History of the paleo-earthquakes along the Sagami Trough, central Japan: Review of coastal paleoseismological studies in the Kanto region

Abstract

North American Plate (Fig. 1). While historical records show that two great earthquakes, the 1703 Genroku Kanto Earthquake (M 8.2) and the 1923 Taisho Kanto Earthquake (M 7.9) (hereafter, the 1703 Genroku Earthquake and the 1923 Taisho Earthquake, respectively), occurred along this trough (Usami et al., 2013), records of earthquakes occurring before the 1703 Genroku Earthquake are ambiguous. However, instead of concentrating on the few remaining historical records of past eras, tectonic geomorphological studies have aimed at recovering information on past earthquakes from marine terraces. Such studies have been conducted since the coseismic uplift associated with the 1923 Taisho Earthquake was discovered along the coasts facing the Sagami Trough (Imamura, 1925; Watanabe, 1929). Although the progress of paleoseismological records of the past 40 years in this area has helped elucidate the history and cycle of interplate earthquakes along the Sagami Trough (e.g. Shishikura, 2003), the observed results do not fully agree with more recently obtained geodetical observation data. The resulting contradictions are very important, not only in terms of scientific understanding, but also because of their relevance when formulating disaster prevention plans for metropolitan areas. In fact, Japanese government offices tasked with disaster prevention measures have recently announced seismic hazard breakdowns for Japan's metropolitan areas (Cabinet Office, 2013; Earthquake Research Committee, 2014), but those efforts did not consider this problem in detail. Therefore, in this paper, I will provide an overview of current research into paleoearthquakes and associated tsunami events in this region, discuss the distribution of the region's seismically active faults, and then examine their possible slip recurrence, terrace uplift magnitudes, and tsunami deposit records. Historical earthquakes and tsunamis along the Sagami Trough 1923 Taisho Kanto Earthquake The 1923 Taisho Kanto Earthquake, which killed more than 105,000 people, was one of the worst natural disasters in recorded Japanese history (Moroi and Takemura, 2004). Significant crustal movements and tsunamis accompanied this earthquake. According to tide gauge data and the re-leveling of benchmarks and triangular points undertaken by the Land Survey Department (1926), the Boso Peninsula, Miura Peninsula, and Oiso coastal area Two subduction zone interplate earthquakes have been recorded along the Sagami Trough, the first in AD 1703 (Genroku Earthquake) and the second in AD 1923 (Taisho Earthquake). While the source areas of these two events overlapped within and around the Sagami Bay, the 1703 Genroku Earthquake had a larger rupture area, which propagated to off the Boso Peninsula. Currently, our understanding of prehistorical earthquakes has been facilitated by Holocene marine terraces and tsunami deposits, through which we have come to the understanding that past Kanto earthquakes can be divided into two types-the Taisho-type and the Genrokutype. Taisho-type earthquakes are ...

Geological and historical evidence of irregular recurrent earthquakes in Japan

“…The coastal uplift at the Miura Peninsula and the tsunamis around Sagami Bay were similar to those during the 1923 Taisho Kanto earthquake. However, the maximum costal uplift at the southern tip of the Boso Peninsula was 4-6 m [39,40], and the tsunami height along the outer coast of the Boso Peninsula was approximately 5 m [41], both being much larger than those during the 1923 earthquake. These suggest that the 1923 and 1703 Kanto earthquakes shared the same source around the Miura Peninsula (purple in figure 4a), but the 1703 earthquake source extended off the Boso Peninsula (green in figure 4a).…”

Cluster Analysis of Marine Terraces and Quantitative Seismotectonic Interpretation of the Boso Peninsula, Central Japan

“…This recurrence pattern is far from the traditional picture of "characteristic earthquakes." Moreover, geodetic inversion via global navigation satellite system (GNSS) (Nishimura et al, 2007;Sagiya, 2004) has raised the problem that the interval time of Genroku-type earthquakes is longer than the time taken to accumulate the strain on the plate interface (250-500 years) even in the shortest inference (Shishikura, 2014).…”

“…We applied the new classificatory method to the southernmost part of the Boso Peninsula, central Japan (Figure 1a). Four distinct levels of Holocene marine terraces, named Numa terraces, are well known as recording uplifts due to subduction-related earthquakes along the Sagami Trough (Nakata et al, 1980;Shimazaki & Nakata, 1980;Shishikura, 2014) (Figure 1b). Because understanding the history of such Sato et al, 2005).…”

Constraining sediment provenance for tsunami deposits using distributions of grain size and foraminifera from the Kujukuri coastline and shelf, Japan

“…Nanayama et al ., ; Sawai et al ., ). Geological studies conducted in Hokkaido (Nanayama et al ., , ; Sawai et al ., , 2009b); Tohoku (Sawai et al ., ; Tanigawa et al ., ) and Kanto (Fujiwara & Kamataki, ; Shishikura, ) have revealed evidence of earthquakes and tsunamis that pre‐date the historical record, extending the timeframe of known events back in time by up to 4000 years. These studies are used to assess the long‐term seismic trends along subduction zones (e.g.…”