1997年9月三水3.7和4.4级地震特征初析

对１９９７年９月２３日和２６日两次三水有感地震的特征进行了初步分析,认为这两次地震具有震前和震后地震活动水平低、面波发育和低震级高烈度等特性;震区的主压应力为北北西方向,两震的受力方向基本一致,但断层面解明显不同。     

Historical and ecological analysis of coral communities in Castle Harbour (Bermuda) after more than a century of environmental perturbation

The coral reefs in Bermuda's Castle Harbour basin have been subjected to varying anthropogenic stressors for over 100 years. These include restriction of water flow through the construction of a causeway in the late 19th century and an extensive dredging and land reclamation operation during World War II. In the 1970s, disposal of bulk waste commenced at a foreshore reclamation site in Castle Harbour. Since 1996 the waste stream has included blocks of cement-stabilized municipal incinerator ash. This study provides a historical and quantitative ecological review of the Castle Habour reef ecosystem as a case study, assessing the responses of the reef to more than a century of anthropogenic disturbance. Measures of the coral community, flow rates, turbidity and sedimentary regimes suggest the present structure of the coral community largely reflects the impacts of the historic dredge and fill operations prior to the establishment of the foreshore dump site. Recent increases in the abundance of some sediment tolerant, massive reef-building coral species (Diploria strigosa and Montastraea cavernosa) suggest adaptation to chronic sediment stress.     

Mapping water quality and substrate cover in optically complex coastal and reef waters: an integrated approach

Sustainable management of coastal and coral reef environments requires regular collection of accurate information on recognized ecosystem health indicators. Satellite image data and derived maps of water column and substrate biophysical properties provide an opportunity to develop baseline mapping and monitoring programs for coastal and coral reef ecosystem health indicators. A significant challenge for satellite image data in coastal and coral reef water bodies is the mixture of both clear and turbid waters. A new approach is presented in this paper to enable production of water quality and substrate cover type maps, linked to a field based coastal ecosystem health indicator monitoring program, for use in turbid to clear coastal and coral reef waters. An optimized optical domain method was applied to map selected water quality (Secchi depth, Kd PAR, tripton, CDOM) and substrate cover type (seagrass, algae, sand) parameters. The approach is demonstrated using commercially available Landsat 7 Enhanced Thematic Mapper image data over a coastal embayment exhibiting the range of substrate cover types and water quality conditions commonly found in sub-tropical and tropical coastal environments. Spatially extensive and quantitative maps of selected water quality and substrate cover parameters were produced for the study site. These map products were refined by interactions with management agencies to suit the information requirements of their monitoring and management programs.