The Ruin of the Roman Temple of Kedesh, Israel; Example of a Precariously Balanced Archaeological Structure Used as a Seismoscope

Gregor Schweppe,Moshe Fischer,Sharon Reamer,Shmuel Marco,Klaus-G Hinzen

doi:10.4401/ag-7152

Gregor Schweppe, Moshe Fischer + Show 3 more

Open Access

https://doi.org/10.4401/ag-7152

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Abstract

In certain regions and under favorable geologic conditions, precariously balanced rocks may form. These types of unusual formations have been used to estimate yield ground motions. Because such balanced rocks have not been ‘unbalanced’, they can be used as a rough estimate for ground motions which have not been reached or exceeded since the balanced formation achieved its contemporary state. We hypothesize that other ancient manmade structures, delicate in terms of stability and particularly those that have survived earthquake ground motions intact, can be used in the same manner. We therefore suggest that these structures act as a highly local seismoscope for determining maximum upper ground motion bounds. We apply the concept of the study of precariously balanced rocks to the ruin of the Roman temple of Kedesh, located in close proximity to a branch of the Dead Sea Transform Fault. The delicate-looking ruin was surveyed with a 3D laser scanner. Based on the point cloud from that survey, a discrete element model of the remaining temple wall was constructed. To test the stability of the model we used 54 analytical ground motion signals with frequencies ranging from 0.3 to 2 Hz and PGAs between 1 and 9 m/s 2 and simulated and measured strong ground motions of eight earthquakes. Two hypothetical local earthquake scenarios, five of which are historical earthquakes of the region and one is a strong motion record of the 1999 Taiwan Chi Chi earthquake were also used to test the hypothesis. None of the simulated earthquakes (historical or assumed) toppled the ruin; only the strong motion record collapsed the structure. The simulations reveal a surprisingly high stability of the ruin of the Roman temple of Kedesh mainly due to the small height to width ratio of the remaining walls. However, ground motion with large PGAs at a low frequency range in EW direction does collapse the remains of the temple.

Highlights

Following the definition by C.F Richter [1958], a seismoscope is a device which indicates the occurrence of an earthquake but does not write a record
The basic concept to use these precariously balanced rocks (PBRs) as seismoscopes is (1) to measure their shape; (2) determine a yield force or acceleration which would be necessary to topple the PBR; (3) estimate the amount of time the formation exists in its present appearance; and (4) estimate the upper limit of ground motion level which has not been exceeded in this time span
In order to quantify the effect of the ground motions, we monitored the motion of the center of geometry of all ashlars during the time window of the modeling, which lasted 7 s for the analytic impulses and 10 s longer than the earthquake records in order to allow all moving ashlars to settle

Summary

Introduction

Following the definition by C.F Richter [1958], a seismoscope is a device which indicates the occurrence of an earthquake but does not write a record. As shown by Hinzen and Montabert [this issue] the software development tool UNITY (see data and resources) is capable of modeling the dynamic behavior of wall-type structures including their internal deformation and collapse pattern.

Results

Conclusion