230 The Philippine Journal of Science ma 



whole or a slip toward the east in connection with the changes 

 which possibly occurred in the deep trough running along the 

 east coast. Therefore, this earthquake must be classified as 

 most typically tectonic, as it occurred along a most definite 

 structural line. 



Earthquakes of 1897. The fearful happenings of this year 

 bring to the mind the somewhat fabulous occurrences of 1641, 

 when earthquakes in Luzon occurred at the same time as erup- 

 tions in Mindanao, Jolo, and Sanguir. During this year destruc- 

 tive tectonic earthquakes were felt in northern Luzon (2), 

 northern Samar (11), Masbate (12), and eastern and western 

 Mindanao (19, 22, 23, 24), while as a climax Mayon Volcano 

 had one of its worst eruptions. The most typical and important 

 of these earthquakes was the one occurring in western Min- 

 danao. Its origin or epicentral area seems to have been under 

 the sea, west of Zamboanga Peninsula, where two very important 

 lines, / — / and D — D, intersect. It must be considered as one 

 of the most memorable of Philippine earthquakes on account 

 of the most extraordinary seismic wave ever noticed in the 

 Archipelago. Furthermore, it seems to have been connected 

 with the rising of some temporary islands near the northwest 

 and northeast coast of Borneo. 



Earthquake of 1902, Illana Bay, Mindanao (23) , shook heavily 

 the districts of Cotabato and Lanao; its epicentral area com- 

 prised part of the bay, where the telegraphic cables were broken 

 and buried under mud ; the eastern coast and plain of Cotabato ; 

 and the northern coast with the uplands of Lanao district as 

 far as the lake. In this last region there had been great volcanic 

 activity during the Tertiary period, as is shown by the basalt 

 flows which cover it and by some old volcanic cones rising toward 

 the south and east; but, during the historic period, only one 

 doubtful eruption is reported. Consequently, considering the 

 wide extension of this earthquake and its effects upon land and 

 the bottom of the sea, it should be classified as tectonic and 

 connected with line M — M. 



Earthquake of November 8, 1912, Sorsogon. The meizo- 

 seismic area of this earthquake where it was felt with intensity 

 VIII-IX, causing considerable damage, was rather small, being 

 only some 35 kilometers long by 10 kilometers broad. It took 

 place in the town of Sorsogon, the mountains to the north and 

 northwest, part of the coast toward the west, and the lowlands 

 extending toward the south-southwest as far as Gubat. Its 

 center nearly coincides with the contact between the volcanic 



