The 2020-2021 Trizonia-Lambiri sequence

From December 2020 to February 2021, a seismic crisis occurred in the western Gulf of Corinth, with two main events of magnitude larger than 5 on January 12, 2021 and February 17, 2021

On March, 19 an informative letter has been sent to potentially interested parties

seismicity : December, January, February.

The overall number of events detected  by the automatic procedure on the real time seismological data and manually located, during the last three months, is of the order of 3000. A more detailed analysis allows detection and location of more than 70000 events.

The observations indicate a « cascade type » of rupture, starting closer to the north side of the Gulf and propagating towards east and west.

Most of the focal mechanisms correspond to rupture on east-west trending normal faults. (Click on Μηχανισμοί Γένεσης to get focal solutions from NKUA on the seismicity page)

However, there are some NNE-SSW strike slip events.

The inclinometer record at MOKI, less than 10km from most of the larger shocks show a coseismic signal followed by a relaxation still to be characterized mainly for the February 17 event.

Distribution of the microseismicity show that both north and south dipping faults might have been activated throughout the sequence.

The connection between the faults involved during the sequence and the known major active faults requires careful analysis which is in process. 

Small displacements (of centimetre amplitude) of several Global Navigation Satellite System (GNSS) stations have been recorded for the two main events and provide constraints on the location of the ruptures. The GNSS displacements imply a seismic moment more than two times larger than the one deduced from the seismological catalogue.

Synthetic Aperture Radar (SAR) interferometry made with images of the Sentinel-1 mission show no deformation except a local ground motion, triggered by the February 17, 2021 event, in the Panagopoula area, immediately west of the eponymous landslide.

Pore pressure migration could have controlled the development of the sequence, as it has been already proposed for previous sequences in the area.