By Hanah Tabios
With the series of tremors hitting primarily the areas of Region IV-A (CALABARZON), Philippine Institute of Volcanology and Seismology (Phivolcs) Director Renato Solidum clarified on Monday that there was no movement in the Valley Fault System (VFS) amid fears of stronger quakes.
Dr. Renato Solidum
(MANILA BULLETIN FILE PHOTO)
“We are not seeing movement of the Valley Fault System but we know that there are seizures in the area and the seizures where generated in 1911 ,” Solidum said in an interview aired over CNN Philippines.
According to the Phivolcs’ website, there are about 30 active fault systems in the Philippines from which possible quakes may originate.
“Two of the most common faults are the Philippine Fault consisting of at least 20 segments distributed from Luzon to Mindanao and the Valley Fault System consisting of two segments transecting the GMMA area,” the VFS Atlas reads.
The Valley Fault System has the east and west segments.
“In Metro Manila, the following key cities are transected by the West Valley Fault (WVF): Marikina, Quezon City, Pasig, Makati, Taguig and Muntinlupa,” it added.
In fact, a movement along the WVF may result in a 7.2-magnitude earthquake categorized as highly destructive.
But Solidum said that the recent earthquake events following Taal volcano eruption might be due to the movement of the seizure or usually called as sudden movement which is why strong quakes are felt.
“We expect that these kinds of earthquakes as similar to what we have been recording up to intensity 5. In some cases, less than magnitude 4. But that can still persist as long as magma is moving up the volcano,” he said.
With the alert status still raised at 4, the director also said that the continuous ground shaking might loosen hazardous smokes from the crater wall of the bigger volcano or the Taal caldera.
“People have to be cautious if there areas are in the steep slopes,” he warned.
On volcanic tsunamis
In an academic journal published by Oregon State University, “volcanic tsunamis can result from violent submarine explosions.”
They can also be caused by a tectonic movement from the volcanic activity or a pyroclastic flow discharge into the sea.
But in the case of Taal, as Solidum explained, the volcanic tsunamis Phivolcs had warned were not generated by earthquakes.
“But instead, when a significant volume of volcanic debris would enter lake water, this can display significant volume of water. So, the water can generate waves toward the shoreline—that’s what we call volcanic tsunamis,” he said.
To note, the same incident was already pictured during the late 1960s and the destructive 1911 eruptions.
“It’s not that high compared to the typically earthquake triggered tsunami in open seas but this can damage and impact people especially on the shore. However, if people would follow the advice that those within the 14 kilometers from the crater need to be evacuated, then, we don’t see people affected by the volcanic tsunami because they are supposed to be out of the coastal areas,” he said.
Though the agency is still monitoring the situation, Solidum warned to expect more earthquakes to still continue as magma is still moving up Taal. In fact, a lava flow was recorded early Monday at 3:20a.m.
He said volcanic lightnings are also common occurrences of the phenomenon as opposite charges rub against each other.
As for the wet volcanic ash, the director said the rain was induced by the eruption as “warm air goes up the upper layer of the atmosphere which causes precipitation or rainfall.”
He said the eruption from the main crater was already filled with water.
With the current situation, Phivolcs continued to call on affected residents within and near the volcanic island to vacate the area.