Omori decay exponent p did not increase with surface heat flow in California, Japan or global aftershock sequences; Japan and global samples showed a decrease

Kisslinger and Jones (1991) reported faster aftershock decay (higher Omori p) where surface heat flow is high in southern California. We tested this in three samples with the IHFC Global Heat Flow Database (release 2024, v2026.03): California-Nevada ComCat (M4.0+, 1986-2025, 501 sequences), Japan JMA (M4.5+, 2000-2024, 176 sequences) and global ComCat (M6.5+, 1995-2025, 158 sequences). A pooled likelihood fit lambda = mu + K t^-p with a fixed pre-event background, free productivity per sequence, and p linear in log10 of the local median heat flow, with magnitude, depth and year controls. Intervals are 95% cluster-bootstrap intervals over spatial cells. The change in p per tenfold heat flow was +0.14 (-0.23 to +0.43) in California-Nevada, -0.59 (-0.88 to -0.09) in Japan and -0.29 (-0.43 to -0.04) globally. Thus the pre-set hypothesis of a positive slope was not supported in any sample, and two samples showed the opposite sign. Productivity per tenfold heat flow changed by a factor of 1.9 (0.5 to 6.9), 4.1 (1.9 to 9.1) and 0.42 (0.21 to 0.84), so it had no common sign. The Japanese slope remained outside the 2011-2020 Tohoku zone and in a low-background subset, but it disappeared when the background was set to zero. The global slope weakened with a low-background subset or a 200 km heat-flow radius. In California, a foreshock-free subset gave a negative slope. Heat flow also marks tectonic setting, so this study cannot isolate a temperature effect.

aftershocks · Omori law · aftershock decay · heat flow · aftershock productivity · Global Heat Flow Database · ComCat · JMA catalog · California · Japan · statistical seismology · damage rheology · cluster bootstrap · null result