IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS006 Poster presentation 1939
Ground penetrating radar for archeoseismological investigations - a case
study from Baelo Claudia, Southern Spain
Mr. Christoph Gruetzner
Neotectonics and Natural Hazards Group RWTH Aachen University, Germany
Klaus Reicherter, Pablo G. Silva
The Roman ruins of Baelo Claudia are situated at the Straits of Gibraltar in the province of Cdiz (Spain),
close to the village of Tarifa. With about 2.000 inhabitants, the city was one of the larger roman
settlements on the Iberian Peninsula and delivered tons of Garum, an ancient fish-dip made of tuna, to
the capital. In the 1st century, an earthquake destroyed wide parts of the infrastructure. Because of the
economic importance the city was rebuild during the Imperial Phase. Later in the 4th century, when the
Roman star already had begun to sink, another destructive earthquake hit Baelo Claudia. It can be
observed in the ruins - the columns and house walls fell on clean pavement and are partly preserved in
this situation - that the event marked more or less the end of Roman settlings in this place. The seismic
source or faults of the earthquakes are not yet clear. Paleoseismological studies showed, however, that
both, the Carrizales and Cabo de Gracia Faults, in the immediate environs of Bolonia might produce a
seismic event big enough to destroy the city. For our study 7 km of ground penetrating radar (GPR)
profiles have been collected in the ruins, using the 300 MHz GSSI antennas and the SIR2 system. The
frequency of 300 MHz provides a good compromise between penetration depth and resolution. In
addition, some 240 cm low-frequency profiles have been taken in order to image the deeper structures
of the area. We aim to find coseismic features like landslides and liquefaction or even buried faults
inside the ancient city. As well we collected subsurface information of the buildings (tilted or destroyed
walls and buildings that are still covered by the post-Roman colluvium). Besides the geological
information, the investigation helps the local archeologists with their future excavations, as many
unknown tombs and constructional features have been discovered during the survey. Our data do not
imply an unknown active fault in the area but document earthquake-related damages like fallen
boulders, tilted walls and the deformation of a buried aqueduct as well as the structure of a small scarp,
crossing the city. The post-Roman colluvium can be easily mapped and distinguished from building rests
and from older deeper-lying sediments. This layer marks the event horizon of the last earthquake after
which the settling stopped. The thickness of the colluvium (or the depth of the event layer) provides
information about erosion and sedimentation processes in the area, including mass wasting.
Furthermore, GPR provides a reliable tool in finding promising locations for probing and/or trenching.
Keywords: paleoseismology, archeoseismology, groundpenetratingradar