Luzon Philippines 1990 (CAR)
On Monday, July 16, 1990, at 4:26 pm local time, a moment magnitude 7.7 earthquake struck northern and central Luzon, resulting in widespread damage and loss of lives.
The epicenter (15.723N, 121.18W) was located in the proximity of Rizal City, north of Cabanuatan. The earthquake was the result of a complex rupture process characterized by two main shocks which occurred during a 1 to 3 minutes period as witnessed by many people. It was caused by a left-lateral movement along the NW striking Philippine Fault Zone, already source of catastrophic earthquakes in the past, and its northern splay known as the Digdig fault.
The earthquake produced a 120 km-long ground rupture that extended from Dingalan to Kayapa with a maximum lateral displacement up to 6.2 meters and vertical displacement up to 2 meters.
Damage was generally localized (particularly west of the fault) related to the effects of local topography and ground conditions. Surprisingly it was not so severe in the proximity of the fault and in the epicentral area as it was in other areas built on soft soils or unstable slopes (e.g. Baguio, Dagupan, Agoo).
The worst affected towns were Baguio, Agoo, Dagupan, Aringay, and Pura where the maximum felt intensity was MM VIII-IX; Tarlac, Cabanatuan, Rizal and Manila suffered partial damage.
Hardest hit was Baguio where 28 buildings (including hotels, hospitals and schools) and 132 residences collapsed or were destroyed and around 350 people killed (http://www.cdc.gov/mmwr/preview/mmwrhtml/00001734.htm).
The earthquake induced widespread liquefaction (and related phenomena: ground settlement and lateral spreading) in the costal area south of San Fernando in La Union, along the Lingayen Gulf and in the Central Plain and triggered thousands of landslides (and rock falls) in central and western Luzon, particularly in the Cordillera Central and Caraballo Mountains.
In Dagupan due to liquefaction an estimated 90% of the buildings in the city centre sank by 1 to 2 meters relatively to the street.
Baguio remained isolated for 48h because of the landslides. Many landslides were triggered by the aftershock swarm (characterized by magnitude as big as 6) and subsequent monsoon rains. The unprecedented extention of landslides resulted in a large enviromental impact.
A peculiar aspect of the earthquake was the widespread damage occurred to the transportation routes due to bridges collapse, road settlements, or road obstructions that isolated many towns (especially in mountain regions), delaying the rescue and relief to the affected people.
According to Rantucci (1995) nearly 100,000 houses were damaged and 40% of them were virtually destroyed. Generally light-weight buildings performed better than the concrete buildings.
In the USGS EXPO-CAT database it is estimated that 3,747,146 people were exposed to intensity VII or higher, out of which about 84% were in rural areas. The exact number of fatalities in this event is not known due to the extensive landslides and the remoteness of some affected mountainous areas.
A first estimation of the casualties was 1283 dead, 2786 injured and 321 missing (NDCC, 1990). According to Rantucci (1995), there were 1666 deaths out of which about 450 were due to landslides, while in addition about 1000 people were reported missing and over 3000 were injured. In EM-DAT the number of people killed is 2412, whereas in PAGER-CAT it is 2430 out of which 1621 were due to ground shaking. 120,000 were the people made homeless (HABITAT, 1990).
Concerning the direct economic loss it ranges from more than 370 million USD (EM-DAT) to more than 770 million USD (NEDA, 1990). HABITAT (1990) stated the direct economic loss to more than 555.5 million USD, while Rantucci (1995) provides a value of 637 million USD in 1991. Munich Re suggests an economic loss of 1 billion USD including 110 million USD in insured losses. Considering the 550 million USD, the ecomomic loss would slightly exceed 1% of Philippines GDP in 1990.
Rantucci G., 1995. Geological Disasters in the Philippines: The July 1990 Earthquake and the June 1991 Eruption of Mount Pinatubo; description, effects and lesson learnt.
National Disaster Coordinating Council (NDCC), 1990.Final Report on the.July, 16, 1990 Earthquake. Nov. 14, 1990.
National Economic and Development Authority (NEDA), 1990. Reconstruction and Development Program.
United Nations Centre for Human Settlements (HABITAT), 1990. Technical report on Luzon earthquake of 16 July 1990, Republic of the Philippines with recommendations for recostruction and development.
Many sources report more than 3,000 insured people (e.g. PAGER-CAT; Rantucci, 1995). The National Disaster Coordinating Council (NDCC), 1990.Final Report on the.July, 16, 1990 Earthquake. Nov. 14, 1990 estimated 2786 injured people.
It is possible that final number of missing could have been reduced to <500.
The number of deaths varies according to the source. It ranges from more than 1283 (NDCC) to 2430 in PAGER-CAT and Utsu catalogue. EM-DAT report 2,412 deaths.
The actual deaths due to slope failures could be higher as many of the missing would be related to landslides.
Rantucci, 1995 estimated around 40000 severely damaged buildings. Many buildings were destroyed by landslides and counting these would be extremely difficult. Also many buildings affected by liquefaction may be counted as destroyed as the degree of sinking and or leaning was often quite severe.
Rantucci, 1995 estimated around 100000 damaged buildings
Economic loss estimates vary from 370 to 1000 million USD. A value of around 700 million USD is considered as the most representative. It is not clear if the above estimates account for insured losses or not.
Munich Re reports 1 billion USD overall economic loss, including 110 million USD in insured losses.