Usage of an early warning and information system Web-site for real-time seismicity in Iceland   总被引：1，自引：1，他引：0  

Deanne Bird  Matthew J. Roberts  Dale Dominey-Howes 《Natural Hazards》2008,47(1):75-94

Iceland has been subjected to destructive earthquakes and volcanic eruptions throughout history. Such events are often preceded by changes in earthquake activity over varying timescales. Although most seismicity is confined to micro-earthquakes, large earthquakes have occurred within populated regions. Following the most recent hazardous earthquakes in 2000, the Icelandic Meteorological Office (IMO) developed an early warning and information system (EWIS) Web-site for viewing near-real-time seismicity in Iceland. Here we assess Web-site usage data in relation to earthquake activity, as recorded by the South Iceland Lowland (SIL) seismic network. Between March 2005 and May 2006 the SIL seismic network recorded 12,583 earthquakes. During this period, the EWIS Web-site logged a daily median of 91 visits. The largest onshore event (M _L 4.2) struck 20 km from Reykjavík on 06 March 2006 and was followed by an immediate, upsurge in usage resulting in a total of 1,173 unique visits to the Web-site. The greatest cluster of large (≥M _L 3) events occurred 300 km offshore from Reykjavík in May 2005. Within this swarm, 9 earthquakes ≥M _L 3 were detected on 11 May 2005, resulting in the release of a media bulletin by IMO. During the swarm, and following the media bulletin, the EWIS Web-site logged 1,234 unique visits gradually throughout the day. In summary, the data reveal a spatial and temporal relationship between Web-site usage and earthquake activity. The EWIS Web-site is accessed immediately after the occurrence of a local earthquake, whereas distant, unfelt earthquakes generate gradual interest prompted by media bulletins and, possibly, other contributing factors. We conclude that the Internet is a useful tool for displaying seismic information in near-real-time, which has the capacity to help increase public awareness of natural hazards.  相似文献   

The response of the climate system to the indirect effects of anthropogenic sulfate aerosol     

K. D. Williams  A. Jones  D. L. Roberts  C. A. Senior  M. J. Woodage 《Climate Dynamics》2001,17(11):845-856

 The indirect effects of anthropogenic sulfate aerosols on the albedo and lifetime of clouds may produce a significant impact on the climate system. A `state of the art' general circulation model (GCM) which includes an interactive sulfur cycle and a physically based cloud microphysics scheme is coupled to a mixed-layer ocean model in order to study the impact of the indirect effects on the coupled climate system. The linearity of the two indirect effects on the model response is also investigated by including each effect separately in the model. The response of the sea surface temperatures (SSTs) and sea ice is found to provide an important feedback on the cooling at high latitudes and the change in meridional SST gradient results in a southward shift of the inter-tropical convergence zone (ITCZ). The sensitivity of the model to the forcing from the indirect effects of sulfate aerosol is found to be similar to, but slightly weaker than that obtained from a doubling of CO₂. Received: 30 August 2000 / Accepted: 3 January 2001  相似文献   

A Field Evaluation of In-Situ Biodegradation of Chlorinated Ethenes: Part 2, Results of Biostimulation and Biotransformation Experiments   总被引：2，自引：0，他引：2  

Lewis Semprini  Paul V. Roberts  Gary D. Hopkins  Perry L. McCarty 《Ground water》1990,28(5):715-727

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Deciphering some unique paleotemperature indicators in halite-bearing saline lake deposits from Death Valley, California, USA     

Sheila M. Roberts  Ronald J. Spencer  Wenbo Yang  H. Roy Krouse 《Journal of Paleolimnology》1997,17(1):101-130

Saline lake deposits are arguably the best source of mid- to low-latitude terrestrial paleoclimate data. Alternating clastic sediments and evaporites of different chemical composition have long been recognized as sensitive records of changes in inflow and aridity related to a variety of climate parameters. Several sources of paleotemperature information from a halite-bearing saline lake deposit are described here – pseudomorphs of a cold-temperature evaporite mineral, homogenization temperatures of fluid inclusions in halite, and stable-isotope compositions of fluid inclusions in halite. Examples of these paleoclimate data come from analysis of the lower half of a 185-m core drilled in Pleistocene saline lake deposits at Death Valley, California. Daily and seasonal temperature variations in saline lake waters create conditions for the appearance and disappearance of temperature-dependent mineral phases. In the Death Valley core, hexagonal-shaped halite crystals, probable pseudomorphs of the cold-temperature hydrous mineral, hydrohalite (NaCl2H₂O), provide evidence of brine temperatures below about 0 °C. Homogenization temperatures of fluid inclusions in primary halite offer an actual (not proxy) record of surface-brine temperatures. Samples with primary fluid-inclusion textures are carefully selected and handled, and data are collected from single-phase aqueous-brine inclusions chilled to nucleate vapor bubbles. Temperature variations are observable at scales of individual halite crystals (hours to days), single halite beds (weeks to months or years), and multiples of beds to entire facies (hundreds to tens of thousands of years). A ¹⁸O/D stable isotope record from the minute quantities of brines in fluid inclusions in halite is accessible using a method recently developed at the University of Calgary. The stable isotope record from the Death Valley core, a complex response to climate variables including temperature, humidity, storm patterns or seasons, and inflow sources, compliments and expands the interpretation emerging from the stratigraphy and homogenization temperatures.  相似文献   

Observations and mechanisms of upwelling in the northern KwaZulu-Natal Bight,South Africa     

MJ Roberts  C Nieuwenhuys 《African Journal of Marine Science》2016,38(1):S43-S63

New in situ time-series data were acquired by two ADCP moorings placed on the shelf off Richards Bay on the east coast of South Africa at depths of 25 m and 582 m between October 2009 and August 2010. The 11-month inshore bottom-temperature record revealed five substantial upwelling events lasting 5–10 days each where temperatures decreased by about 7 °C to 17–18 °C. Satellite sea surface temperature data showed these events to coincide with cold-water plumes occupying the northern wedge of the KwaZulu-Natal (KZN) Bight. Numerous shorter duration (1–2 days) upwelling events with less vivid surface expressions were also observed throughout the entire record where bottom temperature dropped by 2–3 °C. The last four months of the record were characterised by a protracted cool period lacking a seasonal trend but punctuated with oscillations of warm and cooler bottom water. In contrast to earlier studies that suggested upwelling was topographically and dynamically driven by the juxtaposition of the Cape St Lucia offset and the Agulhas Current (a solitary mechanism), our analysis showed almost all major and minor cold-water intrusions to coincide with upwelling-favourable north-easterly winds that simultaneously force a south-westerly coastal current. Ekman veering in the bottom boundary layer of the Agulhas Current, and the concomitant movement of cold water up the slope, was found to coexist at times with coastal upwelling, but its absence did not impede inshore cold-water intrusions, calling into question its role as a primary driver of upwelling. Both major and minor upwelling events were observed to promote phytoplankton blooms in the northern KZN Bight which commonly extended to the Thukela River. Wind-driven upwelling was also observed in the inner bight between Richards Bay and Port Durnford, explaining the ribbon of coastal chlorophyll continuously observed on ocean colour images between Cape St Lucia and the Thukela River. Similarities in upwelling character and mechanisms are observed between the northern KZN Bight and the Florida Current shelf systems.  相似文献   

The resolution sensitivity of the South Asian monsoon and Indo-Pacific in a global 0.35° AGCM     

Stephanie J. Johnson  Richard C. Levine  Andrew G. Turner  Gill M. Martin  Steven J. Woolnough  Reinhard Schiemann  Matthew S. Mizielinski  Malcolm J. Roberts  Pier Luigi Vidale  Marie-Estelle Demory  Jane Strachan 《Climate Dynamics》2016,46(3-4):807-831

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Chokka squid (Loligo vulgaris reynaudii) abundance linked to changes in South Africa's Agulhas Bank ecosystem during spawning and the early life cycle     

Roberts  Michael J. 《ICES Journal of Marine Science》2005,62(1):33-55

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Morphology of largeHalimeda bioherms,eastern Java sea (Indonesia): A side-scan sonar study     

Harry H. Roberts  Charles V. Phipps  Lukman L. Effendi 《Geo-Marine Letters》1987,7(1):7-14

The most extensive and thickestHalimeda bioherms reported from modern seas occur along both open and protected margins of Kalukalukuang Bank, eastern Java Sea (Indonesia). Seismic profiles suggest these features average 20 to 30 m thick (maximum 50 m) and developed over large areas by coalescence of individual mounds. Bioherm morphologies range from numerous small mounds ( 10–20 m diameter) through hay-stack features ( 100 m diameter) to broad swells. Some modern bank bioherms display surface forms that appear related to onbank flow from Makassar Strait. Upwelling of cold, nutritive water is likely responsible for unusualHalimeda productivity and large bioherm development.  相似文献   

Do bottom-intensified diurnal tidal currents shape the alignment of carbonate mounds in the NE Atlantic?     

Martin White  J. Murray Roberts  Tjeerd van Weering 《Geo-Marine Letters》2007,27(6):391-397

Measurements of near-seabed currents at different carbonate mound locations have demonstrated the presence and influence of bottom-magnified diurnal-period tidal motions. These bottom-trapped waves occur at a depth where the product of local vertical density stratification and seabed slope is a maximum. The seabed currents are magnified significantly if the diurnal forcing period is resonant with the combination of stratification and seabed slope. At the Belgica mounds (eastern Porcupine Sea Bight), there is a correlation between the cross-slope alignment of individual carbonate mounds and the direction of the major axis of the largest (diurnal) tides. The pattern suggests that the enhanced tidal currents play a major role in the shape of developing mounds over a long time period. A similar relation appears to hold at the Logachev mounds (SE Rockall Bank), although less clear because tides are not amplified to the same degree. At other mound locations where enhanced diurnal currents are not present, a more irregular distribution is observed. This suggests that the diurnal currents may be important only at certain carbonate mound locations, and that at these locations a more distinctive alignment of mound structures is produced.  相似文献   

Three generations of mud volcanoes on the Louisiana continental slope   总被引：4，自引：2，他引：4  

T. W. Neurauter  H. H. Roberts 《Geo-Marine Letters》1994,14(2-3):120-125

Three mud volcanoes were identified in a small area of the upper continental slope of the Gulf of Mexico. One is actively accreting by small, intermittent eruptions of gas and fluid mud. Eruptions occur from a pool of gas- and oil-saturated muds that upwell and spill over the central crater edge and down the flanks of the coneshaped buildup. A second structure, a possible sand volcano, is in the last stages of activity, with only slight evidence of gas-saturated sediments. The third structure is a dormant mud volcano with furrowed sides and scattered authigenic carbonate plates and rubble but no venting of gas or fluids.  相似文献