Sumatra Earthquakes 4/11 Updates

2 Massive earthquakes out of the Sumatra coast, Indonesia – 5 people killed and 7 injured (all of them indirect)

Most important Earthquake Data:
Magnitude : 8.6 (USGS)
UTC Time : Wednesday, April 11, 2012 at 08:38:30 UTC
Local time at epicenter : Wednesday, April 11, 2012 at 02:38:30 PM at epicenter
Depth (Hypocenter) : 22.9 km
Geo-location(s) :
495 km (308 miles) SW (219°) from Banda Aceh, Sumatra, Indonesia

Update 12/04 – 15:45 UTC
* 50 inmates from the Sigli state prison have not returned after the gates have been opened by the prison management. On the outside cries that the water was rising, state prison director decided to open the gate. It must have been done in chaos as only 13 of the 63 inmates have returned to the prison. The other 50 are on the run with the police coming after them.

– Update 12/04 – 09:56 UTC
* The Minister of Communications and Information Technology, Tifatul Sembiring, has obtained from telecommunication operators that disturbed communications on Sumatra will all be operational again in approx. 3 days
* Schools are not yet recovered of all the havoc and not yet fully operational today
* Minister of Communications and Information Technology, Tifatul Sembiring, reads our pages regularly we think, because he also said today that too many “speaking on the phone” are creating saturation of telecommunications traffic. Click here to read our in-depth reporting of this subject.

– Update 12/04 – 08:44 UTC
* Indonesian authorities have reported that 5 people have been killed by the earthquake on the island of Sumatra. 7 people have been reported injured (1 child is critically injured when she jumped in panic out of a tree). 3 people died of a heart attack. Massive earthquakes have a very emotional impact on Indonesians since in 2004 so many people were killed by a tsunami in the same area as yesterday’s earthquakes. The killed and injured reported so far are indirect fatalities which are related to the earthquake.
* The main airport of Simeulue island (island closest to the epicenter) was closed.  Simeulue had no power and communications were disturbed (unbelievable in terms ! – One should think that after the 2004 tsunami and devastating earthquake, authorities should have a viable system in place to at least reach strategic locations like the main Simeulue airport).
– Based on the injured and killed Sumatrans, this earthquake will be labeled CATDAT ORANGE

– On our Major daily earthquakes list from April 11, you can see an impressive list of aftershocks.  The list is especially long because we are publishing the data of EMSC, GFZ and USGS.

Update 21:55 UTC
The aftershocks are continuously hitting th sea floor. The image below shows the epicenters of the many aftershocks. The red square is the latest one and the square with a white arrow is the mainshock of 8.6. The area where the aftershocks have occurred is approx. 1000 square kilometer? Since the mainshock we have counted 31 M+5 aftershocks. We expect the aftershocks to gradually decrease in strength but at the same time we also expect some very strong ones to happen now and then. Let’s hope that the whole area (especially the Burma Plate and the Sumatra fault) will remain calm.

People in Banda Aceh running away from their location to higher grounds

Update 20:37
Indonesia is checking for damage and casualties but remarkably, no such reports had been received for several hours after the quakes, including in Aceh province, the closest province and the area decimated by the disaster eight years ago. Many people are frightened for further tremors. People want to stay alert because of the fear that more quakes are coming.

Update 18:51 UTC
The small wave caused $220,000 (2 billion rupiah) damage (estimated) to a bridge and a house. Damage to the bridge was in Bubon Arongan

Update 16:23 UTC
Also Indonesia has now lifted the tsunami alert.  We had to wait several minutes to reach the BMKG website, as we were ourselves victims of saturated servers,  we feel pity with the Indonesian seismologists.
Billions of dollars are paid to cover earthquake and tsunami insurances but some seed money to strengthen specialist sites like the seismological agencies and our site are seemingly too much for the insurance companies.  Saturated servers are a common problem for event driven websites like

Update 15:46 UTC
So why was this earthquake the largest non-damaging earthquake ever measured?
a) It occurred 400km+ offshore, thus the earthquake shaking only achieved a maximum intensity of around 5.5-6 in the closest points to land, causing no discernable damage.
b) the earthquake, unlike other major M8+ earthquakes, was a strike-slip earthquake, where plates slide past one another, and not upwards or downwards. Therefore, there was not much offset on either side of the fault and thus the water volume was not significantly displaced and therefore caused NO MAJOR TSUNAMI (highest was at Meulaboh with 1.05m)
c)13 other earthquakes over Mw8 since 1900 have caused no damage, however, the Mw8.6 was the highest by Mw0.4 (around 3 times the ground motion and 7 times more energy than ever before to cause no damage!!!!)
The Mw8.2 earthquake which occurred a couple of hours later was the 3rd largest earthquake recorded to cause no damage.

In one of the many experience reports, a person from Banda Aceh wrote : hard too remain standing, iMac in the office hopping madly all over the desk, people panicking and leaving the city because of tsunami warnings

– So far we there were 23 M5+ aftershocks after the mainshock. 2 of the aftershocks were even bigger than M6

Location of the aftershocks until 15:41 UTC – red blocks are the lastest ones, block with the white arrow in it is the location of the epicenter’s mainshock

Update 15:20 UTC
We got a message on our computer for Maldives touroperator IMPEX Holydays. The touroperator is telling his client travel agencies soon after the earthquake what the situation was at the Maldives. This is truly an ‘example of how today’s communication has to work. Congratulations to Impex Holidays.
“Dear All Partners,
Greetings from Maldives.
We wish to inform all our partners the situation in Maldives is calm although we slightly felt the 8.6 magnitude earth quake which hit Aceh, Indonesia this afternoon.
As of now, 1725 hrs local Maldives time the authorities have extended the tsunami alert time till 1930 hrs due to the second after shock quake.
All inhabited islands as well as the resort islands are on full alert, although sources have informed that the chances of a tsunami is unlikely.
e wish all tourists in Maldives well and pray that we will be safe.”

Update 13:57 UTC 
– A tsunami watch has been cancelled now for the entire Indian Ocean area

Earthquakes since 1900 over M8 that were non-damaging
Today’s 2 earthquakes of Mw8.6 and Mw8.2 are among the Top 13 strongest magnitude non-major damaging event earthquakes of the last 113 years in CATDAT
Mw8.1 – January 13, 2007 – Kuril Islands
Mw8.1 – December 23, 2004 – North of Macquarie Island
Mw8.1 – March 25, 1998 – Balleny Islands Region
Mw8.1 – May 23, 1989 – North of Macquarie Island
(Mw8.1 – January 10, 1971 – Very Minor damage to a church etc. – Papua, Indonesia)
Mw8.5 – October 13, 1963 – Kuril Islands (v. minor damage)
Mw8.2 – November 10, 1938 – Alaska
Mw8.0 – September 20, 1920 – Loyalty Islands Region
Mw8.0 – May 1, 1917 – Kermadec Islands, NZ
Mw8.0 – May 1, 1915 – Kuril Islands
Mw8.0 – January 4, 1903 – Tonga
Mw8.0 – 1902 – Sea of Okhotsk

– Meulaboh (Northern Sumatra)  has recorded waves up to 1.06m
– The second fault solution has been confirmed as a strike-slip  – meaning little chance of tsunami. Probably only minor given the slight dip.
This is the largest non-damaging earthquake for a long time of this magnitude.

– Below this page you will find a very big number of earthquake experience reports from our readers. We thank them all to share their experience with

– The epicenter of the earthquake is located about 100 km to the west of the subduction fault line in the Oceanic part of the Indian plate and not in the direct subduction zone of the plates. The subduction zone is far more dangerous than stress in the oceanic plate itself.  The actual greater area is the intersection in between the Indian Plate, the Australian plate and the Burma plate.

Image courtesy of Kerry Sieh, Tectonics Observatory, California Institute of Technology

– A NOAA employee just told CNN that the max. water level change which has been measured so far was 1 meter, which confirms our earlier expectation that due to the type of the 1th earthquake (strike/slip) the impact would be limited.

– We will still have to wait for the earthquake data of the second massive earthquake.  The mechanism (type of earthquake) is not necessarily the same for both earthquakes

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