The following is my opinion as a member participating in this discussion.
Originally posted by MamaJ
reply to post by JustMike
Good morning Mike! I'm just getting done with my first cup of coffee and it seems as if Cali is still ok, never the less still a lot of activity over
there including the off shore big one.
Earthquake Report is reporting the off shore quake was coming in so conflicted, even with tsunami info because the quake happened on the oceanic plate
and not the North American plate.
Do you mind explaining this in detail for me.
looking at the reports on the Earthquake-Report website
, I can follow what they're talking about in terms of
It seems that there was some delay in reports coming in from the near-regional networks and this puzzled the E-R people because at the strength they
were noting from sites like USGS, it seemed amazing that local people didn't feel it and log on in large numbers to get more info.
The reason they allegedly didn't feel it (much) was because the quake was supposedly not on the plate that
part of the Sth American land mass
sits on, but rather:
...the hypocenter of the earthquake was located in the oceanic plate and not in the North American plate. This event was in
other words an intra-plate event and not a subduction earthquake like most of the earthquakes are in the area.
If the quake did in fact occur intra-plate on the oceanic plate (ie away from an edge of it), then its effects on people on land (and
another plate) would be far less than if it were on a subduction zone boundary -- meaning on or near the edges between two colliding plates where one
edge is pushing down under the other.
So, their explanation makes sense. However, they later posted another update:
USGS has located the epicenter of all events in the subduction zone below the continental plate while snet was putting it more into the
(Both of the above quotes from Earthquake-Report.com at the link given above.)
The current map from USGS shows that they do, indeed, have the quake located on the "land" plate and in the subduction zone:
Source: USGS at this link
(Note that this map will change over
Problem: if the USGS has the quake in the right place -- namely on a subduction zone boundary and
on the same plate as the nearest land is on
-- then why didn't many people feel it at all?
I suspect that the E-R people were right: it's possible the quake was not so close to a subduction zone boundary and was perhaps further west of
where USGS has it. If this is the case it would explain the very limited effects on the nearby regions. And yes, even USGS can get things slightly
wrong. No-one's infallible in the seismic sciences, after all.
Also, do you think it's possible this is volcanic related, I know we were throwing the idea around yesterday and TA made a thread, but it
seems likely to me even more this morning. It's just soooo active and California is basically a huge volcanic state, is it not?? Advise me please.
Volcanic related? Jenn, I have no idea, really. I've mentioned that there could be volcanic influences in some quakes which otherwise seem
"normally" tectonic, but without detailed analyses of seismo traces (wave forms) we're in the dark on this score.
As for Cali, yes, it's volcanic and besides the ongoing hot springs and so forth, there's the Long Valley Caldera and other evidence of much greater
volcanism in the past.
Considering the theory that the Pacific plate is colliding with the Nth America plate all along the western side of the continent, and also that this
action is believed to have partly formed the Cascades and its volcanoes (but not Long Valley), then major movement of the Pacific plate (and related
subduction) could lead to volcanic activity. That's not my opinion, just what I've gleaned from reading reports from those who study these things.
However that doesn't mean that anything cataclysmic is imminent.
These changes have been going on for millions of years and what we've observed
"live" is not even an eyeblink. Geological records suggest that things have not fizzled out completely yet, though.
Best regards and sorry for the lonng reply!
As an ATS Staff Member, I will not moderate in threads such as this where I have participated as a member.