Revealing the Source of the 27 August 1810 Loreto, Baja California, Tsunami from Historical Evidence and Numerical Modelling

摘要

Historical documents revealed that on 27 August 1810 an earthquake affected the Loreto town and the surrounding region, along 200km of the coast of Baja California, Mexico, and damage was considerable due to strong ground motions. However, the 1810 Loreto earthquake, unlike other earthquakes of the nineteenth and twentieth centuries, produced an extensive tsunami flooding on the eastern coast of Baja California, from Loreto to La Paz. We report here the historical account of this event and analyse the source of the related tsunami. Based on the historical record and the tectonic setting, we infer that this earthquake was produced along a transform fault, right-lateral strike slip fault, Farallon fault, on the Baja California Gulf. However, the associated tsunami was disproportionally large if compared with the earthquake intensity (IX) and approximate magnitude (7.4 Mw), fault style, and the relatively late tsunami arrival, i.e. an hour after the earthquake, suggesting that a submarine landslide, triggered by this earthquake, was the suspect source for the Loreto tsunami. We present here historical data and a numerical model of the Loreto 1810 tsunami to elucidate the source, using both the 1810 earthquake and a submarine landslide, and confirm that a submarine landslide is most likely the tsunami-triggering mechanism that followed the 1810 earthquake.