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12-26-2014, 01:15 PM
Thanks Brian,
I will send this post to a couple of Earth scientists I work with, and then maybe to the whole group.
That M~9.2 subduction quake was in a place that many (most?) seismologists thought could not have subduction quakes. That followed Cascadia (USA Pacific northwest), where was thought to be creeping and incapable of a subduction quake until a geologist (Brian Atwater) and others started studying drowned forests. The Sumatra etc quake was followed by Tohoku Japan 2011 M9.0, where seismologists thought only M7.5 to 8.0 subduction quakes were possible, even though geologists (presumably) found tsunami deposits 5 km inland from 869(?) C.E.
(Note that my position is "Research Geologist", not "Research Geophysicist")
Now, there has been a paper published on the North Anatolia fault south through southwest of western Istanbul, proposing that this segment of the fault is also creeping, and that there have been no major quakes on it in the last 1000 years. This is Ergintav et al 2014, Geophysical Research Letter. I read it quickly in August and carefully last week. The paper does state that there could have been some strain accumulation. However, others who do not know enough about the offshore fault may take this to mean they don't have to invest tens of billions of $ equivalent (Lira) to retrofit or replace the numerous 10 story apartment building on less solid ground in west Istanbul. I did not spend the time to carefully re-read the Ambraseys etc series of papers about the locations and extent of historical earthquakes over the last 2000 years, to distinguish between their best estimate of historical epicenters vs. how much of the fault broke.
The lack of rupture vs. rupture over the last 1000 years and longer could probably be tested from an existing French piston core take right within the sea floor fault zone exactly in the deepest part of the bathymetric basin.
I'm not convinced that this segment of the North Anatolian fault is creeping at all. Or, maybe it is creeping in part, like the Hayward fault along the east side of San Francisco Bay, but is still dangerous (1868 earthquake). The reason the authors published creep is that GPS stations near the north coast of Marmara Sea average out to zero elastic strain accumulation. But, these stations are inconsistent with each other, and the fault is quite far offshore. It is possible that the south side of the fault is weaker than the north side, so the flexing is much smaller along the north side. Is complicated as usual.
Strangely, famous geologists and geophysicists insist on publishing that the faults on the Southern Shelf of Marmara Sea are dead (Sengor et al 2014, Le Pichon et al., 2013). Our group (which is now lead by Turkish scientists) have overwhelming evidence that they are active. We spent about 2 days in port in Gemlik, Turkey, in 2013. This City has about 100,000 people. The fault zone comes right through it.
I with others presented a poster by Seda Okay et al at the recent AGU meeting that displayed the southern faulting.
Chris
I will send this post to a couple of Earth scientists I work with, and then maybe to the whole group.
That M~9.2 subduction quake was in a place that many (most?) seismologists thought could not have subduction quakes. That followed Cascadia (USA Pacific northwest), where was thought to be creeping and incapable of a subduction quake until a geologist (Brian Atwater) and others started studying drowned forests. The Sumatra etc quake was followed by Tohoku Japan 2011 M9.0, where seismologists thought only M7.5 to 8.0 subduction quakes were possible, even though geologists (presumably) found tsunami deposits 5 km inland from 869(?) C.E.
(Note that my position is "Research Geologist", not "Research Geophysicist")
Now, there has been a paper published on the North Anatolia fault south through southwest of western Istanbul, proposing that this segment of the fault is also creeping, and that there have been no major quakes on it in the last 1000 years. This is Ergintav et al 2014, Geophysical Research Letter. I read it quickly in August and carefully last week. The paper does state that there could have been some strain accumulation. However, others who do not know enough about the offshore fault may take this to mean they don't have to invest tens of billions of $ equivalent (Lira) to retrofit or replace the numerous 10 story apartment building on less solid ground in west Istanbul. I did not spend the time to carefully re-read the Ambraseys etc series of papers about the locations and extent of historical earthquakes over the last 2000 years, to distinguish between their best estimate of historical epicenters vs. how much of the fault broke.
The lack of rupture vs. rupture over the last 1000 years and longer could probably be tested from an existing French piston core take right within the sea floor fault zone exactly in the deepest part of the bathymetric basin.
I'm not convinced that this segment of the North Anatolian fault is creeping at all. Or, maybe it is creeping in part, like the Hayward fault along the east side of San Francisco Bay, but is still dangerous (1868 earthquake). The reason the authors published creep is that GPS stations near the north coast of Marmara Sea average out to zero elastic strain accumulation. But, these stations are inconsistent with each other, and the fault is quite far offshore. It is possible that the south side of the fault is weaker than the north side, so the flexing is much smaller along the north side. Is complicated as usual.
Strangely, famous geologists and geophysicists insist on publishing that the faults on the Southern Shelf of Marmara Sea are dead (Sengor et al 2014, Le Pichon et al., 2013). Our group (which is now lead by Turkish scientists) have overwhelming evidence that they are active. We spent about 2 days in port in Gemlik, Turkey, in 2013. This City has about 100,000 people. The fault zone comes right through it.
I with others presented a poster by Seda Okay et al at the recent AGU meeting that displayed the southern faulting.
Chris