TITLE:
Decadal Seismicity Prior to Great Earthquakes at Subduction Zones: Roles of Major Asperities and Low-Coupling Zones
AUTHORS:
Lynn R. Sykes
KEYWORDS:
Earthquakes, Subduction, Prediction, Plate Coupling, Asperities
JOURNAL NAME:
International Journal of Geosciences,
Vol.12 No.9,
September
30,
2021
ABSTRACT: Decadal forerunning seismic activity of magnitude Mw ≥ 5.0 is mapped for
all 45 mainshocks of Mw 7.7 to 9.1 at subduction zones of the world from 1993
to mid 2020. The zones of high slip in nearly all great earthquakes were nearly
quiescent beforehand and are identified as the sites of great asperities and
zones of strong seismic coupling. Much forerunning activity occurred at smaller
asperities along the peripheries of the rupture zones of many great and giant
mainshocks. Those sizes of great asperities as ascertained from forerunning
activity generally agree with the areas of high seismic slip as determined by
others from geodetic and tide-gauge data and finite-source seismic modeling.
Asperities are strong, well-coupled portions of plate interfaces. Different
patterns of forerunning activity on time scales of about 5 to 45 years are
attributed to either the sizes and spacing of asperities (or lack of). This
permits many great asperities to be mapped decades before they rupture in great
and giant shocks. Several poorly coupled subduction zones such as Java, Lesser
Sunda, Marianas, Tonga and Kermadec are characterized by few great thrust
earthquakes and little, in any forerunning activity. Rupture zones of many
great and giant earthquakes are bordered either along strike, updip, or downdip
by zones of lower plate coupling. Several bordering regions were sites of
forerunning activity, aftershocks, and slow-slip events. The detection of
forerunning and precursory activities of various kinds should be sought on the
peripheries of great asperities as well as within zones of high co-seismic
slip.