The admissible tsunamigenic source region of 24 September 2013 land-based earthquake - application of backward ray tracing technique

摘要

A minor tsunami of about 50 cm was generated along the coast of Qurayat near Makran subduction zone in the Arabian Sea due to the 24 September 2013 Pakistan earthquake of magnitude 7.6 M-w(mB), although its source was similar to 200 km far inland of the Makran trench. The real-time sea-level observation network in the Arabian Sea recorded minor tsunami arrivals. In an attempt to explain the mechanism of this unusual tsunami, we use backward ray tracing technique to map the admissible region of tsunamigenic source. Basically, in this technique the ray equations are integrated starting from the specific locations of tsunami observations, in all possible directions. The known travel time of the initial waves to the respective tide gauges and tsunami buoys is used in this method. Backward wave front is constructed by joining all end-points of the rays from each of the locations. The region where the envelope of all backward wave fronts converges is considered as the source of the tsunami, which is similar to 470 km from the earthquake epicentre with the location at 24.8 N and 61.5 E. The admissible region identified is an undersea section between Chabahar and Gwadar, where a mud island had appeared subsequent to this earthquake. Convergence of the tsunami source zone and location of the mud island suggest that the sudden uplift must have caused the tsunami.