Soldier's Pen "Quakes and waves"

Soldier's Pen
By BGen. Alexander Cabales (Ret.)

Quakes and waves

                
               One of the major natural calamities that hit the country last year was Typhoon Sendong which severely punished Iligan and Cagayan de Oro Cities on December 16, 2011. It brought about 10 hours of heavy rains that caused flash floods in an area that rarely experiences tropical cyclones.

                Sendong tells us that natural catastrophes can happen anytime at any place even in the most unlikely ones.  Historical statistics can no longer be a basis for predicting a natural occurrence in the future. The Sendong experience was a realization for most local government executives.  Everyone now wants to equip their respective localities to cope with disaster.   It was only unfortunate that the next calamity happened too fast, too soon.

                On February 6 at 11:49 AM, another disaster struck.  This time it was a 6.9 intensity earthquake that ravaged the islands of Cebu, Negros and Panay.   The central western side of Negros Island was the worst hit. The quake's epicenter being very near the town of Tayasan, Negros Oriental,  some 70 - 80 kilometers south of San Carlos City.  An earthquake of such a magnitude was never experienced by anyone in his lifetime in this part of our country.  So, except for one or two schools that conducted earthquake drills for their students, everyone practically didn't know what to do.  There was panic everywhere that affected everyone - the poor and rich alike; the educated and the ordinary folks; and the old and the young.  Even government agencies and offices were caught with pants down.

                Despite the strong quake and the several but milder aftershocks, San Carlos only sustained minor damages.  Its worst effects, though, were the continuing paranoia of the people for the subsequent tremors and the possibility of a tsunami that may have been triggered by the quake.   'Learning' from the experiences of Japan and Indonesia on March 11, 2011 and December 26, 2004, respectively, when tsunamis immediately followed an earthquake, the people started leaving their houses in haste to seek the safety of higher grounds. 

                Phivolcs then issued Tsunami Alert Level 2 about an hour after the quake only to cancel it in about 30 minutes later.  Despite the cancellation and the announcements by the LGU that it was already safe, the people still refused to go back to their homes.  There was disarray and the people were as confused as the Phivolcs personnel were.

                We cannot blame the ordinary folks for their reactions.  The worst fear is always the fear of the unknown. Moreover, there was misinformation or lack of information on the type of disaster that hit them.  Nobody seems to be on top of the situation.

                The reaction of most people to evacuate their homes was spontaneous and immediate even before the tsunami alert was issued at about 1:49 PM on that same day.  This announcement, though late, only 'confirmed' the people's fear that indeed a tsunami might be coming.  Phivolcs never defined nor explained what Tsunami Alert Level 2 was.  Many thought that it was similar to a typhoon signal number 2, the second to the highest typhoon signal and therefore a very devastating one. 

                It fact, Tsunami Alert Level 2, supposedly only advises people living 10 - 40 m from the coastline to watch out for 'unusual waves' that may be as high as one meter.  At the most, only those that are in the 10 - 40 m distance from the coastline may be evacuated if necessary.  It was only later in the day that Phivolcs explained what it was, but then only very few saw or heard it on TV or the radio as most of the people haven't returned to their homes when the it was made.

                 As a layman who has a working understanding of the character of earthquakes and tsunamis, I have always contended that there was no way San Carlos would have been hit by a tsunami after the earthquake on that fateful Monday noon.

                It is true that tsunamis usually follow a quake as in the cases of the Japan and Indonesia.  However, we know that for tsunamis to build up, they would have originated from a large body of water such as the Pacific Ocean (Japan) and the Indian Ocean (Indonesia) with waves traveling at the speed of a jet plane and gathering speed as they near the shore.  The Island of Negros is safely situated between the Islands of Panay and Cebu and is bounded by the 15 nautical mile Tañon Strait on the east, Panay Gulf on the west, Visayan Sea on the north and the Sulo Sea on the south.  These narrow bodies of water can never provide the momentum for a wave to become a tsunami. 

                Plus, the strategic location of Sipaway Island stretched parallel to the city's coastline is a natural barrier so that even ordinary big waves coming from the direction of Cebu are already dissipated when they reach our shores.

                We have also learned that earthquakes that are below 7.5 in intensity of the Richter scale rarely cause tsunamis unless it is reinforced or combined by other climactic phenomena.  Thus, we cannot compare our situation with that of Japan and Indonesia because both were of 9.0 intensity level and both were situated along big bodies of water.                                

If indeed a tsunami were to hit the eastern side of Negros Island, it could have been here in our doorsteps in less than 10 minutes after the quake, not even giving us enough time to recover from our initial shock and long before we can even contemplate on evacuating to safer grounds.

                This is because tsunamis travel at the speed of 500 - 750 kph and considering that Tañon Strait is only 15 nautical miles at its widest point (or the farthest point from which the tsunami could come from).