Résumé
The Himalayan Arc accommodates nearly equal 2 cm/yr of shortening from the India-Eurasia collision, mostly along the Main Himalayan Thrust. Perpendicularly to the main structures, regional cross structures formed by en echelon grabens and half-grabens mark Quaternary extension from central Tibet to the Himalayas. The Yadong-Gulu Rift system is the most striking one with a total length of nearly equal 500 km. Its southernmost segment - the nearly equal 100-km-long Yadong half-graben - entrenches through the Himalayas and forms a 500-to-1500-m-deep asymmetric basin. The average basin surface elevation of nearly equal 4500 m contrasts with high reliefs of the Jomolhari range that reach 7326 m. They are separated by the N15 Yadong normal fault (also called Jomolhari Fault System, JFS) that forms spectacular triangular facets and affects glacial landforms. Though observed as early as the 1980s, offset moraines were never studied in detail in terms of measured displacement or age determination. Recent efforts from paleoclimate studies yielded a high-resolution framework to identify the various stages of Holocene glacial advances and associated moraine formation. These landforms display specific geomorphometric features recognized regionally (ELA, rugosity, crest freshness) that allow correlating across the various glacial valleys within the Yadong Rift and across similar settings in western Bhutan and eastern Nepal. This serves as a robust basis to place our moraine sequence within the Holocene paleoclimatic record and propose formation ages. By combining satellite images from Sentinel-2 (10 m, visible and NIR), Pleiades (0.5 m, visible) and a Pleiades-derived tri-stereo photogrammetric DEM (1 m), we map the fault trace and affected landforms in details and extract topographic profiles to measure vertical offsets. Paleoclimatic age constraints yield age-vs-displacement measurements along the whole 100-km-long JFS and define a chronology of Holocene deformation events. Within the limits of our observations, we conclude that the last surface-rupturing earthquake likely occurred between 3 and 8 ka BP and produced an average surface displacement of nearly equal 2 m. According to scaling relationships, the associated earthquake would have reached Mw 7.2. In addition, cumulative deformation suggests an average vertical slip rate of nearly equal 1 mm/yr for the Holocene.