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  • 1
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    Initiation of plate boundary slip in the Nankai Trough off the Muroto peninsula, southwest Japan (2005)
    In:  Geophys. Res. Lett., Taipei, EGS, vol. 32, no. 12, pp. 1474-1482, pp. L12306, (ISSN: 1340-4202)
    Details
    Publication Date: 2005
    Keywords: Subduction zone ; Plate tectonics ; decollement ; Geol. aspects ; Ocean Drilling Program ; GRL ; 0500 ; Computational ; Geophysics ; (3200, ; 3252, ; 7833) ; 0900 ; Exploration ; Geophysics ; 3000 ; Marine ; Geology ; and ; Geophysics ; 8000 ; Structural ; Geology ; 8100 ; Tectonophysics
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    Global Simulations of Magnetotail Reconnection (2007)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: There is a growing number of observational evidences of dynamic quasi-periodical magnetosphere response to continuously southward interplan etary magnetic field (IMF). However, traditional global MHD simulatio ns with magnetic reconnection supported by numerical dissipation and ad hoc anomalous resistivity driven by steady southward IMF often prod uce only quasi-steady configurations with almost stationary near-eart h neutral line. This discrepancy can be explained by the assumption that global MHD simulations significantly underestimate the reconnectio n rate in the magnetotail during substorm expansion phase. Indeed, co mparative studies of magnetic reconnection in small scale geometries demonstrated that traditional resistive MHD did not produce the fast r econnection rates observed in kinetic simulations. The major approxim ation of the traditional MHD approach is an isotropic fluid assumption) with zero off-diagonal pressure tensor components. The approximatio n, however, becomes invalid in the diffusion region around the reconn ection site where ions become unmagnetized and experience nongyrotropic behaviour. Deviation from gyrotropy in particle distribution functi on caused by kinetic effects manifests itself in nongyrotropic pressu re tensor with nonzero off-diagonal components. We use the global MHD code BATS-R-US and replace ad hoc parameters such as "critical curren t density" and "anomalous resistivity" with a physically motivated di ssipation model. The key element of the approach is to identify diffusion regions where the isotropic fluid MHD approximation is not applic able. We developed an algorithm that searches for locations of magnet otail reconnection sites. The algorithm takes advantage of block-based domain-decomposition technique employed by the BATS-R-US. Boundaries of the diffusion region around each reconnection site are estimated from the gyrotropic orbit threshold condition, where the ion gyroradius is equal to the distance to the reconnection site. Inside diffusion regions ions are treated as nongyrotropic fluid with nonzero off-dia gonal components of the pressure tensor. The primary kinetic mechanism controlling the dissipation in the diffusion region is incorporated into global MHD simulations in terms of spatially localized nongyrotropic corrections to the induction equation. The magnitude of the non-g yrotropic corrections to the electric field and spatial scales of the diffusion regions are calculated self-consistently at each time step of the simulation using local MHD plasma and field parameters at the reconnection site without introduction of any ad hoc parameters. We d emonstrated that magnetotail reconnection is inherently unsteady even when the solar wind is steady. Global MHD simulations with nongyrotropic corrections produce bursts of fast reconnection typically observe d in small-scale kinetic simulations. During the bursts the length of the diffusion region does not exceed 2R(sub E) approximates 12(c/ome ga * pi). The bursts of the fast reconnection last only for a few min utes. After reaching the maximum value the reconnection rate decreases while the length of the diffusion region increases. The decreased ra te, however, is still significantly larger that the steady reconnection rate characteristic for MHD simulations with reconnection supported by numerical resistivity alone. Magnetotail reconnection supported b y nongyrotropic effects results in a tailward retreat of the reconnection site with average speed of the order of 100 km/s, accompanied by magnetotail stretching and thin current sheet formation in the near-E arth plasma sheet. Overall magnetotail response to the steady low-mach-number solar wind with southward IMF exhibits quasi-periodic loading /unloading dynamics typical for frequently observed multiple substorm s.
    Keywords: Geophysics
    Type: 2007 US-Japan Reconnection Workshop; 26-29 Mar. 2007; Saint Michaels, MD; United States
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  • 3
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    Salt Kinematics and InSAR (2005)
    In:  CASI
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    Publication Date: 2005-04-25
    Description: As part of a long-term attempt to learn how the climatic and tectonic signal interact to shape a steady state mountain monitored displacement of a markers in SE termination and also near the summit of a small viscous salt fountain extruding onto the Central plateau of Iran. The marker displacements relate to the first InSAR interferograms of salt extrusion (980913 to 990620) calculated Earth tides, winds, air pressures and temperatures. In the first documented staking exercise, hammered wooden stakes vertically through the surgical marl (c. 1 Ocm deep) onto the top of crystalline salt. These stakes installed in an irregular array elongate E-W along the c.50 m high cliff marking the effective SE terminus of the glacier at Qum Kuh(Centra1 Iran) ,just to the E of a NE trending river cliff about 40 m high. We merely measured the distances between pairs of stakes with known azimuth about 2 m apart to calculate sub horizontal strain in a small part of Qum Kuh. Stakes moved and micro strains for up to 46 pairs of stakes (p strain= ((lengthl-length2)/1engthl) x 10-1) was calculated for each seven stake epochs and plotted against their azimuth on simplified array maps. The data fit well the sine curves cxpected of the maximum and minimum strain ellipses. The first documented stakes located on the SE where the InSAR image show -1 1 to 0 mm pink to purple, 0 to lOmm purple to blue, and show high activity of salt in low activity area of the InSAR image (980913 to 990620).Short term micro strains of stake tie lines record anisotropic expansions due to heating and contraction due to cooling. All epochs changed between 7 to 1 17 days (990928 to000 1 16), showed 200 to 400 micro strain lengthening and shortening. The contraction and extension existed in each epoch, but the final strain was extension in E-W in Epoch land 6, contraction in E-W direction during epochs 2-3-4-5 and 7. The second pair of stakes hammered about 20 cm deep into the deep soils(more than 1 m) , near summit, where the colors change between 19 to 29mm in InSAR image(9809 13 to 990620). Additional information is included in the original abstract.
    Keywords: Geophysics
    Type: Workshop on Radar Investigations of Planetary and Terrestrial Environments; 17; LPI-Contrib-1231
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  • 4
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    Formaldehyde Distribution over North America: Implications for Satellite Retrievals of Formaldehyde Columns and Isoprene Emission (2006)
    In:  Other Sources
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    Publication Date: 2011-08-26
    Description: Formaldehyde (HCHO) columns measured from space provide constraints on emissions of volatile organic compounds (VOCs). Quantitative interpretation requires characterization of errors in HCHO column retrievals and relating these columns to VOC emissions. Retrieval error is mainly in the air mass factor (AMF) which relates fitted backscattered radiances to vertical columns and requires external information on HCHO, aerosols, and clouds. Here we use aircraft data collected over North America and the Atlantic to determine the local relationships between HCHO columns and VOC emissions, calculate AMFs for HCHO retrievals, assess the errors in deriving AMFs with a chemical transport model (GEOS-Chem), and draw conclusions regarding space-based mapping of VOC emissions. We show that isoprene drives observed HCHO column variability over North America; HCHO column data from space can thus be used effectively as a proxy for isoprene emission. From observed HCHO and isoprene profiles we find an HCHO molar yield from isoprene oxidation of 1.6 +/- 0.5, consistent with current chemical mechanisms. Clouds are the primary error source in the AMF calculation; errors in the HCHO vertical profile and aerosols have comparatively little effect. The mean bias and 1Q uncertainty in the GEOS-Chem AMF calculation increase from 〈1% and 15% for clear skies to 17% and 24% for half-cloudy scenes. With fitting errors, this gives an overall 1 Q error in HCHO satellite measurements of 25-31%. Retrieval errors, combined with uncertainties in the HCHO yield from isoprene oxidation, result in a 40% (1sigma) error in inferring isoprene emissions from HCHO satellite measurements.
    Keywords: Geophysics
    Type: Journal of Geophysical Research; Volume 111
    Format: text
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  • 5
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    Volatiles in the Desert: Subtle Remote-sensing Signatures of the Dakhleh Oasis Catastrophic Event, Western Desert, Egypt (2005)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Over the past decade members of the Dakhleh Oasis Project have studied enigmatic signatures in the Pleistocene geologic record of portions of the Dakhleh oasis and palaeo-oasis in Egypt's Western Desert [1,2]. In particular, Si-Ca-Al rich glass melt (Dakhleh Glass, Fig. 1) points to a catastrophic event between c.100,000-200,000 years ago [3] in this well-studied African savannah and freshwater lake Middle Stone Age environment [4,5].
    Keywords: Geophysics
    Type: Workshop on The Role of Volatile and Atmospheres on Martian Impact Craters; 44-45; LPI-Contrib-1273
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  • 6
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    Isotopic Constraints on the Petrology of Martian Meteorites (2005)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The SNC (martian) meteorites exhibit complex isotopic characteristics that yield information both about the ages of individual meteorites as well as information about the petrogenetic processes that produced both individual samples and about the origins of suites and sub-suites within the SNC clan. Here I review these data, reiterate earlier interpretations, and offer some new conclusions.
    Keywords: Geophysics
    Type: Lunar and Planetary Science XXXVI, Part 10; LPI-Contrib-1234-Pt-10
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  • 7
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    Relative Ages of the Highlands, Lowlands, and Transition Zone Along a Portion of the Mars Crustal Dichotomy from Densities of Visible and Buried Impact Craters (2005)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Understanding the fundamental age relationships of the different parts of the Mars Crustal Dichotomy is essential to fully understanding the events that shaped the early history and formation of the surface of Mars. A dominant question is what are the true relative ages of the Northern Lowlands and the Southern Highlands? Using MOLA data from the Mars Global Surveyor and Viking visual images, a dataset of both buried and visible crater diameters was created over a nine million sq km study area of a section of the dichotomy boundary stretching from Arabia Terra to Utopia Planitia. Cumulative frequency plots on a log-log scale were used to determine the relative ages for the Highlands, the Lowlands, and the Transition Zone, separately for the visible, the buried and the combined total (visible+ buried) populations. We find the overall Highland crater population in this area is slightly older than the Lowlands, consistent with previous global studies, but the Lowlands and Transition Zone are also very old and formed at roughly the same time. It appears that the formation of the Lowlands in this region formed contemporaneously with a large-scale resurfacing event in the Highlands, perhaps caused by the process responsible for the Lowland formation.
    Keywords: Geophysics
    Type: Lunar and Planetary Science XXXVI, Part 4; LPI-Contrib-1234-Pt-4
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  • 8
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    The First Six Months of Iapetus Observations by the Cassini ISS Camera (2005)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Since Saturn arrival in June 2004, Iapetus has been studied intensively by the Cassini ISS camera [1] at various ranges. The first of two relatively close flybys in the primary mission occurred on Dec 31, 2004 at an altitude of approx.123,400 km over the northern leading hemisphere, resulting in images with a minimum pixel scale of 740 m. Detailed results of this flyby are given in [2], while this abstract covers the observations obtained earlier. Among the most important discoveries are: (a) Four giant impact basins with diameters between 390 and 550 km were detected, three of them are located in the dark terrain [3]. (b) Data revealed a 〉1300 km long ridge that marks exactly Iapetus' equator within the dark terrain. Individual mountains within the western part of the ridge reach heights of approx.20 km over surrounding terrain [3]. (c) Impact craters were confirmed to be the main geological feature within the dark terrain and at high southern latitudes. (d) There are numerous craters with dark walls roughly facing towards the central parts of the dark hemisphere [3]. (e) Almost all parts of Iapetus have been imaged at least at low resolution (〈 60 km/pxl).
    Keywords: Geophysics
    Type: Lunar and Planetary Science XXXVI, Part 4; LPI-Contrib-1234-Pt-4
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  • 9
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    Searching for Life Underground: An Analysis of Remote Sensing Observations of a Drill Core from Rio Tinto, Spain for Mineralogical Indications of Biological Activity (2005)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Water is unstable on the surface of Mars, and therefore the Martian surface is not likely to support life. It is possible, however, that liquid water exists beneath the surface of Mars, and thus life might also be found in the subsurface. Subsurface life would most likely be microbial, anaerobic, and chemoautotrophic; these types of biospheres on Earth are rare, and not well understood. Finding water and life are high priorities for Mars exploration, and therefore it is important that we learn to explore the subsurface robotically, by drilling. The Mars Analog Rio Tinto Experiment (MARTE), has searched successfully for a subsurface biosphere at Rio Tinto, Spain [1,2,3,4]. The Rio Tinto study site was selected to search for a subsurface biosphere because the extremely low pH and high concentrations of elements such as iron and copper in the Tinto River suggest the presence of a chemoautotrophic biosphere in the subsurface beneath the river. The Rio Tinto has been recognized as an important mineralogical analog to the Sinus Meridiani site on Mars [5].
    Keywords: Geophysics
    Type: Lunar and Planetary Science XXXVI, Part 2; LPI-Contrib-1234-Pt-2
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  • 10
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    RIO Tinto Faulted Volcanosedimentary Deposits as Analog Habitats for Extant Subsurface Biospheres on Mars: A Synthesis of the MARTE Drilling Project Geobiology Results (2005)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Geochemistry and mineralogy on Mars surface characterized by the MER Opportunity Rover suggest that early Mars hosted acidic environments in the Meridiani Planum region [1, 2]. Such extreme paleoenvironments have been suggested to be a regional expression of the global Mars geological cycle that induced acidic conditions by sulfur complexation and iron buffering of aqueous solutions [3]. Under these assumptions, underground reservoirs of acidic brines and, thereby, putative acidic cryptobiospheres, may be expected. The MARTE project [4, 5] has performed a drilling campaign to search for acidic and anaerobic biospheres in R o Tinto basement [6] that may be analogs of these hypothetical communities occurring in cryptic habitats of Mars. This Rio Tinto geological region is characterized by the occurrence of huge metallic deposits of iron sulfides [7]. Late intensive diagenesis of rocks driven by a compressive regimen [8] largely reduced the porosity of rocks and induced a cortical thickening through thrusting and inverse faulting and folding. Such structures play an essential role in transporting and storing water underground as any other aquifers do in the Earth. Once the underground water reservoirs of the Ro Tinto basement contact the hydrothermal pyrite deposits, acidic brines are produced by the release of sulfates and iron through the oxidation of sulfides [9].
    Keywords: Geophysics
    Type: Lunar and Planetary Science XXXVI, Part 6; LPI-Contrib-1234-Pt-6
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