The Use of Interferometric Synthetic Aperture Radar for Isolating the Contribution of Major Shocks: The Case of the March 2021 Thessaly, Greece, Seismic Sequence

Cristiano Tolomei,Massimiliano Maggini,Nicola Angelo Famiglietti,Marco Polcari,Salvatore Stramondo,Riccardo Caputo

doi:10.3390/geosciences11050191

Abstract

We study the surface deformation following a moderate size M5+ earthquake sequence that occurred close to Tyrnavos village (Thessaly, Greece) in March 2021. We adopt the interferometric synthetic aperture radar (InSAR) technique to exploit several pairs of Sentinel-1 acquisitions and successfully retrieve the ground movement caused by the three major events (M5+) of the sequence. The mainshocks occurred at depths varying from ~7 to ~10 km, and are related to the activation of at least three normal faults characterizing the area previously unknown. Thanks to the 6-day repeat time of the Sentinel-1 mission, InSAR analysis allowed us to detect both the surface displacement due to the individual analyzed earthquakes and the cumulative displacement caused by the entire seismic sequence. Especially in the case of a seismic sequence that occurs over a very short time span, it is quite uncommon to be able to separate the surface effects ascribable to the mainshock and the major aftershocks because the time frequency of radar satellite acquisitions often hamper the temporal separation of such events. In this work, we present the results obtained through the InSAR data analysis, and are able to isolate single seismic events that were part of the sequence.

Highlights

The broader Aegean Region is the most seismically active area of the whole Mediterranean and European continent
We organize this section as follows: first we show the interferometric synthetic aperture radar (InSAR) results for each of the three individual events, and for the cumulated case
The mainshock of the sequence, i.e., the ML 6.0 earthquake, occurred on the 3 March at 10:16 (UTC), was investigated considering the ascending SAR pair acquired on the 25 February and the 3 March, respectively

Summary

Introduction

The broader Aegean Region is the most seismically active area of the whole Mediterranean and European continent. Earthquakes are quite frequent in Greece where around than 1–2 strong (M > 6.0) and 5–6 moderate (M > 5.0) events occur on average each year. Starting on 3 March 2021 (Table 1), a seismic sequence affected Thessaly, with major epicenters located at 20 to 30 km WNW of Larissa, the fifth most populous town in Greece. The epicentral area is located between Tyrnavos and Elassona, generating diffuse damage in a number of minor centers within the Antichasia Mountains (Figure 1). Notwithstanding the strong magnitude of the mainshock (ML 6.0, Mw 6.3; NOA and USGS, respectively) there were no deaths or serious injuries due to the relatively low vulnerability of most buildings. The localization of the epicenter was found to be in an area showing low seismicity in recent times

Results

Discussion

Conclusion