Along-strike variations of the partitioning of convergence across the Haiyuan fault system detected by InSAR

Abstract

Oblique convergence across Tibet leads to slip partitioning with the coexistence of strike-slip, normal and thrust motion on major fault systems. A key point is to understand and model how faults interact and accumulate strain at depth. Here, we extract ground deformation across the Haiyuan Fault restraining bend, at the northeastern boundary of the Tibetan plateau, from Envisat radar data spanning the 2001-2011 period. We show that the complexity of the surface displacement field can be explained by the partitioning of a uniform deep-seated convergence. Mountains and sand dunes in the study area make the radar data processing challenging and require the latest developments in processing procedures for Synthetic Aperture Radar interferometry. The processing strategy is based on a small baseline approach. Before unwrapping, we correct for atmospheric phase delays from global atmospheric models and digital elevation model errors. A series of filtering steps is applied to improve the signal-to-noise ratio across high ranges of the Tibetan plateau and the phase unwrapping capability across the fault, required for reliable estimate of fault movement. We then jointly invert our InSAR time-series together with published GPS displacements to test a proposed long-term slip-partitioning model between the Haiyuan and Gulang left-lateral Faults and the Qilian Shan thrusts. We explore the geometry of the fault system at depth and associated slip rates using a Bayesian approach and test the consistency of present-day geodetic surface displacements with a longterm tectonic model. We determine a uniform convergence rate of 10 [8.6-11.5] mm yr −1 with an N89 [81-97] • E across the whole fault system, with a variable partitioning west and east of a major extensional fault-jog (the Tianzhu pull-apart basin). Our 2-D model of two profiles perpendicular to the fault system gives a quantitative understanding of how crustal deformation is accommodated by the various branches of this thrust/strike-slip fault system and demonstrates how the geometry of the Haiyuan fault system controls the partitioning of the deep secular motion.

Crustal Deformation in the India‐Eurasia Collision Zone From 25 Years of GPS Measurements

“…It is the site of two M w ~8 earthquakes in the last century—the 1920 Haiyuan and the 1927 Gulang earthquakes. Except for the estimate of ~10 mm/yr from Daout et al (), previous geodetic studies showed strike‐slip rates of ~4–6 mm/yr along the main Haiyuan Fault (e.g., Cavalié et al, ; Duvall & Clark, ; Jolivet et al, ; Zheng et al, ). Here two profiles HY1 and HY2 across the main Haiyuan Fault give a sinistral rate of ~4–5 mm/yr (Figures e and f) and a shortening rate of ~2–3 mm/yr (Figures S4e and S4f), inconsistent with a present‐day strike‐slip rate of 10 mm/yr.…”

Partitioning of oblique convergence coupled to the fault locking behavior of fold‐and‐thrust belts: Evidence from the Qilian Shan, northeastern Tibetan Plateau

“…A similar, but not identical, pattern of strain partitioning has been interpreted for the Haiyuan Fault and adjacent thrusts, to the east of our study area (102–104°E), by Daout et al . [], based on a combined study of InSAR and GPS data. The two areas are different in terms of the proportions of thrust and strike‐slip deformation and the greater depth of locking further west.…”

“…The best fit oblique detachment slips below a locking depth of 26 ± 8 km and has a dip of 17 ± 4° to the SSW. This locking depth is in close agreement with estimates of the seismogenic thickness from robust earthquake depths (~20 km [ Sloan et al ., ]) and with previous interseismic studies of the Haiyuan fault west of 104°E [ Jolivet et al ., ], which is fully locked, in contrast to the creeping section further east [e.g., Jolivet et al ., ; Daout et al ., ]. The best fit horizontal location of the locked‐creeping transition on the fault is constrained to within 9 km and is in agreement with the mapped surface trace of the Haiyuan Fault, implying a vertical or subvertical structure in the seismogenic upper crust.…”

“…We have used available GPS data (Global Earthquake Model (GEM) Strain Rate Model compilation [ Kreemer et al ., , and references therein]) and simple elastic models to test whether the observed range‐normal and range‐parallel velocities for the Qilian Shan are consistent with interseismic strain accumulation across two shallowly locked, localized faults: a detachment thrust and strike‐slip fault, respectively. This approach is a quantitative test of existing models that propose the existence of an active regional detachment thrust below the Qilian Shan [ Meyer et al ., ; Yin et al ., ; Daout et al ., ] and also allows us to investigate the geometric relationship between strike‐slip and dip‐slip faulting within the range.…”

A Multipixel Time Series Analysis Method Accounting for Ground Motion, Atmospheric Noise, and Orbital Errors

“…For instance, in the field of active tectonics, these methods allow detection of transient slip along active faults or to image slow, longwavelength, strain rates due to interseismic loading across active faults [e.g. Elliott et al, 2008;Jolivet et al, 2012Jolivet et al, , 2013Bekaert et al, 2015;Rousset et al, 2016;Daout et al, 2016]. c ⃝2018 American Geophysical Union.…”