The Philippine Fault System is a major inter-related system of geological faults throughout the whole of the
Philippine Archipelago
The islands of the Philippines, also known as the Philippine Archipelago, comprises about 7,641 islands, of which only about 2,000 are inhabited.tectonic forces compressing the Philippines into what geophysicists call the
Philippine Mobile Belt
In the geology of the Philippines, the Philippine Mobile Belt is a complex portion of the tectonic boundary between the Eurasian Plate and the Philippine Sea Plate, comprising most of the country of the Philippines. It includes two subduction z ...
. Some notable Philippine faults include the Guinayangan, Masbate and Leyte faults.
Philippine Mobile Belt
The Philippine Mobile Belt is composed of a large number of accretionary blocks and terranes. These terranes are long and narrow like the Zambalesophiolites which is at least 400 km long and 50 km wide. The strips generally run north–south and the zones of convergence are usually demarcated by fault lines. The Philippine Mobile Belt is compressed on the west by the Eurasian Plate and two arms of the
Sunda Plate
The Sunda Plate is a minor tectonic plate straddling the Equator in the Eastern Hemisphere on which the majority of Southeast Asia is located.
The Sunda Plate was formerly considered a part of the Eurasian Plate, but the GPS measurements have ...
, and on the east by the Philippine Sea Plate. These tectonic plates have compressed and lifted parts of the Philippines causing extensive faulting, primarily on a north–south axis. All faults in the Philippines are inter-related by the tectonic forces of the
Philippine Mobile Belt
In the geology of the Philippines, the Philippine Mobile Belt is a complex portion of the tectonic boundary between the Eurasian Plate and the Philippine Sea Plate, comprising most of the country of the Philippines. It includes two subduction z ...
, or its tectonic induced volcanism. A more complete understanding can be gained by viewing the faults in the Philippines as an inter-related Philippine Fault System.
Philippine Fault Zone
The Philippine Fault Zone (PFZ) extends 1200 km across the
Philippine archipelago
The islands of the Philippines, also known as the Philippine Archipelago, comprises about 7,641 islands, of which only about 2,000 are inhabited.Philippine Sea Plate.Aurelio, M., 2000. Shear partitioning in the Philippines: Constraints from Philippine Fault and global positioning system data. The Island Arc 9. This left-lateral
strike-slip
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
fault extends NW-SE (N30 – 40 W) accommodating the lateral oblique motion of the subducting Philippine Sea Plate with respect to the Philippine Trench.Besana, G.M., Ando, M., 2005. The central Philippine Fault Zone: Location of great earthquakes, slow events, and creep activity. Earth Planets Science 57, 987–994. It extends from Davao Gulf in the south, bisects the Caraga region at the Agusan River basin, crosses to Leyte and Masbate islands, and traverses Quezon province in eastern Luzon before passing through Nueva Ecija up to the Ilocos region in northwest Luzon. The northern and southern extensions of the PFZ are characterized by branching faults due to brittle terminations. These horsetail faults are indicative of the lateral propagation and further development of the PFZ. The fault's current activity can be observed in Holocene sandstone outcrops on the Mati and Davao Oriental islands. The fault experiences a slip rate of approximately 2-2.5 cm/year.Barrier, E., Huchon, P., Aurelio, M., 1991. Philippine fault: A key for Philippine kinematics. Geology 19, 32–35.
Formation
It is proposed that the Philippine Trench and PFZ represent a ‘shear partitioning’ mechanism, where the oblique physical motions of subduction at the convergent zone resulted in the development of the major strike-slip fault. In the Philippine Sea, the oblique motion of the subducting Philippine Sea Plate resulted in the formation of the Philippine trench and the PFZ back arc fault system. The oblique motion is accommodated by two vector components; one vector perpendicular to the converging Philippine Trench and one vector parallel to the PFZ. Approximately 30% of the oblique motion is accommodated by the PFZ while the remaining proportions are displaced along other regional tectonic features as the Philippine Sea Plate currently subducts below the Philippine archipelago at a rate of 6–8 cm/year. These two tectonic features thus correlate to a similar time of development. The formation of the PFZ was a result of two stages. The first stage began at ~10 Ma, when the northern segments of the PFZ developed due to the convergence of the China Sea Crust underneath the nearby
Manila Trench
The Manila Trench is an oceanic trench in the Pacific Ocean, located west of the islands of Luzon and Mindoro in the Philippines. The trench reaches a depth of about , in contrast with the average depth of the South China Sea of about . It is ...
. The lack of accretionary prism at the Philippine Trench is suggestive of young origin correlating to an early second stage of development (2–4 Ma) with the central PFZ proposed to have developed between 2.7 and 3.8 Ma.
Earthquakes
The central Philippine Fault Zone consisting of the
Guinayangan
Guinayangan, officially the Municipality of Guinayangan ( tgl, Bayan ng Guinayangan), is a 3rd class municipality in the province of Quezon, Philippines. According to the 2020 census, it has a population of 44,045 people.
Guinayangan came from ...
, Masbate, and Central Leyte faults are the most seismically active regions transecting the islands of Bondoc to Leyte. The northern and southern extensions of the Philippine Fault Zone experience infrequent
earthquakes
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
and often described as locked segments which are capable of larger magnitude earthquakes. The largest (M7.0) and most destructive earthquakes are generated along the Guinayangan fault every 30–100 years with slip rates of 20–33 mm/year as determined by GPS and historical records. Moderate earthquakes (M3.0–5.0) are observed along the Masbate fault with frequent aftershocks indicative of continued displacement and regional slip of 5–35 mm/year. The northern and southern segments of the Central Leyte fault experiences different seismic activity dependent on regional geology. While the Southern Central Leyte fault experiences moderate seismic events, the Northern Central Leyte fault creeps at approximately 25 mm/year. Historical data on the PFZ is limited due to the faults geographical location predominantly offshore, lack of complete paleoseismic data and lack of permanent
Global Positioning System
The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...
(GPS) that can trace movements over long periods of time.
Other active fault systems
* 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
Image:PhilippineFaultSystem005.jpg, Tectonic Map of Far Northern Philippines including the Philippine Fault System
Image:PhilippineFaultSystem015.jpg, Tectonic Map of Northern Central Philippines including the Philippine Fault System
Image:PhilippineFaultSystem025.jpg, Tectonic Map of Central Philippines including the Philippine Fault System
Image:PhilippineFaultSystem035.jpg, Tectonic Map of Southern Philippines including the Philippine Fault System
Image:PhilippineFaultSystem045.jpg, Tectonic Map of Far Southern Philippines including the Philippine Fault System
Image:PhilippineFaultSystem019.gif, Tectonic diagram showing Philippine Fault System
Image:PhilippineFaultSystem03.jpg, Diagram of Northern and central sections of the Philippine Fault System
Image:PhilippineFaultSystem13.jpg, Diagram of Northwest Luzon section of Philippine Fault System
Marikina Valley Fault System
The Marikina Valley Fault System, also known as the Valley Fault System (VFS), is a dominantly right-lateral strike-slip fault system in Luzon, Philippines. It extends from Doña Remedios Trinidad, Bulacan in the north and runs through the pro ...