Essay Example on The sea-level curve used for the Elevation Corrections

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The general uplift rates for the Holocene are found to be about 1 0 1 4 mm yr depending on the sea level curve used for the elevation corrections This means that the kind of sea level curve used for such short time periods is of prime importance in the determination of vertical movement rates for a given area It should be noted that uplift rates show general trends when we deal with long periods of time As these periods become shorter it is possible to get faster or slower rates which reflect time intervals of different tectonic activity In areas of intense activity caused by a number of differential movements of faults like Perachora Peninsula and in times of fast sea level changes the correlation of these two factors becomes extremely complicated and even impossible as in the case of the notch and the consolidated beach material filling it at Flabouro The notch comprises an evolutionary signature during the Holocene Around 12 000 years ago when sea level was at about 50m below the present one the formation of the notch occurred 

The height of the notch which is about 1 1m should have taken a few hundred years to form There followed a period of intense tectonic uplift which overcame the rising sea level indicated by the presence of the terrestrial reddish deposit Fig 8b Around 9 000 years ago sea level reached the notch again partly filled it and covered the terrestrial material




The presence of bivalve shells at the base of the notch dated at 7 000 years BP indicates that sea level was at that elevation 1 6m or higher at that time and was eroding the older beach and terrestrial material All of the above are found a few meters above present sea level The existence of archaeological Early Helladic sherds in the beach rocks south of Lake Vouliagmeni permits us to continue to reconstruct the coastal evolution of the study area Between 6 000 BP and the deposition of the Early Helladic shells in the 2 m beachrocks 4 000BP sea level rose by about 0 5 m which is not consistent with the global sea level curve and the estimated rates of uplift This could only be explained by a local tectonic subsidence shown by the partly submerged archaeological site 

Taking into account the estimated uplift rates of 1 0 to 1 4 mm yr and assuming that this event happened during a time period of 1 000 to 1 500 yrs this gives an uplift of 1 0 to 1 6 m indicating a parallel subsidence rate of about 0 5 to 0 7 mm yr This different vertical movement is very normal as the reactivation of the different faults of the area the site could have undergone subsiding movements Therefore the uplift rates are increased reaching rates of about 1 5 to 2 0 mm yr




The increased rate of uplift during the period 20 000 to 10 000 BP which also corresponds to high seismicity rates could be attributed to the hydro isostatic effect representing the loading of the ocean basins by the melting water after the last glacial period Similar results have also been concluded by MCGUIRE et al 1997 for increased volcanic activity in the Mediterranean Using the estimated uplift rates of 1 5 to 2 0 mm yr and an uplift subsidence ratio of 1 2 5 to 1 3 STEIN BARRIENTOS 1985 KING ELIS 1990 a fault slip rate of 5 0 to 7 0mm yr is obtained This slip rate for the Holocene period is also in good agreement with the slip rate of 6 8mm yr obtained for a time period of 350 Kyr of the big offshore fault located north of the Perachora Peninsula mainly responsible for the uplift of a major part Hellenic Journal of Geosciences vol 42 45 56 53 Fig 9a Plot of corrected 14C age versus present elevations a m s l of all the samples b c d e Plots of corrected 14C age versus corrected elevations a m s l of samples according to the sea level curve for the Holocene of SHEPARD 1963 FLEMMING WEBB 1986 WARNE STANLEY 1995 and LAMBECK 1996 respectively 54 Kalliopi Gaki Papanastassiou Dimitris Papanastassiou Hampik Maroukian of the southern Gulf of Corinth ARMIJO et al 1996 It is interesting to note the difference in the rates between the Holocene and the Upper Pleistocene periods


This suggests that the big faults do not have stable rates of movements and they differ considerably in time This is also indicated from the archaeological and historical evidence for catastrophic earthquakes as well as from the instrumentally recorded events which represent paroxystic and quiescence periods of seismic activity of the order of hundreds of years All of the above permit us to maintain that the estimated uplift rate of 1 5 to 2 0 mm yr is a minimum one meaning that tectonism has surpassed eustatism in the last 6 000 yrs The obtained uplift rates were reached by combining the complex active tectonism resulting in various significant landforms the archaeological observations and the absolute dating and therefore could be considered as a reliable approach for this i




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