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(From the publication jointly prepared by : Union of Myanmar [Department of Meteorology and Hydrology, Forest Department, Relief and Resettlement Department, Irrigation Department, Fire Services Department], Myanmar Engineering Society, Myanmar Geosciences Society, Myanmar Information Management Unit and Asian Disaster Preparedness Center; Supported by: Department of International Development (DFID), UK; July 2009)
Geographically, a larger part of Myanmar lies in the southern part of the Himalaya and the eastern margin of the Indian Ocean, hence exposed to bigger earthquakes. Myanmar is earthquake prone as it lies in one of the two main earthquake belts of the world, known as the Alpide Belt that starts from the northern Mediterranean in the west, and then extends eastwards through Turkey, Iran, Afghanistan, the Himalayas, and Myanmar to finally Indonesia.
Earthquakes in Myanmar have resulted from two main sources namely:
Very large over thrusts along the Western Fold Belt have resulted from the former movement, and the Sagaing and related faults from the latter movement. Intermittent jerks along these major active faults have caused the majority of earthquakes in Myanmar. These seismotectonic processes are still going on. The occurrence of intermediate-focus earthquakes (focal depth 70-300 km) along the Western Fold Belt is due to the subduction, and that of shallow-focus earthquakes (focal depth 0-70 km) along the Central Lowlands and Eastern Highlands is mainly due to shallow-depth strike-slip (e.g. Sagaing Fault) and other faulting (Figure 8). Generally, the shallow earthquakes tend to be more destructive than intermediate ones for the same magnitude.
The major seismotectonically important faults in Myanmar are some unnamed major thrusts faults in north-western Myanmar, Kabaw fault along the Kabaw Valley in western Myanmar, the well-known Sagaing Fault and the Kyaukkyan Fault situated west of Naungcho.
The well-known and seismologically very active Sagaing Fault (Win `Swe, 1972 & 1981; Vigny et al., 2003; Soe Thura Tun, 2006) is the most prominent active fault in Myanmar, trending roughly north-south. It has been an originator of a large proportion of destructive earthquakes in Myanmar. This is due to the fact that many large urban centres lie on or near this fault. In fact, of the five major source zones in Myanmar, three lie around this large and dangerous fault. In fact, of the five major source zones in Myanmar, three lie around this large and dangerous fault.
The earthquake generated by sea floor spreading in the Andaman Sea are mostly small to moderate and shallow-focus.
Frequency and Extent of Earthquake
The majority of the earthquakes in Myanmar are mainly confined to three zones. The zones are as follows:
The seismic records show that there have been at least 16 major earthquakes with Richter Scale (RS) ≥ 7.0 within the territory of Myanmar in the past 170 years. The frequency with respect to time maybe summarized at the table below:
Earthquake Prone Locations
The highest intensity zone designated for Myanmar is the Destructive Zone (with probable maximum range of ground acceleration 0.4 – 0.5 g), which is equivalent to Modified Mercalli (MM) class IX. There are four areas in that vulnerable zone; namely, Bago-Phyu, Mandalay-Sagaing-Tagaung, Putao-Tanaing, and Kale Myo-Homalin areas. Although the latter two have major earthquake hazards, they may be less vulnerable as are sparsely populated. Important cities and towns that lie in Zone IV (Severe Zone, with probable maximum range of ground acceleration 0.3 – 04 g) are Taungoo, Taungwingyi, Bagan-Nyaung-U, Kyaukse, Pyin Oo Lwin, Shwebo, Wuntho, Hkamti, Haka, Myitkyina, Taunggyi,and Kunglong. Yangon straddles the boundary between Zone II and Zone III, with the old and satellite towns in the eastern part in Zone III, and the original city in Zone II.
About 75 percent of the Myanmar people are living in the rural areas. Most of their dwellings are still non-engineered structures, which are vulnerable to moderate to high intensity earthquakes. The rate of urban growth increases in some large cities like Yangon and Mandalay. Due to urbanization the vulnerability increases in cities and the level of disaster from earthquake would increase in major cities. On the other hand, some large segments f the active faults have not exhibited any significant seismic activity in the past 50 to 75 years, indicating that the faults are apparently locked and stress is accumulating in those segments (e.g. the southern segment of the Sagaing Fault that is close to Yangon and Bago cities, and the central segment that is close to Mandalay and Sagaing cities). This suggests that a national emergency plan for earthquakes and related disasters is in need, which should also include operating procedure for disaster preparedness and mitigation with strong support of scientific foresight. Vulnerable locations of the country can be studied also on seismotectonic map in which seismically active faults are shown in red lines in comparison with earthquake records.