In terms of both casualties and damage, the 6.9-magnitude earthquake in Cebu that took place on September 30 was far more destructive than the stronger 7.4-magnitude earthquake in Davao Oriental on October 10 — even with the latter being followed by a 6.8-magnitude twin quake the same day.
According to the National Disaster Risk Reduction and Management Council’s (NDRRMC) October 11 situation reports on both incidents, the Cebu earthquake has since recorded at least 74 deaths and 559 injuries, on top of 201,245 affected families (722,919 individuals).
The Davao Oriental quakes, in comparison, left at least seven deaths and 11 injuries, on top of 3,519 affected families (8,436 individuals) as of writing.
This could seem unusual at a glance — an earthquake with a higher magnitude should theoretically be more destructive.
Fittingly enough, the answer lies beneath the surface.
Philippine Institute of Volcanology and Seismology (Phivolcs) Director Teresito Bacolcol on Saturday explained that an earthquake’s depth ultimately impacts how devastating its consequences will be.
“If we assess the impact, what happened in Cebu was more destructive than Davao. Because the one in Cebu, the earthquake’s depth was five kilometers. The one in Davao was 23 kilometers,” Bacolcol said in a mix of English and Filipino during a news forum.
“This is because the seismic energy, as it travels from the source underground, will rise… as it goes up, its strength becomes weaker.”
“So, if it’s 23 kilometers, once it reaches the surface, it’s not as strong, and if it only runs upward for five kilometers, the seismic energy remains stronger once it reaches the top,” he added.
