Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology
Fig. 4: Impact patterns of toppled block walls (see Fig. 2 for dimensions). Rows and columns contain the patterns for constant frequency
and peak ground acceleration, respectively. Coordinates of the corner points of the vertical middle plane of the blocks are used to plot
the final block position. Blocks upright at the end of the experiment appear as straight lines. Colors indicate the differences in ground
motion components: x‐comp, xz‐comp, xy‐comp, xyz‐comp. As only the contact forces to the neighboring blocks and the ground were
regarded in this model, the rubble piles categorized as case (3) do not show the real situation, as blocks do not interact with distant
neighbors. However in case of toppling types (1) and (2) the impact pattern is completely covered by the model.
CONCLUSIONS
Two discrete element models, one of a simple 3‐part
column and one of a 52‐block wall were used to study
principal aspects of their dynamic behaviour, failure
mechanisms, and final resting positions of the displaced
blocks. Even though rigid block models with visco‐elastic
contact forces do not include elastic deformations within
the individual blocks, they give insight in the general
dynamic behaviour of simple structures.
Sensitivity studies of the behaviour of a totally rotational
symmetric column were based on a measured earthquake
ground motion. This motion from the Parkfield
earthquake in 2005 shows a clear horizontally polarized
motion at the time of the largest displacement. Even such
highly impulsive movement produces progressively
diverging dynamic behaviour of the column when small
stochastic changes in the range of 1/10,000 of the PGD
are applied. The chaotic character of the dynamic
response indicates how problematic a detailed prediction
of failure mechanisms is. The experiments in which 5% to
10% of the tests the columns survived the dynamic load,
even though the change in the input ground motion was
in the range of any measuring accuracy of seismic
motions show that statistical approaches are necessary to
predict ground motion parameters, which lead to failure
of structures similar to those used in these tests.
Tests of a block wall with (unrealistic) simple sinusoidal
ground motions indicate a relation between the impact
patterns of the blocks on the ground after toppling.
49
However to interpret field cases like the one shown in
Fig.1, a more complicated situation that includes the
influence of corners must be taken into account. Small
changes of shape of the base and top in the column
model lead to significant change in the toppling behaviour
and indicate the importance of precise measurements
and careful reconstruction during the construction of
archaeoseismic models for dynamic tests.
The discrete element method is an appropriate tool for
basic studies of dynamically loaded structures, with
realistic earthquake‐related ground motions. Combined
with 3D laser scans and stochastic approaches it will help
to advance quantitative archaeoseismology.
Acknowledgements: Parts of this study were financed by
Deutsche Forschungsgemeinschaft (DFG HI660/2.‐1). H.
Kehmeier assisted with model calculations. I thank R. Kovalev for
his help and support in the model set up and S.K. Reamer for
discussions and improving the manuscript.
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