The Short Rupture Interval of The Westernmost Nam Ma Fault in the Past Millennium

While many hazardous earthquakes struck the Golden Triangle Area between Myanmar, Thailand and Yunnan area in the past several decades, the behavior of active faults within this region is still largely unknown due to the lack of detailed investigations. Here, we present the paleoseismological survey result for the westernmost section of the 220-km-long Nam Ma Fault, which ruptured during the M_w6.8 Tarlay earthquake on 24 March, 2011. Our analysis of two hand-dug trenches across the 2011 fault surface rupture reveals clear evidence of multiple rupture events prior to the most recent Tarlay earthquake. Our data suggest the preceding event prior to the Tarlay earthquake occurred sometime between 14^thto 15^thcentury, and another plausible event is likely occurred before 10^thcentury. The relatively short rupture interval found in our trench site is consistent with our earlier interpretation that the westernmost Nam Ma fault tends to rupture once at least every 1000 years on average. Such result, again, suggests a ≥2 mm/yr plausible slip-rate of the Nam Ma fault, inferred from the ~12-km Maekong River offset.