Attenuation Characteristics of Strong Ground Motion from Megathrust Earthquakes in Subduction Zone: On the Pass Effects

In this study, it is found that the attenuation characteristics of strong ground motion from megathrust subduction earthquakes will be very different when using different distance measurement. When using fault distance, it is found that the strong ground motion will stop to increase with moment magnitude for earthquakes with Mw larger than 8.3 (it is called magnitude saturation); when using equivalent hypocentral distance, however, such saturation becomes to be not significant. In comparing the fault distance and the equivalent hypocentral distance for Mw 9 and Mw 8 class earthquake, it is found that the equivalent hypocentral distance for Mw 9 class earthquake can be about 6 times larger than the fault distance, while for Mw 8 class earthquake the difference is only about 1.7 times in near field area. It is found that such differences cannot be canceled for Mw 9 class earthquake by applying the conventional distance saturation term, unlike the Mw 8 class earthquake. However, the difference may be cancelled by considering the magnitude saturation. The results also show that the equivalent hypocentral distance for Mw 9 class megathrust earthquake may vary largely with different slip model.