I awoke this morning to news paper headlines of “Large quake rocks Tokyo” and people telling me there was a big quake in Tokyo. So I was alarmed and quickly went to the tsunami warning center and started looking at headlines and then data.
To my surprise there was no tsunami and no great damage to Tokyo but when I read the first summary of the quake I could see why. The quake was nowhere near Tokyo and was at great depths.
The quake was 400+ km from Tokyo to the south west where there is a deep trench that extends from the same fault zone that had the 9.0 quake last year. This quake was to the west of this trench in the crustal material that was subducted by that trench and was 348 km below the surface of the crust. At that depth the part that fractured in the quake has no direct connection to the surface except through the plastic like upper mantle. This really dampens the wave and spreads it out so there was nothing destructive at the surface. People in Tokyo who were walking didn’t notice the quake.
The quake is interesting because of where it happened, the deep tench (not the Mariana Trench but connected to it) and the mechanism for the it happening and what t can tell us about the semi liquid mantle. As far as headline worthy quakes though the one that just happened in Christchurch is scarier.
- Tonga to New Zealand earthquake zone (echlinm.wordpress.com)
- Yet another 5.0 in Christchurch NZ (echlinm.wordpress.com)