…it’s bad enough that the faultline exists; but it’s worse when you’re clueless where.
Have you seen the new, detailed The Valley Fault System Atlas from Philippine Institute of Volcanology and Seismology (Phivolcs) ? It is a handbook with 33 map sheets of cities traversed by the East Valley Fault and West Valley Fault. You need to register at the Philvocs website in order to download the atlas. In case you are having difficulty downloading (and after registration at the site), you can download the atlas here .
The 100-km West Valley Fault traverses 18 cities and municipalities: Quezon City, Marikina City, Makati City, Pasig City, Taguig City and Muntinlupa City; Doña Remedios Trinidad and Norzagaray and San Jose Del Monte City in Bulacan; Rodriguez municipality in Rizal; San Pedro City, Biñan City, Sta. Rosa City, Cabuyao City and Calamba City in Laguna; and Carmona, General Mariano Alvarez and Silang in Cavite.
Ask yourself: Is my house standing on an earthquake fault line? Another question is what is the value of this new information? What should people do if they find out that they live on top of a fault line or .5 km away or 5 km away? If your home is sitting on top of the fault line, you need to move out of that area. Whether one’s home is a kilometer or more away, it is important to check the structure of their homes through this “House self-check”.
This “House self-check” from Philvocs serves to understand and evaluate the integrity of your house and its vulnerability to strong earthquakes. The initial result will verify whether your house was properly built and have followed appropriate construction procedures and recommended measures or if it will require necessary strengthening.
This evaluation is initially intended for 1 to 2-storey Concrete Hollow Block (CHB) houses, including those residences with small shops, offices, garages and the like. It will help the house owners of this type to evaluate their houses by themselves and to understand the likely behavior of their houses during a strong earthquake.
Watch this video: Concrete Hollow Block House testing by JICA and PHIVOLCS (via Pia Ranada)
It is highly recommended however, that the state of your house must be consulted to the proper authorities. The Engineers/Experts of your Local Government Unit may have recommended methods using affordable or low-cost materials to strengthen your house (specifically its walls) in order to protect it from collapse, and to minimize possible falling debris during strong earthquake ground shaking.
This safety evaluation tool intends to provide more understanding and guidance whether your CHB house conformed with the minimum construction standard.
– It is assumed that building construction standards were most likely observed if authorized people took charge of the construction.
– It rates the chance that your house was built compliant to the recent earthquake-resistant building standards similar to special seismic detailing introduced in 1992.
– If damaged by previous earthquakes and disasters and not repaired, the structure is weakened making it vulnerable to a partial or total collapse during a strong ground shaking.
– The shape of the house influences its behavior during strong ground shaking. Box-type or rectangular-shaped houses behave better than those with irregular or unsymmetrical configurations.
– It is assumed that supervised expansion or extension leads to safer and stronger structures.
– The use of standard 6” CHB for external walls produces more stable and stronger structures. This was realized in the Full Scale Shaking Table Test conducted for CHB houses on two models on Feb 2011 in Tsukuba, Japan. Avoid using sand and gravel taken from the shorelines and beaches as materials for CHB, mortar, plaster and concrete mix for foundation for they are known to corrode the steel bars over time resulting to thinner diameter and loss of bond.
– Steel bars embedded in CHB walls, concrete columns, floors and foundation resist the impact of ground shaking. The use of the standard 10 millimeters diameter steel bars spaced at 40 centimeters from side to side and properly connected and tied to steel bars laid every 3 layers of CHB (~60 centimeters) prevent collapse of walls during earthquakes.
– Walls wider than 3 meters span without any perpendicular walls or supports are susceptible to collapse in a strong ground shaking.
– The shaking table test for CHB Houses exhibited that the unanchored gable part of the wall show larger horizontal movement during strong ground shaking. It is recommended that well-reinforced and well-anchored CHBs or light materials be used for the gable wall.
– Reinforced concrete wall foundation resists shaking, slipping and tilting better than stone-foundations.
– Rock or stiff-soil provides better support. Soft soils usually amplify strong ground shaking and tend to spread and subside the ground which may worsen damage to structure. For houses on slopes, tie beams or continues wall foundation prevent uneven settlement during strong ground shaking.
– It is important to observe the state of our house over time. Regular house maintenance must be done to prevent deteriorations like sagging roof, chipped-off plasters and cracks on walls.