Tide gauges recorded clear earthquake offsets at few sites, and only Tohoku 2011 changed decadal sea-level rates, in a global PSMSL screen for 1900-2025

Question: how frequently do shallow earthquakes change tide-gauge records of relative sea level (RSL)? Approach: we paired 1,633 PSMSL RLR monthly gauge records with USGS ComCat earthquakes (depth 70 km or less, 1900-2025). Gauges within 1.5 rupture lengths (L, Wells and Coppersmith 1994) of the epicentre were 'near'. Gauges at 3-6 L gave a control set from the same events and epochs. For M 6.5 or more, we measured the initial RSL offset (months 1-6 after the event minus a 10-year pre-event trend fit) and scaled it by placebo dates of the same gauge. For M 7.5 or more, we measured the change in RSL rate (years 1-11 minus years -15-0) at merged sites, with one intercept for each series. A Student-t fit to the control values gave p-values, and Benjamini-Hochberg (FDR 10%) selected discoveries. Results: of 277 usable near pairs (114 events), 6 offsets from 5 earthquakes passed (Tohoku 2011 at Ofunato +757 mm and Onahama +497 mm; Niigata 1964; central Chile 1971; Rat Islands 1965; Guantanamo 1947). 4 of the 6 were within 0.5 L. Of 166 near site-event rate pairs (38 events), only 4 Tohoku sites passed: rate changes of -34 to -63 mm/yr in 2012-2021, which show fast postseismic uplift. Near rate changes were only weakly larger than control (Mann-Whitney p 0.038). At 0.25-1.5 L the median absolute change (3.5-5.3 mm/yr) was close to the control value (3.5 mm/yr). The two Tohoku offsets reversed by 45-47% after 5-10 years. PSMSL series did not end more frequently near M 7.5 or more events (1.9% vs 1.9%). Limitations: most great earthquakes (Alaska 1964, Chile 1960 and 2010, Sumatra 2004) have no near gauge with data before and directly after the event. We used epicentral distance, not slip models. Great events have no ocean reference series. We chose the volcano and other-event filters after we inspected the control tail; without them, 3 offsets and 0 rate changes pass.

tide gauge · relative sea level · vertical land motion · coseismic offset · postseismic deformation · PSMSL · ComCat · Tohoku 2011 · earthquake cycle · false discovery rate