Strong quake in Myanmar

Strong quake in Myanmar

  • Earth In The News
11 Nov 2012

A magnitude 6.8 earthquake occurred on the Sagaing fault in Myanmar on November 11, 2012. The Sagaing fault is a major fault in Southeast Asia between the India and Sunda (Eurasia) plates. This strike-slip fault (side-to-side motion) is part of a broad zone of deformation that includes the India-Asia collision zone to the north and extension of the Andaman Sea to the south.

Many large earthquakes occurred on this 1200km-long fault during the 20th century: in August 1929 (M ~7), May 1930 (M 7.2), December 1930 (M 7.3), September 1946 (M 7.3 and M 7.6), July 1956 (M 7) and January 1991 (M 6.9). As a result, scientists of the Myanmar Earthquake Committee (MEC) and the Earth Observatory of Singapore (EOS) have collaborated intensively in the past few years to study the Sagaing fault and install GPS stations in the country.

The November 11 earthquake and its four aftershocks (with magnitudes ranging from M 5 to M 5.8) occurred north of the city of Mandalay, along a stretch of the Sagaing fault that had a big earthquake in 1946. EOS director Kerry Sieh notes: “the section from Mandalay northward has experienced several other big earthquakes in the past century, whereas the section further south, which includes Nay Pyi Daw, the country’s capital, has not”. Although the segment of the Sagaing fault from Mandalay to Nay Pyi Daw has not ruptured in the recent past, this does not mean that there is no seismic hazard in that particular region.

Myanmar scientists are already planning a field expedition to document the surface rupture of the November 11 earthquake. Finding the surface rupture is of major importance to fully understand the fault’s behaviour. The search may be difficult as this part of the fault is parallel to the Irrawaddy River and the rupture is possibly in an area where the Sagaing fault is a network of smaller faults. Researchers will also use satellite imagery to try to trace the surface rupture remotely.

Research on the active faulting of this region has been presented at the annual meeting of the American Geophysical Union in San Francisco on December 7, 2012 ( The coseismic slip of the 2011 Tarlay earthquake in eastern Myanmar: constraints from InSAR and field investigations. Yu Wang; Yunung N. Lin; Soe Thura Tun; Saw Ngwe Khaing; Mark Simons; Kerry E. Sieh, Session T52A-04, 11:05 am)

The map on the left shows the main tectonic features around the Sagaing fault.
The map on the right shows major earthquakes since the 18th century. The coloured patches show estimated rupture patches of older earthquakes, while the "beach-ball" symbols show earthquakes recorded by seismometers in modern times. The "beach ball" represents a focal mechanism, which shows an estimate of motion along the earthquake fault. To learn more about focal mechanism, see http://earthquake.usgs.gov/learn/topics/beachball.php

Credits: Wang Yu et al, 2012. Figure yet unpublished.

 

Red lines show the active faults mapped with satellite data (90-m SRTM and 15-m ASTER). Green dots show the relocated epicentres of the Sagaing fault earthquakes throughout the 20th century (Hurukawa, N., and P. Maung Maung, 2011). Grey boxes show the approximate rupture patch of each earthquake, based on the relationship between earthquake magnitude and the surface rupture length (Wells and Coppersmith, 1994). Seismic intensity records were also used to locate the possible rupture area of these historical events (e.g, May-1912, Aug-1929, May-1930, Dec-1930). Red dots are the major cities in Myanmar.
The November 11, 2012 earthquake occurred on a section of the fault that possibly ruptured previously in September 1946. The November 11, 2012 earthquake is shown by the orange "beach ball" symbol, which represents the Central Moment Tensor (CMT) Mwc solution from U.S Geological Survey. The fault-plane solution agrees well with the Sagaing fault orientation mapped with satellite imagery.
NTf: NanTing fault; LHf: Lashio fault; NPf: Nampawng fault.
Credits: Wang Yu et al, 2012

References: 

Wang, Y., K. Sieh, et al. (2011). "Earthquakes and slip rate of the southern Sagaing fault: insights from an offset ancient fort wall, lower Burma (Myanmar)." Geophysical Journal International 185(1): 49-64.

Hurukawa, N. and P. Maung Maung (2011). "Two seismic gaps on the Sagaing Fault, Myanmar, derived from relocation of historical earthquakes since 1918." Geophys. Res. Lett. 38(1): L01310.

Wells, D. L. C., Kevin J. (1994). "New Empirical Relationships among Magnitude, Rupture Length, Rupture Width, Rupture Area, and Surface Displacement." Bulletin of the Seismological Society of America 84(4): 974-1002.

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