[Island Chris]

There was a swarm of quakes along a WNW-ESE line offshore Honshu over the last week, with the largest M6.7 and a couple of other M6+. The two I checked were thrust, consistent with subduction. This may be along the north edge of the 2011 rupture? Today, there are scattered M4+ quakes farther south, including a M4.6 near Tokyo.

Chris

[Skywise]

(02-23-2015, 02:03 PM)Island Chris Wrote: There was a swarm of quakes along a WNW-ESE line offshore Honshu over the last week, with the largest M6.7 and a couple of other M6+. The two I checked were thrust, consistent with subduction. This may be along the north edge of the 2011 rupture? Today, there are scattered M4+ quakes farther south, including a M4.6 near Tokyo.

Chris

I never thought about it before, but do subduction zones experience progressive failure like transform faults? Like the North Anatolian?

Brian

[Island Chris]

Brian,

I don't see why not. If you break part of a continuous subduction zone, I would think the next part would have added shear stress; it would be slightly advanced towards failure. There were adjacent M8 subduction earthquakes in Japan in, I think, 1944 and 1946. Sumatra failed in December 2004 and then a part of the same subduction zone failed a few months later (March 2005?), just south of the Equator. I'm not sure if the two together ruptured adjacent parts or if there was an unbroken gap. There was at least one additional M8 in the Sumatra area south of the equator. This is all from memory, and my memory is not what it used to be.

On the other hand, if a subduction zone is 100 years from failure and you advance it 5 years, it is still 95 years to the quake. For the right-lateral North Anatolian fault, the only remaining seismic gap from 20th century quakes is in Marmara Sea off of Istanbul and west of there: it has now been 15 1/2 years and no quake. A paper was published in 2014 saying that the fault was creeping there, but I have my doubts.

Chris