The asperity model and the nature of large subduction zone earthquakes.

Abstract

Regional variations in the rupture characteristics of large shallow earthquakes
\nin circum-Pacific subduction zones are interpreted in the context of the asperity model of
\nheterogeneous stress distribution on the fault plane. It is assumed that the degree of
\nseismic coupling between the downgoing and overriding plates is reflected in the maximum
\nearthquake rupture dimensions in each region, and that gross features of the regional
\nstress distribution can be inferred from the rupture process of large earthquakes. The
\nresults of numerous studies of the historic record and detailed source process of large
\nsubduction zone events are summarized for each region. The systematic variation in
\nmaximum rupture extent in different zones indicates that four fundamental categories of
\nbehavior are observed. These are (1) the Chile-type regular occurrence of great ruptures
\nspanning more than 500 km; (2) the Aleutian-type variation in rupture extent with
\noccasional ruptures reaching 500 km in length, and temporal clustering of large events; (3)
\nthe Kurile-type repeated failure over a limited zone of 100-300 km in length in isolated
\nevents; and (4) the Marianas-type absence of large ruptures. The rupture processes
\nassociated with each category have distinctive features. The great earthquakes of category
\n(1), such as the 1964 Alaskan event, are often preceded by a prolonged period of increased
\nseismicity, and the body wave source process is characterized by a long duration (~ 120
\nsec) time function. The earthquakes in category (2) are usually preceded by seismic
\nquiescence and may occur as doublets or multiplets. The body wave source time functions
\nof these events tend to consist of several long duration (30 to 60 sec) discrete ruptures.
\nCategory (3) events commonly have a precursory quiescence followed by extensive
\nforeshock activity, and the body waves are complicated since they result from a sequence
\nof short duration (< 30 sec) ruptures. Interpreting these features with the asperity model
\nindicates that the stress distribution in categories 1,2,3, and 4 are characterized by very
\nlarge asperities and strong coupling, large but discrete asperities, numerous smaller
\nasperities, and an absence of significant asperities, and large component of aseismic slip,
\nrespectively.