tectonic setting of synorogenic gold deposits of the pacific rim abstract more than 420 million oz of gold were concentrated in circum pacific synorogenic quartz lodes mainly during two periods of continental growth one along the gondwanan margin in the palaeozoic and the other in the northern pacific basin between 170 and 50 ma these ores have many features in common and can be grouped into a single type of lode gold deposit widespread throughout clastic sedimentary rock dominant terranes the auriferous veins contain only a few percent sulphide minerals have gold silver ratios typically greater than 1 1 show a distinct association with medium grade metamorphic rocks and may be associated with large scale fault zones ore fluids are consistently of low salinity and are co2 rich in the early and middle palaeozoic in the southern pacific basin a single immense turbidite sequence was added to the eastern margin of gondwanaland deformation of these rocks in southeastern australia was accompanied by deposition of at least 80 million oz of gold in the victorian sector of the lachlan fold belt mainly during the middle and late devonian lesser devonian gold accumulations characterized the more northerly parts of the gondwanan margin within the hodgkinson broken river and thomson fold belts additional lodes were emplaced in this flyschoid sequence in devonian or earlier palaeozoic times in what is now the buller terrane westland new zealand minor post devonian growth of gondwanaland included terrane collision and formation of gold bearing veins in the permian in australia s new england fold belt and in the jurassic early cretaceous in new zealand s otago schists collision and accretion of dozens of terranes for a 100 m y long period against the western margin of north america and eastern margin of eurasia led to widespread latest jurassic to eocene gold veining in the northern pacific basin in the former location late jurassic and early cretaceous veins and related placer deposits along the western margin of the sierra nevada batholith have yielded more than 100 million oz of gold additional significant ore forming events during the development of north america s cordilleran orogen included those in the klamath mountains region california in the late jurassic and early cretaceous the klondike district yukon by the early cretaceous the nome and fairbanks districts alaska and the bridge river district british columbia in the middle cretaceous and the juneau gold belt alaska in the eocene gold bearing veins deposited during the late jurassic and early cretaceous terrane collision that formed the present day russian far east have been the source for more than 130 million oz of placer gold the abundance of gold bearing quartz carbonate veins throughout the gondwanan north american and eurasian continental margins suggests the migration and concentration of large fluid volumes during continental growth such volumes could be released during orogenic heating of hydrous silicate mineral phases within accreted marine strata the common temporal association between gold veining and magmatism around the pacific rim reflects these thermal episodes melting of the lower thickened crust during arc formation slab rollback and extensional tectonism and subduction of a slab window beneath the seaward part of the forearc region can all provide the required heat for initiation of the ore forming processes

carbon mineralization and oxygen dynamics in sediments with deep oxygen penetration lake superior to understand carbon and oxygen dynamics in sediments with deep oxygen penetration we investigated eight locations 160 318 m depth throughout lake superior despite the 2 4 weight percent organic carbon content oxygen penetrated into the sediment by 3 5 to 12 cm at all locations such deep penetration is explained by low sedimentation rates 0 01 0 04 cm yr 21 high solubility of oxygen in freshwater and a shallow 2 cm bioturbation zone in response mainly to oxygen variations in the bottom waters the sediment oxygen penetration varied seasonally by as much as several centimeters suggesting that temporal variability in deeply oxygenated sediments may be greater than previously acknowledged the oxygen uptake rates 4 4 7 7 mmol m 22 d 21 average 6 1 mmol m 22 d 21 and carbon mineralization efficiency 90 of deposited carbon were similar to those in marine hemipelagic and pelagic sediments of comparable sedimentation rates the reactivity of organic carbon was found to decrease with age similarly to the power law documented in marine environments the burial flux of carbon into the deep sediment 0 7 mmol m 22 d 21 was 2 5 of the previously estimated primary production maximum volume specific carbon degradation rates were 0 3 1 5mmol cm 23 d 21 bioturbation coefficient near the sediment surface was 3 8 cm 2 yr 21 these results indicate that carbon cycling in large freshwater systems conforms

a revised earthquake catalogue for south iceland in 1991 a new seismic monitoring network named sil was started in iceland with a digital seismic system and automatic operation the system is equipped with software that reports the automatic location and magnitude of earthquakes usually within 1 2 min of their occurrence normally automatic locations are manually checked and re estimated with corrected phase picks but locations are subject to random errors and systematic biases in this article we consider the quality of the catalogue and produce a revised catalogue for south iceland the area with the highest seismic risk in iceland we explore the effects of filtering events using some common recommendations based on network geometry and station spacing and as an alternative filtering based on a multivariate analysis that identifies outliers in the hypocentre error distribution we identify and remove quarry blasts and we re estimate the magnitude of many events this revised catalogue which we consider to be filtered cleaned and corrected should be valuable for building future seismicity models and for assessing seismic hazard and risk we present a comparative seismicity analysis using the original and revised catalogues we report characteristics of south iceland seismicity in terms of b value and magnitude of completeness our work demonstrates the importance of carefully checking an earthquake catalogue before proceeding with seismicity analysis

magnitude estimation using the covered areas of strong ground motion in earthquake early warning 1 we collected the strong motion accelerograms with peak ground acceleration pga larger than 100 gal 1 gal 1 0 cm s 2 from large crustal earthquakes in taiwan recorded by the taiwan strong motion instrumentation program tsmip stations to find an empirical relationship between the area of high pga and the corresponding earthquake magnitude we found that the logarithms of the areas inside the pga contours have a linear relation to the corresponding earthquake magnitudes we propose that this relationship might be able to rapidly define the earthquake magnitude while providing sufficient seismic station coverage and might have practical application in earthquake early warning eew and rapid reporting systems the proposed magnitude estimation method is directly related to the level of strong surface shaking and is inherently suitable for the purpose of the eew and rapid reporting systems

using borehole records to estimate magnitude for earthquake and tsunami early warning systems this paper presents a new application of the ground motion prediction equations gmpes to estimate the event magnitude for earthquake and tsunami early warning systems this technique incorporates borehole strong motion records along with surface recordings provided by kiban kyoshin network kik net stations we analyzed strong ground motion data from earthquakes with moment magnitude m ranging from 5 0 to 8 1 recorded by kik net stations provided by japan s national research institute for earth science and disaster prevention nied over the interval of 1998 to 2010 we used 2160 strong ground motion accelerograms with peak ground acceleration pga larger than 10 cm s2 recorded by borehole seismographs and 890 waveforms with pga larger than 80 cm s2 recorded by surface seismographs to derive gmpes for pga and peak ground velocity pgv in japan these gmpes are used as the basis for regional magnitude determination predicted magnitudes from pga values mpga and predicted magnitudes from pgv values mpgv were defined separately for borehole and surface recordings mpga and mpgv strongly correlate with the moment magnitude of the event provided that at least 20 records for each event are available the results show that mpgv from borehole data has the smallest standard deviation among the estimated magnitudes and provides an accurate early assessment of earthquake magnitude we demonstrate that incorporation of borehole strong ground motion records immediately available after the occurrence of large earthquakes significantly increases the accuracy of earthquake magnitude estimation and improves earthquake and tsunami early warning systems performance

geochemical controls on internal phosphorus loading in lake of the woods abstract sediment phosphorus p diagenesis and release in polymictic systems are poorly understood here we determine the mechanistic controls on the processes that drive p release from the sediments in lake of the woods low the vertical distributions of the relevant diagenetic parameters including oxygen ph redox potential dissolved p iron fe and other metals in the porewater were measured and the fluxes of dissolved oxygen and p across the sediment water interface swi at the four locations in low were quantified we characterized solid p speciation and analyzed the iron and corresponding metal contents in five sediment p binding forms short term diffusive fluxes of p ranged between 0 3 and 7 8 mg m 2d 1 controlled by the mineralization of freshly deposited organic matter and the redox sensitive iron cycle long term net p release rates were between 0 21 and 9 96 mg m 2d 1 controlled by the diagenetic remineralization of p binding pools which regulates long term sediment p releases hypoxia may have led to the release of previously stored fe p in the sediments which has likely increased internal p loading for a timescale that is longer than seasonal while fe sorbed phosphorus is the major barrier for p release in the surface sediments p is immobilized in deep sediments via the formation of calcium ca p aluminum al p and possibly vivianite our study demonstrates the importance of sediments as sources of the productivity limiting nutrient phosphorus reveals the geochemical controls on sediment p release and helps further the understanding of how sediments regulate water quality and affect eutrophication and the possibility of algal blooms

a model for a seismic computerized alert network in large earthquakes damaging ground motions may occur at large epicentral distances because of the relatively slow speed of seismic waves it is possible to construct a system to provide short term warning as much as several tens of seconds of imminent strong ground motions from major earthquakes automated safety responses could be triggered by users after receiving estimates of the arrival time and strength of shaking expected at an individual site although warning times are likely to be short for areas greatly damaged by relatively numerous earthquakes of moderate size large areas that experience very strong shaking during great earthquakes would receive longer warning times

mesozoic cenozoic deformation in the canadian cordillera the record of a continental bulldozer abstract a possible mesozoic cenozoic trajectory for the north american craton is outlined from latitude changes of the craton derived from a revised apparent polar wander path and from westward movement of the craton based on the assumption that africa has been the least mobile continent geographically since the latest paleozoic during each of five time intervals that span 220 million years the craton trajectory had a different vector each vector appears to be reflected in the canadian cordillera by the dominant style and orientation of structures formed during that interval for much of the past 220 million years the meridionally oriented western margin of the pangea laurasia north america plate has been the site of arc magmatism where weak arc back arc lithosphere sandwiched between strong ocean floor and craton lithospheres at times coupled across convergent or transform plate boundaries focused and recorded strain when the craton apparently moved due westward between 180 160 ma and 120 60 ma the dominant structures formed then record orogen normal compression and were accompanied by orogeny structures formed during the earlier episode are mainly in the eastern and interior cordillera and their formation shortly followed or coincided with accretion of most terranes to the craton margin in the later episode compressional structures span the entire cordillera which emerged as a tectonic and physiographic entity before and between these intervals when the craton apparently moved mostly northwestward mainly geological and paleomagnetic considerations indicate some terranes moved southward sinistrally relative to the craton after 60 ma southwestward movement of the craton was concurrent with large northward dextral strike slip faults that disrupted the newly established ancestral cordillera the coincidence between the age of structures that record dominant orogen normal compression at times when the craton apparently moved due westward and orogen parallel displacements when the craton had either northward or southward components of motion suggests the craton acting as a continental bulldozer was the primary driver of cordilleran deformation and orogenesis

magnitude estimation for the 2011 tohoku oki earthquake based on ground motion prediction equations this study investigates whether real time strong ground motion data from seismic stations could have been used to provide an accurate estimate of the magnitude of the 2011 tohoku oki earthquake in japan ultimately such an estimate could be used as input data for a tsunami forecast and would lead to more robust earthquake and tsunami early warning we collected the strong motion accelerograms recorded by borehole and free field surface kiban kyoshin network stations that registered this mega thrust earthquake in order to perform an off line test to estimate the magnitude based on ground motion prediction equations gmpes gmpes for peak ground acceleration and peak ground velocity pgv from a previous study by eshaghi et al in the bulletin of the seismological society of america 103 2013 derived using events with moment magnitude m 5 0 1998 2010 were used to estimate the magnitude of this event we developed new gmpes using a more complete database 1998 2011 which added only 1 year but approximately twice as much data to the initial catalog including important large events to improve the determination of attenuation parameters and magnitude scaling these new gmpes were used to estimate the magnitude of the tohoku oki event the estimates obtained were compared with real time magnitude estimates provided by the existing earthquake early warning system in japan unlike the current operational magnitude estimation methods our method did not saturate and can provide robust estimates of moment magnitude within 100 s after earthquake onset for both catalogs it was found that correcting for average shear wave velocity in the uppermost 30 m v text s 30 improved the accuracy of magnitude estimates from surface recordings particularly for magnitude estimates of pgv mpgv the new gmpes also were used to estimate the magnitude of all earthquakes in the new catalog with at least 20 records results show that the magnitude estimate from pgv values using borehole recordings had the smallest standard deviation among the estimated magnitudes and produced more stable and robust magnitude estimates this suggests that incorporating borehole strong ground motion records immediately available after the occurrence of large earthquakes can provide robust and accurate magnitude estimation

magnitude determination using strong ground motion attenuation in earthquake early warning 1 we use 1661 strong motion accelerograms with peak ground acceleration pga larger than 80 gal 1 gal 1 0 cm s2 from 77 earthquakes recorded by the taiwan strong motion instrumentation program tsmip stations to derive a strong motion attenuation relationship this relationship can be used to dynamically define a mpga magnitude for earthquakes using earthquake locations determined by earthquake early warning process the mpga magnitude using this strong motion attenuation relationship corresponds well with mw given a sufficient number of pga readings mems micro electro mechanical systems acceleration sensor could be widely used for ground motion monitoring purposes thus we propose that once a large earthquake has begun that we might be able to use strong near field tens of kilometers pga values to quickly estimate the earthquake s magnitude which would improve earthquake early warning

a new method of quickly estimating epicentral distance and magnitude from a single seismic record rapid estimation of the epicentral distance and magnitude is of fundamental importance for early earthquake detection and warning systems we present a novel method of estimating the epicentral distance from a single seismic record in a short amount of time in order to quantitatively evaluate the difference in observed seismic waveforms we introduced a simple function with the form of bt exp at and determined a and b in terms of the least squares method by fitting this function to the initial part of the waveform envelope we have found that log b is inversely proportional to log where is the epicentral distance this relation holds true regardless of the earthquake magnitude by using this relation we can roughly estimate the epicentral distance nearly immediately after the p wave arrival then we can readily estimate the magnitude from the maximum amplitude observed within a given short time interval after the p wave arrival by using an empirical magnitude amplitude relation that includes the epicentral distance as a parameter manuscript received 11 january 2002

an automatic processing system for broadcasting earthquake alarms in japan most of the damage caused by large earthquakes is concentrated within areas less than about 100 km from the focal regions we have developed an earthquake alarm system that determines earthquake parameters within a few seconds of the p wave s arrival at the closest station and then transmits the earthquake information before the s wave arrival in areas of possible serious earthquake damage since an earthquake alarm system requires the determination of reliable earthquake parameters as quickly as possible it is unreasonable to wait until waveform data from numerous stations have been collected for analysis for this reason we have developed a novel method of determining the hypocentral location by using the arrival times for only a few stations as well as the lack of p wave arrivals at other stations at a given time the use of not yet arrived data makes it possible not only to determine reliable hypocenter parameters within a few seconds but also to detect erroneous arrival time readings and remove them automatically since the available waveform data increases with time the system was designed to redetermine earthquake parameters every second our method was deployed in a real time system starting in july 2002 the real time system locates 10 20 events per day which includes a few felt earthquakes occurring in and around japan it was shown from the waveform data for about 100 felt earthquakes that almost all the events except those far from the network could be located within a few seconds when most of seismic energy has not even arrived at some stations close by we recently started widespread broadcasting of earthquake information in real time by using a satellite transmission system

empirical distance attenuation and the local magnitude scale for the central united states seismic waveform data from the cooperative new madrid seismic network cnmsn the u s national seismograph network usnsn and stations operated by the u s geological survey and the incorporated research institutions for seismology iu are corrected to the theoretical wood anderson response and the peak amplitudes are used to determine a local magnitude scale for the central united states the distance correction function can be expressed as graphic 1 with amplitude a in millimeters and hypocentral distance r in kilometers showing a weak attenuation with distance synthetic seismograms are calculated based on a detailed crustal model obtained from local well log acoustic data in the mississippi embayment to examine the effect of structure on station factors the results show that the mississippi embayment sediment as a whole may amplify seismic waves at some specific frequencies such as 0 5 and 5 0 6 0 hz with a factor less than 4 0 and may not amplify seismic waves in the frequency band from 0 5 to 9 9 hz on average even though the amplification factors do increase with the source magnitude estimations for b values and magnitudes of earthquakes with a return period of 500 yr in the central united states are performed based on the original new madrid catalog m d or m blg and the newly created m l catalog results show that the b value is smaller for the m l catalog 0 790 yielding one m 7 5 event every 500 yr a result that converges with the paleoearthquake estimate for the region on average the relation between m l and m d or m blg for 1 5 m d 5 0 can be expressed as m l 1 008 m d 0 0714 1 embed inline graphic 1 gif

sedimentary phosphorus dynamics and the evolution of bottom water hypoxia a coupled benthic pelagic model of a coastal system the present study examines oxygen and phosphorus dynamics at a seasonally hypoxic site in the arkona basin of the baltic sea a coupled benthic pelagic reactive transport model is used to describe the evolution of bottomwater solute concentrations as well as pore water and sediment profiles aerobic respiration dominates remineralization with iron reduction denitrification and sulphate reduction playing secondary roles while other pathways are negligible sediments represent a significant oxygen sink chiefly due to the aerobic degradation of organic matter as well as nitrification and iron oxyhydroxide precipitation most phosphorus deposited in sediments is in organic matter yet cycling is dominated by iron bound phosphorus due to rapid dissimilatory iron reduction coupled with aerobic iron oxyhydroxide formation sustained hypoxia results in an initial decrease in sediment phosphorus content due to dissolution of phosphorus bearing iron oxyhydroxides resulting in a pulse of phosphate to overlying waters although an organic rich layer is formed under low oxygen conditions enhanced remineralization of organic phosphorus relative to organic carbon tempers sedimentary phosphorus accumulation upon reoxygenation of bottom waters after a decade of sustained hypoxia oxygen concentrations do not immediately achieve values observed prior to hypoxia because the organic rich layer creates a higher benthic oxygen demand artificial reoxygenation of bottom waters leads to a substantial increase in the ironbound phosphorus pool the total phosphorus content of the sediment however is unaffected a relapse into hypoxia would consequently produce a large pulse of phosphate to the overlying waters potentially exacerbating the situation

extrusion of high pressure cache creek rocks into the triassic stikinia quesnellia arc of the canadian cordillera implications for terrane analysis of ancient orogens and palaeogeography

detrital zircon geochronology and regional correlation of metasedimentary rocks in the coast mountains southeastern alaska u pb ages have been determined for 55 detrital zircon grains from a metasedimentary sequence along the west flank of the coast mountains in southeastern alaska these rocks belong to the port houghton assemblage which consists of upper paleozoic pelitic and psammitic schist metaconglomerate metabasalt and marble the port houghton assemblage rests unconformably on metamorphosed and deformed mid paleozoic arc type volcanics endicott arm assemblage which gradationally overlie upper proterozoic lower paleozoic continental margin strata tracy arm assemblage three main clusters of ages are present 330 365 ma 19 grains 1710 2000 ma 27 grains and 2450 2680 ma 6 grains additional grains are approximately 2334 2364 and 3324 ma comparison of these ages with detrital zircon ages in other cordilleran assemblages supports previous interpretations that metasedimentary rocks in the coast mountains i form a southwestern continuation of the yukon tanana terrane of eastern alaska and yukon

real time seismic warning with a two station subarray one of the most basic problems in seismology is earthquake location in particular the ability to quickly locate a large potentially devastating earthquake is of fundamental importance in a real time warning system where speed is a key factor in determining the level of success of such systems we have developed a simple method that uses only the two earliest p wave arrival times in a seismic array assuming a simple velocity model these arrivals are used to construct a hyperbolic curve on which the approximate epicenter of the earthquake is expected to lie epicentral location along this hyperbola is further constrained by using the fact that the p waves arriving at the other stations in the array are not first arrivals when applied to p wave seismic data from the hector mine earthquake in california and a smaller event in the central united states model results show agreement with actual earthquake locations although there is an inherent uncertainty in the subarray method of locating large earthquakes this may be an acceptable trade off in an early warning system in view of the time a few to tens of seconds saved by not waiting for other p arrivals whereas the main goal of this report is to present the location method we also show that the station closest to the hector mine earthquake had recorded about 0 3 and 1 mm of ground motion within 2 and 3 sec respectively of the arrival of the p waves thus indicating that a large event had occurred manuscript received 18 september 2003

cache creek terrane entrapment oroclinal paradox within the canadian cordillera exotic and far traveled oceanic crustal rocks of the cache creek terrane cc are bordered by less exotic quesnel qn and stikine st arc terranes to the east north and west all of these terranes are enveloped by an arcuate belt of displaced continental margin rocks the kootenay ko nisling ns and parts of the yukon tanana ytt terranes that have indirect ties to ancestral north america na initial 87sr 86sr isopleths conform to this arcuate pattern such a pattern of concentric belts presents a geological conundrum how did the qn st and cc come to be virtually enveloped by terranes with ties to na past and current models that explain assembly of the canadian cordillera are deficient in their treatment of this problem we propose that early mesozoic qn and st were joined through their northern ends as two adjacent arc festoons that faced south toward the cache creek ocean panthalassa oceanic plateau remnants within the cc today were transported from the tethyan realm and collided with these arcs during subduction of the cache creek ocean counterclockwise oroclinal rotation of st and ns terranes in the late triassic to early jurassic caused enclosure of the cc rotation continued until these terranes collided with qn in the middle jurassic paleomagnetic declination data provide support for this model in the form of large average anticlockwise rotations for permian to early jurassic sites in st but moderate clockwise rotations for sites in qn specific modern analogues for the cordilleran orocline include the yap trench where the caroline rise is colliding end on with the mariana arc and the banda arc located on the southeastern tail of the asian plate which is being deformed into a tight loop by interactions with the australian and pacific plates

engineering implications of ground motions from the northridge earthquake the magnitude duration and frequency content of ground motions from the northridge earthquake are analyzed and compared to predictive relationships typically used in engineering design and to the 1994 uniform building code ubc a relationship between maximum horizontal acceleration on soil versus maximum horizontal acceleration on rock is presented based on strong motion recordings at free field sites the effect of geologic conditions on localized damage patterns is shown to be important for this earthquake although many of the sites within the affected region are stiff soil sites classified as s1 or s2 sites by the ubc the results of preliminary seismic site response analyses performed at two deep alluvial sites indicate that much of the observed site amplification can be captured by one dimensional wave propagation analyses

timing of cache creek ocean closure insights from new jurassic radiolarian ages in british columbia and yukon and their significance for canadian cordillera tectonics the closure of the cache creek ocean during the jurassic led to the structuration of the canadian cordillera to reassess the timing of this major tectonic event this study proposes a biochronolog

contrasting tectono stratigraphy and structure in the coast belt near chilko lake british columbia unrelated terranes or an arc back arc transect stratigraphy and structural styles vary greatly in two areas of the coast belt near chilko lake chilcotin ranges in the east and coast mountains in the west no definite continuity between the two belts has been established in the pre mid cretaceous geology but this area may be a long lived episodic magmatic arc and nearby arc related basin the stratigraphic contrasts may reflect inherent differences between an arc and related basinal sequence triassic volcanic arc sequences are part of the stikine western belt and cadwallader eastern belt terranes which may be part of the same arc the jurassic is represented by one dated pluton in the west compared with almost continuous deposition of volcanogenic clastic rocks in the east lower cretaceous sequences in the west and east may represent a volcanic arc and back arc basin the taylor creek group albian is the first definitive link between the two belts and represents an arc and intra arc or back arc basin the structural evolution of the two be

revised ml determination for crustal earthquakes in taiwan the local magnitude scale m l is an empirically derived scale anchored to a zero magnitude reference event richter defined the amplitude of ground shaking at an epicentral distance of 100 km for a zero magnitude earthquake in southern california the crustal attenuation characteristics of taiwan result in a relatively high ml when compared to moment magnitude mw we therefore define a revised ml scale for crustal earthquakes in the taiwan region that is more consistent with mw using observed peak ground shaking and mw we determine a new log a0 curve of ground shaking versus hypocentral distance r for a zero magnitude earthquake and station correction factors the log a0 curve determined in this study is log a r 0 332 1 568 log r 0 280 0 using this new log a0 curve and station corrections the new ml is more consistent with mw with a 0 2 magnitude unit uncertainty the new log a0 curve has a value of 2 80 at the distance of 100 km compared to the anchor point of log a0 3 at the same distance as defined by richter for southern california this means that the current ml estimates in taiwan which use richter s definition average 0 2 magnitude units larger than their mw the station correction factors also determined are large from 0 40 to 0 52 magnitude units the use of station corrections in routine seismic network operation in taiwan will improve magnitude estimates this is particularly important for smaller events when recording stations may be pre dominantly on either hard rock or soft soil sites which could lead to under or overestimates of the magnitude by up to half a magnitude unit

the yukon tanana terrane part of north america at 215 ma from paleomagnetism of the taylor mountain batholith alaska abstract the massive unmetamorphosed 212 ma taylor mountain batholith underlies 648 km2 of the yukon tanana terrane ytt in east central alaska and intrudes klippen thrust sheets of the fortymile river assemblage and the chicken metamorphic complex structural evidence indicates that the batholith is neither tilted nor rotated about a vertical axis paleomagnetic analysis of 295 specimens from 24 sites in the batholith and cross cutting mafic dikes isolates a stable primary characteristic remanent magnetization in magnetite with unblocking temperatures of 500 to 585 c that places the batholith s paleopole at 61 4 n 102 2 e n 17 95 5 2 on the north american apparent polar wander path apwp at 215 5 ma 1 the taylor mountain paleopole alone and all ytt paleopoles together show that the ytt has been a para autochthonous part of the north american margin since the late triassic further the intermontane belt imb paleopoles are distinct from the north american and ytt paleopoles prior to the mid eocene and provide two apwp segments one imb segment includes the quesnel cache creek eastern coast belt and northern stikine terranes and the second more speculative imb segment includes the central and southwestern stikine and methow terranes this analysis supports tectonic models for the northern cordillera in which the imb terranes were obducted onto north america during the late cretaceous to mid eocene co eval with the laramide orogeny

factors controlling long term phosphorus efflux from lake sediments exploratory reactive transport modeling abstract we perform for the first time a global sensitivity analysis on a generic diagenetic reaction transport model rtm to elucidate the effects of environmental thermodynamic and kinetic factors on the magnitudes of phosphorus release fluxes from aquatic sediments under a range of conditions typically found in lake sediments our model includes the processes that describe redox sensitive phosphorus releases the so called classical model and processes by which phosphorus mobilization is affected by porewater sulfate on decadal and longer time scales sediment phosphorus effluxes are primarily determined by sedimentation flux of reactive organic matter sedimentation flux of iron oxyhydroxides concentrations of dissolved oxygen and sulfate at the sediment water interface and the rate at which phosphate is immobilized in reduced sediment we show that the effects of these factors on phosphorus effluxes are interdependent and discuss the mechanisms of such interactions the dominant pathways by which dissolved sulfate increases phosphorus efflux in iron rich hypoxic sediments are discussed in detail in contrast to short term phosphorus releases such as described by the classical model long term phosphorus retention is controlled by phosphorus removal to deep reduced sediment rather than processes at the sediment water interface hence the results of short term laboratory or in situ studies such as sediment incubations experiments cannot be unequivocally extended to long time scales our results provide explanations to the reports that lake restoration measures such as restricting phosphorus inputs to a lake or oxygenating the lake s hypolimneon or both in the long term often fail to decrease sediment phosphorus effluxes the re deposition of sediment substances after their release into the water column the feedback often overlooked in sediment rtms can critically affect the magnitude and dynamics of phosphorus efflux from sediments depending on sediment history the same set of external boundary conditions can generate diagenetic regimes with either high or low phosphorus effluxes bistability

cache creek ocean closure or enclosure exotic tethyan faunas within the cache creek terrane contrast markedly with faunas and lithologic associations in the adjacent quesnel and stikine terranes in northern british columbia and southeast yukon all three terranes are enveloped in the north by pericontinental rocks of the yukon tanana terrane a geometry that imposes severe constraints on terrane assembly models for the northern canadian cordillera our solution to the problem invokes a northern join between the stikinia and quesnellia arcs through the yukon tanana terrane forming an orocline that encloses the cache creek terrane this model involves 1 collision of a linear oceanic plateau at the cusp between quesnellia and stikinia 2 anticlockwise rotation of stikinia about an axis in the yukon tanana terrane 3 simultaneous enclosure of the cache creek ocean and 4 emplacement of quesnellia onto the margin of ancestral north america and the cache creek terrane onto stikinia during final closure of the orocline early mesozoic paleomagnetic declinations in stikinia are permissive of the large anticlockwise rotations predicted by the model similar large scale rotations and ocean basin enclosure are common features in the southwest pacific this model accounts for paleozoic and younger linkages between yukon tanana and both northern stikinia and quesnellia the striking similarity between triassic jurassic arcs east and west of the cache creek terrane and the profound early mesozoic deformational event in the yukon tanana terrane

u pb zircon geochronology of lower jurassic and paleozoic stikinian strata and tertiary intrusions northwestern british columbia new u pb zircon ages are reported from western stikinia devonian and pennsylvanian ages of volcanic rocks at oweegee dome confirm the presence of pre permian strata and with paleozoic and triassic detrital zircons from lower jurassic sandstone they help to demonstrate pre lower jurassic deformation and uplift the absence of pre paleozoic inherited zircon from all samples is consistent with nd sr isotopic data which suggest that stikinia consists mainly of juvenile crust u pb ages for posttectonic intrusions suggest that structures in skeena fold belt in the kinskuch area formed prior to eocene time five ages for felsic volcanic rocks from stratigraphically well constrained upper parts of the hazelton arc are approximately 196 199 ma and suggest near contemporaneity for cessation of volcanism in the areas studied the sinemurian or late sinemurian early pliensbachian ages are older than previously reported u pb and biostratigraphic ages for presumed correlative rocks to the west and westward migra

determination of earthquake early warning parameters τ c and pd for southern california summary we explore a practical approach to earthquake early warning in southern california by determining a ground motion period parameter c and a high pass filtered displacement amplitude parameter pd from the initial 3 s of the p waveforms recorded at the southern california seismic network stations for earthquakes with m 4 0 at a given site we estimate the magnitude of an event from c and the peak ground motion velocity pgv from pd the incoming threecomponent signals are recursively converted to ground acceleration velocity and displacement the displacements are recursively filtered with a one way butterworth high pass filter with a cut off frequency of 0 075 hz and a p wave trigger is constantly monitored when a trigger occurs c and pd are computed we found the relationship between c and magnitude m for southern california and between pd and pgv for both southern california and taiwan these two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning in the area around the station where onset of strong ground motion is expected within seconds after the arrival of the p wave when the station density is high the methods can be applied to multistation data to increase the robustness of onsite early warning and to add the regional warning approach in an ideal situation such warnings would be available within 10 s of the origin time of a large earthquake whose subsequent ground motion may last for tens of seconds

biogeochemical mechanisms controlling phosphorus diagenesis and internal loading in a remediated hard water eutrophic embayment abstract phosphorus p levels in eutrophic lakes with restricted external p inputs often show hysteresis resulting from sediment p diagenetic recycling hard water oxygenated lakes are often thought to be less susceptible to p release from sediment due to precipitation of p with calcium carbonate and p sorption on iron fe oxyhydroxides in oxidized surface sediments however perpetuated eutrophic conditions in many hard water oxygenated lakes persist despite drastic reduction of external p inputs what limits p sediment binding capacity and drives its release from sediments in such lakes is often less understood here we characterize sediment p diagenetic processes driving persistent internal loading in the bay of quinte a hard water polymictic embayment of lake ontario canada we used a multifaceted approach combining a comprehensive three year study of sediment p binding forms recent sediment stratigraphy and accumulation high spatial resolution measurement of dissolved oxygen redox potential and ph across the sediment water interface and depth profiles of nutrient and metals concentrations in pore water despite oxygenated bottom water conditions p diffusive fluxes during summer are substantial 1 6 5 mg p m2 day representing as much as 50 of external p inputs estimated rates of benthic organic carbon degradation indicate that anaerobic organic p mineralization in anoxic sediments is the main driver of p release which is strongly influenced by fe reduction estimated rates of benthic organic carbon degradation indicate that anaerobic organic p mineralization in anoxic sediments is the main driver of p release in surface sediment the redox sensitive p is the prevailing diagenetically reactive p phase emphasizing strong coupling with ferric fe while this indicates substantial p sorption on fe oxyhydroxides their spare binding capacity is limited as reducible fe p ratios are close to sorption limit the calcium carbonate bound p increased with sediment depth at the expense of redox sensitive p suggesting diagenetic sequestration into apatite with sediment burial however only 40 of diagenetically reactive p forms which account for 2 3 of the total p in surface sediment are permanently retained during burial importantly our data show that in fact significant p flux occurs in shallow areas with an apparent discordance with concurrent measures of long term p release from the sediments these results also demonstrate that short term measures cannot be extrapolated to long term estimates and vice versa

geochemistry of marine sediments by david j burdige princeton nj princeton university press 2006 609 pages 110 line figures 33 tables 85 00 cloth

locating and modeling regional earthquakes with two stations 1 we developed a new technique caploc to retrieve full source parameters of small seismic events from regional seismograms which include origin time epicenter location depth focal mechanism and moment magnitude despite rather complicated propagation effects at short periods a simple localized one dimensional model can well explain signals of periods 3 10 s if we break the three component records into different segments and allow differential time shifts among them these differential time shifts once established from a calibration process or a well determined tomographic map can be used together with p wave travel times to refine an event s location in this study we tested whether our new method could produce satisfactory results with as few as two stations so that we can improve source estimates of poorly monitored events with sparse waveform data we conducted the test on 28 events in the tibetan plateau the focal mechanisms and locations determined from only two stations agree well with those determined from a whole passcal array in particular our new method produces better locations than international seismological centre with the average mislocation error reduced from 16 to 5 km we also tested whether an event s depth and mechanism can be determined separately from its epicenter relocation in a two step approach we find that the two step approach does not always give the correct solution but the reliability of a solution can be evaluated using a reduced chi square value

magnitude estimation using the first three seconds p wave amplitude in earthquake early warning 1 pd is the peak amplitude of displacement in the first three seconds after the arrival of the p wave we investigated the attenuation of pd with the hypocentral distance r in southern california as a function of magnitude m and obtained the following relationship log pd 3 463 0 729 m 1 374 log r 0 305 given an earthquake location determined by the p wave arrival times at stations close to the epicenter this relationship can be used to define a so called pd magnitude of earthquakes our result shows that for earthquakes in southern california the pd magnitudes agree with the catalog magnitudes with a standard deviation of 0 18 for events less than magnitude 6 5 therefore pd is a robust measurement for estimating the magnitudes of earthquakes and has practical application in earthquake early warning systems citation wu y m and l zhao 2006 magnitude estimation using the first three seconds p wave amplitude in earthquake early warning geophys res lett 33 l16312 doi 10 1029 2006gl026871

a catalog of taiwan earthquakes 1900 2006 with homogenized mw magnitudes taiwan has a relatively complete catalog of earthquakes since the first seismograph was installed in 1897 however due to changes in seismographic characteristics network coverage and observational practice the definition and procedure for magnitude determination were different during different time periods recognizing a complete catalog of earthquakes with consistent magnitudes is essential for delineating seismicity patterns and assessing seismic hazards for taiwan efforts have been made to convert the original magnitudes of earthquakes in taiwan based on various magnitude scales to a common m l or m s magnitude scale unfortunately the m l or m s magnitude scales chosen for previous studies all are subject to a fundamental limitation of saturation toward large earthquakes besides these studies are nearly two decades old in order to avoid this limitation and to follow the current trend we have chosen in this study to convert original magnitudes of various scales to a common m w scale in this study we used two independent methods for magnitude conversion in the first method we converted the original magnitudes to m w through empirical relations between these magnitudes and m w this magnitude is called the old m w in the second method we used the best fitting a and b values to convert the original magnitudes to m w this magnitude is called the new m w the converted m w magnitudes from both methods have resulted in significant improvements over the original magnitudes and are in good agreement with each other nevertheless by examining the log10 n versus m w plots we found better linearity and tighter overlap among different time periods for the new m w than for the old m w thus we chose the new m w as the unified magnitude for the catalog of taiwan earthquakes finally a list of 899 earthquakes from 1900 to 2006 with m w 5 5 is presented graphic 1 see the earthquake lists available in the electronic supplement to this article the list is considered complete for the whole period from 1900 to 2006 1 embed inline graphic 1 gif

precambrian crust beneath the mesozoic northern canadian cordillera discovered by lithoprobe seismic reflection profiling 1 the cordillera in northern canada is underlain by westward tapering layers that can be followed from outcrops of proterozoic strata in the foreland belt to the lowermost crust of the orogenic interior a distance of as much as 500 km across strike they are interpreted as stratified proterozoic rocks including 1 8 0 7 ga supracrustal rocks and their basement the layering was discovered on two new deep seismic reflection profiles in the yukon line 3 650 km and northern british columbia line 2 1245 km in two segments that were acquired as part of the lithoprobe slave northern cordillera lithospheric evolution snorcle transect in the mackenzie mountains of the eastern yukon the layering in line 3 is visible between 5 0 and 12 0 s 15 to 36 km depth it is followed southwestward for nearly 650 km 500 km across strike and thins to less than 1 0 s 3 0 3 5 km thickness near the moho at the yukon alaska international boundary in the northern rocky mountains of british columbia the upper part of the layering on line 2 correlates with outcrops of proterozoic 1 76 1 0 ga strata in the muskwa anticlinorium at this location the layering is at least 15 km thick and is followed westward then southward into the middle and lower crust for 700 km 300 km across strike it disappears as a thin taper at the base of the crust 150 km east of the coast of the alaskan panhandle the only significant disruption in the layering occurs at the tintina fault zone a late to postorogenic strike slip fault with up to 800 km of displacement which appears as a vertical zone of little reflectivity that disrupts the continuity of the deep layering on both profiles 300 km apart the base of the layered reflection zone coincides with the moho which exhibits variable character and undulates in a series of broad arches with widths of 150 km in general the mantle appears to have few reflections however at the southwest end of line 3 near the alaska british columbia border a reflection dips eastward from 14 0 s to 21 0 s 45 to 73 km depth beneath exposed eocene magmatic rocks it is interpreted as a relict subduction surface of the kula plate our interpretation of proterozoic layered rocks beneath most of the northern cordillera suggests a much different crustal structure than previously considered 1 ancient north american crust comprising up to 25 km of metamorphosed proterozoic to paleozoic sediments plus 5 10 km of pre 1 8 ga crystalline basement projects westward beneath most of the northern canadian cordillera 2 the lateral 500 km by at least 1000 km and vertical up to 25 km extent of the proterozoic layers and their internal deformation are consistent with a long lived margin for northwestern north america with alternating episodes of extension and contraction 3 the detachments that carry deformed rocks of the mackenzie mountains and northern rocky mountains are largely confined to the upper crustal region above the layering 4 accreted terranes include thin klippen that were thrust over north american pericratonic strata e g yukon tanana and terranes such as nisling and stikinia that thicken westward as the underlying proterozoic layers taper and disappear 5 the ages of exposed rocks are not necessarily indicative of the ages of underlying crust a frequent observation in lithoprobe interpretations so that estimates of crustal growth based on surface geology may not be representative

a prototype earthquake warning system for strike slip earthquakes a prototype expert system has been developed to provide rapid warning of earthquakes while they are occurring warning times of up to 100 seconds will be possible in the complete system several accelerometers are distributed at intervals within a few kilometers of a known fault data are telemetered to a central computer which implements the expert system the expert system incorporates specific information about the type of fault to be monitored and includes simple rules for estimating the fault slip rupture length and seismic moment all in real time if the seismic moment exceeds a preset value an alarm may be issued the prototype is designed for deployment on near surface strike slip faults such as the san andreas and has been successfully tested with data from the 1979 imperial valley and 1984 morgan hill earthquakes crucial concepts have also been tested using synthetic data calculated for a model of the 1857 fort tejon earthquake parkfield california could be used as a test site

quick and reliable determination of magnitude for seismic early warning this article reports efforts toward using real time earthquake monitoring by the taiwan central weather bureau to meet the needs of seismic early warning twenty three sets of strong motion data from moderate earthquakes m 5 0 in the taiwan area are used to demonstrate the feasibility of this goal for earthquakes larger than ml 5 epicenters can be reliably determined in about 15 sec after the arrival of the p wave at the nearest station the earthquake magnitude m l cannot be determined in the same time frame due to incomplete recording of shear waves at some stations however the magnitude based on the first 10 sec of signal ml10 can be related to ml as follows ml 1 28 ml10 0 85 0 13 our results show that the real time strong motion system routinely used by the cen tral weather bureau can be used to determine epicenters and magnitudes in about 30 sec after occurrence of earthquakes in taiwan such information hopefully can be used to reduce damage to society

late jurassic magmatism metamorphism and deformation in the blue mountains province northeast oregon an early to mid mesozoic record of sedimentation magmatism and metamorphism is well developed in the blue mountains province of northeast oregon detailed studies both north and south of the blue mountains province e g terranes of the intermontane belt klamath mountains and western sierra nevada have documented a complex middle to late jurassic orogenic evolution however the timing of magmatic metamorphic and deformational events in the blue mountains and the significance of these events in relationship to other terranes in the western north american cordillera remain poorly understood in this study we investigate the structural magmatic and metamorphic histories of brittle to semibrittle deformation zones that indicate widespread late jurassic orogenesis in the blue mountains province folding and faulting associated with contractional deformation are primarily localized along terrane boundaries e g baker wallowa and baker izee olds ferry boundaries and within the composite baker oceanic melange terrane e g bourne greenhorn subterrane boundary these brittle to semibrittle deformation zones are broadly characterized by the development of e w oriented slaty to spaced cleavage in fine grained metasedimentary rocks of the baker terrane e g elkhorn ridge argillite approximately n s bivergent folding and n and s dipping reverse and thrust faulting on opposite flanks of the baker terrane similarly oriented contractional features are also present in late middle triassic to early late jurassic i e oxfordian stage ca 159 ma sedimentary rocks of the john day and huntington areas of northeast oregon radiometric age constraints from youngest detrital zircons in deformed sedimentary rocks and crystallization ages of postkinematic plutons which intrude the deformation zones limit deformation to between ca 159 and ca 154 ma we suggest that the widespread approximately n s directed contractional features in the blue mountains province record a short lived intense early late jurassic deformational event and preserve an example of upper crustal strain localization associated with terminal arc arc collision between the olds ferry and wallowa island arc terranes the age interval of deformation in the blue mountains province is younger than middle jurassic deformation in the canadian cordillera and klamath mountains siskiyou orogeny and predates classic nevadan orogenesis

mid cretaceous transtension in the canadian cordillera evidence from the rocky ridge volcanics of the skeena group the age relations geochemistry and sedimentology of the rocky ridge formation of the skeena group are used to test competing tectonic reconstructions for the mid cretaceous canadian cordillera as well as the timing and location of the accretion of the insular superterrane pollen and macrofossil assemblages indicate that these intrabasinal basalts were erupted along the southern margin of the bowser basin in the early albian to early cenomanian single crystal fusion and step heating 40ar 39ar dating of hornblendes in one basalt flow from the uppermost part of the formation yielded middle cenomanian ages of 94 3 0 4 95 6 1 6 and 95 0 1 6 ma vesicular basalt flows interbedded with crystal rich tuff breccias contain evidence for hot emplacement as pyroclastic flows individual eruptive centers are identified by their proximal facies paleoflow indicators within the lava flows paleoflow indicators within interbedded volcaniclastic fluvial deposits geochemical differences and geographic isolation of volcanic deposits major and trace element geochemistry from 20 sampled lava flows indicates an alkali basalt composition for the volcanics the basalts of the northern rocky ridge volcanic center show enrichment of light rare earth and large ion lithophile elements with strong negative nb ta anomalies whereas the basalts of the southern tahtsa lake volcanic center show depletion to slight enrichment of light rare earth elements slight enrichment of large ion lithophile elements with minimal negative nb ta anomalies the geochemistry combined with paleogeographic and regional tectonic reconstruction suggests a continental arc setting with intraarc extension the presence of deeper marine facies to the west and the lack of a western sediment source in the skeena group indicate that the technically active insular superterrane was not west of the study area during mid cretaceous time thus we reconsider the omineca belt as the main axis of a mid cretaceous continental arc placing the intermontane superterrane in the intraarc to forearc position with the rocky ridge volcanics erupted along the forearc side of the omineca arc coeval regional strike slip faulting and reconstructed oblique plate convergence suggest a transtensional setting for rocky ridge intraarc extension an electronic supplement of tables a1 a2 may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type exit to leave the system paper 95tc03496 mid cretaceous transtension in the canadian cordillera evidence from the rocky ridge volcanics of the skeena group kari n bassett and karen l kleinspehn diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

origin and diagenesis of polyphosphate in lake sediments a 31pߚnmr study polyphosphate poly p was detected with the use of 31 p nuclear magnetic resonance nmr spectroscopy in sediments from a large variety of lakes with different trophic state and morphometry in the top 0 5 cm of sediment poly p was 1 5 to 11 4 of total p nonreactive phosphorus nrp in the naoh fraction often classified as organically bound phosphate was up to 46 inorganic poly p in some surface sediments the poly p content equalled the iron fixed phosphorus determined by chemical phosphorus fractionation sediments were probably supplied with poly p by sedimentation because there were substantial amounts of poly p in plankton and settling seston as demonstrated with sediments of lake petersdorf benthic organisms can also contribute to the formation of poly p up to 0 11 mg p g dry weight 21 under favorable aerobic conditions poly p is more rapidly transformed into single orthophosphate during diagenesis than other inorganic and organic p species the transformation of organic p compounds and poly p can contribute significantly to the release of p during diagenesis and should be considered along with the reductive dissolution of p sorbed to iron oxihydroxides

topography effect at the critical sv wave incidence possible explanation of damage pattern by the whittier narrows california earthquake of 1 october 1987 abstract buildings damaged by the whittier narrows california earthquake of 1 october 1987 were concentrated in several areas most of which were located 8 to 10 km from the epicenter corresponding to the critical incidence for sv waves and were near topographic irregularities such as the northern part of whittier just south of puente hills the purpose of this study is to show the possibility that this anomalous damage pattern is due to the amplification by the topographic irregularity when sv waves are near critical incidence first we examined the accelerograms obtained at the usgs station 7215 bright ave nearest to downtown whittier and conclude that the dominantly eastwest motion observed at the station is due to the influence of the building in which accelerograms were recorded we next demonstrate that strong ground motions recorded by 12 stations in the epicentral area show a polarization direction pattern that is primarily sv type which is consistent with a simple thrust fault located at the hypocenter then we calculated the response of a two dimensional hill with the height 0 3 km and the width 2 4 km to 1 a plane sv wave with a nearly critical angle of incidence 2 a horizontal line force 3 a haskell type 2d dislocation source and 4 a bouchon type 2d multiple crack source the results show that the amplification due to the hill relative to the flat surface is more than 1 5 for all the source models since this amplification is nearly independent of the source type and spectrum we conclude that the combined effect of the topographic irregularity and critically incident sv waves might be responsible for the concentration of damage observed during the whittier narrows earthquake

crustal structure beneath taiwan using frequency band inversion of receiver function waveforms receiver function analysis is used to determine local crustal structure beneath taiwan we have performed preliminary data processing and polarization analysis for the selection of stations and events and to increase overall data quality receiver function analysis is then applied to data from the taiwan seismic network to obtain radial and transverse receiver functions due to the limited azimuthal coverage only the radial receiver functions are analyzed in terms of horizontally layered crustal structure for each station in order to improve convergence of the receiver function inversion frequency band inversion fbi is implemented in which an iterative inversion procedure with sequentially higher low pass corner frequencies is used to stabilize the waveform inversion frequency band inversion is applied to receiver functions at six stations of the taiwan seismic network initial 20 layer crustal models are inverted for using prior tomographic results for the initial models the resulting 20 1ayer models are then simplified to 4 to 5 layer models and input into an alternating depth and velocity frequency band inversion for the six stations investigated the resulting simplified models provide an average estimate of 38 km for the moho thickness surrounding the central range of taiwan also the individual station estimates compare well with the recent tomographic model of and the refraction results of rau and wu 1995 and the refraction results of ma and song 1997

near source ground motion along strike slip faults insights into magnitude saturation of pgv and pga empirical data suggest that peak ground acceleration pga and peak ground velocity pgv saturate as a function of magnitude for large magnitude ruptures close to the fault because data are sparse in the near source region of large magnitude events we have explored this question by simulating large magnitude strike slip earthquakes we use kinematic simulations to generate ground motion for a strike slip fault that has a large aspect ratio length width we consider both homogeneous or heterogeneous rupture models we find that close to the fault along strike profiles of pgv and pga increase to a maximum at a certain epicentral distance and then decrease to an asymptotic level beyond this distance critical factors for predicting ground motion are the position of an observer along strike the depth of the hypocenter below the top of the fault and the ratio of rupture velocity to shear wave velocity to understand the cause of the amplitude variation of along strike profiles of pgv and pga we use the isochrone method and the concept of the critical point to investigate how the geometry and kinematic parameters interact to produce the computed ground motion we construct a predictor based on the critical point that does well in predicting the position of the maximum of pgv and pga for stations close to the fault for heterogeneous rupture models we find that the behavior is more complex though the general observation that along strike profiles of pgv and pga increase to a maximum and then decrease still holds this has implications for empirical attenuation relationships that essentially average the ground motion for all stations along strike with the same distance to the fault

relationship between peak ground acceleration peak ground velocity and intensity in taiwan based on the strong motion data set from the 1999 chi chi taiwan earthquake and a shaking damage statistics database we investigated the correlations between strong ground motions and earthquake damage fatalities and building collapses through a regression analysis as a result the current earthquake intensity scale i t is placed on a more reliable instrumental basis this is necessary for the real time seismic monitoring operation in taiwan where programs for earthquake rapid reporting rrs and earthquake early warning ews are actively pursued it is found that the earthquake damage statistics give a much closer correlation with the peak ground velocity pgv than with the peak ground acceleration pga the empirical relationship between pgv and the intensity i t determined in this study can be expressed as i mathrm t 2 14 times mathrm log 10 mathrm pgv 1 89 this pgv based intensity is particularly useful in real time applications for damage prediction and assessment as the damage impact of high pgv is much more important for mid rise and high rise buildings that are characteristic of a modern society for smaller earthquakes m m

one minute after strong motion map effective epicenter and effective magnitude abstract this article reports the recent progress on real time seismic monitoring in taiwan particularly the real time strong motion monitoring by the taiwan central weather bureau9s telemetered seismic network cwbsn which is presently aiming at rapid reporting immediately after a large earthquake occurrence if rapid reporting can be achieved before the arrival of the strong shaking earthquake early warning will become possible cwbsn has achieved the generation of the intensity map epicenter and magnitude within 1 min of the occurrence of a large earthquake both rapid reporting and early warning are principally applied to large m 5 events the requirement of on scale waveform recording prompted cwbsn in 1995 to integrate strong motion sensors e g force balance accelerometers into its telemetered seismic monitoring system time domain recursive processing is applied to the multi channel incoming seismic signals by a group of networked personal computers to generate the intensity map from the isoseismal contours an effective epicenter is immediately identified that resides in the middle of the largest usually the 100 gal contour curve of the intensity map an effective magnitude is also defined that can be derived immediately from the surface area covered by the largest usually the 100 gal contour curve for a large event with a finite rupture surface the epicenter and magnitude so derived are more adequate estimates of the source location and of the strength of destruction the effective epicenter gives the center of the damage area it stands in contrast with the conventional epicenter location which only gives the initial point of rupture nucleation the effective magnitude reflects more closely the earthquake damage potential instead of the classical magnitude definition that emphasizes the total energy release the cwbsn has achieved in obtaining the above crucial source information well within 1 min this time can further be reduced to better than 30 sec as illustrated by the example in this article showing that earthquake early warning is indeed an achievable goal the rapid reporting and early warning information is electronically transmitted to users to allow rapid response actions with or without further human intervention

mineralization pathways in lake sediments with different oxygen and organic carbon supply the intensity and pathways of mineralization of sedimentary organic matter were investigated in eutrophic lake zug switzerland in a depth transect 25 180 m from oxic to anoxic bottom water we recorded in situ sediment pore water concentration profiles of o2 n o and nh z with a benthic lander system equipped with both oxygen and ion selective electrodes anaerobic sedimentary mineralization ranged from 13 1 to 34 9 mmol carbon c m22 d21 and increased linearly with water depth as determined from the nh z flux rates in the anoxic pore water and the molar c nitrogen n ratio of the surface sediment a parallel increase of the total organic carbon concentration of the sediment was attributed to lateral transfer of resuspended sedimentary matter denitrification was estimated from nitrate profiles and contributed only 1 5 3 2 to the total organic carbon mineralization at any water depth aerobic respiration and oxidation of reduced compounds were calculated from o2 microprofiles and pore water data of dissolved mn ii fe ii s ii and ch4 when the o2 concentration exceeded 0 15 mmol l 21 in the sediment overlying water 41 58 or 12 4 18 1 mmol c m 22 d 21 was mineralized aerobically whereas at lower concentrations 0 04 mmol l21 92 of organic carbon was mineralized anaerobically total benthic mineralization of organic carbon was 26 9 34 9 mmol c m22 d21 a budget including particulate as well as dissolved reduced compounds in the sediment indicated that 95 of the anaerobic mineralization was due to methanogenesis oxidation of ch4 consumed 39 56 of the o2 at the sediment water interface oxygen exposure times for these sediments were estimated to be on the order of weeks to months these time spans are too short to change the reactivity spectrum of sedimentary organic matter

influence of water column anoxia on the elemental fractionation of carbon and phosphorus during sediment diagenesis abstract organic carbon oxidation and benthic total phosphorus flux measurements from sites covering a range of bottom water oxygen concentrations have been compiled the data show that p regeneration relative to carbon oxidation is much more extensive in sediments overlain by oxygen depleted waters these results are consistent with studies showing that low oxygen bottom water concentrations correlate with reduced total phosphorus burial efficiencies and enhanced organic carbon burial efficiencies based on these observations a positive feedback is proposed between water column anoxia enhanced benthic phosphorus regeneration and marine productivity this feedback may help explain the widespread accumulation of organic rich marine sediments from anoxic waters observed in the geologic record

toward earthquake early warning in northern california 1 earthquake early warning systems are an approach to earthquake hazard mitigation which takes advantage of the rapid availability of earthquake information to quantify the hazard associated with an earthquake and issue a prediction of impending ground motion prior to its arrival in populated or otherwise sensitive areas one such method earthquake alarm systems elarms has been under development in southern california and more recently in northern california event magnitude is estimated using the peak amplitude and the maximum predominant period of the initial p wave elarms incorporates ground motion prediction equations and algorithms from shakemap for prediction of ground motions in advance of the s wave arrival the first peak ground motion estimates are available 1 s after the first p wave trigger and are updated each second thereafter for the duration of the event the elarms methodology has been calibrated using 43 events ranging in size from ml 3 0 to mw 7 1 that occurred in northern california since 2001 we present the results of this calibration as well as the first implementation of elarms in an automated noninteractive setting and the results of 8 months of noninteractive operation in northern california between february and september 2006 elarms successfully processed 75 events between md 2 86 to mw 5 0 we find that the elarms methodology processed these events reliably and accurately in the noninteractive setting the median warning time afforded by this method is 49 s at the major population centers of the bay area for these events the magnitude estimate is within an average of 0 5 units of the network derived magnitude and the ground motion prediction from elarms is within an average of 0 1 units of the observed modified mercalli intensity

upper triassic takla group volcanic rocks stikine terrane north central british columbia geochemistry petrogenesis and tectonic implications the upper triassic takla group volcano sedimentary assemblage is part of the stikine terrane of the intermontane belt in the canadian cordillera and covers an area of more than 30 000 km2 in a belt up to 50 km wide and more than 800 km long in the mcconnell creek area of north central british columbia the assemblage consists of plagioclase clinopyroxene phyric dominantly basaltic to andesitic flows and pyroclastic rocks interlayered with volcanogenic sedimentary rocks compositionally the volcanic rocks are intermediate between tholeiitic and calc alkaline their mantle normalized trace element patterns are characterized by a moderate large ion lithophile element enrichment and nb and ti depletion suggesting that magmatism occurred in a volcanic arc setting flat heavy rare earth element chondrite normalized patterns with la yb n ratios from 2 to 4 5 suggest that the parent magma was produced by mantle melting in the spinel stability field the low sr isotopic ratios 87sr 86sri approximately equa

evidence for enhanced phosphorus regeneration from marine sediments overlain by oxygen depleted waters phosphorus regeneration and burial fluxes determined from in situ benthic flux chamber and solid phase measurements at sites on the californian continental margin peruvian continental slope north carolina continental slope and from the santa monica basin california are reported comparison of these sites indicates that o2 depleted bottomwaters enhance p regeneration from sediments diminishing overall phosphorus burial efficiency based on these observations a positive feedback linking ocean anoxia enhanced benthic phosphorus regeneration and marine productivity is proposed on shorter timescales these results also suggest that o2 depletion in coastal regions caused by eutrophication may enhance p regeneration from sediments thereby providing additional p necessary for increased biological productivity

seismic tomography of taiwan improved constraints from a dense network of strong motion stations in this study a large collection of 41 141 s p times from the untapped records of the taiwan strong motion instrumentation program tsmip network is combined with the p and s wave arrival times from the taiwan central weather bureau seismic network cwbsn to image the v p and v p v s structures beneath taiwan the records from the 680 tsmip stations throughout taiwan in the past 15 years enhance the path coverage and the resolution in the tomography inversions tremendously our result for the v p structure largely confirms previous studies but brings better constraint on the v p v s structure the colliding luzon volcanic arc is characterized by a belt of high v p and high v p v s with high seismicity that includes the offshore islands of lutao and lanyu and the coastal ranges in eastern taiwan at the depth between about 13 and 25 km this high v p v s belt can be traced to the subduction zone in the region between hualian and ilan in the deeper portion the shallow portions of the southwestern coastal plain and the pingtung region are also characterized by a belt of high v p v s with lower seismicity most of the events occurred at the base of the high v p v s zones we suggest that material strength in those regions may be too low to accumulate stress which may indicate water saturated young sediments finally the central range region is characterized by a low v p v s belt