Subducting Slab Ultra-Slow Velocity Layer Coincident with Silent Earthquakes in Southern Mexico
Teh-Ru Alex Song,1,*
Donald. V. Helmberger,2
Michael R. Brudzinski,3
Robert W. Clayton,2
Paul Davis,4
Xyoli Pérez-Campos,5
Shri K. Singh5
Great earthquakes have repeatedly occurred on the plate interface
in a few shallow-dipping subduction zones where the subducting
and overriding plates are strongly locked. Silent earthquakes
(or slow slip events) were recently discovered at the down-dip
extension of the locked zone and interact with the earthquake
cycle. Here, we show that locally observed converted
SP arrivals
and teleseismic underside reflections that sample the top of
the subducting plate in southern Mexico reveal that the ultra-slow
velocity layer (USL) varies spatially (3 to 5 kilometers, with
an
S-wave velocity of ~2.0 to 2.7 kilometers per second). Most
slow slip patches coincide with the presence of the USL, and
they are bounded by the absence of the USL. The extent of the
USL delineates the zone of transitional frictional behavior.
2 Seismological Laboratory, Division of Geological and Planetary Science, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA.
3 Department of Geology, Miami University, 114 Shideler Hall, Oxford, OH 45056, USA.
4 Department of Earth and Space Sciences, Center of Embedded Network Systems (CENS), University of California, Los Angeles (UCLA), 595 Charles Young Drive East, Los Angeles, CA 90095–1567, USA.
5 Instituto de Geofísica, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica s/n, Ciudad Universitaria, D.F. 04510 Distrito Federal, México.
* To whom correspondence should be addressed. E-mail: asong{at}ciw.edu
