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We present a geometric analysis of a quasi-static single degree of freedom elastic slider with a state and rate dependent friction law. In particular, we examine and characterize the regime of chaotic motions displayed by the Dieterich-Ruina model. We do so by numerically reducing the chaotic attractors to a family of unimodal maps and discuss why this suggests complex behaviour in the dynamical system.

A 22.4 m-long shallow firn core was extracted during the 2006/2007 field season from coastal Adélie Land. Annual layer counting based on sub-annual analyses of δ18O and major chemical components was combined with 6 reference years associated with nuclear tests and non-retreat of summer sea ice to build the initial ice core chronology (1947–2007), stressing uncertain counting for 8 years. We focus here on the resulting δ18O and accumulation records. With an average value of 21.9 ± 6.8 cm w.e. y-1, local accumulation shows multi-decadal bell-shaped variations, peaking in the 1980s, but no long-term trend. Similar results are obtained for δ18O, also characterized by a remarkably low (2.6 ‰) and variable amplitude of the seasonal cycle. The ice core data are compared with regional temperature and stake area accumulation measurements, variations in sea ice extent, and outputs from a high resolution atmospheric general circulation model including stable water isotopes (ECHAM5-wiso) and a regional atmospheric model (MAR), both nudged to ERA atmospheric reanalyses. A significant linear correlation is identified between δ18O and regional temperature data, especially in winter. No significant relationship appears with regional sea-ice extent nor with Dumont d'Urville wind speed. The model-data comparison highlights the inadequacy of ECHAM5-wiso simulations prior to 1979, possibly due to the lack of data assimilation to constrain atmospheric reanalyses. Systematic biases are identified in the ECHAM5-wiso simulation, such as an over-estimation of the mean accumulation rate and its inter-annual variability, a strong cold bias, and an under-estimation of the mean δ18O value and its inter-annual variability. As a result, relationships between simulated δ18O and temperature are weaker than observed. Such systematic precipitation and temperature biases are not displayed by MAR, suggesting that model resolution plays a key role along the Antarctic ice sheet coastal topography. Inter-annual variations in ECHAM5-wiso temperature and precipitation accurately capture signals from meteorological data and stake observations, and are used to refine the initial ice core chronology within 1 year. After this adjustment, remarkable positive (negative) δ18O anomalies are identified in the ice core record and the ECHAM5-wiso simulation, respectively in 1986 and 2002 (1998–99). Despite uncertainties associated with post-deposition processes and signal to noise issues in one single coastal ice core record, we conclude that one single ice core can correctly capture major annual anomalies in δ18O as well as multi-decadal variations. These findings highlight the importance of improving the network of coastal high resolution ice core records, and stress the skills and limitations of atmospheric models for accumulation and δ18O in coastal Antarctic areas, particularly important for the overall East Antarctic ice sheet mass balance.

Earthquakes are among the most complex terrestrial phenomena, and modeling of earthquake dynamics is one of the most challenging computational problems in science. Computational capabilities have advanced to a state where we can perform wavefield simulations for realistic three-dimensional earth models, and gain more insights into the earthquakes that threaten California and many areas of the world. The Southern California Earthquake Center initiated a major earthquake research program called TeraShake to perform physics-based numerical simulations of earthquake processes for large geographical regions, at high resolution, and for high frequencies. For a large scale simulation such as TeraShake, optimization problems tend to emerge that are not significant in smaller scale simulations. This involves both large parallel computation and also massive data management and visualization coordination. In this paper, we describe how we performed single-processor optimization of the TeraShake AWM application, optimization of the I/O handling, and optimization of initialization. We also look at the challenges presented by run-time data archive management and visualization. The improvements made to the TeraShake AWM code enabled execution on the 40k IBM Blue Gene processors and have created a community code that can be used by seismologists to perform petascale earthquake simulations.

[1] The WDC system was created to archive and distribute data collected from the observational programs of the 1957-1958 International Geophysical Year. Originally established in the United States, Europe, Russia, and Japan, the WDC system has since expanded to other countries and to new scientific disciplines. The WDC system now includes over 51 Centers in 12 countries. The WDCs have been very successful over the last 50 years in meeting the needs of ICSU programs. However, in the next 50 years, the WDC system will need to evolve to accommodate the changing needs of ICSU and the global scientific community. Advances in information technology, as promoted by the electronic Geophysical Year, the implementation of new global scientific programs and the rapid increase in global, high-speed network connectivity will require the WDC system to adapt their current infrastructure, reorient their activities and implement new modes of operation. New requirements of existing ICSU programs like the IGBP, the activities of the new international science years (IPY, IHY, eGY, IYPE) and the implementation of the far reaching, long-term, Global Earth Observation System of Systems, will make new demands on the WDCs. The WDC system will respond by placing emphasis on modernizing its capabilities, expanding the WDCs into new disciplines, broadening the System geographically, especially into developing countries, and being more proactive in addressing new requirements from the ICSU and global scientific community. INDEX TERMS: 1794 History of Geophysics: Instruments and techniques; 1799 History of Geophysics: General or miscellaneous; 0525 Computational Geophysics: Data management; 9820 General or Miscellaneous: Techniques applicable in three or more fields; KEYWORDS: Electronic Geophysical Year, WDC System, GEOSS, space weather, monitoring systems, data mining, near-earth space environment.

The Southern California Earthquake Center digital library publishes scientific data generated by seismic wave propagation simulations. The output from a single simulation may be as large as 50 Terabytes of data and 400,000 files. The total size of the digital library is over 130 Terabytes with nearly three million files. We examine the data Grid capabilities required to manage this scale of simulation output, and the implementation of these capabilities in a digital library built on top of the Storage Resource Broker data Grid. We also examine the capabilities that will be needed in the future as the scale of simulation output increases to petabytes of data.

The Campus Earthquake Program (CEP) of the University of California (UC) started in March 1996, and involved a partnership among seven campuses of the UC—Berkeley, Davis, Los Angeles, Riverside, San Diego, Santa Barbara, Santa Cruz—and the Lawrence Livermore National Laboratory (LLNL). The aim of the CEP was to provide University campuses with site-specific assessments of their earthquake strong motion exposure, to complement estimates they obtain from consultants according to the state-of-the-practice (SOP), i.e. Building Codes (UBC 97, IBC 2000), and Probabilistic Seismic Hazard Analysis (PSHA). The Building Codes are highly simplified tools, while the more sophisticated PSHA is still somewhat generic in its approach because it usually draws from many earthquakes not necessarily related to the faults threatening the site under study. Between 1996 and 2001, the site-specific studies focused on three campuses: Riverside, San Diego, and Santa Barbara. Each campus selected 1–3 sites to demonstrate the methods and procedures used by the CEP: Rivera Library and Parking Lots (PL) 13 and 16 at UCR, Thornton Hospital, the Cancer Center, and PL 601 at UCSD, and Engineering I building at UCSB. The project provided an estimate of strong ground motions at each selected site, for selected earthquake scenarios. These estimates were obtained by using an integrated geological, seismological, geophysical, and geotechnical approach, that brings together the capabilities of campus and laboratory personnel. Most of the site-specific results are also applicable to risk evaluation of other sites on the respective campuses. The CEP studies have provided a critical assessment of whether existing campus seismic design bases are appropriate. Generally speaking, the current assumptions are not acknowledging the severity of the majority of expected motions. Eventually, both the results from the SOP and from the CEP should be analyzed, to arrive at decisions concerning the design-basis for buildings on UC campuses. Published by Elsevier Ltd.

We expand here the description of the Antarctic temperature variability during the long interglacial period occurring ~400 thousand years before present (Marine Isotopic Stage, MIS 11). This is achieved thanks to new detailed deuterium measurements conducted on the EPICA Dome C ice core, Antarctica, with a ~50 year temporal resolution. Despite an ice diffusion length reaching ~8 cm at MIS 11 depth, the data allow to highlight a variability at multi-centennial scale for MIS 11, as it has already been observed for the Holocene (MIS 1). Differences between MIS 1 and MIS 11 are analysed regarding the links between multi-millennial trends and sub-millennial variability. The EPICA Dome C deuterium record shows an increased variability and a shift in the observed periodicities at the onset of the final cooling phase of MIS 11, with stronger millennial to multi-millennial variability. Our findings are robust with respect to sensitivity tests on the somewhat uncertain MIS 11 duration.

The Southern California Earthquake Center initiated a major large-scale earthquake simulation called TeraShake. The simulations propagated seismic waves across a domain of 600x300x80 km at 200 meter resolution, some of the largest and most detailed earthquake simulations of the southern San Andreas fault. The output from a single simulation may be as large as 47 terabytes of data and 400,000 files. The execution of these large simulations requires high levels of expertise and resource coordination. We describe how we performed single-processor optimization of the application, optimization of the I/O handling, and the optimization of execution initialization. We also look at the challenges presented by run-time data archive management and visualization. The improvements made to the application as it was recently scaled up to 40k BlueGene processors have created a community code that can be used by the wider SCEC community to perform large scale earthquake simulations.

[1] The small footprint (∼70 m) and ∼172 m along-track spacing of the Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud and land Elevation Satellite (ICESat) provides unprecedented horizontal resolution for a satellite altimeter. This enables ICESat to map many previously unresolved features on ice shelves, such as crevasses, rifts, grounding zones and ice fronts. We present examples of ICESat-derived elevation data showing topography over rifts on the Amery and Ross ice shelves, widths of rifts and as estimates of the thickness of melange (a collection of ice and snow trapped inside the rifts). We show that melange thickness remains constant over the ICESat data period and tends to be thicker in older rifts. We validate the ICESat-derived melange depth estimate with an in situ measurement on the Ross Ice Shelf.

The primary goal of the Ice, Cloud and land Elevation Satellite (ICESat) mission is ice sheet elevation change detection. Confirmation that ICESat is achieving its stated scientific requirement of detecting spatially-averaged changes as small as 1.5 cm/year requires continual assessment of ICESat-derived elevations throughout the mission. We use a GPS-derived digital elevation model (DEM) of the salar de Uyuni, Bolivia for this purpose. Using all twelve ICESat passes over the salar survey area acquired to date, we show that the accuracy of ICESat-derived elevations is impacted by environmental effects (e.g., forward scattering and surface reflectance) and instrument effects (e.g., pointing biases, detector saturation, and variations in transmitted laser energy). We estimate that under optimal conditions at the salar de Uyuni, ICESat-derived elevations have an absolute accuracy of

The basic approach of the Campus Laboratory Collaboration (CLC) project is to combine the substantial expertise that exists within the University of California (UC) system in geology, seismology, geotechnical engineering, and structural engineering to evaluate the effects of large earthquakes on UC facilities. These estimates draw upon recent advances in hazard assessment, seismic wave propagation modeling in rocks and soils, dynamic soil testing, and structural dynamics. The UC campuses currently chosen for applications of our integrated methodology are Riverside, San Diego, and Santa Barbara. The basic procedure is first to identify possible earthquake source regions and local campus site conditions that may affect estimates of strong ground motion. Combined geological , geophysical, and geotechnical studies are conducted to characterize each campus with specific focus on the location of particular target buildings of special interest to the campus administrators. The project will then drill and log deep boreholes next to the target structure, to provide direct in-situ measurements of subsurface material properties and to install uphole and downhole 3-component seismic sensors capable of recording both weak and strong motions. The boreholes provide access to deeper materials, below the soil layers, that have relatively high seismic shear-wave velocities. Analysis of conjugate downhole and uphole records provides a basis for optimizing the representation of the low-strain response of the sites. Earthquake rupture scenarios of identified causative faults are combined with the earthquake records and nonlinear soil models to provide site-specific estimates of strong motions at the selected target locations. The predicted ground motions are then used as input to the dynamic analysis of the buildings.

Space geodesy as a scientific discipline is in the very unique and enviable position of marrying fast developing technology with rapidly expanding scientific goals. As high precision techniques become more easily accessible to the scientific community, the range of problems which geodesists can address in earnest expands to incorporate issues previously deemed too formidable to be treated successfully. Recent workshops (Mueller and Zerbini, 1989; NASA, 1991) resulted in fairly comprehensive reviews of the opportunities opened by space geodesy, and in specific recommendations concerning the areas in which to focus attention. In the context of an International Global GPS Service, we take a somewhat specialized point of view and focus on science issues that cannot be addressed properly in the absence a global network, as well as applications which would benefit directly and substantially from such a network. These science goals can then be embodied in a set of specific objectives, which provide a context for network design. The rationale for a “Common, Global, Integrated, Fundamental Network”, has been discussed by Knickmeyer (1990) and Boucher (1990).

The comparative study of two methods of the proteolysis of IgG with the aim of obtaining F(Ab)2-fragments from the blood sera of patients and healthy donors has been made. Different methods for the isolation of F (ab)2-fragments, such as gel filtration on Sephadex G-200, affinity chromatography on protein A-BrCN-sepharose, reprecipitation with zinc sulfate, have been analyzed. For further work the method of the peptic decomposition of whole serum with subsequent salting out with ammonium sulfate and gel filtration on Sephadex G-200 has been chosen.

We have considered the problem of elastic wave velocities in a matrix containing aligned ellipsoidal fluid-filled cracks. This problem is relevant to a variety of geophysical applications, including crustal and mantle seismology and the behavior of stressed and dilatant rock. When the cracks are ellipsoids of revolution, the composite is transversely isotropic and is describable with five elastic constants. For aligned oblate spheroids the major reduction in velocity occurs along the axis of symmetry. The opening of new cracks, the widening of old cracks, or the reduction of pore pressure accompanying crustal dilatancy can be expected to cause a large decrease in compressional velocity and considerable compressional wave anisotropy.

Assuming lithospheric plates to be rigid, we systematically invert 68 spreading rates, 62 fracture zones trends and 10^6 earthquake slip vectors simultaneously to obtain a self-consistent model of instantaneous relative motions for eleven major plates. The inverse problem is linearized and solved iteratively by a maximum likelihood procedure. Because the uncertainties in the data are small, Gaussian statistics are shown to be adequate. The use of a linear theory permits (1) the calculation of the uncertainties in the various angular velocity vectors caused by uncertainties in the data, and (2) quantitative examination of the distribution of information within the data set. The existence of a self-consistent model satisfying all the data is strong justification of the rigid plate assumption. Slow movement between North and South America is shown to be resolvable. We then invert the trends of 20 linear island chains and aseismic ridges under the assumptions that they represent the directions of plate motions over a set of hot spots fixed with respect to each other. We conclude that these hot spots have had no significant relative motions in the last 10 My.

We investigate one-dimensional waves in a standard linear solid for geophysically relevant ranges of the parameters. The critical parameters are shown to be T*= t_u/Q_m where t_u is the travel time and Q_m the quality factor in the absorption band, and τ^(-1)_m, the high-frequency cut-off of the relaxation spectrum. The visual onset time, rise time, peak time, and peak amplitude are studied as functions of T* and τ_m. For very small τ_m, this model is shown to be very similar to previously proposed attenuation models. As τ_m grows past a critical value which depends on T*, the character of the attenuated pulse changes. Seismological implications of this model may be inferred by comparing body wave travel times with a ‘one second’ earth model derived from long-period observations and corrected for attenuation effects assuming a frequency independent Q over the seismic band. From such a comparison we speculate that there may be a gap in the relaxation spectrum of the Earth's mantle for relaxation times shorter than about one second. However, observational constraints from the attenuation of body waves suggest that such a gap might in fact occur at higher frequencies. Such a hypothesis would imply a frequency dependence of Q in the Earth's mantle for short-period body waves.

The dislocation microstructure of mantle materials can account simultaneously for long-term steady-state creep, and for stress wave attenuation at seismic frequencies. The hypothesis that a single microstructural model explains therheology for characteristic times ranging from 1 to 1010 seconds can be used to restrict the class of permissible rheological models for the mantle. W e review steady-state dislocation dam ping models in order of increasing complexity, and reject those which do not satisfy laboratory data or geophysical constraints. This elimination procedure leads us to consider an organized microstructure, in which most dislocations are found inside subgrain walls. The cells contain relatively few dislocation links. These are free to bow under small, i.e. seismic, stresses. The time constant of this mechanism is controlled either by the diffusion of kinks or of point defects bound to the dislocation line. The glide of intragrain dislocations explains the m agnitude and frequency range of seismic attenuation. Steady-state creep is governed by recovery through climb and annihilation in cell walls. Under conditions of jog undersaturation, climb is controlled by jog formation in addition to self-diffusion, and the model requires a higher creep activation energy than for self-diffusion, in agreement w th observations on olivine. Quantitative agreement with laboratory data is achieved if the density of cell-wall dislocations is one to two orders of magnitude higher than the density of intracell dislocations. Self-diffusion is probably controlled by silicon diffusion at low pressure and by oxygen diffusion at high pressure. T he long-term tectonic stress is the dominant factor determining scale lengths; as a result, the total strength of the relaxation associated with bowing of intracell dislocation links is fixed by the geometry and is of the order of 10 % . This limits the width of the seismic absorption band to 2 -3 decades in frequency for each mantle mineral. T he actual position of the seismic absorption band is determined primarily as a result of a trade-off between temperature, pressure and tectonic stress. This model provides a physical framework within which the quality factor and viscosity are related via the dislocation microstructure.

A simple, approximate (‘transparent’) solution is derived for the near-field radiation emitted by a spherical cavity expanding in an initial pure shear prestress field. Near-field terms, their propagation and decay are discussed for a variety of growth histories, and are shown to be rather insensitive to the detailed variations of rupture velocity. The transparency approximation is shown to be adequate in the near field as well as in the far field; the main effect is a slight narrowing of far-field pulses. Time domain moment estimators at close range are more reliable for the S wave than for the P wave since transverse pulses are not as strongly contaminated by near-field effects.

Summary. Stress relaxation due to a growing cavity in a uniformly prestressed (pure shear) elastic medium is investigated, using the transparent source approximation of Archambeau (1972). A simple representation of the far-field radiation is obtained. A planar, circular dislocation of same growth history as the cavity is constructed which yields the same far-field pulses, except for geometrical effects. It is shown that different ‘equivalent’ dislocations must be used to model P and S pulses wherever the rupture velocity is trans-sonic. Simple analytical forms for the far-field pulses are derived which hold even in the case of relatively complicated source growth history. The dependence of waveforms on the various source parameters is illustrated by selected waveform calculations. It is suggested that this model yields an adequate representation of the far-field tectonic release radiation from underground explosions.

The transient and impulse responses (Green's function) for one-dimensional wave propagation in a standard linear solid are calculated using a Laplace Transform method. The spectrum of relaxation times is chosen so as to model a constant Q medium within an absorption band covering a broad frequency range which may be chosen so as to include the seismic frequencies. The inverse transform may be evaluated asymptotically in the limit of very long propagation times using the saddle point method. For shorter propagation times the method of steepest descent may be modified so as to yield an accurate first motion approximation. The character of the small amplitude precursor to the large amplitude ‘visible’ signal is investigated analytically. It is shown that the signal velocity is intermediate between the high-frequency (‘unrelaxed’) and the low-frequency (‘relaxed’) limits of the phase velocity.

Spontaneous failure in a solid medium is described as a localized transition of the material from one physical state to another, characterized in part by contrasting rheological properties and density. Such a process is viewed as a local disordering of the relatively ordered structure of the solid due to any variety of causes, such as massive microfracturing or shear melting, and can be confined to a very thin zone, but nevertheless of finite volume such that a volumetric transition energy can be defined. This leads to the description of failure as a generalized phase transition in a prestressed continuum, with instability and transition zone growth being driven by the energy contributions from the relaxation of stress in the surrounding medium. Direct application of mass, momentum and energy conservation to such a generalized phase transition leads to ‘jump’ conditions specified on the growing boundary surface of the transition zone, that relate the rupture growth to discontinuous changes in the dynamic field variables across the failure zone boundary. These field discontinuities are, in turn, related to the localized changes in physical properties induced by failure. Dynamical conditions for rapid spontaneous failure growth in a stressed medium are investigated in some detail, and we find that the failure boundary growth can be simply expressed in terms of energy ‘failure condition’ and a dynamic growth condition specifying the rupture velocity. These results imply that the integral energy change associated with earthquakes is in the range 10^4−10^6 erg/g. Further the failure growth rate is shown to be expressible in terms of the rheological properties of the material before and after failure. For shear melting resulting in a low viscosity fluid, for example, the rupture velocity will be near the shear velocity of the original material. A general Green's function solution for the radiation due to stress relaxation in the medium surrounding the growing failure zone is given and provides the basis for detailed computations of the strain or displacement field changes due to spontaneous failure processes. In particular, it is shown that the jump conditions for the growing transition zone boundary appear naturally as surface integral terms over the boundary. Since these boundary conditions contain the failure rate explicitly, then these terms include effects that have not been represented in previous integral representations of the radiation field resulting from failure. Further, we show that the formal Green's integral representation for the dynamical wave field can be used with known, simple Green's functions to generate approximate solutions for complex failure processes occurring in media with inhomogeneous material properties and prestress.

Simple and convenient formulae are derived which describe the transformation of a multipolar expansion under an arbitrary proper rotation of the reference frame. When combined with the corresponding formulae for a translation, these results show how multipolar representations of source fields transform under any proper displacement of the reference frame. Particular emphasis is placed on the seismic source problem; however, these results find applications in many other physical problems.

We have constructed a model of the three-dimensional velocity structure in the crust and upper mantle beneath NTS. This model was obtained by inversion of teleseismic travel times from NTS explosions reported for a set of globally distributed seismograph stations. Although the geometry is conceptually the reciprocal of the classical geometry involving a localized network and distributed teleseismic sources, several important differences emerge. In particular, the data are contaminated by different error processes, and different correction terms need be applied to the raw travel time data. We present algorithms which take advantage of the large number of raw data initially available to improve to some extent the signal-to-noise ratio, and lead to a reduction of the inverse problem to computationally manageable size. In addition, we show how projection operators can be used to formulate an equivalent inverse problem with smaller dimensions which is insensitive to unknown baseline corrections and similar nuisance parameters. Finally, we develop an algorithm which permits further reduction in problem size by grouping redundant data with minimal loss of information and with further noise reduction.

The objective is to investigate the role of dislocations in both creep and attenuation. Attenuation in the mantle at seismic frequencies is thought to be caused by the glide of dislocations in the subgrains. Both kink and impurity drag can contribute to the glide time constant. The kink-formation, or Peierls barrier, model for dislocation glide is seen as a low-temperature, high-frequency mechanism most appropriate for pure systems. It is noted that a small amount of impurity drag brings the dislocation glide characteristic time into the seismic band at upper-mantle temperatures. The attenuation and creep behavior of the mantle are related by way of the dislocation structure. Analysis of the various possible mechanisms is facilitated by casting them and the geophysical data in terms of a pre-exponential characteristic time and an activation energy.

A contribution from members of the PAGES Past Interglacials (PIGS) Working Group. ABSTRACT: Whereas millennial to submillennial climate variability has been identified during the current interglacial period past interglacial variability features remain poorly explored because of lacking data at sufficient temporal resolutions. Here we present new deuterium data from the EPICA Dome C ice core documenting at decadal resolution temperature changes occurring over the East Antarctic plateau during the warmer than today last interglacial. Expanding previous evidence of instabilities during the last interglacial multicentennial subevents are identified and labeled for the first time in a past interglacial context. A variance analysis further reveals two major climatic features. First an increase in variability is detected prior to the glacial inception as already observed at the end of Marine Isotopic Stage 11 in the same core. Second the overall variance level is systematically higher during the last interglacial than during the current one suggesting that a warmer East Antarctic climate may also be more variable.