Study of active tectonics of western Greece using InSAR-seismology and structural geology
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Date
2024-09-04
Authors
Τσιρώνη, Βαρβάρα
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Abstract
This dissertation explores the impact of space geodetic techniques like InSAR and GNSS time-series analysis on active tectonic structures in Western Greece. The study focuses on the Paliki peninsula, which is near the transform fault (CTF), to provide insights into active shortening produced by compressional deformation across western Cephalonia through a comprehensive analysis of geodetic data, including InSAR and GNSS. Our analysis covers the period from 2016 to 2022 and leverages LiCSBAS, an open-source package, for InSAR time series analysis with the N-SBAS method. The results of the InSAR analysis demonstrate deformation rates between 2 and 5 mm/yr in the line-of-sight (LOS) direction of the satellite. Also, the study produced new E-W and Up-Down velocity maps, which may have a large impact on seismic hazard assessment. The results show a 1.5 mm/yr E-W shortening between Paliki (Lixouri) and central Cephalonia (Argostoli), equivalent to 187 ns/yr of shortening rate. The Paliki peninsula is uplifting with an average rate of 1 mm/yr, and the maximum values of uplift are located in the southwestern part of the peninsula with a rate of about 2 mm/yr. The seismic fault activated during the 3 February 2014, M6.1 earthquake onshore Paliki can be traced in the maps as a kinematic discontinuity. The dissertation’s results suggest a complex deformation pattern on the Paliki peninsula with strain accumulation along strike-slip and reverse-slip faults.
New velocity maps were produced for the Aitolia-Akarnania region. The study also confirms the creeping behavior along the Katouna-Stamna Fault (KSF) in the Aitolia-Akarnania
region, with the observed offset of velocity across the fault trace playing a key role in the interseismic behavior of the fault. A new dataset of focal mechanisms of about 40 earthquakes for the Aitolia & Akarnania region was constructed, revealing the complex seismicity pattern of the area. The third case study mapped the Psathopyrgos fault through time-series analysis, revealing a possible rupture or passive slip on the Psathopyrgos fault plane or triggering mechanisms of the second and third stages of the seismic sequence of 2021. The data also confirmed a right-lateral slip deficit along the western segment of the Psathopyrgos fault, confirming the presence of creeping behavior along this type of faulting. The non-tectonic movements recording by InSAR showed slow ground motions that represent slow moving landslides. The kinematic behaviour of active landslides at several localities in the area of Panachaikon Mountain, Achaia (Peloponnese, Greece) were studied using Sentinel (C-band) InSAR time series analysis. The average displacement maps were obtained for the period 2016–2021. The maximum displacement rate of each landslide is located at about the center of it. The average E-W velocity of the Krini landslide is ∼3 cm/year (toward the east) and 0.6 cm/year downward. The line-of-sight (LOS) velocity of the landslide (descending orbit) compares well to a co-located GNSS station within (±) 3 mm/yr. Our results also suggest a correlation between rainfall and landslide motion. For the Krini landslide, a cross-correlation analysis of our data suggests that the mean time lag was 13.5 days between the maximum seasonal rainfall and the change in the LOS displacement rate. Furthermore, the amount of total seasonal rainfall controls the increase in the displacement rate, as 40–550 per cent changes in the displacement rate of the Krini landslide were detected, following to a seasonal maximum of rainfall values at the nearby meteorological station of Kato Vlassia. According to our results, it seems that large part of this mountainous region of Achaia suffers from slope instability that is manifested in various degrees of ground displacement greatly affecting its morphological features and inhabited areas.The study found a correlation between rainfall and landslide motion, with the displacement rates of the Krini active landslide increasing after a period of rainfall. These findings have significant implications for the study of slow-moving landslides, offering new perspectives on the correlation of the displacement rate of a landslide with the amount of total rainfall.
The dissertation focuses on elastic block modelling to understand the overall kinematics of western Greece. Western Greece is a high-seismicity area marking a shift from collision to subduction. West of the CTF, the Apulian carbonate platform abuts against the NW Greece-Albania foreland. East of the CTF, the old Mesozoic Ionian oceanic lithosphere subducts beneath the Peloponnese. The dissertation studied the kinematics in this region by modeling the GNSS velocity field using an elastic block approach to determine the rotations of tectonic blocks and the rate of slip deficit accumulation along major crustal faults. We use a comprehensive horizontal velocity field derived from continuous GNSS data covering western Greece and southern Italy. We find that the overall kinematics is well described by the rotation of five (5) tectonic blocks. These blocks consist of the Apulian block, which corresponds to the Apulian platform, central Greece, Peloponnese, and the Ionian-Akarnania Block. The Ionian-Akarnania is bounded by the CTF, the Graben of Amvrakikos, the KSF, and the Movri fault zone (MFZ). Additionally, we propose the existence of a micro-block, the South Aitolia Block (SAB), which is located between the Trichonis Lake and the Gulf of Patras. Our model finds right-lateral strike-slip motion (∼16 mm/yr) and a small reverse component of slip (∼4 mm/yr) along the CTF. The motion transfers to the triple junction in Preveza, where the boundary in Epirus between the Apulian platform and northwestern Greece to the north receives the collision act through active shortening along that boundary with ∼7 mm/yr. The gulf of Amvrakikos undergoes rapid extension at ∼10mm/yr. The KSF has a rapid slip rate that fluctuates in value, and it’s possible that the long-term slip rate reflects the fault’s creeping behaviour. The MFZ shows right-lateral relative motion, with a possible small normal component along the zone. Overall, the regional kinematics is well explained by the trenchward motion of a single Ionian- Akarnania block having faster velocity than central Greece but a velocity slower than Peloponnese. The IAB block experiences internal deformation, and the Kyllini-Cephalonia Fault (KCF) seems to control a pattern of distributed deformation inside the block. The model provides the first consistent kinematic model at the scale of western Greece, solving for the effects of rigid block rotations and elastic strain accumulation at major crustal faults. Also, the study suggests that the subduction of the Nubia plate beneath Eurasia does not control the overall deformation regime on western Greece.
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Keywords
InSAR-GNSS, Block modelling, Active tectonics, Deformation, Western Greece