![Picture](/uploads/2/7/2/4/27249943/4745592.png?513)
The islands of the Philippines are located on a converging zone where the Eurasian plate (west of the Philippines) is subducting under the Philippines Sea Plate (east of the Philippines). Because of the subduction zone, many active faults exist under Luzon Island that affect Manila.
There are two opposing subduction systems: the Philippine Trench subduction zone on the east and the Manila Trench subduction zone to the west.
The Marikina Valley Fault System (MVFS) is a group of dextral strike-slip faults, and is the closest active fault to Manila (Wong et al). The system contains two segments: West Valley Fault and East Valley Fault, both of which pass through Marikina city. To the east of the MVFS lies the Philippine Fault Zone (PFZ), which is separated by a transform fault system that connects it to the East Luzon Trough. The geomorphic evidence suggests that repeated rupturing along the MVFS existed until at least the late Holocene (Rimando et al, 2006).
This fault system poses a serious threat of a large scale earthquake on the city of Manila. Researchers predict magnitudes of earthquakes from this fault to reach 7.3-7.7 (Rimando et al, 2006). More information on the city's risk of earthquake damage can be found in the Issues and Hazards page.
The convergence between the Philippine Sea Plate and Philippine Island Arc System is estimated to be 28 to 39 mm/yr (Galgana et al., 2007).
There are two opposing subduction systems: the Philippine Trench subduction zone on the east and the Manila Trench subduction zone to the west.
The Marikina Valley Fault System (MVFS) is a group of dextral strike-slip faults, and is the closest active fault to Manila (Wong et al). The system contains two segments: West Valley Fault and East Valley Fault, both of which pass through Marikina city. To the east of the MVFS lies the Philippine Fault Zone (PFZ), which is separated by a transform fault system that connects it to the East Luzon Trough. The geomorphic evidence suggests that repeated rupturing along the MVFS existed until at least the late Holocene (Rimando et al, 2006).
This fault system poses a serious threat of a large scale earthquake on the city of Manila. Researchers predict magnitudes of earthquakes from this fault to reach 7.3-7.7 (Rimando et al, 2006). More information on the city's risk of earthquake damage can be found in the Issues and Hazards page.
The convergence between the Philippine Sea Plate and Philippine Island Arc System is estimated to be 28 to 39 mm/yr (Galgana et al., 2007).
Off the coast of the city, the Manila Trench is situated in the Pacific Ocean, created by the subduction of the Sunda Plate (part of Eurasian Plate) under the Philippine Mobile Belt. The Manila Trench reaches a depth of about 5,400 meters, and stretches north-south as a trending trench (Lewis et al, 1984). The Manila Trench is responsible for the belt of volcanoes on the west side of Luzon Island and associated local seismic activities. As shown in the figure above, the Manila Trench is overlain by pelagic and hemipelagic sediment layers transported from uplifted collision zones by gravity-controlled processes (Lewis et al, 1984). These sediments are transported to the trench by plate motions. The subduction zone at the Manila Trench has 2 troughs (West Luzon Trough and North Luzon Trough) that together extend 800 km parallel to the Manila Trench.
![Picture](/uploads/2/7/2/4/27249943/7648011.png?445)
Taking a closer look at the Metro Manila region, we can see how many faults affect the city. The map on the left shows the active crustal faults within 100km of the center of Manila. With the large Marikina Fault System in highest proximity, the city can be severely impacted by any activity of these faults.
The 1990 M 7.7 Luzon earthquake had an average
rupture depth of 20 km (Yoshida and Abe, 1992), also suggesting that Luzon has a relatively thick seismogenic crust that can be assumed for other faults within the region.