Earthquakes, faults and
transverse ridges—The Collision of Benham Rise into Luzon
The Benham Rise has docked into N Luzon, causing:
the collapse of what used to be the East Luzon Trench into a
deformed shallow trough;
seismicity that lacks the depth and structure of a normal
series of earthquakes which suggests that thrust faulting in
central Sierra Madre (or along the E Luzon Trough) leads to
strike-slip faulting in Central Luzon;
the creation/conversion of curved, imbricate strike-slip
faulting along N- and NW-trending faults into a plate
deformation of the northern edge of Luzon into transverse
ridges that terminate the N-S grain of the Cordilleras,
Cagayan Basin and northern Sierra Madre.
from supporting the concept that Benham Rise has sutured with N
Luzon, these features define the block that is moving NNW with the
Philippine Sea Plate due to this collision.
section of N Luzon is therefore moving with the Philippine Sea
Plate. This makes the western boundary of the Philippine Sea Plate
not on the E Luzon Trough but further west than previously known.
This boundary is now being defined as the broad range of deformation
marked by the set of N- and NW-trending strike-slip faults where the
NNW motion of the plate is accommodated. This plate boundary
includes the Digdig Fault which caused the 1990 Luzon Earthquake.
north, the plate boundary of the Philippine Sea Plate is terminated
by another wide zone of deformation—this time marked by imbricate
transverse E-W trending ridges near the northern coast of Luzon.
This section of Luzon is deforming by crustal shortening and
thickening, providing the buffer that reduces the effect of the NNW
vector of the Philippine Sea Plate in the Taiwan convergence zone.
moving as part of the Philippine Sea Plate, N Luzon is also
internally deforming through faulting on the western edge and in its
interiors, collisional orogeny on the northern edge, continuing
crustal shortening on its contact with the Benham Rise, and an en
echelon set of faults within the block. These tectonic processes
define the nature of seismicity, uplift rates, convergence and
deformation and possibly the distribution of mineral and hydrocarbon
resources within this region of the Philippine archipelago.