DEVELOPMENT
OF
SEISMOLOGICAL OBSERVATION NETWORK
IN THE
PHILIPPINES
Enrico A. Mangao
Philippine Institute of Volcanology and Seismology (PHIVOLCS)
•
SUMMARY
• Since the establishment of its seismological stations in 1948, the Philippines has
developed at a rather slow pace, from 8 to 35 stations in more than 50 years.
But this maybe understandable as the country had other priorities in poverty
alleviation, health, and education. However, the increasing number of volcano
and earthquake related disasters, local and international, did not fail to alarm
the populace including the national leadership. They have come to realize that
the hazards posed by earthquakes and volcano eruptions are for real and
something will have to be done to understand their possible effects and
somehow mitigate their impacts.
• In the last few years, with the help of Japan International Cooperation Agency
(JICA), the Philippines have undergone radical improvementｓ in its volcano and
seismological observation.
Having installed additional instruments to
complement the 35 volcano and seismic stations, the project almost doubled this
number using telemetry stations operated-on via satellite.
•
INTRODUCTION
► Seismological studies in the Philippines date back to colonial times
when the Jesuit fathers, in cooperation with the Weather Bureau,
operated a seismograph station from 1890 onwards. Seismologists
associated with this station kept careful records of felt earthquakes
and one of them, Fr. Repetti, published a comprehensive list of felt
earthquakes and their impacts beginning in the latter part of the
sixteenth century and continuing up until 1959.
► Today, the Philippine Institute of Volcanology and Seismology
(PHIVOLCS) is the main organizational body mandated to study
earthquakes, following the transfer of the seismological function from
PAGASA in 1984. PHIVOLCS’ principal objectives are to avert disasters
and mitigate hazards from geotectonic processes. One of its
programs, the Seismological Observation and Earthquake Prediction,
is geared towards increasing our understanding of the causes, effects,
nature and physics of earthquakes and earthquake zones in the
country. This includes related events such as tsunami, liquefaction,
landslides and faulting.
• PLATE TECTONICS
►
The Philippines, lying between two major
tectonic plates and with active faults crisscrossing the archipelago, is one of the more
seismically active countries in the world. The
northwestward moving pacific plate is
presently pushing the Philippine sea plate
beneath the eastern side at the rate of about
7 cm. per year.
The oceanic parts of the slow-moving Eurasian plate are
being subducted along the western side of Luzon and
Mindoro islands at the rate of 3 cm. per year. The
southeastward component of the Eurasian plate motion is
now sustaining the active collision of the continental block
of Palawan with Mindoro, and of the northern sections of
the Zamboanga peninsula with western Mindanao.
These plate interactions and movements along the active
faults are responsible for the present-day high seismicity
of the Philippine archipelago.
•SEISMICITY
►
At least five earthquakes per day
occur in the Philippines. Based on
the distribution of epicenters, the
most seismically active part of the
country is its eastern section
containing eastern Mindanao, Samar
and Leyte with an average of 16
perceptible earthquakes per year.
This is due to the active subduction
process going on along the Philippine
Trench.
►
The other relatively active parts are
found at the western side of
Northern Luzon and the area in the
vicinity of Lubang Island and
Mindoro. The presence of the East
Luzon Trench, Casiguran Fault and
the northern segment of the
Philippine Fault Zone all make the
places at and near Dingalan Bay and
Casiguran earthquake-prone. The
high frequency of earthquakes in the
offshore areas of Lubang Island and
northern Mindoro may be due to the
activities of the Lubang Fault.
•Philippine Destructive Earthquakes and Their Impacts
Date
Epicenter
Intensity
Surface
Magnitude
Depth
km
02 July 1954
Casualty Injured
Bacon, Sorsogon
VII
6.5
60
13
101
01 April 1955
Lanao del Sur,
Sur,
Mindanao
VII
7.6
96
291
713
02 August 1968
Casiguran,
Casiguran, Aurora
VII
7.3
52
270
600
07 April 1970
Baler, Quezon
VII
7.3
40
15
200
17 March 1973
Ragay Gulf, Bicol
VII
7.0
33
14
100S
17 August 1976
Moro Gulf,
Mindanao
VII
7.9
30
3,739
8,000
16 July 1990
Rizal,
Rizal, Nueva Ecija
VIII
7.8
35
1,283
2,786
15 November 1994
North of Mindoro
Island
VIII
7.1
7
78
430
•NETWORK
► As the Jesuit order from its headquarters in Ateneo de Manila University
continues to operate three seismograph stations, the Philippine Weather
Bureau (now PAGASA) began to operate seismograph stations on its own in
1948 and had a network of eight stations. With the exception of the principal
station in Diliman, Quezon City, the instruments were located at
meteorological stations where the rock is not suitable for high-magnification
operation. For this reason, the instruments all operated at low-magnification
operation, in the 1000 to 5000 range.
► In the middle of 1970’s, with the improvement of roads and the availability of
electric power, PAGASA was able to find quiet locations for seismic
observation. It was at this time that the UNESCO established its seismic
network in the country under the Regional Seismological Network for South
East Asia Project. PAGASA have established seven new stations with
equipment provided by UNESCO and funded by the United Nations
Development Program (UNDP).
► The project has maintained 11 stations, eight of which were newly
established while the rest were renovations of the old buildings. The new
instruments were Kinemetrics short period seismographs with magnification
range from 28,000 to 225,000 at 0.3 seconds, and using Ranger Seismometer
SS-1. Old stations used Teledyne Geotech with S-13 seismometers, or the
Hosaka 3-component smoke-type instruments. It was on this set-up when the
seismological function was assumed by PHIVOLCS.
► After the Luzon
Earthquake of 1990,
PHIVOLCS realized the
necessity of establishing a
denser network to monitor
earthquakes more
quantitatively. Although
far from being ideal,
PHIVOLCS haｄ 35
permanent stations and
six telemetry stations by
1995. Except for a strong
period seismograph in the
main office, all the other
stations had purely short
period seismographs. With
this set-up we have
accumulated a larger
earthquake database and
the quality of epicenter
locations have improved
c o n s i d e r a b l y .
Palo Seismic Station
• JICA PROJECT
►
In 1998, Japan International Cooperation Agency (JICA) and
PHIVOLCS began exploratory talks on improving the seismological and
volcano observation of the Philippines using state-of-the-art instruments
to be provided for by the government of Japan through JICA. In 1999,
the Phase-I of the JICA project has commenced.
• Instruments
►
►
In 2000, new instruments have already been set-up in all 35 stations.
These stations were equipped with the Kelunji-D series digital
seismograph recorder with 3-component accelerometer (Geotech PA-22),
and 3-component seismometer (Geotech S13-J). In addition, Baguio and
Tagaytay stations have 3-component broadband seismometer (Guralp
CMG-3T).
By 2004, Phase-II of the JICA Project have been installed. PHIVOLCS is
currently operating 29 manned and 29 satellite-fed seismic stations. It
also operates 9 broadband stations and maintains 6 Metro Manila
telemetry seismic stations.
Philippine
Network
2004
► 29 Manned Stations
► 29 Unmanned Stations
► 6 Volcanological Observatories
► 6 Metro Manila Seismic Telemetry
► 10 Metro Manila Strong Motion
Stations
•Unmanned Station
Inside
Outside
• INTERNATIONAL COOPERATIONS
►
►
►
The Disaster Prevention and Research Institute (DPRI) of Kyoto University of
Japan, maintains three broadband recording systems in Luzon since 1997. STS-1 is
installed in Baguio City, while the STS-2 seismometers are installed in Palayan City
and in Guinayangan, Quezon. This undertaking is under the Ocean Hemisphere
network Project (OHP) which aims to investigate the structure and dynamics of the
Earth’s interior.
The Global Alliance of Regional Networks (GARNET) was introduced in the
Philippines in early 1998, using the telemetry network of PHIVOLCS located
around the vicinity of Metropolitan Manila area. The primary goal of GARNET is to
enhance international cooperation, coordination and communication through the
teleseismic waveform data exchange among regional and national seismic
networks for selected earthquakes worldwide to study the Earth’s deep structure.
Last year, however, GARNET has been discontinued with the expectations of
broadband network to be installed in selected areas around the country.
PHIVOLCS Tsunami Detection stations is at its early stage being financed by the
Government of Finland. The project aims to enhance and strengthen the capability
of selected coastline communities to avert casualties and immediately respond to
threats from far-field tsunamis through intensive information campaign focused on
an effective warning system developed through collaborative activities between
local government officials, scientists and primary stakeholders.
•
►
INTERNATIONAL COOPERATIONS (cont’d)…
The
Metro
Manila
Strong
Motion
Array
Network (MMSTAR) in
collaboration with Tokyo
Institute of Technology
(TIT), started in 1998 to
provide basic materials
used in strong motion
prediction for possible
future events near Metro
Manila.
The
network
consists of 10 Kinemetrics
digital accelerographs and
are deployed in different
subsurface
geological
conditions
in
the
Metropolis. The data are
archived and added to the
Metro
Manila
strong
motion database.
K2
Strong Motion Accelerograph
by KINEMETRICS
•
►
The United Nations Global Program for Integration of Public
Awareness and the Science of Disaster (UNDP-IPASD) donated
CSCAN (Crustal Stress and Community Awareness Network). It is a
project that aims to involve the community in earthquake detection
and safety. The piezomagnetic sensors installed in 10 stations in
Luzon Island are used to monitor crustal stress changes in the rock
that may serve as precursor to an impending large earthquake.
The mode of receiving crustal stress data from field stations are
as follows:
a. data are gathered by trained resident volunteers.
b. data are sent by fax or email.
c. data are processed by both Chinese and Philippine scientists.
• Crustal Stress
Sensor & Recorder
•
FUTURE PLANS
►
Among the continuing and projected activities under this program
are studies on earthquake source mechanisms, strong ground motions,
delineation of seismic/aseismic zones, foreshocks, seismic expectancy
and other prediction techniques. This program, along with the Volcano
Monitoring and Eruption Prediction Program generates information
needed for earthquake disaster preparedness planning, vulnerability or
risk studies, earthquake disaster mitigation studies, and information
campaigns.
► Aside from basic contributions to seismological research in the
Pacific region, PHIVOLCS expects to develop and adapt technologies
necessary to improve monitoring, seismological research, earthquake
prediction and disaster mitigation.
THANK YOU!
PLATE TECTONICS