GEOLOGICAL SOCIETY OF THE PHILIPPINES
EVIDENCES OF RECENT FAULT MOVEMENTS IN EASTERN METRO MANILA
Excavations for public and private infrastructures along the Diliman Escarpment and in Marikina Valley in Eastern Metro Manila have exposed areas with clear evidences of fault slippages that post-date the Marikina Graben.
The dominant structures were sub-vertical strike-slip shears that trend N45-65E, and less prominently as cross-fractures striking N40W. Right lateral slippages were common in the Libis-Ortigas area, while left lateral shears were observed in the Fort Bonifacio and Ateneo-U.P. areas. Less common were indications of low-angle thrust movements to the northeast were seen in Fort Bonifacio and in the Barangka-Balara area. No large-scale strike-slip displacement in any outcrop was observed.The Diliman Escarpment had been associated with the Marikina Valley as a bounding normal fault, but expected structures with normal displacements were rarely observed. Photographs are presented and discussed in the context of a structural sketch to impress a segmental activation of certain fault zones, which may indicate a northeastward strain build up in Metro Manila and vicinity. Commercial buildings and residential structures continue to be located in the stress zones.
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