The Mediterranean’s Largest Ever Earthquake Originates from ‘Normal Faults’

An earthquake event that destroyed nearly all the towns in Mediterranean region followed by a devasting tsunami some time in 365 CE, in historical data, was identified with a Hellenic subduction zone (HSZ) event with a magnitude of 8.0 or higher. Scientists stated otherwise, revealing in a new study that the 'giant quake' was all along caused by normal faults.

Surely it has been quite a revelation that evidence of region's largest historically documented earthquake suggests that the most common type of fault was behind the Holocene coseismic uplift in Greece.

The uplift was so vast it exposed 'fossil beach' along the Crete coastline by up to 9 m. The fossil beach provided a major source of data for scientists to record the event.

In addition, other areas uplifted at the time included Cephalonia and Zante in the Ionian Islands, Lechaion and the Perachora Peninsula in the Gulf of Corinth, the Pelion coast of Thessaly, Antikythira and the whole of western Crete, a coastal sector near Alanya in southern Turkey, and the entire Levant coast from Hatay (Turkey) to Syria and the Lebanon.

The Origin

Previous studies assumed that the fossil beach was uplifted during a single earthquake in 365 CE, based on radiocarbon ages and historical earthquake reports. However, new data from exposed fossil shorelines recorded a unique finding that the uplift originated on normal faults.

"Our findings collectively favor the interpretation that damaging earthquakes and tsunamis in the Eastern Mediterranean can originate on normal faults, highlighting the potential hazard from tsunamigenic upper plate normal fault earthquakes," researchers said.

The 365 CE earthquake and uplift of the Krios paleoshoreline was centered on the Phalasarna fault and Sfakia fault zone offshore Crete.

While it is known that previous evidence considered the epicenter lies above the Hellenic subduction zone (HSZ) the largest, fastest, and most seismically active plate boundary in Europe, dislocation modeling suggests that the HSZ megathrust is unable to reproduce the paleoshoreline uplift in a single event.

Researchers admit that there is no enough radiocarbon data, historical reports, and archeologic findings that can make them distinguish between single and multi‐stage uplift of the Krios paleoshoreline. However, 32 new data points and computer modeling pointed out earthquake cluster on normal faults.

"Based on these findings and the better consistency with the long‐term record of crustal extension in the region, we favor a normal faulting origin for the 365 CE and earlier earthquakes," researchers concluded.

Future direction for tectonics and seismic hazard and understanding

The 365 CE event has undeniably shaped our current understanding of tectonics and seismic hazard of the densely populated Eastern Mediterranean.

Little did we know that multiple normal faults can be more dangerous than the unpredictable Hellenic subduction zone more than we can imagine. A wise man once said, "Never judge a book by its cover."

New findings suggest reassessment in terms of earthquake predictions and modeling. Researchers believe that we need a more comprehensive hazard characterization and adequate understanding of Mediterranean tectonics and earthquake hazards.