HELIKE WAVE NOTCHES

On the footwall of the Helike and Aegeira faults (Fig.1.1) well defined notches are cut by waves into cemented and brecciated limestones. These notches at present lie at +1.7, +2.3, +3.5, and 5.5m above sea-level (Stewart 1996) (Fig. 10.1) The above mentioned notches, dated using 14C on marine shells (L. Lithophagus, and Dendropoma), correlated with the eustatic sea level curve for Holocene in the Mediterranean given by Flemming and Webb (1986), show a variable rate of uplift during the last 8000 years (Table 1; Fig. 10.2)

 

TABLE 1:

Period

Uplift rates

1950AD - 1000BC

2.0 – 2.5 mm/yr

1000BC – 6000BC

Tectonic quiescence

6000BC – 8000BC

2.1 – 2.6 mm/yr

 

The uplift rates in Table 1 are considered rather high to be attributed only to episodic co-seismic uplifting on the footwall of the Helike and the Aegeira faults and other mechanisms may also be responsible for this uplift (Stewart 1996) like:

  1. cumulative effect of uplift on other faults offshore and/or
  2. regional aseismic uplifting due to the underplating along the Hellenic subduction.

These notches have also been studied by Mouyaris et al (1992), who ascribed them to slightly different heights above sea level than Stewart (1996), and therefore estimating different uplift rates.

Pirazzoli et al 2004 studying sea level changes in the same locations comment that there is no clear evidence of individual fossil shorelines and therefore the relative sea-level did not remain slable for long periods. However, the presence of marine fossils at 9.3 and 11.5m at Aegira (Mavra Litharia) and Paralia Platanon, (Fig. 10.3 & 10.4) dated at 5550 – 5040 BC and 2890 – 2930 BC respectively in comparison with the height of sea level at that time as given by Bard et al 1996 suggest an uplift of 3.2 mm/yr for Aegira (Mevra Litheria) and 2.4mm/yr at Paralia Platanon.

These uplift rates are much higher than those estimated by McNeill et al 2004, 2006 based on the uplift of marine terraces for the last 400.000 years and those by Koukouvalas et al 2001 based on palaeoseismological studies for the last 3.000years.

 

Fig. 10.1: notches at present lie at +1.7, +2.3, +3.5, and 5.5m above sea-level (Stewart 1996) 

Fig. 10.2:  a variable rate of uplift during the last 8000 years

Fig. 10.3: Detail of a raised Holocene Cladocora reef at Mavra Litharia. (Photo P.A.P. no. D570, Aug. 1992) (From Pirazzoli et al 2004)

Fig. 10.4: Remnants of Lithophaga and other in situ marine crusts capping this limestone rock, on the seaside of the road near Platanos, show that this outcrop was completely submerged during the Holocene (Photo P.A.P. no. G73, June 1997). (From Pirazzoli et al 2004)

 

 

References:

Flemming N. & Webb C. 1986. Tectonic and Eustatic coastal changes during the last 10.000 years derived from archaeological data. Z. Geomorphologie 62:1-25

Mouyaris N., Papastamatiou D., Vita-Finzi C. 1992. The Helike Fault?  Terra Nova 4:124-129

Pirazzoli P., Stiros S., Fontugne M., Arnold M. 2004. Holocene and Quaternary uplift in the central part of the southern coast of Corinth Gulf (Greece) Marine Geology 121:35-44

Stewart I. 1996. Holocene uplift and Palaeoseismicity on the Elike fault, Western Gulf of Corinth, Greece. Annali di Geophysica, 39:575-588.

Stewart I. and Vita-Finzi C. 1996. Coastal uplift on active normal faults. The Eliki fault, Greece. Geophys. Res. Letters 33, 1853-1856

 

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