| Popis: |
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. |
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