October 31, 1975 Tsunami: Philippine Trench, Philippines

Ref #10958:1975, Oct 31. This earthquake occurred at 4:28 PM on Oct 31, 1975. The epicenter was in the offshore area east of Samar Is. The nearest towns, about 70 km away from the epicenter, are rural municipalities of the provinces of N. and E. Samar.Recent investigations done in 2009 disclosed eyewitnesses from the E. Samar towns of Can-avid, San Policarpo and Taft for this particular earthquake. In San Policarpo, which is about 50 km from epicenter, the tsunami was observed after strong shaking by two individuals who were 11 and 13 years old at that time. The eyewitnesses were Mr. Cesar Moratal and Ms. Fe Moratal who are from Bgy Binogawan. They mentioned that it was high tide at that time and after the shaking they noticed that the sea receded by as much as 50 m and then went back slowly and flooded the shore by as much as 60 m inland.

In Can-avid which is about 68 km from the epicenter, the tsunami was observed by Mr Zosimo Miso who was 11 years old when the earthquake happened. He was in their barangay (Bgy Rawis) when, after the shaking, he saw waves about 2.5 m high which inundated as far as 120 m inland.

Other eyewitnesses interviewed were from the town of Taft, which is about 78 km from the epicenter. The Taft eyewitnesses interviewed by Joan Salcedo, Vilma Hernandez and Nolan Evangelista in 2009 were Ms Ana Apable who was 34 years old when the tsunami occurred, Mayor Francisco Adalim who was 19 years old and municipal planning officer Roberto Hilario who was 8 years old when the tsunami occurred. Ms Apable stated that while on a banca on Taft River, she felt a strong water oscillation and observed strong water current. Then she observed rise in water level which lowered immediately. Later, fish were found on the canals inland. Meanwhile, Mayor Adalim observed people running in panic during the earthquake, then almost knee-high sea water entered the plaza area. Mr Hilario noted that height was greater than 1.5 m and that there were 3 waves.

Hatori (1994) also gave a tsunami magnitude of 2 for this event and attributed one death to this earthquake although none of the above accounts mentioned any death.

Tsunami probability ranking is "positive". Tsunami height is estimated to be 2 m in San Policarpo, Can-avid and Taft.

Ref #1187:Tsunami with a max height of 4 m was generated. Ref #417:1975, Oct 31. A strong earthquake at a mag of 7.2 occurred on the Philippines. Its epicenter was located northeast of Samar Is. A tsunami was observed which claimed 1 life. Nearly 30 houses were washed away on the eastern coast of Samar Is. This tsunami was recorded by Japanese tide gauges on the Pacific Coast of Kyushu Is, in the Kanto region, on the Izu Peninsula, and on the Bonin Is. In Nase and on Ishigaki Jima (Ryukyu Is) the tsunami was not recorded by tide gauges. This tsunami was also recorded on Okinawa, on Yap Is, on Wake Is, on Truk Is. Ref #11135:The mag 7.4 earthquake of Oct 31, 1975, occurring northeast of Samar Is, Philippine Is, as reported in the Dec 1975 ITIC NL, generated a tsunami that was recorded as far away as Japan and Wake I. The Philippine Bureau of C&GS has sent ITIC an account of a local tsunami, and a marigram from the Legaspi Tsunami Warning Station showing a tsunami wave of approximately 1 foot. According to the report, people living on the eastern coast of Samar Is and Catanduanes stated that waves of 5 to 10 feet were experienced. Additional reports indicated some damage was caused by the tsunami. Ref #1757:An earthquake on Oct 31 in the Philippine Is (12.5 N, 126 E) generated a tsunami that killed 1 person and swept away about 30 houses on the east coast of Samar Is. The tsunami was recorded with an amplitude of 6 cm at Wake island and 3 cm at Truk.