Transcript phil. fault system

• The plate tectonics in the
Philippines is complex and
includes plate boundaries that are
changing rapidly. Several microplates are getting squeezed
between two convergent plate
margins.
• Stratigraphic evidence indicates
cessation and reactivation of
subduction at some trenches. The
currently active volcanoes in the
Philippines define two north-south
trending arcs.
• The scale and type of
volcanism varies from
monogenetic cinder cone fields to
large stratovolcanoes and
calderas. Composition of volcanic
rocks range from tholeiitic basalt
to andesite to shoshonite.
• The scale and type of volcanism varies from monogenetic cinder
cone fields to large stratovolcanoes and calderas. Composition of
volcanic rocks range from tholeiitic basalt to andesite to shoshonite.
• Black triangles = active subduction zones with "teeth" on the overriding plate, white triangles = inactive subduction zones with "teeth"
on the over-riding plate, arrows = transform or major strike-slip faults,
red triangles = volcanoes active in the last 10,000 years. Plates and
micro-plates shown in different colors. Based on Divis (1983).
Volcanoes from Simkin and Siebert (1994).
Indeed the plate is squeezed in
between the Eurasian plate and
the Pacific Plate, but the situation
is more complex than that. The
Philippine Islands are surrounded
by complex plate boundaries,
and the Philippines Plate rather
consists of several micro-plates squeezed in between two
convergent plate margins.
The lines with black triangles are
active subduction zones with
teeth on the over-riding plate.
Lines with white triangles are
passive subduction zones with
teeth on the over-riding plate. The
major Philippine fault zone is
shown as a black line with arrows
showing the movement direction.
The volcanoes Pinatubo and
Mayon are shown as red dots.
The volcanoes of the
Philippines are probably the
most deadly in world. They are
concentrated in a northern
volcanic arc above and east of
the north-western subduction
zone (Manila Trench) and in a
southern volcanic arc above and
west of the south-eastern
subduction zone (Philippine
trench).The Sulu trench also
produce a (discontinuous) line of
active volcanoes.
The Mayon volcano may be
associated with the transform
fault that connects the eastern
and the western subduction
zones. This transform fault is
offset by the younger northsouth directed Philippine Fault.
 The Eurasian Plate is being
subducted along the western side of
Luzon and Mindoro at a rate of
3cm/year. The Philippine Fault Zone
decouples the northwestward motion
of the Pacific with the southwestward
motion of the Eurasian Plate.
Movements along other active faults
are responsible for the present-day
high seismicity of the Philippine
Archipelago.
In the west, more steeply eastdipping subduction of the
Eurasian Plate (South China Sea
basin and the transitional oceaniccontinental crust of the Palawan
block) along the 560 mile (900
km) length of the Manila and Sulu
trenches produces a
discontinuous line of active
volcanoes from Taal in the south
to Iraya in the north. Volcanism
associated with this subduction
zone began about 10 million
years ago.
In the east, shallow west-dipping
subduction of the Philippine Plate
at the Philippine Trench produces
a line of volcanoes from Balut in
the south to Mayon in the north.
Based on Divis (1983).
Volcanoes in an east-west zone
across central Luzon may be
associated with a "leaky"
transform fault that connects the
two subduction zones. The
transform fault is offset to the
right by the younger Philippine
Fault. Based on Divis (1983).
Map of Philippine
Plate from USGS
marking one of the
many eartquakes in
the area.
Major Tectonic
Boundaries:
Subduction Zones purple and
Transform Faults green
The Philippine Fault Zone which
trends N40°w is widely
accepted as a major strike-slip
fault comparable to the San
Andreas fault. An area in southeastern Luzon, commonly
regarded as part of the main
fault zone, has been studied in
an effort to date the faulting and
to establish its nature and
extent.
• Two main episodes of faulting are recognized,
one late Miocene on northerly faults, one PlioPleistocene on north-westerly faults. Both these
episodes involve considerable dip-slip
movements and the two principal Recent faults
which have been recognized are also of dip-slip
type.
• Geomorphological evidence shows that the
whole area has been subjected to Recent
episodic but areally uniform uplift.
• Direct evidence of strike-slip movements is slight and the
structural relations argue against major post-Miocene
strike-slip movements. The possibility of earlier strike-slip
cannot be excluded and the fault and fold systems show
a good correlation with those predicted following the
theory of Moody & Hill (1956).
• Possibly therefore the faults on which the main Miocene
and later dip-slip movements occurred were initiated
during earlier strike-slip episodes. A pre-Tertiary episode
of left-lateral strike-slip in the Rift followed by a Miocene
episode of right-lateral strike-slip on conjugate primary
faults can be tentatively inferred. The direct evidence of
faulting in the Rift, however, relates only to the PlioPleistocene activity of the morphogenic phase.
• Luzon is situated in a
Plate Boundary Zone
(PBZ), an actively
deforming region where
earthquakes and tectonic
motion are prevalent .
• These are direct
consequences of rapid
convergence between the
Philippine Sea Plate and
the Sundaland Plate (part
of the Eurasian Plate)
along dual, opposing
subduction in the Manila
Trench (western margin),
and along the East Luzon
Trough-Philippine Trench
(eastern margin).
• The Philippine Fault System is an inter-related system
of faults throughout the whole of the Philippine
Archipelago, primarily caused byt ectonic forces compressing
the Philippines into what tectonic geophysicists call the Philippine
Mobile Belt
• The Philippine Mobile Belt is composed of a large number of
accretionary blocks and strips. Most strips are long and narrow like
the Zambales ophiolites which is at least 400 km long and 50 km
wide.
• The strips generally run north-south and the zones of convergence
are usually demarkated by fault lines. The Philippine Mobile Belt is
compressed on the west by the Eurasian Plate and two arms of
the Sunda Plate, 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. The
main fault runs most of the length of the
Philippines and is called the Philippine Fault.
• In northern Luzon, the fault has become braided
and is no longer single. All faults in the
Philippines are inter-related by the tectonic
forces causative of the Philippine Mobile Belt, or
its tectonic induced volcanism.
Tectonic Map of Far Northern
Philippines including the
Philippine Fault System
Tectonic Map of Northern
Central Philippines
including the Philippine
Fault System
Tectonic Map of Central
Philippines including the
Philippine Fault System
Tectonic Map of
Southern Philippines
including the Philippine
Fault System
Tectonic Map of Far
Southern Philippines
including the Philippine Fault
System
Tectonic Map of
the Philippines
showing the
Philippine Fault
System generally
Northern and
Central portions
of Philippine
Fault System
Northwest Luzon
segment of Philippine
Fault System