Aftershocks May Portend Major Philippine Earthquake A diagram of
the Philippine Trench showing historic large earthquakes of
magnitude 7.0 or great, as well as the motions of tectonic
plates. CREDIT: Ye, et al./GRL Vol. 39 Aftershocks shook the
Philippines for more than two weeks after a magnitude-7.6 quake
rocked the region on Aug. 31, 2012. A team of seismologists
monitoring the aftershocks and plotting their whereabouts
noticed an odd pattern. "Typically, if you locate aftershocks
they sort of outline the fault that ruptures. This time they
didn't," said Thorne Lay, a geophysicist at the University of
California, Santa Cruz who was part of the team. "Instead they
were shallower and had very different fault geometries." The 7.6
quake happened at a fault within the Philippine Sea Plate, which
is subducting beneath the Philippine Microplate. Some of the
unusual aftershocks were so called "intraplate" ruptures, like
the original quake, but happened at a shallower depth. And
others of the unusual aftershocks we