13:45 〜 15:15
[HDS08-P01] 震度データからの震度7地震の予測等頻度線の作成
キーワード：地震、震度、頻度
Intensity 7 earthquakes were recorded in Hyogo, Niigata, Miyagi, Kumamoto and Hokkaido. Before these earthquakes, people had rarely talked about the earthquakes in these regions, and people in these regions did not seem to be prepared for big earthquakes. This unpreparedness contrasts with the frequent media coverage of the yet-to-come Tokai and Nankai-Trough earthquakes. So, what are the real ‘risks,’ we mean the rate of occurrence, of big earthquakes? Can we reasonably estimate these risks and contribute to improvement of peoples’ well-preparedness to the big earthquakes? Of course, people in seismology have long been tackling this problem, and we got a lot of practical instructions from them. Our approach, however, is purely of data analytics. We do not mean to object to seismological approach, but we just would like to show how the risks can be seen with our based-on-only-intensity-data approach. In this paper, we calculated the expected rates of occurrence of intensity 7 at more than a thousand seismic stations and draw the nationwide equifrequency contour lines. For this, we make use the linear relationship between the logarithm of occurrence and intensity of earthquakes found by Usami and Katsumata (1973).
We use the data from Japan Meteorological Agency (JMA) and counted the occurrence of earthquakes greater than or equal to each intensity and plotted the logarithm of the counts against the intensities, at each observation station in the database. We exclude the stations whose operation is less than 10 years. We also removed the stations with too few counts. As Usami and Katsumata show, we found good linear relationship in these plots, and estimated the rate of occurrence of the earthquake by extrapolating the lines calculated from the intensity 3—5 earthquakes.
Our estimates show the five prefectres experienced intensity 7 earthquakes contains the points of highest 10% of the expected occurrence. In addition we found that the slopes of the log-occurrence—intensity relations differ from place to place. That is, regions experiencing less frequent earthquakes of intensity 3 or 4 do not necessarily have less earthquakes of intensity 7. One epitomizing example is the Great Hanshin-Awaji Earthquake: the slopes in the Hyogo area stations are gradual and rate of occurrence of mid-range earthquakes is low, but the expected frequency of intensity 7 earthquake is as high as Tokyo.
As for the preparedness of the people, the whitepaper on disaster management, 2016 shows that the ratio of people who thought there would be a disaster in 30 years are less in the prefectures facing Japan sea (excluding Kyoto and Hyogo, adding Kumamoto), and high in those of Pacific side. We found a rough relationship that the lower ratio of the expectations of disaster roughly corresponding to the places of low occurrence rate of mid-range earthquakes. Our research reveals that the rate of occurrence of disastrous earthquakes these low-expectation region can be high, and hope that our map contributes to the improvements of preparedness to earthquakes for these regions.
Japan Meteorological Agency, Shindo data, https://www.data.jma.go.jp/eqev/data/bulletin/shindo.html
Usami T and Katsumata M, Intensity-frequency relation for felt-earthquakes in Japan, Quarterly Journal of Seismology, 38, 15—21, (1973).
Cabinet Office of Japan, Whitepaper on disaster management 2016 (2016).
We use the data from Japan Meteorological Agency (JMA) and counted the occurrence of earthquakes greater than or equal to each intensity and plotted the logarithm of the counts against the intensities, at each observation station in the database. We exclude the stations whose operation is less than 10 years. We also removed the stations with too few counts. As Usami and Katsumata show, we found good linear relationship in these plots, and estimated the rate of occurrence of the earthquake by extrapolating the lines calculated from the intensity 3—5 earthquakes.
Our estimates show the five prefectres experienced intensity 7 earthquakes contains the points of highest 10% of the expected occurrence. In addition we found that the slopes of the log-occurrence—intensity relations differ from place to place. That is, regions experiencing less frequent earthquakes of intensity 3 or 4 do not necessarily have less earthquakes of intensity 7. One epitomizing example is the Great Hanshin-Awaji Earthquake: the slopes in the Hyogo area stations are gradual and rate of occurrence of mid-range earthquakes is low, but the expected frequency of intensity 7 earthquake is as high as Tokyo.
As for the preparedness of the people, the whitepaper on disaster management, 2016 shows that the ratio of people who thought there would be a disaster in 30 years are less in the prefectures facing Japan sea (excluding Kyoto and Hyogo, adding Kumamoto), and high in those of Pacific side. We found a rough relationship that the lower ratio of the expectations of disaster roughly corresponding to the places of low occurrence rate of mid-range earthquakes. Our research reveals that the rate of occurrence of disastrous earthquakes these low-expectation region can be high, and hope that our map contributes to the improvements of preparedness to earthquakes for these regions.
Japan Meteorological Agency, Shindo data, https://www.data.jma.go.jp/eqev/data/bulletin/shindo.html
Usami T and Katsumata M, Intensity-frequency relation for felt-earthquakes in Japan, Quarterly Journal of Seismology, 38, 15—21, (1973).
Cabinet Office of Japan, Whitepaper on disaster management 2016 (2016).