bluuebunny/crossref_metadata_2025 huggingface dataset:
A method for mapping apparent stress and energy radiation applied to the 1994 Northridge Earthquake Fault Zone—Revisited
Authors: McGarr A. , Fletcher J. B.
Published: February 2004

McGarr and Fletcher (2000) introduced a technique for estimating apparent stress and seismic energy radiation associated with small patches of a larger fault plane and then applied this method to the slip model of the Northridge earthquake (Wald et al., 1996). These results must be revised because we did not take account of the difference between the seismic energy near the fault and that in the far‐field. The fraction f(vR) of the near‐field energy that propagates into the far‐field is a monotonic function that ranges from 0.11 to 0.40 as rupture velocity vR increases from 0.6β to 0.95β, where β is the shear wave speed. The revised equation for apparent stress for subfault ij is
, where ρ is density, D(t)ij is the time‐dependent slip, and Dij is the final slip. The corresponding seismic energy is
, where A is the subfault area. Our corrected distributions of apparent stress and radiated energy over the Northridge earthquake fault zone are about 35% of those published before.
Dynamic triggering of earthquakes: The linear slip‐dependent friction case
Authors: Voisin Christophe
Published: February 2004

This paper is devoted to the modeling of dynamic triggering of earthquakes by a sinusoidal plane wave. I consider a 2D antiplane finite fault of length L under a linear slip‐dependent friction law, characterized by a nondimensional weakening parameter β. The finite fault is perturbed by an incident sinusoidal stress wave of wavelength λ and amplitude a. The positive pulse of the wave loads the fault and promotes the instability, while the negative pulse tends to heal the initiation process that may lead to the rupture. The occurrence of triggering depends on the balance between the loading terms and the intrinsic mechanics of the fault. Both amplitude and frequency exert a clock advance effect on the triggering. A threshold in frequency for the incident wave to trigger the rupture is revealed, which depends on the non‐dimensional weakening parameter β and separates a nontriggering domain with stable slip from a triggering domain with unstable slip.
Long‐lived tracer patterns in the summer polar stratosphere
Authors: Orsolini Yvan J.
Published: February 2004

A three‐dimensional off‐line simulation of the transport of the long‐lived source gas N2O in the summer stratosphere has been made with a global model. We found long‐lived westward‐propagating patterns resulting from the slow advection of coarsely‐mixed structures of ex‐vortex air and midlatitude air. The mixing of the air masses with these two different characteristics is a slow process that lasts from spring until late summer. In the regime of summer easterlies above 20 km, we found evidence of long‐lived, “fossil” debris from the polar vortex even in August.
Comment on Hurst Exponent
Authors: Kärner Olavi
Published: February 2004

Analysis of the Nile river level height time series enabled Harold Edwin Hurst to derive an empirical tH (H > 0.5) law. Reanalysis of the data shows that the result may cause some misunderstanding in using the terms persistence and antipersistence to characterize the series' governing process.
Identification and origins of iron sulfides in Czech Loess
Authors: Shi C. D. , Zhu R. X. , Suchy V. , Zeman A. , Guo B. , Pan Y. X.
Published: February 2004

Multiple rock‐magnetic and non‐magnetic techniques were employed to identify iron sulfides in late Pleistocene Czech loess deposits. The results indicate that iron sulfides in the loess at Znojmo section are mainly pyrrhotite and pyrite, with stoichiometry ranging from Fe10S11 to FeS2. Although early pedogenic origin of fine sulfide fraction can not be ruled out, scanning electron microscopy (SEM) of individual grains and microscopic observations of magnetic extracts show that iron sulfide grains are probably of detrital origin. Potential sources of these sulfides may have been eluvium loams above hypothetical ore deposits in the vicinity of the section or glacifluvial sediments from nearby glacial margins. Framboidal pyrite forms, now completely replaced by iron oxides, suggest that some particles of biogenic sulfides may have also been transported into loess from presumably fluvial sediments.
Numerical simulation of love wave generation in the Ilan Basin, Taiwan, during the 1999 Chi‐Chi Earthquake
Authors: Furumura Mitsuko , Furumura Takashi , Wen Kuo‐Liang
Published: February 2004

During the 1999 Chi‐Chi, Taiwan, earthquake (Mw7.6), large amplitude fundamental‐mode Love wave with a predominant period of around 5 sec was observed in the Ilan Basin, northeastern Taiwan. The Love wave was generated near the edge of the basin and propagated toward its center during which its amplitude and duration increased and its phase velocity decreased. Numerical 2‐D modelings of SH‐wave propagation using a structural model of the Ilan Basin reproduced the generation process and propagation characteristics of the Love wave from multiple SH‐wave reflections between the free‐surface and dipping sediment/basement interface. The simulation results also suggest that long‐period Love wave was not generated during aftershocks, because the predominant period of the incident S‐wave was too short to resonate in the thick sediments of the Ilan Basin.
Atmosphere sounding by GPS radio occultation: First results from CHAMP
Authors: Wickert Jens , Reigber Christoph , Beyerle Georg , König Rolf , Marquardt Christian , Schmidt Torsten , Grunwaldt Ludwig , Galas Roman , Meehan Thomas K. , Melbourne William G. , Hocke Klemens
Published: February 2004

The first radio occultation measurements of the CHAMP (CHAllenging Minisatellite Payload) satellite using Global Positioning System (GPS) signals have been performed on February 11, 2001. By the end of April 2001 more than 3000 occultations were recorded. Globally distributed vertical profiles of dry temperature and specific humidity are derived, of which a set of 438 vertical dry temperature profiles is compared with corresponding global weather analyses. The observed temperature bias is less than ∼1 K above the tropopause and even less than 0.5 K in the altitude interval from 12 to 20 km at latitudes >30°N. About 55% of the compared profiles reached the last kilometer above the Earth's surface. In spite of the activated anti‐spoofing mode of the GPS system the state‐of‐the‐art GPS flight receiver aboard CHAMP combined with favorable antenna characteristics allows for atmospheric sounding with high accuracy and vertical resolution.
An ICME observed by Voyager 2 at 58 AU and by Ulysses at 5 AU
Authors: Paularena K. I. , Wang C. , von Steiger R. , Heber B.
Published: February 2004

Between days 175 and 180 (June 24 through 29) of 1999, the PLS instrument on Voyager 2 observed alpha particle enhancements with fractional percentages of alpha to proton number densities exceeding 10%. Ulysses (located at 5.3 AU) observed at least two candidate source features for these enhancements. To identify the correct source structure, a 1D MHD model was used to propagate the Ulysses plasma data to the Voyager radial position (58.2 AU). An ICME‐related alpha enhancement observed by Ulysses beginning on day 331 (November 27), 1998 appears to be the correct feature. While a speed jump and cosmic ray decreases were observed by Ulysses in conjunction with this alpha enhancement, the timing of these features differed markedly at Voyager 2. The speed jump arrival‐time difference is due to the faster propagation of the shock relative to the rest of the ejecta. It is unclear what mechanism is responsible for the delay in the cosmic ray decrease. Nevertheless, we have demonstrated that alpha enhancement signatures of ICMEs can be used to track these features to heliospheric distances >50 AU.
Signature of pending earthquake from electromagnetic anomalies
Authors: Eftaxias K. , Kapiris P. , Polygiannakis J. , Bogris N. , Kopanas J. , Antonopoulos G. , Peratzakis A. , Hadjicontis V.
Published: February 2004

Two electromagnetic (EM) anomalies have been detected in the VLF frequency band before the Athens earthquake (EQ) (Mw=5.9, Sept. 7, 1999) with the following characteristics: (i) The first and second anomaly lasted for 12 and 17 hours respectively with a cessation of 12 hours; (ii) The second anomaly ceased at about 9 hours before the EQ; (iii) The larger anomaly, the second one, contains approximately 80% of the total EM energy received; (iv) No EM disturbance has been recorded in the VHF frequency band unlike with other cases, e.g., the Kozani Grevena and Egion‐Eratini earthquakes. The fault modeling of the Athens EQ, based on information obtained by radar interferometry, predicts two faults. The main fault segment is responsible for 80% of the total energy released, while the secondary fault segment for the remaining 20%. Moreover, a recent seismic data analysis supports the hypothesis that a two‐event solution for the Athens EQ, is more likely than a single event solution. In addition, the absence of surface rupture explains the absence of EM detection in the VHF frequency band. The present analysis reveals that the properties of the preseismic electromagnetic anomalies might be considered as signatures of a pending earthquake.
Severe and extensive denitrification in the 1999–2000 Arctic winter stratosphere
Authors: Popp P. J. , Northway M. J. , Holecek J. C. , Gao R. S. , Fahey D. W. , Elkins J. W. , Hurst D. F. , Romashkin P. A. , Toon G. C. , Sen B. , Schauffler S. M. , Salawitch R. J. , Webster C. R. , Herman R. L. , Jost H. , Bui T. P. , Newman P. A. , Lait L. R.
Published: February 2004

Observations in the 1999–2000 Arctic winter stratosphere show the most severe and extensive denitrification ever observed in the northern hemisphere. Denitrification was inferred from in situ measurements conducted during high‐altitude aircraft flights between January and March 2000. Average removal of more than 60% of the reactive nitrogen reservoir (NOy) was observed in air masses throughout the core of the Arctic vortex. Denitrification was observed at altitudes between 16 and 21 km, with the most severe denitrification observed at 20 to 21 km. Nitrified air masses were also observed, primarily at lower altitudes. These results show that denitrification in the Arctic lower stratosphere can approach the severity and extent of that previously observed only in the Antarctic.
Effects of tropical convection on the predictability of the Sahel summer rainfall interannual variability
Authors: Thiaw Wassila M. , Kumar Vadlamani
Published: February 2004

Tropical convection as inferred from OLR, and global SST, are used as predictor fields in separate canonical correlation analysis (CCA) experiments. The experiments are based on 43‐year (1955‐98) observed SST data and 20‐year (1979‐98) OLR record. The aim is to study the role of tropical convection in improving the predictions of the interannual variability of the Sahel summer rainfall. Forecast skills for OLR and SST predictor fields are estimated using a cross‐validation scheme. Average region‐wide correlation skill for OLR is 0.368, which is slightly higher than skill for SST based on a 43‐year record (0.308). However, much of the skill in the latter is associated with long term trends. Skill for OLR outperforms significantly that of SST based on a 20‐year historical record. Hindcasts for the Jul‐Sep Sahel rainfall in 1997 and 1999 show an improvement over SST in the predictions of the interannual variability where OLR is used as predictor field.
Sediment effect on tsunami generation of the 1896 Sanriku Tsunami Earthquake
Authors: Tanioka Yuichiro , Seno Tetsuzo
Published: February 2004

The 1896 Sanriku earthquake was one of the most devastating tsunami earthquakes, which generated an anomalously larger tsunami than expected from its seismic waves. Previous studies indicate that the earthquake occurred beneath the accretionary wedge near the trench axis. It was pointed out recently that sediments near a toe of an inner trench slope with a large horizontal movement due to the earthquake might have caused an additional uplift. In this paper, the effect of the additional uplift to tsunami generation of the 1896 Sanriku tsunami earthquake is quantified. We estimate the slip of the earthquake by numerically computing tsunamis and comparing their waveforms with those recorded at three tide gauges. The estimated slip for the model without the additional uplift is 10.4 m, and those with the additional uplift are 5.9–6.7 m. This indicates that the additional uplift of the sediments near the trench has a large effect on the tsunami generation.
Emerging patterns of simulated regional climatic changes for the 21st century due to anthropogenic forcings
Authors: Giorgi Filippo , Whetton Peter H. , Jones Richard G. , Christensen Jens H. , Mearns Linda O. , Hewitson Bruce , vonStorch Hans , Francisco Raquel , Jack Chris
Published: February 2004

We analyse temperature and precipitation changes for the late decades of the 21st century (with respect to present day conditions) over 23 land regions of the world from 18 recent transient climate change experiments with coupled atmosphere‐ocean General Circulation Models (AOGCMs). The analysis involves two different forcing scenarios and nine models, and it focuses on model agreement in the simulated regional changes for the summer and winter seasons. While to date very few conclusions have been presented on regional climatic changes, mostly limited to some broad latitudinal bands, our analysis shows that a number of consistent patterns of regional change across models and scenarios are now emerging. For temperature, in addition to maximum winter warming in northern high latitudes, warming much greater than the global average is found over Central Asia, Tibet and the Mediterranean region in summer. Consistent warming lower than the global average is found in some seasons over Southern South America, Southeast Asia and South Asia, while cases of inconsistent warming amplification compared to the global average occur mostly in some tropical and southern sub‐tropical regions. Consistent increase in winter precipitation is found in northern high latitude regions, as well as Central Asia, Tibet, Western and Eastern North America, and Western and Eastern Africa regions. The experiments also indicate an increase in South Asia and East Asia summer monsoon precipitation. A number of regions show a consistent decrease in precipitation, such as Southern Africa and Australia in winter, the Mediterranean region in summer and Central America in both seasons. Possible physical mechanisms that lead to the simulated changes are discussed.
High‐resolution atmospheric absorption by water vapor in the 830–985 nm region: Evaluation of spectroscopic databases
Authors: Smith K. M. , Newnham D. A.
Published: February 2004

We present high spectral resolution (0.05 cm−1) ground‐based measurements of direct solar absorption in the clear‐sky atmosphere by water vapor over the 830 to 985 nm (10,150–12,050 cm−1) region. Observations were made from the Rutherford Appleton Laboratory on several days in different seasons during 1999. Using these observations water vapor line data in HITRAN and the ESA‐WVR database, derived from new laboratory measurements and theoretical calculations, are evaluated. Examples of inter‐comparisons between these databases and high‐resolution atmospheric transmittance spectra are given. The ESA‐WVR and HITRAN 2000 databases were found to give consistently better representations of clear‐sky absorption by water vapor in our measurements than previous editions of HITRAN, confirming that spectroscopic errors in databases account in part for discrepancies between modeled and observed short‐wave absorption.
The physical mechanism of nitric oxide formation in simulated lightning
Authors: Navarro‐González Rafael , Villagrán‐Muniz Mayo , Sobral Hugo , Molina Luisa T. , Molina Mario J.
Published: February 2004

We report an experimental assessment of the contributions of the shockwave and the hot channel to the production of nitric oxide by simulated lightning. Lightning in the laboratory was simulated by a hot plasma generated with a pulsed Nd‐YAG laser. The temporal evolution of electric breakdown in air at atmospheric pressure was studied from the nanosecond to the millisecond time scale by shadowgraphy and interferometry techniques. The shockwave front velocity was determined to be about 60 km s−1 at 20 ns and the temperature behind the shock front was estimated to be about 105 K. The production yield of nitric oxide by shock heating is estimated to be: P(NO) (3±2) × 1014 molecule J−1. In contrast it was calculated that the production yield of NO by the hot channel is as much as P(NO)=(1.5±0.5) × 1017 molecule J−1. To the extent our simulation is an accurate representation of natural lightning, the hot channel is the dominant region for nitrogen fixation.
Observational evidence for the role of denitrification in Arctic stratospheric ozone loss
Authors: Gao R. S. , Richard E. C. , Popp P. J. , Toon G. C. , Hurst D. F. , Newman P. A. , Holecek J. C. , Northway M. J. , Fahey D. W. , Danilin M. Y. , Sen B. , Aikin K. , Romashkin P. A. , Elkins J. W. , Webster C. R. , Schauffler S. M. , Greenblatt J. B. , McElroy C. T. , Lait L. R. , Bui T. P. , Baumgardner D.
Published: February 2004

Severe and extensive denitrification, chlorine activation, and photochemical ozone loss were observed throughout the lower stratosphere in the 1999–2000 Arctic vortex. A large number of air parcels sampled between late February and mid‐March, 2000, were photochemically intercomparable for chemical O3 loss rates. In these air parcels, the temporal evolution of the correlations of O3 with the NOy remaining after denitrification provides strong evidence for the role of NOy in moderating O3 destruction. In 71%‐denitrified air parcels, a chemical O3 destruction rate of 63 ppbv/day was calculated, while in 43%‐denitrified air parcels the destruction rate was only 43 ppbv/day. These observational results show that representative denitrification models will be required for accurate prediction of future Arctic O3 changes.
The complete (3‐D) surface displacement field in the epicentral area of the 1999 MW7.1 Hector Mine Earthquake, California, from space geodetic observations
Authors: Fialko Yuri , Simons Mark , Agnew Duncan
Published: February 2004

We use Interferometric Synthetic Aperture Radar (InSAR) data to derive continuous maps for three orthogonal components of the co‐seismic surface displacement field due to the 1999 Mw7.1 Hector Mine earthquake in southern California. Vertical and horizontal displacements are both predominantly antisymmetric with respect to the fault plane, consistent with predictions of linear elastic models of deformation for a strike‐slip fault. Some deviations from symmetry apparent in the surface displacement data may result from complexity in the fault geometry.
Observations of vertically thick polar stratospheric clouds and record low temperature in the Arctic Vortex
Authors: Kivi Rigel , Kyrö Esko , Dörnbrack Andreas , Birner Thomas
Published: February 2004

On 12 and 13 January 2001 backscatter sondes launched at Sodankylä, Finland (67°N, 27°E) detected an extraordinarily thick polar stratospheric cloud layer of more than 8 km vertical extent. On these days the polar vortex passed over northern Scandinavia. This provided synoptic‐scale low stratospheric temperatures leading to the formation of both liquid and solid phase particles. Two days later, on 15 January 2001, a regular radiosonde measured record low temperature of 176.7 K at an altitude of 25.2 km at the vortex edge. High vertical resolution radiosonde profiles and meteorological analyses indicate strong mountain wave activity on this day. This provides further evidence that the coldest temperatures in the Arctic lower stratosphere occur as a consequence of mountain wave cooling under cold synoptic‐scale background conditions.
MISR aerosol optical depth retrievals over southern Africa during the SAFARI‐2000 Dry Season Campaign
Authors: Diner D. J. , Abdou W. A. , Bruegge C. J. , Conel J. E. , Crean K. A. , Gaitley B. J. , Helmlinger M. C. , Kahn R. A. , Martonchik J. V. , Pilorz S. H. , Holben B. N.
Published: February 2004

This paper presents, for the first time, retrievals of aerosol optical depths from Multi‐angle Imaging Spectro‐Radiometer (MISR) observations over land. Application of the MISR operational algorithm to data taken over southern Africa during the SAFARI‐2000 dry season campaign yields results that compare favorably with coincident surface‐based measurements taken by the AERONET radiometer network.
On the mid‐depth circulation in the Labrador and Irminger Seas
Authors: Käse R. H. , Biastoch A. , Stammer D. B.
Published: February 2004

A numerical circulation model with 1/6° resolution and an accurate topography formulation explains details of the observed circulation in the Irminger and Labrador Seas that were recently revealed by Lavender et al. [2000]. We show that the recirculation pattern is established through a locally wind induced flow controlled by the bottom topography and enhanced through remote baroclinic forcing by the dense plume of Denmark Strait overflow water. The basic circulation is a robust feature in a hierarchy of model setups. It exists in the purely barotropic case driven by steady winds and is even maintained when realistic daily forcing is added. The narrow recirculation zone is manifested by a sea level depression spanning from the Denmark Strait across the Irminger into the Labrador Sea.
On the tradeoff of the solar and thermal infrared radiative impact of contrails
Authors: Myhre Gunnar , Stordal Frode
Published: February 2004

Global calculations of the radiative forcing due to contrails from aircraft are performed. A contrail distribution computed based on aviation fuel consumption and radiative transfer models for solar and thermal infrared radiation have been used. A substantially smaller net radiative forcing due to contrails (about 0.01 Wm−2) is estimated in comparison to former studies, emphasizing the strong sensitivity of this value to uncertainties in the longwave and shortwave contribution. The solar forcing is negative and the magnitude maximizes for high solar zenith angles. Altering the time for aircraft traffic has the potential for reducing the radiative forcing due to contrails, and under certain assumptions made in this paper giving a net zero forcing.
A nested modeling study of elevation‐dependent climate change signals in California induced by increased atmospheric CO2
Authors: Kim Jinwon
Published: February 2004

Dynamically downscaled climate change signals due to increased atmospheric CO2 are investigated for three California basins. The downscaled signals show strong elevation dependence, mainly due to elevated freezing levels in the increased CO2 climate. Below 2.5 km, rainfall increases by over 150% while snowfall decreases by 20–40% in the winter. Above 2.5 km, rainfall and snowfall both increase in the winter, as the freezing levels appear mostly below this level. Winter snowmelt increases in all elevations due to warmer temperatures in the increased CO2 climate. Reduced snowfall and enhanced snowmelt during the winter decreases snowmelt‐driven spring runoff below the 2.5 km level, where the peak snowmelt occurs one month earlier in the increased CO2 climate. Above 2.5km, increased winter snowfall maintains snowmelt‐driven runoff through most of the warm season. The altered hydrologic characteristics in the increased CO2 climate affect the diurnal temperature variation mainly via snow‐albedo‐soil moisture feedback.
Can a state of the art atmospheric general circulation model reproduce recent NAO related variability at the air‐sea interface?
Authors: Josey Simon A. , Kent Elizabeth C. , Sinha Bablu
Published: February 2004

Recent studies claim that useful predictability of the North Atlantic Oscillation (NAO) up to several years in advance may be possible using atmospheric models in which the sea surface temperature (SST) is specified from observations. Achieving this goal requires that such models adequately capture the observed variation in the NAO at interannual as well as interdecadal timescales. We investigate whether this is the case by comparing interannual variability in the HadAM3 atmospheric model with observations in the SOC air‐sea flux dataset for 1980‐1995. We find that the model NAO time variation does not correspond to that observed, thus claims of multiannual predictability need to be viewed with caution. In addition, analysis of the observations reveals that NAO related SST anomalies do not exert a significant heat flux feedback on the atmosphere at seasonal to interannual timescales.
Size of Popocatepetl Volcano explosions (1997–2001) from waveform inversion
Authors: Cruz‐Atienza V. M. , Pacheco J. F. , Singh S. K. , Shapiro N. M. , Valdés C. , Iglesias A.
Published: February 2004

Several volcanic explosions have been recorded since April 1997 at broadband seismic stations located around the Popocatepetl volcano, Mexico. We have inverted waveforms of ten of these explosions to estimate the following source parameters: depth, duration, magnitude and direction of the single force, F. The crustal structure used in generating Green's function at nearest stations is derived from the inversion of teleseismic receiver functions at the broadband permanent station PPIG, located 5 km north of the volcano. This inversion reveals a low velocity zone at ∼8 km beneath the summit with high Poisson ratio, possibly related to the magma chamber. We find that F scales with τ, the duration of the source‐time function, as F ∝ tau². Based on this relationship we determine an impulse magnitude scale, Mk. This magnitude is tied to the Mount Saint Helens initial explosive phase of May 18, 1980, whose magnitude is estimated as 4.6. Mk of the ten Popocatepetl explosions ranges between 1.8 and 3.2. Finally, we also propose an equivalent formula for rapid estimation of magnitude of future Popocatepetl explosions, which requires filtered amplitudes at PPIG.
Effects of explosion energy and depth to the formation of blast wave and crater: Field Explosion Experiment for the understanding of volcanic explosion
Authors: Goto Akio , Taniguchi Hiromitsu , Yoshida Mario , Ohba Tsukasa , Oshima Hiromitsu
Published: February 2004

We made field explosion experiments as an analogue of volcanic explosion to understand the relationship between the explosion condition and the resultant surface phenomena. The main parameters we employed were explosion depth and explosion energy. Through the experiments we confirmed that scaled depth, which is the depth divided by cube root of energy, is the main parameter determining the properties of explosive volcanism. The energy assigned to blast wave decreased exponentially against the scaled depth. The scaled crater diameter became maximum when the scaled depth was about 4 × 10−3 m/J¹/³.

Scaled crater diameters by nuclear, chemical subsurface and some volcanic explosions were almost the same. From the scaling law, the overpressure at crater rim was estimated to be several MPa, which corresponded to typical rock strength. Probably the ground‐forming materials were broken inside the area where overpressure exceeded their strength.
Little Ice Age sea surface temperature variability in the southwest tropical Pacific
Authors: Corrège Thierry , Quinn Terry , Delcroix Thierry , Le Cornec Florence , Récy Jacques , Cabioch Guy
Published: February 2004

We present a 60‐year near‐monthly record of tropical sea surface temperature (SST) during the Little Ice Age derived from coupled Sr/Ca and U/Ca analysis of a massive coral from New Caledonia (southwest tropical Pacific). The record indicates that, from 1701 to 1761, surface temperatures were on average 1.4°C cooler than during the past 30 years. This cooling was accompanied by strong interannual to interdecadal oscillations that changed the background state. Correlations between SST changes and the Southern Oscillation and the Pacific Decadal Oscillation are evolutive and appear to depend on the background state.
Thermally enhanced mimetic fabric of magnetite in a biotite granite
Authors: Trindade R. I. F. , Mintsa Mi Nguema T. , Bouchez J. L.
Published: February 2004

The thermally induced growth of mimetic magnetite after biotite is here demonstrated by the equivalence of anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) after heating of biotite single crystals and whole rock specimens from a magnetite‐free granite (Elba Island, Italy). It is concluded that between 500° and 725°C magnetite nucleates and grows within and parallel to the biotite cleavages yielding a magnetic fabric mimetic of the biotite fabric. At higher temperatures magnetite undergoes partial haematization, accounting for the decrease in remanence, susceptibility and anisotropy degree. This experiment may be used as a proxy for fabric study of granites having composite (tourmaline + biotite) paramagnetic fabrics in which the fabric of biotite can be selectively thermally enhanced.
Support for tropically‐driven pacific decadal variability based on paleoproxy evidence
Authors: Evans Michael N. , Cane Mark A. , Schrag Daniel P. , Kaplan Alexey , Linsley Braddock K. , Villalba Ricardo , Wellington Gerard M.
Published: February 2004

Two independent proxy reconstructions of sea surface temperature reflect a common pattern of Pacific decadal sea surface temperature variability over the past two centuries. Since the pattern extends to both the northern and southern hemispheres, this result supports the idea that Pacific decadal variability is a basin‐wide phenomenon originating in the tropics.
Transient fault slip in Guerrero, southern Mexico
Authors: Lowry Anthony R. , Larson Kristine M. , Kostoglodov Vladimir , Bilham Roger
Published: February 2004

The Guerrero region of southern Mexico has accumulated more than 5 m of relative plate motion since the last major earthquake. In early 1998, a continuous GPS site in Guerrero recorded a transient displacement. Modeling indicates that anomalous fault slip propagated from east to west along‐strike of the subduction megathrust. Campaign GPS and leveling data corroborate the model. The moment release was equivalent to an Mw≥6.5 earthquake. No M>5 earthquakes accompanied the event, indicating the frictional regime is velocity‐strengthening at the location of slip.
Quantitative 3D‐fracture analysis by means of microfocus X‐Ray Computer Tomography (µCT): An example from coal
Authors: Van Geet Maarten , Swennen Rudy
Published: February 2004

Since the introduction of medical computer tomography (CT) in geological sciences, many applications have been worked out. However, its limited resolution (optimal 60 × 60 × 1000 µ³) restricts its general use. Enhanced resolution is achieved with synchrotron X‐ray tomography, but these instruments are expensive and have a limited access. Another technique is microfocus X‐ray tomography of which the advantages will be discussed. This instrument is more accessible than synchrotron facilities. It furthermore has a superior resolution (present‐day 10 × 10 × 10 µm³) compared to medical CT. In this study, a thorough calibration is performed on samples of 8 mm in diameter and fracture widths from 0 to 400 µm. A statistical evaluation shows that the beam hardening artefact can be neglected and the standard deviation on aperture measurements of 100 µm is about 15 µm. The application of quantitative fracture aperture analysis will be demonstrated on a coal sample whereby a good correlation (r=0.94) with fracture analysis by reflected light microscopy is illustrated.
Frictional fusion due to coseismic landsliding during the 1999 Chi‐Chi (Taiwan) ML 7.3 Earthquake
Authors: Lin Aiming , Chen Allen , Liau Ching‐Fei , Lee Chyi‐Tyi , Lin Chuan‐Chia , Lin Po‐Shen , Wen Shu‐Ching , Ouchi Toru
Published: February 2004

Fused materials (pseudotachylytes) generated from landsliding during the 1999 Chi‐Chi (Taiwan) ML7.3 earthquake are found on the glide plane in Mio‐Pliocene interbedded shale and siltstone. The pseudotachylytes occur as thin layers on the glide plane and as veins injected into cracks in the host rocks, which are a few mm to 1 cm in thickness. Typical melting textures within the pseudotachylyte include vesicles, glassy matrices, flow structures, and rounded and embayed clast shapes. Powder X‐ray diffraction analysis has revealed a glass content of up to 50 wt% within the pseudotachylyte. Physical conditions of pseudotachylyte formation are estimated to have been <1.5 MPa corresponding to ca.40 m depth, at a temperature of at least 1100∼1600 °C. The geological and petrological data suggests that these pseudotachylytes formed by frictional melting generated from coseismic landsliding during the Chi‐Chi earthquake.
Seismological evidence on the geometry of the Orogenic System in central‐northern Ecuador (South America)
Authors: Guillier B. , Chatelain J.‐L. , Jaillard É. , Yepes H. , Poupinet G. , Fels J.‐F.
Published: February 2004

Analysis of the spatial distribution of seismicity beneath central Ecuador from a temporary network gives new insights on two main points of the Ecuadorian tectonics. Major structures in the Ecuadorian Andes are East‐dipping Late Jurassic to Paleogene sutures reactivated by present‐day compression. The oceanic plate is plunging continuously down to a depth of about 200 km with a dip of 25°–35°. We also show that the coastal plain acts as a buttress transmitting stresses to the Andes, beneath which deformation is concentrated.
Neutron diffraction study of hydrous phase G: Hydrogen in the lower mantle hydrous silicate, phase G
Authors: Suzuki Akio , Ohtani Eiji , Kondo Tadashi , Kuribayashi Takahiro , Niimura Nobuo , Kurihara Kazuo , Chatake Toshiyuki
Published: February 2004

A neutron powder diffraction study was performed to determine the sites occupied by hydrogen in the structure of DHMS phase G, which is stable at the pressure‐temperature conditions of the transition zone and lower mantle. The diffraction data from small samples (about 3 mg) were collected by using a highly sensitive imaging plate detector at the BIX‐3 beamline at JRR‐3M nuclear plant in JAERI Tokai Laboratory, Japan. The present neutron diffraction data reveal that hydrogen (and deuterium) is located in the 6k site of Wykoff letter in the MO6 layer of the phase G structure with the space group
. The bond lengths of O‐H and O‐D are 1.1(4) and 0.8(3) Å, respectively. This result is consistent with previous Raman spectroscopic studies of this phase.
Remote sensing of global wetland dynamics with multiple satellite data sets
Authors: Prigent Catherine , Matthews Elaine , Aires Filipe , Rossow William B.
Published: February 2004

This study is the first global effort to quantify seasonality and extent of inundation with a suite of satellite observations, including passive and active microwave along with visible and infrared measurements. A clustering technique which merges the satellite observations is used to detect inundation. Monthly flooded areas are then calculated by estimating pixel fractional coverage of flooding using the passive microwave signal and a linear mixture model with end‐members calibrated with radar observations to account for vegetation cover. The global results, comprising natural wetlands, irrigated rice, and lakes/rivers, indicate a minimum inundated area for the July 1992‐June 1993 period of 2.16×106km², about 38% of the maximum 5.75×106km², to be compared to maximum areas of 5.83×106km² and 5.70×106km² from independent data sets. Comprehensive evaluation requires substantial additions to the sparse observational record now available.
Crustal deformation rates in central and eastern U.S. inferred from GPS
Authors: Gan Weijun , Prescott William H.
Published: February 2004

Analysis of continuous GPS observations between 1996 and 2000 at 62 stations distributed throughout the central and eastern United States suggests that the area is generally stable. Seven of the 62 stations show anomalous velocities, but there is reason to suspect their monument stability. Assuming the remaining 55 stations are stable with respect to interior North America, we have found the North America‐ITRF97 Euler vector (−1.88°±1.04°N, 77.67°±0.39°W, 0.201°±0.004° Myr−1) that minimizes the RMS station velocity. Referred to fixed North America, all of these velocities are less than 3.2 mm yr−1. Motion of several stations suggests the Mississippi embayment may be moving southward away from the rest of the continent at a rate of 1.7±0.9 mm yr−1. The motion of the embayment produces a large gradient in velocity which, in turn, implies the highest seismic moment accumulation rate that we found. Although the highest rate is only marginally significant, the fact that it occurs near New Madrid, where earthquake risk is thought to be high, argues that the anomaly may be real. Nevertheless, the identification of the anomaly remains tentative.
The role of Bright Desert Regions in shaping North African climate
Authors: Knorr Wolfgang , Schnitzler Karl‐Georg , Govaerts Yves
Published: February 2004

Albedo changes have long been recognized as an important element of land surface‐climate interaction in the North African region, despite a general lack of adequate albedo data. Here, a new broadband surface albedo data set derived from a geostationary satellite with a recently developed bidirectional retrieval algorithm is used in a series of two climate simulations with the ECHAM4 general circulation model. We find that compared to traditionally assumed albedo values, the new data improve simulated precipitation over North Africa considerably when compared to observations. The results suggest that a series of large, extremely bright desert areas suppress the northward advance of the North African monsoon, considerably reducing summer rainfall of the southern Sahara desert margins and the Sahel. The unusually high albedo of the southern Sahara thus implies an even larger impact of desert albedo to the climate of North Africa than previously assumed.
Mixing at fracture intersections: Influence of channel geometry and the Reynolds and Peclet Numbers
Authors: Stockman Harlan W. , Johnson Joel , Brown Stephen R.
Published: February 2004

The 3D lattice Boltzmann (LB) method was used to model mixing at three types of continuous fracture intersections: planar, fluted (containing parallel grooves), and rough‐walled. Peclet number (Pe) varied from 3 to 400, and Reynolds number (Re) varied from 0.5 to 100. In both planar‐ and rough‐walled intersections, the mixing ratio (Mr) decreases with increasing Pe, though the decrease is less dramatic for the rough‐walled geometry. In planar‐walled intersections, the Mr decreases with increasing Re; however, the fluted and rough‐walled intersections show the opposite trend. Overall, the impact of inertial effects is slight for Re ≤ 10. The effects of channel length are also small; the calculated Mr varies little for LB simulations with length/width ≥ 1.
Impact of the Indian Ocean dipole on the relationship between the Indian monsoon rainfall and ENSO
Authors: Ashok Karumuri , Guan Zhaoyong , Yamagata Toshio
Published: February 2004

The influence of the recently discovered Indian Ocean Dipole (IOD) on the interannual variability of the Indian summer monsoon rainfall (ISMR) has been investigated for the period 1958‐1997. The IOD and the El Niño/Southern Oscillation (ENSO) have complementarily affected the ISMR during the last four decades. Whenever the ENSO‐ISMR correlation is low (high), the IOD‐ISMR correlation is high (low). The IOD plays an important role as a modulator of the Indian monsoon rainfall, and influences the correlation between the ISMR and ENSO. We have discovered that the ENSO‐induced anomalous circulation over the Indian region is either countered or supported by the IOD‐induced anomalous meridional circulation cell, depending upon the phase and amplitude of the two major tropical phenomena in the Indo‐Pacific sector.
Micro‐tsunami from a local interplate earthquake detected by cabled offshore tsunami observation in northeastern Japan
Authors: Hino R. , Tanioka Y. , Kanazawa T. , Sakai S. , Nishino M. , Suyehiro K.
Published: February 2004

A micro tsunami from an interplate earthquake (Mw 6.1) was observed in 1998 on ocean bottom tsunami meters (OBTMs) deployed east off the northeastern Japan. The offshore tsunami data without complex distortions due to the coastal topography enable us to estimate reliable tsunami source parameters. The observed amplitude was about 1.5 cm at epicentral distance less than 100 km. We numerically computed the tsunami waveform by solving the linear Boussinesq equations. The observed tsunami waveforms are well explained by synthetic waveforms assuming the fault width of 10–15 km. The depth of the fault is estimated as 5–10 km below the seafloor, which is in good agreement with the location of the plate boundary defined by previous seismic studies.
Shear‐wave splitting to test mantle deformation models around Hawaii
Authors: Walker Kristoffer T. , Bokelmann Götz H. R. , Klemperer Simon L.
Published: February 2004

Seismic anisotropy allows us to study mantle deformation, and it can thus help to constrain mantle flow in the vicinity of hotspots. Hypotheses for the cause of seismic anisotropy in this environment include the “parabolic asthenospheric flow” (PAF) model: radial flow from a mantle plume impinging on a moving lithosphere is dragged by the plate in the direction of absolute plate motion. In map view, this gives a parabolic pattern of flow, opening in the direction of plate motion. We present new shear‐wave splitting observations from land and ocean stations around the Hawaiian Islands that can be explained by the parabolic flow model. The observations suggest asthenospheric anisotropy under the Hawaiian islands, which may be explained if dislocation‐creep persists to deeper depths there than in other regions, perhaps due to the higher temperatures near hotspots.
Quantitative classification of canyon systems on continental slopes and a possible relationship to slope curvature
Authors: Goff John A.
Published: February 2004

A recent analysis of continental slopes (Adams and Schlager, 2000) has established three basic shapes for classification: exponential, linear, and Gaussian. Examples of each of these shapes can be found on the middle US Atlantic margin, where sufficiently high‐quality bathymetry data are available to investigate the systems of erosional canyons that incise the slopes. Significant morphological differences can be noted visually in these examples, suggesting that canyon systems can be classified in a quantitative manner. Here it is proposed that canyon system morphology can be distinguished by the downslope progression of cross‐slope statistical parameters, particularly RMS relief. On the linear slope, rms relief decreases with depth, whereas rms relief increases on the exponentially shaped slope. On the Gaussian shaped slope, rms relief is roughly constant, with minor variations. This straightforward method of classification may hold great promise for systematically investigating relationships between slope canyons and their formative environments.
Seasonal variability of thermal fronts in the northern South China Sea from satellite data
Authors: Wang Dongxiao , Liu Yun , Qi Yiquan , Shi Ping
Published: February 2004

The 8‐year (1991–1998) Pathfinder sea surface temperature data have been applied here to produce the objectively derived seasonality of the oceanic thermal fronts in the northern South China Sea from 17°N to 25°N. Several fronts have been clearly distinguished, namely, Fujian and Guangdong Coastal Water, Pear River Estuary Coastal, Taiwan Bank, Kuroshio Intrusion, Hainan Island East Coast and Tonkin Gulf Coastal fronts. The frontal patterns in winter, spring and summer are quite similar, whereas individual fronts display different modes of seasonal variability due to different mechanisms favoring those fronts.
Non‐linear effects of internal tides on the generation of the tidal mean flow at the Hebrides Shelf Edge
Authors: Xing Jiuxing , Davies Alan M.
Published: February 2004

Using a numerical model we demonstrate the importance of non‐linear processes associated with internal tides in the generation of the mean flow at the Hebrides shelf edge. The along slope current can be of the order of 5 cm s−1, which is smaller but significant compared with the oceanic slope current of 20 cm s−1. Moreover the cross slope current can be of the same order and in the down slope direction. The location of the peak along slope current is close to the region of convergence of internal tidal wave energy flux. This suggests that the internal tidal wave energy is transferred to the mean flow. We also show that the mean flow due to this process can be more important than that induced by the bottom front arising from differential tidal mixing at the shelf edge.
Influence of the earthquake cycle and lithospheric rheology on the dynamics of the Eastern California Shear Zone
Authors: Malservisi R. , Furlong K. P. , Dixon T. H.
Published: February 2004

The Eastern California Shear Zone is bounded by the high heat flow region of the Basin and Range province and the low heat flow region of the Sierra Nevada block. This difference in thermal state influences the rheology of the lower crust/upper mantle, resulting in a viscosity contrast between the two regions. We analyze the effect of such a contrast on the kinematics and dynamics of the shear zone with numerical models. This viscosity contrast drives asymmetric strain accumulation in the upper crust, producing an asymmetric surface velocity field. An additional consequence of this strain pattern is the potential for asymmetric co‐seismic displacement during an earthquake.
A new global satellite‐based sea surface temperature climatology
Authors: Armstrong Edward M. , Vazquez‐Cuervo Jorge
Published: February 2004

A new approach to the generation of a global sea surface temperature (SST) climatology from satellite data is presented. This work is an extension of Casey and Cornillon [1999] who demonstrated the overall superiority of constructing a global climatology using exclusively advanced very high resolution radiometer (AVHRR) Pathfinder satellite SST data vs. blended in situ/satellite data. In this implementation, a global pentad (five day) climatology was derived from daily 9 km AVHRR Pathfinder SST data through Gaussian interpolation and averaging. Performance of this climatology with respect to the Casey 9 km pentad satellite and Reynolds 1° monthly climatologies was then investigated by examining the standard deviation of the anomaly data set constructed by subtracting climatological SST observations from co‐located long‐term in situ SST observations. In all areas examined this new climatology, hereafter referred to as the JPL pentad climatology, demonstrated modest improvements over the other climatologies.
Transition regions and their role in the relationship between sea surface height and subsurface temperature structure in the Atlantic Ocean
Authors: Mayer Dennis A. , Molinari Robert L. , Baringer Molly O'Neil , Goni Gustavo J.
Published: February 2004

Expendable bathythermograph (XBT) profiles and TOPEX/Poseidon altimeter data (T/P) are compared for the years 1993 through 1997 to determine how much can be understood about water column variability from XBT's given only sea height anomalies (SHA) from T/P. Our focus is on the annual cycle along two well sampled XBT sections in the Atlantic Ocean from 10°S to 40°N. Regions of transition are identified that separate the mid‐latitudes where surface buoyancy fluxes dominate the forcing of sea level, from those in the equatorial region where thermocline effects dominate. Zones of transition occur in the vicinity of troughs where small fluctuations in SHA belie the true nature of water column variability. Here, surface and thermocline variability tend to cancel each other. Thus, the character of SHA in transition regions emphasizes how important direct observations can be in interpreting satellite altimetric observations correctly when both surface and thermocline variability are important but are compensating in nature.