Earthquake Measurement at Miyako. 



By 

 F. Omori, D. Sc, 



Professor of Seismology, Tokyo Imperial University, 

 and 



K. Hirata, 



Director of the Meteorological Observatory of Miyako. 



With Plates XVII— XXIII. 



1. The Meteorological Observatory of Miyako (lat. 39°38^ 

 long. 141°59^) is situated on a small promontary of palaeozoic 

 rocks, 30 m. in height, which separates the two towns of 

 Miyako and Kiiwagasaki. As, besides, the prevailing formation 

 in this part of the Pacific coast of the Main Island is the 

 granite, the following seismographical observations at Miyako 

 are to be regarded as good illustrations of earthquake measure- 

 ments in a rocky district. 



The seismograph used was one of the Gray-Milne type, 

 which records, by means of a pair of horizontal pendulums and 

 compensated vertical springs, the earthquake motion in three 

 rectangular components on a smoked paper wapped round a 

 revolving drum, started, as usual, on the occurrence of an 

 earthquake by a sensitive electric contact-maker. 



2. There were 27 earthquakes, which gave diagrams suf- 

 ficiently large and distinct to be measured. Their dates and 

 time^ of occurrence are given in the following table : 



1. The time is given in the First Normal Japan Time, namely, that of longitnde 

 135° E. 



