episodic seafloor mud brecciation due to great subduction zone earthquakes the nankai trough off southwest japan has an 1300 yr historical record of great earthquakes including the most recent the a d 1944 tonankai m 8 2 earthquake evaluation of the activity of an individual submarine fault is difficult when only onland observations are available submarine core records can pinpoint individual fault activity here we present integrated ocean drilling program iodp nankai trough seismogenic zone experiment data from the shallow portion iodp expedition 316 drilled and cored several holes in the shallow portion of the offshore tonankai earthquake area including sites in the hanging wall of a margin dominating splay fault that has previously been interpreted to have ruptured coseismically during megathrust earthquakes x ray computed tomography scanning revealed that the uppermost core at one site contains repeated occurrences of mud breccia radioisotope dating of the uppermost mud breccia indicates a deposition time consistent with the 1944 tonankai earthquake suggesting that the mud breccia layers result from episodic brecciation caused by seismic shaking mud brecciation provides a potential new tool to reconstruct ancient earthquake history in subduction zones

density specific surface area and correlation length of snow measured by high resolution penetrometry precise measurements of snow structural parameters are crucial to understand the formation of snowpacks by deposition and metamorphism and to characterize the stratigraphy for many applications and remote sensing in particular the area wide acquisition of structural parameters at high spatial resolution from state of the art methods is however still cumbersome since the time required for a single profile is a serious practical limitation as a remedy we have developed a statistical model to extract three major snow structural parameters density correlation length and specific surface area ssa solely from the snowmicropen smp a high resolution penetrometer which allows a meter profile to be measured with millimeter resolution in less than 1 min the model was calibrated by combining smp data with 3 d microstructural data from microcomputed tomography which was used to reconstruct full depth snow profiles from different snow climates alpine arctic and antarctic density correlation length and ssa were derived from the smp with a mean relative error of 10 6 16 4 and 23 1 respectively for validation we compared the density and ssa derived from the smp to traditional measurements and near infrared profiles we demonstrate the potential of our method by the retrieval of a two dimensional stratigraphy at kohnen station antarctica from a 46 m long smp transect the result clearly reveals past depositional and metamorphic events and our findings show that the smp can be used as an objective high resolution tool to retrieve essential snow structural parameters efficiently in the field

snow saltation threshold measurements in a drifting snow wind tunnel wind tunnel measurements of snowdrift in a turbulent logarithmic velocity boundary layer have been made in davos switzerland using natural snow regression analysis gives the drift threshold friction velocity ut assuming an exponential drift profile and a simple drift to friction velocity relationship measurements over 15 snow covers show that ut is influenced more by snow density and particle size than by ambient temperature and humidity and varies from 0 27 to 0 69 m s 1 schmidt s threshold algorithm and a modified version used in snowpack a snow cover model agree well with observations if small bond sizes are assumed using particle hydraulic diameters obtained from image processing bagnold s threshold parameter is 0 18 roughness lengths z0 vary between snow covers but are constant until the start of drift threshold roughness lengths are proportional to u 2 t the influence of macroscopic objects on the roughness length is shown by the lower values measured over the smooth and flat snow surface of the wind tunnel 0 04 z0 0 13 mm compared to field measurements mean drifting snow grain sizes for mainly new and partly decomposed snow are 100 175 mm and independent of surface particle size this paper describes the results of a series of experiments investigating the form of the wind velocity boundary layer over a snow surface with and without drift this information is essential to help calculate the energy balance at the snow surface and also to assess mass movement of snow by wind the process of drift is important both over relatively flat terrain such as antarctic regions where it contributes to mass balance and also in mountainous terrain where accumulation on steep slopes can contribute to the danger of avalanches the velocity boundary layer over a surface is often de scribed by a log law where the wind speed at a particular height is a function of the surface friction velocity u and aerodynamic roughness length z0 stull 1988 the param eters uand z0 are then used to model the fluxes of heat and water vapour from the surface which are important not only for snowpack development marks and dozier 1992 lehn ing and others 2002b but also for mass balance calculations cline 1997 liston and sturm 1998 box and others 2004 aerodynamically rough solid surfaces have roughness lengths independent of u schlichting and gersten 2003 the same does not always hold over granular surfaces such as snow or sand above the threshold friction velocity ut particles will be entrained and transported by drift at low wind speeds this drift will be predominantly saltation where particles follow parabolic paths over the surface bagnold 1941 p 10 37 these drifting particles increase the aerodynamic roughness of the surface owen 1964 summarized earlier research relating to the aerodynamic effects of drifting particles and developed a theoretical framework to explain this effect together these suggest two

the layered character of snow covers snow studies have generally ignored the layered nature of snow covers having achieved a good understanding of the properties and processes in homogeneous snow snow scientists should develop more insight into the evolution of the layers and their effects on overall snow response many of the outstanding problems in snow studies can only be solved by dealing with snow as a layered medium the various mechanisms by which layers are generated their effects and some of the outstanding research problems are described here

deformable backstop as seaward end of coseismic slip in the nankai trough seismogenic zone abstract wide angle seismic surveys performed in the last decade have clarified the 3 d crustal structure along the nankai trough the geometry and velocity structure of the southwestern japan subduction zone are now well constrained comparing these observations with the rupture distribution of historic great thrust earthquakes it appears that the coseismic rupture occurred along plate boundaries deeper than the wedge backstop boundary the boundary between the neogene quaternary accretionary wedge and the crust forming the backstop from the view of spatial relationship both rupture distributions of the last two large events and the crust forming the backstop are considerably retreated from the trough axis in the west and east off the kii peninsula in both areas seamount or ridge subduction is apparent in seismic results geomorphological data and geomagnetic data the landward indentation of the deformable backstop which corresponds to the crustal block of old accreted sediments may be formed by seamount subduction according to published results of sandbox modeling in particular the subducted seamount may be a structural factor affecting the recession of the crustal block forming the backstop

subducted seamount imaged in the rupture zone of the 1946 nankaido earthquake the nankai trough is a vigorous subduction zone where large earthquakes have been recorded since the seventh century with a recurrence time of 100 to 200 years the 1946 nankaido earthquake was unusual with a rupture zone estimated from long period geodetic data that was more than twice as large as that derived from shorter period seismic data in the center of this earthquake rupture zone we used densely deployed ocean bottom seismographs to detect a subducted seamount 13 kilometers thick by 50 kilometers wide at a depth of 10 kilometers we propose that this seamount might work as a barrier inhibiting brittle seismogenic rupture

case for northward transport of baja and coastal southern california paleomagnetic data analysis and alternatives this paper which accompanies the preceding article by gastil reviews cretaceous paleomagnetic evidence for baja and coastal southern california like cretaceous paleomagnetic data for the cordillera as a whole results from baja and southern california require northward transport of 1000km or more relative to interior north america agreement between independent results for different rock types and experimental techniques is overwhelming dextral shear driven by right oblique subduction readily accounts for the paleomagnetic results alternative explanations such as experimental errors rock magnetic effects anomalous geomagnetic behavior errors in dating or local structure are inadequate improbable or both some geologists have difficulty reconciling the findings of paleomagnetism with their own results hence as emphasized by gastil a conflict and enigma exist to resolve them will require a willingness on both sides to honestly scrutinize basic assumptions

seismological monitoring on the 2003 tokachi oki earthquake derived from off kushiro permanent cabled obss and land based observations abstract japan marine science and technology center installed a cabled geophysical observatory system off kushiro hokkaido island in july 1999 this observatory system comprises three ocean bottom seismographs obss two tsunami gauges and a geophysical geochemical monitoring system 4 years and 2 months after the installation a megathrust earthquake the 2003 tokachi oki earthquake 26th september in japan standard time jst mjma 8 0 occurred along a plate boundary underneath a forearc basin where the system is located the system recorded clear unsaturated seismograms just at 28 6 km from the epicenter this paper demonstrates advantages brought by the cabled observatory to record the megathrust earthquake showing how earthquake detectability is improved dramatically combining permanent obs and land based observations around the region and importance of the in situ monitoring on the seismogenic zone in the present study processing obss and land based network together and comparing magnitudes of common observed earthquakes with national authorized network event detection level improved down to m 1 5 which is much lower than the previously designed as down to m 2 comparing detection level before and after installing obss we found dramatic improvement of the earthquake detection level in the interesting region real time continuous observations of microearthquakes since 1999 have brought us tremendous findings first a seismic quiescence started about 10 days before the 2003 tokachi oki earthquake second aftershock distribution is not uniform over the focal area and can be divided into several sub regions which might indicate an existence of several asperities we think that the geophysical observations helped to understand the initiation process of the rupture of the 2003 tokachi oki earthquake and that observations including seismological geodynamic hydrogeological and the other multidisciplinary observations would provide a clue to future understanding of seismogenic processes at subduction zones

the slip distribution of the 1946 nankai earthquake estimated from tsunami inversion using a new plate model abstract a new model for the shape of the philippine sea plate psp subducting beneath southwest japan was constructed by combining marine seismic survey results and seismicity data this resulted in a plate model that is generally 3 5 km shallower than previous estimates and contains new details of plate boundary structure near the nankai trough axis we estimated the slip distribution of the 1946 nankai earthquake by inverting tsunami waveforms using the new plate boundary model and found that the large slip off cape muroto and seismic moment were reduced by about 10 from the previous estimate of tanioka and satake 2001a however we also found reason to suspect the tide gauge closest to the epicenter at shimotsu and this resulted in a much more substantial reduction in the amount of slip in the eastern segment of the rupture area we also find that our new rupture model correlates well with features of the subducting plate boundary such as a large subducting seamount off cape muroto kodaira et al 2000a this suggests that such features have an important effect on either earthquake rupture propagation or the interseismic accumulation of elastic strain energy or both

earthquake source nucleation a physical model for short term precursors abstract ohnaka m 1992 earthquake source nucleation a physical model for short term precursors in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 149 178 this paper deals with a quasistatic leading to a quasidynamic at a later time nucleation process that precedes the earthquake dynamic rupture and models of the earthquake source nucleation are put forward based on physical principles a quasistatic to quasidynamic rupture nucleation process is an intrinsic part of the ensuing earthquake dynamic rupture in other words the nucleation process itself is an short term or immediate precursor that occurs in a localized zone during the earthquake nucleation premonitory slip proceeds in the localized nucleation zone and shear stress also decreases gradually in the zone since slip weakening occurs during the nucleation immediate foreshock activity is a part of the nucleation process leading to the mainshock dynamic rupture therefore hypocentral locations of foreshocks are necessarily restricted to lie near the mainshock hypocentre onset of the mainshock rupture whether or not foreshocks occur during the mainshock nucleation depends on how the rupture growth resistance varies on a local to small scale since patches of greater rupture growth resistance are considered to prevail on a local to small scale in the fault zone carrying immediate foreshocks would be one of the major characteristics of earthquakes that nucleate within the brittle seismogenic layer when a mainshock earthquake nucleates within the brittle seismogenic layer and its hypocentre is located near the base of the seismogenic layer immediate foreshocks for this mainshock are necessarily restricted to lie within a localized region shallower than hypocentral depth of the mainshock by contrast the nucleation process below the base of the seismogenic layer is aseismic in nature so that carrying no conspicuous foreshocks would be a common characteristic of interplate earthquakes that nucleate below the base of the brittle seismogenic layer the breakdown strength p the breakdown stress drop b and the critical slip displacement dc are indicative of the rupture growth resistance to estimate depth variations of these parameters the effects of the normal stress n and temperature t on those parameters are examined using available data so far published the combined effects of n and t on p in the brittle to semibrittle regime are found to be represented empirically by p n t po n 1 cosh 50 t 40 sinh 50 t exp 2000 t where po n 135 7 0 750 n and t is measured in k and n in mpa it is found that dc increases sharply with t but is insensitive to n above 300 c while dc depends on n but is insensitive to t below 300 c on the basis of these results variations in p dc and b at mid crustal depths are estimated for quartzo feldspathic rocks for a given geothermal gradient

experimental assessment of owen s second hypothesis on surface shear stress induced by a fluid during sediment saltation a widely used yet thus far unproven fluid dynamical hypothesis originally presented by p r owen 50years ago states that the surface shear stress induced by a fluid on the ground during equilibrium sediment saltation is constant and independent of the magnitude of the fluid velocity and consequently the particle mass flux this hypothesis is one of the key elements in almost all current model descriptions of sediment erosion we measured the surface shear stress in a drifting sand wind tunnel and found owen s hypothesis being merely an approximation of the real situation a significant decrease of the fluid stress with increasing wind velocities was measured for low to intermediate particle mass fluxes for high particle mass fluxes owen s hypothesis essentially holds although a slight increase of the fluid stress was measured

subducting seamounts and deformation of overriding forearc wedges around japan abstract two subducting seamounts under inner trench slopes have been identified around japan on the basis of magnetic anomalies morphology and geological structure the first one is located under the foot of the inner trench slope at the junction between the japan trench and the kuril trench another one occurs beneath the slope slightly seaward of the tosabae the basement high at the trench slope break along the nankai trough off shikoku the magnetic anomalies of seamount origin are accompanied by the characteristic morphology of a forearc wedge i e a swell landward and a depression seaward the seamounts beneath the inner trench slopes have preserved magnetization showing reasonably consistent directions which suggests that the subducting seamounts have kept roughly their original shapes the morphology of the forearc wedge can be explained by a subducting seamount on the oceanic crust pushing the forearc material forward and upward deformation of the forearc wedge by the subducting seamount extends to the forearc basin the seamounts are stronger and less deformable than the inner slope material and are not offscraped onto inner trench slopes two other examples of deformed inner trench slopes around japan which can be explained by subduction of topographic highs are presented one example is a depression on the foot of the inner trench slope northeast of the junction between the kyushu palau ridge and the nankai trough another one is an area of complex morphology of the inner trench slope along the japan trench around the daiichi kashima seamount

new discoveries in dynamics of an m8 earthquake phenomena and their implications from the 2003 tokachi oki earthquake using a long term monitoring cabled observatory at the 2003 tokachi oki earthquake of m8 seafloor phenomena such as a generation process of tsunami seafloor uplifts turbidity current etc were observed using a cabled observatory installed on the seafloor the turbidity current was observed as a benthic storm caused presumably by the mainshock the seafloor uplifts were observed at the mainshock and continuously after the mainshock the uplifts were 0 35 0 37 and 0 12 m for epicentral distances of 25 5 31 4 and 81 7 km respectively after the mainshock a continuous uplift of the seafloor is observed at all three pressure gauge locations indicating that there was a change in the state of friction on the plate boundary interface by the mainshock in this paper we first show what was observed using the cabled observatory installed right above the focal area of the earthquake and then we discuss to summarize these phenomena associated with the earthquake its possible causes and future directions in long term monitoring of seismogenic processes

rotating circular flume a rotating flume installed at the national water research institute in burlington ontario canada to undertake basic research on cohesive sediment dynamics is described the flume is 5 0 m in mean diameter 0 30 m in width and 0 30 m in depth an annular cover plate ring which can be transversed in the vertical direction fits inside the flume with a radial clearance of 1 5 mm on either side and makes contact with the water surface the flume and the ring can be rotated independently at speeds ranging from 0 to 3 rpm the flume is equipped with a laser doppler anemometer a laser particle size analyzer and a preston tube a set of performance tests carried out in this flume indicate that generation of a nearly two dimensional flow field is possible if both the flume and the ring are rotated simultaneously in opposite directions flows generated by keeping the flume stationary and rotating only the ring were found to contain a strong secondary circulation cell and a large variation of bed shear stress

circum pacific seismic potential 1989 1999 the seismic potential for 96 segments of simple plate boundaries around the circum pacific region is presented in terms of the conditional probability for the occurrence of either large or great interplate earthquakes during the next 5 10 and 20 years i e 1989 1994 1989 1999 and 1989 2009 this study represents the first probabilistic summary of seismic potential on this scale and involves the comparison of plate boundary segments that exhibit varying recurrence times magnitudes and tectonic regimes presenting these data in a probabilistic framework provides a basis for the uniform comparison of seismic hazard between these differing fault segments as well as accounting for individual variations in recurrence time along a specific fault segment and uncertainties in the determination of the average recurrence time