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Valley Fault System •
Macolod Corridor – broad left-lateral fracture zone. •
Lubang-Verde Passage fault system – located offshore between Batangas peninsula and Mindoro Island, following the northwest–southeast alignment of Verde and Lubang islands (thus the name) and essentially strike-slip (left-lateral) fault. •
Mindoro/Aglubang Fault – break in slope between mountainous western Mindoro and the flat lands of eastern. •
Sibuyan Sea Fault – located offshore north of Masbate; using bathymetric (SeaMarc) and paleomagnetic data gathered in the northern section of the Sibuyan Sea, Sarewitz and Lewis (1991) were led to conclude that the Sibuyan Sea Fault is relayed with the Verde Passage Fault, both left-lateral faults, by an aborted spreading center under a transtensional tectonic regime. •
Legaspi Lineament – long SE-trending linear feature emanating from Pasacao in the Ragay Gulf area, passing through Lake Bato then to Legaspi City and considering its morphological prominence and seismic activity, it deserves to be elevated in category from a less significant lineament to a fault. •
Tablas Lineament – tectonic boundary between the North Palawan microcontinental block and the western edge of the Philippine Mobile Belt. It trends northerly as it separates Buruanga peninsula from the Antique Range in Panay Island, and passes offshore northwards east of Tablas Island. The present geodynamic setting of the Philippines obliges the Tablas Lineament to operate as a right-lateral strike-slip fault. Its structure appears to connect with the Negros Trench southwards. •
Mindanao Fault – a prominent NW-trending linear fracture zone on the western third of Mindanao Island and has 2 distinct segments, including that which separates the Daguma Range from the Cotabato Basin corresponding to the Cotabato Fault segment. This segment is highly linear and has features suggestive of normal faulting although it may have been a left lateral strike slip fault during its early history. The Quaternary Mt. Parker volcano is located at the western end of this fault and, on radar images, seems to be cut by the fault and terraces formed by Quaternary limestone mark the Daguma Range. These, together with the young morphology of incised river valleys, suggests a young age for the fault along which the Daguma Range was uplifted. Although Quaternary in age, it still has to be ascertained whether the fault is active or not (Quebral, 1994). The Sindangan Fault segment represents the northern continuation of the fault towards northern Zamboanga. Focal mechanism solutions of earthquakes offshore and narrow shear zones transecting recent gravel deposits suggest active left-lateral faulting (Pubellier and others, 1991). •
Offshore Cebu-Bohol faults (?) – occasional occurrence of low to moderate magnitude, shallow-seated earthquakes between Cebu and Bohol, some capable of causing significant damage to infrastructure, is the subject of current discussions on the possible existence of active faults in the region. Such earthquake generators are most likely offshore, as there have so far been no indications of active faulting within the islands of Cebu and Bohol. Active fault studies are spearheaded by PHIVOLCS. ==Gallery==