Abstract

Studies of strong ground motion of the 2008 great Mw 7.9 Wenchuan earthquake indicate that the horizontal‐component peak ground acceleration (PGA) is significantly enhanced within the 100‐ to 300‐km fault distance range. In this article, through analysis of waveform recordings of Wenchuan aftershocks of single earthquakes at multiple stations and multiple earthquakes at single stations, we confirm the existence of large‐amplitude SmS within the critical epicentral region (100300  km) in this area, with amplitude consistently 3–5 times stronger than direct S. Based on synthetic modeling of the horizontal‐component peak ground velocity (PGV) and PGA attenuation relationships, it is found that in the same epicentral distance range, the postcritical SmS arrivals clearly enlarge the amplitude, which also explains the increased PGA values of the Wenchuan mainshock within the critical distance range. We also quantify the influence of SmS on the ground‐motion amplitudes and modify an existing model to obtain a new hinged‐trilinear attenuation model of this area, which provides a better fit to the recorded PGA amplitudes of the Wenchuan mainshock.

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