Skip to comments.‘It’s a blessing Philippines spared’—scientists
Posted on 09/01/2012 7:47:05 PM PDT by SeekAndFind
The earthquake that struck off the east coast of the Philippines on Friday night packed energy equivalent to 32 Hiroshima atomic bombs, but a combination of factors spared the Filipinos destruction from a catastrophe, scientists said on Saturday.
Director Renato Solidum of the Philippine Institute of Volcanology and Seismology (Phivolcs) said the 7.6-magnitude quake would have been more strongly felt had its epicenter been on land or if there was more vertical displacement of ocean water, triggering a destructive tsunami, as what happened in the Moro Gulf quake that killed thousands of people in southern Mindanao and Sulu in 1976.
Asked if he considered it a miracle, Solidum replied: Its always a blessing when damage from an earthquake is minimal. I believe in God but there are scientific explanations for what happened.
We were lucky, said University of the Philippines (UP) geologist Alfredo Mahar Lagmay. He said the Philippines was fortunate that the earthquake did not meet the conditions of a larger-scale disaster: power, proximity and the kind of structures in the affected places.
The 7.6-magnitude earthquake struck 106 kilometers east of Guiuan town, Eastern Samar, at a depth of 34.9 km, the US Geological Survey (USGS) said. The Phivolcs placed the epicenter a bit farther at 112 km east of Guiuan, in the Philippine Trench.
The Tsunami Warning Center in Hawaii raised a Pacific-wide tsunami alert, but canceled the warning shortly after the temblor generated only small waves.
The temblor killed one person in Cagayan de Oro City, knocked out power in several towns, and spurred panic about a tsunami that ended up generating only tiny waves.
Only minor damage
Executive Director Benito Ramos of the National Disaster Risk Reduction and Management Council (NDRRMC) identified the dead as Emelita Ubalde of Barangay Lapasan, Cagayan de Oro City, whose house was buried in a landslide when the quake, felt at intensity 3 in the city, struck at 8:47 p.m. on Friday.
Thousands of villagers who fled their coastal homes after Friday nights quake returned home on Saturday, but hundreds more still jittery from the temblor remained in evacuation centers, disaster officials said.
Ramos said the quake generated no large tsunamis and caused only minor damage, including cracks on buildings and several bridges.
The temblor was certainly strong enough, Solidum told the Inquirer. He said a magnitude 7 quake has energy equivalent to 32 Hiroshima atomic bombs, while magnitude 8 would be equivalent to 1,024 Hiroshima atomic bombs.
Magnitude is a measure of the energy released at the source of an earthquake. It is different from intensity, which gauges the strength of tremors in specific places, and is determined according to its effects on people, structures and the environment, according to the USGS.
Typically, a large-magnitude earthquake should generate a large-scale tsunami, Solidum said. That was also the prediction of the US Pacific Tsunami Warning Center. So when [it did not happen], we did a review and analyzed the earthquake, we found that there was also a horizontal movement, so the tsunami it generated was not that much, he said.
On Friday, the Phivolcs reported earthquake intensities ranging from 5 to 7 mostly in coastal areas facing the Pacific Ocean. Intensity 7 was registered in the towns of Guiuan, Oras, Sulat, Gen. MacArthur and Llorente, and Borongan City, in Eastern Samar; and Tacloban City in Leyte.
According to the Phivolcs, people would feel an intensity 7 quake strongly, with considerable damage to poorly built structures, cracks on roads and dikes, heavy objects and furniture falling, and most people are frightened and run outdoors.
This could have been the scenario if Friday nights earthquake had originated on land, Solidum said. Instead, what happened was it hit off shore, 112 km east of Guiuan, Eastern Samar, so the shaking was not felt very much, he said.
On the other hand, an undersea quake also entailed its own set of considerable dangers, especially that of a tsunami, Solidum said.
Expecting a giant tsunami, Phivolcs urged immediate evacuation of residents in coastal towns in the Visayas for three hours after the earthquake struck, but lifted the warning at past midnight, about an hour after the US Pacific Tsunami Warning Center canceled its own alert.
The quake generated tsunami waves of less than half a meter off Siargao Island, and 19-centimeter waves off Surigao, heights that Solidum said he considered nonthreatening, or, at most, only posed some danger to the beach.
From their seismic readings of the quake, which was tectonic in origin, Solidum said Phivolcs scientists could explain why.
The motion of the quake was not fully vertical. There were some horizontal elements to the motion, he said. This means there was not much rising of the seabed, so the vertical displacement of the water was not significant, Solidum said.
Solidum said the closest example of an earthquake approximating the characteristics of Fridays temblor he could think of was the Moro Gulf earthquake of 1976. But that was much more destructive.
The 7.9-magnitude quake, of tectonic origin, struck in August 1976, with the epicenter in the Celebes Sea near the islands of Mindanao and Sulu. The quake generated a powerful tsunami that killed more than 5,000 people.
UPs Lagmay said the Philippines escaped, nearly unscathed, from seven types of earthquake-wrought hazards: tsunami, ground shaking, liquefaction (of soil), ground rupture, ground subsidence (sinking), landslides and fires.
But as you can see, even though we had intensity 6 to 7, which is already strong, there wasnt much shaking of the ground because the epicenter was too far away, Lagmay, also executive director of the governments Project Noah (Nationwide Operational Assessment of Hazards), told the Inquirer.
Lagmay said the heavily hit areasin Samar, Leyte and Surigaowere not densely populated and did not have clusters of tall buildings and other structures, unlike urban centers. If this happened in the Manila Trench, there would have been a much bigger effect, he said.
Echoing Solidums explanation, he said a giant tsunami did not materialize because of the sideways movement of the quake. Thus, there was not enough displacement of water that could send walls of water crashing on the shores, as in the earthquake and tsunami disasters in Japan in March 2011.
But Lagmay said the decision of the Phivolcs to issue a tsunami warning and advise the immediate evacuation of coastal residents in affected areas was justified, as there was no surefire way of predicting the impact of an earthquake.
While the event is occurring, it is just right to issue a tsunami alert, because at that point, you still dont know whats going to be the [effects] of the earthquake, he said.
Just because we were lucky this time does not mean we should be complacent, Lagmay said. The Philippines, one of the countries sitting on the Pacific Ring of Fire, remains a place where big earthquakes can strike at any time, he said.
Other big quakes
The last big quakes to hit the Philippines were the 7.1-magnitude earthquake in Mindoro in November 1994 and the 7.9-magnitude earthquake in Baguio in July 1990, the Phivolcs Solidum said.
In the meantime, Solidum said residents of the coastal villages affected by Friday nights quake should prepare for aftershocks, which could be felt for weeks, or even months after the earthquake.
He said the strongest aftershocks, so far, were two that immediately followed the main seismic event, one 6.4 in magnitude and the other 6.8 in magnitude, at 9:14 p.m. and 9:27 p.m. on Friday, respectively.
As of Saturday morning, more than 150 aftershocks have been felt in the quake-affected places, most of them mild, Solidum said. In general, most seismic events will be followed by smaller events, he said, meaning weaker aftershocks.
Its been two days since we have heard fron the relatives in the Palo area. It appears there was not a major diaster, losing a few thousand wont make news...
Last nights quake was nothing compared to the Negros quake (25 miles from me) early this year.
I just barely detected last night’s quake.
I do not think I am subject to any large tsunamis. Even though I live on a beach, I am surrounded by other land areas, and not exposed to the open Pacific.
I wrote the Tsunami center for advise last Feb., but so far no reply.
As posted earlier, one can sign up for the USGS earthquake notification system. I get an email advising of any quake in the world.
Glad to hear from you.
Hope that you and yours are doing well.
I'm here in the Philippines and there was a report of only one person being killed and that was from a landslide caused by the quake.
Thanks for that info.
I spend a lot of time in the PI and in SE Asia in general and I get kinda jaded by the carefree attitude the governments in the region take to their citizens.
Hope you are doing well..maybe we can get together and have a few Red Horse next time I’m there..
I’ve been in contact with a sweet young thing who lives there. She was really scared by this one, but it appears there was little damage, except stuff falling off shelves.
I was chatting with her at the time the quake hit. She went off line for a few minutes.
I am VERY thankful it did not trigger a tsunami. Our entire high school, about 50 students, were camping on a retreat that night on a beach which would have received the full impact of that wave. If we could have gotten word to them, there is a possibility of the students scrambling up amcliff or into coconut palms. Those on the beach would be in trouble.
the quake was in the south, but there’s been a lot of rain and minor flooding on and off all over for the past two weeks. Try calling them on a cellphone if you are worried...
Checked in with your fiancee via Facebook to make sure you all were OK , and she assured me all was AOK .
“Checked in with your fiancee”
My fiancee??? Geee, I am always the last to know, hahahaha.
That is how she updated here Facebook profile . Congrats ! ; )
UP's Lagmay said the Philippines escaped, nearly unscathed, from seven types of earthquake-wrought hazards: tsunami, ground shaking, liquefaction (of soil), ground rupture, ground subsidence (sinking), landslides and fires.Thanks SeekAndFind.
Their cellphone tower is down or power is still out
...hope they are okay..
They just had another 7.0 or so in Mindanao which is plenty south of you Alex, but I hope you and your wife and little one are doing well.
I read the Manila paper and it seems damage was minimal.
Anyways, just wanted to see how you’re doing.
Take care Alex.
We felt nothing here, and heard nothing about it on internet, not even from the USGS that sends me an email whenever there is a quake anywhere in the world.
Here’s a brief story about the quake:
Reports were 6.1 to 6.4 on the Richter scale, but the quake was so deep that it was barely felt.
“Heres a brief story about the quake:”
Well, I dunno..Hard to understand the Fox report. It would scare anyone from even visiting here, haha.
It is strange that in my four years here I felt only the Negros quake, 25 miles from me, but it was no great shake,
(more of an interesting curiosity) and one other very slight tremor from another quake that was far from here.
As for tsunamis, I do not see how they would be a factor except for those exposed to the wide open Pacific.
I have tried to get an opinion from the Tsunami research center, but still waiting for a reply for the past year.
I had written to them after the Negros quake, and they said that they would get back to me, haha.
Living on the beach, I do want to know the potential for massive waves, but I am not exposed to the open Pacific.