Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

Two filters are used for processing the scans in FARO
Scene: (1) a stray filter removes scan points that result
from hitting two objects e.g. at edges and scan points that
result from hitting no object within the working area of
the scanner (e.g. laser points to the sky); (2) the second
filter removes noisy points. So‐called “dark” scan points
reflect only a very small amount of the light beam and
increase the noise in the scan. After the application of the
filters, the photos are attached and the pointcloud is
colorized. The last step is to export the colored scan to
the Reconstructor software, where points outside the
area of interest are removed and additional filters can be
applied.
DAMAGES
The damage zone of the cesspit was investigated in detail.
It is limited to a 2.5 m x 3.5 m wide area at a depth
between 3.5 m and 6.0 m measured from the top (47.5–
45.0 m a.s.l.). At a depth of 4.0 m the major damage area
includes the entire perimeter of the cesspit resulting in a
nearly complete separation of the cesspit walls.
Fig. 3: Deviation of the points of the uppermost 6 m of the cesspit
vs. the depth below surface level. For clarity only 1 out of 1000
measured points is shown. The symbols show the azimuth of each
point
To further quantify the damage, the measured cesspit
surface was compared to an ideal cylinder with a
diameter of 2.38 m and a length of 6.46 m. The ideal
cylinder was fixed using the points from the cesspit and a
best‐fit routine. The resulting cylinder was aligned to the
local reference system. The deviation was also calculated
from a smaller ideal cylinder. The color codes in Fig. 2B
illustrate the deviations between the cesspit and the ideal
1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology)
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cylinder. In Fig. 3, the directional data are shown
compared to the ideal best‐fit cylinder (grey line).
The data show a maximum displacement between 8 and
20 cm in the depth range 3.5 to 6.0 m. At a depth of 4.0 m
the damage area of the northeastern wall is clearly visible
(green diamonds in Fig. 3). These results correspond to
similar measurements from a Roman well located 15 m
east of the cesspit that also exhibits strong deformations,
here at a depth of 38‐44 m a.s.l. The area of investigation
is located at the slope of a former sidearm of the Rhine
River. In both, the cesspit and the Roman well, the
damage zones are at the level of the natural ground. A
medieval well ca. 20 m to the South, however shows no
significant damages, suggesting a terminus ante quem.
The large deviations in the first meter of the cesspit in
figure 3 result from the inlet and the doming of the
construction at the top.
DISCUSSION
We present a case study for application of 3D laser
scanning in archaeology and archaeoseismology. Due to
safety reasons, it was not possible to excavate the entire
medieval cesspit in the Archaeological Zone Cologne,
without successive restorations. The 3D laser scanning
allowed reconstruction of a virtual cesspit model in its
unrestored condition. When the excavation is finished
and the pit secured, differences between the original and
the final excavated structure can be further quantified. In
addition, the 3D virtual model allows quantification of
damages at a resolution of 1‐2 mm. To investigate the
cause of these damages (e.g. anthropogenic, seismogenic
etc.) the damage database thus created provides a
foundation for further numerical analysis of the structures
to be combined with additional geodetic data and the
archaeological results, in particular estimates for absolute
time scales.
Acknowledgements: The project is financed by the Deutsche
Forschungsgemeinschaft (DFG Hi660/2‐1). We are grateful to the
staff of the Archaeological Zone Cologne for the cooperation.
Sharon K. Reamer helped shaping the manuscript.
References
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