August 3, 2007 Tsunami: Mostaganem, Algeria

Ref #14272:

Mostaganem, Algeria, August 03, 2007. On that Friday afternoon, twelve people were killed on local beaches by a sudden wave with an estimated run-up of 7–10 m at Petit Port (Pelinovsky and Kharif 2008). The origin of this phenomenon, which affected a 40-km stretch of coastline (El Watan 2007) but was not reported at other locations in the Mediterranean, has been speculative and controversial.

Amir et al. (2013) suggested that the wave could have resulted from an earthquake located only 19 km away from Petit Port, at 36.24◦ N, 0.06◦ E. This event, given a magnitude of mb = 5.4 by the Euro-Mediterranean Seismological Center (EMSC), is too small to generate a tsunami by itself, but it could conceivably have triggered a landslide; larger events are known to have generated tsunamis through this process along the western Algerian coastline, notably in 1954 and 1980 (Heezen and Ewing 1955; Solov’ev et al. 1992). The problem with this interpretation is that the earthquake took place five days after the tsunami, on August 08, 2007 at 21:26 GMT, as documented by no fewer than 13 reporting agencies, including the ISC-EHB and ISC-GEM catalogs (Weston et al. 2018; Storchak et al. 2015), the origin of this confusion being probably that the news of the tsunami attack was released by local officials only on Wednesday, August 08. By contrast, no events in the western Mediterranean are known on August 03, although a small earthquake ( ML = 2.4 ) was detected on the previous day (August 02, 2007), also at 21:26 GMT (obviously adding to the confusion), but in eastern Algeria, 470 km from Mostaganem and 32 km inland, which rules out any role in the generation of a tsunami, even through an ancillary landslide.

In this context, the possibility remains, at least in principle, of a “silent” landslide triggered by an unreported seismic event. However, an underwater landslide of a volume sufficient to generate a metric tsunami should have been detected as a hydroacoustic signal […] we failed to identify any potential signal on August 03, 2007.

Finally, a number of media including French “reference” newspapers (e.g., Le Figaro 2007; Le Monde 2007) reported speculation that the Mostaganem waves had been generated by the testing of weaponry as part of a secret foreign mission in Algerian waters, even suggesting the implosion of a submarine. Such a scenario remains highly improbable, since a gross order-of-magnitude estimate of the yield necessary to generate a metric tsunami at distances on the order of at least 10 km would approach 1 kt […]

Rather, we explore here the possibility of a meteotsunami to explain the Mostaganem disaster. We were able to document a particularly impressive signal at Cartagena, Spain (CART), only 200 km from Mostaganem (Fig. 13), where it clearly emerges from the background noise in the raw seismograms and lasts on the order of 10 h. In itself, this property is clearly more characteristic of a meteotsunami than of landslide-generated ones.

In summary, our investigations of seismic records at three Spanish stations reveal the presence of signals sharing characteristics with those from documented cases of meteotsunamis, which suggests that an atmospheric disturbance existed in the western Mediterranean Basin on August 03, 2007. It is then proposed that the tragic events at Mostaganem were also derived from that system.