Morphotectonics of the Central Sagaing fault West of Mandalay: Trace of the 1839 Ava Earthquake Rupture

Abstract:

Using high-resolution optical satellite imagery, and a 3-10 m resolution digital elevation model derived from declassified CORONA imagery, we mapped the trace of the central Sagaing fault and associated geomorphic features along the western flank of the Sagaing Hills. This approximately 350-km-long stretch of the Sagaing fault, which slips at about 2 cm/yr, lies only ~ 10 km west of the densely populated city of Mandalay. Much of this stretch of the fault has not produced a major earthquake (M > 7+) for over one century, and therefore is one of the potentially most dangerous seismic sources in SE Asia.

Our new geomorphic mapping reveals more complex deformation patterns along the western side of the Sagaing Hills than hitherto pictured on published maps. The CORONA DEM shows clear evidence of on-going dextral transpression along the fault, consistent with the minor shortening component revealed by GPS (e.g., Socquet et al., 2006). Several hundreds of meters long, right-stepping step-overs characterize the fault north of the well-known Yega-In pull-part basin/lake, forming a series of overlapping dextral scarps at the surface.

Our preliminary field and remote sensing observations suggest that the 1839 Ava earthquake, which may be the latest, largest destructive event along this section of the fault, was a great earthquake. We found minimum right-lateral displacements of about 5 to 7 meters. Such large amounts of plausibly single event co-seismic offsets suggest that the M_w magnitude of the 1839 earthquake may have ranged between 7.4 to 8+, which could scale with up to 300+ km rupture length (e.g., Biasi and Weldon, 2006) along the central Sagaing fault seismic gap, between Sagaing and Naypyidaw.