vm, a, 4 Saderra Maso and Smith: Seismic Disturbances 207 



ward of the Philippines have not yet located anything like such 

 tremendous depths. We may then conceive of the Philippine 

 Islands as being at the edge of the continental platform or on 

 the brink of a tremendous "Graben" (Plate I). This platform 

 was subsequently raised above sea level and complexly folded at 

 the time of what is known as the "Miocene revolution" which 

 extended from New Hebrides through the Philippines north- 

 ward to Japan; westward across Burma, India, Persia, and 

 Egypt; northward to the Vienna basin; and westward even to 

 the Pyrenees. Following this crumpling of the crust, a gradual 

 tilting of the Philippine block toward the east seems to be going 

 on at the present time. This is evident from the raised coral 

 reefs on the western coast of northern Luzon, the western coast 

 of Palawan, and from the raised deltas and beaches on the 

 western coast of Zamboanga Peninsula with the existence of 

 drowned river basins which we know of as certain on the 

 eastern coast of Luzon, and at other points in the Archipelago 

 about which we can conjecture although we have no definite 

 information. 



Von Richthofen, 17 ten years ago, noticed a peculiarity of the 

 Philippine Archipelago in connection with the Japanese, Riu Kiu, 

 Kurile, and Aleutian chains of islands; namely, a series of arcs 

 with their convex sides turned toward the Pacific. One of 

 these arcs is well marked in the Philippines by the tectonic line 

 passing through southeastern Luzon, Samar, and the Eastern 

 Cordillera of Mindanao. Northern Luzon does not conform very 

 well to this arc, but we may imagine that there has been a fault 

 and offset at the narrow portion of Luzon at the northern end 

 of Tayabas Peninsula. 



Besides this dominant curved line, and those parallel to it 

 in the eastern part of the Archipelago, there are in the Philip- 

 pines several other distinct tectonic lines as shown in Plate II. 

 One of these is the Palawan line, another is the Sulu Archipelago 

 line, others are the parallel lines through Panay, Negros, and 

 Cebu — all trending northeast and southwest. Masbate seems 

 to be the "keystone" in the Philippine structure. The eastern 

 prong of this island conforms closely with the outermost arc 

 of the Archipelago, while the western prong conforms with one 

 of the northeast-southwest lines passing through eastern Panay. 



" Geomorphologische Studien aus Ostasien, Sitzungsber. d. k. pr. Akad. 

 d. Wiss. z. Berlin (1902), 40, 944-975. 



