Searching for the 1912 Maymyo earthquake: New evidence from paleoseismic investigations along the Kyaukkyan Fault, Myanmar

摘要

The Great Burma earthquake (MsGR 8.0; Ms 7.6-7.7) occurred on May 23rd, 1912, and was one of the most remarkable early 1900's seismic events in Asia as described by Gutenberg and Richter (1954). The earthquake, focused near Maymyo, struck the Northern Shan State in eastern Myanmar. Contemporary evaluation of damage distribution and oral accounts led to a correlation between the earthquake and the topographically prominent Kyaukkyan Fault near the western margin of the Shan Plateau, although direct evidence has never been reported. This study aims to find evidence of paleoseismic activity, and to better understand the relationship between the 1912 earthquake and the Kyaukkyan Fault. Paleoseismic trenching along the Kyaukkyan Fault revealed evidence of several surface rupturing events. The northernmost trench exposes at least two visible rupture events since 4660 +/- 30 BP: an older rupture stratigraphically constrained by AMS C-14 dating to between 4660 +/- 30 BP and 1270 +/- 30 BP, and a younger rupture formed after 1270 +/- 30 BP. The presence of pottery, bricks and cookingrelated charcoal in the younger faulted stratigraphy demonstrates Kyaukkyan Fault activity within human times, and a possible correlation between the younger rupture and the 1912 Maymyo earthquake is not excluded. The southern paleoseismic trench, within a broad transtensional basin far from bounding faults, exposes two (undated) surface ruptures. Further study is required to correlate those ruptures to the events dated in the north. These preliminary paleoseismological results constitute the first quantitative evidence of paleoseismic activity along the northern similar to 160 km of the Kyaukkyan Fault, and support existing evidence that the Kyaukkyan Fault is an active but slow-slipping structure with a long interseismic period.