5:15 PM - 5:30 PM
[S04-4-03] Estimation of source regions of large earthquakes from felt reports of JMA seismic intensity database - Evaluation of applicability to historical large earthquakes -
Can felt reports of historical documents be used to estimate the source of large earthquakes? Before establishing a new methodology, we show that the source area of recent three large earthquakes (2004 Niigata-Ken Chuetsu, 2008 Iwate-Miyagi, and 2011 Fukushima-Hamadori earthquakes) can be imaged from the spatial distribution of felt reports by using the JMA seismic intensity database. Our preliminary results imply the possibility that the large earthquake source can be constrained from spatial and temporal distribution of felt reports.
For the case of the 2004 and 2008 earthquakes, number of aftershocks with felt reports decreases with increasing distances at epicentral distance <100 km from the mainshock, while they fluctuate at epicentral distance >100 km, probably due to site condition and/or attenuation structure. This indicates that the effects of site amplification near surface and heterogeneous attenuation structure should be properly taken into consideration in a new methodology to estimate source of historical earthquakes. For the case of the 2011 earthquake, the number of aftershocks with felt reports fluctuated even within 100 km from the mainshock, because of the aftershocks following the 2011 Tohoku-oki earthquake.
Source of a historical large earthquake has been traditionally estimated from distribution of or casualties recorded in historical literature. However, the damage was caused by not only a ground shaking but also tsunami, massive fire and/or landslide. In addition, the distribution of building damage is strongly controlled by the population density and elapsed years since constructed. In some historical literature, earthquakes that were felt without any damage are also reported as well as damage description from major earthquakes, whereas these were not fully utilized except for several previous studies (e.g., Matsui and Oike, 1997; Satake, 2002; Matsu'ura and Tsuji, 2010).
For the case of the 2004 and 2008 earthquakes, number of aftershocks with felt reports decreases with increasing distances at epicentral distance <100 km from the mainshock, while they fluctuate at epicentral distance >100 km, probably due to site condition and/or attenuation structure. This indicates that the effects of site amplification near surface and heterogeneous attenuation structure should be properly taken into consideration in a new methodology to estimate source of historical earthquakes. For the case of the 2011 earthquake, the number of aftershocks with felt reports fluctuated even within 100 km from the mainshock, because of the aftershocks following the 2011 Tohoku-oki earthquake.
Source of a historical large earthquake has been traditionally estimated from distribution of or casualties recorded in historical literature. However, the damage was caused by not only a ground shaking but also tsunami, massive fire and/or landslide. In addition, the distribution of building damage is strongly controlled by the population density and elapsed years since constructed. In some historical literature, earthquakes that were felt without any damage are also reported as well as damage description from major earthquakes, whereas these were not fully utilized except for several previous studies (e.g., Matsui and Oike, 1997; Satake, 2002; Matsu'ura and Tsuji, 2010).