Metro Manila (CNN Philippines, December 3) — Aftershocks from the magnitude 7.4 earthquake that struck in waters off Hinatuan town in Surigao del Sur on Saturday night are not expected to trigger a tsunami, state seismologists said Sunday.
In a press briefing, the Philippine Institute of Volcanology and Seismology (Phivolcs) explained that aftershocks are generally one degree lower than the main earthquake.
“The main shock is (magnitude) 7.4 so we would expect a (magnitude) 6.4 earthquake (in the aftershocks), which is not capable of generating a tsunami,” Phivolcs Director Teresito Bacolcol said.
Immediately after the tremor, Phivolcs warned of tsunamis expected to hit affected areas between 10:37 p.m. and 11:59 p.m. on Saturday, but canceled the alert at 3:23 a.m. on Sunday.
In Surigao del Sur, the city of Tandag experienced intensity V or “strong” shaking while intensity VI (very strong) was felt in the city of Bislig.
As of 10 a.m. on Sunday, Phivolcs said it has recorded over 650 aftershocks.
Bacolcol said movement along the Philippine Trench located to the east of Mindanao caused the magnitude 7.4 quake.
He added that the Surigao del Sur quake was not triggered by the magnitude 6.8 tremor that hit in waters off Sarangani, Davao Occidental on Nov. 17.
“Hindi po stress transfer ang nangyari dito,” Bacolcol said. “Stress transfer happens sa faults na magkakalapit just a few kilometers apart. Dito magkalayo ang Cotabato Trench at Philippine Trench.”
[Translation: What happened here is not stress transfer. It occurs when a fault triggers another fault that is just a few kilometers away. Here, the Cotabato Trench and the Philippine Trench are far apart.]
The Cotabato Trench, which caused the Sarangani quake, is located on the southwestern coast of Mindanao.
