Ground Rupture of the February 06, 2012 Negros Earthquake

Rolly E. Rimando1, R.B. Lim1, R.J. Garduque1 and J.M. Rimando2

1Department of Science and Technology - Philippine Institute of Volcanology andSeismology
2University of the Philippines - National Institute of Geological Sciences

Abstract

A 75 km-long, NNE-oriented ground rupture associated with the February 06, 2012 Negros earthquake (Mb6.9) was mapped on the eastern side of the island from Vallehermoso to the north and Bindoy to the south. The ground rupture length and scarp heights are consistent with an earthquake of its magnitude and nature of movement. The dominantly vertical displacement (west side up) is consistent with a west-dipping, NNE-oriented thrust fault, as indicated by focal mechanism solutions. This faulting mechanism is kinematically congruent with the stress field orientation associated with the other active faults in the area. The trace closely followed the coastline making a sinuous pattern of rupturing, similar to that of the Chelongpu fault ground rupture of the 1999 Chi-Chi (Taiwan) earthquake. The ground rupture of the February 06, 2012 Negros earthquake followed a pre-existing but previously unmapped active fault trace that is marked by morphotectonic features, mostly by terrace-forming scarps. Scarp types are similar to scarp variants displayed by recent thrust ground ruptures mapped elsewhere. The length, rupture pattern, and offset of man-made structures are distinct from those associated with erosion, landslide, and liquefaction. The ground rupture snaked through the seaward limits of highly populated centers that it almost went unnoticed and kept to a minimum the resulting damage.