coulomb stress changes following the 2012 mw 7 8 haida gwaii canada earthquake implications for seismic hazard this article examines spatial changes to the local stress field resulting from the 28 october 2012 m w 7 8 haida gwaii earthquake off the west coast of moresby island british columbia this event occurred on a northeast dipping potentially blind thrust fault rather than on the subvertical queen charlotte fault qcf that represents the pacific north american plate boundary this was the largest earthquake along the canadian portion of this plate boundary since the 1949 m s 8 1 queen charlotte earthquake the u s geological survey coulomb software is used to quantitatively estimate the effect of the mainshock on the background stress field the known aftershock nodal planes and the nearby qcf we use two different mainshock finite fault models both of which are seismologically derived by lay et al 2013 and hayes 2013 separately and subsequently adapted by k wang to account for the motion detected at four nearby global positioning system stations see nykolaishen et al 2015 for more information we also use the best located set of aftershocks with information provided by a temporary array of ocean bottom seismometers results indicate an apparent clustering of aftershocks slightly seaward of the main thrust which is consistent with the modeled zone of promoted normal failure likely related to extension in the footwall using existing models we found a high number of aftershocks to be consistent with triggering by the mainshock suggesting that static stress is a dominant control in the months following a large earthquake in this area further we find loading greater than the triggering threshold on the qcf in an area interpreted as a seismic gap this work improves understanding of the evolving seismic hazard along the queen charlotte margin and tests the usefulness of coulomb modeling in this complex tectonic environment online material figures of focal mechanisms and maximum coulomb stress change and table of aftershock moment tensor parameters

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

oblique slip on the puysegur subduction interface in the 2009 july mw 7 8 dusky sound earthquake from gps and insar observations implications for the tectonics of southwestern new zealand summary the mw 7 8 dusky sound earthquake of 2009 july 15 was the largest earthquake in new zealand in the past 80 yr and is the only major subduction interface earthquake in the new zealand historical record we have estimated the coseismic and early post seismic slip distribution in the earthquake by inversion of gps and differential interferometric synthetic aperture radar dinsar observations we show that slip during the earthquake was highly obliqueandessentiallyintheaustralia pacificrelativeplatemotiondirection failureoccurred onaca 80by50kmpatchofthesubductioninterfacewithmaximumslip5 6m inthisregion the offshore alpine fault carries up to 30 mm yr 1 of slip before terminating at resolution ridge near the southern end of the 2009 slip patch the southernmost part of the alpine fault trace lies near the up dip end of the 2009 slip patch and the fault probably exists only within the crust of the over riding plate in this region terminating at shallow depth where it meets the subduction interface there is no evidence for rupture of the alpine fault during the 2009 event however coulomb stress changes from the subduction earthquake have brought this section of the alpine fault closer to failure in contrast to many subduction zones undergoing oblique subduction where the slip in major earthquakes is partitioned into more or less pure thrustearthquakesonthesubductioninterfaceandstrike slipearthquakesinthebackarc thisis a case where the majority of the subduction interface slip is not partitioned with only a shallow convergence zone west of the strike slip alpine fault undergoing contraction approximately normal to subduction zone strike north of the 2009 earthquake region the alpine fault lies further east relative to the subduction interface and partitioning between strike slip on the alpine fault and trench normal thrusting on the subduction interface takes place in a more typical fashion our results provide the first clear demonstration of non partitioned oblique slip between the australian and pacific plates offshore of southern new zealand

freshwater impacts recorded in tetraunsaturated alkenones and alkenone sea surface temperatures from the okhotsk sea across millennial scale cycles 1 we present records of phytoplankton produced alkenones down a long piston core which reveal changes of sea surface temperature sst and sea surface salinity sss in the southwestern okhotsk sea over the past 120 ka between 20 and 60 ka b p alkenone derived temperatures typically increased by 6 c 8 c from periods corresponding within a few hundred years to stadials to those corresponding to interstadials recorded in greenland ice cores the abundance of c37 4 alkenone relative to total c37 alkenones percent c37 4 a possible proxy for salinity indicated that during most low sss was associated with high sst the warm freshwater events might be related to 1 a decline in the supply of saline water entering the okhotsk sea through the soya strait 2 strengthening of the freshwater supply from the amur river and precipitation over the okhotsk sea associated mainly with increased asian summer monsoon activity and 3 the effect of melting sea ice these findings increase our understanding of the close linkage between high and low latitudes in relation to climate change and the synchronicity of climate changes within a few centuries between the pacific and the atlantic sides of the northern hemisphere

hydrographic biases in global coupled climate models and their relation to the meridional overturning circulation comparison of the volumetric s distribution of models participating in the climate model intercomparison project 3 cmip3 indicates that these models differ widely in their ability to represent the thermohaline properties of water masses relationships between features of the quasi equilibrium hydrographic mean state of these models and aspects of their overturning circulations are investigated this is achieved quantitatively with the help of seven diagnostic hydrographic stations these few stations were specifically selected to provide a minimalist schematic of the global water mass system relationships between hydrographic conditions in the north atlantic measured with a subset of these stations suggest that hydrographic properties in the subpolar north atlantic are set by the circulation field of each model pointing towards deficiencies in the models ability to resolve the gulf stream north atlantic current system as a major limitation since diapycnal mixing and viscosity parameterizations differ across cmip3 models and exert a strong control on the overturning it is likely that these architectural differences ultimately explain the main across model differences in overturning circulation temperature and salinity in the north atlantic the analysis of properties across the quasi equilibrium states of the cmip3 models agrees with previously reported relationships between meridional steric height gradients or horizontal density contrasts at depth and the strength of the deep water cell robust relationships are also found in the southern ocean linking measures of vertical stratification with the strength of the abyssal circulations across the cmip3 models consistent correlations between aspects of the quasi equilibrium hydrography in the southern ocean and the sensitivity of the abyssal cell to increasing radiative forcing by 2100 were found using these relations in conjunction with modern hydrographic observations to interpolate the fate of the abyssal cell suggests that the southern abyssal cell may decrease by roughly 20 by the end of the century similar systematic relationships between the quasi equilibrium hydrographic states of the models and the sensitivity of their atlantic deep water cell could not be found

retreating alpine glaciers increased melt rates due to accumulation of dust vadret da morteratsch switzerland the automatic weather station aws on the snout of the vadret da morteratsch switzerland has delivered a unique 12 year meteorological dataset from the ablation zone of a temperate glacier this dataset can be used to study multi annual trends in the character of the surface energy budget since 2003 there has been a substantial darkening of the glacier tongue due to the accumulation of mineral and biogenic dust the typical surface albedo in summer has dropped from 0 32 to 0 15 we have analysed the implications of the lowered albedo for the energy balance and the annual ablation for the 4 year period 2003 06 the decreased albedo caused an additional removal of about 3 5 m of ice calculations with an energy balance model show that the same increase in ablation is obtained by keeping the ice albedo fixed to 0 32 and increasing the air temperature by 1 7 k our analysis confirms that for retreating glaciers the deposition of dust from exposed side moraines on the glacier surface constitutes an important feedback mechanism the mineral dust stimulates the growth of algae lowers the surface albedo enhances the melt rates and thereby facilitates the further retreat of the glacier snout

what is the thermohaline circulation the term thermohaline circulation is widely used in the context of past and future climate change in his perspective wunsch argues that there are many different and inconsistent definitions for this term he defines ocean circulation in terms of mass fluxes which are largely driven by surface forces such as wind and tides and argues that thermohaline circulation should only refer to the separate transport of heat and salinity in the ocean

spatiotemporal distribution of events during the first week of the 2012 haida gwaii aftershock sequence abstract we systematically relocated the 2012 haida gwaii aftershock sequence by re examining continuous seismic waveforms of the canadian national seismographic network cnsn because of the sparse station density in the source area and the offshore location of the majority of events precise determination of hypocenters is extremely challenging constraints on the back azimuth and incident angle of ray paths were derived from the cross correlation of three component waveforms and incorporated into the locating process to improve the results we located 1228 aftershocks for the first week after the mainshock effectively double the size of the cnsn routine earthquake catalog the distribution of aftershocks tends to form two linear trends roughly parallel to the strike of the plate margin in the northwest southeast direction the trend located updip from the mainshock within the subducting pacific plate appears to have three clusters spanning a lateral distance of 80 km the other trend coincides with the surface trace of the queen charlotte fault qcf spanning the northern two thirds of the main rupture zone the overall area of aftershock distribution is 120 km 40 km aftershocks overlap the southern part of the estimated rupture zone of the 1949 earthquake with no activity in the seismic gap farther to the south therefore it is likely that the 2012 earthquake only partially released the accumulated stress on the strike slip transform fault system in this scenario the possibility of a major strike slip earthquake along the southernmost part of the qcf should not be ignored online material table of source parameters of relocated mainshock and aftershocks

impacts of the october 2012 magnitude 7 8 earthquake near haida gwaii canada on 27 october 2012 a magnitude m w 7 8 earthquake occurred in the sparsely populated region of haida gwaii british columbia canada formerly called the queen charlotte islands this was the second largest recorded earthquake in canadian history it was felt throughout british columbia and as far away as the yukon alberta and montana roughly 1600 km from the epicenter in some locations notably on haida gwaii the perceivable shaking lasted 1 5 2 min with very strong shaking for about 30 s strong ground motions recorded at three locations in the region reached a maximum horizontal acceleration of 0 2 g fortunately this earthquake resulted in very limited damage partly because of the relatively large distance more than 60 km between population centers and the fault rupture and partly because of seismic resistance of the generally low wood frame construction found on the islands we examine the various physical effects from the shaking e g tsunami landslides building damage loss of hot springs cataloged by field crews and reported by the inhabitants of haida gwaii and the surrounding regions these will serve as a guide toward the potential impact from future large earthquakes on the various haida gwaii communities through a community decimal intensity evaluation of people s accounts it was revealed that although intensities were close to expected near the source zone regional intensities were lower than predicted by the conventional western north america theoretical relation finally the october 2012 earthquake may be used as a scenario event for moderate subduction earthquakes in other more populated areas of british columbia canada and the world online material abridged did you feel it reports

evidence of wadati benioff zone triggering following the mw 7 9 little sitkin alaska intermediate depth earthquake of 23 june 2014 the 23 june 2014 mw 7 9 earthquake that struck the rat islands region of alaska was a rare intermediate depth event followed by a vigorous aftershock sequence the earthquake s location within a regional network has allowed us to study it in rich detail double difference relocations of aftershocks and static stress modeling reveal some intriguing features most aftershocks are not located on the main shock rupture plane but are concentrated in the adjacent wadati benioff zone in areas of increased stress further a secondary plane of seismicity aligns well with a moderately dipping nodal plane reported by the global centroid moment tensor project and the separation of these locations and the main shock hypocenter from the slab indicates that the main shock ruptured into the oceanic mantle

rupture process of the 2012 mw 7 8 haida gwaii earthquake from an empirical green s function method abstract this article examines rupture processes of the 28 october 2012 m w 7 8 haida gwaii earthquake off the coast of british columbia canada using an empirical green s function egf technique the haida gwaii earthquake was the largest event along the canadian portion of the pacific north american plate boundary since the m s 8 1 queen charlotte earthquake of 1949 it occurred along a potentially blind thrust fault dipping gently to the northeast rather than the main subvertical queen charlotte fault surface waveforms from a 2001 m w 6 3 event located only 15 km from the 2012 epicenter and with similar mechanism are used as an egf and deconvolved from those of the 2012 mainshock the resulting source time functions contain minimal path effects focal mechanism effects and instrument response so the waveforms display only properties of the 2012 mainshock rupture itself by examining azimuthal variations in these source time functions we constrain parameters such as average rupture velocity extent and directivity in addition information is obtained about the possible existence of major subevents and their relative locations results indicate two subevents within this rupture the first 12 km south and updip of the epicenter and the second approximately 28 km from the first along a heading parallel to the queen charlotte terrace 323 overall the rupture front propagated roughly 50 km at an azimuth of 308 5 this evidence for directivity to the northwest is important given that earthquakes with strong directivity such as the 2002 m w 7 9 denali earthquake have been shown to be capable of triggering earthquakes thousands of kilometers away in this case we suggest that northwest directivity of this earthquake is responsible for amplification of surface waves observed at seismic stations in alaska gomberg 2013 and may provide a potential link between this 2012 event and the 2013 craig alaska earthquake online material figure of all relative source time functions used in directivity analysis

bering strait throughflow and the thermohaline circulation received 25 august 2005 revised 10 november 2005 accepted 14 november 2005 published 21 december 2005 1 in this study we employ a global coupled climate model to show that the bering strait is important to the variations of the thermohaline circulation three experiments are analyzed a present day control run and two freshwater hosing runs results show that as the thermohaline circulation weakens due to freshwater forcing in the northern north atlantic the bering strait throughflow weakens and even reverses its direction and the export of the arctic freshwater into the northern north atlantic is reduced or the arctic even takes freshwater from the latter thus helping the thermohaline circulation to recover relatively quickly after the end of the freshwater hosing citation hu a and g a meehl 2005 bering strait throughflow and the thermohaline circulation geophys res lett 32 l24610 doi 10 1029 2005gl024424

transition from locked to creeping subduction in the shumagin region alaska 1 gps velocities from the alaska peninsula are modeled to determine the extent of locking on the alaska aleutian subduction interface the observations which span from the semidi islands to sanak island encompass the 1938 mw 8 3 rupture zone and the transition into the shumagin gap model parameters are optimized using a simulated annealing method coupling variation along strike of the plate interface show a nearly fully locked 90 subduction zone at the semidi islands decreasing to about 30 locked at the shumagin islands and freely slipping to the west of the shumagins independent rupture of the shumagin segment could produce repeated mw 7 6 earthquakes unless a significant fraction of the slip on the interface occurs as afterslip following large earthquakes southwest directed velocities at most of the sites may be attributed to clockwise rotation of a bering block

causes of a fresher colder northern north atlantic in late 20th century in a coupled model abstract observational evidence indicates that in the northern north atlantic especially in the labrador sea almost the whole column of the ocean water is fresher and colder in late 20th century than in 1950 1960s here we analyze a four member ensemble of the 20th century simulations from a coupled climate model to examine the possible causes for these observed changes the model simulations resemble the observed changes in the northern north atlantic the simulated results show that a decreased meridional freshwater divergence and an increased meridional heat divergence associated with a weaker thermohaline circulation in the north atlantic are the primary causes for the freshening and cooling in the northern north atlantic the increased precipitation less evaporation tends to enforce the freshening but the reduced sea ice flux into this region tends to weaken it on the other hand the surface warming induced by a higher atmospheric co2 concentration tends to heat up the northern north atlantic but is overcome by the cooling from increased meridional heat divergence

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

modeling the effect of freshwater pulses on the early holocene climate the influence of high frequency climate variability freshwater 4 67 10 14 m 3 into the labrador sea at three different constant rates 1 5 sv 1 sv 1 10 6 m 3 s 1 i n 10 years 0 75 sv in 20 years and 0 3 sv in 50 years for each rate five ensemble experiments have been performed varying in initial conditions the freshwater pulses produce a weakening of the thermohaline circulation the perturbed state is in agreement with proxy evidence for the 8 2 ka event two types of recovery of the thermohaline circulation occurred differing in time scale 1 200 years and 2 200 years in the experiments with 10 year and 20 year pulses both types of recovery were observed this suggests that the model response is unpredictable in the range of parameters studied here it is hypothesized that the unpredictability is associated with annual to decadal climate variability our results demonstrate that several types of recovery may exist with the same kind of perturbation the interpretation of events observed in proxy data may be thus more complex than realized until now since the magnitude and duration of climatic events caused by freshwater pulses is likely to depend strongly on nonlinear dynamics inside the coupled atmosphere sea ice ocean system index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4255 oceanography general numerical modeling 4532 oceanography physical general circulation 4215 oceanography general climate and interannual variability 3309 9325 information related to geographic region atlantic ocean keywords holocene thermohaline circulation predictability meltwater coupled climate model

introduction to the special issue on the 2012 haida gwaii and 2013 craig earthquakes at the pacific north america plate boundary british columbia and alaska the 27 october 2012 m w 7 8 haida gwaii thrust earthquake and the 5 january 2013 m w 7 5 craig strike slip earthquake are the focus of this special issue they occurred along the transform boundary between the pacific and north american plates fig 1 the most identifiable feature of the plate boundary the strike slip queen charlotte fault might be viewed as typical of continent ocean transform faults because it separates the continental crust of the north american plate from oceanic crust of the pacific plate for most of its length however the current relative plate motion of about 5 cm yr is highly oblique to the queen charlotte fault causing a transpressive plate boundary in the region figure 1 location map for the 2012 m w 7 8 haida gwaii and 2013 m w 7 5 craig earthquakes which occurred on the pacific north american plate boundary approximate rupture zones for the two events are shown in yellow whereas other significant events on the plate boundary are depicted by their aftershock zones red 1949 queen charlotte fault orange 1970 cape st james blue 1972 sitka the epicentral positions are given by stars and the focal mechanisms are plotted in a lower hemisphere projection the black arrows indicate pacific north american relative motion the queen charlotte terrace is located west of the queen charlotte fault and is interpreted to be a narrow accretionary prism inset the earthquakes occurred offshore the western margin of northern north america barbs indicate subduction of the juan de fuca jdf plate and smaller plates beneath north america at the cascadia subduction zone csz transform plate boundaries between continental and oceanic crust are often depicted as both simple and common in reality such continent ocean transform boundaries are neither for example the san andreas fault in california carries continental crustal fragments along with it on the seaward side

detecting thermohaline circulation changes from ocean properties in a coupled model 1 significant changes of the thermohaline circulation thc are likely to cause abrupt climate change here we intend to find a simple measure to detect changes in thc through examining several factors proposed to control the thc variations using a coupled climate model these factors are equatorial south atlantic upper ocean temperature southern ocean freshening inter basin sea surface salinity contrast and meridional steric height gradient three experiments are analyzed a present day control run a freshwater hosing run and a 1 co2 run results show that if freshwater flux is the primary cause all examined factors can predict the thc changes if both thermal and haline forcings are involved only the atlantic meridional steric height gradient gives a consistent measure of the thc variations a new result presented here is that the inter basin sea surface temperature contrast between north atlantic and north pacific is found to be an indicator of thc changes

the pacific atlantic seesaw and the bering strait 1 paleo proxy data and previous modeling studies both indicate that the massive discharge of icebergs into the north atlantic may have led to a nearly collapsed atlantic meridional overturning circulation amoc resulting in a seesaw like climate change between the north pacific and north atlantic with a warming in the former and a cooling in the latter here by using a fully coupled climate model we show that this pacific atlantic seesaw associated with changes of the amoc can only occur when the bering strait is closed as this strait is closed the oceanic communication between the north pacific and atlantic is cut off when amoc collapses the north atlantic becomes cooler but the north pacific becomes warmer due to the buildup of the pacific meridional overturning circulation which transports more warm and salty subtropical water into the north pacific leading to seesaw like climate changes in the two ocean basins

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

constraining turbulent heat flux parameterization over a temperate maritime glacier in new zealand the turbulent sensible and latent heat fluxes are important components of the surface energy balance over glaciers in the southern alps of new zealand contributing over half the energy available for ablation during large melt events to calculate these terms confidently in glacier mass balance models it is essential to use appropriate parameterizations for surface roughness and atmospheric stability eddy covariance measurements at brewster glacier were obtained over an ice surface to help facilitate an assessment of the calculation of the turbulent heat fluxes the roughness length for momentum was found to be 3 6 x 10 3 m while the roughness lengths for temperature and humidity were two orders of magnitude smaller in agreement with surface renewal theory a monte carlo approach was used to assess the uncertainty in turbulent heat fluxes calculated using the bulk aerodynamic method it was found that input data and roughness length uncertainty could not explain underestimates of observed sensible heat fluxes during periods with low wind speed and large temperature gradients during these periods a katabatic wind speed maximum alters the formulation of the turbulent exchange coefficient to that typically observed in a neutral atmosphere and this has implications for glacier mass balance sensitivity

stress distribution along the fairweather queen charlotte transform fault system tectonic loading and coulomb stress transfer are modeled along the right lateral fairweather queen charlotte transform fault system using a three dimensional boundary element program the loading model includes slip below 12 km along the transform as well as motion of the pacific plate and it is consistent with most available global positioning system gps displacement rate data coulomb stress transfer is shown to have been a weak contributing factor in the failure of the southeastern sitka segment of the fairweather fault in 1972 hastening the occurrence of the earthquake by only about 8 months failure of the sitka segment was enhanced by a combination of cumulative loading from below 95 by slip of about 5 cm yr since 1848 by stress transfer about 1 from major earthquakes on straddling segments of the queen charlotte fault m 8 1 in 1949 and the fairweather fault m 7 8 in 1958 and by viscoelastic relaxation about 4 following the great 1964 alaska earthquake modeled by pollitz et al 1998 cumulative stress increases in excess of 7 mpa at a depth of 8 km are projected prior to the m 7 6 earthquake coulomb stress transferred by the rupture of the great m 9 2 alaska earthquake in 1964 bufe 2004a also hastened the occurrence of the 1972 event but only by a month or two continued tectonic loading over the last half century and stress transfer from the m 7 6 sitka event has resulted in restressing of the adjacent segments by about 3 mpa at 8 km depth the occurrence of a m 6 8 earthquake on the northwestern part of the queen charlotte fault on 28 june 2004 the largest since 1949 also suggests increased stress the cape st james segment of the fault immediately southeast of the 1949 queen charlotte rupture has accumulated about 6 mpa at 8 km through loading since 1900 and stress transfer in 1949 a continued rise in earthquake hazard is indicated for the alaska panhandle and queen charlotte islands region in the decades ahead as the potential for damaging earthquakes increases

measurement and parameterization of aerodynamic roughness length variations at haut glacier d arolla switzerland spatial and temporal variations in aerodynamic roughness length z0 on haut glacier d arolla switzerland during the 1993 and 1994 ablation seasons are described based on measure ments of surface microtopography the validity of the microtopographic z0 measurements is established through comparison with independent vertical wind profile z0 measurements over melting snow slush and ice the z0 variations are explained through correlation and regression analyses using independent measurements of meteorological and surface variables and parameterizations are developed to calculate z0 variations for use in surface energy balance melt models several independent variables successfully explain snow z0 variation through their correlation with increasing surface roughness caused by ablation hollow formation during snow melt non linear parameterizations based on either accumulated melt or accumulated daily maximum temperatures since the most recent snowfall explain over 80 of snow z0 variation the z0 following a fresh snowfall on an ice surface is parameterized based on relationships with the underlying ice z0 snow depth and accumulated daily maximum temperatures none of the independent variables were able to successfully explain ice z0 variation although further comparative studies are needed the results lend strong support to the microtopo graphic technique of measuring z0 over melting glacier surfaces

climate response to external sources of freshwater north atlantic versus the southern ocean abstract the response of an atmosphere ocean general circulation model aogcm to perturbations of freshwater fluxes across the sea surface in the north atlantic and southern ocean is investigated the purpose of this study is to investigate aspects of the so called bipolar seesaw where one hemisphere warms and the other cools and vice versa due to changes in the ocean meridional overturning the experimental design is idealized where 1 sv 1 sv 106 m3 s 1 of freshwater is added to the ocean surface for 100 model years and then removed in one case the freshwater perturbation is located in the atlantic ocean from 50 to 70 n in the second case it is located south of 60 s in the southern ocean in the case where the north atlantic surface waters are freshened the atlantic thermohaline circulation thc and associated northward oceanic heat transport weaken in the antarctic surface freshening case the atlantic thc is mainly unchanged with a slight weakening toward the end of the integration this w

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

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

response of thermohaline circulation to freshwater forcing under present day and lgm conditions responses of the thermohaline circulation thc to freshwater forcing hosing in the subpolar north atlantic ocean under present day and the last glacial maximum lgm conditions are investigated using the national center for atmospheric research community climate system model versions 2 and 3 three sets of simulations are analyzed with each set including a control run and a freshwater hosing run the first two sets are under present day conditions with an open and closed bering strait the third one is under lgm conditions which has a closed bering strait results show that the thc nearly collapses in all three hosing runs when the freshwater forcing is turned on the full recovery of the thc however is at least a century earlier in the open bering strait run than the closed bering strait and lgm runs this is because the excessive freshwater is diverged almost equally toward north and south from the subpolar north atlantic when the bering strait is open a significant portion of the freshwater flowing northward into the arctic exits into the north pacific via a reversed bering strait throughflow which accelerates the thc recovery when the bering strait is closed this arctic to pacific transport is absent and freshwater can only be removed through the southern end of the north atlantic together with the surface freshwater excess due to precipitation evaporation river runoff and melting ice in the closed bering strait experiments after the hosing the removal of the excessive freshwater takes longer and this slows the recovery of the thc although the background conditions are quite different between the present day closed bering strait run and the lgm run the thc responds to the freshwater forcing added in the north atlantic in a very similar manner

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

on the link between the two modes of the ocean thermohaline circulation and the formation of global scale water masses a close link between the formation of global scale water masses such as north atlantic deep water nadw and antarctic intermediate water aaiw and two stable modes of the thermohaline circulation thc is investigated in a coupled model in the upper 2 3 km of the atlantic the thc modes are characterized by meridional overturning circulations of opposite sign with either a dominance of the aaiw cell over the nadw cell off thc mode or vice versa on thc mode a transition between these thc modes is controlled by the relationship between the densities in the source regions of formation of aaiw and nadw water masses this is shown by applying a freshwater perturbation in the region of enhanced aaiw formation in the southern ocean to obtain a hysteresis loop of the nadw circulation transitions between the two modes of the thc occur when the densities in the source regions of aaiw and nadw become comparable to each other

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

ablation modeling and surface energy budget in the ablation zone of laohugou glacier no 12 western qilian mountains china glacier surface melting can be described using energy balance models we conducted a surface energy budget experiment to quantify surface energy fluxes and to identify factors affecting glacial melt in the ablation zone of laohugou glacier no 12 western qilian mountains the surface energy budget was calculated based on data from an automatic weather station and turbulent fluxes calculated using the bulk aerodynamic approach were corrected using measurements from an eddy covariance system simulated mass balances were validated by stake observations net shortwave radiation was the primary component of the surface energy balance 126 w m 2 followed by sensible heat flux net longwave radiation 45 w m 2 and latent heat flux 12 8 w m 2 represented heat sinks the bulk aerodynamic method underestimated sensible and latent heat fluxes by 3 4 and 1 2 w m 2 respectively the simulated total mass balance of 1703 mm w e exceeded the observed total by 90 mm w e daily positive accumulated temperature and low albedo were the main factors accelerating glacier melt an uncertainty assessment showed that mass balance was very sensitive to albedo and varied by 36 when albedo changed by 0 1

sensitivity of the thermohaline circulation to tropical and high latitude freshwater forcing during the last glacial interglacial cycle recent studies indicate that the tropical freshwater budget of the atlantic is modulated by changes in el nine southern oscillation enso if anomalies of the atlantic freshwater balance persist on the order of decades these might have a large influence on the north atlantic thermohaline circulation thc here we present a sensitivity study in which we use a model scenario for enso behavior during the last 120 kyr to force a simplified model of the thc with corresponding freshwater exchange between the tropical atlantic and pacific if the steady state strength of the north atlantic thc is similar to the present day its response to the forcing is of the order of 1 3 sv 1 sv 10 6 m 3 s 1 no mode changes of the thc are simulated for reasonable values of the coupling constant between freshwater exchange and enso if on the other hand the steady state overturning is significantly weaker a collapse of the thc occurs due to forcing from the tropics the modeled thc variation due to tropical freshwater perturbations are compared to those resulting from middle and high latitude freshwater forcing due to long term growth and decay of northern hemisphere ice sheets it is found that both forcings are of similar amplitude except during the deglaciation when high latitude forcing dominates a possible out of phase relationship between deep water formation in the north pacific and north atlantic is also explored

a comparison of the receiver structure beneath stations of the canadian national seismograph network three component broadband data from the recently deployed canadian national seismograph network provide a new opportunity to examine the structure of the crust and upper mantle beneath the canadian landmass receiver function analysis is an ideal method to use with this data set as it can provide constraints on the s velocity structure beneath each station of this seismograph network this analysis method is particularly useful in that it provides site specific information i e within 5 15 km of the station low velocity layers can be identified and it is possible to examine structure to upper mantle depths in this study receiver functions were computed for each of the 19 stations that made up the seismograph network in june 1994 five stations sampling a variety of tectonic environments including the appalachian orogen the canadian shield the western canadian sedimentary basin and the cascadia subduction zone were chosen for detailed modelling the results presented here are the first estimates of the s velocity structure beneath these five stations for those stations where comparisons can be made with seismic reflection and refraction results there is excellent agreement in eastern canada simple receiver functions and clear moho ps conversions at most stations indicate a relatively transparent crust and a moho depth of 40 45 km in northwestern canada moho ps phases indicate a crustal thickness of 33 38 km beneath inuvik northwest territories the moho is interpreted as two velocity steps separated in depth by 5 km and an upper mantle low velocity zone is near 47 km depth in western canada the data indicate a mid crustal low velocity zone beneath edmonton the moho of the subducting juan de fuca plate is interpreted at 52 krn depth beneath southern vancouver island several stations exhibiting complex receiver functions warrant further study they include stations at scheffewille quebec in the canadian shield deer lake newfoundland on the boundary of the grenville province and the appalachian orogen and yellowknife northwest territories at the intersection of the churchill and slave provinces and the western plains

the use of bulk and profile methods for determining surface heat fluxes in the presence of glacier winds a one dimensional second order closure model and in situ observations on a melting glacier surface are used to investigate the suitability of bulk and profile methods for determining turbulent fluxes in the presence of the katabatic wind speed maximum associated with glacier winds the results show that profile methods severely underestimate turbulent fluxes when a wind speed maximum is present the bulk method on the other hand only slightly overestimates the turbulent heat flux in the entire region below the wind speed maximum and is thus much more appropriate for use on sloping glacier surfaces where katabatic winds dominate and wind speed maxima are just a few meters above the surface

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

aseismic zone and earthquake segmentation associated with a deep subducted seamount in sumatra the subduction of topographic features has been linked both to earthquake generation and the segmentation of faults seismic imaging reveals a seamount subducted to 40 km depth below sumatra that is associated with an aseismic zone suggesting that at this location the seamount reduces coupling of the slab and overriding plate

paleocean circulation during the last deglaciation a bipolar seesaw hughen et al 1998 have documented that during the first 200 years of younger dryas time the 14c content of atmospheric co2 increased by 50 and that during the remainder of this 1200 year duration cold event it steadily declined the initial increase in 14c c was likely the result of a reduction in the atlantic s conveyor circulation however were the subsequent radiocarbon decline due to the rejuvenation of this potent heat pump then it is difficult to understand why the climate conditions in the northern atlantic basin remained cold throughout the younger dryas modeling exercises by stocker and wright 1996 mikolajewicz 1998 and schiller et al 1998 show that if the conveyor is terminated the transfer of radiocarbon into the deep sea shifts to the southern ocean thereby stabilizing the atmospheric 14c c ratio paleoclimatic evidence from the antarctic continent suggests that this model based scenario might have been played out in the real world while the younger dryas cooling has been documented in many places around the world including new zealand denton and hendy 1994 sowers and bender 1995 using their 18o in o2 based correlation between the ice core 18o in ice records for antarctica and greenland have demonstrated that in antarctica the younger dryas was a time of maximum warming the point of this paper is that the steep rise in 18o rise in antarctic ice which commenced close to the onset of the younger dryas might have been caused by heat released to the atmosphere in response to an increase in deep sea ventilation in the southern ocean

atlantic deep circulation controlled by freshening in the southern ocean received 5 may 2003 accepted 18 june 2003 published 24 july 2003 1 numerical simulations with a climate model of intermediate complexity are used to illustrate the effect of meridional moisture transport in the southern hemisphere mid latitudes on the meridional overturning circulation moc and heat transport in the atlantic a novel feature of the model is a diapycnal mixing scheme in the ocean which ensures low values of diffusivity about 10 5 m 2 s 1 in the pycnocline it is shown that the atlantic moc northward oceanic heat transport and the associated air sea heat flux anomalies are all proportional to the southward moisturetransport from subtropical tosubpolarregions inthe southern hemisphere the effect of the intensified ocean circulation on sea surface temperature and salinity is also illustrated index terms 4532 oceanography physical general circulation 4516 oceanography physical eastern boundary currents 4283 oceanography general water masses citation saenko o a a j weaver and a schmittner atlantic deep circulation controlled by freshening in the southern ocean geophys res lett 30 14 1754 doi 10 1029 2003gl017681 2003

the atlantic pacific seesaw abstract a global oceanic teleconnection of salinity meridional overturning circulation moc and climate of the north atlantic and north pacific is proposed simulations with a global climate model show that an extraction of freshwater from the pacific results not only in an increase of salinity there but also in a decrease of salinity in the atlantic as a result a pacific moc develops while the atlantic moc collapses without freshwater perturbation in the atlantic similarly an input of freshwater to the atlantic leads not only to a decrease of salinity there but also to an increase of salinity in the pacific the atlantic moc collapses whereas the pacific moc develops without freshwater perturbation in the pacific the mechanism behind this antiphase atlantic pacific relationship is the positive feedback between ocean circulation and salinity contrasts originally proposed by stommel to operate between low and high latitudes here the authors show that the same mechanism operates on the atlan

analysis of meteorological data and the surface energy balance of mccall glacier alaska usa we report on analysis of meteorological data for the period 27 may 20 august 2004 from two automatic weather stations on mccall glacier alaska usa aimed at studying the relationship between climate and ablation one station is located on a mountain ridge and the other in the ablation area where we also analyzed the energy balance the weather station on the glacier measured an average temperature of 5 38c at 2m height above surface and wind speed of 3 1ms 1 at 3m height a sonic height ranger and ablation stakes indicate a specific mass balance of 1 94 0 09mw e between 15 june and 20 august the specific mass balance calculated from the surface energy balance 2 06 0 18mw e is in close correspondence to this the latter is the sum of 0 12mw e of snowfall 0 003mw e of deposition and 2 18mw e of melt net radiation contributes 74 of the melt energy compared to ablation measurements in the early 1970s summer ablation was large this increase is explained by a combination of a relatively higher net radiation a lower albedo and larger turbulent heat fluxes that led to more energy being available for melting no single meteorological variable can be isolated as being the principal reason for the high ablation however the lower ice albedo 0 19 is possibly due to ash deposits from forest fires

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

melt and surface sublimation across a glacier in a dry environment distributed energy balance modelling of juncal norte glacier chile previous estimates of melt and surface sublimation on glaciers of the subtropical semiarid andes 29 34 s have been obtained at few specific locations but it is not clear how ablation components vary across the entire extent of a glacier in this dry environment here we simulate the distributed energy and mass balance of juncal norte glacier 33 s during a 2 month summer period forcing fields of near surface air temperature and wind speed are generated using two methods accounting for the main physical processes that shape their spatial variations simulated meteorological variables and ablation agree well with observations on the glacier tongue and reveal complex patterns of energy and mass fluxes ablation decreases from 70 mm w e d 1 at the low albedo glacier terminus 3000 m where almost 100 of total ablation corresponds to melt to 75 of total ablation our simulations provide the first glacier scale estimates of ablation components on a glacier in the study region and better reproduce the observed and expected spatial variations of melt and surface sublimation in comparison with more simple assumptions such as linear gradients and uniform wind speeds

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

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

sensitivity of static stress calculations to the earthquake slip distribution 1 the apparent strong correlation between coulomb stress changes and the spatial distribution of aftershocks suggests the possibility of making near real time estimations of areas at risk of experiencing off fault aftershocks in order to do this in practice a number of issues must first be addressed including the extent to which the main shock slip must be known in detail before a meaningful stress map can be constructed here we investigate this issue by constructing a time ordered sequence of slip solutions for the landers earthquake computing coulomb stress changes for each solution and quantitatively comparing the stress field with the observed aftershocks by 1 resolving the coulomb stress change onto the aftershock nodal planes and calculating the percentage of events consistent with triggering and 2 constructing a two dimensional map of coulomb stress and computing the correlation coefficient between the positive and negative areas and the locations of the aftershocks we find that slip solutions based on empirical relations and either focal mechanism or moment tensor data produce stress fields inconsistent with the observed spatial distribution of aftershocks whereas slip solutions incorporating the correct rupture geometry but greatly simplified slip produce stress fields consistent with the aftershock distribution when very near fault events are excluded we further find that resolving stress perturbations onto earthquake nodal planes and computing the percentage of events experiencing positive coulomb stress provides a poor measure of success because of the limited range of structures on which events occur and the compatibility of the main shock stress field with these structures our results support the hypothesis that coulomb stress changes affect the spatial distribution of aftershocks and suggest that meaningful calculations of coulomb stress can be made as soon as an earthquake s rupture geometry is well constrained

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

freshwater teleconnections and ocean thermohaline circulation 1 asymmetry of the atlantic and pacific sea surface salinity sss is recognized as an important element of the global ocean thermohaline circulation however a threshold of such asymmetry that may trigger a true global deep ocean conveyor has not yet been examined a combined effect of the atlantic pacific and the southern ocean surface salinity asymmetries also has not yet been clearly shown we address these issues and conclude that atlantic pacific sss asymmetry is one of the most critical elements for maintaining the global ocean conveyor our experiments suggest albeit preliminary that high latitudinal freshwater impacts as a mechanism of altering global ocean thermohaline circulation may be less effective than inter basin freshwater communications

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

gps observations of crustal deformation associated with the 2012 mw 7 8 haida gwaii earthquake abstract on 28 october 2012 an m w 7 8 earthquake occurred off the west coast of haida gwaii british columbia although past large events at this margin reflect strike slip motion between the pacific and north american plates e g 1949 m s 8 1 this earthquake involved low angle thrust faulting with a slip direction almost perpendicular to the margin a consequence of slip partitioning at this obliquely convergent margin to refine regional source models we investigated the coseismic and postseismic displacements using a network of global positioning system gps sites coseismic movement at the campaign site closest to the coast and about 30 km from the epicenter is 115 cm to the south southwest with 30 cm of subsidence the only continuously recording gps station on haida gwaii at the time of the earthquake about 80 km from the epicenter provides a robust coseismic displacement estimate of 22 cm to the south southwest the coseismic results are consistent with a shallow dipping thrust rupture underlying the queen charlotte terrace immediately seaward of the queen charlotte fault these results allowed us to update rupture models that were originally derived from seismic waveforms and tsunami data estimates of cumulative postseismic horizontal displacements over about one year from seven sites are up to 6 cm with a systematic along strike variation in azimuth from south southwest to southeast from north to south in the study area besides viscoelastic stress relaxation these postseismic trends may indicate afterslip on the deeper plate interface beneath northern moresby island and possibly aseismic slip along the queen charlotte or subparallel faults offshore of southern moresby island online material figures of three component daily position estimates from bernese analysis at global positioning system tracking stations on haida gwaii and the adjacent mainland

mechanism diversity of the loma prieta aftershocks and the mechanics of mainshock aftershock interaction the diverse aftershock sequence of the 1989 loma prieta earthquake is inconsistent with conventional models of mainshock aftershock interaction because the aftershocks do not accommodate mainshock induced stress changes instead the sense of slip of the aftershocks is consistent with failure in response to a nearly uniaxial stress field in which the maximum principal stress acts almost normal to the mainshock fault plane this orientation implies that i stress drop in the mainshock was nearly complete ii mainshock induced decreases of fault strength helped were important in controlling the occurrence of after shocks and iii mainshock rupture was limited to those sections of the fault with preexisting shear stress available to drive fault slip

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

a 22 month record of surface meteorology and energy balance from the ablation zone of brewster glacier new zealand multi annual records of glacier surface meteorology and energy balance are necessary to resolve glacier climate interactions but remain sparse especially in the southern hemisphere to address this we present a record from the ablation zone of brewster glacier new zealand between october 2010 and september 2012 the mean air temperature was 1 2 c at 1760 m a s l with only a moderate temperature difference between the warmest and coldest months 8 c long term annual precipitation was estimated to exceed 6000 mm a 1 with the majority of precipitation falling within a few degrees of the freezing level the main melt season was between november and march 83 of annual ablation but melt events occurred during all months annually net radiation was positive a source of energy and supplied 64 of the melt energy driven primarily by net shortwave radiation net longwave radiation was often positive during cloudy conditions in summer demonstrating the radiative importance of clouds during melt turbulent sensible and latent heat fluxes were directed towards the surface in the summer months accounting for just over a third of the energy for melt 34 the energy gain associated with rainfall was small except during heavy events in summer

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

the atlantic freshwater budget as a diagnostic for the existence of a stable shut down of the meridional overturning circulation 1 which physical processes effectively determine the stability regime of the atlantic meridional overturning circulation moc is not yet fully understood we investigate the role of the oceanic freshwater transport into the basin employing a coupled model of intermediate complexity by modifying the longitudinal variation of surface salinities near the southern border at 33 s the amount of salt flowing out of the atlantic via the brazil current can be regulated in turn this will influence whether the moc exports or imports salt water the latter is associated with a basin scale salinity overturning feedback which can be either positive or negative pulse experiments strongly suggest that its sign determines the existence of a monostable or bistable regime in our model

aerodynamic stability and turbulent sensible heat flux over a melting ice surface the greenland ice sheet the turbulent sensible heat flux to a melting ice surface is calculated from wind speed and air temperature at 2 m over the ice surface assuming a certain wind profile with the appropriate surface roughness the aerodynamic stability of the boundary layer over melting ice is examined by comparing sensible heat fluxes for logarithmic and log linear wind profiles where the logarithmic profile is strictly valid only for neutral conditions increasing stability reduces the sensible heat flux to the glacier surface and introduces a non linear relation between heat flux and air temperature the stability effect is greatest at low wind speeds and fairly small at the high wind speeds that are common over the ice sheet earlier estimates of ablation by energy balance modelling may be too large due to neglect of stability but this was almost offset by using a surface roughness that was too small the log linear wind profile should be used in future energy balance models to take account of stability but more research is needed on the parameters of the profile as well as on the surface roughness

observed relations between snowfall microphysics and triple frequency radar measurements recently published studies of triple frequency radar observations of snowfall have demonstrated that naturally occurring snowflakes exhibit scattering signatures that are in some cases consistent with spheroidal particle models and in others can only be explained by complex aggregates until recently no in situ observations have been available to investigate links between microphysical snowfall properties and their scattering properties in this study we investigate for the first time relations between collocated ground based triple frequency observations with in situ measurements of snowfall at the ground the three analyzed snowfall cases obtained during a recent field campaign in finland cover light to moderate snowfall rates with transitions from heavily rimed snow to open structured low density snowflakes the observed triple frequency signatures agree well with the previously published findings from airborne radar observations a rich spatiotemporal structure of triple frequency observations throughout the cloud is observed during the three cases which often seems to be related to riming and aggregation zones within the cloud the comparison of triple frequency signatures from the lowest altitudes with the ground based in situ measurements reveals that in the presence of large 5 mm snow aggregates a bending away in the triple frequency space from the curve of classical spheroid scattering models is always observed rimed particles appear along an almost horizontal line in the triple frequency space which was not observed before overall the three case studies indicate a close connection of triple frequency signatures and snow particle structure bulk snowfall density and characteristic size of the particle size distribution

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

multiple equilibria of an asymmetric two basin ocean model abstract an ocean general circulation model is used to examine the role of model geometry and surface buoyancy and wind stress forcing in the asymmetry of the global thermohaline circulation the model domain is a highly idealized atlantic and pacific linked by a circumpolar ocean in the south and the integrations are performed under mixed boundary conditions diagnosed from spinups under various temperature and salinity profiles constructed from the present day climatology the model exhibits a tendency to favor either a conveyor type circulation with sinking in the northern north atlantic and upwelling in the north pacific or a southern sinking state with deep sinking in the antarctic only this bias is not dictated solely by the hydrological cycle nor apparently by the greater northern extension of the atlantic basin but presumably by the overall asymmetry of the geometry equilibria with northern sinking in both basins can appear however when the winds in the southern ocean are reduced or th

field survey following the 28 october 2012 haida gwaii tsunami this article documents the near field effects of the largest tsunami of 2012 globally which occurred following canada s second largest recorded earthquake on a thrust fault offshore western haida gwaii on october 28 utc despite a lack of reported damaging waves on the coast of british columbia largest amplitudes were recorded in hawaii three field surveys in the following weeks and months reveal that much of the remote unpopulated uninstrumented coastline of western haida gwaii was impacted by significant tsunami waves that reached up to 13 m above the state of tide runup exceeded 3 m at sites spanning 200 km of the coastline greatest impacts were apparent at the heads of narrow inlets and bays on western moresby island where natural and manmade debris with a clear oceanward origin was found on the forest floor and caught in tree branches inferring flow depths up to 2 5 m bays that see regular exposure to storm waves were generally less affected at these sites a storm origin cannot be ruled out for the debris surveyed logs disturbed from their apparent former footprints on the forest floor at the head of pocket inlet provide evidence of complex runup backwash and oblique flow patterns as noted in other tsunamis discontinuous muddy sediments were found at a few sites sedimentation was not proportional to runup lessons learned from our study of the impacts of the haida gwaii tsunami may prove useful to future post tsunami and paleotsunami surveys as well as tsunami hazard assessments

fine scale sediment structure and geochemical signature between eastern and western north atlantic during heinrich events 1 and 2 abstract heinrich iceberg rafting events 1 and 2 h1 and h2 in the labrador sea are identified by their typical nepheloid flow deposit sedimentary structure high bulk carbonate increase in iceberg rafted detritus ird and depletion of 18o in the surface dwelling foraminifer neogloboquadrina pachyderma s h layers in this region have sedimentological characteristics different than those in the north atlantic and consist of ird interspersed in pelagic sediments high resolution 14c ams dates allowed us to delineate the leads and lags in instability between different ice streams of the former laurentide ice sheet lis our data suggest that the discharge from the hudson strait ice stream was followed by cumberland sound ice sheet during h1 and h2 new radiogenic isotopes from the ice proximal and surficial sediments of the greater hudson strait region and labrador sea h0 h1 and h2 layers suggest that carbonate rich layers were only derived from hudson strait not baffin bay fine scale structure of h1 and h2 intervals in labrador sea slope cores is characterized by two lithic peaks dominated by detrital carbonate grains and a single peak in cores from the central labrador sea a similar pattern in the structure of h1 and h2 is observed along the western european margin these findings contrast with north atlantic h1 and h2 intervals which are characterized by a peak of carbonate rich grains followed by a peak of quartz and volcanic grains this comparison with north atlantic and western european margin cores leads us to suggest that the coupling or lack thereof between the lis and european ice sheet is related to the depositional processes occurring along the margins as well as the distance from the sources and the ability of the oceanic currents to disperse icebergs any significant change in ice sheet dynamics would be recorded close to the ice sheet margin while distal locations would only record extreme events we hypothesize that the discordance between the findings reported in the literature is most likely similar to the difference between the upper slope deep labrador sites and the flemish pass site described in this contribution but requires vigorous testing

the queen charlotte islands refraction project part ii structural model for transition from pacific plate to north american plate discussion the oceanic continental boundary west of the queen charlotte islands is marked by the active queen charlotte fault zone motion along the fault is predominantly dextral strike slip but relative plate motion and other studies indicate that a component of convergence between the oceanic pacific plate and the continental north american plate presently exists this convergence could be manifest through different types of deformation oblique subduction crustal thickening or lateral distortion of the plates in 1983 a 330 km offshore onshore seismic refraction profile extending from the deep ocean across the islands to the mainland of british columbia was recorded to investigate i structure of the fault zone and associated oceanic continental boundary and ii lithospheric structure beneath the islands and hecate strait to define the regional transition from pacific plate to north american plate and thus the nature of the convergence two dimensional ray tracing and synthetic seismogram modelling of many

seismic potential of the queen charlotte alaska aleutian seismic zone the 5000 km long queen charlotte alaska aleutian seismic zone is subdivided into 17 unequally sized segments their boundaries are delineated based on the prior distribution of large and great earthquakes the 17 segments are chosen to represent areas likely to be ruptured by characteristic earthquakes this term usually implies repeated breakage of a plate boundary segment by either a large or great earthquake whose source dimensions remain consistent from cycle to cycle this definition does not exclude the possibility that occasionally adjacent characteristic earthquake segments may break together in a single giant event that is larger than the characteristic size outlined conversely a segment can also sometimes break in a series of smaller ruptures formal computations of the conditional probabilities for future large and great earthquakes in the 17 segments of the queen charlotte alaska aleutian seismic zone are based on the following data sets and findings 1 recurrence intervals from historic and geologic data 2 direct recurrence time estimates based on rates of relative plate motion and the size or displacement of the most recent characteristic event in each segment and 3 the application of a lognormal distribution of recurrence times for large and great earthquakes results of these computations indicate seven areas that have high i e 60 conditional probabilities for the recurrence of either large or great earthquakes within the next 20 years 1988 2008 these areas include cape st james yakataga the shumagin islands unimak island and the fox delarof and near islands segments of the aleutian arc when a shorter time interval is considered 1988 1998 those segments more likely to rupture in large ms 7 7 7 rather than great earthquakes have a high conditional probability these areas include the unimak fox and delarof islands segments the largest uncertainties in these forecasts stem from the short historic record providing a single recurrence time estimate for some segments or widely varying estimates for others from the unknown importance of aseismic slip and from a vague definition of characteristic earthquake size in fact characteristic earthquake size may not be a time invariant quantity

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

high latitude salinity effects and interhemispheric thermohaline circulations a general circulation model for the ocean is used to investigate the interaction between the global scale thermohaline circulation and the salinity distribution it is shown that an equatorially asymmetric circulation can be maintained even under equatorially symmetric basin geometry and surface forcing multiple equilibrium solutions are obtained for the same forcing by perturbing the high latitude salinity field in an otherwise equatorially symmetric initial condition the timescale of the transition from the symmetric circulation to an asymmetric circulation depends critically on the sign of the initial salinity perturbation

a scale dependent model to represent changing aerodynamic roughness of ablating glacier ice based on repeat topographic surveys turbulent fluxes make a substantial and growing contribution to the energy balance of ice surfaces globally but are poorly constrained owing to challenges in estimating the aerodynamic roughness length z0 here we used structure from motion sfm photogrammetry and terrestrial laser scanning tls surveys to make plot scale 2 d and 3 d microtopographic estimations of z0 and upscale these to map z0 across an ablating mountain glacier at plot scales we found spatial variability in z0 estimates of over two orders of magnitude with unpredictable z0 trajectories even when classified into ice surface types tls derived surface roughness exhibited strong relationships with plot scale sfm z0 estimates at the glacier scale a consistent increase in z0 of 0 1 mm d 1 was observed space for time substitution based on time since surface ice was exposed by snow melt confirmed this gradual increase in z0 over 60 d these measurements permit us to propose a scale dependent temporal z0 evolution model where unpredictable variability at the plot scale gives way to more predictable changes of z0 at the glacier scale this model provides a critical step towards deriving spatially and temporally distributed representations of z0 that are currently lacking in the parameterisation of distributed glacier surface energy balance models less

ephemeral plate tectonics at the queen charlotte triple junction three plate boundaries the queen charlotte transform the cascadia subduction zone and the juan de fuca ridge meet in a complex triple junction offshore vancouver island some interpretations of the plate tectonics of the region have included the explorer ridge the dellwood knolls and the tuzo wilson volcanic field as part of the spreading system requiring up to three triple junctions in the region new seabeam bathymetry interpreted with existing regional data sets indicate that the dellwood knolls and tuzo wilson volcanic field are not independent plate boundaries but the result of leaky transform tectonics between two overlapping transform faults seismicity shows that the explorer plate is being deformed by pacific north american relative motion as a new transform plate boundary forms and cuts off the explorer ridge the system is evolving to a single triple junction at the northern terminus of the juan de fuca ridge where it meets the nootka deformation zone thus the explorer microplate which was spawned 5 ma is an ephemeral adjustment to mechanical difficulties at the triple junction this new model implies that the explorer subduction zone is no longer active ephemeral oceanic microplates have also existed at pacific north american triple junctions off southern california and baja california

coulomb stress evolution along xianshuihe xiaojiang fault system since 1713 and its interaction with wenchuan earthquake may 12 2008 abstract the curved left lateral strike slip xianshuihe xiaojiang fault system xxfs in southwestern china extends at least 1400 km in the eastern margin of the tibetan plateau fieldworks confirm that the xxfs is one of the longest and most seismically active faults in china the strain released by the slip motion on the xxfs is related to the convergence between the indian and eurasian plates the entire fault system has experienced at least 35 earthquakes of m 6 in the recent 300 years and almost all segments of the system have been the locus of major historical earthquakes since the xxfs region is heavily populated over 50 million people understanding the migration of the large earthquakes in space and time is of crucial importance for the seismic hazard assessment in this region we analyze a sequence of 25 earthquakes m 6 5 that occurred along the xxfs since 1713 and investigate their influence on the 2008 mw7 9 wenchuan earthquake occurred on the adjacent longmenshan fault in our analysis the relevant parameters for the earth crust are constrained by seismic studies the locations and geometries of the earthquake faults as well as the rupture distributions are taken from field observations and seismological studies results from the coulomb failure stress modeling indicate significant interactions among the earthquakes after the 1713 earthquake 19 out of 24 earthquakes occurred in the positive stress zone of the preceding earthquakes the other 5 earthquakes located in the area without significant stress changes induced by the preceding events in particular we can identify 4 visible earthquake gaps with increasing seismic hazard along the xxfs consistent with the findings from the paleo seismological studies the seismic activity and tectonic motion on the xxfs reduced the coulomb stress accumulation at the hypocenter of 2008 mw7 9 wenchuan earthquake implying that the wenchuan earthquake might not be triggered directly by the seismic activities on the xxfs on the other hand the coulomb failure stress induced by the wenchuan earthquake has increased in a region of 125 km long segment of the xxfs northwest of kangding city

synchronization of polar climate variability over the last ice age in search of simple rules at the heart of climate s complexity evidence is presented supporting the hypothesis of polar synchronization which states that during the last ice age and likely in earlier times millennial scale temperature changes of the north and south polar regions were coupled and synchronized the term synchronization as used here describes how two or more coupled nonlinear oscillators adjust their initially different natural rhythms to a common frequency and constant relative phase in the case of the polar regions heat and mass transfer through the intervening ocean and atmosphere provided the coupling as a working hypothesis polar synchronization brings new insights into the dynamic processes that link greenland9s dansgaard oeschger do abrupt temperature fluctuations to antarctic temperature variability it is shown that consistent with the presence of polar synchronization the time series of the most representative abrupt climate events of the last glaciation recorded in greenland and antarctica can be transformed into one another by a 2 phase shift with antarctica temperature variations leading greenland9s this plus the fact that remarkable close simulations of the time series are obtained with a model consisting of a few nonlinear differential equations suggest the intriguing possibility that there are simple rules governing the complex behavior of global paleoclimate

change in motion of pacific plate at 5 myr bp alignments of volcanoes such as the hawaiian seamount chain record the passage of oceanic plates over mantle plumes or hot spots and changes in the orientation of a seamount chain may indicate changes in the direction of motion of the plate within the hotspot frame of reference1 this hypothesis can be tested for the pacific plate by comparing data from the hawaiian volcanoes with tectonic movements inferred from the geology of adjacent plates we have now found that the motion of the pacific plate changed to a more northerly direction 5 myr ago probably as a result of the detachment of a piece of pacific sea floor which had been subducted beneath the fiji plateau during the tertiary

increasing seismicity in southern tibet following the 2015 mw 7 8 gorkha nepal earthquake abstract we conducted a systematic detection of micro seismicity in southern tibet 1 6 days before and 4 4 days after the 2015 mw 7 8 gorkha nepal earthquake our study employs 368 template events listed in the china earthquake networks center cenc catalog with the waveform based matched filter technique we detected five times more earthquakes than listed in the cenc catalog during our study period the seismicity in southern tibet shows a significant increase immediately following the gorkha nepal earthquake including two normal faulting events the mw 5 8 tingri and mw 5 3 nyalam earthquakes about 3 and 11 h after the mainshock respectively although the static stress changes cfs showed a slightly better correlation with the seismicity rate changes than the peak dynamic stress changes cfs t the absolute value of the static stress change at the epicenter region of the mw 5 8 tingri earthquake is 10 kpa roughly two orders smaller than the peak dynamic stress change of 2 2 mpa although we are unable to identify the primary triggering mechanism it is evident that the 2015 nepal earthquake triggered widespread seismicity in southern tibet our results highlight the potential increase of seismic hazard in southern tibet due to the occurrence of major thrust earthquakes along the himalaya frontal thrust faults

stress in western canada from regional moment tensor analysis more than 180 regional moment tensor rmt solutions for moderate sized earthquakes m 4 are used to examine the contemporary stress regime of western canada and provide valuable information relating to earthquake hazard analysis the overall regional stress pattern shows mainly ne sw oriented p axes for most of western canada with local variations in the northern cordillera the maximum compressive stress direction 1 varies from east west to north south to ne sw from south to north the stress direction 1 is consistent with the p axis direction for the largest earthquakes except in the central and northern mackenzie mountains where there is a 16 difference the yakutat collision zone shows a steady change in 1 from east west in the east to north south in the west in the canada united states border region rmt solutions suggest a north south compressional regime may extend through southern british columbia and northern washington to the eastern cordillera in the vancouver island puget sou

seismic consequences of warm versus cool subduction metamorphism examples from southwest and northeast japan warm and cool subduction zones exhibit differences in seismicity seismic structure and arc magmatism which reflect differences in metamorphic reactions occurring in subducting oceanic crust in southwest japan arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth in northeast japan arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth thermal petrologic models predict that oceanic crust subducting beneath southwest japan is 300 to 500 c warmer than beneath northeast japan resulting in shallower eclogite transformation and slab dehydration reactions and possible slab melting