Source area and rupture parameters of the 31 December 1881 Mw = 7.9 Car Nicobar earthquake estimated from tsunamis recorded in the Bay of Bengal

Abstract

On the morning of 31 December 1881 a submarine earthquake beneath the Andaman Islands generated a tsunami with a maximum crest height of 0.8 m that was recorded by eight tide gauges surrounding the Bay of Bengal. Since the earthquake occurred 8 years before the construction of the world's first teleseismic recording seismometer, little has been known about its rupture parameters or location. Waveform and amplitude modeling of the tsunami indicate that it was generated by a Mw = 7.9 ± 0.1 rupture on the India/Andaman plate boundary resulting in 10–60 cm of uplift of the island of Car Nicobar. The rupture consisted of two segments: the northern 40‐km‐long segment is separated from the southern 150‐km‐long segment by a 100‐km region corresponding to the westward projection of the West Andaman spreading center. The main rupture occurred between 8.5°N and 10°N with a total area of 150 km × 60 km dipping 20°E with a mean slip of 2.7 m. The recurrence time for 1881‐type events is estimated to be 114–200 years on the basis of inferred GPS convergence rates and inferred plate closure vectors, although slip partitioning in the region may extend this estimate by as much as 30%.