Aftershock distribution and the fault of the mainshock.

Nobuo Hurukawa, 2003/05/22

(Updated 2003/05/23)


The mainshock and immediate aftershocks within 20 hours were relocated by the MJHD method. Since standard errors of hypocenters are large, it is difficult to identify the fault of the mainshock. If we assume that a strike of the mainshock fault is N54E that is obtained by Yagi, aftershocks distribute along a plane dipping northwestward. Therefore, the nodal plane dipping northwestward may be the mainshock fault plane. The mainshock occurred at a deeper part of the fault. This is consistent with Yagifs result.

Note: Absolute locations, especially focal depths, are unreliable because of few nearer stations and the small number of events.

Data: Recent Worldwide Earthquake Activity by the US Geological Survey (       

Method: Modified Joint Hypocenter Determination (MJHD) by Hurukawa


Fig. 1. Hypocenters relocated by the MJHD method.


Fig.2 Hypocenters located by USGS.


Fig. 3. Stations used in relocation.