ABSTRACT
Seismic hazard is defined in terms of the probability of exceeding a certain ground motion in a specific area, and is typically discussed in terms of Peak Ground Acceleration (PGA). Predicted PGA values for specific regions are commonly reported in national seismic building codes and therefore PGA is used extensively in earthquake engineering practice throughout the world. A new method to constrain expected earthquake PGA values, by back analysis of finite block displacements in historic masonry structures, is presented here. To demonstrate the new approach two archeological masonry structures that exhibit seismogenic damage are used as illustrative examples: 1) a 2000 year old Nabatean (Roman Period) arch in which the keystone slid downward during an earthquake of an uncertain date (Fig. 16.1a), and 2) a 1400 year old Byzantine church in which a series of parallel granite and marble columns toppled down in the same direction, most probably due to an earthquake that struck the region in 749 AD (Fig. 16.1b). Both sites are located along the seismically active Dead Sea rift system.
