Fault mechanics and post-seismic deformation at Bam, SE Iran

Abstract

S U M M A R YThe extent to which aseismic deformation relaxes co-seismic stress changes on a fault zone is fundamental to assessing the future seismic hazard following any earthquake, and in understanding the mechanical behaviour of faults. Here we use models of stress-driven afterslip and viscoelastic relaxation, in conjunction with post-seismic InSAR measurements, to show that there has been minimal release of co-seismic stress changes through post-seismic deformation following the 2003 M w 6.6 Bam earthquake. Our analysis indicates the faults at Bam remain predominantly locked, suggesting that the co-plus interseismically accumulated elastic strain stored downdip of the 2003 rupture patch may be released in a future M w 6 earthquake. Our observations and models also provide an opportunity to probe the growth of topography at Bam. We find that, for our modelled afterslip distribution to be consistent with forming the sharp step in the local topography over repeated earthquake cycles, and also to be consistent with the geodetic observations, requires either (1) far-field tectonic loading equivalent to a 2-10 MPa deviatoric stress acting across the fault system, which suggests it supports stresses 60-100 times less than classical views of static fault strength, or (2) that the fault surface has some form of mechanical anisotropy, potentially related to corrugations on the fault plane, that controls the sense of slip.

Dominant Controls of Downdip Afterslip and Viscous Relaxation on the Postseismic Displacements Following the Mw7.9 Gorkha, Nepal, Earthquake

“…On the other hand, downdip afterslip in the first 14 months after the 1999 Chi‐Chi earthquake only released 7% of the coseismic moment (Hsu et al, ). For the 2001 Kokoxili, 2003 Bam, and 2008 Wenchuan events, relatively low ratios are also estimated within the first few years (Huang et al, ; M. H. Huang, personal communication, 2017; Ryder et al, ; Tan et al, ; Wimpenny, et al, ).…”

“…For the Kokoxili, 2003Bam, and 2008 Wenchuan events, relatively low ratios are also estimated within the first few years (Huang et al, 2014;M. H. Huang, personal communication, 2017;Ryder et al, 2011;Tan et al, 2013;Wimpenny, et al, 2017).…”

Coseismic and Postseismic Deformation of the 2016 MW 6.2 Lampa Earthquake, Southern Peru, Constrained by Interferometric Synthetic Aperture Radar

“…For this phenomenon, we also saw at Bam earthquake. At Bam earthquake, the modeled stress‐driven afterslip (the maximum amplitude is 60–90 cm) is also localized (Wimpenny et al, ), with a maximum amplitude 4–6 times larger than the kinematic model (13.6 cm; Fielding et al, ) spanning similar time intervals. The temporal evolution of surface displacement (Figure ) is fit less well than the spatial pattern (Figure S12).…”

“…The value of V 0 and aσ may vary in different events, such as 5 mm/year and 5.5 MPa for the 2003 Bam earthquake (Wimpenny et al, ) and 20 mm/year and 0.7 MPa for the 2004 Parkfield earthquake (Barbot et al, ), respectively. Following Wimpenny et al (), we varied the constitutive parameters V 0 and aσ to seek an appropriate model based on observed LOS time series. The used LOS observations are extracted from the four boxes in Figure .…”

Strain Partitioning and Present‐Day Fault Kinematics in NW Tibet From Envisat SAR Interferometry

“…InSAR is a powerful tool to map precisely and over large areas surface displacements (e.g., Bürgmann et al, ; Hooper et al, ). This technique has been widely employed in earthquake and fault studies (e.g., Jolivet et al, ; Pathier et al, ; Rousset et al, ; Sudhaus & Jónsson, ; Wimpenny et al, ), volcanic dike intrusions (e.g., Cervelli et al, ; Grandin et al, ; Manconi & Casu, ; Pedersen & Sigmundsson, ), landslide monitoring (e.g., Fruneau et al, ; Hilley et al, ; Schlögel et al, ; Strozzi et al, ; Wasowski & Bovenga, ), urban subsidence (e.g., Amelung et al, ; Bawden et al, ; Fruneau & Sarti, ; López‐Quiroz et al, ), permafrost freeze‐thaw cycles (e.g., Chang & Hanssen, ; Daout et al, ; Liu et al, ; Short et al, ), or water vapor mapping (e.g., Hanssen et al, ; Wadge et al, ). However, for small deformation signals in high mountainous areas, such as interseismic deformation, the approach suffers from major limitations due to high topographic gradients and unsuitable valley flank orientations relative to the synthetic aperture radar (SAR) view angle, snow cover, or atmospheric delays.…”