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Note concerning possible mechanisms for non‐double‐couple earthquake sources
Author(s) -
Frohlich Cliff,
Riedesel Mark A.,
Apperson K. Denise
Publication year - 1989
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl016i006p00523
Subject(s) - geology , seismology , slip (aerodynamics) , slab , planar , geometry , fault (geology) , geophysics , physics , computer graphics (images) , mathematics , computer science , thermodynamics
Some earthquake sources are not double couples, i.e , they are not due solely to slip along a simple, planar fault surface. One possible explanation for such sources is that they occur because of source complexity, namely, they consist of simultaneous or time‐separated double‐couple subevents along different fault surfaces. For intermediate depth earthquakes consisting of only two subevents, we illustrate how non‐double‐couple earthquakes might occur (1) near the edges of subducting lithospheric slabs; or (2) in the interior of a slab if an earthquake with a downdip P (or T) axis triggers a “bending” subevent along the inside (outside) of the slab. We can choose between an edge, inside‐bending or outside‐bending interpretation by comparing the downdip direction of the Wadati‐Benioff zone and the orientation of the moment tensor axes. While slip along a curved fault surface can produce a non‐double‐couple source, this can occur only for a limited class of slip and fault geometries. Non‐double‐couple sources can never be produced by double‐couple subevents if (1) the subevents occur along parallel fault planes; (2) the subevents occur on a cylindrical fault surface, with slip due to rotation about the cylinder axis; or (3) the subevents occur on a cylindrical fault surface, with slip parallel to the axis.