Surface heat flow did not clearly change the aftershock decay exponent p in California (1990-2025) or Japan (1999-2024); high Salton Trough p values came from swarm-like sequences

Kisslinger and Jones (1991) found that the Omori decay exponent p of southern California aftershock sequences (1933-1988) increased with surface heat flow. We tested this claim with later data. We selected 439 onshore shallow M 4.0-7.3 mainshocks from ComCat (California and western Nevada, 1990-2025) and 245 onshore Mj 4.0-7.6 mainshocks from the JMA catalog (1999-2024). Heat flow is the median of IHFC Global Heat Flow Database sites within 30 km. We fitted p with two estimators: single-sequence maximum-likelihood fits with a random-effects meta-regression, and a stacked profile likelihood that uses every sequence. Both control magnitude and depth, and the 95% intervals come from a cell bootstrap. In California, the common p was near 1.0 in all heat-flow terciles. The stacked slope was +0.10 per doubling of heat flow (-0.15 to +0.39), and all 7 design changes included zero. Salton Trough sequences again had high p (median 1.60 against 1.16 elsewhere in southern California), but only the swarm-like sequences (foreshock excess or a small magnitude gap) had high p (median 1.86). Without swarm-like sequences, the California slope was -0.10 (-0.34 to +0.13). Swarm-like sequences were more common in hot crust in California (18% to 33%). In Japan, the slope was +0.02 (-0.30 to +0.23) for all sequences. For sequences that are not swarm-like, it was +0.19 (+0.01 to +0.37), but we added this subset after the first results, so it is a lead only. A first selection rule kept the Joshua Tree 1992 sequence, which Landers aftershocks invaded; this one sequence made a false Kisslinger-Jones-like trend. Limitations: surface heat flow is a rough temperature proxy, the swarm rule is simple and post hoc, Japan has few usable sequences, and we did not refit the 1933-1988 sequences.

aftershocks · Omori law · decay exponent · heat flow · earthquake swarms · Salton Trough · California · Japan · ComCat · JMA catalog · replication · null result · Kisslinger-Jones