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91.
Jonathan Corcoran Gary Higgs Chris Brunsdon Andrew Ware 《The Professional geographer》2007,59(4):521-536
This article reports on the results from a spatiotemporal analysis of disaggregate fire incident data. The innovative analysis presented here focuses on the exploration of spatial and temporal patterns for four principal fire incident categories: property, vehicle, secondary fires, and malicious false alarms. This research extends previous work on spatial exploration of spatiotemporal patterns by demonstrating the benefits of comaps and kernel density estimation in examining temporal and spatiotemporal dynamics in calls for services. Results indicate that fire incidents are not static in either time or space and that spatiotemporal variation is related to incident type. The application of these techniques has the potential to inform policy decisions both from a reactive, resource‐allocation perspective and from a more proactive perspective, such as through spatial targeting of preventive measures. 相似文献
92.
Allen K. Kennedy Jörn-Frederik Wotzlaw James L. Crowley Mark Schmitz Urs Schaltegger Benjamin Wade Laure Martin Cristina Talavera Bryant Ware Thi Hao Bui 《Geostandards and Geoanalytical Research》2023,47(2):373-402
Twelve apatite samples have been tested as secondary ion mass spectrometry (SIMS) reference materials. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis shows that the SLAP, NUAN and GR40 apatite gems are internally homogeneous, with most trace element mass fractions having 2 standard deviations (2s) ≤ 2.0%. BR2, BR5, OL2, AFG2 and AFB1, which have U > 63 μg g-1, 206Pb/204Pb > 283, and homogeneous SIMS U-Pb data, have respective isotope dilution thermal ionisation mass spectrometry (ID-TIMS) ages of 2053.83 ± 0.21 Ma, 2040.34 ± 0.09 Ma, 868.87 ± 0.25 Ma, 478.71 ± 0.22 Ma and 473.25 ± 0.09 Ma. Minor U-Pb heterogeneity exists and accurate SIMS results require correction with the 3D Concordia-constrained common Pb composition. Among the studied samples, AFG2 and BR5 are the most homogeneous U-Pb reference materials. The SIMS sulfur isotopic compositions of eight of the apatites shows they are homogeneous, with 2s for both 103δ34S and 103δ33S < 0.55‰. One apatite, BR96, has Δ33S = -0.36 ± 0.2‰. The apatite samples have ID-TIMS 87Sr/86Sr between 0.704214 ± 0.000030 and 0.723134 ± 0.000035. 相似文献
93.
The continental slope of the northern Gulf of Mexico is diapirically controlled and is comprised of coalescing salt sheets, salt withdrawal basins, salt ridges, salt tongues and sills, and submarine canyons. Bathymetric information from single-beam data has resulted in several published maps. Many of the map areas have been remapped, using multibeam surveys, by the US National Ocean Service, and names have been given to the major physiographic features. The multibeam program was discontinued before complete coverage of the slope was accomplished. We provide charts of the remaining areas with names of features that have been accepted by the US Board of Geographic Names. 相似文献
94.
This special issue ofGeo-Marine Letters Benthic Boundary Layer Processes in Coastal Environments includes 20 papers devoted to results of recent near-shore experiments supported by the Coastal Benthic Boundary Layer (CBBL) program. Experiments were conducted in gas-rich muddy sediments of Eckernförde Bay of the Baltic Sea and on relict sandy sediments of the West Florida Sand Sheet. In this introductory paper we present scientific justification for experiments and summarize preliminary results. 相似文献
95.
Kenneth S. Davis Niall C. Slowey Ingo H. Stender Hannelore Fiedler William R. Bryant Gunther Fechner 《Geo-Marine Letters》1996,16(3):273-278
The relationship between spatial variations of the properties of sea-floor sediments and acoustic backscatter from the surface of the sea floor on the continental shelf off of Panama City, Florida, USA, is investigated using surficial sediment grab samples and digital side-scan sonar data. Acoustic backscatter strength has a high, direct correlation with the mean grain size of the sediments. Acoustic backscatter strength also correlates directly with the carbonate content of the sediments, particularly in medium-and coarse-sand facies, because large, irregularly shaped, carbonate particles affect both the mean grain size of the sediments and the roughness of the surface of the sea floor. 相似文献
96.
William R. Bryant John R. Bryant Mary H. Feeley Gregory R. Simmons 《Geo-Marine Letters》1990,10(4):182-199
Bathymetric charts of the continental slope of the northwestern Gulf of Mexico reveal the presence of over 90 intraslope basins
with relief in excess of 150 m. The evolution and the general configuration of the basins are a function of halokinesis of
allochthonous salt. Intraslope-interlobal and intraslope-superlobal basins occupy the upper and lower continental slope, respectively.
Other structures on the slope associated with salt tectonics are the Sigsbee Escarpment, the seaward edge of the Sigsbee salt
nappe, and the Alaminos and Keathley canyons. Major erosional features are the Mississippi Canyon and portions of a submarine
canyon on the southern extreme of the Sigsbee Escarpment. 相似文献
97.
Origin,physical, and mineralogical nature of red clays: The Pacific Ocean Basin as a model 总被引:2,自引:0,他引:2
Extensive examination of North Pacific Basin red clays by scanning and transmission electron microscopy reveals that the mean constituent of the red clays are illite-rich argillaceous or shale clasts, quartz and authigenic smectite. The main source of the shale clasts and quartz are aeolian in nature and are derived mainly from African and Asian shales. Illite-rich argillaceous or shale clasts are identifiable by their morphology (high degree of roundness), selected area diffraction, and their unique fracture characteristics created by an ultra thin-sectioning process. This allows for the identification and differentiation of illite-rich shale clasts from other clays, including detrital illite, kaolinite, and smectite. Geotechnical examination of the red clays indicate that they are overconsolidated: the preconsolidation stress is in all cases larger than the vertical effective stress. The overconsolidation is attributed to the strong bonding of argillaceous or shale clasts, quartz and other particulate matter by x-ray amorphous and well developed crystalline sheets of authigenic smectite characterized by high surface activity. 相似文献
98.
Free gas is ubiquitous at shallow sediment depths of the northern margin of the Gulf of Mexico. Gassy sediment patches are
between 250 and 500 m in horizontal size. Often the gassy layers are within 100 m from the sea floor and are only a few meters
thick. Both biogenic and thermogenic gas hydrates have been recovered. Stability values of temperature and pressure indicate
that hydrates can exist in water depths less than 500 m. Gassy sediment geoacoustic parameter values are not well constrained
because of a lack of concurrent measurements of acoustic properties and sediment gas content. For Gulf of Mexico gassy sediment,
some reportedin situ values of sound speed are reduced by an order of magnitude below values for water saturated sediments. More commonly, sound
speed is reduced from water saturated sediment values by only 15 to 50 percent. 相似文献
99.
Seismic expression of sedimentary volcanism on the continental slope,northern Gulf of Mexico 总被引:2,自引:1,他引:2
High-resolution geophysical data define acoustically amorphous, mounded structures on the upper, middle, and lower continental
slope of the northern Gulf of Mexico. Physical samples and observations within this unique seismic facies show gassy sediments,
sometimes in hydrated form and, in places, as chemosynthetic communities. The geologic setting of these mounds suggests that
the process of formation falls on the continuum of mud volcanoes to mud diapirs. 相似文献
100.
High-resolution seismic profiles of Eckernförde Bay and the adjacent Baltic Sea were collected, and the geoacoustic properties of sediments there were measured. Bulk densities averaged ~ 1.35 g cm–3 and ranged from ~ 1.2 to ~ 1.7 g cm–3. Compressional wave velocities in gas-free sediments averaged ~ 1460 m s–1 and ranged from ~ 1425 to ~ 1555 m s–1. In nongassy sediments, bulk density variations typically controlled changes of acoustic impedance. Impedance changes were usually too small and closely spaced to be resolved seismically, although, at certain sites, significant impedance changes are far apart enough that they correlate one-to-one with seismic reflectors. Where free gas is present, velocity decreases and wave energy is scattered, causing a prominent seismic reflector. 相似文献