The 2019–2020 Khalili (Iran) Earthquake Sequence—Anthropogenic Seismicity in the Zagros Simply Folded Belt?

Abstract

We investigate the origin of a long‐lived earthquake cluster in the Fars arc of the Zagros Simply Folded Belt that is colocated with the major Shanul natural gas field. The cluster emerged in January 2019 and initially comprised small events of Mn ∼ 3–4. It culminated on 9 June 2020 with a pair of Mw 5.4 and 5.7 earthquakes, which was followed by >100 aftershocks. We assess the spatiotemporal evolution of the earthquake sequence using multiple event hypocenter relocations, waveform inversions, and Sentinel‐1 Interferometric Synthetic Aperture Radar (InSAR) measurements and models. We find that the early part of the sequence is spatially distinct from the 9 June 2020 earthquakes and their aftershocks. Moment tensors, centroid depths, and source parameter uncertainties of 15 of the largest (Mn ≥ 4.0) events show that the sequence is dominated by reverse faulting at shallow depths (mostly ≤4 km) within the sedimentary cover. InSAR modeling shows that the Mw 5.7 mainshock occurred at depths of 2–8 km with a rupture length and maximum slip of ∼20 km and ∼0.5 m, respectively. Our results suggest that the 2019–2020 Khalili earthquake sequence was likely influenced by operation of the Shanul field, though elevated natural seismicity in the Zagros makes the association difficult to prove. Understanding how to distinguish man‐made from natural seismicity is helpful for hazard and risk assessment, notably in the Zagros, which is both seismically active and rich in oil and gas reserves.

Structural controls on coseismic rupture revealed by the 2020Mw 6.0 Jiashi earthquake (Kepingtag belt, SW Tian Shan, China)

“…suggest that this may be a common feature of Zagros ruptures (Roustaei et al, 2010;Jamalreyhani et al, 2021). Another possible mechanism could be due to structural complexities in the fault geometry.…”

Chronicle of Processes Leading to the 2018 Eruption at Mt. Etna As Inferred by Seismic Ambient Noise Along With Geophysical and Geochemical Observables

“…We obtained moment tensors (MTs) for the events M L > 3.9 based on a Bayesian bootstrap probabilistic joint inversion method by using the Grond software (Heimann et al., 2018; Kühn et al., 2020). The method provides the uncertainties for the model parameters of resulting moment tensor inversion (e.g., depth) and has been applied to different regions recently—for example, in Southeastern Anatolia (Büyükakpınar et al., 2021), Zagros Simply Folded Belt (Jamalreyhani et al., 2021), and AlpArray seismic network (Petersen et al., 2021). The MTs were calculated via waveform inversion in both time and frequency domains using three‐component data (R, T, and Z).…”

Effects of large aftershocks on spatial aftershock forecasts during the 2017–2019 western Iran sequence

“…The seismicity in Zagros generally consists of low to moderate magnitude events (Barnhart et al 2013;Karasözen et al 2017) distributed across a ∼200-km-wide zone. These earthquakes commonly occur on blind faults (Berberian 1995), located beneath the Hormuz Salt Formation within the sedimentary cover and basement between 8 and 14 km (Jackson & Fitch 1981;Ni & Barazangi 1986;Baker et al 1993;Hessami et al 2001;Jamalreyhani et al 2021).…”