Strong quake in Myanmar
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.
Ref:http://www.earthobservatory.sg/news/strong-quake-myanmar
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