Indonesia Earthquake 1/10

Massive earthquake out of the coast of Northern Sumatra, Indonesia – Tsunami alert lifted

Last update: January 11, 2012 at 8:22 am by By 

January 10, 2012 By 

Earthquake overview : A massive earthquake occurred several hundred km out of the Sumatra Banda Aceh coast. Theoretical calculations concluded that no widespread tsunami would occur in the Pacific Ocean. Indonesian authorities have however called a tsunami alert for many areas in Sumatra.

WISE TSUNAMI ADVICE in case you are living or traveling to an earthquake rich area of the world and are residing close to the coast :  EVACUATE IMMEDIATELY TO HIGHER GROUNDS (10 to 30 meters higher than sea level) IF :

– strong shaking goes on for 30 seconds or longer
– the authorities are calling for an evacuation
– you see a fast unusual retreating sea

Triggers of today’s massive earthquake :
The January 10, 2012 earthquake off the west coast of northern Sumatra, Indonesia, occurred as a result of strike-slip faulting within the oceanic lithosphere of the Indo-Australia plate, approximately 100 km to the southwest of the major subduction zone that defines the plate boundary between the Indo-Australia and Sunda plates offshore Sumatra. At the location of this earthquake, the Indo-Australia plate moves north-northeast with respect to the Sunda plate at a velocity of approximately 52 mm/yr.
While they are rare, large strike-slip earthquakes are not unprecedented in this region of the Indo-Australian plate. Since the massive M 9.1 earthquake that ruptured a 1300 km long segment of the Sumatran megathrust plate boundary in December of 2004, two Mw 6.2 strike-slip events have occurred within 50 km of the January 10 2012 event, on April 19 2006, and October 4 2007. These events seem to align with fabric of the sea floor in the diffuse boundary zone between the Indian and Australian plates. (summary as described by USGS)

Update : At midnight UTC,  4 aftershocks ranging from 4.8 to 4.9 have been listed by USGS.

Update : The tsunami alert was maintained longer at Simeulue  island (Aceh province) as this island was closest to the epicenter. Although Simeulue was not indicated as a place at risk by the GDACS simulation, authorities do not want to take any risk.

Important update : Indonesian authorities have lifted the earlier called Tsunami alert. People in Banda Aceh reported a retreating sea after the earthquake occurred, just like it happened in 2004 during the devastating tsunami who killed more than 200,000 people.  Luckily no reports about any serious waves so far.

Update : We know from earlier experiences in Indonesia that local people often do not trust the authoritiesand remain in safe locations even if the authorities ask them to return to their house and pick up their daily life. Additionally, rumors are often spread that an even heavier earthquake and tsunami will be triggered. Rumors are one of the major problems after earthquakes.

Update : Indonesian media are reporting that BMKG, the local Indonesian seismological agency, has lowered the magnitude from 7.6 to 7.1. BMKG triggered an early warning tsunami alert to the local agencies. BMKG received reports that people fled their houses almost automatically for a safe location. No reports as yet from the real wave heights. People have been asked to stay in the safe places for a longer time and not to return to heir houses to soon.

Update : A lot of panic amongst the Sumatra population when they felt the earthquake and when the tsunami sirens went off.

Red bullets are indicating Tsunami alert from the Indonesian authorities

Update : MetroTV Indonesia is one of the only channels reporting on the earthquake and potential tsunami risk. The image at right shows where the Indonesian authorities have called a tsunami alarm for the coastal areas.

Update : Based on the GDACS data, the time that the waves may have reached Simeulue and Northern Sumatra is over now.  We expect final experience reports soon.

Update : We still cannot reach BMKG, the Indonesian seismological agency via the Internet due to too heavy demand.  This happened also in the USA during the Virginia earthquake (USGS).

Update : If all theoretical data will be confirmed, this was a LUCKY ESCAPE, but this earthquake will have send vibrations of fear through the population of Northern Sumatra.

Update : The GDCAS image below shows very well the propagation of the tsunami wave from the epicenter versus the northern part of Sumatra, including Banda Aceh.  GDACS has calculated based on historical earthquakes and lots of additional data, that the waves in Northern Sumatra will be max. 0.4 meter

Tsunami wave distribution and height – Image courtesy GDACS

Update : Indonesian media are currently reporting a SR magnitude of 7.6
TSUNAMI ALERT has been called by the local BMKG for parts of the country (unclear at this moment, but certainly the islands and Sumatra, including Banda Aceh). Our experience is that people in Indonesia are mostly not waiting for an alert but are auto-evacuating when a strong shaking for more than 30 second occurs.
Indonesian media are only reporting earthquake numbers , no background information yet

Fault line west of the Sumatra coast

Update : Magnitudes and depths as calculated by other seismological agencies :
EMSC : M 7.3 @ 10 km
GEOFON (Germany) : M 7.1 @ 10 km
CEN (China) : M 7.2 @ 20 km

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