New Constraints on the Mechanism and Rupture Area for the 1905 Mw 7.8 Kangra Earthquake, Northwest Himalaya

Previous interpretations of the 4 April 1905 Mw 7: 8 +/- 0: 2 Kangra earthquake assumed pure thrust slip on a gently dipping plane with dimensions on the order of 55 km down-dip and 100-150 km along strike. However, the identification of recent surface slip on a 60-km-long strike-slip fault, the Kangra Valley fault (KVF), above the northwestern corner of the inferred thrust, raises the intriguing possibility that moment release in 1905 may have been partly, or wholly attributable to dextral slip. We use geodetic strain data to constrain maximum dextral slip on the mapped fault trace of the KVF to less than 0.6 m, equivalent to an M-w = 6.8 earthquake, but find that 1.1 +/- 0.25 m of subsurface reverse slip occurred along approximate to 190 km of the mapped Jawalmukhi thrust fault. Reevaluated macroseismic data for the 1905 earthquake and insights from the distribution of felt intensities above the 2015 Gorkha earthquake, however, suggest that the Kangra coseismic rupture extended only approximate to 100 km along strike. In the time period following the 1905 earthquake, afterslip to the southeast of the mainshock either preceded or accompanied a large aftershock sequence (6.4 < M-w < 6.8) located near the down-dip end of this extended slip zone.