摘要:

Based on 770 laboratory measurements of void ratio (e) and effective overburden pressure (p) from the upper 2 m of sediments in Eckemfoerde Bay, Baltic Sea, a new empirical model for estimating dynamic shear modulus (μ) was developed as

ISSN:1064-119X    

DOI:10.1080/10641199809379960

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Adequate suppression of ground roll in seismic data acquisition is imperative to improve the signal‐to‐noise (S/N) ratio. This requires designing of source and receiver patterns. In this article, a computer‐aided procedure for computation and online plotting of source, receiver, and their combined (source + receiver) pattern response curves is presented. The space between the source elements and the receiver elements need not necessarily be the same. It is hoped that this software will cater to the needs of field geophysicists, as this job is currently carried out manually, a subjective, cumbersome, and time‐consuming process. Further, it should also help field geophysicists in selecting patterns more judiciously in order to meet the desired objectives.

ISSN:1064-119X    

DOI:10.1080/10641199809379961

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A brief summary of past marine mineral exploration strategies is given and compared to present strategies. Focus is presently on exploration efforts in the Exclusive Economic Zones (EEZs), particularly in the coastal and near‐coastal realms, although ferromanganese nodules and massive sulfides at mid‐ocean ridges are still of significant interest. A relatively new radiometric mineral exploration tool, assaying the ocean floor through continuous measurement by gamma‐ray spectrometry, is described. Preliminary data gathered with a prototype sonde in Danish waters are presented.

ISSN:1064-119X    

DOI:10.1080/10641199809379962

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Synechococcus(photoautotrophic cyanobacteria) are among the major primary producers in the oligotrophic open ocean. Potential environmental impacts of bottom water and sediment intrusion on theSynechococcuspopulation in the surface water column of the northeast equatorial Pacific were investigated during the KODOS (Korea Deep Ocean Study) 95–2 cruise. The growth ofSynechococcuswas limited primarily by Fe deficit and secondarily by nitrogenous nutrients. Since bottom water and sediment are abundant in both inorganic nutrients and trace metab, the addition of bottom water‐sediment slurry to surface water samples stimulated the growth ofSynechococcus.Our results together with other experimental estimation suggest that certain impacts could occur on the photoautotrophic plankton biomass in the water column by the surface discharge of bottom water and sediment during large‐scale and long‐term commercial mining of Mn nodules. More quantitative estimation for those environmental aspects in the water column is necessary for the construction of environmentally affiliated mining systems in the future.

ISSN:1064-119X    

DOI:10.1080/10641199809379963

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Although the relationship between submarine hydrothermal activity and earthquakes was recognized over 20 years ago, it has still not been precisely defined. Faulting and permeability control fluid flow in the oceanic crust and therefore submarine hydrothermal activity at mid‐ocean ridges. Microearthquakes associated with submarine hydrothermal activity tend to be small in magnitude and occur in swarms. Swarms of microearthquakes associated with hydrothermal vents are thought to be related to cracking of the oceanic crust. The depths of the microearthquakes may mark the brittle‐ductile transition which denotes the downward limit of seawater circulation into the oceanic crust. The maximum depth of microearthquakes on the Mid‐Atlantic Ridge is 10 km, compared with 3 km on the East Pacific Rise. The brittle layer tends to be thinnest where mid‐ocean spreading rates are fastest. Seismic pumping is a mechanism for the transport of hydrothermal fluids within fractures and may account for stockwork mineralization within the ocean crust. Submarine hydrothermal mineralization is episodic on time scales ranging from 1 to 105years and is controlled by volcanic and tectonic processes in a manner not yet completely understood. Emphasis in the study of submarine hydrothermal activity is changing from observation to long‐term monitoring. The U.S. Navy's Sound Surveillance System (SOSUS) has been very successful in detecting megaplume events caused by dike injection on the Juan de Fuca and Gorda Ridges. The long‐term deployment of large arrays of ocean bottom seismometers on the ocean floor will become routine in the future. Such a program will contribute to an understanding of the factors controlling the episodicity of submarine hydrothermal activity and mineralization on the sea floor. On the Izu‐Bonin Arc, hydrothermal mineralization has been observed in a number of volcanic Calderas. This region appears to have many advantages for the future monitoring and evaluation of microseismicity in hydrothermally active areas.

ISSN:1064-119X    

DOI:10.1080/10641199809379964

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:1064-119X    

DOI:10.1080/10641199809379959

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor