Where a gong is struck changes its sound from harmonic chime to noisy shimmer

Evidence

The orchestral gong is shown struck in two different places—out from the center and at the center (Figure 4.33, upper left and right, respectively). The difference in acoustic output is profound. When struck at the center, the result is a quasi-harmonic set of components and an extremely strong low-frequency component that rings on for a very long time (some 30 seconds in this example). When struck away from the center, a gong produces its characteristic sound of a noisy shimmering, and the spectral effect of this is very clearly portrayed in the spectrogram, where there are noise components extending up in frequency to around 3.5 kHz. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1317

Categorization

• CANDY: A fun bar-stool fact: striking a gong dead-center makes it ring on for ~30 seconds with a huge low tone, while off-center gives the classic noisy shimmer.
• QUESTION: Why does center striking produce quasi-harmonic components while off-center striking drives noisy ones up to 3.5 kHz? Physical explanation would deepen the psychoacoustic stake.
• corroborated: 3 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1317