Wednesday, 23 March 2011

Marikina Valley fault line, earthquakes and what to do...

After the devastating 9.0 magnitude earthquake that hit Japan and triggered the 10m tsunami, experts reveal a grim scenario for Manila.

According to National Institute of Geological Science Mahar Lagmay, the Philippines experience at least 5000 earthquakes each year and a 5.0 magnitude is normal fare. The last strong intensity, 7.9-magnitude earthquake happened 21 years ago on July 16, 1990 (Luzon earthquake that toppled Hyatt Terraces Hotel) and 4 years earlier, on August 17, 1976 (Moro Gulf earthquake).  He said "statistically, the metropolis is likely to be hit on an average by a strong (Intensity VII) earthquake every 17 years; moderately strong (Intensity VIII) earthquake every 79 years; and extremely strong earthquake (Intensity IX) in 112 years."

There are five seismic source zones in the Philippines: (1) Markina Valley Fault System (right photo), (2) Philippine Fault Zone, (3) Lubang Fault, (4) Casiguran Fault and (5) Manila Trench. The Marikina Valley Fault and the Philippine Fault Zone are the ones which can strongly affect Manila.

The Marikina Valley Fault extends all the way North of Angat and cuts through Quezon City, Pasig, Taguig,  Muntinlupa, Sta. Rosa all the way down to the fringes of Tagaytay (click google map here to check location). The magnitudes predcted from the Marikina Valley fault varies from 6-7.0 (Nelson et al, 2000) to 7.2 (MMEIRS, 2004) to a maximum of 7.7 (Rimando & Kneufer, 2006).  Lagmay said that a 7.0 to 7.9 magnitude is considered a ‘major earthquake’ and may cause serious damage with an intensity of VII or higher. Residents living 5m from the left/right of the fault line are warned of the potential damage caused by an earthquake. This is, possible collapse of structures caused by ground shaking and worst, ground rupture. Those living near coastal and river sediments may experience destructive effects due to ground liquefaction.

Based on the evidences of movement collected through the years and using the elastic rebound theory, he said that there is a strong indication that a 7.2 magnitude earthquake may occur. And if this happens, the 2004 MMEIRS earthquake model scenario for a Valley Fault of magnitude 7.2 (referred to as Model 8 or ‘worst case’) estimates: 170,000 residential houses collapse, 340,000 residential houses will be partly damaged, 34,000 persons will die,114,00 persons will be injured. Secondary disaster includes fire breakout that may burn approximately 1,710 hectares and 18,000 additional lives lost. Also, infrastructures and lifelines will also be heavily damaged.

Recently the Metropolitan Manila Development Authority (MMDA) has drawn up an earthquake response plan called  "Oplan Metro Yakal". Under the plan, in case of an intensity 8 earthquake, fuel shall be rationed; in case of an intensity 7, classes in all levels will be suspended for three days or more; and in case of a high magnitude quake, all grocery stores will be kept open from 6 a.m. to 10 p.m, (assuming they have not collapsed). Four evacuation sites were designated for the different sectors in Manila: North- Veteran’s golf course in Quezon City; South - Villamor golf course in Pasay City; East- Wack Wack golf course in Mandaluyong City; and West - Intramuros golf course in Manila.


Indeed as the saying goes, it is better to be safe than sorry. Lagman offered tips for earthquake safety and awareness: (1) estimate the size of the earthquake that may occur; (2) given the size, estimate what the shaking will be; (3) given the shaking, estimate the response of different types of buildings.

To plan for an earthquake, he advised to establish a meeting place where all family members can reunite (for those with children, find out about earthquake plans developed by the school),  secure items at home for things that could fall or move; and to remember that transportation may be disrupted and best to prepare an emergency surivval kit that is good for 72 hours. The kit should contain essential provisions like water (about 3.5 lites or gallon per person per day), food, a whistle, flashlight and extra batteries, a first aid kit with necessary medicine, antiseptic, scissors, bandages. Rice, easy to open canned goods, noodles and a transistor radio is good to have. Have emergency cash and important documents like passports and hospital records within reach and wear sturdy shoes. 

Lastly, in case of earthquake, the best protective action is to "duck-cover-hold". Below is Philvoc's guide on what to do before-during-after an earthquake:

 

1 comment:

tulisanes said...

For a fairly thorough if not complete list of subdivisions and communities, including the visual identification of houses and buildings directly on top of the MARIKINA VALLEY FAULTLINE SYSTEM, pls. visit my blog at:

http://tulisanes.wordpress.com/

as you will not be disappointed, pls. pass on this information to others, too. thank you!