Posted at 03/01/2012 9:18 PM | Updated as of 03/02/2012 2:42 PM
MANILA, Philippines – The Philippine Institute of Volcanology
and Seismology (Phivolcs) on Thursday inspected the West Valley Fault
in an effort to mitigate the risks that come with an active fault.
The fault spans 90 to 100 kilometers and passes through several areas
in Metro Manila as well as Bulacan, Rizal, Cavite and Laguna.
Philvolcs said the fault is still very active.
“Makikita natin na madalas kumilos ang fault. Kailangan paghandaan
ang pagkilos ng fault na ito,” said Phivolcs director Renato Solidum.
The agency wants to determine how often the fault moves and how intense the movement is.
“Posibleng magnitude 7.2 dito sa fault manggaling ang lindol at
intensity 8 to intensity 9 shaking. Ang intensity 8 destructive
earthquake na ‘yon,” Solidum said.
Soil samples from the West Valley Fault will be sent abroad for analysis.
Results are expected within two months and will be used to help
government prepare for the effects of another massive earthquake.
Meanwhile, the National Disaster Risk Reduction and Management
Council (NDRRMC) also conducted a nationwide earthquake drill Thursday.
NDRRMC executive director Benito Ramos said they have been doing the
drills every quarter to raise awareness since no one really knows when
the next big earthquake will strike next.
Residents of Negros Oriental are still reeling from the 6.9-magnitude earthquake that hit the province last month.
Aside from the dozens of fatalities, many lost their homes and millions of pesos of infrastructure were destroyed.
The cause of the earthquake was a blind fault—a fault line that had been previously undiscovered. -- Reports from Jasmin Romero, ABS-CBN News; ANC
What causes a tsunami?... A tsunami is a large ocean wave that is caused by sudden motion on the ocean floor. This sudden motion could be an earthquake, a powerful volcanic eruption, or an underwater landslide. The impact of a large meteorite
could also cause a tsunami. Tsunamis travel across the open ocean at
great speeds and build into large deadly waves in the shallow water of a
From Wikipedia, the free encyclopedia
Benham Plateau (coordinates: 17°N 125°ECoordinates: 17°N
125°E), also known as the Benham Rise, is a seismically active undersea region
and extinct volcanic ridge east of the Philippines, in the Philippine Sea.
Under the Philippine Sea lies a number of Basins including the West Philippine
Basin (WPB) of which inside the Basin is located the Central Basin Fault
(CBF). The Benham Plateau is located in the CBF and its basement probably
represents a micro-continent. Several scientific surveys have been made on
the feature to study its nature and its impact on tectonic subduction,
including one about its effects on the 1990 Luzon earthquake, which devastated
the northern city of Baguio. The area is currently claimed, as part of its
continental shelf, by the Republic of the Philippines, which has lodged a claim
with the United Nations Commission on the Limits of the Continental Shelf on
April 8, 2009.
Benham Rise is a submerged extinct volcanic ridge located at
16 degrees 30 minutes N, 124 degrees 45 minutes E off the coast of Luzon, with
the size of about 250 km in diameter and rises over 2,000 meters above the sea
floor, from below 5,000 meters below sea level to above 3,000 meters below sea
level. Its area is close to the Benham Seamount, located at 15 degrees 48
minutes N, 124 degrees 15 minutes E. The precise location is somewhere near the
east of the Philippine Trench and near the south of the East Luzon Trench, both
of which absorb the subducting force of the Philippine Sea Plate under the
Philippine Mobile Belt, a collage of large blocks of that crust that
amalgamated prior to the collision of the Philippine Sea Plate with the
The origin of the landform, along with a fellow landform,
the Urdaneta Plateau (a remnant of mantle plume), is identified in one study as
at least five sequences of propagating rifts, probably triggered by mantle
flowing away from the mantle thermal anomaly. Its presence of the landform
disrupts the continuity of this region (known as the Philippine-East Luzon
Trench) by continuously colliding with the Sierra Madre mountain range of
eastern portion of the island of Luzon. Though it is generally thought that the
Philippine Sea Plate is being subducted under the Philippine Mobile Belt, under
the rules of tectonic subduction, there appears to be a resistance to this
because of the presence of the landform, and instead, the plate is being
displaced into the northern portion of Luzon to the west.
The geophysical features of the plateau may have been the
result of an early Miocene collision event between the Benham Rise and the
eastern margin of Luzon, which may have also allowed the inception of the NW
striking strand of the Philippine fault. These forces may have impacted the
shape of the island of Luzon because of the basaltic sea floor resisting the
subduction that may have also cause the bending of the Philippine Fault. The
active basins in Central Luzon, which trace an asymmetrical V shape, is the
best place to observe recent tectonic evolution of the fault system.
The landform is presumably named after Admiral Andrew
Ellicot Kennedy Benham (1832–1905) by American surveyors who were the probable
discoverers of the geological feature. He was a United States Navy officer, who
served with both the South Atlantic and West Gulf Blockading Squadrons during
the American Civil WarThere has been speculation in the scientific community
about the nature of the landform. Following the major 16 July 1990 Luzon
earthquake, scientists reconsidered their fault models and decided it likely
that Benham Plateau has similarly displaced the Philippine Fault System to the
westAfter analysing older models such as that of Pinet and Stephan (1989),
scientists reconsidered their fault models. They thought that it is highly likely
that the Benham Plateau is still displacing Central Luzon and the Philippine
Fault System to the west, which may have had an impact in causing such a
catastrophic earthquake. The 20 second to 50 second wave in the 1990 quake that
developed a new east-west sub-fault was so strong that it terminated
disastrously at the city of Baguio in Benguet, Cordillera. Several scientific
surveys, conducted between 2004 to 2008, collected hydrographic data that
determined the morphology of the seabed in the region. Additional data from
international bathymetric surveys and an analysis of international research
projects were collected to support the findings.
Despite its proximity to the archipelago, the plateau was
previously not included in the territory of the Philippine Islands. On 8 April
2009, the Republic of the Philippines lodged a partial territorial waters claim
with the United Nations Commission on the Limits of the Continental Shelf in
relation to the continental shelf in the region of Benham RiseIt was submitted
as part of petition expanding the archipelago's baselines and exclusive
economic zone through a law that also included other claims involving disputed
territories of the Kalayaan Islands (Spratly Islands) and Scarborough Shoal.
Although the landform, in itself, is not disputed, the petition still received
some criticism inside and outside the country because of its controversial
natureAccording to the government's claim, based on a set of guidelines by the
Commission on the Limits of the Continental Shelf, the area satisfies the
350-mile constraint line since the outer limits of the continental shelf are
located landward of the constraint line, which is located 350 miles from the
baselines where the measurement of the breadth of the territorial sea begins
The Congress of the Philippines enacted Republic Act No.
9522, also known as the Archipelagic Baselines Law, which is the basis of the
claim. According to the document the region is bounded by the Philippine Basin
on the north and east, and by Luzon on the west and south. It asserted that,
according to scientific data based on seismic, magnetic, other geological
features, the Benham Rise is an extension of the Philippines’ continental
shelf. In summary, the baselines, the basis used for delineating the maritime
territorial and jurisdictional zones (including the continental shelf), conform
with the requirements of the UN Convention of the Law of the Sea (UNCLOS). The
claim is only a partial claim since the law that allows the Philippines to
expand its territorial boundaries also includes islands in the South China Sea.
According to, Philippine Environment Secretary Ramon
Paje,the United Nations is expected to come out with a decision by the middle
of 2012 on the Philippines’undisputed claim over the 13- million hectare Benham
Rise. Paje told the Senate during a hearing on the Department of Environment
and Natural Resources (DENR) proposed P16.990- billion budget for 2012 that the
country’s claim over Benham Rise would be recognized by the UN as part of the
territory and extension of the continental shelf of the Philippines. The Philippines filed the claim in 2008 in
compliance with the requirements of the UN Convention on the Law of the Sea
By Alain Bernard,1 Ulrich Knittel,2 Bernd Weber,2 Dominique Weis,1 Achim Albrecht,3 Keiko Hattori,4 Jeffrey Klein,5 and Dietmar Oles2
1 Department of Geology, CP 160/02, Université Libre de Bruxelles, 50 Ave. F.D. Roosevelt, B-1050 Brussels, Belgium.
2 Institut für Mineralogie und Lagerstättenlehre,
Wüllnerstrasse 2, D-52056 Aachen, Germany. Now at: Institut für
Geowissenschaften/Mineralogie Saarstr. 21, D-55099 Mainz, Germany.
3 Department of Chemistry, Rutgers University, Piscataway, NJ
08855; now at: EAWAG/ETH, Umweltphysik, 8600 Duebendorf, Switzerland.
4 Department of Geology, University of Ottawa, Ottawa, K1N 6N5 Canada.
5 Department of Physics, The University of Pennsylvania, Philadelphia, PA 19104.
The June 1991 activity of Mount Pinatubo erupted about 5 cubic
kilometers of magma, mainly during the paroxysmal June 15 eruption. Most
of the erupted magma was dacite with an overall constant composition
(64.5 weight percent SiO2) but with variable amounts of phenocrysts. Small volumes of andesite (56 weight percent SiO2)
characterized the June 7-12 dome-building phase and the June 12
eruption. This andesite contains inclusions of a primitive basalt (50.6
weight percent SiO2). The dacite is extraordinarily enriched
in sulfur (1,474 to 2,211 ppm sulfur), most of which is present as
phenocrysts and microphenocrysts of anhydrite. The dacite also contains
xenocrystic olivine, which, because of abundant chromite inclusions, is
considered to be of juvenile nature. Major and trace element
compositions of dacite and andesite display the same geochemical
features as the other silicic rocks from the Bataan arc volcanoes of the
Philippines. Strontium and neodymium isotopic compositions of all 1991
dacite and andesite and their phenocrysts are identical, with 87Sr/86Sr = 0.7042 to 0.7043 and 143Nd/144Nd
= 0.51286 to 0.51298. The basalt contains slightly more radiogenic
strontium and slightly less radiogenic neodymium. The isotopic
signatures are in agreement with the volcano's location, which is
relatively far from the North Palawan continental terrane (NPCT)
collision zone as compared with the Macolod corridor, Luzon, or the
Mindoro segment. These compositions suggest also that an unusually large
contamination by marine sediments is not likely to explain the large
sulfur enrichment observed in the Pinatubo magma. Dacite and andesite
also have identical lead isotopic compositions characterized by high 208Pb/204Pb and 207Pb/204Pb for relatively low 206Pb/204Pb,
while the basalt contains slightly more radiogenic lead. The basalt is
likely to have been generated by partial melting of peridotite because
of its high MgO content and high forsterite content of olivine
pheno-crysts and the abundance of chromite inclusions. It is close to
the primitive basalts found in the Macolod corridor.
The Philippine Fault System
is an inter-related system of faults throughout the whole of the Philippine Archipelago,
primarily caused by tectonic 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 (see
Gallery). 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
A more complete understanding can be gained by viewing the faults in
the Philippines as an inter-related Philippine Fault System.
The Philippine fault, probably active since the Middle Miocene
is a recent example of the north-south strike-slip fault zones of
Luzon. The N150E segment, which breaks the meridian continuity of the
Philippine Fault system in Luzon, is located to the west of Benham Plateau
on the western edge of the Philippine Sea Plate. The N150E fault
probably has a recent genesis and could be a mechanism to absorb
backwards the convergence between Benham Plateau and the east Luzon arc.
Following the major 1990 Luzon earthquake,
scientists reconsidered their fault models and following the lead of
Pinet and Stephan (1989), thought it likely that Benham Plateau is still
displacing central Luzon and the Philippine Fault System to the west,
and so caused the 1990 Luzon earthquake. The 20 second or 50 second wave
in the 1990 quake developed a new east-west sub-fault, which terminated
disastrously at Baguio.