Aftershock distribution and the fault of the mainshock.

Nobuo Hurukawa, 2003/01/23

Updated on 2003/01/27

The mainshock and 5 immediate aftershocks were relocated by the MJHD method. Since they distribute along the plane dipping north-northeastward, we can conclude that the mainshock fault plane is the nodal plane of the moment tensor solution that dips north-northeast with a gentle angle and that this is an interplate earthquake. The length of the aftershock area is about 40km along the coast line and the mainshock occurred at the east-southeast edge of the fault. These results are consistent with the result by Dr. Yagi.

Note: Absolute locations, especially focal depths, are unreliable because of no nearer stations and the small number of events.

Data: Recent Worldwide Earthquake Activity by the US Geological Survey (http://neic.usgs.gov/neis/bulletin/)

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.