascadia onshore offshore site response submarine sediment mobilization and earthquake recurrence local geologic structure and topography may modify arriving seismic waves this inherent variation in shaking or site response may affect the distribution of slope failures and redistribution of submarine sediments i used seafloor seismic data from the 2011 to 2015 cascadia initiative and permanent onshore seismic networks to derive estimates of site response denoted sn in low and high frequency 0 02 1 and 1 10 hz passbands for three shaking metrics peak velocity and acceleration and energy density sn varies similarly throughout cascadia and changes primarily in the direction of convergence roughly east west in the two passbands sn patterns offshore are nearly opposite and range over an order of magnitude or more across cascadia sn patterns broadly may be attributed to sediment resonance and attenuation this and an abrupt step in the east west trend of sn suggest that changes in topography and structure at the edge of the continental margin significantly impact shaking these patterns also correlate with gravity lows diagnostic of marginal basins and methane plumes channeled within shelf bounding faults offshore sn exceeds that onshore in both passbands and the steepest slopes and shelf coincide with the relatively greatest and smallest sn estimates at low and high frequencies respectively these results should be considered in submarine shaking triggered slope stability failure studies significant north south sn variations are not apparent but sparse sampling does not permit rejection of the hypothesis that the southerly decrease in intervals between shaking triggered turbidites and great earthquakes inferred by goldfinger et al 2012 2013 2016 and priest et al 2017 is due to inherently stronger shaking southward

variability of near term probability for the next great earthquake on the cascadia subduction zone the threat of a great m 9 earthquake along the cascadia subduction zone is evidenced by both paleoseismology data and current strain accumulation along the fault on the basis of recent information on the characteristics of this subduction system we estimate the conditional probabilities of a great earthquake occurring within the next 50 years and their variabilities the most important vari ation is associated with the existence of episodic slow slip on the deep portion of the subduction interface we show that these events modulate the conditional probability dramatically over their 14 month cycle during the 2 week slow slip events the weekly probability of a great earthquake is about 30 to 100 times as high as it is during any week of the rest of the year near term probabilities also vary significantly with the assumed distribution of earthquake recurrence intervals under a reference scenario of unimodal distribution of recurrence intervals about 500 600 years the 50 year conditional probability is low 0 12 at a 95 confidence interval how ever under a tantalizing bimodal distribution hypothesis this probability could be either four times as high 6 45 or four times as low less than 1 depending on whether the current interval is short 350 years or long 850 years

the continental margin off oregon from seismic investigations in april and may 1996 a geophysical study of the cascadia continental margin off oregon and washington was carried out aboard the german rv sonne as a cooperative experiment between geomar the usgs and coas offshore central oregon which is the subject of this study the experiment involved the collection of wide angle refraction and reflection data along three profiles across the continental margin using ocean bottom seismometers obs and hydrophones obh as well as land recorders two dimensional modelling of the travel times provides a detailed velocity structure beneath these profiles the subducting oceanic crust of the juan de fuca plate can be traced from the trench to its position some 10 km landward of the coastline at the coastline the moho has a depth of 30 km the dip of the plate changes from 1 5 westward of the trench to about 6 5 below the accretionary complex and to about 16 further eastward below the coast the backstop forming western edge of the siletz terrane an oceanic plateau that was accreted to north america about 50 ma ago is well defined by the observations it is located about 60 km to the east of the deformation front and has a seaward dip of 40 at its seaward edge the base of the siletz terrane seems to be in contact with the subducting oceanic crust implying that sediments are unlikely to be subducted to greater depths the upper oceanic crust is thinner to the east of this contact than to the west at depths greater than 18 km the top of the oceanic crust is the origin of pre critical reflections observable in several land recordings and in the data of one ocean bottom instrument these reflections are most likely caused by fluids that are released from the oceanic crust by metamorphic facies transition

dehydration induced porosity waves and episodic tremor and slip episodic tremor and slip ets along the subduction interface takes place where there is abundant evidence for elevated near lithostatic pore pressures at sufficiently great depths 30 45 km that chemical dehydration reactions must act as their dominant source we simulate fluid and heat flow while tracking the location of a vertically oriented one dimensional column of material as it subducts through the slow slip and tremor zone the material in the column is transformed through a pressure dependent and temperature dependent dehydration reaction that we describe with a generalized nonlinear kinetic rate law column deformation is largely dominated by viscous creep with a closure rate that depends linearly on porosity this behavior causes the dehydration reaction to generate traveling porosity waves that transport increased fluid pressures within the slow slip region to explore the possibility that the observed periodicity of slow slip and tremor in subduction zones can be explained by the migration of such porosity waves we derive a dispersion relation that accurately describes our numerical results we also obtain an expression for how the thickness of the dehydrating layer is expected to vary as a function of the parameters in the reaction rate law although the amplitudes of pore pressure perturbations rival those that are produced by known external forcings e g tides or passing surface waves our analysis suggests that given reasonable estimates of rock viscosity permeabilities in the range 6 5 10 15 to 5 10 10 m2 are required for porosity wave trains to form at periods comparable to those of slow slip and tremor

fault slip rates at depth from recurrence intervals of repeating microearthquakes unique attributes in sequences of recurring similar microearthquakes at parkfield california provide a means for inferring slip rate at depth throughout the active fault surface from the time intervals between sequence events application of the method using an 11 year microseismicity record revealed systematic spatial and temporal changes in the slip rate that were synchronous with earthquake activity and other independent measures of fault zone slip if this phenomenon is found to be generally common behavior in active faults it forms the basis for a method to monitor the changing strain field throughout a seismogenic fault zone

thermoluminescence dating of sediments abstract the potential for using the thermoluminescence behaviour of sediments for dating them was first recognized by soviet scientists g v morozov and v n shelkoplyas and for over a decade their tl dates obtained from a variety of sediments have appeared in the soviet literature since 1977 tl sediment dates have been published by six additional groups using a variety of methods in this review we describe the principles of tl dating the various methods used and contrast tl dating of sediments with the now well accepted tl dating of pottery we conclude that while tl dating has the potential to solve many sedimentary problems more fundamental research needs to be carried out before such dates should be accepted a set of criteria for acceptable dates is proposed

variations in fault slip and strain accumulation at parkfield california initial results using two color geodimeter measurements 1984 1988 repeated length measurements of several geodetic baselines near parkfield california have revealed significant variations in the local rates of shallow fault slip and strain this network of baselines surveyed several times each week straddles the san andreas fault in the transition zone between the creeping section to the northwest and the locked section to the southeast the length measurements characterized by a precision approaching 0 1 ppm reveal large fluctuations in the rates of baseline extension principal mode analysis of the length change data indicates that the two largest components of the signal are 1 secular extensions and contractions consistent with surface slip on the main strand of the san andreas fault and 2 a large seasonal oscillation with no obvious spatial coherence on most of these baselines the second component appears to be in phase with seasonal rainfall when data from the baselines with the largest amplitude of the seasonal signal are excluded the remaining data can be modeled in terms of both spatial and temporal variations in surface slip variations in the components of the changes in uniform strain and the possible displacement of the central monument in this radial network in parameterizing this model the spatial variation of slip beneath the near surface is reflected by changes in shear strain although the computed secular shear is highly dependent upon the specified parameterization of surface slip the data are consistent with the hypothesis that slip at intermediate depths lags behind the surface slip rate however the range in models that fit the data does not necessarily imply that there is a deficit in slip at depth relative to the surface comparison of the inferred values of surface slip from the model with the observed fault slip measured by very short baseline creep meters indicates close agreement in secular rates but the short term variations observed with the creep meters are either highly attenuated or nonexistent in the modeled slip since the modeled slip is a spatial average which smooths out possible short wavelength variations in the surface slip for which the creep instruments are most sensitive an interesting conclusion from the two color data is that surface slip on the san andreas fault appears to be spread over a 2 km wide zone on the south flank of middle mountain but is confined to a very narrow zone to the south as the fault passes through the center of the network this conclusion is dependent upon the assumption that a few critical monuments are stable and track tectonic displacements in the long term finally the largest observed strain change is an extensional strain coincident with the kettleman hills earthquake m5 5 in august 1985

tl stratigraphy of pre weichselian loess from nw europe using feldspar coarse grains abstract a new feldspar relative tl dating method is proposed that enables dating of pre weichselian loess older than 130 ka by applying the additive dose technique and the mejdahl s exponential extrapolation to alkali feldspar coarse grains the method is applied to loess deposits from various reference loessic sections of nw europe our relative tl age estimates are consistent with the information provided by the regional stratigraphy furthermore they lead to a clear separation of the pre weichselian periods of loess deposition in the time period 130 ka 300 ka

postseismic response of repeating aftershocks the recurrence intervals of repeating earthquakes on the san andreas fault in the loma prieta aftershock zone follow the characteristic 1 t decay of omori s law a model in which these earthquakes occur on isolated patches of the fault that fail in stick slip with creep around them can explain this observation in this model the recurrence interval is inversely proportional to the loading rate due to creep logarithmic velocity strengthening friction predicts 1 t decay in creep rate following the mainshock the time dependence of recurrence is inconsistent with a simple viscous constitutive relationship which predicts an exponential decay of loading rate thus our observations imply postseismic slip at seismogenic depth under a power law rheology the time dependence of postseismic deformation measured geodetically may be diagnostic of whether postseismic deformation is caused by creep or possible viscoelastic deformation at greater depths

a seismic reflection profile across the cascadia subduction zone offshore central oregon new constraints on methane distribution and crustal structure in 1989 we conducted an onshore offshore seismic experiment to image the crustal structure of the cascadia forearc in this paper we discuss the processing and interpretation of a multichannel seismic reflection profile across the continental margin that was collected as part of this effort this profile reveals several features of the forearc that were not apparent in an earlier coincident reflection profile one of the most important of these features is a very strong bottom simulating reflection bsr beneath the midslope region that is nearly continuous from water depths of about 1500 m to 600 m where it appears to crop out on the seafloor the pressure and temperature conditions at the bsr derived from our observations are remarkably consistent with the experimentally determined phase diagram for a methane hydrate seawater system over a broad range of temperatures and pressures assuming hydrostatic pressure and the temperature gradiant measured near the base of the continental slope during ocean drilling program odp leg 146 interval velocities and reflection coefficients derived from the data indicate that the bsr represents a contrast between sediment with a small amount of hydrate overlying sediment containing free gas consistent with results obtained during leg 146 although the regional distribution of the anomalously strong bsr beneath the midslope is poorly known we speculate that it may be related to apparent slope instability the data also provide constraints on the thickness and geometry of the siletz terrane which is the basement beneath the shelf and acts as the subduction zone backstop a deep reflection which might mistakenly be interpreted to be moho if coincident large aperture data were not available is interpreted to be the base of the siletz terrane a recently active strike slip fault zone that overlies the seaward edge of the siletz terrane suggests that the siletz terrane controls the location of decoupling of the subduc tion complex from the rest of the forearc

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

an inverted continental moho and serpentinization of the forearc mantle volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back arc region but the forearc mantle in the corner of the wedge is thought to be significantly cooler here we explore the structure of the mantle wedge in the southern cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers we find very low shear wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an inverted continental moho which reverts to normal polarity seaward of the cascade arc this observation provides compelling evidence for a highly hydrated and serpentinized forearc region consistent with thermal and petrological models of the forearc mantle wedge this serpentinized material is thought to have low strength and may therefore control the down dip rupture limit of great thrust earthquakes as well as the nature of large scale flow in the mantle wedge

source parameters of aftershocks of the 1991 costa rica and 1992 cape mendocino california earthquakes from inversion of local amplitude ratios and broadband waveforms abstract source parameters of aftershocks of the 22 april 1991 m w 7 7 costa rica and the 25 april 1992 m w 7 1 cape mendocino california earthquakes are determined using a grid search inversion of p sh and sv amplitude ratios recorded by sparse local networks of three component broadband and short period stations the inversion procedure consists of computing synthetic seismograms for three fundamental fault orientations for all source receiver pairs over a range of source depths calculating the complex envelopes of the observed and synthetic seismograms to determine peak amplitudes of p sh and sv waves combining the fundamental fault amplitudes for all possible values of strike dip and rake at 10 increments and determining the best fault orientation and depth as the one that yields the smallest misfit between observed and synthetic p sh p sv and sv sh amplitude ratios the ambiguity in the sense of motion on the nodal planes arising due to the use of amplitude ratios is resolved by examining p wave polarities the sensitivity of source parameters to uncertainties in earthquake location and crustal structure is explored for events with good station coverage focal mechanism determinations are stable for a wide range of assumed values of crustal structure earthquake location and depth source parameters for many of the largest events m 3 4 are also determined by inversion of broadband displacement waveforms using a similar grid search technique comparable results were obtained using both broadband waveforms and amplitude ratios focal mechanism solutions for 20 aftershocks of the costa rica earthquake reveal a complicated faulting geometry indicating active thrust normal and strike slip faults in the back arc of costa rica the 1992 cape mendocino earthquake occurred at the intersection of the north american gorda and pacific plates while the mainshock was associated with underthrusting of the gorda plate beneath the north american plate fault plane solutions for 70 of the 38 largest aftershocks indicate that these events result from either motion between the gorda and pacific plates or from internal deformation within the gorda plate

the parkfield california earthquake prediction experiment five moderate magnitude 6 earthquakes with similar features have occurred on the parkfield section of the san andreas fault in central california since 1857 the next moderate parkfield earthquake is expected to occur before 1993 the parkfield prediction experiment is designed to monitor the details of the final stages of the earthquake preparation process observations and reports of seismicity and aseismic slip associated with the last moderate parkfield earthquake in 1966 constitute much of the basis of the design of the experiment

paleoatmospheric consequences of co2 released during early cenozoic regional metamorphism in the tethyan orogen the eocene was the warmest epoch of the cenozoic with published estimates of eocene atmospheric co2 content ranging from two to six times the current value calculations of co2 consumption by silicate weathering show that co2 fluxes to the atmosphere of ca 1018 myr could account for inferred paleocene eocene atmospheric co2 contents and the resulting greenhouse effect would have contributed to eocene warmth extensive portions of the tethyan orogen underwent regional metamorphism culminating in the eocene prograde metamorphism may have been contemporaneous with the late paleocene global warming we calculated the amount of metamorphic co2 produced at depth in the himalayan orogen with data on the timing of the india asia collison duration of prograde regional metamorphism and proportions and bulk compositions of metamorphic co2 source rocks if co2 was generated at a constant rate over a 10 myr period of prograde metamorphism in the himalayan orogen we estimate that ca 1018 1019 moles myr of metamorphic co2 were produced at depth significant expulsion of metamorphic co2 to the atmosphere may have occurred by focused fluid flow along shear zones such as the extensive main central thrust in the himalayan orogen an additional ca 1018 myr could have been contributed by eocene regional metamorphism in the mediterranean tethys i e from the alps to turkey the extensive metamorphism associated with the india asia collision and the closing of tethys may have contributed to co2 greenhouse warming in the early to mid cenozoic

thermoluminescence dating of periods of loess deposition and soil formation in normandy the least incomplete records of pleistocene climate change come from the study of deep sea sediments in which the stratigraphic record of oxygen isotope variations reflecting terrestrial ice volume is the primary correlation medium on continents the available record is far less complete because many of the characteristics of glaciation are erosional rather than depositional the areas of loess deposition may provide the best deposits in which to develop relatively complete regional stratigraphies that may be compared with the deep sea record1 2 in this study we use thermoluminescence tl dating of loess and of soil developed on loess to test this model we have confined ourselves to the last complete glacial cycle within which the reproducibility of the age determinations is similar to the time resolution of most deep sea core records

downdip landward limit of cascadia great earthquake rupture 1 this paper examines the constraints to the downdip landward limit of rupture for the cascadia great earthquakes off western north america this limit is a primary control for ground motion hazard at near coastal cities the studies also provide information on the physical controls of subduction thrust rupture globally the constraints are 1 locked transition zones from geodetic deformation gps repeated leveling tide gauges 2 rupture zone from paleoseismic coastal marsh subsidence paleogeodesy 3 temperature on the thrust for the seismic aseismic transition 4 change in thrust seismic reflection character downdip from thin seismic to thick ductile 5 fore arc mantle corner aseismic serpentinite and talc overlying the thrust 6 updip limit of episodic tremor and slip ets slow slip 7 rupture area associations with shelf slope basins 8 depth limit for small events on the thrust and 9 landward limit of earthquakes on the nootka transform fault zone the most reliable constraints for the limit of large rupture displacement 10 m are generally just offshore in agreement with thermal control for this hot subduction zone but well offshore central oregon and near the coast of northern washington the limit for 1 2 m rupture that can still provide strong shaking is less well estimated 25 50 km farther landward the fore arc mantle corner and the updip extent of ets slow slip are significantly landward from the other constraints surprisingly there is a downdip gap between the best other estimates for the great earthquake rupture zone and the ets slow slip in this gap plate convergence may occur as continuous slow creep

contrasting stable isotope behavior between calcite and dolomite marbles lone mountain nevada late proterozoic to cambrian carbonate rocks from lone mountain west central nevada record multiple post depositional events including 1 diagenesis 2 mesozoic regional metamorphism 3 late cretaceous contact metamorphism related to the emplacement of the lone mountain granitic pluton and 4 tertiary hydrothermal alteration associated with extension uplift and intrusion of silicic porphyry and lamprophyre dikes essentially pure calcite and dolomite marbles have stable isotopic compositions that can be divided into two groups one with positive 13c values from 3 1 to 1 4 pdb and high 18o values from 21 5 to 15 8 smow and the other with negative 13c values from 3 3 to 3 6 and low 18o values from 16 9 to 11 1 marbles also contain minor amounts of quartz muscovite and phlogopite brown and blue luminescent clear smooth textured quartz grains from orange luminescent calcite marbles have high 18o values from 23 9 to 18 1 while brown luminescent opaque rough textured quartz grains from red luminescent dolomite marbles typically have low 18o values from 2 0 to 9 3 the 18o values of muscovite and phlogopite from marbles are typical of micas in metamorphic rocks with values between 10 4 and 14 4 whereas mica d values are very depleted varying from 102 to 156 no significant lowering of the 18o values of lone mountain carbonates is inferred to have occurred during metamorphism as a result of devolatilization reactions because of the essentially pure nature of the marbles bright luminescence along the edges of fractures quartz cements and quartz overgrowths in dolomite marbles low d values of micas negative 13c values and low 18o values of calcite and dolomite and depleted 18o values of quartz from dolomite marbles all indicate that meteoric fluids interacted with lone mountain marbles during the tertiary partial oxygen isotopic exchange between calcite and low 18o meteoric fluids lowered the 18o values of calcite resulting in uniform quartz calcite fractionations that define an apparent pseudoisotherm these quartz calcite fractionations significantly underestimate both the temperature of metamorphism and the temperature of post metamorphic alteration partial oxygen isotopic exchange between quartz and meteoric fluids also resulted in 18o depletion of quartz from dolomite marbles this partial exchange was facilitated by an increase in the surface area of the quartz as a result of its dissolution by meteoric fluids the negative 13c values in carbonates result from the oxidation of organic material by meteoric fluids following metamorphism stable isotopic data from lone mountain marbles are consistent with the extensive circulation of meteoric hydrothermal fluids throughout western nevada in tertiary time