Root-Mean-Square Distance and Effects of Hanging Wall/Footwall

Abstract eng:
The hanging wall/footwall effects (HW/FW effects) are obvious in the near-fault ground motions of Chi-Chi earthquake, Taiwan, on September 21, 1999. The main cause of HW/FW effects is believed that the hanging wall sites are on general closer to the dipping fault than the sites at the same rupture distances (Drup) located on the footwall, that is to say, the rupture distance is unable to capture the general proximity of a site to a dipping fault plane. In order to overcome the shortcoming of the rupture distance, the root-mean-square distance (Drms) is introduced in this paper. Using the root-mean-square distance, the attenuation relationships of PGA are developed. By examining the residuals from the Chi-Chi earthquake-specific attenuation relations, the systematic differences between PGA of the hanging wall sites and the median attenuation for Chi-Chi earthquake are not found. This result confirms that the HW/FW effect is a geometric effect caused by the asymmetry of dipping fault. Therefore, the HW/FW effects on the near-fault ground motions can be ignored in the future attenuation analysis if we use the root-mean-square distance as the source-to-site distance measure.

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