In the Himalayas the Eocene deformation phase is called the Eohimalayan event. By means of a forward and backward balanced cross section along a classical traverse through the Tethyan Himalaya we constrain Eohimalayan SW vergent folding and SW directed thrusting in a belt above a basal thrust at 10 km depth. This thrust is located at the structural position of the Southern Tibetan Detachment System with a NE directed normal sense displacement suggesting Miocene reactivation of a major Eocene contractional fault. Stepwise palinspastic restoration demonstrates that this Eocene contractional fault has been subsequently openly folded due to southwestward propagation of the Himalayan Thrust System.

Paleoseismological investigations, brittle fault analysis, and paleostrain calculations combined with the interpretation of satellite imagery and flood wave modeling were used to investigate the seismic and associated glacial hazard potential in Eastern Lunana, a remote area in NW Bhutan. Seismically induced liquefaction features, cracked pebbles, and a surface rupture of about 6.8 km length constrain the occurrence of M ≥ 6 earthquakes within this high‐altitude periglacial environment, which are the strongest earthquakes ever been reported for the Kingdom of Bhutan. Seismicity occurs along conjugate sets of faults trending NE‐SW to NNW‐SSE by strike‐slip and normal faulting mechanism indicating E‐W extension and N‐S shortening. The strain field for these conjugate sets of active faults is consistent with widespread observations of young E‐W expansion throughout southern Tibet and the north Himalaya. We expect, however, that N‐S trending active strike‐slip faults may even reach much farther to the south, at least into southern Bhutan. Numerous glacial lakes exist in the investigation area, and today more than 100 × 106 m3 of water are stored in moraine‐dammed and supraglacial lakes which are crosscut by active faults. Strong earthquakes may trigger glacial lake outburst floods, and the impact of such flash floods may be worst 80 km downstream where the valley is broad and densely populated. Consequently, tectonic models of active deformation have to be closely linked with glacial hazard evaluation and require rethinking and modification.

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We present fault analyses from the exhumed middle crustal slab of the High Himalaya in eastern Lunana in NW Bhutan. Fault planes from within two-mica, tourmaline-bearing leucogranites, leucogranitic rocks and migmatites indicate a complex brittle fault pattern with two distinct fault groups. A first group of faults (D1) characterized by chlorite, quartz and tourmaline slickenfibres is mainly defined by steeply SSE-dipping oblique-slip normal faults, and by shallowly NNW-dipping normal faults. A second, younger group of faults (D2) characterized by cataclasis products comprises strike-slip faults displaying conjugate patterns and E-and W-dipping conjugate normal faults, all which indicate E-W extension. Cross-cutting relationships amongst the O 1 fault group demonstrate that progressively steeper members of the fault group become younger within the NNW-dipping faults and become older within the SSE-dipping faults. These are all postdated by the D 2 fault group. The D l fault group indicates that the slab experienced ongoing NNW-SSE extension (i.e. flow) via brittle fault accommodation, contemporaneous with fault rotation. This may reflect rotation of the entire upper orogen due to movement over deeply located major ramp structures formed by out-of-sequence thrusting (Kakhtang Thrust) within the High Himalayan Slab of the Bhutan Himalaya.

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