The 2019-2020 Khalili (Iran) earthquake sequence - anthropogenic
seismicity in the Zagros Simply Folded Belt?
Léa Pousse‐Beltran
School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada- Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, UGE, ISTerre, 38000 Grenoble, France
Author ProfileAbstract
We investigate the origin of a long-lived earthquake cluster in the
Fars arc of the Zagros Simply Folded Belt that is co-located with the
major Shanul natural gas field near the small settlement of Khalili. The
cluster emerged in January 2019 and initially comprised small events of
w 5.4 and 5.7 earthquakes, which were followed by > 100
aftershocks. We assess the spatio-temporal 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 June 9, 2020 earthquakes and
their aftershocks. Moment tensors, centroid depths, and source parameter
uncertainties of fifteen 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 modelling
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 strongly suggest that
the 2019-2020 Khalili earthquake sequence was influenced by the
operation of the Shanul field, making these the first known examples of
gas extraction anthropogenic earthquakes in Zagros. Understanding the
genesis of such events to distinguish man-made seismicity from natural
earthquakes is helpful for hazard and risk assessment, notably in
Iran which is both seismically-active and rich in oil and gas reserves.