vni, a, 4 Saderra Maso and Smith: Seismic Disturbances 201 



One of these lines ran from the volcano to the coast through the 

 town of Lemery, and the other from Taal Volcano to the barrio 

 of Sinisian, making with the sea a triangular strip several square 

 kilometers in area. This whole block dropped a meter or more, 

 so that the sea washed inland for a distance of a kilometer over 

 the main highway along this coast. The road between Lemery 

 and Sinisian had to be reconstructed. The damage to buildings 

 in the town of Lemery was considerable. Fortunately no very 

 large structures were located along these lines, but had there 

 been any the property loss would have been much more con- 

 spicuous. We may not see in our lifetime a recurrence of dis- 

 asters either at Messina or San Francisco, but the time will 

 surely come when there will be further displacement along these 

 great earth rifts. It is true that there never will be as great 

 disasters in the Philippines, due to the fact that most of the 

 Filipinos live in basket-like houses which are the very safest at 

 the time of an earthquake, but large engineering works have been 

 constructed, others are being planned, and large public buildings 

 are continually being built ; hence it is of vital importance thor- 

 oughly to investigate this question in the light of all the data we 

 now possess. 



The scope of the present paper is: (1) To outline the physio- 

 graphy and geomorphology of the Philippines; (2) to discuss 

 the kinds and distribution of the rock formations and the major 

 structural features of the Islands; (3) in the light of these, to 

 show the origin of each of the important seismic disturbances of 

 the past; and (4) to draw some practical conclusions. 



We are of the opinion that most of the seismic disturbances in 

 the Philippines should be attributed not to volcanoes but to 

 displacements along the major structure lines of the Philippine 

 Islands. In view of the catastrophe of Taal Volcano and of 

 eruptions at other points like Camiguin and Mayon, the layman 

 is apt to have his perspective altered, and he is naturally prone 

 to attribute certain phenomena to causes which are not causes but 

 are results of factors not yet ascertained. It should be borne 

 in mind that volcanoes are merely incidents in the growth of the 

 Archipelago. Both volcanoes and earthquakes may be traced 

 to the existence of lines of weakness and crustal displacements. 

 Many earthquakes are due entirely to volcanic phenomena, but 

 we believe we can prove that the major earthquakes and the 

 majority of earthquakes in the Philippine Archipelago are not 

 due to vulcanism. 



