vni, a, 4 Saderra Maso and Smith: Seismic Disturbances 217 



which have occurred since that time, we have the distribution 

 of tectonic epicenters 21 as given on the map (Plate II) . 



The region which has suffered the most from violent earth- 

 quakes during the past fifty years is without doubt eastern 

 Mindanao and particularly the Agusan Valley. We have no 

 seismic data of this region from a period more remote than 

 1889, but this is doubtless owing to the undeveloped state of 

 that part of the Archipelago and to the consequent lack of 

 communication with the outside world. The great deep-sea 

 trough which exists along the east coast of this part of the 

 island indicates that many earthquakes must have occurred there 

 since it first began to form. The same may be said of the coasts 

 of Samar which also are exposed to the influence of the same 

 "deep," and hence that they also are as unstable as the eastern 

 coast of Mindanao. The principal epicenter of Samar is near 

 the northeast coast. 



In the Island of Mindanao there exist also the following 

 seismic regions : The Gulf of Davao and the district of Cotabato 

 between Apo Volcano and Illana Bay ; the coast along Illana Bay 

 and the district of Lanao ; the extreme western part of the island 

 near Zamboanga. Basilan Island and the Sulu Archipelago 

 are also in a region of great seismicity, although the epicenters 

 seem to lie in the neighboring seas. The district of Dapitan in 

 the northwest is affected by a submarine epicenter situated 

 between Dapitan and southern Negros. All the central part of 

 northern Mindanao comprised within the district of Misamis 

 appears to be a region of much greater stability, but the neigh- 

 boring Island of Camiguin has suffered much at different times 

 from volcanic earthquakes. 



The Visayan Islands, in addition to what has already been 

 mentioned of Samar, have two regions of great seismicity, Panay 

 and Leyte. An epicenter lies in the Uoilo Straits between Panay 

 and Negros, while within the Island of Panay at a distance of 

 about 30 kilometers from the southeast coast there is another 

 more important one where originate very violent earthquakes, 

 but apparently of the rockfall type. In Leyte there are two 

 volcanic epicenters, one in the southeast and the other in the 

 north and northeast, and there is probably a rockfall epicenter 

 to the west close to the Camotes Islands. 



The Islands of Cebu and Bohol, and perhaps also Oriental 

 Negros, may be considered as stable. However, Oriental Negros 



81 The word "epicenter" is used in the broad sense, as the region where 

 important earthquakes originate. 



