The Michoacán Tsunami of 19 September 2022 on the Coast of Mexico: Observations, Spectral Properties and Modelling

Abstract

The Mw 7.6 earthquake of 19 September 2022 within the coastal zone of Michoacán, Mexico, generated a major tsunami that was recorded by six coastal tide gauges and a single offshore DART station. All seven instruments were located within 250 km of the source. No tsunami was detected at larger distances. Maximum wave heights were observed at Manzanillo (172 cm) and Zihuatanejo (102 cm). Numerical modelling of the event closely reproduced the coastal and offshore tsunami records and shows that the tsunami energy radiated seaward from the source as a narrow “searchlight” beam directed normal to the source and mainland coast. Estimates of the frequency content (“colour”) of the 2022 tsunami event, and that generated in 2017 by the much stronger (Mw 8.2) Chiapas earthquake further up the coast, reveal a marked difference in the tsunamigenic response. Whereas the 2017 tsunami was mostly long-period (“reddish”), with 87% of the total tsunami energy at periods >35 min, the 2022 tsunami was short period (“bluish”) with 91% of energy at periods <35 min. A noteworthy feature of the 2022 event was the seismically generated seiches observed at Puerto Vallarta, which had a recorded period of about 7 min, began immediately after the main earthquake shock, and persisted for about one hour.