Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

80 PATA Days 2024 1 2 T H I N T E R N AT I O N A L I N Q U A M E E T I N G O N PA L E O S E I S M O L O G Y , A C T I V E T E C T O N I C S A N D A R C H A E O S E I S M O L O G Y ( PATA ) , O C T O B E R 6 T H - 1 1 T H , 2 0 2 4 , L O S A N D E S , C H I L E K E Y W O R D S Main Himalayan Thrust, Main Frontal Thrust, Siwalik, earthquake surface rupture Bollinger Laurent (1) Riesner Magali (1, 2) Klinger Yann (3) Rizza Magali (2) Laporte Marine (1) Shah Chanda (4) Adhikari Lok Bijaya (4) Sapkota Soma Nath (4) (1) CEA, DAM, DIF, F-91297 Arpajon, France. (2) Aix Marseille Univ, CNRS, IRD, Coll France, CEREGE, Aix-en-Provence, France. (3) Institut de Physique du Globe de Paris, CNRS, Université Paris Cité, Paris, France (4) Department of Mines and Geology, Lainchaur, Kathmandu, Nepal *Email: Laurent.bollinger@cea.fr SURFACE RUPTURE OF HISTORICAL EARTHQUAKE(S) AT THE FRONT OF THE CHANDRA BAGH, EASTERN NEPAL A B S T R A C T We present here a new paleoseismological site located in eastern Nepal at the front of the Chandra Bagh, a salient of the topographic front, in a region affected by multiple embryonic folds ahead of the Main Frontal Thrust. Well-preserved evidence of recent faulting is still exposed there in a natural river-cut cliff along the east bank of the Chapin river. The cliff exposes sands and siltstones separated by north-dipping thrust faults that emerge at the foot of a 30-metre-high cumulative scarp. The 34 AMS radiocarbon dates, from detrital charcoals sampled in the river-cut cliff and in nearby terraces, constrain the timing of the sedimentary processes and predate the earthquake surface rupture. The results show that the surface rupture necessarily occurred after the 12th century. Two major historical earthquakes have been documented in the region, the 1255 AD and 1934 earthquakes, which could be candidates for association with the Chapin Khola observations, demonstrating that the earthquake ruptures propagating in this region are not always blind. I N T R O D U C T I O N The Himalayan topographic front is relatively linear in central Nepal between 84.75 and 86.55E (Figure 1). In fact, the successive folds and fault segments that are exposed along the Siwalik front in the region are partially aligned, with only minor step-offs that do not exceed 5 km, the distance that separates the topographic front between the east and west of the river Ratu (Figure 1).