Recently,
news reports regarding a Magnitude 7.2 earthquake scenario
in Metro Manila has triggered numerous queries and
reactions among concerned citizens. The reports were
obviously culled from a recently concluded study called
Earthquake Impact Reduction Study for Metropolitan
Manila (MMEIRS) sponsored by Japan International Cooperation
Agency (JICA), with PHIVOLCS and the Metropolitan Manila
Development Authority (MMDA) as Philippine counterparts.
Following are clarifications, which we hope would put
the news reports in proper perspective.
The Magnitude 7.2 earthquake in Metro Manila is
not a prediction but a SCENARIO that is useful
for urban planning
and formulation of disaster mitigation strategies.
A M7.2 earthquake is the estimated largest
credible earthquake
that can be generated by movement of the Valley Fault
System (VFS, a.k.a. Marikina Fault) - which runs
right through Metro Manila - based on available
geological
and seismological data. That is, IF the VFS moves,
a M7.2 earthquake CAN be generated. This could
produce
ground shaking up to Intensity VIII or IX (measured
using the 10-step PHIVOLCS Earthquake Intensity
Scale) in Metro
Manila. MMEIRS did consider other possible sources
of earthquake (Philippine Fault, Lubang Fault,
Manila Trench,
etc.), and found the VFS the biggest threat to Metro
Manila.
The above estimate of earthquake hazard is very
reasonable. However, the study does not quantify
the likelihood of
such an event. MMEIRS used a deterministic method
in assessing the hazard - i.e., we determined
the VFS as
a worst-case source of earthquake, and estimated
the probable maximum earthquake this fault
can generate.
This method is different from a probabilistic approach,
where one estimates the likelihood of an event over
a specified time, say, 50 years. So, geologically
speaking
(over an unspecified time), the VFS moving - thus
generating an earthquake up to M7.2 - is inevitable.
We knew this
even before MMEIRS. We do not know, however, WHEN
this will happen. Earthquake prediction is
still an elusive
quest anywhere in the world. For an appreciation
of the risk, suffice to say that historically,
the Metro Manila
area has indeed been repeatedly affected by disastrous
earthquakes. What we therefore recommend is to systematically
prepare for such an eventuality.
MMEIRS focuses on the effects of a big earthquake
in Metro Manila and how best to prepare for such
an event.
The estimates of damage & casualties are based on
empirical observations worldwide, considering population,
number of buildings, construction practices, etc. They
are very rough estimates, but they do indicate what we've
expected all along: damage & casualty CAN be very
high, especially considering that the metropolis is host
to 14 million people. So the study makes recommendations
at various levels of government (national, regional,
local), as well as at community level where NGOs & POs
can play a big role. Community-based disaster management
exercises were in fact conducted in pilot areas during
the course of the study. The recommendations are aimed
at reducing the potential damage and casualty in case
of a large earthquake. We believe these recommendations
are the more important output of MMEIRS.
MMEIRS is a landmark study. Especially because
its product was enhanced by inputs from various
stakeholders
that
comprised the MMEIRS Technical Working Group during
the course of the study. The stakeholders included
local
government units, member agencies of the National
Disaster Coordinating Council and other national
government agencies,
utility companies, professional organizations,
and academic institutions. In support of MMEIRS,
the
Metro Manila
Council has adopted a resolution “declaring the
commitment to make Metro Manila seismically safe,
and establishing
the mutual aid agreement among the local government
units of Metro Manila in the event of disasters”.
We hope this helps to clarify the news reports.
Although we promote disaster risk awareness and
preparedness,
we do not wish to cause unnecessary panic or
despair among the people, so we enjoin everyone
to help
us in prudently distributing this information.
Disaster
risk
mitigation efforts should be deliberate, systematic,
coordinated and continuous.
To see an overview of MMEIRS, please click
this link,
or visit www.mmeirs.org.
For more information, please visit our office
at C.P. Garcia Ave., U.P. Campus Diliman,
Quezon City.
PHIVOLCS-DOST
05 November 2004
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