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What is liquefaction — and why should NCR prepare for it in case of The Big One?




Metro Manila must also prepare for liquefaction, or the temporary weakening of sediments in soil, following the next big earthquake that may hit the National Capital Region.
 
Philippine Institute of Volcanology and Seismology (PHIVOLCS) Director Renato Solidum said on GMA News TV's "Balitanghali" that areas with sand deposits and low water tables as well as those that are flood-prone at are higher risk of having their sediments base give way.
 
"Lugar na mabuhangin at mababaw ang tubig, na solido ito bago lumindol, ay parang ang kilos ay likido or liquid habang lumilindol. Kumbaga lumalambot yung lupa," Solidum said.
 
Adobe or clay does not liquefy easily and makes up Metro Manila's innermost layer of soil. However, the adobe naturally slopes off near Manila Bay and a shift in the adobe by Laguna Lake allows sand to fill in gaps left by the soil.
 
Because of this, areas like Malabon, Manila, Pasay, Marikina, Pateros, Pasig, and the coastal area of Muntinlupa have the highest liquefaction potential.
 
"Kapag gumagalaw yung butil ng buhangin, may pressure yung tubig, ang tendency ngayon ng tubig ay lumabas. Lalabas siya sa ibabaw para magkakaroon ng fountain ng tubig saka kasama buhangin," Solidum said.
 
Solidum said that buildings that have collapsed due to liquefaction posed a bigger threat in post-earthquakes situations than houses sunk in the sediment.
 
"Typically, kung ang bahay ay dahan-dahang lulubog, walang mamamatay... Ang talagang delikado sa buhay ay yung nag-collapse o nahulog yung iba't-ibang bahagi," he said.
 
"Pagkatapos ng lindol, kung ang mga kalsada leading to critical facilities like hospitals ay hindi magamit dahil nagkabitak-bitak na sa kalsada, babagal ang pagdating ng behikulo na may bitbit na mga injured."
 
Good foundation and thorough preparation can minimize the after-effect of the quake, even amid liquefaction.
 
"Hindi naman ibig sabihin ng merong liquefaction ay delikado na... Marami pong paraan na pwede pong gawin para hindi naman masyadong maapektohan ang mga bahay o buildings," Solidum said.
 
He added that buildings on reclaimed areas are safe as long as they have deep foundations or are firmly connected underground, but reminded institutions and families to factor in liquefaction in their emergency plans.
 
"Dapat i-recognize 'yan na panganib na dapat paghandaan," Solidum said. —Rie Takumi/JST, GMA News