Historical Seismograms - Evidence from the AD 2000 Izu Islands ...

Historical Earthquakes and the Seismograms in Taiwan 245In the east area of the island, between 23.5' N to 24.5' N and 121.5' E to123.0' E, the percentage of earthquake occurrence is high - 58.2%. This meansthat over half of the earthquakes in the Taiwan region occur in this area of theisland - especially within 23.5' N to 24.5' N and 121.5' E to 122.0' E, the mostactive seismic region in Taiwan.The highest percentage of energy release, 15.6%, occurs within 22.0' N to 22.5' Nand 121.0' E to 121.5' N. Northeast of Hwalien (between 24.0' N to 24.5' N and122.0' E to 122.5' E) and southeast of Hwalien (between 23.5' N to 24.0' N and121.5' E to 122.0' E) the percentages are 10.0% and 9.9%, respectively. In the westpart of the island, however, the percentage of energy release in almost all grids isless than 1.0%. The largest percentage, 2.3%, is found in the area between 23.0' Nto 23.5' N and 120.5' E to 121.0' E.Figure 3 also shows that the earthquakes in Taiwan are distributed from northeastto southwest, and that the most active seismic area is on east Taiwan betweenHwalien and Ilan. Further, even though the percentage of earthquake occurrence isnot high in the area between Taitung and Lanyu (22.0' N to 22.5' N and 121.0' E to121.5' E), that area has the highest percentage of energy release in Taiwan, whichmeans that large-magnitude earthquakes occur there frequently.Historically, 12 disastrous earthquakes have occurred in this region between 1644and 1897 (see Table 1). Since 1897, 73 disastrous earthquakes have occurred inTaiwan area according to records at CWB (see Table 2). The most severe shocks,occurring on April 21, 1935 in the Hsinchun-Taichung area (magnitude 6.6), killed3,276 people and injured 12,053. The most recent destructive earthquake was amagnitude 6.3 in Tainan on January 18, 1964. This strong shock killed 106 people,injured 650, and collapsed more than 10,502 houses.Table 1. Catalog of Disastrous Earthquakes beforeInstrumental Observation, 1644 to 1896Date Districts damaged RemarksJuly 30, 1644Nov. 1, 1720Jan. 29, 1736Dec. 11, 1776Aug. 7, 17921816June 27, 1839Dec. 3, 1848June 5, 1862Dec. 18, 1867Apr. 19, 1881Apr. 22, 1892TainanTainanTainan, ChiayiChiayiChiayi, ChanhuaIlanChiayiYunlin, ChanhuaTainan, Chiayi, ChanhuaKeelungTaipeiTainanCrack and tilt of castle wallHouses destroyed, number of lives lostMany people diedHouses destroyed, number of lives lostMore than 100 people killedNumber of houses destroyedHouses destroyed, landslideHouses destroyedHouses destroyed, many people killedNumber of houses were washed awayby tsunami and several hundred peopledrownedHouses destroyed, some people killedand woundedNumber of houses destroyed