PHIVOLCS Discovers 3 Fault Lines in Cebu

Ground imaging using LIDAR. Photo credit: USGS.
Example of land forms near active faults.  Photo credit: USGS.
Example of land forms near active faults.
Photo credit: USGS.

Volcanologists from the Philippine Institute of Volcanology and Seismology (PHIVOLCS) have announced the discovery of 3 possible fault lines traversing the island of Cebu, fault lines which could cause a series of earthquakes with yet unknown intensities or magnitudes.  This discovery was revealed by Jeffrey Perez, supervising science research specialist of PHIVOLCS, in a presentation before the Provincial Board (PB) of Cebu.

Perez announced that overhead satellite imagery was used to identify these 3 new fault lines, with all 3 plotted in a hazard map created by the government agency.  Although he did not specify the names of the towns or cities which could be set along these newly discovered fault lines, he did mention that 1 traverses Central Cebu while 2 lie opposite each other in the interior parts of southern Cebu.

Based on the Cebu provincial map, some of the towns in southern Cebu include Ginatilan, Malabuyoc, and Alegria to the west side of the island, opposite Oslob, Ginatilan, Boljoon, Alegria, and Alcoy to the east.  Central Cebu includes Toledo City, the mountain areas near the boundary of Cebu City and Balamban, Talisay, Mandaue, Lapu-Lapu, Danao, and the Cebu Metropolitan Area.

Perez adds that PHIVOLCS is also planning on using more aerial photographs to clearly identify these new fault lines, mapping them out, and identifying possible risk areas.  Also, the agency is still conducting studies to determine the possible magnitude or strength of the earthquakes which could be generated along these fault lines just in case they move.  Local government leaders were urged to stay alert and prepare for the possible rupture of these areas, taking into consideration the risks that their constituents may have undergo when such eventuality occurs in the future.

PB Member Jose Ribomapil Holganza Jr. questioned Perez whether there exists an instrument or device which could be placed on the ground to detect the faults instead of merely relying on aerial assessments.  Perez admitted that such geophysical instruments are actually available but not used by the agency because these are too expensive.  These instruments could easily pinpoint and detect the exact location of the fault.

How Geologists Identify Faults

Ground imaging using LIDAR. Photo credit: USGS.
Ground imaging using LIDAR.
Photo Credit: USGS.

There are many different kinds of fault lines occurring on the earth’s surface, many of which may require extensive studies and the use of several geologic instruments to identify. For example, creeping faults are those that move in lateral motion very slowly all the time.  Although moving, its speed is so slow that it could take decades before an offset becomes noticeable.  Such faults could be identified by comparing photographic evidence of structures on the ground or more clearly in aerial surveys by studying the topography, especially of natural features like ridges, valleys, and streams.

More sophisticated methods are now available to detect fault lines even before earthquakes occur to reveal them.  Laser Imaging Detection And Ranging (LIDAR) is one of the newest available, with laser light projected from an airplane detailing images of the ground surface. Using advanced software, LIDAR is able to remove vegetation to reveal the ground in a computer-generated image which can be used to identify the active faults.

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