ALBERT

Description: Advances in synthetic aperture radar (SAR) interferometry have enabled the seamless monitoring of the Earth’s crust deformation. The dense archive of the Sentinel-1 Copernicus mission provides unprecedented spatial and temporal coverage; however, time-series analysis of such big data volumes requires high computational efficiency. We present a parallelized-PSI (P-PSI), a novel, parallelized, and end-to-end processing chain for the fully automated assessment of line-of-sight ground velocities through persistent scatterer interferometry (PSI), tailored to scale to the vast multitemporal archive of Sentinel-1 data. P-PSI is designed to transparently access different and complementary Sentinel-1 repositories, and download the appropriate datasets for PSI. To make it efficient for large-scale applications, we re-engineered and parallelized interferogram creation and multitemporal interferometric processing, and introduced distributed implementations to best use computing cores and provide resourceful storage management. We propose a new algorithm to further enhance the processing efficiency, which establishes a non-uniform patch grid considering land use, based on the expected number of persistent scatterers. P-PSI achieves an overall speed-up by a factor of five for a full Sentinel-1 frame for processing in a 20-core server. The processing chain is tested on a large-scale project to calculate and monitor deformation patterns over the entire extent of the Greek territory—our own Interferometric SAR (InSAR) Greece project. Time-series InSAR analysis was performed on volumes of about 12 TB input data corresponding to more than 760 Single Look Complex Sentinel-1A and B images mostly covering mainland Greece in the period of 2015–2019. InSAR Greece provides detailed ground motion information on more than 12 million distinct locations, providing completely new insights into the impact of geophysical and anthropogenic activities at this geographic scale. This new information is critical to enhancing our understanding of the underlying mechanisms, providing valuable input into risk assessment models. We showcase this through the identification of various characteristic geohazard locations in Greece and discuss their criticality. The selected geohazard locations, among a thousand, cover a wide range of catastrophic events including landslides, land subsidence, and structural failures of various scales, ranging from a few hundredths of square meters up to the basin scale. The study enriches the large catalog of geophysical related phenomena maintained by the GeObservatory portal of the Center of Earth Observation Research and Satellite Remote Sensing BEYOND of the National Observatory of Athens for the opening of new knowledge to the wider scientific community.

Description: In March 2021 three strong earthquakes with magnitudes (⁠Mw ⁠) of 6.3, 6.0, and 5.2 occurred in Thessaly plain, Greece, on 3, 4, and 12 March, respectively. The modeling of all the three sources, by inversion of Interferometric Synthetic Aperture Radar and Global Positioning System data, indicates a northeast–southwest‐trending extensional stress field with indications for northeast‐dipping sources. The unmapped fault source of the first mainshock (⁠Mw 6.3) is located approximately 6 km to the southwest of the known Larissa fault (LF). Moreover, the fault that was activated during the second mainshock (⁠Mw 6.0) appears to be located more to the north, bordering the Titarisios river valley to the southwest, whereas the third mainshock (⁠Mw 5.2) appears to be triggered at a fault segment located further to the northwest. The Coulomb stress analysis using the slip distributions of the three aforementioned mainshocks revealed a unilateral triggering of the second and third event toward the northwest, and explained the spatial development of the entire aftershock sequence. Furthermore, among the already known active faults in the broader area, only the LF was brought closer to failure as a result of the imparted stress changes.

Description: Published

Description: 2584–2598

Description: 3T. Fisica dei terremoti e Sorgente Sismica

Description: JCR Journal