Geology Blogging -Athens Earthquake
Image Courtesy USGS earthquake hazards programme
A while ago I posted a long-ish piece about the after-effects of the Aceh incident, the visible spreading of the Great Rift Valley, , and that future seismic activity resulting from the stress placed on the tripartite plate junction there was possible . Following recent seismic activity in Bam, Iran it seems that the stress is being also communicated to the Aegean:
? 2006 The Associated Press
ATHENS, Greece ? An undersea earthquake with a magnitude of at least 6.7 shook Greece on Sunday and was felt as far away as Egypt and Jordan, officials said.
The quake struck at 1.34 p.m. local time (6:34 a.m. EST) was centered near the island of Kythira, about 125 miles south of Athens, the Athens Geodynamic Institute said.
Three people were slightly injured, and Kythira’s airport and buildings in the southern island of Crete suffered minor damage, authorities said.
The Athens Geodynamic Institute said the magnitude was 6.9, while the U.S Geological Survey said it measured 6.7
Map of the Agean basin showing faults
Image Credit , Francois Rosselet, Institut de G?ologie et Pal?ontologie Section des Sciences de la Terre
“The Mediterranean basin and the surrounding area constitute the most western portion of the Alpine-Himalayan chain, which is a complex collision system originated by the interaction between the Euro-Asiatic, African, Arabian, and Indian plates. This system includes also from W to E the Pyrenees, Alps, Maghrebs, Apennines, Dinarids, Ellenides, Carpathians, Balkans, Pontides and Taurides chains as well as the Caucasus and to the E the Himalayan chain”
“The Ellenic arc is generated by the active subduction of the oceanic lithosphere in the east Mediterranean with a NE-SW direction. It is a very small and bent arc with a slab subducting at a low angle (about 30?), which can be inferred from the fact that the seismicity prevails at intermediate depths rather than deep. The arc separates the southern Mediterranean, about 3 km deep and which is undeformed, from the Aegean sea that has a notably complex structure. At the centre of the Aegean sea there is a series of volcanic systems almost parallel to the trench and forming the internal arc (Milos, Antimilos, Antiparos, Santorini, Kos, Yali, Nisiros, etc) (Le Pichon & Angelier 1979 – Taymaz et al, 1991) (figure 11). Its northwest termination occurs at the latitude of the Ionian islands while the eastern one, which is particularly argued, was described before (v. East Anatolian-Cipro?s arc ? Dead Sea fault)”
Kythira has historically been the site of much strong seismic activity. There was a 5.9 event on November 5 2004 and a much more devstating earthquake in the region in 1953.
More in-depth reading is available via Greece’s Insitute of Geodynamics website.
(On a more personal note – as I was jumping up and down shouting ‘I was right, I was right!” on hearing of the Aegean earthquake, I was sharply reminded by Martin that there are real people on the end of earthquakes. Luckily there weren’t very many this time, but i will in future try to be a little less heartless.)
Update On Kashmir:
Kashmir could ‘face more quakes’
By Aamer Ahmed Khan
BBC News, Manshera
The recent quake ruptured a 100km length of Kashmir
One of the world’s leading seismologists has warned of the possibility of more earthquakes in the Kashmir region over the next 50 years.Roger Bilham told the BBC News website that Kashmir could experience quakes more severe than the one which killed more than 73,000 people in October.
Mr Bilham has been working in quake-affected areas of Pakistan for the past two months. He is considered an authority on the Himalayan faultline.
Mr Bilham said his research, using data stretching back 500 years, had shown that huge amounts of energy had been stored in the faultline but it was unevenly distributed.
“This meant that when (the tectonic plates) do go, they are very likely to go with a very large earthquake,” he said.
“Our study basically showed that there were four places that could have a magnitude 8.2 earthquake or more.
“It also showed that the Kashmir region could have something like a magnitude eight earthquake.”
Mr Bilham said the 8 October earthquake occurred at the very end of what he called the Himalayan tectonics.
From what we know of Kashmir’s history, there may well be a sequence of earthquakes spread over the next 50 years.
“What we know is that it ruptured a 100km length of the Kashmir region, diagonally from the north-west to the south-east.
“Also, it ruptured from very close to the surface down to a depth of 30-40km.”
One can get idea of the extent of the havoc wreaked below the surface by the fact that the Himalayas slipped about three to four metres within about 15 seconds.
The mountains behind Muzaffarabad, around the epicentre, actually rose by about a metre, releasing an energy equivalent of a 30 megaton nuclear explosion.
These figures, if juxtaposed with historical data, paint a worrying picture.
[…]
According to Mr Bilham, the north-west tip of the rupture which extends to “the mountains behind Muzaffarabad” has recorded the expected number of aftershocks.
Bilham has been working in the quake-hit areas for the past two months.
But the south-eastern tip of the rupture, which extends to the plains below the Himalayas, has shown “a surprising and worrying calm”.
“This means that pressure is building up around the south-eastern tip,” he said.
In other words, it means that should the faultline slip in the south-east, the shockwave is very likely to travel towards the plains of Punjab – possibility extending down to the historic city of Lahore. ” ( All emphasis mine)
