Was the 1941 Andaman earthquake tsunamigenic? Comments on “Inundation studies for Nagapattinam region on the east coast of India due to tsunamigenic earthquakes from the Andaman region” by Srivastava et al. 2012

Abstract

The question whether the 1941 Andaman earthquake did generate a damaging tsunami that impacted the islands and the eastern coast of India is not easily resolvable owing primarily to the non-availability of both instrumental and historical data. The available information on the 1941 Andaman earthquake is somewhat limited because of the difficulties emanating from a war in which Andaman Island was part of eastern war theater. The recent paper by Srivastava et al. (2012) deals with modeling of inundation of the 1941 earthquake along the Nagapattinam Coast on the southeastern India, which implicitly assumed that the 1941 earthquake was indeed tsunamigenic. Our findings, however, do not support such a supposition. Here, we present our arguments on the non-tsunamigenic status of the 1941 Andaman earthquake. The Andaman–Nicobar region is known to have experienced a few large earthquakes in the past (Fig. 1; inset), the biggest being the Mw 9.1 2004 earthquake. Among the historically earlier earthquakes, only those in 1881 (Mw 7.9) and 1941 (Mw *7.7) seemed to be significant (Rogers 1883; Jhingran 1952). The 1881 and the June 26, 1941, earthquakes are known to have sourced off the western margin of the Car Nicobar and Middle Andaman Islands, respectively (Rajendran et al. 2003; Bilham et al. 2005). The 1881 earthquake off the Car Nicobar Island had generated tsunami that impacted the Nicobar coast and the south eastern coast of India (Ortiz and Bilham 2003), an observation validated by direct measurements of tidal gages (Rogers 1883). The 1881 event, significant among the past earthquakes, caused a tsunami surge not exceeding 0.75 cm at Car Nicobar (Rogers 1883); wave height of 0.25 m was measured from the tide gauge stations at Madras (Chennai) on the east coast of India (Ortiz and Bilham 2003). However, there are no reliable reports of any tsunami impact due to the 1941 Andaman earthquake either from the Andaman and Nicobar Islands or from the east coast of India (Rajendran et al. 2007). To verify the reported non-occurrence of tsunami, which by itself was intriguing, this author had conducted detailed interviews with some of the senior residents in Port Blair, South Andaman, who had experienced the 1941 earthquake. They all said that they had experienced the earthquake in Port Blair, but not a tsunami. This was further verified