M8.6 EARTHQUAKE GENERATES LOCAL TSUNAMI IN INDONESIA, 11 APRIL 2012

A M8.6 shallow strike-slip earthquake occurred at 0838 UTC 11 April 2012 off the coast of northern Sumatra, Indonesia, and was followed by a second shallow M8.2 strike-slip aftershock at 1043 UTC (USGS).  Both generated small local tsunamis with a maximum of 1.06 m measured at 1007 UTC in Meulaboh, Indonesia located about 395 km west southwest of the epicenter.  Waves heights up to 0.4 m were recorded throughout the region and as far away as Rodrigues Island, Mauritius in the western Indian Ocean (0.22 m wave amplitude).  Amateur video of the tsunami arriving in Indonesia was captured.

Since October 2011, Regional Tsunami Service Providers (RTSP) of Australia, India and Indonesia have been serving as the primary sources for tsunami advisories for the Indian Ocean, with the PTWC and Japan Meteorological Agency (JMA) continuing to operate a parallel service until the end of 2012. The RTSP provide tsunami alerts directly to national tsunami warning centers in each country, and the countries use the advice to assess and issue warnings and advisories to their populations.  The PTWC issued an Indian-Ocean wide Tsunami Watch at 0845 UTC, and JMA issued Tsunami Watch Information at 0855 UTC. PTWC cancelled its tsunami watch at 1318 UTC.

Public bulletins are available from the Australia, India, and Indonesia RTSPs, and from the PTWC.

This region of the Indo-Ausralian plate has been seismically very active throughout history, and includes the great M9.1 earthquake of 26 December 2004 that generated the deadliest tsunami ever killing nearly 230,000 in Indonesia and across the Indian Ocean. Immediately following the disaster, the IOC of UNESCO took the lead in coordinating activities and immediate action to establish an Indian Ocean Tsunami Warning and Mitigation System (IOTWS). The response included the start of an interim Advisory Service in 2005 through the PTWC in Hawaii and the JMA in Tokyo, and in 2011 the start of the permanent RTSPs for the Indian Ocean.

Captions: Left: PTWC RIFT model simulation showing the predicted maximum off-shore tsunami wave amplitudes from the 0838 MTC 11 April 2012 strike-slip earthquake. Right top: Tsunamis recorded on the Hanimaadhoo, Maldives coastal sea level gauge (PTWC). The 1st tsunami (0.23 m amplitude) was generated by the M8.6 0838 UTC earthquake and the 2nd tsunami (0.18 m amplitude) was generated by the M8.2 1043 UTC earthquake. Right bottom: DART 23401 deep-ocean instrument in the Bay of Bengal clearly shows the 2 tsunamis (WC/ATWC)

DEVASTATING TSUNAMIS IN THE PACIFIC

The Pacific Ocean and its adjacent marginal seas are the largest, most diverse, and most tsunami-prone of any of the earth’s oceans. Pacific Ocean nations face and must be prepared for distant, and local tsunami threats. In the past, Member States depended primarily on the international advice services of the Pacific Tsunami Warning Center (PTWC), Northwest Pacific Tsunami Advisory Centre (NWPTAC), and West Coast / Alaska Tsunami Warning Center (WC/ATWC) to inform their National Tsunami Warning Centre decisions.  But lessons learned recently on how to best prepare for local and regional tsunamis acknowledges that every country needs tp address the threat themselves through improved and expanded National Tsunami Warning Centre and Disaster Management Office capacities targeting coastal communities, and through formal regional collaboration. On 11 March 2011, the Pacific experienced and responded to its third destructive local tsunami in three years.  Following the 29 September 2009 Samoa Tsunami that killed 192 in Samoa, American Samoa, and Tonga, and the 27 February 2010 Chile Tsunami that killed 124 in Chile, Japan is now facing a tremendous effort to analyze its national response and preparedness in order to better mitigate its tsunamis losses in the future.

South Pacific Tsunami Event 29 September 2009

Chile Tsunami Event 27 February 2010

Japan Tsunami Event 11 March 2011