Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

Furthermore this region in central Greece undergoes a
rapid main extension in N‐S direction with approximately
6‐15 mm/a (Kokkalas et al., 2007b). The Kaparelli fault is
an active normal limestone fault scarp with a height of
about 3 ‐ 5 m. The last major earthquake occurred in
winter 1981. Three events with magnitudes greater than
6 were measured. During the night of the 24 th ‐25 th
February the fist two events had a magnitude of 6.7 and
6.4 and the third event on the 4 th March reached
magnitude 6.3 (Hubert et al., 1996). After those events 2‐
D roughness analyses (Stewart, 1996), cosmogenic dating
(Benedetti et al., 2003), trenching (Kokkalas et al., 2007)
and deformation monitoring by using a dense network of
Fig. 3: A) The southern segment of the Kaparelli fault.
B) One scan position and the scarp layout
non‐permanent GPS stations and extensometers (Ganas
et al. 2007) have been carried out especially on the
Kaparelli fault. Benedetti et al. (2003) assumed three
events from his cosmogenic dating. The results give
evidence for events at 20±3 ka, 14.5±0.5 ka and 10.5±0.5
ka. According to that the time intervals between slip
events are 3000‐9000 years, 4000‐5000 years and 10000‐
11000 years. Kokkalas et al. (2007) results of the trench
show again three events at around 7.5 ka, 5.8 ka and 1.4
ka. So that now seven events include the 1981
earthquake are proposed
FUNDAMENTALS OF LIDAR
The terrestrial laser scanning (TLS) was established as a
good data acquisition in geoscience and geological
engineering in difficult accessible areas. As the TLS has a
high spatial and temporal resolution it is an effective
remote sensing technology for reconstruction, monitoring
and observation of mass movement phenomena and
related hazards. The raw point cloud dataset includes the
distance between object and TLS, the x‐, y‐ and z‐
coordinates and the received intensity. With the
integrated digital camera the panchromatic information is
recorded. Furthermore, the working capabilities of TLS in
geosciences are based in the area‐measured data in
safety range (> 600m). Successful investigations in
geosciences with TLS were published by e.g. Kuhn &
Prüfer (2007) for mass movement observation on the
island Rügen, Travelletti et al. (2008) for landslide
monitoring, Rabatel et. al. (2008) for mass balance of
rockfall in the Alps or by Slob et. al. (2007) for fracture
systems. The fundamental principle of LiDAR (Light
1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology
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Detection And Ranging) is to generate coherent laser
beam with little beam divergence by stimulated emission.
The electromagnetic waves are reflected by surfaces and
the receiver detects portions of the backscattered signal.
Fig. 4: The terrestrial laser scanner ILRIS 3D from Optech in the
field
The laser ranging system is based on measuring the time‐
of‐flight of the short laser signal. The range or distance to
the target is calculated from the time elapse of the pulse
between the transmitter and receiver, and, the speed of
the laser pulse. For the pulse detection the first pulse, the
last pulse or the strongest pulse can be selected. In our
case we used the TLS ILRIS‐3D from Optech Inc., Ontario,
CA (Fig.4). The technical Data of ILRIS‐3D show table1.
Table 1: Technical Data
Data sampling rate 2500 points per sec.
Beam divergence 0.00974°
Minimum spot step 0.00115°
Laser wavelength 1500nm
Raw range accurancy 7mm @ 100m
Raw positional accurancy 8mm @ 100m
Digital camera Integrated digital
camera
Scanner field of view 40° x 40°
DATA ACQUISITION AND FIRST RESULTS
Major aims of the investigation were to find quantitative
and qualitative data for the reconstruction of surfaces and
to analyze the tectonic geomorphology and
paleoseismology of active faults with TLS to reconstruct
fault history and activity along surface rupturing scarps. In
this context, the detailed structural analysis of rock
surfaces is fundamental and can be realized by a HRDEM.
The scarp surface was scanned where Benedetti et al.
(2003) took samples for the cosmogenic dating method
(Fig. 3B). For high quality data, the terrestrial laser
scanner should detect the object from different points of
view. Hence a relative complete point cloud can be
produced. In this case we have four scan positions with
eleven scan windows for the circa 35m long scarp. The
density of points by the scans ranges between 1mm to
5.1mm.
The scan sequence is composed of approximately 94
million points.