On a Sunday afternoon on the 9th of July in 551 CE, faults not far from Beirut broke resulting in a powerful (M_W = ~7.5) earthquake(s) and tsunami. The earthquake is documented in roughly a dozen sources, some contemporaneous, and is corroborated with geologic and archaeoseismic evidence. Geologic evidence suggests that the epicenter was either offshore or on land but close to the sea. The sources suggest that the epicenter was not far from Beirut. There was likely extensive damage to coastal towns from Tripolis to Tyre. Damage may have been more limited south of Tyre and north of Laodicea. The earthquake was felt as far away as Alexandria, Egypt and, according to the sources, Palestine, Syria, east of the Jordan River (labeled as Arabia), and parts of Mesopotamia. Some sources suggest there was seismic damage in the Galilee which may be supported by paleoseismic evidence in Bet Zayda. This earthquake has been widely cited as the cause of 6th century archaeoseismic evidence in far away Petra, el-Lejjun, and Areopolis but this destruction was more likely caused by the Inscription at Areopolis Quake which struck an area south of the Dead Sea a few decades later.

A little over half a dozen sources described a tsunami on the Phoenician (Lebanese) coast which started with an ebbing of the sea. Clear tsunamigenic evidence is lacking but there is probably some evidence in Beirut which two of the sources specifically say was struck by the tsunami. Cores taken from the ancient harbors of Byblos, Sidon, and Tyre did not encounter tsunamites in their Late Byzantine/Islamic sections although the cores from Sidon and Tyre may suffer from a hiatus during this time period due to later harbor dredging. Tsunamigenic evidence may or may not be present in Caesarea and nearby Jisr al-Zakra. Researchers have suggested that the probable tsunamite identified in cores from Caesarea and Jisr al-Zakra dates to the Holy Desert Quake of the 749 CE Sabbatical Year Sequence and if a tsunami did strike that far south in 551 CE, the deposit it left was reworked by the 749 CE tsunami. While modeling performed by Salamon et al. (2024) suggests that Caesarea would have likely been unaffected by the tsunami that affected Beirut, shaking from the 551 CE Beirut Quake could have generated a tsunami via offshore shelf collapse closer to Caesarea. The strength of the 551 CE Beirut Quake (M_W = ~7.5) and the distance from Beirut to Caesarea makes this a possibility.

Although evidence has not been found for a 6th century CE tsunamigenic event in Byblos, Morhange et al. (2006:91) reported 6th century CE coastal uplift there and Elias et al. (2007) found evidence for ~80 cm of vertical uplift in the vicinity of Tabarja located ~20 km NE of Beirut. Elias et al. (2007) also claimed to have discovered a previously unknown thrust fault system offshore which they called the Mount Lebanon Thrust. They surmised that the 551 CE Beirut Quake was a result of fault movement on this thrust system and estimated M_w = ~ 7.4–7.6 for the 551 CE Beirut Quake.

Faysal et al. (2023) made use of better seismic data than was available to Elias et al. (2007) (3D vs. 2D) and found that they could not confirm the existence of a Mount Lebanon Thrust Fault System. They also concluded that what Elias et al. (2007) interpreted as “fresh” seafloor seismic ruptures that may have generated the 551 CE tsunami were in fact surface expressions of underlying salt tectonics. Faysal et al. (2023) suggested the Latakia Ridge as a candidate for the fault rupture that created the 551 CE Beirut Earthquake.

Salamon et al. (2024) constructed a geographic database of Intensity values for various seismic effects compiled from textual, archaeoseismic, and geologic evidence and performed seismic modeling and tsunami simulation to assess seismotectonic possibilities for the 551 CE Beirut quake. They concluded that “either the thrust system noted as Mount Lebanon Thrust underlying Lebanon” or “the intermittent transpressive Tripoli-Batroun-Jounieh-Damour fault zone along the Lebanese coast are the best candidate sources for the 551 AD earthquakes and tsunami.” Both possibilities explained the initial tsunamigenic ebbing as well as the ~ 80 cm of coseismic uplift on the Phoenician (Lebanese) coast. Salamon et al. (2024) found that models and simulations with the Latakia Ridge did not produce coastal uplift or a tsunami. Salamon et al. (2024) further noted that Hall et al. (2005) suggested that the Latakia Ridge was primarily a strike-slip fault — unlikely to generate a tsunami. However, as noted by Salamon et al. (2024) and Faysal et al. (2023), the 551 CE tsunami could have been caused by an off-fault offshore shelf collapse.

The sources may also suggest that there were two earthquake shocks. First came the shock that caused the tsunami and then some time later there was an earthquake shock that was described as being synchronous with the return of the sea to its regular level. Sources also mention an earthquake-induced rockslide near Botrys ( modern Batroun) and a fire that raged in Beirut for two months until three days of rain put it out. Emperor Justinian I is reported to have sent funds to pay for rebuilding efforts in the affected cities but Beirut (then known as Berytus) was reconstructed to a smaller size.