Incorporating Persistent Scatterer Interferometry and Radon Anomaly to Understand the Anar Fault Mechanism and Observing New Evidence of Intensified Activity

Abstract

Interferometric Synthetic Aperture Radar (InSAR) monitors surface change and displacement over a large area with millimeter-level precision and meter-level resolution. Anar fault, with a length of ~200 km, is located in central Iran. Recent seismological studies on the fault indicated that it is approaching the end of its seismic cycle. Although a large earthquake is imminent, the mechanism of the fault is not well understood. Therefore, understanding and discovering the mechanism of Anar fault remains a challenge. Here, we present an approach of displacement fault analysis utilizing a combination of InSAR data obtained from the persistent scatterer interferometry (PSI) method and 178 Sentinel-1 images (ascending and descending) (2017–2020). We incorporated groundwater samples from 40 wells, radon concentration anomaly mapping, Global Positioning System (GPS), and 3D displacement measurement acquired over four years (2016–2020). We investigated and monitored the deformation of the fault plate’s behavior over the last three years (2017–2020) to explore new evidence and signature of displacement. The results show that the time series analysis in the fault range has an increasing displacement rate in all dimensions. We observed that the line-of-sight (LOS) displacement rate varied from −15 mm to 5 mm per year. Our calculations show that the E–W, N–S, and vertical displacement rates of the fault blocks are 2 mm to −2 mm, 6 mm to −6 mm, and 2 mm to −4 mm per year, respectively. An anomaly map of the radon concentration shows that the complete alignment of the high concentration ranges with the fault strike and the radon concentration increased on average from 23.85 Bq/L to 25.30 Bq/L over these three years. Therefore, we predict rising the radon concentration is due to the increase in activity which resulted in a deformation. Finally, our findings show that the Anar fault is an oblique and right-lateral strike-slip with a normal component mechanism. We validated the proposed method and our results by comparing the GPS field data and PSI measurements. The root mean square error (RMSE) of the PSI measurement is estimated to be 0.142 mm. Based on the supporting evidence and signature, we conclude that the Anar fault activity increased between 2017 and 2020.

Strain and Moment Rates from GPS and Seismological Data in Northern Iran: Implications for an Evaluation of Stress Trajectories and Probabilistic Fault Rupture Hazard

“…Strike-slip faults with an acute angle related to the stress direction include segments with en-echelon arrays which show the sense of shearing and lateral motion on the fault planes [92][93][94][95][96][97]. In the area, most fault systems (even those with present reverse mechanisms) indicate clear en-echelon segmentation.…”

Flexural-slip folding in buckling phases of orogenic belts: Insight into the tectonic evolution of fault splays in the East Iran orogen

“…Currently, East Iran's orogen follows a curved pattern to the east and west in its southern and northern domains, respectively (Figure 1B). This orogenic belt which is located between the Afghan block in the east and sub-zones of Central Iran (e.g., the Lut block) in the west includes the fastest-slipping faults in eastern Iran (Figure 1B) (Walker and Khatib, 2006;Mehrabi et al, 2021;Rashidi et al, 2021). The Nehbandan (West Neh and East Neh branches), Nosrat-Abad and Kahourak faults within the East Iran orogen constitute the eastern boundary of the Lut block, and the Sabzevaran, Gowk, and Nayband faults determine the western boundary of the Lut block (Figure 1B) (Hashemi et al, 2018;Rashidi et al, 2020).…”

Structure and kinematics of active faulting in the northern domain of Western and Central Alborz, Iran and interpretation in terms of tectonic evolution of the region

“…The current-day configuration and faults distributions with different mechanisms in the Alborz had been accompanied by a change in the stress direction from N-S to NE-SW in Pliocene (Allen et al, 2003;Jackson et al, 2002). Various studies have been done on strain rate for the Iranian plateau and its structural sub-zones (e.g., Rashidi et al, 2022;Mehrabi et al, 2021;Raeesi et al, 2017;Zarifi et al, 2014;Masson et al, 2004). Recent studies of the strain and stress fields in northern Iran indicated ~N35.5 • E as the mean stress direction for the Alborz (Rashidi and Derakhshani, 2022).…”