Correspondences

What is linked, what is not

Each arc joins two phenomena tested on this site. Green and animated: clear link (correlation significant at 5 % after correcting for autocorrelation, or a response outside chance in an event study). Grey: inconclusive test. A statistical link alone does not establish causation.

Clear link
Inconclusive

Hypotheses tested

Clear links

correlation p < 0.05 or epochs outside chance

Causation demonstrated

a correlation demonstrates none

Arc width from |r| of the stored result; several tests between the same phenomena are drawn as stacked arcs.

Hypothesis tested: A tsunami is born when an earthquake suddenly moves the sea floor: it takes a submarine earthquake, shallow and large enough to lift a wide area. The probability should therefore rise with magnitude and collapse for deep earthquakes (Okal, 2011).

Events used

417

Shallow earthquakes followed by a tsunami

53.2 %

less than 70 km; 417 tsunamis for 986 M ≥ 7 earthquakes

Deep earthquakes followed by a tsunami

5.3 %

70 km and deeper; difference p < 0,001

Rise with magnitude (z)

9.4

Cochran–Armitage, p < 0,001

Chance coincidences

0.0 %

0 match(es) with dates shifted by 30 days

Period analysed

1950 → 2025

computed on Oct 25, 2026 · engine v1.0

Share of earthquakes followed by a tsunami

Magnitude	Depth	Tsunamis / earthquakes	Share (95 % CI)	Wave ≥ 1 m
7.0–7.5	< 70 km	213 / 513	42 % [37 ; 46]	10 %
7.0–7.5	≥ 70 km	1 / 161	1 % [0 ; 3]	0 %
7.5–8.0	< 70 km	141 / 194	73 % [66 ; 78]	30 %
7.5–8.0	≥ 70 km	10 / 57	18 % [10 ; 29]	2 %
8.0–8.5	< 70 km	39 / 41	95 % [84 ; 99]	66 %
8.0–8.5	≥ 70 km	1 / 7	14 % [3 ; 51]	0 %
8.5 +	< 70 km	12 / 13	92 % [67 ; 99]	92 %

Aligned series (CSV)

Method and sources

Earthquakes of the USGS ComCat catalogue of magnitude 7 or more, from 1950 to the last complete year; probable or definite tsunamis of seismic origin from the NCEI/WDS database. An earthquake is “followed by a tsunami” when a tsunami of the database occurs the same day (within one day) with an epicentre within 300 km. Rates per class of magnitude and depth (shallow: less than 70 km), Wilson 95 % intervals. Tests: Cochran–Armitage for a rate rising with magnitude (shallow earthquakes), two-proportion z-test between shallow and deep earthquakes. Control: the same matching with the tsunami dates shifted by 30 days measures chance coincidences.

Computation parameters

{
    "tests": "Cochran–Armitage trend over the magnitude classes (shallow events); two-proportion z-test shallow vs deep",
    "control": "tsunami dates shifted by 30 days",
    "matching": "same day ± 1 and epicentres within 300 km",
    "tsunamis": "NCEI/WDS, causes 1–5 (seismic), validity 3–4",
    "intervals": "Wilson 95 %",
    "earthquakes": "USGS ComCat, M ≥ 7, 1950 to the last complete year",
    "depth_classes": "shallow < 70 km"
}

Inputs : usgs.earthquakes.m7.yearly (127 pts, run #3247) · ncei.tsunamis.yearly (127 pts, run #3723)

Reading this result

The control finds almost no chance coincidence: the matching is reliable. Land earthquakes stay in the denominator (the catalogue does not say whether the epicentre is at sea), which lowers the rates of small magnitudes. “Tsunami” counts here any recorded wave, even of a few centimetres; the last column gives the share with a wave of at least 1 m. Large deep earthquakes (Bolivia 1994, Sea of Okhotsk 2013) produced no notable tsunami. Correlation is not causation: common factors (seasons, cycles, trends) or coincidence can produce it. The p-values account for autocorrelation (effective n) but not for preprocessing choices; the confidence interval comes from a block bootstrap. The limits of the source data apply.

SOURCES OF THIS PAGE

USGS ComCat earthquakes M ≥ 4.5 (FDSN event service): U.S. Geological Survey, Earthquake Hazards Program (2017). Advanced National Seismic System (ANSS) Comprehensive Catalog of Earthquake Events and Products. Accessed through the FDSN event web service. · doi:10.5066/F7MS3QZH · source page ↗
Licence : U.S. Government work, public domain; cite USGS ANSS ComCat · retrieved on Oct 25, 2026 · SHA-256 c9efda8729d3…
NCEI/WDS Global Historical Tsunami Database: National Geophysical Data Center / World Data Service: NCEI/WDS Global Historical Tsunami Database. NOAA National Centers for Environmental Information. · doi:10.7289/V5PN93H7 · source page ↗
Licence : U.S. Government work, public domain; cite NCEI/WDS · retrieved on Oct 25, 2026 · SHA-256 6955e2d6b325…
Okal (2011): Okal, E. A. (2011). Tsunamigenic earthquakes: past and present milestones. Pure and Applied Geophysics, 168(6–7), 969–995. · doi:10.1007/s00024-010-0215-9
Licence : Published literature; cited

Earthquakes and tsunamis Shallow and powerful: a tsunami becomes almost certain

What is linked, what is not

Share of earthquakes followed by a tsunami