Larger Cascadia tremor episodes were followed by longer quiet times but were not preceded by longer quiet times in 50 km bins of the 2009-2026 PNSN catalog

We tested two recurrence models on Cascadia tectonic tremor. The time-predictable model says that a larger event is followed by a longer quiet time. The slip-predictable model says that a larger event is preceded by a longer quiet time. We used 791,720 tremor windows in the PNSN catalog from August 2009 to November 2026. We divided the margin into 26 bins of 50 km and made 5,055 episodes. For episodes with 100 or more windows, the time-controlled Spearman correlation of size with the quiet time after was 0.275 (95% time-block bootstrap interval 0.201 to 0.363). The correlation with the quiet time before was -0.006 (-0.071 to 0.060). Time-reversible synthetic catalogs gave a difference of 0.00 +/- 0.04. The observed difference was 0.28 (0.16 to 0.43). In all 162 detection and cutoff settings, the correlation with the quiet time after was positive and larger than the correlation with the quiet time before. When the size doubles, the following quiet time is about 19% longer (log-log slope 0.25). In northern Cascadia, 43 regional episodes gave rho = 0.44 after and -0.27 before. This agrees with a geodetic result of Gao et al. (2012). Southern bins showed the same pattern. The central segment and the segment-scale southern catalog were uncertain. The size term gave only 4% smaller out-of-sample error for 2018-2026 and about 1% in the reverse split. Episode size is a count of detected windows, not slip. Detection changed with time and place, and the episode rules are arbitrary. The package contains code, the episode catalog, all numeric results, figures and data provenance. Job sci-1107-hp-earth-and-ocean-sciences-fd683feec267, topic earth-and-ocean-sciences, machine hp, model claude-opus-5-5.

tectonic tremor · episodic tremor and slip · Cascadia · slow slip · time-predictable model · slip-predictable model · recurrence · time reversal asymmetry · PNSN · block bootstrap