There was a M6.9 a bit more than a day ago on the North Aegean Trough, which is formed by the north Branch of the North Anatolian fault, which is the same fault as the one that passes about 15 km south of Istanbul, a few hundred km to the east. I left Rhode Island for the first time in 6 months to visit family in Philadelphia, so was not in home office, looked at focal mechanism, and then flipped it in my brain and sent email to some scientists that I work with on this fault and said it was left-lateral, a backwards earthquake, which makes not sense for one that large. So, I had to send a later email to correct that before they thought I was too clueless. The part of that fault branch to the east, from eastern Saros Gulf across the connection of Gallipoli peninsula, last had a deadly earthquake in 1912. A paper published a couple months ago (I am a co-author, but disagree with certain things) suggests the next part east, in Central Basin Marmara Sea, has not had a major quake for 700 or 800 years. That is very long for a fault accumulating strain at ~18 mm/yr.
Odd, I thought I made another post yesterday here. Maybe I previewed it but did not post it. Anyhow, the link brings up the last 7 days of quakes for Turkey, The quake and aftershocks are at upper left, and you can click on a quake there and it zooms in. I am making a figure to post. The aftershocks form a 100 km-long zone along the north branch of the North Anatolian fault.
05-27-2014, 04:27 PM (This post was last modified: 05-27-2014, 04:42 PM by Island Chris.)
Hi all,
Making this graphic took several hours, and I had to be a bit careful to give credit, thus all the references. The red dots with numbers are epicenters and AD=CE years (this year being 2014). I did this compilation for the McHugh et al paper but they chose not to use this type of figure (so is my figure). This work did not include Saros Gulf, where the May ~24 2014 M6.9 right-lateral earthquake propagated into. So, unlikely that the last M6.8+ earthquake there was in year 468. If people ask, I will check.
OK, let's see if I can get the .jpg:
Chris
OK, checked Ambraseys 2002 and Meghraoui et al., 2012.
Ambraseys puts M6.8 and larger epicenters near the mouth of Saros Gulf for 1859 and 1893, and within Saros Gulf (east end of the aftershock on the figure I posted) in 484, 1625, and 1659. Meghraoui et al 2012 Fig. 14 have the 1776B and 1912 earthquakes (and others) rupture pretty far west into Saros Gulf. The point of these posts are partly to look at the earthquake history because the M6.9 quake of the other day will presumably advance the occurrence of the next similar quake both to the east and west of the recent rupture. The history includes large earthquakes in the same year (1766, and 1999 East of Marmara Sea), and on the same day (1343).
Another credit for the graphic: The figure was made with IHS-Kingdom Suite software. I appreciate the donation of this software by IHS-Global to University of California, Santa Barbara.
(05-28-2014, 11:21 AM)Island Chris Wrote: Another credit for the graphic: The figure was made with IHS-Kingdom Suite software. I appreciate the donation of this software by IHS-Global to University of California, Santa Barbara.
Chris
I was gonna ask what was used. Very informative. Also the link to the Turkey quake map.
Is it just me, or do the aftershocks appear to be to the right (east) of the epicenter? Perhaps indicating the direction of slip and resultant change in the static stress field?
Instanbul's got it coming in from both ends. Hopefully it won't happen until after they get their act together re building codes etc....
Yes, looks like the propagation of the quake was from west to east. Propagation affects the ground motion: the ground motion is stronger in the direction of propagation, in this case to the east. But, I doubt propagation direction is related to static stress changes. That is more likely related just to slip, including how much slip.
I'd say the big question is whether the segment east of this recent rupture is close to failure, after it broke in 1912. Also, how far a rupture might propagate once it got started. If Holocene (last 11,000 years or so) and GPS geodetic strain accumulation is between 15 and 20 mm/yr, as has been published, then that is 1 1/2 to 2 m of strain accumulation. But, "slip predictable" does not work on some faults, as shown by Weldon and others for the San Andreas at Wrightwood, where there is clustering in time. And, such clustering has been suggested by McHugh and others 2014, for the North Anatolian fault in Central basin of Marmara Sea (reference on the figure).
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