Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology)
A COMPREHENSIVE CLASSIFICATION OF EARTHQUAKE ARCHAEOLOGICAL
EFFECTS (EAE) FOR STRUCTURAL STRAIN ANALYSIS IN ARCHAEOSEISMOLOGY
M. A. Rodríguez‐Pascua (1), R. Pérez‐López (1), J.L. Giner‐Robles (2), P. G. Silva (3),
V.H. Garduño‐Monroy (4) and K. Reicherter (5)
(1) Departamento de Investigación y Prospectiva Geocientífica, Instituto Geológico y Minero de España. C/ Ríos Rosas, 23. 28003‐Madrid.
SPAIN. ma.rodriguez@igme.es, r.perez@igme.es
(2) Dpto. Geología. Facultad de Ciencias. Universidad Autónoma de Madrid. Cantoblanco. Tres Cantos. Madrid. SPAIN. jlginer@gmail.es
(3) Dpto. Geología Universidad Salamanca, Escuela Politécnica Superior de Ávila, 05003‐Ávila. SPAIN. E‐mail: pgsilva@usal.es
(4) Universidad Michoacana. Morelia. Michoacán, 58060 MEXICO. vgmonroy@zeus.umich.mx
(5) Lehr‐und Forschungsgebiet Neotektonik und Georisiken. RWTH Aachen University. Lochnerstr. 4‐20. 52056 Aachen, GERMANY.
k.reicherter@nug.rwth‐aachen.de
Abstract: One of the key arguments in Archaeoseismology consists to identify how quantity of the observed damage is related with ancient
earthquakes. Abandonments, ruins or wars are general causes assumed by archaeologists and natural disasters are rarely considered. In this
work, we propose a comprehensive classification of Earthquakes Archaeological Effects (EAE) with the aim of carry out geological structural
analysis. The objective of this classification is to recognize the tectonic strain field responsible of the buildings damage and the relationship
with the potential earthquake or related‐earthquake natural disaster. Several examples at Baelo Claudia (South of Spain) of such EAEs are
shown.
Key words: earthquake archaeological effect, strain field, structural geology, archaeoseismology.
INTRODUCTION
Strain structures detected in archaeological sites affecting
to buildings, monuments, defensive constructions etc.,
could have different origins, for example seismic origin,
intervening slope process, unstable soils, differential
overburden during the burial process, or simply collapsed
remains due to eventual building abandonment or war
destruction, etc. For this reason, it is necessary identify
the trigger mechanism of the damaged structure to assign
a seismic origin. There are various works devoted to this
question (e.g. Stiros, 1996, Nur and Cline, 2000, Bottari,
2003, Kovach, 2004, and Nur and Burgess, 2008). These
authors developed a compilation of criteria for identifying
earthquake occurrence from archaeological data. With
this aim, we propose a preliminary classification of
earthquake archaeological effects (EAE) based on the type
of EAE (coseismic, postseismic), description (impact, wall
tilting, floor folding, etc.) and the location of the effects
(related to the geologic effects or to the fabric of the
building) (Fig.1). The relevance of this classification is for
the reason that, once the EAE is recognized, it is possible
to analyze the strain field related with the seismic source
by applying the classical structural techniques on strain
analysis (both ductile and brittle analyses).
The anisotropy inherent in the seismic wave (i.e. the
direction of the seismic ray propagation), generates a
strain field constrained by the seismic source parameters:
distance from the archaeological site to the epicentre,
magnitude of the earthquake, hypocentral depth, type of
arrival wave, etc. This fact implicates that the ductile and
brittle structures affecting monuments, walls and
buildings could be analysed using the classic structural
techniques developed in geology. The results obtained
from this analyses, allow us to reconstruct the coseismic
strain ellipse, oriented according to the type of the
earthquake (normal, reverse or strike‐slip) and defined by
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the principal strain axes: ey (maximum horizontal
shortening), ex (minimum horizontal shortening) and ez (
vertical axis).
CLASSIFICATION OF EAE
The interest of in the characterization of EAE is to
recognize archaeoseismic damage due earthquake
phenomena from other damage assigned to ruins, wars or
abandonment, among others. Furthermore, a good
establishment of potential EAE in a particular
archaeological site supports indirect information of the
seismic source for earthquake hazard assessment.
Following the recent classification of earthquake
environmental effects (EEE) established in the ESI‐07
Intensity Scale (Michetti, et al., 2007) we propose a
classification of EAE based on strain structures due to
“coseismic effects” (direct or primary effects) and
structures generated by “postseismic effects” (indirect or
secondary effects) (Fig. 1). This subdivision separates
effects related with the seismic source from those effects
“as a consequence” of a large earthquake affecting a
populated site.
PRIMARY COSEISMIC EFFECTS
We have divided the primary coseismic effects in (1)
geological effects and (2) building fabric effects (Fig. 1).
Geological effects
These effects are well described from the macroseismic
scale of environmental earthquake effect (ESI07, Michetti
et al., 2007). This scale separates primary effects as fault
scarp, surface rupture, and tectonic uplift/subsidence
from secondary effects as liquefaction, landslides,
tsunamis, etc.