October 16, 2013 12:52 AM
By: Edgar Mana-ay for thedailyguardian.net
(The writer is a professional member of the Geological Society of America)
THE recent earthquake with the epicentre at Carmen, Bohol that was felt here in Iloilo and as far as northern Mindanao is a sober reminder that earthquakes are part and parcel of our lives here on earth, hence we have to understand it, accept it, adjust to it and even predict it.
The earthquake’s epicentre was rather deep at 45 kilometers, hence it had far reaching influence as far as Mindanao.
The populace should have a mind set of understanding and acceptance of earthquakes so that we remove the fear that effectually robs us of reacting intelligently when such calamities occur. As a backgrounder, planet earth is not solid mass. Living creatures including man stay on the skin of the earth called the EARTH CRUST whose thickness varies from 30 to 100 km., which is floating on a semi-molten mass called the mantle.
Imagine a Sunkist or Valencia orange, its skin or peel is equivalent to the earth crust but in the case of the earth, its skin or crust is NOT solid but cut into segments called TECTONIC PLATES or FAULTS and these segments as they float on the earth’s semi-molten mantle are constantly rubbing against each other. As pressure builds up on the rubbing surfaces, one plate will have to give way or collapse or sub-duct (go under the other plate) and an earthquake is produced.
As of this writing, Philvocs has yet to identify what tectonic plates collided or this may be the first time they discovered a new fault under Carmen, just like the Negros Oriental earthquake two years ago when the agency realized for the first time that a fault existed in that area.
One of the most famous and best studied faults in the world is the San Andreas Fault which slices through the state of California passing the cities of Los Angeles and San Francisco where most of our relatives in the US lives. The collision between the Pacific Plate and the North American Plate produces an annual displacement of 2 inches/year and this surface separation of land mass can be seen from an airplane. The San Andreas Fault caused the 8.3 magnitude earthquake in 1906 which levelled the city of San Francisco and the 6.7 earthquake in 1994 which caused extensive damage in Los Angeles.
It is predicted that a BIG ONE in magnitude 8 to 9 in the Richter scale will occur by year 2032! If this happens (God forbid!), it will cause the following damages: buildings shifted off foundations, ground badly cracked, underground pipes broken, rails bent, landslides from river banks and slopes, bridges destroyed, few if any concrete structures remain standing, earth slumps and there will be land slip in soft grounds, sand and mud shifted horizontally on beaches and flat lands. In other words, it will totally destroy Los Angeles or San Francisco city!
Since earthquakes are inevitable and we cannot control them, it is but prudent for man to adjust to the forces of nature. Earthquakes don’t kill; it is the building because some are so old (just like those which collapsed in Cebu) that they should have been condemned years ago or because of inadequate design, substandard materials and construction methods (like the Hall of Justice?). This was glaringly manifested in the Haiti earthquake where more than 10,000 died.Because of graft and corruption, nobody followed the building and zoning codes.
In Los Angeles, high rise buildings are now designed to be slightly elastic so that energy from a shock is dissipated harmlessly instead of fracturing support columns and floors. There are many more and it is up for our City Engineer to provide the specifications (do they know?) and enforce it strictly so that we can prepare for a big earthquake in the future.
Forecasting earthquakes is notoriously difficult because they are so complex. Hundreds of variables are involved and no two fault systems are exactly the same. This writer before had worked as a fault finder (not the kind of fault in the mind of the readers!) and it’s a very high tech and complex science in identifying even the most minor of cracks.
Extensive investigation such as core drilling to study stratigraphic throw and displacement are needed to determine whether it is an active or inactive fault as what this writer has done in geo-tech studies for the mining industry. Minor faults are most often the sources of uncontrolled underground water and are anathema to underground mining.
Some rules to follow during earthquakes: During shaking – If it catches you indoor, do not run outside. Stay under a table to shield you. If inside a moving car, stop the car but stay inside. If it catches you in the open, stay in the open but away from buildings;after shaking – Check gas and electrical lines for damages, do not light a fire unless you are sure there is no gas or fuel leakage. Do not do “tsismis” or gossiping over the phone (cell or landline) to keep it free because somebody might be calling you for help.
