Historical evidence in the reconstruction and characterization of tsunami generation - the example of the great tsunami of 22 June 1932, the Pacific coast of Mexico

The magnitude of the damage caused by tsunamis in the past decade has induced the need to expand our knowledge about tsunami dynamics and behavior, and to apply this knowledge in hazard assessment. This study proposes the application of multidisciplinary analysis, including historical and ethnographic techniques, in the reconstruction and characterization of tsunamis with no instrumental record. This study uses the case study of the 22 June 1932 tsunami, the second most destructive recorded in the Pacific Coast of Mexico, which reached wave heights of up to 12 m and devastated several coastal communities. The tsunami generation mechanisms have not yet been defined; two hypotheses about their origin are proposed: 1) seismic, and 2) by a submarine landslide. By screening historical archives, conducting interviews with local witnesses, and applying GIS mapping, we identified four key components of the tsunami dynamics that point out to tsunami generation mechanisms: time of arrival, directivity, affected area, and maximum wave heights at the coast. Based on the compiled historical data, we applied numerical models, using the GEOWAVE and FUNWAVE codes, and two possible mechanisms of tsunami generation, seismic slip and a submarine landslide. The results showed that given the location of the tsunamigenic source, the time of arrival to the coast, directivity, affected area, and maximum tsunami wave heights at the coastline, a submarine landslide best fits with the observed and documented tsunami behavior of the June 22, 1932 tsunami. We demonstrate here that the use of historical and ethnographic technics contributes and complements the modeling of events not recorded by instrumental methods, and aids in reveling their origin.