Seismic Storm
last updated 23 April 2024
A well-known, but not well documented phenomenon in seismology is temporal clustering of stronger earthquakes, typically magnitude ≥ 5.6. Unlike earthquake swarms of small to moderate earthquakes in a specific region, temporal but not spacial clustering happens relatively often, when stronger earthquakes occur at various places across the planet in a short time. Here we present examples to demonstrate and categorize this phenomenon.
While averages are often presented to indicate earthquake occurrence per category, e.g. a magnitude ≥ 6 earthquake per 2.7 days, in reality stronger earthquakes usually do not occur on average, but rather in a temporal cluster fashion. One obvious example is the occurrence of five magnitude ≥ 7 earthquakes in four days — from 11 to 14 August 2021:
2021-08-14 12:29:09 7.2 HAITI REGION
2021-08-14 11:57:42 7.0 ALASKA PENINSULA
2021-08-12 18:35:20 8.1 SOUTH SANDWICH ISLANDS REGION
2021-08-12 18:32:55 7.5 SOUTH SANDWICH ISLANDS REGION
2021-08-11 17:46:13 7.1 MINDANAO, PHILIPPINES
This temporal cluster of major earthquakes occurred after a convergence of specific planetary geometry on 9-10 August 2021, that was addressed as early as 6 (see here) and 8 (see here) August. Average occurrence of magnitude ≥ 7 earthquakes is 20-24 days. Obviously this is not what happens in reality; absence of magnitude ≥ 7 earthquakes has been observed for up to 175 days, such as in the first half of 2017, or the total absence of magnitude ≥ 6.5 earthquakes during May, June and July 2018, while average occurrence of this earthquake category is about 10 days. A similar and related phenomenon is the occurrence of multiple major (M ≥ 7.5) earthquakes in a relatively short times, such as in December 2016:
2016-12-25 14:22:26 7.6 ISLA CHILOE, LOS LAGOS, CHILE
2016-12-21 00:17:17 6.7 KEPULAUAN BARAT DAYA, INDONESIA
2016-12-17 10:51:09 7.9 NEW IRELAND REGION, P.N.G.
2016-12-08 17:38:46 7.8 SOLOMON ISLANDS
2016-12-08 14:49:46 6.7 OFF COAST OF NORTHERN CALIFORNIA
2016-12-06 22:03:33 6.5 NORTHERN SUMATRA, INDONESIA
Average occurrence of these major earthquakes is about 3-4 per year. Without observation of planetary and lunar geometry temporal clustering of stronger earthquakes and seismic storm in particular, when temporal clustering is intense during several days, cannot be well explained.
Since 2023 we closely monitor temporal clustering of earthquakes with magnitude ≥ 5.6, as they appear to be related to specific planetary and lunar geometry. While earthquakes with magnitudes between 5.6 and 6.2 occur frequently on average, they actually tend to occur in temporal clusters. We categorize 'minimal' clustering, 'obvious' clustering and 'severe' clustering or seismic storm. Recent examples are provided below.
SSGI common, 7-16 August 2021: severe seismic storm
SSGI common, 19-27 January 2023: obvious clustering
SSGI common, 3-12 September 2023: obvious clustering, small seismic storm
SSGI common, 8-17 October 2023: obvious clustering
SSGI common, 2-11 April 2024: seismic storm, minimal clustering