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the significance of anthropogenically induced subsidence be quantified and 

 possibly controlled as early as possible. 



Very simple and sensitive compaction meters have been utilized in 

 quantifying this effect in the vicinity of Osaka and Niigata, Japan among 

 other locations. A schematic of two such gages is presented in Fig. 2.7. 

 Each installation consists of an outer casing lining a hole drilled to some 

 depth, h. The inner pipe of slightly smaller diameter is founded on the 

 stratum at depth h. Thus the relative vertical movement between the top of 

 the inner pipe and the general ground level represents the total compaction 

 over the upper sediment column of thickness, h. To establish differential 

 compaction, several such devices would be required at each location of 

 interest. Ideally installations would be made near tide gages and also 

 remote from cities but say inland and in the same geological formations as 

 those near the tide gages. These gages would commence yielding valuable 

 data immediately, and it may be possible to supplement the compaction data 

 collected with models using data representing the geological formations and 

 the history of past ground fluids extraction to estimate earlier 

 compaction. Such results would be invaluable in providing more reliable 

 estimates of past and future eustatic sea level rise. 



New Tide Gage Data - Referring to Figs. 2.3 and 2.4a, it is clear that 

 the southern hemisphere is especially deficient in long-term tide gage 

 data. A number of relative short-term tide gage records are available 

 along the east and west coasts of South America; however, there needs to be 

 an effort on an international basis to install and maintain additional 

 gages to provide a representative distribution. In addition to the 

 southern hemisphere, more insular tide gages and tide gages along the open 

 coast are needed. A first phase effort could be a survey to identify such 

 sites . 



Satellite Altimetry - This new technology should soon yield absolute 

 vertical accuracies of centimeter accuracy. Thus, sounding much of the 

 ocean surface would allow much broader coverage and very importantly does 

 not require reliance on coastal measurements. It would appear appropriate 

 to continue a dense network of tide gages for sea level rise purposes for 



