The Haiyuan fault is a major left-lateral fault located at the northeastern rim of Tibet. We use ERS InSAR data covering two adjacent tracks across its central segment (the ”Tianzhu seismic gap”) to characterize its mechan-ical behavior for the period 1993-1998. Interferograms are corrected for orbital and tropospheric errors, then se-lected for stacking depending on their signal to noise ra-tios, to derive average velocity maps for both indepen-dent tracks. A steep velocity gradient is observed across the fault, consistent with a left-lateral slip at a rate of 6.3 ±2 mm/yr below a locking depth of about 1.7 km. Such a small apparent locking depth may be indicative of tran-sient superficial creep or related to a weak fault zone. Key words: ...