1693 Sicily earthquake | earthquake characteristics

Earthquake characteristics

Main faults of the Siculo-Calabrian rift zone

January 9 foreshock

A destructive earthquake occurred two days before the mainshock at 21:00 local time, centered in the Val di Noto. It had an estimated magnitude of 6.2 and a maximum perceived intensity of VIII–XI on the Mercalli intensity scale. Intensities of VIII or higher have been estimated for Augusta, Avola Vecchia, Floridia, Melilli, Noto Antica, Catania, Francofonte, Lentini, Scicli, Sortino and Vizzini.[5] Augusta lies well outside the main zone of severe shaking; its extensive damage is probably due to its construction on unconsolidated sediments.[12]

From the shape and location of the area of maximum damage, this earthquake is thought to have been caused by movement on the Avola fault.[12]

January 11 mainshock

The earthquake lasted for four minutes, according to contemporary accounts.[1] The estimated magnitude of 7.4 is taken from the extent and degree of the recorded damage, with a very large area that reached X (Extreme) or more on the Mercalli scale. The maximum shaking reached XI in the towns of Buscemi, Floridia, Melilli, Occhiola and Sortino.[5]

The source of the January 11 earthquake is debated. Some catalogues give an onshore epicentre without any direct association with a known structure, while others propose that the source was offshore due to the associated tsunami, involving either rupture along a normal fault, part of the Siculo-Calabrian rift zone,[12] or rupture along the subduction zone beneath the Ionian Sea.[7] An analysis of the distribution of tsunami run-ups along the coast suggests that a submarine landslide triggered by the earthquake is the most likely source, in which case the tsunami provides no constraint on the epicenter.[13] A landslide origin is supported by the observation of possible landslide bodies along the Hyblean-Malta escarpment.[8]

Historic documents in the Archivo General de Simancas mention dozens of aftershocks, some as late as August 1694, and some reportedly as strong as the initial quake of January 11, 1693.[14] Aftershocks continued until at least 1696, with their effects concentrated in towns along the coast, supporting an epicenter either near the coast or offshore.[12]

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