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| 26 Earthquakes in and around Marinduque from Feb. 19 - March 4, 2017 |
The 2017 destructive Surigao earthquake last Feb.10 at 6.7 magnitude damaged 300 houses and collapsed seven bridges.
But the most devastating quake prior to that was the 7.2 magnitude 2013 Bohol earthquake, said to have released underground a tremendous amount of energy equivalent to more than 30 Hiroshima atomic bombs.
No doubt these events are a wake up call for all Filipinos in the Philippines to brace for possible earthquakes that may strike elsewhere in the country anytime.
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| The Central Marinduque Fault |
On October 20, 2006, Phivolcs reported a 5.3 magnitude earthquake in Marinduque around 10:30 p.m. with tremors reaching as far as Tagaytay and Quezon City.
The next day with the epicenter located 35 kilometers south and 89 degrees west of Boac, Marinduque a second earthquake struck at 1:27 am.. The Lubang and Marinduque faults were identified as the sources of the earthquake.
The Marinduque quake’s epicenter according to Phivolcs was traced to the eastern segment of the Lubang Fault located offshore between Mindoro island and Marinduque. Five major aftershocks and more than 700 minor aftershocks were recorded.
The quake caused no damage to property but sent many residents in Marinduque to panic. Phivolcs' Renato Solidum said that despite the earthquake at the Lubang Fault, people should remain alert against "the big quake", but said there is no way to predict where or when the big quake will occur.
2013 Marinduque swarms and the Bohol earthquake
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| 2013 Bohol earthquake. Photo: Marianne Bermudez |
Intrigued by the possibility that the Marinduque earthquake swarms could have triggered the Bohol tremors, I threw the question to the dedicated administrator of Earthquake-Report, Armand Vervaeck (Belgium). He responded in part as follows:
"Nobody will be able to tell you as science isn't able to make prognoses in strength and time. Swarms are not unusual and 98/100 nothing important happens thereafter. In some cases (like in l'Aquila Italy) swarms are precursors of something bigger to come. So I don't think that something will happen BUT we are not really sure about this :))
"Taken into account the location of the Marinduque quakes, they could also have been the trigger to free the Bohol energy BUT nobody will be able to prove that."Then came a scientific report two years later, in 2015, about Italian scientists discovering that seismic pressure transfers up to 1,000 km causing other earthquakes elsewhere! Story below.
The distance between Marinduque and Bohol is only 458.85 km, which is only half of the stated distance.
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| Distance between Marinduque and Bohol is only 468.85 km. This distance is equal to 291.33 miles and 252.99 nautical miles. How earthquakes can trigger copycat quakes 1000 kilometres away |
New Scientist, 21 September 2015
“Seismic waves unleashed during Wednesday’s magnitude 8.3 earthquake in Chile could have triggered aftershocks as far as 1000 kilometres away.
That’s because they can shake up grains of rock wedged inside distant faults. According to computer models, even weak waves at the right frequency could be enough to start a new quake by vibrating that grist into a more slippery, liquid-like layer.
Earthquakes often happen when two tectonic plates that have been pressed together suddenly slip. But we’ve seen that major earthquakes like 1992’s Landers earthquake in California can also send out waves that spark copycat quakes 1000 kilometres away, even though the waves get weaker as they travel.
The mysterious remote triggering of quakes may have also played a role in events in Chile in 2014, and Japan in 2011.
“We were wondering: how could it happen that a very tiny wave with a very small amplitude could trigger earthquakes a thousand kilometres away?” says Lucilla de Arcangelis of the Second University of Naples in Italy.
One idea is that sound waves can lather up the grains between the two plates in a way that decreases friction, to make a slip easier. Now a team including de Arcangelis has built a computer model that shows the process as it happens.
They found that seismic waves could trigger an earthquake in the simulated fault only if they came in a narrow range of frequencies. If the fault was just about to slip, it would hasten the process by starting vibrations in that range. Only the frequency really mattered – weak waves, or even waves that would actually push in the direction against a slip, could still induce an earthquake.
“Each fault will have its own acoustic resonance frequency,” de Arcangelis says. “If a signal arrives at this frequency, the fault that without perturbation would be quiet will trigger an earthquake.”
Combined with a 2005 lab experiment that also showed a resonant frequency could jiggle glass beads in a fake fault into slipping, this simulation could suggest that actual faults have specific frequencies they’re susceptible to.
