Computer Science
Scientific paper
Sep 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004eostr..85..339l&link_type=abstract
EOS Transactions, AGU, Volume 85, Issue 36, p. 339-340
Computer Science
11
Geodesy And Gravity: Crustal Movements-Interplate (8155), Seismology: Earthquake Dynamics And Mechanics, Forum
Scientific paper
Kelin Wang and Timothy Dixon (Eos, 85(18), 4 May 2004, p. 180) thoughtfully advocate paying close attention to semantics in descriptions of fault zone properties and kinematics, an increasingly important issue given the distinct usages of terms such as ``coupling'' by separate disciplines involved in the multidisciplinary study of earthquake faulting. We are in full accord with their advocacy of unambiguous language, such as the description of a nonsliding fault segment as being ``not slipping'' rather than ``strongly coupled'' in the absence of any information about the frictional or stress state of that segment. While several of Wang and Dixon's recommended ``simple expressions'' have clear merits, we feel that their advocacy of ``locked'' to equate to ``not slipping'' is not an improvement, and that their accompanying illustration of dislocation models of subduction zone megathrusts is potentially misleading. Wang and Dixon critique a simple, one-dimensional dislocation model for an interplate thrust event, for which conventional thinking is that the principle seismogenic zone is not sliding between earthquake ruptures but that there is steady sliding occurring along the shallow and deep extensions of the thrust plane. These stable sliding portions of the fault plane are assumed to be regions of velocity-strengthening frictional conditions; they accommodate relative plate motions without earthquake failure, although portions may be conditionally stable, driven to failure by the high strain rates (large changes in slip velocity) that accompany rupture of the main seismogenic zone. Wang and Dixon argue that this model is ``incorrect'' and that the updip region is not slipping steadily, and should be viewed as ``locked,'' along with the unstable sliding region. They invoke an analogy involving a book on a level table with no shear stress being applied; and it is correctly asserted that this stable equilibrium state does not allow strength or nature of frictional coupling to be deduced. However, this analogy seems irrelevant to the situation of interplate thrust faults, which are not in a state of stable equilibrium and are being continuously loaded by forces associated with slab-pull, ridge-push, and lateral loading by slip of adjacent segments both along the strike and dip of the megathrust.
Lay Thorne
Schwartz Susan Y.
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