SEISMIC ZONE MAP OF MYANMAR(REVISED VERSION, 2005) Explanatory Account Dr. Maung Thein and U Tint Lwin Swe February 2006 (Prepared under the auspices of Myanmar Earthquake Committee) 1. Introduction This map is the revised version of the first seismic zone map of Myanmar prepared by Dr. Maung Thein, Dr. Sone Han, U Tint Lwin Swe and Daw Tin Htay Mu in August 2003, (Maung Thein et al., 2003). This revision was made by Dr. Maung Thein, U Tint Lwin Swe, and Dr. Sone Han in December, 2005. This project is a part of public service works by Myanmar Earthquake Committee in cooperation with Myanmar Geosciences Society. The main purpose is to have an updated and more probable seismic zone map, thereby enhancing its reliability and usefulness. Also, it may be a fairly creditable contribution to the World Seismic Safety Initiatives (WSSI) programme. It is hoped that this map will be more than of academic and general interest as it is useful as outlined in Section 5. Furthermore, it is also hoped that it may contribute to the mitigation of earthquake hazards in Myanmar to some extent. For easier comprehension and effective communication, title, subtitles and the explanation on the map and the explanatory account are given in both English and Myanmar. Moreover, a new column of general descriptions for the seismic zones is added in the explanation box. 2. Seismicity and Seismotectonics First, it is necessary to know briefly about the seismicity and seismotectonics of the Myanmar Region. Myanmar indeed is earthquake-prone (see Figure 1) 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. 2 92 93 94 95 96 97 6. 98 99 100 101 7. 28 28 27 27 INDIA a 5.5 26 a a 26 a 3. Myitkyina 2. 25 25 a 24 23 Haka BAN- CHINA 24 5. 2.5 a a Lashio 23 a Mandalay 22 GLA- 22 DESH Sagaing Fault a 21 20 Large Earthquakes within and near Myanmar (with dates and magnitudes) Locations are shown by circled numbers 1. 2. 3. 4. 5. 23 May 1912 8 July 1918 27 Jan 1931 26 June 1941 12 Sept 1946 15 Sept 1946 6. 29 July 1947 7. 15 Aug 1950 Keng Tung 1. 21 a Sittway 3.2 20 a 19 19 a 18 18 THAILAND INDIA PLATE Yangon 17 5.5 5 6 M 7 M 8 2.5 16 TE LE T a Subduction zone 15 MA 14 BU R 14 5.5 M M Plate motion in cm/yr PL A 15 17 a 2.5 16 (8.0) (7.6) (7.6) (7.7) (7.5) (7.75) (7.9) (8.7) 13 Andaman Rift 13 Collision zone 4. 12 Active spreading ridge 12 Thrust fault 11 11 a 3.7 10 10 92 93 94 95 96 97 98 99 100 Major active faults 101 Figure 1. SEISMOTECTONIC MAP OF THE MYANMAR REGION (Earthquake data: NEIC for the period 1964-2004; from other sources for 1912 - 1963. Tectonic boundaries and fault locations are mainly based on GIAC reports (1997, 2000)). 3 The seismic records show that there have been at least 16 major earthquakes with magnitude (M) ≥ 7.0 within the territory of Myanmar in the past 170 years. Among these, the following four and 1975 Bagan Earthquake arranged chronologically, were quite destructive: Innwa (Ava) earthquake of 23 March 1839 (M > 7.0), Maymyo earthquake of 23 May 1912 (M 8.0), Bago (Pegu) earthquake of 5 May 1930 (M 7.3), Sagaing earthquake of 16 July 1956 (M 7.0), and Bagan earthquake of 8 July 1975 (M 6.8). The seismotectonics of Myanmar is shown in Figure 1. Earthquakes in Myanmar have resulted from two main causes: (1) the continued subduction (with collision only in the north) of the northward-moving Indian Plate underneath the Burma Platelet (which is a part of the Eurasian Plate) at an average rate of 4.0 – 6.0 cm/yr; and (2) the northward movement of the Burma Platelet from a spreading centre in the Andaman Sea at an average rate of 2.5 – 3.0 cm/yr. Very large overthrusts 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. Figure 2 indicates that 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. Generally speaking, 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 thrust faults in northwestern Myanmar, Kabaw Fault along the Kabaw Valley in western Myanmar, the well-known Sagaing Fault, and the Kyaukkyan Fault situated east of Naungcho. Here, the well-known and seismologically very active Sagaing Fault deserves a brief special mention. It 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 seismic source zones in Myanmar, three lie around this large and dangerous fault. As shown in Figure 1, it is a right lateral strike-slip fault extending from south of Putao, west of Katha, through Sagaing, along the eastern flank of Bago Yomas, then through Bago, and finally into the Gulf of Mottama for a total distance of about 1500 km. Moderate and major earthquakes 4 28 26 24 22 20 18 16 14 12 10 92 94 96 98 100 5 6 28 27 26 Myitkyina 25 24 23 Lashio Haka Mandalay 22 Keng Tung 21 20 Sittway 19 18 Yangon 17 16 15 14 13 12 11 3.7 10 92 93 94 95 96 97 98 99 100 101 102 Figure 4. Earthquake hazard level map of Myanmar showing 84 percentile zero second horizontal ground acceleration at firm rock using known earthquake data set for the period 1912 - 2004 (NEIC and other sources). Contour interval is of 0.1 g (1.0 g = 980 cm/s/s). 7 that occurred on or near this large fault are (from north to south): Bago (1927, 1930M 7.3), Phyu (1930 – M 7.3), Swa (1929), Pyinmana (1931), Innwa (1839 – M > 7.0), Amarapura (1855), Mandalay (1871, 1931), Sagaing (1956 – M 7.0), Tagaung (1991 – M 7.3), Wuntho (1946 – M 7.5), Myitkyina (1931 – M 7.6), and Putao (1906) In figure 3 is shown the apparent segmentation of the Sagaing Fault into three parts on mainland Myanmar as indicated by the clusters of earthquake epicentres and regionwise earthquake frequencies. These three segments correspond to the three Zone V areas, namely, Bago-Taungoo, Mandalay-Sagaing-Tagaung, and PutaoTanaing areas. Two seismic gaps can be noted in Figure 3; one in the YamethinMeiktila area, and another in the Bago area. During historical times, the former has had low seismic activity, whereas the latter has had high seismic activity and a fairly long history of earthquakes. In fact, Bago earthquake of 5 May 1930 was a very destructive one. So, the Bago seismic gap (for the last 40 years) seems to suggest that stress may have been accumulating for at least a moderate earthquake in the Bago area. 3. Construction of the Map This map is more refined and better supported by more seismic and seismotectonic data and information together with some inferences. As in the previous map, the data and information are of four kinds, with emphasis on i and ii. i. Regional and local seismotectonics with special reference to major active faults. ii. Past earthquake data, records, and information including intensity maps in MM scale, if available. (e. g., Maung Thein, 2001). iii. Distribution and density of earthquake epicentres with M ≥ 5.0. iv. Spatially correlated peak horizontal ground acceleration (PGA) computed for various seismic events (e. g., Figure 4). The above information leads to the delineation of at least five seismic source zones (Seismogenic Zones). These are (1) northwesternmost Myanmar zone, (2) Mandalay-Sagaing-Tagaung zone, (3) Bago-Taungoo zone, (4) northern Shansouthern Yunnan zone, and (5) northern Andaman Sea zone. 8 4. Meanings in the Map The map is a probable intensity zoning map. The approach is mainly empirical and historical in the sense that it makes use of past seismic events and history to make educated guesses about probable regionwise intensities in the future. (It is hoped that a probabilistic seismic risk (or earthquake hazard) map based on horizontal ground acceleration, which is preferred by design engineers, will be constructed in due course). As shown in the map, five seismic zones are demarcated and named (from low to high) Zone I (Low Zone), Zone II (Moderate Zone), Zone III (Strong Zone), Zone IV (Severe Zone), and Zone V (Destructive Zone), mainly following the nomenclature of the European Macroseismic Scale 1992. (It should be mentioned that in some countries, there are zones higher than Zone V as used here). For each zone, a probable range of ground acceleration in g values and equivalent Modified Mercalli (MM) Scale classes are given. The highest intensity zone designated for Myanmar is the Destructive Zone (with probable intensity range of 0.4 – 0.5 g) which is equivalent to MM class IX. There are four areas in that zone; namely, Bago-Phyu, Mandalay-Sagaing-Tagaung, Putao-Tanaing, and Kale Myo-Homalin areas. The latter two, however, would not have major earthquake hazards as they are only sparsely populated. Important cities and towns that lie in Zone IV (Severe Zone, with probable intensity range of 0.3 – 0.4 g) are Taungoo, Taungdwingyi, Bagan-Nyaung-U, Kyaukse, PyinOoLwin, Shwebo, Wuntho, Hkamti, Haka, Myitkyina, Taunggyi, and Kunglong. Yangon straddles the boundary between Zone II and Zone III, with the old and new satellite towns in the eastern part in Zone III, and the original city in Zone II. Regarding the probable range of ground acceleration (in g values; where 1.0 g = 980 cm/s2 or 32 ft per second per second) expected in various seismic zones (Column 3 in Explanation Box), it should be noted that the range of g values given for a zone is for those places with soft and medium stiff soils in an affected area ⎯ in general, the higher value is for soft soils, and the lower value is for medium stiff soils; the g value will be lower for other places with stiff soils or bedrocks. It is for this reason that seismic microzone maps are required for earthquake-prone big cities. The average g value in the various seismic zones may be taken as the “zone factor” of ground acceleration. Thus, the zone factors would be 0.065 g, 0.125 g, 0.25 g, 0.35 g, and 0.45 g for Seismic Zones I, II, III, IV, and V, respectively. Regarding the Modified Mercalli (MM) Scale classes (Column 4), the level of probable damage and destruction may be summarized as in Table 1. 9 Table 1 Zone MM Classes V IX Probable Damage Examples of Damage Major damage Considerable damage designed structures in specially Major damage in good RC buildings IV VIII – IX Considerable damage Considerable damage in good RC buildings Major damage buildings in ordinary brick III VIII Moderate damage Moderate damage in good RC buildings Considerable damage in ordinary brick buildings II VII Minor damage Minor damage in good RC buildings Moderate damage in ordinary brick buildings I VI Slight damage Minor damage buildings in ordinary brick 5. Usefulness The main uses of this map are as follows: i. For educational purposes. In teaching appropriate courses in environmental geology, tectonics, seismology, civil engineering, earthquake engineering, natural hazards management, regional planning ii. For public awareness of regionwise earthquake hazards. iii. For earthquake information in regional planning. iv. For earthquake information in major construction and public works projects. 10 References GIAC, 1997. Report of Geodynamics of India and Asia Collision, GIAC Project. GIAC, 2000. Report of Geodynamics of India and Asia Collision, GIAC Project. Maung Thein, 2001. Mitigation and Earthquake Hazards in Myanmar (in Myanmar with abstract in English). Jour. Myan. Acad. Tech., v. 1, no. 2, p. 124 – 134. Maung Thein, Sone Han, Tint Lwin Swe, Tin Htay Mu, 2003. Seismic Zone Map of Myanmar (A3 size) with an explanatory note (9 p.) NEIC, 2004. Earthquake data of Myanmar Region for 1964 – 2004. 11 91 29 92 93 94 95 96 97 98 99 100 101 102 29 SEISMIC ZONE MAP OF MYANMAR (REVISED VERSION, 2005) 28 27 28 (Shown with probable maximum intensities in g values and MM classes) Putao jrefrmEdkifiH ivsifZkefrsm;jyajryHk III 0 (jyifqifa&;qGJxm;aomyHk-2005) II (tjrifhqHk;a&mufEdkifonfh jyif;xeftm;rsm;udk 26 g wefzdk;rsm;ESifh MM twef;rsm;wdkYjzifh jyxm;onf/) 25 0 Hkamti 50 50 100 miles 100 150 27 km 200 26 V Myitkyina 25 Homalin IV INDIA Bamaw 24 V Tagaung Kale Myo III 24 Kunglong V Lashio 23 22 CHINA Muse Wuntho Haka 23 Shwebo IV PyinOoLwin Monywa Mandalay Sagaing BANGLADESH 22 III Kyaukse IV III 21 Meiktila Myauk U 21 Taunggyi IV Tachileik II LAOS III Magway Taungdwingyi Pyinmana Loikaw Sittway 20 Keng Tung Bagan Taungoo Pyay 19 20 19 Phyu Thandwe BAY OF BENGAL IV 18 Pathein THAILAND Bago II 17 18 II Hinthada Pa-an Yangon V Maubin 17 Mawlamyine III GULF OF MOTTAMA 16 I 16 15 15 CoCo Island 14 Dawei EXPLANATION SEISMIC ZONE 13 12 ivsifZkef V III II 10 I 91 I 13 jzpfEdkifaomajrjyifivsif nDaomjyifqifxm; a,bk,saz:jycsuf vdIif;oGm;t&Sdefwefzdk;rsm; wl rmu,fvDtwef;rsm; IV 11 EQUIVALENT PROBABLE RANGE OF MODIFIED MERCALLI GROUND ACCELERATION SCALE CLASSES GENERAL DESCRIPTION 14 &Sif;vif;az:jycsuf 92 Destructive Zone 0.4 - 0.5 g IX Severe Zone 0.3 - 0.4 g VIII - IX 0.2 - 0.3 g VIII 0.1 - 0.15 g VII zsufpD;rIrsm;Zkef II jyif;xefZkef Strong Zone tm;jyif;Zkef Moderate Zone tm;vwfZkef 11 Kawthaung Low Zone 94 95 Printed by Myanmar Earthquake Committee December 2005 VI 0.05 - 0.07 g tm;enf;Zkef 93 12 Myeik 96 97 98 99 100 Revised by Dr. Maung Thein, U Tint Lwin Swe and Dr. Sone Han (December 2005) 101 10 102 28 28 Putao 27 Khanti 26 26 Myitkyina 25 Homelin Mu-se 24 24 Tagaung Kalaewa Lashio 22 Bagan Myauk U 23 Shwebo Pyin Oo Lwin Monywa Sagaing Mandalay LATITUDE LONGITUDE Haka Kyaing Tone Penlon Meikhtila Taunggyi Tachilake Magway Taungdwingyi Pyinmana Loikaw 20 Pyay Taungngu 22 21 20 19 18 18 Bago Hpa-an Yangon Pathein Myaung Mya Phyapon 17 16 16 LEGEND CoCo Island Dawei 14 15 M >= 5 14 M >= 6 13 0 12 Myeik M >= 7 92.5 94 95.5 97 98.5 10 % FREQUENCY M >= 8 Kawthaung 10 5 100 Figure 3. Apparent segmentation of the Sagaing Fault into three parts on mainland Myanmar as indicated by the cluster of earthquake epicentres (left) and relative frequency of earthquake occurrences (right).Two seismic gaps in the Yamethin-Meiktila and Bago areas can be noted. (Earthquakes with magnitude ≥ 5.0 for the period 1964-2004). 15 20