Ancient earthquake ruins may indicate future earthquakes near the Dead Sea fault

Interdisciplinary research into archaeological sites in Israel indicates a different error from what was originally thought to have caused the city’s destruction in the eighth century and may rupture again.

Written by Vanessa Viates, Scientific Writer

Quote: Vieites, V., 2020, Ancient earthquake ruins may indicate future earthquakes near the Dead Sea fault, Temblor, http://doi.org/10.32858/temblor.137

In the Israeli city of Tiberias, on the western shore of Lake Tiberias, are debris believed to be the result of a series of large earthquakes that occurred in the mid-eighth century. But the lack of useful measurements and data on earthquakes in the region before the twentieth century prevented researchers from classifying the ancient series of earthquakes as the most likely cause of damage in Tiberias. Using a combination of geological, archaeological and historical evidence, scientists have now found that the natural rift, including the surface rupture, along the Dead Sea is linked to the mid-eighth century earthquakes, indicating that a similar seismic event could happen again.

This deformed wall in the ruins of Tiberias, along with other ancient and archaeological evidence, reveals a superficial rupture in the eighth century. Credit: Francesca Ferrario

Strong vibration in the past

“The region is known to have experienced strong earthquakes in the past,” says Francesca Ferrario, an earth scientist at the University of Insubria in Italy and lead author of the new study in the journal Tectonics. This included earthquakes in the eighth, eleventh, eighteenth and nineteenth centuries. Ferrario says that there have been no strong earthquakes in Tiberias since the invention of modern devices. Therefore, seismologists have classified the seismic hazards in Tiberias based on literary sources and historical documentation of past earthquakes. However, having to rely solely on agents of paleoseism makes it difficult to determine the exact location, number of past earthquakes and any associated damage, she says. Knowing what type of damage has been inflicted in past earthquakes is important for classifying current seismic hazards.

Paleontology and Archeology Research

Ferrario and a team of geologists and archaeologists studied three sites likely to be home to remnants of 8th century earthquakes: an ancient Roman theater, the city’s southern gate and a water reservoir. Archaeologists analyzed and dated the archeology and found that only the oldest part of the theater, which was built in the 1st century, was damaged by the rupture of the surface, suggesting that ancient earthquakes (not modern earthquakes) were responsible for the wreckage.

Geologists on the team studied the geomorphology along the Sea of ​​Galilee to characterize faults and surface faults. They analyzed a digital elevation model of the area’s slopes, sides, and contour lines, along with 20th-century aerial photographs of the terrain. Next, the geologists mapped features likely to be related to tectonic activity, such as slopes or anomalies in river networks.

Panoramic view of the Roman amphitheater damaged by earthquakes in the 8th century. Credit: Francesca Ferrario

“From the geological site alone, we cannot say that the damage is caused by the earthquake,” Ferrario says. But the use of archeology along with geology helped them attribute the damage in Tiberias to the powerful seismic events of the mid-eighth century.

what is wrong?

Ferraro says that the rift along the Sea of ​​Galilee, that is, the fault of the Dead Sea to the east and the crack in the western borders of the Jordan Valley to the west, may make Tiberias vulnerable to earthquakes in the future. According to Ferrari, the two faults are connected but can move independently of each other or simultaneously, with the potential to cause multi-fault faults, resulting in earthquakes greater than those of a single fault. The team reported that a single rupture can cause an event with a magnitude of 6.9, whereas a multi-hole event could cause a magnitude of 7.6. Since the seismic literature already contains a large amount of scientific data about the Dead Sea fault, researchers have focused their investigations on the western boundary fault of the Jordan Valley, and carefully scanned it in the new study.

“Our research is the first to document the initial surface rift associated with the mid-eighth century event,” says Ferrario, noting that the new study only indicates that the rupture of the western border of the Jordan Valley ruptures in ancient earthquakes. Although it is possible that the Dead Sea fault has also been involved in past seismic events, Ferrario says, scientists cannot say from the new study whether the two faults separated long ago on their own (i.e. individual fault rupture) or together ( That is, multi-hole rupture). “The two errors have a different kind of movement – normal movement versus fatal slip – which has implications in terms of assessing risk,” she says.

Although the western boundary fault of the Jordan Valley is shorter than the Dead Sea fault, Ferrario says, it “poses a new potential threat” to Tiberias, and is akin to this fault. She said that the rupture of the surface due to this fault, and the ability of this fault to rupture with the fault of the Dead Sea, causing larger earthquakes, was not considered in advance when assessing the risk of earthquakes in that region.

Tiberias high-risk

Jan Klinger, director of the Tecton Laboratory at the Paris Institute for Geophysics, who was not involved in the new work, says the study is “a wonderful mixture of archeology and paleontology.” He says the study “brings more evidence to the large data set already in place along this fault system of previous earthquakes, and documents surface deformation for a given site, helping to identify the potential location of some of the fault sections involved in the [mid-eighth century] Seismic crisis “.

The Dead Sea Fault is a major limitation of the plate that can be compared to the San Andreas Fault in terms of length, albeit slower, [slipping] At 5 mm [0.2 inches] Per year compared to the San Andreas Fault, which [slips] At 35 mm [1.4 inches] Clinger says. He adds that the slow movement of the Dead Sea Rift means “fewer large earthquakes,” occurring every 400 to 600 years or more. In the era of modern machinery, the only earthquake of its remarkable magnitude was the 1995 Nuweiba earthquake, which had a magnitude of 7.3, which affected the southern part of the fault, in the Gulf of Aqaba, he said. This earthquake damaged nearby settlements, triggered tsunamis and killed 11 people (Frucht et al., 2019). The new study indicates that severe earthquakes, albeit rare, may occur in Tiberias. “[The 1995] The earthquake is here to remind us that large and potentially destructive earthquakes are occurring along the Dead Sea fault, “says Klinger.

Thus, Ferraro says, it is important for the municipality of Tiberias to know precisely where the potential surface faults lie along the faults so that policymakers can implement appropriate engineering practices to avoid a great deal of seismic damage if one or several faults rupture again.

Further reading

Ferrario, MF, Katz, O., Hillman, A., Livio, F., Amit, R., & Michetti, AM (2020). Surface fault in the middle of the eighth century AD along the Dead Sea fault in Tiberias (Lake Tiberias, Israel). Tectonics, 39, e2020TC006186. https://doi.org/10.1029/2020TC006186.

Frucht, E., Salamon, A., Gal, E., Ginat, H., Grigorovitch, M., Tov, RS, & Ward, S. (2019). New view of the tsunami resulting from the diversion of the Dead Sea, 1995 7.2 MW of Nuweiba earthquake, along the Gulf of Eilat – Aqaba. Seismic Research Letters, 90 (4), 1483-1493. https://doi.org/10.1785/0220190004

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