Three magnitude 5+ earthquakes shook Luzon within half an hour of one another today.
The United States Geological Services (USGS) recorded a 5.7-magnitude quake east-northeast of Mabini, Batangas, just after 3pm. This was felt in neighbouring provinces and as far away as Metro Manila.
Then, less than two minutes later, a 5.9 quake struck south-southwest of Tanuan, also near Batangas, which was the location of a 5.4 quake four days ago that has been followed by more than 500 aftershocks.
Then, almost exactly 20 minutes later, a third magnitude 5 quake struck west-northwest of Taysan in the same province.
At the time of writing, the Philippine Institute of Volcanology and Seismology (Phivolcs) has only recorded the first of these quakes, which it pegs at magnitude 5.6 with a depth of 27 kilometres.
Phivolcs director Renato Solidum said no damage was expected, but aftershocks were likely.
He has again urged residents of Metro Manila and nearby areas to be prepared for a devastating quake that could kill thousands.
“Everyone must learn from the recent effects of the magnitude 6.7 earthquake in Surigao del Norte,” he said. “If a similar event happens in a highly urbanised area, the effects can be more devastating.”
Scientists at Phivolcs have long been warning that the West Valley Fault is overripe for dramatic activity.
The fault, Mr Solidum said, tends to move every 400 years or so. The last major quake along the fault was in 1658 — or 357 years ago.
“Therefore, fault can move within our generation,” he said. “But to say exactly when this will move, there is no evidence to use, for us to to say exactly when.”
However, although it’s impossible to predict an exact date, Mr Solidum said preparations should start now. “That means that there are some buildings which need to be inspected and evaluated and retrofitted and that is a massive endeavour.
“If we do not start doing this, we cannot make the number of casualties much less that what can be expected.”
The 62-mile fault runs beneath the cities and towns of Bulacan, Rizal, Metro Manila, Cavite and Laguna.
A 2004 study, conducted with the assistance of Japanese seismologists, demonstrated how a magnitude 7.2 quake could kill up to 34,000 people and injure untold others, while causing calamitous damage to buildings and infrastructure.