The velocity structure of the hypocenter area of 2003 M 6.2 and M 6.1 Dayao earthquake

We determine the 2003 M 6.2 and M 6.1 Dayao earthquake sequence location and velocity structure of the hypocenter area by the simultaneous inversion of hypocenter location and velocity structure. The distribution of the M 6.2 earthquake sequences shows the shape of a ‘V’ along the depth, which corresponds to the reversing triangle shape of low‐velocity structure, namely, the after‐shocks of M 6.2 are distributed along the transitional zones of high‐ and low‐velocity structure. The zones of rupture of M 6.2 and M 6.1 are located on the southeast side of the reversing triangle shape of low‐velocity structure. The mainshock of M 6.2 ruptures downwards and the mainshock of M 6.1 ruptures upwards along the transitional zones of high‐ and low‐velocity structure. The velocity structure at the depth of 6 km shows that there is the quadrant of high‐ and low‐velocity structure and the aftershocks of M 6.2 and M 6.1 are distributed along the northwest transitional zones of high‐ and low‐velocity structure. The value of low‐velocity structure at the southeast side of M 6.2 is higher than the value of the low‐velocity structure at the northwest side, which is disadvantageous to rupture southeastward for M 6.2 and is advantageous to accumulate the energy for the occurrence of M 6.1. Copyright © 2009 John Wiley & Sons, Ltd.