Cause of right-lateral strike-slip movement in recent seismic activity in the Hazara-Kashmir Syntaxis, NW Himalaya
Abstract
This paper reinvestigates the causes of right-lateral strike-slip (RLSS) component in the Focal Mechanism Solutions (FMS) for 16 aftershocks of magnitude ≥ 4.0. The aftershocks lie in a NW-SE trending zone between the Indus Suture and the Hazara-Kashmir Syntaxis, mostly in the Hazara, Banna and Kaghan nappes. The FMS indicate thrusting/reverse faulting to be the dominant mechanism with prominent right-lateral strike-slip component. The rupture planes have NW-SE trend and NE dip.
Four types of FMS have been obtained: reverse/thrust with prominent RLSS component, reverse/thrust with minor RLSS component, pure RLSS and pure Normal. On the basis of the nature, strike, dip and depths of these FMS, two possibilities can be proposed. The NW striking, shallow dipping (<450NE) FMS (1, 13 and 16) having depths ≥ 10 km and reverse/thrust mechanism with minor RLSS component are due to the Indus Kohistan Seismic Zone (IKSZ). It is, therefore, proposed that instead of pure thrust/reverse blind zone as indicated by previous workers, the IKSZ comprises some RLSS faults as well. Alternatively, the NW striking, steeply dipping (> 45o NE) FMS having depth ≤ 10 km and reverse/thrust mechanism with prominent (2-6, 8-10, 12, 14, 15, 17) to pure RLSS component (FMS 7) are due to the Balakot-Bagh Fault (BBF), a surface trace of the IKSZ. Hence, either the BBF is not a pure reverse fault but has a prominent RLSS component, or it is RLSS fault. One normal FMS (11) is considered to be an anomaly in the data. The horizontal principal stress axis (P-axis) for all the FMS follows NNE-SSE direction except for FMS 6, and is similar to the observations made by the previous workers.
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