2022 Luzon earthquake

On July 27, 2022, at 8:43:24 a.m. (PHT), an earthquake struck the island ofLuzonin thePhilippines. The earthquake had a magnitude of 7.0 Mw, with an epicenter inAbraprovince.Eleven people were reported dead and 615 were injured. At least 35,798 homes, schools and other buildings were damaged or destroyed, resulting in ₱1.88 billion (US$34 million) worth of damage.
Thetectonics of the northern Philippinesand around the island of Luzon are complex. Luzon is bounded to the east and west bysubduction zones. In the southern part of Luzon, the subduction zone is located east of the island along thePhilippine Trench, where thePhilippine Sea platesubducts westward beneath theSunda plate. In northern Luzon, where the July 27 earthquake occurred, the subduction zone location and direction changes, with another trench (Manila Trench) located west of Luzon and the Sunda plate subducts eastward beneath the Philippine Sea plate. The complexity ofplate tectonicson and around Luzon is evidenced by the diversity offaulting mechanismsin large earthquakes. Magnitude 7 or greater earthquakes in this region since 1970 have exhibited reverse, normal, and strike-slip faulting. These active plate boundaries lead to high seismic activity. Since 1970, 11 other earthquakes of magnitude 6.5 or larger have occurred within 250 km (155 mi) of the July 27, 2022, earthquake. The largest of these earthquakes was amagnitude 7.7 strike-slip earthquakeon July 16, 1990, located approximately 215 km (134 mi) south of the July 27 earthquake. At least 1,600 people died and more than 3,000 people were injured in the 1990 earthquake. The 1990 earthquake also causedlandslides,liquefaction,subsidence, andsand boilsin theBaguio–Cabanatuan–Dagupanarea.
The earthquake occurred as a result of oblique-reverse faulting. Preliminary analysis indicates that the earthquake occurred on either of a low-anglereverse faultdipping to the east with a small component of left-lateral (strike-slip) motion, or on a steeply dipping reverse fault dipping to the northwest with a small component of right-lateral motion. The earthquake depth, mechanism, and location are consistent with the earthquake having occurred in the Philippine Sea plate above the Sunda plate. The Sunda plate subducts eastward beneath Luzon with the plate boundary located off the western coast of Luzon. According to the USGS, theseismic momentreleased was 5.4e+19N-m, corresponding to a moment magnitude of 7.1 (Mw). A finite fault obtained fromseismic inversionsuggestruptureoccurred along an east-dipping thrust fault, and produced a maximum displacement of 0.9 m (2 ft 11 in).
It was reported as 7.3 Msby thePhilippine Institute of Volcanology and Seismology(PHIVOLCS).The report was later revised to an earthquake of 7.0 Mwwith the epicenter 3 km (1.9 mi)N 25°WofTayum,Abraat a depth of 17 km (11 mi).Despite being a relatively shallow event, nosurface ruptureswere identified. Afocal mechanismanalysis indicate rupture on a reverse fault with either a northeast–southwest striking, steep dipping (69°) plane or a north–south, shallow dipping (8°) plane.
PHIVOLCS initially suspected the earthquake may have occurred on theAbra RiverFault. Geologists had been aware of the potential for large earthquakes on the fault. The last known earthquake on the fault was in 1868, measuring 4.0–5.0 in magnitude.The Abra River Fault is a northern extension of the Philippine Fault Zone. As it runs through Luzon, it splays into three branches that runs beneath the southernSierra Madre mountains, the CentralCordillera Mountainsbefore terminating at the northern coast of the island. The three branches strike north–south and are named (west to east) the Vigan-Agao Fault, the Abra River Fault and the Digdig Fault, respectively. The Philippine Fault Zone is associated withPlioceneandQuaternaryupliftof the Cordillera Mountains. The Abra River and Digdig faults display pure strike-slip displacement, while the Vigan-Agao Fault display a large thrust component. In the northern part of Luzon, the Digdig Fault display a normal component.
However the steep-dipping plane and slip sense associated with the Abra River Fault is not consistent with rupture on it. The fault which produced the mainshock had a shallow dip angle and produced oblique-reverse displacement.A scientific journal published by Rimando and others in 2022 revealed the earthquake did not occur on any of the known faults in the area. Modelling of the earthquake indicate a source west of and parallel to the Abra River Fault. Pure dip-slip displacement of 95 cm (37 in) occurred at depths of 13–16 km (8.1–9.9 mi).
At least 3,496aftershockswere recorded by PHIVOLCS,with magnitudes in the range of 1.4 to 5.1.Sixty-three were strong enough to be felt.On July 28, PHIVOLCS revised the depth of focus of the earthquake to 15.0 km (9 mi).The strongest aftershock occurred on October 25, measuring Mww6.4, and having a maximum intensity of VII (Very destructive) on thePHIVOLCS earthquake intensity scale.It caused extensive damage to thousands of infrastructures including homes and roads, and left 139 people injured.Two days later, four soldiers giving aid to the affected area were attacked by theNew People's Army, leaving two of them dead, another injured and one missing.At least 409 aftershocks were recorded by October 26.
On thePHIVOLCS earthquake intensity scale(PEIS), intensity VII (Destructive) was instrumentally recorded inVigan, corresponding to an intensity of VII (Very strong) in theModified Mercalli Intensity Scale.The maximum intensity of VIII (Very destructive) was experienced in isolated areas.Intensity VII was reported inBuclocandManabo,Abra. In Vigan, Sinait, Bantay, San Esteban (in Ilocos Sur), Laoac (in Pangasinan), and Baguio, shaking corresponding to intensity VI (Very strong) was reported.
In an interview with a local radio station, Renato U. Solidum, the head of PHIVOLCS,it was felt with "relatively moderate intensity" inManila, the capital of the Philippines.
Despite the earthquake having an inland epicentre, a tsunami of around 0.08 m (0.26 ft) was observed inCurrimao,Ilocos Norte.Instances ofsoil liquefactionwere also recorded in Abra, Ilocos Norte, particularly along theSolsonaBasin, and Ilocos Sur.
PHIVOLCS stated that there was notsunamithreat,and an alert was not issued. Due to the inland epicenter, the earthquake could not cause seafloor uplift and trigger large waves. However, PHIVOLCS noted that shorelines and enclosed bodies of water may experienceseichesdue to oscillation from the earthquake.
According to theNational Grid Corporation of the Philippines(NGCP), power services in Manila and the surrounding provinces were uninterrupted. The NGCP said that load tripping may have occurred.
Commanders of thePhilippine National Police(PNP) in Luzon were tasked to cooperate with the regional Risk Reduction and Management Office to maximize relief operations. All PNP infrastructures were also inspected for damage.The Army and Coast Guard also were dispatched to the affected areas.
PresidentBongbong Marcosconducted a press briefing addressing the disaster and was scheduled to fly to Abra.He was expected to coordinate with national and local government establishments in relief efforts,but was "staying away" at the present. He added that this was so that the local government could carry out their procedures without "disturb(ing) the work (of local officials)".President Marcos has also called for telecommunication companies to give free communication to areas where transmission towers had collapsed.Local authorities stated that work and schools would be suspended in parts of Ilocos Norte to allow damage assessments to take place.
In the Ilocos region, theDepartment of Social Welfare and Development(DSWD) said that it would be ready to serve the affected. More than 17,410 family food packs and 9,291 non-food items had been prepared and stored at warehouses, ready for distribution. An additional ₱2.70 million (US$48.6 thousand) was set as standby for emergency response.Work and school was also suspended in Baguio by its mayor.
TheGovernor of Abra, Dominic Valera, declared the entire province under a state of calamity. Province officials also authorized the use of 58 percent of the Calamity Reserve Fund for relief efforts.TheHouse of Representativessaid it would allocate funds in the national budget to restore damaged buildings, including affected heritage and cultural buildings.UNICEFsaid that emergency supplies were on standby to support government relief efforts and to assist affected children and families.
Eleven fatalities were reported, including four from a landslide,and at least 616 people were injured.More than 513,330 people were affected, of which, 57,022 were displaced.
A total of 35,798 homes were affected, including 686 which were totally damaged.An additional 177 healthcare infrastructures were destroyed.Over 8,000 schools were affected.Eleven schools inCentral Luzon, nine in theCagayan Valley, eight from theCordillera Administrative Regionand seven in the Ilocos Region, were seriously damaged.
TheDepartment of AgricultureandNational Irrigation Administrationalso reported damage estimated at ₱56.4 million (US$1.02 million). TheNational Irrigation Administrationestimated around ₱22.7 million (US$406,942) worth of damage to irrigation systems. There was an additional 2,383 buildings damaged, incurring a loss of ₱1.81 billion (US$32.5 million). Total damage was estimated to be worth ₱1.88 billion (US$34 million).
A preliminary survey of damage suggested at least 80 percent ofAbrawas affected.A power outage occurred across the province due to destroyed power lines. Many businesses were disrupted. Residents stayed outside their homes and were left without food.One villager died when he was hit by falling cement slabs in his house.InBangued, a person died when the walls of adormitorycollapsed, and an additional 44 were injured due to falling debris.A 59-year-old resident fromTubodied of his injuries after the roof of his house collapsed.
The bodies of four people were recovered from a landslide.Historical churches in the province were also affected. The Shrine of San Lorenzo Ruiz in Bangued sustained major damage and one of its bell-towers was reduced to rubble.TheTayum Churchinthe town of the same namealso sustained damage.Over 640 displaced people took refuge at the town plaza.Two bridges, one in Manabo and Bangued, respectively, were affected.Schools,and 20 government properties were damaged.At least 31 landslides were reported, and a partially collapsed hospital was evacuated.Road infrastructures including three bridges were damaged.
Officials inBaguiostated that several crucial roadways were affected by debris. Thirty-three buildings were damaged.Road closures affected motorists alongKennon Road,Baguio–Bua–Itogon National RoadandBenguet–Nueva Vizcaya Road, leaving only theAspiras–Palispis Highwayopen.Patients atBaguio General Hospitalwere evacuated.A student atSaint Louis Universitywas injured during a panic.
A total of 32 towns and two cities received damage, with the heaviest in Vigan.Nearly 100 homes were heavily damaged.Heritage sites in theUNESCOWorld Heritage CityofViganwere damaged, including theVigan Cathedraland old-century houses, as well as few toppled power lines along Calle Crisologo.Parts of the old historic belfry ofBantay Churchinthe town of the same namealso crumbled to the ground.It was felt strongly inIlocos Surfor 30 seconds or longer.
The earthquake was felt strongly inMetro Manila, where minor damage to a hospital and several other buildings were reported.The earthquake prompted theManila Metro Rail Transit Systemto suspend service during rush hour.Operations resumed at 10:12 a.m, with the exception ofLRT Line 2due to inspections.Occupants ofthe Senate buildingin Pasay were also evacuated.
InApayao, officials noted that two structures were damaged.Sixty-one schools were damaged, including 76 classrooms which were completely destroyed.InKalinga, a worker fell from a building and suffered leg fractures.One fatality was also reported in the province.InIlocos Norte, bricks fell from old buildings, including at an elementary school. Cracks also appeared in the public market.
ThePhilippine Ports Authority(PAA) said that hairline cracks occurred in a building at the Port ofCurrimao, Ilocos Norte, and at a passenger terminal inClaveria, Cagayan.InAsipulo,Ifugao, a landslide partially buried an ambulance; four occupants including a pregnant woman escaped unhurt.There were two deaths in Benguet,including one inLa Trinidad, who died due to falling debris from a collapsed building.At least 62 buildings were damaged in the province.