Dennis Gasgonia

What is a doublet earthquake? Phivolcs explains twin quakes that rattled Davao

Article (news)

Job Manahan

ABS-CBN News

<p>MANILA — A rare “doublet” or two back-to-back strong earthquakes occurred in Davao Oriental this Friday, Phivolcs said, but the agency allayed concerns this could trigger a stronger temblor in the province.</p><p>On Friday morning, a magnitude 7.4 quake struck waters 44 kilometers northeast of Manay town, immediately killing at least 2 individuals.  </p><p>Past 7 p.m. the same day, a magnitude 6.8 undersea earthquake also happened, with Phivolcs saying this is a separate earthquake.  </p><p>In a news briefing in Quezon City, Phivolcs Director Teresito Bacolcol said the twin quakes were not related. The magnitude-6.8 earthquake cannot also be considered as an aftershock.</p><p>“It’s a separate event. We have a term for that, it is a doublet. These are closely timed events and they happen almost in the same area and they have almost the same magnitude,” said Bacolcol. </p><p>He said that aftershocks are defined as shocks that are one magnitude lower than the main shock.</p><p>“Ang main shock is magnitude-7.4 and the aftershock we would expect is just magnitude 6.4,” he added.  </p><p>While considered rare, a doublet already happened in the country in 1992 and most recently in 2023. It usually occurs in the same fault, the official said. </p><p>“They usually occur when a fault or an earthquake generator is quite complicated, causing a trigger of sequence of earthquake events. It is very common for the Philippines,” he said. </p><p>The doublet quake happened in the Philippine Trench, he said.</p><p>“Again, same source, same area and closely timed sila,” according to the Phivolcs director. </p><p>Asked if the doublet earthquake could trigger a stronger earthquake in the province, Bacolcol answered in the negative. </p><p>“If it will trigger another event, higher? The probability is very small kasi kung magti-trigger pa siya ng mas malaking event – magnitude-7.5 or 7.6 – yung mga nangyayaring events natin that would become foreshock then we’ll have the main shock,” he said. </p><p>“The determination ng foreshock is always in the hindsight,” he said.</p><div><a href="https://www.abs-cbn.com/news/health-science/2025/10/10/phivolcs-no-connection-in-cebu-la-union-davao-quakes-1725"><strong>Phivolcs: No connection in Cebu, La Union, Davao quakes</strong></a></div><p>As of 8 a.m. on Saturday, Phivolcs had recorded 808 aftershocks, with 335 plotted and 13 felt. The magnitudes ranged from 1.2 to 5.8, based on data from the Mati Seismic Station.</p><p>The National Disaster Risk Reduction and Management Council (NDRRMC) said at least seven have reportedly died because of the strong quakes in Davao Oriental, while nearly 2,500 families continue to stay in evacuation centers because of the aftershocks.</p><div><br/></div><div><strong>RELATED VIDEO</strong></div><div><span class="fr-video fr-deletable fr-fvc fr-dvb fr-draggable" contenteditable="false" draggable="true"><iframe width="640" height="360" src="https://www.youtube.com/embed/rze7x9MW9Ws?&amp;wmode=opaque&amp;rel=0" frameBorder="0" allowfullscreen="" class="fr-draggable"></iframe></span> </div>

<p>A rare “doublet” or two back-to-back strong earthquakes occurred in Davao Oriental this Friday, Phivolcs said, but the agency allayed concerns this could trigger a stronger temblor in the province.</p>

A rare “doublet” or two back-to-back strong earthquakes occurred in Davao Oriental this Friday, Phivolcs said, but the agency allayed concerns this could trigger a stronger temblor in the province.