After Typhoon Sendong, another calamity in the form of an earthquake struck Negros Island around noontime on Feb. 6, 2012. The quake’s intensity was measured between 6 and 7 on the Richter scale, depending on the location of the closest measuring station, and had its origins in the offshore area of Tayasan municipality in Negros Oriental.
The initial jolt tremor was followed by a series of tremors of lesser intensity for several days.
Severely-hit were the towns of Tayasan, La Libertad, and Guihulngan, some 70 kilometers north of Dumaguete City.
The quake caused significant damage to buildings and roads in the areas. It also caused several deaths, mostly due to landslide.
This particular earthquake caught some Phivolcs authorities off guard, mainly because this area had no history of a major earthquake.
What also made it perplexing for the authorities was that the area was not included in the fault maps of the Philippines.
This observation reminds us of Mt. Pinatubo which erupted despite the earlier declaration that it had been dormant for 600 years.
The Tayasan fault, in my opinion, may be inherent to the area since it is situated between the islands of Negros and Cebu.
If you look at the map of these two opposing islands, you will notice that the islands of Negros and Cebu appear to fit like pieces of a jigsaw puzzle. This pattern appears to support the theory that millions of years ago, these two islands were once joined together. Their separation may have been facilitated by the formation of a fault line which is now covered by sea (i.e.Tanon Strait).
Although geohazard maps have been produced for Negros Island, very few people know about their existence because of poor dissemination of information.
The major fault lines of Negros include the Negros Volcanic Arc, which runs north-south and central to the island, connecting the North Negros Volcanoes, Canlaon Volcano, and Talinis-Balinsasayao Volcanoes; and the Negros Trench, which is an offshore fault line.
The Negros Trench is a long fault line which runs from Mindanao to Panay, and passes southwest of Negros Island.
The size and location of this trench is believed to have the capacity to produce tsunamis particularly in the coastal areas facing Sulu Sea.
On the other hand, the Tayasan fault is not a potential tsunami generator for reasons that it is located in relatively shallow waters, and is constricted by the islands of Negros and Cebu.
The earthquake that shook Negros last Feb. 6 was an eye opener in the sense that tremors can occur in undefined fault lines. There is a need to know where these fault lines are so we can prepare to protect ourselves from earthquakes and landslides.
It is also equally important that we identify these geohazard areas so that proper precautionary measures are put into place when building roads and other infrastructures.