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Estimation of the moment magnitude and local site effects of a postulated Late Bronze Age earthquake: Mycenaean citadels of Tiryns and Midea, Greece

Previously interpreted archaeological and geological field data from the Argive Basin, Greece, have been used to hypothesized that the nearby Late Bronze Age Mycenaean citadels of Tiryns and Midea, which settled on bedrock, might record synchronized co-seismic structural damage due to earthquake ground-shaking at ca. 1190 BCE, the end of the Mycenaean palatial period. However, from a quantitative archaeoseismological perspective, this hypothesis has flaws: ( a ) it overlooks that several structures excavated in the undeformed Holocene sediments lack evidence of co- seismic structural damage and damage is only documented for sturdier structures within the citadels, ( b ) it leaves unexplained the moment magnitude of the ‘causative’ surface-rupturing earthquake, and ( c ) disregards the role of local site effects on surface ground-motion. The plausibility of the previously proposed earthquake hypothesis is tested by estimating the earthquake magnitude of the alleged ancient earthquake and its local site effects at and around the citadels, assuming that the earthquake truly occurred. A retrospective geotechnical site microzonation coupled with the calculation of seismic amplification factors, surface ground-motions, and earthquake intensity account for the local site effects assessment. The present numerical modeling results indicate that the citadels and contemporaneous adjacent structures of the peasants had a lower and higher seismic hazard, respectively. Seismic amplification factors, earthquake-induced ground shaking, and seismic intensity are indeed lower for Tiryns than for Midea. Therefore, these results refute the idea of seismically induced destruction of the citadels and challenge the plausibility of the earthquake hypothesis. The previously archaeologically documented destruction patterns unlikely represent physical evidence of co-seismic damage by the archaeologically proposed earthquake. Other explanations ought to be sought to elucidate the interpreted destruction pattern seen in these Mycenaean centers.