Shallow creep on the Haiyuan Fault (Gansu, China) revealed by SAR Interferometry

• Published in: Journal of Geophysical Research: Solid Earth 2012-06, Vol.117 (B6), p.n/a
• Main Authors: Jolivet, R., Lasserre, C., Doin, M.-P., Guillaso, S., Peltzer, G., Dailu, R., Sun, J., Shen, Z.-K., Xu, X.
• Format: Article
• Language: English
• Subjects: active faults; Continental dynamics; creep; Earth Sciences; Earth, ocean, space; Earthquakes; Exact sciences and technology; Fault lines; Geodetics; Geology; Geophysics; InSAR; Interferometry; interseismic period; Load distribution; Plate tectonics; Rock deformation; Sciences of the Universe; Seismic activity; seismic cycle; Seismic hazard; Surface velocity; Tibet
• ISSN: 0148-0227; 2169-9313; 2156-2202; 2169-9356
• DOI: 10.1029/2011JB008732

Interferometric synthetic aperture radar data are used to map the interseismic velocity field along the Haiyuan fault system (HFS), at the north‐eastern boundary of the Tibetan plateau. Two M ∼ 8 earthquakes ruptured the HFS in 1920 and 1927, but its 260 km‐long central section, known as the Tianzhu seismic gap, remains unbroken since ∼1000 years. The Envisat SAR data, spanning the 2003–2009 period, cover about 200 × 300 km2 along three descending and two ascending tracks. Interferograms are processed using an adapted version of ROI_PAC. The signal due to stratified atmospheric phase delay is empirically corrected together with orbital residuals. Mean line‐of‐sight velocity maps are computed using a constrained time series analysis after selection of interferograms with low atmospheric noise. These maps show a dominant left‐lateral motion across the HFS, and reveal a narrow, 35 km‐long zone of high velocity gradient across the fault in between the Tianzhu gap and the 1920 rupture. We model the observed velocity field using a discretized fault creeping at shallow depth and a least squares inversion. The inferred shallow slip rate distribution reveals aseismic slip in between two fully locked segments. The average creep rate is ∼5 mm yr−1, comparable in magnitude with the estimated loading rate at depth, suggesting no strain accumulation on this segment. The modeled creep rate locally exceeds the long term rate, reaching 8 mm yr−1, suggesting transient creep episodes. The present study emphasizes the need for continuous monitoring of the surface velocity in the vicinity of major seismic gaps in terms of seismic hazard assessment. Key Points Imaging spatial variations of interseismic strain along a strike‐slip fault InSAR data resolves shallow slip anomaly between locked sections of a fault Method developments improve InSAR data resolution to a subcentimeter level