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

250 Pao Hua Lee‘. . . an earthquake, the most severe ever experienced on the island sincethe first day of the Dutch, . . . It occurred on the 18th of December 1867,and the vicinity of the town of Kelung sustained the greatest damage, . . .Foreigners in the Custom service reported that at Kelung about 15 shockswere felt during the day, but that it was the first movements that causedthe damage. In 15 seconds after the first perceptible shock the damage wasdone, and the town of Kelung was in ruins. The force of the earthquakemay be judged when it is noted that the water of Kelung Harbor ranout, leaving the bottom of the bay exposed. Fortunately, there were noforeign vessels present, but the Chinese junks that were there, large andsmall, were in one second left dry on the bottom and in another, weredashed into the town with fearful speed to work havoc on the remaininghouses left near the shore. Multitudes of fish were thrown upon the shoreand were promptly gathered by the populace . . . The number of lives lostis unknown. It is doubtful if a count was made, but probably severalhundred perished . . .” [Note: ‘Kelung’ is now spelled ‘Keelung’.]Another tsunami occurred in 1917. On east coast of Taiwan, its wave height wasreported 3.7 meters, but there was no damage description.4. Historical SeismogramsThe Central Weather Bureau has retained about 350,000 seismographic recordssince 1897. The oldest records in existence, though not complete, are of 1929 comingfrom Wiechert seismographs. Seismograms earlier than 1929 were all lost.By 1987, all seismograms in the Central Weather Bureau will be photographicallyreproduced in microfilm for archives. Now, there are 20,000 records of Taipeiseismographs from 1956 to 1982 which have been put into microfiche already. Thesize of the above mentioned microfiche is 10 x 15 cm containing 6 images that canbe enlarged 22 times for reading. Each microfiche includes the information such astime, station name, type of seismograph and its reduction rate. All these recordsare arranged by station, year, and type of seismograph in archives.For user’s easy access, an index will be provided and when all seismograms havebeen microfilmed, a catalog will be accordingly made. For international data exchange,we will prepare a duplicate copy set to supply World Data Center A.5. Discussion and ConclusionsSince 1897, 73 significant disastrous earthquakes have occurred in Taiwan areaaccording to records at CWB. Among them are 19 major earthquakes, those havingmagnitudes of 7.0 or larger. Forty-four of the 73 earthquakes occurred on land, and29 occurred on west Taiwan (see Figure 4). Although most of the earthquakes haveoccurred in the east region of Taiwan, a mountainous area with few inhabitants,earthquakes in the west region have been more damaging to life and property.Therefore, earthquake risk is higher in the west than in the east. Earthquake riskis especially high in the Chaiyi-Tainan area, and moderately high in the areas ofHwalien-Ilan and Taitung-Lanyu.