Geological evidence for an unusually large tsunami on the Pacific coast of Aomori, northern Japan

Abstract

To assess long-term tsunami inundation history, we studied a wetland on the Pacific coast of Aomori, Japan, at the northern end of the Japan Trench. We found five sand sheets interbedded in freshwater mud and peat, three of which contained brackish diatoms indicating deposition by marine inundation. We identified the youngest sand sheet, deposited AD 1480-1770, as a tsunami deposit based on its lateral extent (>1 km) from the shoreline at the time of its deposition. Although this area has been struck by many tsunamis generated by earthquakes along the Japan Trench as well as along the Kuril and Peru-Chile trenches, no tsunami recorded at least in the past 120 years has inundated the coast as far inland as this tsunami deposit is distributed. We therefore infer that it was deposited by an unusually large tsunami. Historical and geological evidence for tsunamis in north-east Japan suggests that possible sources are the AD 1611 Keicho earthquake along the Japan Trench, a 17th-century earthquake along the Kuril Trench, or an unknown large earthquake.

Shorter intervals between great earthquakes near Sendai: Scour ponds and a sand layer attributable to A.D. 1454 overwash

“…First, great earthquakes can recur aperiodically, as in a long geologic record of tsunami deposits that mark earthquakes along the Kuril Trench [ Sawai et al ., ]. Second, rupture modes along the Japan Trench are difficult to determine without paleoseismological evidence in the north [ Tanigawa et al ., ] and in the south as well. Third and most important, it is not clear, from tsunami geology on Sendai Plain, whether the 869, 1454, and 2011 tsunamis were approximately similar in size and source area.…”

New evidence for the presence of Changbaishan Millennium eruption ash in the Longgang volcanic field, Northeast China

“…B-Tm, used as an isochronous marker, has been detected in tsunami, marine, and lake sediments in Japan and surrounding region (e.g. Furuta et al, 1986;Nakagawa et al, 2002;Ikehara, 2003;Nanayama et al, 2003Nanayama et al, , 2007Okuno et al, 2011;Hughes et al, 2013;Tanigawa et al, 2014). Consequently, the CMA offers a unique chance to link these sediment sequences across Northeast China to the Japan areas.…”

Three Thousand Year Paleotsunami History of Southern Part of Japan Trench

“…Since the 2011 Tohoku-oki event, many researchers have studied paleotsunami deposits along the Paci c coasts facing the Japan Trench to reevaluate paleotsunami histories along the central to northern parts of the Japan Trench (e.g., Goto et al 2015Goto et al , 2019Inoue et al 2017;Ishimura and Miyauchi 2015;Ishizawa et al 2018Ishizawa et al , 2019Kusumoto et al 2018;Minoura et al 2013;Sawai et al 2012;Sawai et al 2015;Takada et al 2016;Takeda et al 2018;Tanigawa et al 2014a;Tanigawa et al 2014b;Watanabe et al 2014, see also Sawai 2017, accepted). For instance, two event layers for the past 6000 years were reported in a meadow of Misawa city, Shimokita Peninsula, Aomori prefecture ( Fig.…”

“…For instance, two event layers for the past 6000 years were reported in a meadow of Misawa city, Shimokita Peninsula, Aomori prefecture ( Fig. 1, Tanigawa et al 2014b). In the Sanriku region, the recurrence interval of the huge tsunamis was estimated as 290-390 years (Ishimura and Miyauchi 2015), 500-750 years (Takada et al 2016) or 400-600 years (Inoue et al 2017).…”