The Vulnerability of the Philippines to Natural Hazards and

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					 The Vulnerability of the Philippines to Natural Hazards and the Disaster
                           Risk of Metro Manila
                                 Raymundo S. Punongbayan

                     Philippine Institute of Volcanology and Seismology,
                           Department of Science and Technology,
                                  Metro Manila. Philippines


                                         ABSTRACT

The Philippine Archipelago occupies part of the western segment of the Ring of Fire and
faces a wide open sea to the east that serves as a spawning ground for typhoons. This
tectonogeographic setting of our archipelago renders it vulnerable to many natural hazards
and their adverse impacts. The Philippines has over 200 volcanoes, 22 of which are classified
as active and 21 as potentially active. Active volcanoes, when they erupt, send forth life-
threatening hazards in the form of hot pyroclastic flows; later, when the loosely consolidated
deposits of these flows are rained upon, they get remobilized as lahars or mudflows that bury
human settlements and agricultural lands lying along their paths. In general, the emplacement
of these volcanoes and the active nature of some of them can be related to the still-ongoing
subduction of oceanic lithospheres along two opposing trench systems bounding the
Philippine Archipelago. Similarly, its very high level of seismicity and the generation of large
magnitude (and sometimes, tsunamigenic) earthquakes from active faults and trench systems
are subduction-related. However, despite the fact that the Philippines had been shaken by
thousands of earthquakes in the past, only 80 of these, since historic time, can be considered
destructive. The most recent devastating one is the 16 July 1990 M7.8 Northern Luzon
Earthquake. It adversely affected three cities and many towns; caused widespread
liquefaction in several places; induced about a million landslides; created a ground rupture
120 kilometers long with a maximum horizontal displacement of 6.1 meters and a maximum
vertical displacement of 2.2 meters; killed 1283 and injured 2786 people; and, brought about
damage to property, infrastructure and agricultural lands worth 18.7 billion pesos (~US$375
million). For an earthquake of such magnitude, the low casualty count is remarkable. Other
countries hit by a similar earthquake had reported deaths ranging in the tens to hundreds of
thousand. Perhaps, the reasons for the low casualty count are the generally rural setting of
Northern Luzon and the widespread use of wooden materials while constructing houses in
this area. Metro Manila, a highly urbanized area, is about 100 kilometers away from the
epicenter and was shaken at Intensity VI to Intensity VII (based on Philippine Earthquake
Intensity Scale of I to X). What if the epicenter is only 10 kilometers away?

Metro Manila is a fusion of cities and towns that had been carved out from provinces adjacent
to Manila and Quezon City. At present, it has a population of about 10 million people and,
thus, qualifies as one of the megacities of the world. Its built-up areas range from shanties of
informal settlers to high-rise buildings in several business and commercial centers of the
metropolis. It is where you find the seat of the Philippine government as well as those of
banking, industrial and other commercial enterprises. Unfortunately, the eastern section of
Metro Manila is transected by an active fault (now known as Valley Fault System) that is
capable of generating a M7.0 or larger earthquake when it moves. With increasing
vulnerability due to increasing number of people and other elements at risk, it is to be
expected that the disaster risk of Metro Manila will increase over time. Many studies have
been, are being and will be conducted by Japanese colleagues coming from several
institutions in cooperation with Filipino counterparts to identify, assess and treat risks due to
ground shaking in case the Valley Fault System moves in the future. Perhaps, from this
meeting at the International Institute for Applied Systems Analysis (IIASA) new co-
operations and new ideas may arise for a more comprehensive approach to disaster risk
management.