Insight into the 2017–2019 Lurestan arc seismic sequence (Zagros, Iran); complex earthquake interaction in the basement and sediments

Abstract

Summary Despite its high seismogenic potential, the details of the seismogenic processes of Zagros Simply Folded Belt (SFB) remains debated. Three large earthquakes (Mw 7.3, 5.9, and 6.3) struck in the Lurestan arc of the Zagros SFB in 2017 and 2018. The sequence was recorded by seismic stations at regional, and teleseismic distances. Coseismic surface displacements, measured by Sentinel-1A/B satellites, provide additional data and a unique opportunity to study these earthquakes in detail. Here, we complement previous studies of the coseismic slip distribution of the 12 November 2017 Mw 7.3 Ezgeleh earthquake by a detailed analysis of its aftershocks, and we analyzed the rupture process of the two interrelated earthquakes (25 August 2018 Mw 5.9 Tazehabad and the 25 November 2018 Mw 6.3 Sarpol-e Zahab earthquakes). We model the surface displacements obtained from Interferometric Synthetic Aperture Radar (InSAR) measurements and seismic records. We conduct non-linear probabilistic optimizations based on joint InSAR and seismic data to obtain finite-fault rupture of these earthquakes. The Lurestan arc earthquakes were followed by a sustained aftershock activity, with 133 aftershocks exceeding Mn 4.0 until December 30, 2019. We rely on the permanent seismic networks of Iran and Iraq to relocate ∼700 Mn 3 + events and estimate moment tensor solutions for 85 aftershocks down to Mw 4.0. The 2017 Ezgeleh earthquake has been considered to activate a low-angle (∼17°) dextral-thrust fault at the depth of 10–20 km. However, most of its aftershocks have shallow centroid depths (8–12 km). The joint interpretation of finite source models, moment tensor, and hypocentral location indicate that the 2018 Tazehabad and Sarpol-e Zahab earthquakes ruptured different strike-slip structures, providing evidence for the activation of the sinistral and dextral strike-slip faults, respectively. The deformation in the Lurestan arc is seismically accommodated by a complex fault system involving both thrust and strike-slip faults. Knowledge about the deformation characteristics is important for the understanding of crustal shortening, faulting, and hazard and risk assessment in this region.

Earthquake Source Parameters in Zagros Region (Iran) From the Time -Evolutive P-wave Displacement

“…Feng et al, [20] have proposed a hypocenter at 15 km depth along a basement fault that is causative for the 2017 earthquake in the Zagros region where large earthquakes have not been documented for several centuries. A coseismic source model proposed by Jamalreyhani et al, [21] suggested an oblique thrust mechanism and a fault plane with a low dip angle in the Precambrian basement. In several studies, two high slip asperities are revealed for this event with a maximum slip of about 5 to 6 m [20,[22][23].…”

Earthquake source parameters in Zagros region (Iran) from the time-evolutive P-wave displacement

“…Feng et al 21 have proposed a hypocenter at 15 km depth along a basement fault that is causative for the 2017 earthquake in the Zagros region where large earthquakes have not been documented for several centuries. A coseismic source model proposed by Jamalreyhani et al 22 suggested an oblique thrust mechanism and a fault plane with a low dip angle in the Precambrian basement. In several studies, two high slip asperities are revealed for this event with a maximum slip of about 5 to 6 m 21 , 23 , 24 .…”

Co-seismic slip of the 18 April 2021 Mw 5.9 Genaveh earthquake in the South Dezful Embayment of Zagros (Iran) and its aftershock sequence

“…The region presents one of the youngest continental collision zones on Earth and hosts frequent episodes of moderate to large shallow seismicity (e.g. Talebian and Jackson, 2004;Nissen et al, 2019;Jamalreyhani et al, 2022) (Figure 1). The Zagros changes morphology along and across strike, likely reflecting differences in the sedimentary cover -in particular its overall thickness and the spatial extents of weak, detachment-forming evaporitic layers.…”

“…The advent of InSAR and recent improvements in seismic station coverage have allowed focused studies of major earthquake sequences that can shed light on these questions. A long-standing question in the ZFTB is the extent to which the Precambrian basement and the thick Phanerozoic sedimentary layer participate in the observed seismicity (McQuarrie, 2004;Mouthereau et al, 2007;Talebian and Jackson, 2004;Jamalreyhani et al, 2022). Nissen et al (2011) suggested a vertical separation of the seismicity in the Zagros, implying that most of the moderately-sized events (M w 5-6), especially those in the ZSFB, happen in the competent segment of the sedimentary layer and most the aftershocks in the basement, mostly triggered by stress perturbations.…”

“…Recent studies show the variety of deformation styles and seismicity in different parts of the ZFTB (e.g. Nissen et al, 2019;Jamalreyhani et al, 2019Jamalreyhani et al, , 2022Jamalreyhani et al, , 2021b. The outer part of the ZFTB, named Zagros Foreland Folded Belt (ZFFB), is subdivided into four tectono-stratigraphy domains (Figure 1): from SE to NW, the Fars Arc, the Dezful Embayment, the Lurestan Arc, and the Kirkuk Embayment.…”