Indonesia massive M 7.5 earthquake - Hardest hit : Mentawai Islands

Topographic map of Mentawai Islands, Indonesia...

North and South Pagai - Image via Wikipedia

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16:20 UTC UPDATE :
No news from the islands which where the most hit so far. We maintain our RED earthquake level as we predict that the shaking would have been very strong on South Pagai. Luckily, this island is scarcely populated. The lack of modern cities with stone and concrete buildings can be the fortunate element in this massive earthquakes. As far as we can see, most villages on the islands are rather primitive and have wooden houses.  Lets hope that this earthquake will not come in our extensive list of  "deadly earthquakes".

16:04 UTC UPDATE :
2 Aftershocks measuring M 5.2 have hit the same greater epicenter area. We expect that many more aftershocks will hit the same area the coming hours, days and even weeks

As expected by,  the Indonesian government  has lifted the tsunami alarm quite soon. All simulations gave only limited tsunami waves on nearby islands which have been reached soon after the first very heavy shock.

We will have to anxiously wait until reports from the islands are coming in.
Pagai island will have experienced a STRONG to VERY STRONG shaking of VII to VIII Modified Mercalli.
USGS has no demographic data on Pagai.
Sumatra mainland will be escaping the heaviest shocks of this earthquake as only IV will be experienced in the nearest towns of the island. Padang with 840,000 inhabitants and Bengkulu with 310,000 inhabitants will be rather safe.
Following the demographic data from GDACS it is expected that 1,817 people live in an radius of 50 km around the epicenter. 23,877 in a radius of 100 km and 413,617 in a radius of 200 km. This data is preliminary as the exact location of the epicenter has still to be calculated.
Pagai is part of the Mentawai Islands. All Mentawai Islands had a sensus count of 38,300 inhabitants.

The Mentawai Islands are a chain of about seventy islands and islets off the western coast of Sumatra in Indonesia. Siberut (4,030 km²) is the largest of the islands. The other major islands are Sipura, North Pagai (Pagai Utara) and South Pagai (Pagai Selatan). The islands lie approximately 150 km off the Sumatran coast, across the Mentawai Strait. The indigenous inhabitants of the islands are known as the Mentawai people. The Mentawai Islands have become a noted destination for surfing. (Source Wikipedia)

Origin of the earthquakes
The Mentawai Islands lie above tha Sunda megathrust, a seismically active zone responsible for many great earthquakes. This megathrust runs along the southwestern side of Sumatra island, forming the interface between the Eurasian Plate and Indo-Australian Plate.
Earthquake and tsunami activity has been high since the 2004 Indian Ocean earthquake.
In 1833, the region was hit with an earthquake possibly similar in size to the 2004 Indian Ocean Earthquake[2] and also another large one in 1797.

Most important Earthquake Data:
Magnitude : 7.5
Monday, October 25, 2010 at 09:42:25 PM at epicenter
Depth (Hypocenter) : 33 km
Geo-location(s) :
240 km (149 miles) S (184°) from Padang, Sumatra, Indonesia
Near the shores of the island of Pagai (part of the Mentawai Islands)

Links to important maps
USGS Did You Feel It Map
Google satellite map of the area showing the kind of terrain the earthquake took place
USGS Shaking map
USGS historic earthquakes map
USGS Pager map
GDACS Green Earthquake Alert (Global Disaster Alert and Coordination System)
GDACS Green Tsunami alert
Nearest LIVE seismograph in Papua New Guinea

* GDACS (Global Disaster Alert and Coordination System) provides near real-time alerts about natural disasters around the world. GDACS is a Joint Initiative of the United Nations and the European Commission

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