Sagaing Eathquake for Myanmar Nov 11,2012

USGS Works Toward Seismic Safety in Burma

Geophysicists’ visit lays a foundation for future collaboration between the United States and Government of Burma aimed at mitigating earthquake risk

October 29, 2012 at 12:59 pm By Susan Hough, Brian Heidel and Mark Petersen

The country of Burma straddles a complex and highly active earthquake zone — the junction between the Himalayan front to the northwest of the country and, to the south/southeast, the subduction zone responsible for the enormous magnitude-9.3 Sumatra earthquake and ensuing tsunami of 2004. A record of damage to ancient and beautiful pagodas throughout Burma’s cities and countryside attests to the past occurrence of major earthquakes. Few of these damaging earthquakes, however, have occurred during the 20^th century. There is an urgent need for steps to mitigate earthquake risk in Burma, as it is not a question of “if” future large earthquakes will occur, but rather “when.” With our knowledge of earthquakes, it is certain that significant earthquake disasters will occur in the country’s future, and earthquake hazards remain poorly characterized. Exacerbating the concern, southern Burma, including the country’s most populous city, Rangoon, sits on the Irrawaddy Delta, underlain by a thick blanket of soft sediments that would significantly amplify earthquake shaking.

The Schwedagon pagoda, Burma’s most revered shrine, has been damaged multiple times by earthquakes throughout its long history.

As Burma’s government moves forward with political and economic reform, it has also shown greater openness to working with U.S. government agencies on a variety of issues. The U.S. Geological Survey is using this opportunity to work with seismology and disaster management experts to help design a long-term disaster risk reduction program for Burma that will assess seismic hazard and take steps to reduce risk. As a first step to launching this project, USAID’s Office of Foreign Disaster Assistance (OFDA) sponsored an initial visit May 21-25, 2012, by USGS research geophysicists Susan Hough and Mark Petersen and USAID/OFDA regional adviser Brian Heidel.

The U.S. government team met with counterparts from the Burmese government, including the Department of Meteorology and Hydrology and the Ministry of Social Welfare, Relief, and Resettlement, as well as United Nations agencies and nongovernmental organizations such as the Myanmar Earthquake Commission and the Myanmar Engineering Society. The visit culminated with a lively half-day Earthquake Preparedness Planning workshop that was well-attended by key staff from all of the above-mentioned groups.

The May 2012 visit focused on an assessment of needs and gaps in current earthquake risk-assessment programs. Through meetings and site visits, the U.S. team identified high-priority future program activities that will be addressed by future USAID/OFDA-supported USGS missions. Most importantly, the visit laid a foundation for future collaboration between the United States and Government of Burma aimed at mitigating earthquake risk. As Burma enters a new period of economic expansion and potentially rapid construction growth, these steps will be of vital importance to help ensure that the earthquake resilience of Burma’s future development will match the enormous resilience of its people.

Strong quake in Myanmar on 11-November-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 will be presented at the upcoming annual meeting of the American Geophysical Union in San Francisco on December 7, 2012. (AGU schedule: 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)

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.

Figure 1: Neotectonic map of the region (click map for high-resolution version)

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.

Figure 2: Neotectonic map, zoom on Sagaing fault (click map for high-resolution version)

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

9_wang2011-GJI

 Other want to seen Myanmar Earthquakes history....
- Myanmar earthquake of March 24, 2011 - Magnitude 6.8
- Male (မလယ္) Earthquake (11-11-2012), Myanmar
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Myanmar earthquake of March 24, 2011 - Magnitude 6.8

Myanmar earthquake of March 24, 2011 - Magnitude 6.8 When continents collide, there are far-reaching consequences. A magnitude 6.8 earthquake struck eastern Myanmar, near the border with Thailand and Laos, at a depth of 10 km, at 20:25 local time (13:55 UTC) on Thursday, March 24th, 2011. As of Sunday, March 27, the death toll had reached 104. There is no evidence that this earthquake is related to recent earthquakes in Japan. Rather, the earthquake in Myanmar occurred on an active fault that is part of a broad zone of deformation resulting from the collision of the Indian subcontinent with the Eurasian landmass. The most dramatic manifestations of the collision of India with Asia are the Himalaya, the tallest mountain range in the world, and the Tibetan Plateau, the tallest and largest plateau in the world. However, the effects don't stop there; this collision has been forcing blocks of the Eurasian landmass toward the east-southeast for over 35 million years. Thus active earthquake faults riddle not only the Himalaya and Tibetan Plateau, but also regions far to the north and east, toward Mongolia and Beijing, and also to the southeast, through Sichuan and Yunnan into Myanmar, Thailand, Vietnam, and Laos. (Figures 1 and 2). Figure 1. Map of the regional tectonic setting of the March 24th Tarlay (Myanmar) earthquake (Figure modified from Tapponnier and others, 1982). The red dot within the white square shows the location of the earthquake. The white square outlines the area shown in Figure 3. Figure 2. Animation showing the tectonic evolution of India and Asia over the past 50 million years. (Produced in 2002 by Prof. Paul Tapponnier and a team from the French Centre National de la Recherch Scientifique for the exhibition "Himalaya-Tibet: Le Choc de Continent" at the Muséum National d'Histoire Naturelle in Paris. Based on the work published in Replumaz and Tapponnier, 2003.) Zooming closer in to eastern Myanmar and northern Thailand and Laos, we find the crust* of the Earth behaving a bit like a stack of books that is toppling over on a shelf (Figures 3, 4, and 5). Unlike subduction zones where one plate dives under another, in this region the rocks on either side of the earthquake faults are sliding side-to-side as India continues is northward voyage. Side-to-side motion along two major earthquake faults, the Sagaing Fault in Myanmar and the Red River fault in Vietnam and Yunnan (Figure 1), is accomodating both of the northward motion of India and the southeasterly motion of China. In between these two major faults, the Earth's crust is broken into a series of blocks that are slowly rotating clockwise as a result. The edges of the blocks themselves are faults; it appears that the March 24th earthquake occurred on one of these faults, the Nan Ma fault (as mapped by Le Dain and others, 1984, and Lacassin and others, 1998; Figure 4). Figure 3. (Click the image for a higher-resolution version.) Location map of Tarlay (Myanmar) earthquake of March 24th. The northward motion of India, shown as the largest white arrow at about 40 millimetres per year, is causing motion on the Sagaing and Red River Faults (this relative motion is shown by the smaller white arrows). The motion on these major faults is driving motion on a series of faults in between, including the Nan Ma fault where the earthquake occurred. An analogy of this fault motion is shown in Figure 5. The white square indicates the area shown in Figure 4. Figure modified from Tapponnier and others (2001). Figure 4. (Click the image for a higher-resolution version). Map of the local tectonic setting of the March 24th Mong Hpayak (Myanmar) earthquake. The earthquake epicentre is shown by the red star; the portion of the Nam Ma fault that is likely to have slipped in the earthquake is shown by the red line. The two white arrows show where the Mekong River has been offset (shifted) by 12 km over the past few million years by motion on the Nan Ma Fault. The areas shaded in yellow are extensional sedimentary basins. Figure 5. Analogy of the style of deformation in the region around the March 24th Tarlay (Myanmar) earthquake. Motion along the major Sagaing and Red River faults has caused the crust in between to deform as rotating blocks, as when a row of books topples over to the side on a shelf. A series of left-lateral faults slip in between the blocks; the Nan Ma Fault is one of these faults. This mechanism is aptly called "bookshelf faulting." For reference, the Sagaing Fault runs roughly north-south. Over the past few million years, motion on the Nan Ma Fault has offset (shifted) the Mekong River by 12 kilometres (Figure 4, between the two white arrows; see Lacassin and others, 1998). This 12-km offset would not have occurred smoothly, nor all at once, but rather in a series of small jumps as earthquakes periodically caused the rocks to shift. Imagine travelling in a boat down the Mekong River as you approach this fault from the north; once you reach the fault, you would turn left to follow the river. For this reason, we call these kinds of faults "left-lateral" faults, meaning that if you stand on one side of the fault, it looks like land on the other side has shifted to the left. Based on inital estimates of the earthquake location, it appears likely that the earthquake was caused by motion on the western segment of the Nan Ma Fault. The direction of motion inferred from seismograph readings is also consistent with the left-lateral motion that is typical of this fault. We do not yet know how much the rocks may have slipped in the March 24th earthquake, nor do we know for sure whether the fault actually broke to the surface. Other earthquakes on similar faults at similarly shallow depths (10 km) and similar magnitude (6.8) are typically accompanied by a couple of metres of slip at the surface over a segment of the fault a few tens of kilometres long. Field study at the site of this earthquake would shed important new light on the nature of this earthquake. There is no evidence to connect earthquakes that occur far apart on the Earth, such as this earthquake and the Tohoku (Japan) earthquake of March 11th. There are cases, however, of earthquakes on one portion of a fault increasing the stresses on other portions of the fault and on closely neighbouring faults. This earthquake in Myanmar likely increased stresses on the eastern part of the Nan Ma Fault. Unfortunately, we don't have enough information about these faults to say whether the earthquake hazard has changed in neighbouring areas. Scientists from the Earth Observatory of Singapore are currently undertaking projects, both at a regional scale and in western Myanmar, Nepal, India/Bangladesh, and China, to learn more about the earthquake faults associated with the great collision of India and Asia. These faults have been much less well-studied than faults in areas such as Japan and California, yet can be at least as devastating, as the 2008 Wenquan (Sichuan) earthquake (Figure 3) showed all too clearly. Figure 6: Left lateral offset of paddy boundaries caused by slippage of the Nam Ma fault during the earthquake of March 24th. Photo courtesy of Soe Thura Tun of the Myanmar Earthquake Committee. * It is actually the lithosphere of the Earth that is involved in fault and plate motions, which includes the crust and the very uppermost part of the mantle. We use the term "crust" in this article because it is more widely understood. References: Lacassin, R., Replumaz, A., Leloup, P. H., 1998, Hairpin river loops and slip-sense inversion on southeast Asian strike-slip faults, Geology, 26, 703. Le Dain, A. Y., Tapponier, P., and Molnar, P., 1984, Active faults and tectonics of Burma and surrounding regions, Journal of Geophysical Research, 89, 453. Replumaz A. and P. Tapponnier, Reconstruction of the deformed Collision Zone between India and Asia by backward Motion of Lithospheric Blocks, Journal of Geophysical Research, vol. 108, N°B6, 2285, 2003. Tapponnier, P., Peltzer, G., Le Dain, A. Y., Armijo, R., and Cobbold, P., 1982, Propagating extrusion tectonics in Asia: New insights from simple experiments with plasticine, Geology, 10, 611. Tapponnier P. , Xu Zhiqin, F. Roger, B. Meyer, N. Arnaud, G. Wittlinger, Yang Jingsui, Oblique, Stepwise Rise and Growth of the Tibet Plateau, Science, vol 294, pp. 1671-1677, 2001 Contributors: Text: Jamie McCaughey, Prof. Paul Tapponnier Figures: Yves Descatoire (Fig. 3 and 4), Liow Hon Sang (Fig. 5), Prof. Paul Tapponnier, Soe Thura Tun of the Myanmar Earthquake Committee (Fig. 6) [This article published 25-March-2011, 10:51 UTC; updated 28-March-2011]