Abstract
A 75 km-long, generally NE-striking ground rupture associated with the 6 February 2012 MW 6.7 (Mb 6.9) Negros earthquake was mapped on the eastern side of Negros Island, Philippines. It closely follows a previously unmapped, pre-existing fault trace along the coast which is marked mostly by terrace-forming scarps. The dominance of vertical separation (west side up) is consistent with a west-dipping reverse fault, as indicated by focal mechanism solutions. The ground rupture map eliminates the ambiguity in the focal mechanism solution regarding the orientation, sense of motion, and location of the seismogenic fault plane, which are indispensable in the assessment of seismic hazards and the nature and distribution of deformation. This study uses the ground rupture map of the 2012 Negros earthquake in sorting out the mechanism of deformation in the Visayas Islands region. The ground rupture’s length is well within the aftershock area while its scarp heights are consistent with an earthquake of its magnitude and nature of movement. The 2012 Negros earthquake rupture’s pattern, scarp types, and offset of man-made structures are similar to those of recent reverse/thrust ground ruptures mapped globally and are distinct from those associated with erosion, landslide, and liquefaction. The onshore coseismic reverse fault of the Negros earthquake, which contradicts a model of coseismic slip on an offshore blind thrust fault by previous workers, represents the first thoroughly mapped ground rupture of its kind in the Philippines. The ground ruptures of the 2012 Negros and 2013 Bohol earthquakes, along with the Philippine Trench and the Philippine Fault Zone (PFZ), represent a complex shear partitioning mechanism in the Visayas Islands region. This departs from the current simple shear partitioning model for the region and is distinct from those for other regions along the PFZ and adjacent subduction zones. This study shows how an appreciation of morphotectonic features can lead to a better understanding of the distribution of deformation and the nature of earthquake hazards.
Highlights
On 6 February 2012 (03:49 UTC/11:49 AM local time), a magnitude (MW ) 6.7 earthquake struck the island of Negros in Visayas, Central Philippines (Figure 1A)
The 6 February 2012 Negros earthquake is associated with a ~75-km ground rupture which closely follows the eastern shores of northern Negros Island
The ground rupture can be followed along the eastern coast of Negros Island from Bindoy in the south to Vallehermoso in the north
Summary
On 6 February 2012 (03:49 UTC/11:49 AM local time), a magnitude (MW ) 6.7 earthquake struck the island of Negros in Visayas, Central Philippines (Figure 1A). Showing the Philippine archipelago and its currently mapped active tectonics features according to SP—Sunda Plate, PSP—Philippine Sea Plate, MT—Manila Trench, NT—Negros Trench, ST—Sulu. The 2012 Negros earthquake, the historically strongest earthquake to strike Negros Island, provides a valuable opportunity to document a previously unmapped reverse fault. While the importance of documenting the recent occurrence of events with reverse/thrust faulting mechanisms from the standpoint of hazard assessment is widely recognized [8], the ground ruptures should be mapped accurately through the appreciation of the physical evidence, the foremost of which is geomorphological in nature. With the occurrence and precise mapping of the ground rupture of the 2012 Negros earthquake and ground ruptures of the other recent reverse/thrust events, a more complex model of shear partitioning can be drawn with greater confidence
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
