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05-31-2015, 12:14 PM
Brian,
As you know the M7.4 (?) foreshock for the Tokoku quake was shallow and consistent with thrusting on the subduction zone. Well agreed on seismotectonics and logic would say that such a quake would advance the time of a quake on the adjoining parts of the same fault, which is what happened. The M7.8 very deep quake is nothing like this. It was a stretching focal mechanisms and USGS suggested it was within the subducting slab (as probably all major to great very deep quakes are).
But, I came on Earthwaves for this post because of a shallow M6.2 quake today on the other side of the trench from the M7.8. But if the M7.8 was within the subducting Pacific Plate, this one was also within the same plate. And this one was also normal. I don't know whether static stress changes from the M7.8 could have advanced / triggered the 6.2. They are distant enough in both depth and horizontal distance one would think the effect would be weak.
There are other ways to trigger an earthquake than static stress, as we have discussed here. That includes seismic wave shaking. My gut feeling is that there is something else going on that is not known or not understood. Back when John Vidale was posting and there were a bunch of large quakes in a few days on both sides of Baja California, he, and us, brought up strain transients.
Brian, I know you know most or all of this, but others, including lurkers, may not.
Hey Duffy, one would wonder about your anomaly a few days before, but it seems really unlikely that such a deep 7.8 could affect the ionosphere in advance.
Chris
As you know the M7.4 (?) foreshock for the Tokoku quake was shallow and consistent with thrusting on the subduction zone. Well agreed on seismotectonics and logic would say that such a quake would advance the time of a quake on the adjoining parts of the same fault, which is what happened. The M7.8 very deep quake is nothing like this. It was a stretching focal mechanisms and USGS suggested it was within the subducting slab (as probably all major to great very deep quakes are).
But, I came on Earthwaves for this post because of a shallow M6.2 quake today on the other side of the trench from the M7.8. But if the M7.8 was within the subducting Pacific Plate, this one was also within the same plate. And this one was also normal. I don't know whether static stress changes from the M7.8 could have advanced / triggered the 6.2. They are distant enough in both depth and horizontal distance one would think the effect would be weak.
There are other ways to trigger an earthquake than static stress, as we have discussed here. That includes seismic wave shaking. My gut feeling is that there is something else going on that is not known or not understood. Back when John Vidale was posting and there were a bunch of large quakes in a few days on both sides of Baja California, he, and us, brought up strain transients.
Brian, I know you know most or all of this, but others, including lurkers, may not.
Hey Duffy, one would wonder about your anomaly a few days before, but it seems really unlikely that such a deep 7.8 could affect the ionosphere in advance.
Chris