October 11, 1918 Tsunami: Mona Passage, Puerto Rico, US Territories

1918, October 11, 10:14 local time. A severe earthquake at 10:14 Local Time in the Mona Passage, west of Puerto Rico was caused by displacement along four segments of a normal fault, oriented N-S in the Mona Canyon (Ref #267). A tsunami with runup heights reaching 6 m followed the earthquake, causing extensive damage along the western and northern coasts of Puerto Rico, especially to those villages established in a flood plain.

Many of the runup heights associated with this event were measured by Reid and Taber (Ref #1078) using water marks on visible objects. Other heights were provided by reliable witnesses who were interviewed by Reid and Taber during their visit to Puerto Rico and St. Thomas for four weeks in late 1919.

In the disastrous tsunami that lashed the northwest coast at Aguadilla in 1918, 30 People were said to have drowned at Aguadilla alone. This was later revised to 32 victims, The eight deaths of victims drowned at Punta Agujereada by the waves 5.5 to 6 meters in height brought the initial tally of people drowned for these two locations to 40. The greatest number of fatalities was said to be from the tsunami, The official death toll for this event was placed at 116. This total must have been earthquake fatalities only, since at Mayagiiez, "more than 100" deaths were reported, plus the 4 deaths at Ponce (totaling 104). When added to the tsunami victim count of 40, this would tally 144. In 1997, Mercado Irizarry (personal communication, 1997a) [ref #266] updated the tsunami death toll, with the report October 11, 1918, Puerto Rico of an account by an "old, very well known gentleman in Aguadilla." He said, “deaths should have exceeded 100; the reason was that many persons were unaccounted for and, therefore, not included in the official toll." Even more recently, Dillon et al. (1999) reported that 91 people were killed by the tsunami in northwestern Puerto Rico. With the significantly higher totals of those who perished from the waves, the total fatalities for the disaster from both the earthquake and tsunami approaches a number greater than 200. (ref #1492)

A 1918 M 7.5 earthquake resulted in a tsunami that killed at least 91 people in northwestern Puerto Rico. (ref #1591)

Immediately following the shock a tsunami broke upon the shore, drowning many persons and destroying many native dwellings. Property damage was estimated at about $4 m and 116 lives were lost. (Ref #1128)

We have identified a submarine landslide with steep headwall and sidewalls scarps 15 km off the northwestern coast of Puerto Rico using newly available multibeam bathymetry and multichannel seismic reflection profiles. Based on these new data we postulate that the landslide, which was induced by the earthquake, was responsible for the generation of the tsunami. Supporting this idea is the documented rupture of submarine telegraph cables by landslides in the area of our mapped landslide during the earthquake (Reid and Taber, 1919). The landslide, which is well marked by fresh and steep scarps, is 9 km wide by 9 km in length in the excavation area, and it has an average thickness of 140-150 m. (ref #5215)

The landslide scar in southern Mona rift likely formed several hundreds to thousands of years before 1918; hence, the tsunami could not have been generated by the associated landslide movement, as previously suggested in Lopez- Venegas et al. (2008 ref #5215, 2015) and Hornbach et al. (2008) [...] The reported submarine cable damage and breaks could be caused by smaller rock falls from steep outcrops, and not by the presumed movement of a 140 m thick, 9 km wide tsunami-generating landslide. (ref #13410)

116 deaths, $29 m damage. (ref #1250)

View a calculated tsunami-travel-time map.