bluuebunny/crossref_metadata_2025 huggingface dataset:
Incoherent scatter radar observations of the cusp acceleration region and cusp field‐aligned currents
Authors: Nilsson H. , Kirkwood S. , Moretto T.
Published: February 2004

Incoherent scatter radar measurements are used to study the E region and lower F region in the cusp proper. At the equatorward edge of the cusp a region of enhanced ionization is found, indicating precipitation of either electrons of about 1 keV energy or protons of about 3 keV. The signature is found at the same altitude, around 150 km, as the maximum of the solar EUV produced ionization, but is clearly recognizable. The position and likely proton energies indicate that this is probably the ionospheric signature of the cusp acceleration region. Regions of low electron densities are also found in the same altitude region, which may be explained by downward field‐aligned currents causing depletions in the E and lower F region. First‐order estimates show that dense field‐aligned currents are needed to cause the observed depletions, possibly as dense as 30 μA/m2. The ionization in the cusp acceleration region, and the depletion caused by downward field‐aligned currents both influence the Pedersen conductivity of the ionosphere, and the resulting conductivity gradients strongly influence the small‐scale field‐aligned currents flowing in the cusp region.
Lava rise ridges of the Toomba basalt flow, north Queensland, Australia
Authors: Whitehead P. W. , Stephenson P. J.
Published: February 2004

Unusually long lava rises occur in the distal portion of the Toomba basalt flow, up to 120 km from the source. In the Lolworth creek region, three parallel lava rise ridges occur over a 6 km section. Two of these ridges are continuous for the entire 6 km. The ridges average 7 m in height and range from 35 m to 300 m in width. Lava inflation clefts are numerous, and lava rise pits also occur. Down flow, a single lava rise ridge, averaging 18 m high and up to 500 m wide, extends for a further 10 km. This ridge has a generally level surface with abrupt edges sloping between 45° and 90°. Accurate surveys across the ridges show that in some cases there has been some stretching of the surface, presumably prior to the formation of the prominent clefts. The ridges were formed from an initially thin flow that was inflated by a continuous layer of lava that underlay almost the entire width of each ridge, rather than by a system of lava tubes of more limited dimensions. Inflated material represents over 90% of the volume of the distal parts of the flow. Estimates of the time required to inflate the lava rise ridges range from 60 days to a year.
Periodic deformation of oceanic crust in the central Indian Ocean
Authors: Krishna K. S. , Ramana M. V. , Rao D. Gopala , Murthy K. S. R. , Rao M. M. Malleswara , Subrahmanyam V. , Sarma K. V. L. N. S.
Published: February 2004

New seismic reflection profiles of ≈5370 km, running through the Ocean Drilling Program Leg 116 sites and Deep Sea Drilling Project Sites 215 and 218, were obtained to investigate the spatial extent, timing, and nature of the Tertiary deformation of the equatorial central Indian Ocean. Analyses of the data revealed basement and sedimentary structures and structural unconformities that resulted from the release of compressional forces. Long‐wavelength (150–300 km) anticlinal basement structures with 1–2 km relief and tight folding and high‐angle faulting (5–20 km long) of oceanic basement and overlying sediments exist between the Afanasy Nikitin seamount and the Ninety east Ridge. The deformation zone extends from 10°S to the north up to ≈7°N latitude. The changes in the regional basement trend along 87°E longitude between latitudes 11°S and 15°N coincide with the significant tectonic events of the first major plate reorganization occurred in the eastern Indian Ocean at 90±5 Ma and changes in the Indian plate motion at 65±5 Ma. The basement deformation at selected places, a widespread unconformity of the upper Miocene, and subsequent younger unconformities (lower Pliocene and upper Pleistocene) indicate that the deformation activity might have begun earlier than the generally believed age of 7.5 Ma and appears to be periodic. The upper Miocene and upper Pleistocene deformational unconformities are, in general, observed south of 1°S, while the basement deformation and lower Pliocene deformational unconformity are mostly present in the area north of 1°S. It is surmised that the compressional stresses built up since the hard collision of India with Eurasia may have released for a short period prior to the early Miocene time and deformed the oceanic basement in the northeastern Indian Ocean. Thereafter the stress regime seems to have transferred to the north of the Indian shield and caused deformation of the continental lithosphere. Later, the activity reoccurred during the late Miocene (≈7.5 Ma), early Pliocene (≈4 Ma) and late Pleistocene (≈0.8 Ma) with a cyclicity of ≈3.5 m.y. and deformed the oceanic crust and sedimentary strata in the central Indian Ocean.
A delineation of the Nojima fault ruptured in the M7.2 Kobe, Japan, earthquake of 1995 using fault zone trapped waves
Authors: Li Yong‐Gang , Aki Keiiti , Vidale John E. , Alvarez Mark G.
Published: February 2004

We used four linear seismic arrays of portable seismometers at the northern Awaji Island, Japan, to record fault zone trapped waves from aftershocks of the 1995 M7.2 Hyogoken Nanbu (Kobe) earthquake from April to June 1996. Three arrays were deployed across the Nojima fault, which ruptured during the mainshock, while one array was deployed across the Higashiura fault, which did not break recently. We observed significant fault zone trapped waves with relatively large amplitudes and the long wave train following S waves only when both the stations and aftershocks were located close to the Nojima fault. The coda‐normalized spectral amplitudes of trapped waves show a maximum peak at 4–7 Hz, which decreases rapidly with distance from the fault trace. The normalized amplitudes of trapped waves also show a decrease with hypocentral distance along the fault, giving an apparent Q of approximately ∼25 at 4–7 Hz. In comparison, the array across the Higashiura fault recorded much shorter wave trains with higher frequencies after S arrivals for the same events. We simulate these trapped waves as S waves guided in a low‐velocity waveguide sandwiched between high‐velocity wall rocks. We find an adequate fit by using a waveguide 60 m wide at the northern site and 30–40 m wide elsewhere along the Nojima fault, a waveguide S velocity of 1.5–1.7 km/s, and a Q value of 25. For the Higashiura fault, the S velocity is 2.5 km/s, and the Q value is 80. The locations of aftershocks for which we observed fault zone trapped waves show that the Nojima waveguide is 9 km long and dips southeastward at 80°–85° to a depth of ∼16 km. It extends 6 km farther south westward along the Asano fault, though there are no obvious surface breaks along it. However, the waveguide is disconnected from the Suma fault on the main island, which was also ruptured during the Kobe earthquake, possibly because of the existence of an offset between the Nojima fault and the Suma fault.
Rake dependent rate and state friction
Authors: Sleep Norman H.
Published: February 2004

The sliding direction within the fault plane, conventionally defined as the rake, changes with time during earthquakes. To aid studies of this process, the formalism for rate and state friction is extended by using tensors to include anisotropy of the fault surface from sliding with variable rake. The evolution of the state variable ψ and porosity within a fault zone are considered to be decoupled from anisotropic damage, which is represented by a tensorLijkl, which has the usual symmetries of elastic constants. Letting the strain rate from sliding within the fault zone be, a permitted evolution equation forLiswheretis time, and ε2and ε1are strains to create new anisotropic damage and to undo preexisting anisotropic damage, and the second invariant of the‐strain rate tensor is. The instantaneous coefficient of friction for unidirectional sliding iswhere μ0is the steady state coefficient of friction at‐shear strain rate,aandbare small constants,is the shear strain rate, ψ is a state variable that represents damage, and ψ a normalizing factor. The tensor flow law is thenwhereis a normalization strain rate,Dijkl≡ δikδil+ δilδjk‐Lijkl, where δijis the Kronecker delta, ΔPis the effective normal traction, |τ|2≡ 1/2τijiτijis the second invariant of the shear traction, and τresis resolved shear traction in the sliding direction. Transient strengthening of a fault zone followed by gradual weakening occurs when the rake is suddenly changed.
Numerical simulations of flood basalt lava flows: Roles of parameters on lava flow morphologies
Authors: Miyamoto Hideaki , Sasaki Sho
Published: February 2004

Using a three‐dimensional numerical simulation model of lava flow, we studied the effects of parameters on the morphologies of simple flood basalt lava flows. The model can provide a more realistic description of morphologies of lava flows than two‐dimensional models because it can evaluate the complex relationship between erupted volume and length of lava by considering lateral spreading of flows. Moreover, our model can calculate lava morphologies on a very moderate slope or even on a flat plane without mesh direction dependency. It can simulate not only small‐scale flows on individual volcanoes but also large‐scale (>100 km) flows without numerical instability. Although the length of a lava flow is controlled by many parameters including rheological properties and eruption rate, the length is not a simple function of these parameters. We confirm that small changes in parameters such as slope angle and viscosity can affect the length of the flow. Increasing the eruption rate up to 107 m3/s makes basaltic lava flows longer. However, at eruption rates higher than 107 m3/s on 0.3° slopes, flow length does not increase beyond that of the 107 m3/s eruption rate due to volume conservation of erupted lava. Thus eruption conditions cannot be estimated from the length of a lava flow alone. Therefore the estimated eruption rate obtained by previous two‐dimensional models, which essentially estimate eruption rate from the length of the flow, will not always reveal useful values. On the other hand, the width of a simple lava flow is a good measure of its eruption rate because the width is mainly controlled by the eruption rate and yield strength. A simple lava whose width is greater than 100 km was almost certainly emplaced at eruption rates higher than 107 m3/s if the yield strength of the flow is in a basaltic range.
Topography of the 660‐km seismic discontinuity beneath Izu‐Bonin: Implications for tectonic history and slab deformation
Authors: Castle John C. , Creager Kenneth C.
Published: February 2004

We analyze the P wave codas of 65 paths from deep northwestern Pacific earthquakes recorded by arrays of stations in Germany, the western United States, India, and Turkmenistan. We identify a phase resulting from a near‐source S‐to‐P conversion at a nearly horizontal discontinuity ranging in depth from 650 to 730 km, which we interpret as a thermally depressed spinel to perovskite and magnesiowüstite phase transition. We migrate these data along with 39 more from Wicks and Richards [1993], accounting for three‐dimensional ray bending by the sloping discontinuity, to produce a high‐resolution topography map of the 660‐km discontinuity in the Izu‐Bonin region. Assuming an equilibrium phase transition, we interpret the discontinuity depth in terms of local temperatures. The slab, if defined by a thermal anomaly greater than −400°K, is only about 100 km thick near 28°N suggesting the slab is penetrating into the lower mantle with little or no advective thickening. Farther to the north, however, cold material appears spread out over a wide region, consistent with the slab having been laid down flat on the 660‐km discontinuity as the trench retreated 2000 km eastward. Both the narrow slab to the south and the flat‐lying slab to the north are consistent with recent high‐resolution tomographic images. The depression to 745 km along the arc is consistent with a maximum thermal anomaly of about 1100°K. Along the entire arc, the depression occurs directly beneath the deepest earthquakes, even where seismicity is dipping at 45° and stops at 450 km depth, suggesting that the slab steepens to a vertical dip at the deepest seismicity. This change to a vertical orientation suggests that the slab loses strength temporarily through a physical process which causes the seismicity to increase dramatically and then abruptly cease.
Self‐potential and magnetic surveying of La Fournaise volcano (Réunion Island): Correlations with faulting, fluid circulation, and eruption
Authors: Michel Sylvie , Zlotnicki Jacques
Published: February 2004

Self‐potential (SP) and magnetic surveys have been performed on the basaltic La Fournaise volcano (Réunion Island, Indian Ocean) between 1989 and 1992. The 1992 SP mapping of the inner caldera (Enclos Fouqué) reveals high relative positive SP anomalies. They are interpreted as related to a large hydrothermal system. A large SP anomaly of 2 V is centered on the terminal cone. A horseshoe‐shaped positive SP anomaly intersects the cone. This anomaly outlines the main arcuate fracture zone (MFZ), oriented north‐south on the cone and extending to the northeast and southeast away from the summit. The zone controls the volcano dynamism. Most of the fissure eruptions occur along this volcanotectonic axis. A second mechanical weakness axis is evidenced by a positive SP anomaly lying along a 120°N trend. Both volcanoes of the island, Piton des Neiges and later La Fournaise, have been built up along it. A large structure with reverse magnetization is found at the southeastern tip of this axis. This 120°N axis is interpreted as an old regional structure associated with a lithospheric weakness zone located beneath Réunion Island. The SP anomalies are thought to be of electrokinetic origin. In the central part of the volcano, along the MFZ, and the 120°N axis, positive SP data suggest hydrothermal upwelling caused by thermal transfer from the magma chamber and the dikes of the last eruptions. Away from the summit, SP data suggest groundwater infiltrates the massif by gravity effect. Changes of the SP with time are related to volcanic activity. The SP anomaly associated with main fracture zone has been generated by the 23 eruptions occurring between 1981 and 1992. Short‐time local SP anomalies that disappear in a few months are associated with individual eruptions.
Tectonic history of the Pacific‐Farallon‐Phoenix triple junction from Late Jurassic to Early Cretaceous: An abandoned Mesozoic spreading system in the Central Pacific Basin
Authors: Nakanishi Masao , Winterer Edward L.
Published: February 2004

In the Central Pacific Basin, an abandoned, NE trending spreading ridge is evident on the satellite gravity map and is confirmed in bathymetric and magnetic data. Our identification of magnetic anomaly lineations flanking the abandoned ridge suggests that between chrons M21 (147 Ma) and M14 (135 Ma) it was the plate boundary between the Pacific plate and a microplate, which we here name the Trinidad microplate. The configuration of the Pacific‐Farallon‐Phoenix triple junction until chron M22 (149 Ma) was fault‐fault‐ridge (FFR). After chron M22, the Pacific‐Farallon‐Phoenix triple junction changed its configuration. The reorganization of the triple junction led to the birth of the Trinidad microplate in its vicinity. Around chron M15 (136 Ma), the spreading ridge between the Pacific plate and the Trinidad microplate was abandoned and the Magellan microplate was born and remained active till chron M9 (128.5 Ma). After welding of the Magellan microplate to the Pacific plate, the triple junction had a ridge‐ridge‐ridge (RRR) configuration until the major reorganization around chron M0 (120 Ma).
Properties of seismic fault zone waves and their utility for imaging low‐velocity structures
Authors: Ben‐Zion Yehuda
Published: February 2004

A two‐dimensional solution for the scalar wave equation in a model of two vertical layers between two quarter spaces is used to study properties of seismic waves in a laterally heterogeneous low‐velocity structure. The waves, referred to as seismic fault zone waves, include head waves, internal fault zone reflections, and trapped waves. The analysis aims to clarify the dependency of the waves on media velocities, media attenuation coefficients, layer widths, and source‐receiver geometry. Additional calculations with extreme low‐velocity layers provide examples that may be relevant for volcanic and geothermal domains. The interference patterns controlling seismic fault zone waves change with the number of internal reflections in the low‐velocity structure. This number increases with propagation distance along the structure, decreases with fault zone width, and increases (for given length scales) with the velocity contrast. The relative lateral position of the source within the low‐velocity layer modifies die length scales associated with internal reflections and influences the resulting interference pattern. Low values of Q affect considerably the dominant period and overall duration of the waves. Thus there are significant tradeoffs between propagation distance along the structure, fault zone width, velocity contrast, source location within the fault zone, and Q. The lateral and depth receiver coordinates determine the particular point where the interference pattern is sampled and observed motion is a strong function of both coordinates. The zone connecting sources generating fault zone waves and observation points with appreciable wave amplitude can be over an order of magnitude larger than the fault zone width. Calculations for cases with layer P wave velocity of ∼200 m s−1, modeling a vertical dike or crack with fluid and gas, show conspicuous persisting oscillations. The results resemble aspects of seismic data in volcanic domains. If these waves exist in observed records, their explicit recognition and modeling will help to separate source and structural effects and aid in the interpretation of volcano‐seismology signals. Although the tradeoffs in parameters governing seismic fault zone waves are significant, each variable has its own signature, and the parameters may be constrained by additional geophysical data. Simultaneous modeling of many waveforms with an appropriate solution can resolve the various parameters and provide a high‐resolution structural image.
Two‐way coupling between Vesuvius eruptions and southern Apennine earthquakes, Italy, by elastic stress transfer
Authors: Nostro Concetta , Stein Ross S. , Cocco Massimo , Belardinelli Maria Elina , Marzocchi Warner
Published: February 2004

During the past 1000 years, eruptions of Vesuvius have often been accompanied by large earthquakes in the Apennines 50–60 km to the northeast. Statistical investigations had shown that earthquakes often preceded eruptions, typically by less than a decade, but did not provide a physical explanation for the correlation. Here, we explore elastic stress interaction between earthquakes and eruptions under the hypothesis that small stress changes can promote events when the Apennine normal faults and the Vesuvius magma body are close to failure. We show that earthquakes can promote eruptions by compressing the magma body at depth and opening suitably oriented near‐surface conduits. Voiding the magma body in turns brings these same normal faults closer to Coulomb failure, promoting earthquakes. Such a coupling is strongest if the magma reservoir is a dike oriented normal to the regional extension axis, parallel to the Apennines, and the near‐surface conduits and fissures are oriented normal to the Apennines. This preferred orientation suggests that the eruptions issuing from such fissures should be most closely linked in time to Apennine earthquakes. Large Apennine earthquakes since 1400 are calculated to have transferred more stress to Vesuvius than all but the largest eruptions have transferred to Apennine faults, which may explain why earthquakes more commonly lead than follow eruptions. A two‐way coupling may thus link earthquakes and Vesuvius eruptions along a 100‐km‐long set of faults. We test the statistical significance of the earthquake‐eruption correlation in the two‐way coupling zone, and find a correlation significant at the 95% confidence level.
The Roza Member, Columbia River Basalt Group: A gigantic pahoehoe lava flow field formed by endogenous processes?
Authors: Thordarson T. , Self S.
Published: February 2004

We present studies on the physical volcanology of the ∼15 Ma Roza Member of the Wanapum Formation in the Columbia River Basalt Group. The Roza Member represents a compound pahoehoe flood basalt lava flow field, with an area of ∼40,300 km2 and a volume of ∼1300 km3. It consists of 4 major lava flows each composed of numerous, decimeter to kilometer long pahoehoe lobes. Roza lavas feature a wide range of pahoehoe surface structures, such as lava rise plateaus, tumuli, and surface breakouts, and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas. An integral component of the Roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from Hawaii and Iceland, both at the same scale and at much larger scales. We identify a three‐part division of the sheet lobes into basal crust, lava core, and lava crust, which are interpreted as the equivalent to the bottom crust, the liquid lava core, and the surface crust of an active inflating pahoehoe lobe. The upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling. This relationship is used to calculate the emplacement time for individual Roza sheet lobes and to derive a first‐order estimate on the duration of the Roza eruption. The results indicate that the emplacement of individual Roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years. We propose that the Roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth. As the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of <0.1 °C/km and allowed for efficient transport of lava over distances up to 300 km.
Carbon dioxide and helium emissions from a reservoir of magmatic gas beneath Mammoth Mountain, California
Authors: Sorey M. L. , Evans W. C. , Kennedy B. M. , Farrar C. D. , Hainsworth L. J. , Hausback B.
Published: February 2004

Carbon dioxide and helium with isotopic compositions indicative of a magmatic source ( δ13C = −4.5 to −5‰,3He/4He = 4.5 to 6.7 RA) are discharging at anomalous rates from Mammoth Mountain, on the southwestern rim of the Long Valley caldera in eastern California. The gas is released mainly as diffuse emissions from normal‐temperature soils, but some gas issues from steam vents or leaves the mountain dissolved in cold groundwater. The rate of gas discharge increased significantly in 1989 following a 6‐month period of persistent earthquake swarms and associated strain and ground deformation that has been attributed to dike emplacement beneath the mountain. An increase in the magmatic component of helium discharging in a steam vent on the north side of Mammoth Mountain, which also began in 1989, has persisted until the present time. Anomalous CO2discharge from soils first occurred during the winter of 1990 and was followed by observations of several areas of tree kill and/or heavier than normal needlecast the following summer. Subsequent measurements have confirmed that the tree kills are associated with CO2concentrations of 30–90% in soil gas and gas flow rates of up to 31,000 g m−2d−1at the soil surface. Each of the tree‐kill areas and one area of CO2discharge above tree line occurs in close proximity to one or more normal faults, which may provide conduits for gas flow from depth. We estimate that the total diffuse CO2flux from the mountain is approximately 520 t/d, and that 30–50 t/d of CO2are dissolved in cold groundwater flowing off the flanks of the mountain. Isotopic and chemical analyses of soil and fumarolic gas demonstrate a remarkable homogeneity in composition, suggesting that the CO2and associated helium and excess nitrogen may be derived from a common gas reservoir whose source is associated with some combination of magmatic degassing and thermal metamorphism of metasedimentary rocks. Furthermore, N2/Ar ratios and nitrogen isotopic values indicate that the Mammoth Mountain gases are derived from sources separate from those that supply gas to the hydrothermal system within the Long Valley caldera. Various data suggest that the Mammoth Mountain gas reservoir is a large, low‐temperature cap over an isolated hydrothermal system, that it predates the 1989 intrusion, and that it could remain a source of gas discharge for some time.
Paleointensity determination, magnetic domain structure, and selection criteria
Authors: Perrin M.
Published: February 2004

This special section is focused on the impact of Kittel's theory of magnetic domains on rock magnetism, and this paper is focused on the implications for paleointensity determinations. Absolute paleointensity determination is based on specific properties of thermoremanent magnetizations (TRMs), mainly the linear dependence of a TRM's intensity on the inducing field and the additivity and independence of partial TRMs. These properties are exhibited by populations of noninteracting single‐domain (SD) grains but not by populations of multidomain grains. The situation is more complex in the pseudo‐single‐domain population, the most common one in natural rocks usable for paleointensity studies, which sometimes exhibit SD‐like behavior but not always. If the experiments were restricted to SD rocks, it would not be possible to find enough outcrops to have the spatial and temporal resolution needed for interpretation of the data in terms of geodynamo. However, as paleointensity determination is very time consuming, a preselection of suitable samples is necessary. A new procedure will be proposed using a direct test of partial TRM's properties with a fully automated experiment, fast to implement.
Clinoform development by advection‐diffusion of suspended sediment: Modeling and comparison to natural systems
Authors: Pirmez Carlos , Pratson Lincoln F. , Steckler Michael S.
Published: February 2004

Clinoforms are the building blocks of prograding stratigraphic sequences. These sigmoid‐shaped surfaces can be found forming today on modern deltas. Sedimentation rate profiles over the clinoform surface of these deltas show low rates of sediment accumulation on both topset and bottomset regions, with a maximum accumulation rate on the upper foreset region. We present a model for the formation of clinoforms that relies on the interpretation of modern clinoform sedimentation as a result of the distribution of shear stresses at the mouth of a river. Model clinoform surfaces are generated using an equation for the conservation of suspended sediment concentration, together with a conservation of fluid equation for simple time‐averaged flow velocity fields. In the model, suspended sediment is adverted horizontally into a basin, and gravitational settling of sediment particles is counteracted by vertical turbulent diffusion. In shallow water, shear stresses are too large to allow deposition, and sediment bypasses the topset region. With increasing water depth, near‐bed shear stresses decrease, and sediment is allowed to deposit at the foreset region, with gradually decreasing rates toward deeper water. This sedimentation pattern leads to progradation of the clinoform surfaces through time. The clinoform surfaces produced by the model capture the fundamental morphological characteristics of natural clinoforms. These include the gradual slope rollover at the topset and bottomset, steeper foreset slopes with increased grain size, and an increase in foreset slope through time as clinoforms prograde into deeper water. Because the parameters controlling the model clinoforms have a direct relation to physical quantities that can be measured in natural systems, the model is an important step toward unraveling the physical processes associated with these deposits.
Magnetotelluric imaging of the Society Islands hotspot
Authors: Nolasco Rita , Tarits Pascal , Filloux Jean H. , Chave Alan D.
Published: February 2004

In April‐June 1989, seafloor magnetotelluric data across and along the leading edge of the Tahiti hotspot were obtained. The magnetotelluric response functions were found to be strongly influenced by bathymetric and island effects, and a new procedure for modeling and removing this distortion using a thin sheet approach combined with the measured water depths is introduced. The corrected response functions are consistent with a two‐dimensional structure. Inversion of the data shows a slightly higher conductivity (relative to a reference site located away from the hotspot) down to 130 km depth beneath the active area southeast of Tahiti underlain by a more resistive structure. There is a suggestion for a change in conductivity in the 400–450 km depth range, which is consistent with elevated temperatures. This result is consistent with a mantle plume of limited extent (less than 150 km radius) located near the leading edge of the Tahiti hotspot. The magnetotelluric data provide no evidence for lithospheric thinning or for a strong thermal influence over a large area, as would be required by a superswell model.
Nonlinear sediment response during the 1994 Northridge earthquake: Observations and finite source simulations
Authors: Field Edward H. , Zeng Yuehua , Johnson Paul A. , Beresnev Igor A.
Published: February 2004

We have addressed the long‐standing question regarding nonlinear sediment response in the Los Angeles region by testing whether sediment amplification was similar between the Northridge earthquake and its aftershocks. Comparing the weak‐ and strong‐motion site response at 15 sediment sites, we find that amplification factors were significantly less for the main shock implying systematic nonlinearity. The difference is largest between 2 and 4 Hz (a factor of 2), and is significant at the 99% confidence level between 0.8 and 5.5 Hz. The inference of nonlinearity is robust with respect to the removal of possibly anomalous sediment sites and how the reference‐site motion is defined. Furthermore, theoretical ground‐motion simulations show no evidence of any bias from finite source effects during the main shock. Nonlinearity is also suggested by the fact that the four sediment sites that contain a clear fundamental resonance for the weak motion exhibit a conspicuous absence of the peak in the strong motion. Although we have taken the first step of establishing the presence of nonlinearity, it remains to define the physics of nonlinear response and to test the methodologies presently applied routinely in engineering practice. The inference of nonlinearity implies that care must be exercised in using sediment site data to study large earthquakes or predict strong ground motion.
Teleseismic estimates of radiated seismic energy: The E/M0 discriminant for tsunami earthquakes
Authors: Newman Andrew V. , Okal Emile A.
Published: February 2004

We adapt the formalism of Boatwright and Choy for the computation of radiated seismic energy from broadband records at teleseismic distances to the real‐time situation when neither the depth nor the focal geometry of the source is known accurately. The analysis of a large data set of more than 500 records from 52 large, recent earthquakes shows that this procedure yields values of the estimated energy, EE, in good agreement with values computed from available source parameters, for example as published by the National Earthquake Information Center (NEIC), the average logarithmic residual being only 0.26 units. We analyze the energy‐to‐moment ratio by defining Θ = log10(EE/M0). For regular earthquakes, this parameter agrees well with values expected from theoretical models and from the worldwide NEIC catalogue. There is a one‐to‐one correspondence between values of Θ that are deficient by one full unit or more, and the so‐called “tsunami earthquakes”, previously identified in the literature as having exceedingly slow sources, and believed due to the presence of sedimentary structures in the fault zone. Our formalism can be applied to single‐station measurements, and its coupling to automated real‐time measurements of the seismic moment using the mantle magnitude Mm should significantly improve real‐time tsunami warning.
Paleoseismicity of the 1981 Corinth earthquake fault: Seismic contribution to extensional strain in central Greece and implications for seismic hazard
Authors: Collier Richard E. L. , Pantosti Daniela , D'Addezio Giuliana , De Martini Paolo Marco , Masana Eulàlia , Sakellariou Dimitris
Published: February 2004

We present paleoseismological trenching results for the active Skinos Fault, which ruptured the surface on the Alkyonides Gulf basin margin in the 1981 Gulf of Corinth earthquake sequence. Three trenches expose evidence of up to six previous events which are comparable to the 1981 deformation in terms of size and geometry. Vertical displacement produced by the 1981 earthquake ranged from 0.45 to 1.3 m at the Bambakies Fan trench sites, decreasing towards the eastern fault tip east of the trenches. Trench 1 reveals two previous events with vertical displacements between 0.5 and 1.2 m since 390 A.D. Trench 2 reveals five or six previous events, but these are not dated. Trench 3 reveals four previous events since 670 A.D. Vertical displacements associated with interpreted paleoearthquakes at the trench sites are ≤1.2 m. The recurrence interval on the Skinos Fault is estimated to average 330 years. However, significant variation in recurrence interval is allowed by the available radiometric dates. Average vertical displacement rates derived from the trenches are in the range 0.7–2.5 mm/yr. A similar long‐term average vertical displacement rate of 1.2–2.3 mm/yr is estimated for the lifespan of the basin‐bounding fault. This equates to a horizontal seismic strain contribution of ≤2.5 mm/yr from the Skinos Fault. This local seismic strain rate overlaps, within error, with geodetically determined velocities across the Alkyonides Gulf assumed to represent uniform deep‐crustal strain. Thus seismic deformation on the basin‐bounding fault system may take up the major part of extension across the basin, and aseismic strain is not necessitated by the data. If correct, this would imply that geodetically determined strain rates may be used as a proxy for potential seismic moment release in seismic hazard analyses for this region.
Improved ocean tide loading corrections for gravity and displacement: Canada and northern United States
Authors: Lambert A. , Pagiatakis S. D. , Billyard A. P. , Dragert H.
Published: February 2004

Within 100 km of the North American coastline, ocean tide loading effects are ∼1 order of magnitude larger than the present‐day precision of absolute gravity (1 μGal) and continuous, differential Global Positioning System (GPS) measurements (3–8 mm). In relation to the precision of these measurements, ocean loading effects on gravity tend to be larger than the effect of loading on GPS measurements. Even at sites hundreds of kilometers from the coast, ocean tide loading can affect superconducting gravimeters at a level of 1 order of magnitude higher than the precision with which tidal constituents amplitudes can be resolved (0.1 μGal). In order to reduce contamination of high‐precision geodetic measurements by ocean tide loading, a numerical representation of the nearshore ocean tide load constituents, M2, S2, N2, O1, K1, has been developed using available ocean tide, numerical, modeling results for Canadian waters. The nearshore ocean tides are represented by a grid of cells, ranging in size from 0.125° to 0.5°, in which the amplitude and phase lag of tidal constituents are constant and which are bounded, in general, by lines of constant latitude and longitude. The detailed nearshore tidal representation was originally designed to supplement the global 1°×1° model of Schwiderski, but computations have also been carried out using the FES95.2, global model. Ocean tide loading computations that include the more detailed coastal ocean tide representations yield 10–20% changes in tidal correction values. A significant reduction in the variance of absolute gravity residuals is observed at Vancouver Island absolute gravity stations when the more detailed coastal model is used, but a considerable, unexplained residual remains at Holberg at the northwestern tip of Vancouver Island. Computations based on the FES95.2 model yield slightly smaller gravity residuals at west coast sites but only at the measurement precision level. Ocean loading effects on daily GPS positions in the Western Canada Deformation Array are adequately predicted by the Schwiderski global ocean tide loading model. Data from the Canadian Superconducting Gravimeter Installation, Gatineau, Quebec, for M2and O1were compared with ocean tide load modelling results for the Schwiderski and FES95.2 global ocean tide models enhanced by the nearshore model. With the enhancement, the two models agree with each other to within the expected computational uncertainty of 0.1 μGal for both M2and O1. Both models predict an ocean loading effect at O1within 0.1 μGal of the observed effect; however, the predicted loading effect for M2is still 0.2 μGal smaller than the observed effect, which suggests that there is still room for improvement in semidiurnal ocean tide models for the east coast of North America. The enhanced ocean tide loading models will become more important in the future when gravity and position are measured at subcentimeter precision over periods shorter than 24 hours.
Investigations in the character of QTL affecting negatively correlated milk traits
Authors: Freyer G. , Sørensen P. , Kühn C. , Weikard R.
Published: January 2004

The primary aim of this study was to investigate the quantitative trait loci (QTL) on BTA6 that affect negatively correlated milk traits, using bivariate covariance component analysis of milk yield and fat (or protein) content, protein yield and fat content, and fat yield and protein content. A set of five different genetic models was adapted to differentiate trait‐specific QTL in close linkage from pleiotropy. Using a grand‐daughter design consisting of five half‐sib families from the German Holstein population and 298 sons genotyped for 16 microsatellite markers on BTA6, we found significant trait‐specific QTL for fat content and protein yield, 24 cM apart. Markers BM1329 and FBN12 bracketed the QTL for fat content, and the region between TGLA37 and FBN13 most likely harbours a QTL for protein yield. The analysis based on the close linkage model fully confirmed this result. Despite the pure QTL findings confirming results from the literature, distinguishing pleiotropic and closely linked QTL for competitive traits is a new aspect. Our multivariate analysis results did not suggest a pleiotropic QTL for the investigated negatively correlated traits. The QTL‐based trait correlations were discussed as an important aspect of modelling that needs to be considered in the future.
Bayesian comparison of test‐day models under different assumptions of heterogeneity for the residual variance: the change point technique versus arbitrary intervals
Authors: López‐Romero P. , Rekaya R. , Carabaño M. J.
Published: January 2004

Test‐day milk yields from Spanish Holstein cows were analysed with two random regression models based on Legendre polynomials under two different assumptions of heterogeneity of residual variance which aim to describe the variability of temporary measurement errors along days in milk with a reduced number of parameters, such as (i) the change point identification technique with two unknown change points and (ii) using 10 arbitrary intervals of residual variance. Both implementations were based on a previous study where the trajectory of the residual variance was estimated using 30 intervals. The change point technique has been previously implemented in the analysis of the heterogeneity of the residual variance in the Spanish population, yet no comparisons with other methods have been reported so far. This study aims to compare the change point technique identification versus the use of arbitrary intervals as two possible techniques to deal with the characterization of the residual variance in random regression test‐day models. The Bayes factor and the cross‐validation predictive densities were employed for the model assessment. The two model‐selecting tools revealed a strong consistency between them. Both specifications for the residual variance were close to each other. The 10 intervals modelling showed a slightly better performance probably because the change point function overestimates the residual variance values at the very early lactation.
Genetic polymorphism at CSN1S2 locus in two endangered sicilian goat breeds
Authors: Marletta D. , Bordonaro S. , Guastella A. M. , D'Urso G.
Published: January 2004

In this study we surveyed two endangered Sicilian goat breeds (Girgentana and Argentata dell'Etna) for genetic polymorphism at the CSN1S2 locus. In a total of 537 goats, we detected CSN1S2A, CSN1S2B, CSN1S2C° (CSN1S2C + CSN1S2E), CSN1S2D, CSN1S2F and CSN1S2O alleles by means of various polymerase chain reaction (PCR), allele specific‐PCR (AS–PCR) and PCR‐restriction fragment length polymorphism (RFLP) reactions with the aim of improving the knowledge of the genetic resource of these two breeds. Three and five alleles, with six and twelve genotypes, were identified at CSN1S2 locus, in Girgentana and Argentata, respectively. Argentata dell'Etna showed a higher degree of genetic variation. The allelic and genotypic distribution seems to be significantly different (p < 0.001) in the two breeds. In Argentata the rare null allele (CSN1S2O) was found at low frequency (0.033); this genetic peculiarity makes its preservation worthwhile.
Implementation issues for Markov Chain Monte Carlo methods in random regression test‐day models
Authors: Jamrozik J.
Published: January 2004

Markov Chain Monte Carlo methods made possible estimation of parameters for complex random regression test‐day models. Models evolved from single‐trait with one set of random regressions to multiple‐trait applications with several random effects described by regressions. Gibbs sampling has been used for models with linear (with respect to coefficients) regressions and normality assumptions for random effects. Difficulties associated with implementations of Markov Chain Monte Carlo schemes include lack of good practical methods to assess convergence, slow mixing caused by high posterior correlations of parameters and long running time to generate enough posterior samples. Those problems are illustrated through comparison of Gibbs sampling schemes for single‐trait random regression test‐day models with different model parameterizations, different functions used for regressions and posterior chains of different sizes. Orthogonal polynomials showed better convergence and mixing properties in comparison with ‘lactation curve’ functions of the same number of parameters. Increasing the order of polynomials resulted in smaller number of independent samples for covariance components. Gibbs sampling under hierarchical model parameterization had a lower level of autocorrelation and required less time for computation. Posterior means and standard deviations of genetic parameters were very similar for chains of different size (from 20 000 to 1 000 000) after convergence. Single‐trait random regression models with large data sets can be analysed by Markov Chain Monte Carlo methods in relatively short time. Multiple‐trait (lactation) models are computationally more demanding and better algorithms are required.
Estimates of genetic parameters for Boran, Friesian and crosses of Friesian and Jersey with the Boran cattle in the tropical highlands of Ethiopia: reproduction traits
Authors: Demeke S. , Neser F. W. C. , Schoeman S. J.
Published: January 2004

A study with the objectives of estimating breed differences, heterosis and recombination effects as well as heritabilities (h2) and repeatabilities (r2) for age at first calving (AFC), calving interval (CI), days open (DO) and number of services per conception (SPC) was conducted using reproduction records collected from 1496 cows comprising purebred Boran (B), Friesian (F), crosses of Friesian and Jersey (J) with Boran breeds. The crossbred cow groups included four F × B crosses [1/2F:1/2B(F1), 1/2F:1/2B(F2), 5/8F:3/8B and 3/4F:1/4B], three J × B crosses [1/2J:1/2B(F1), 1/2J:1/2B(F2) and 3/4J:1/4B] and one three‐breed cross (1/4F:1/4J:1/2B). The crossbreeding parameters were estimated using a repeatability animal model for CI, DO and SPC, and a unitrait animal model for AFC. The overall least‐squares means estimated were: 38.3 ± 0.26 months, 435 ± 4 days, 145 ± 10 days and 1.58 ± 0.03 (number) for AFC, CI, DO and SPC, respectively. The breed additive effects of F and J were only significant (p < 0.01) for AFC. Relative to B, both F and J additive contributions for AFC were −5.4 ± 0.5 and −5.5 ± 1.9 months, respectively. Crossing the B with F and J breeds also resulted in significant heterosis (p < 0.05) ranging from 10 to 21% in all traits. The estimated recombination loss was only significant for AFC (2.8 ± 1.0 months) for F × B crosses. Heritability estimates were high for AFC (0.44 ± 0.05) and low for CI (0.08 ± 0.03), DO (0.04 ± 0.03) and SPC (0.08 ± 0.02). The corresponding estimates for the repeatability (r2) were 0.14 ± 0.02 and 0.14 ± 0.02 for CI and DO, respectively. The permanent environmental effect for SPC was zero. These findings show that breed differences between F or J and B, and the individual cow variations are low for reproductive traits studied, except for AFC. Heterotic effects seem to be the major genetic causes for the improved reproductive performances in both the F × B and J × B crossbred cows.