AN EXTENDED GLOBAL CATALOGUE OF 'GIANT' (MW ≥ 8.8) EARTHQUAKES

‘Giant’ earthquakes, termed herein as those with a moment magnitude of Mw8.8 and higher, have significant, often devastating, regional impacts. Ground shaking from these earthquakes continues for several minutes over a large area as the rupture can extend for several hundred kilometres. The damage from ground shaking is often overshadowed, however, by the impact of sizeable tsunamis that typically accompany giant earthquakes. Most global catalogues of moderate to large earthquakes are considered complete only as far back as 1900AD: too short a period to gain a good appreciation of giant earthquake recurrence characteristics. This paper sets out to extend the global catalogue of giant earthquakes as far back as possible in time, as well as to estimate the extent of the rupture zone associated with each of these earthquakes and to infer their moment magnitudes. These estimates are based on a range of lines of evidence including: the regional extent of significant damage from strong shaking; the duration of shaking; the nearfield and far-field tsunami impacts, and the evidence of coseismic subsidence and/or uplift. The worldwide record of giant earthquakes is considered complete back to 1700AD since when there have been 18 earthquakes in this size range. The record is also considered largely complete (but potentially missing 20-30% of events, in regions with shorter written records), back to 1550AD, a baseline date reflecting the start of detailed written observations by Spanish colonists along the coasts of western South and Central America. Both in terms of the numbers of such earthquakes, and their seismic moment release, there appears to be a fairly consistent distribution of giant earthquake activity through time, with no suggestion in the active 18th Century for example, of any appearance of clustering, as has been proposed by some based on the temporal distribution of giant earthquakes seen since 1800AD.