Abstract

• The Yangon city is located on the convergence of the Yangon and the Bago rivers where the north-south trending ridge in the middle is made up of Miocene rocks and associated river terrace alluviums. Several major earthquakes visited this region frequently, some of which caused major damage to the built environment including ancient monuments and religious structures. There are a few noticeable events in the 20th century with their epicenters fell in and near the city such as the 1927 Rangoon Earthquake, the 1930 Bago earthquake, and the 1978 Dedaye Earthquake of which Yangon felt intensity from VI to VIII. Recently, slight to moderate earthquakes happened in the northern Yangon area (M5.1), causing damage to buildings and structures. Furthermore, several small-magnitude earthquakes were recorded in the city of Yangon itself. Therefore, an attempt has been made to understand the mechanism and sources of these events. Knowing the background geology of the area, field surveys were carried out to identify the regional structural trends and seismically active elements. Survey works include outcrop mapping of geological elements from which structural trends, sense of shear, and stress orientation can be interpreted. Generally, the observed faults have strikes of approximately N-S, NNW-SSE, NE-SW, and WNW-ESE directions. Field structural data also show right lateral and oblique reverse motion with the direction of maximum principle stress in NNE-SSW to NE-SW directions. In addition to field geological surveys, moment tensor solutions of significant earthquakes published by seismological centers are used to identify the nature of movement when the respective earthquakes happened. The recent events at the northern Yangon areas are found to be related to the WNW-ESE structural trend with an agreement of fault motion between seismic moment tensor and geological structural results. Several major geological lineaments are observed by distinct geomorphological expressions: some of them are often associated with earthquakes such as the Sagaing Fault in the east, the Dedaye Fault and faults near the Ma-u-bin area in the west, the Bago Yoma Fault, the Htan-ta-bin and Satthwartaw in the north and some cross faults in the Bago Yoma. Some concealed faults in the Ayeyawady Delta and off-coast of Pyapon and some faults of the Yangon are also highlighted in this paper as seismically active. In terms of fault size and seismicity of each area, the potential hazard that each tectonic element can give rise to is also discussed.