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Earthquakes, Tsunamis and HarboursA Geoarchaeological GPR-Based Approach for Depicting the Spatial Characteristics of Human Structures and Natural Hazards in Ancient Falasarna Harbour
Published in Luisa M. S. Gonçalves, Hugo Rodrigues, Florindo Gaspar, Nondestructive Techniques for the Assessment and Preservation of Historic Structures, 2017
Michael Styllas, Klisthenis Dimitriadis
GPR is a nondestructive, fast, low-cost and precise investigation technique that uses reflected electromagnetic (EM) waves. In modern archaeology, nondestructive geophysical site assessment methods are of great importance as they are used to provide a fast and accurate picture of subsurface conditions, prior to any excavation works. Contemporary to its archaeological applications, GPR has shown its potential for detecting stratigraphic architecture, layer boundaries and sand-body geometry (e.g. Koster et al., 2014 and references therein). A dense grid of GPR data allows for analyses of the lateral extent of specific sediment for relatively large areas to be quickly undertaken. During tsunami deposit surveys, a shallow groundwater table and/or seawater intrusions may limit GPR measurements. This is because high electrical conductivities reduce penetration depths and data quality. More limiting factors include uneven and/or rough surface conditions, changes in lithology and soil humidity, anthropogenic modification of the subsurface and the presence of metallic objects or other radar wave sources. Fine grain sizes can influence the resolution of GPR, for example high clay content in subsurface layers can lead to attenuation of the EM waves. In the Ancient Falasarna archaeological site, field methodology involved a two-step procedure. An initial coverage of an irregular grid of GPR profiles was carried out to discern the broad extent of tsunami deposits and locate sub-areas of archaeological interest, where a more intensive research is required, followed by denser grids along the sub-areas to map all human-made structures in the vicinity of the harbour with the best possible accuracy.
Rheological behavior of tsunami run-up water containing alluvial deposit at coastline of Kedah, Malaysia
Published in Noor Amila Wan Abdullah Zawawi, Engineering Challenges for Sustainable Future, 2016
A.K. Philip, H.M. Teh, S.H. Shafiai, A. Jaafar, A.H.M. Rashidi
Referring to trench T1-B, both the characteristic of tsunami sediment found by Hawkes et al. (2007) i.e. fine sand and fining upward sequence were observed in the 3 alternating layers of sand and mud soil. Mud cap was present, sandwiched between two sand layers. Erosional contact between the 10 cm mud deposit and sand layers was also recorded in the geologic layer. Nonetheless, rip-up clast was absent. Altogether, this confirms plausible existence of tsunami deposit at T1-B.
Tectonic activity and the history of Wairau Bar, New Zealand’s iconic site of early settlement
Published in Journal of the Royal Society of New Zealand, 2019
As mentioned above, Polynesians arrived in New Zealand about 800 years ago (Anderson 2014). Except for the date assigned to the earlier event by Clark et al. (2015) (between about CE 1070 and CE 1150), Event 1 could have given rise to the Māori tradition described above—the subsidence possibly being enough to explain the reference in the Māori traditions to the creation of the lagoons (King et al. 2017). The dates for Event 1 are on samples that stratigraphically bracket the event. Dates measured to fix the younger age limit of Event 1, however, are on unidentified wood fragments (Clark et al. 2015), and thus have an unknown and possibly large inbuilt age, making them unsuitable for defining a minimum age (McFadgen 1982). Those for the older age limit are on peat, reeds and plant fragments from a peaty palaeosol stratigraphically just below the tsunami deposit (Clark et al. 2015). The boundary between the tsunami deposit and upper surface of the palaeosol is a sharp contact, interpreted as probably a result of scouring removing the upper surface of the palaeosol (Clark et al. 2015), which would expose older organic matter in the soil. Furthermore, radiocarbon dating buried soil organic matter usually overestimates the true date of burial (Wang et al. 1996). It is likely, therefore, that the dates on the peat (NZA36394), the reeds (NZA53727) and the plant fragments (NZA55432) all therefore have inbuilt age (Figure 5), but how much inbuilt age is difficult to quantify. The radiocarbon dates for Event 1 thus provide a maximum date of about CE 1070 with an unknown inbuilt age for the event, but not a minimum date (Figure 5).