The 15
February
2003
Masbate
earthquake
along
the
Philippine
Fault
Zone,
Philippines
Besana,
G.M.1,2,
Daligdig,
J.A.,
Tuņgol,
N.M.,
Abigania,
M.I.T.,
Santos,
B.H.,
Peņarubia,
H.,
Punongbayan,
B.J.T.,
Papiona,
K.L.,
Arante,
R.,
Maximo,
R.,
Torrevillas,
L., Dela
Cruz, R.
and
Lumbang,
R.
Philippine
Institute
of
Volcanology
and
Seismology
(PHIVOLCS)
Department
of
Science
and
Technology,
Philippines
1 Also
at
National
Institute
of
Geological
Sciences
University
of the
Philippines
2 Now at
Earthquake
and
Volcano
Disaster
Research
Center
Graduate
School
of
Environmental
Studies,
Nagoya
University,
Japan
In the
evening
of 15
February
2003 a
Ms 6.2
earthquake
struck
the
province
of
Masbate.
Epicentral
locations
by
PHIVOLCS
indicated
that the
event
was
generated
along
the
Masbate
Segment
of the
Philippine
Fault
Zone (PFZ)
in
central
Philippines.
The
epicenter
was
located
offshore
of
Magcaraguit
Island
[12.2O
N,
123.8O
E] about
22
kilometers
deep and
approximately
28
kilometers
SE of
Masbate
City.
Reports
from the
Quick
Response
Team (QRT)
deployed
in
Masbate
on 18
February
2003 and
the
succeeding
field
surveys
evaluated
the
extent
of
damages
in the
province
and
verified
& mapped
the
resulting
ground
rupture.
The 15
February
2003
event
produced
at least
20km
long
ground
rupture
onland
with
maximum
horizontal
displacements
of 1.61m
with a
maximum
of
intensity
of
Intensity
VIII
along
the
ground
rupture.
Moreover,
intense
ground
shaking
and
damages
were
documented
near and
along
the
epicentral
area.
Damages
were
generally
observed
on
structures
like
school
buildings,
bridges
and
irrigation
canals.
Phenomena
like
tsunami,
landslides,
rockslides
and
liquefaction
were not
observed
except
for the
tsunami
in
northwestern
part of
Ticao
Island.
Aftershocks
were
observed
near and
along
epicentral
area and
lasted
for
several
months.
Based on
PHIVOLCS
historical
data and
other
information
gathered
from
fieldwork,
the
average
return
period
of large
magnitude
earthquakes
along
the
Masbate
Segment
of PFZ
is 10
years.
Considering
the
frequency
of the
earthquake
in this
area,
the
following
are some
of the
steps
recommended
for
implementation:
a)
Information
dissemination
about
earthquakes
together
with the
implementation
of an
annual
earthquake
drill
especially
in
schools
and
government
offices;
b)
Installation
of
permanent
benchmarks
along
the
Masbate
Segment
wherein
future
movement
will be
measured;
c)
Immediate
and
thorough
study on
the
structural
soundness
of all
structures
by the
concerned
authorities;
and d)
Identification
of
evacuation
sites
and
evacuation
routes.