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SAMOA’S NEW AND IMPROVED SEISMIC
MONITORING
Presented at the
Samoa Conference III: Opportunities and challenges for a sustainable
cultural and natural environment
25-29 August 2014
National University of Samoa, Apia, Samoa
By Tessa Tafua and Siosinamele Lui
Introduction
‘The trembling rock brings knowledge from afar: - read the signs!’ Emil Wiechert’s (a professor
of Geophysics in Göttingen) words are engraved on a plaque in Gottingen Germany above the
entrance of a Seismograph vault that was installed in 1902, the same year the Apia
Observatory was established. These instruments have aided the great minds before us in the
field of geophysics with knowledge about the structure and physical properties of the deeper
earth’s interior. This phrase basically tells us that the movement of tectonic plates is our best
means of understanding the behaviour of the earth’s interior. It is therefore the aim of scientists
to create instruments that can listen to these tremors, analyse and decipher what it means.
Samoa, like most Pacific Island Countries is exposed to a number of natural and technological
hazards, ‘some of these hazards are seasonal, such as tropical cyclones, floods and droughts.
Others are an ever present threat, such as earthquakes, volcanic eruption, tsunamis, epidemics,
industrial hazards, and exotic plant or animal diseases (NDMO Plan, 2005, 2011).
While Samoa’s location places it far away from the Pacific Ring of Fire, this does not make it
any less vulnerable to seismic activities, Samoa is located approximately less than 200km from
the Northern-Tear fault of the Tongan-Kermadec Subduction zone and an active underwater
volcano to the east of the island chain near American Samoa. This proximity to a seismically
active region increases Samoa’s vulnerability to both earthquakes and tsunamigenic events. A
tsunami generated in this region can have a travel time of less than 10 minutes before impacting
the Samoa islands.
Historically, not much is known beyond the 1700’s about tsunamis affecting the Samoan I slands
although records show that the islands were affected by approximately three tsunamis
associated with an earthquake and volcanic eruptions in the late Nineteenth to early Twentieth
Century (NOAA, 2014)
Figure 1: The diagram is a model of tsunami travel times (Source: Tide tool Software)
Since the establishment of the Samoa Observatory in 1902, Samoa has relied solely on external
sources such as Pacific Tsunami Warning Center (PTWC) in Ewa Beach, Hawaii and the United
States Geological Survey (USGS) for the monitoring and issuance of warnings for earthquakes
and tsunamis.
The intention of this paper is to focus on the monitoring of earthquakes and tsunamis for the
Samoa Region, highlighting the new and improved seismic monitoring and warning system
installed, its components, methods to test the components and health of the system by merging
earthquakes catalogues developed by international institutions and lastly shed some light on
issues that could affect the long term sustainability of the monitoring system.
Earthquakes, tsunamis, and volcanoes are comprised of Samoa’s top five priority natural
hazards in the ‘National Disaster Management Plan (NDMP) 2008 – 2011, 2011-2014. ’The
NDMP clearly identified this risk and this necessitated the need to develop Samoa’s own
earthquake monitoring network and tsunami warning system.
Benefits of Seismic networks
Seismic monitoring aides in the long-term mitigation of seismic risk in a region or country as
well as resolving the seismotectonics. Seismic hazards maps of the region can be created from
analysis of the data which would enable the development and implementation of proper
building codes. In the long term, building codes are very effective in mitigating seismic risk.
Monitoring of seismicity in a volcanic region is also dedicated to volcanic risk mitigation through
the prediction of eruptions. Another important function of seismic networks is for explosion
monitoring, particularly underground nuclear explosions (ed. Bormann 2002). The goal of a
seismic network is the determination of accurate earthquake location and for that purpose we
generally need at least three stations (ed. Bormann 2002).
Drivers for installation
While there were projects that existed prior to 2009 which implemented activities to address the
capacity building aspects associated with these hazards (such as public education and
awareness programmes, and institutional strengthening through the development and
incorporation of hazard agency response plans), modest attention has been given to the
scientific monitoring aspects of these hazards. Samoa did not have the capability to monitor
local geophysical events based on the absence of a national seismic (earthquake) observation
network. Such a network will enable the enhancement of knowledge and understanding of local
earthquake events, their nature, and their likely impacts. Most importantly, it will serve to
increase resilience at all levels to these hazards through the incorporation of obtained
information into national and sectoral development plans.
The respective Hazard Response Plans for tsunamis, earthquakes, and volcanoes highlight the
need for developing and strengthening local capability to monitor the respective events using
scientific techniques. The preferred activity which would complement such objectives is the
establishment of a local real-time seismic monitoring network comprised of earthquake
monitoring stations deployed at selected sites on both Upolu and Savaii. This would enable the
ability to monitor the events in a multi-geophysical hazards context; as volcanic activity can be
monitored using seismic data, and the issuance of local tsunami early warnings are based
primarily on earthquake data. In analogy, the system can be viewed as a one-stop-shop for
geophysical hazards monitoring, and would serve as the foundation for strengthening the
system with associated and newer technology in the medium to long term.
EARTHQUAKE AND TSUNAMI MONITORING SYSTEM
Prior to 2009, Samoa co-hosted one auxiliary seismic station with USGS located at Afiamalu.
The Afiamalu seismic station (AS095) was installed and certified as an international station in
1960 with affiliation to the parent USGS network but only became part of the Global
Seismographic Network (GSN) in 1993 and was a certified station in 2004 to be part of the
International Monitoring Station (IMS) Network which uses data from seismic stations to
monitor the Nuclear Test Ban Treaty (CTBTO).
Data from Afiamalu is transmitted via VSAT to the Pacific Tsunami Warning Center in Ewa
Beach Hawaii near real time and to the International Data Center (IDC) of the Comprehensive
Nuclear Test-Ban Treaty Organisation (CTBTO), and the Albuquerque Seismological
Laboratory (ASL) every half hour From there, the data gets sent to relevant stakeholders such
as the National Earthquake Information Center (NEIC) in Boulder, Colorado, PTWC, and the
Incorporated Research Institutes in Seismology (IRIS) Data Management Center (DMC) in
Seattle, Washington.
Figure 2: The red circle on Upolu Island indicates the AFI IMS/GSN real-time auxiliary
seismic station location.
AFI AS095 Auxiliary Seismic Station Instrumentation:
Global Seismic Network (GSN) System:
The GSN is a cooperative partnership between IRIS and the U.S. Geological Survey (USGS),
coordinated with the international community, to install and operate a global, multi-use scientific
facility as a societal resource for Earth observations, monitoring, research, and education. GSN
instrumentation is capable of measuring and recording with high fidelity all seismic vibrations
from high-frequency, strong ground motions near an earthquake to the slowest global Earth
oscillations excited by great earthquakes. (IRIS, 2014).
The GSN system has been operational since August 1993. The instrumentation used includes
the long period Streckeisen STS-1 Very Broad Band 3 component; 1 vertical and 2 horizontals,
and the short period seismometer is Streckeisen STS-2, which is also a broad band
seismometer. The low gain seismometer is a Kinemetrics FBA-23 Accelerometer.
Quanterra Q680 data acquisition system (which has 12-channels), is used to digitize, process,
and record the seismic data. The digitizer sample rate for the STS-1’s is 20 samples per
second (SPS). The long period (1 SPS), very long period (0.1 SPS), and the ultra long-period
(0.01 SPS) channels are derived from the broad band channels. The STS-2 channels are
recorded continuously at 40 SPS, and events only at 80 SPS. The FBA-23 channels are
recorded continuously at 1 SPS and events at 80 SPS. The instruments are robust but needs
maintenance and repairs after every five years.
International Monitoring System (IMS):
The IMS interface was deployed in September 2004, and has been operational since then.
Data transmission to Vienna is via a GCI (Global Communications Infrastructure) remote
installation VSAT.
IMS/GSN Data Analyses:
Local seismic analysis and monitoring was very limited,, it was heavily dependent on
assistance and information provided by international Seismic Data Centers. Seismic data used
to be monitored via the Live Internet Seismic Server (LISS). Once an event has been identified,
the data is accessed and downloaded via a dial-up telephone modem. The software used to
analyze the data is called the DIMAS Seismic Analysis software (DSAS); a single station
analytical software capable of producing relatively accurate results of magnitude, p-wave and s
- wave arrival times and phases, although the software is not very efficient in determining
location and depth parameters. This meant that warnings were delayed and access to the right
and timely information was problematic.
Figure 3: Afiamalu Station Live Heliplot Source:
(http://earthquake.usgs.gov/monitoring/operations/heliplots_gsn.php)
Limitations of the single station monitoring system
Operating a seismic station and having access to the data did not mean much in terms of
monitoring and analysis. Apart from data access and analytical issues, the Pacific is sparsely
populated with seismic stations, good and accurate analysis is dependent on seismic data from
many stations, the closer the event to a densely populated (seismic stations) region, and the
more accurate and faster analysis can be. When a seismic event occurs, the energy from it
travels around the globe, and it takes time for the seismic waves to reach a seismic station
before data is recorded and transmitted globally. The closest international seismic station to
Samoa is in the Cook Islands, New Zealand, Australia, South Korea and some stations in
South America.
Early Warning System
The Samoa Meteorology Division (SMD) of the Ministry of Natural Resources and Environment
(MNRE) is responsible for monitoring geohazards such as earthquakes, tsunamis, volcanic
eruptions and the like. It is the Geosciences Section of SMD that issues national warnings
against these hazards based on the analysis and data collected. This information is then
disseminated out to the public
ublic through media outlets and relevant stakeholders for the
activation of their response plans already in place.
Figure 4: Flow Chart for Tsunami Warning prior to the new system
The warning system or alert system is made up of the detection and monitoring
monitoring equipment and
is disseminated nationally over the radio, national television, sirens, telephones, cellular, text
messages, the use of traditional modes of communications, church and school bells.
New and Improved Monitoring System
In 2009 before the earthquake and tsunami that devastated the Samoan Islands, an agreement
was signed between the government of Samoa and the government of the People’s Republic of
China to establish Samoa’s first seismic network to monitor earthquakes, in
increase our
resilience to earthquakes and tsunamis, as well as to improve our early warning system already
in place. This project was scheduled to start in late 2009 but was later altered to mid 2010 due
to the effects of the tsunami.
The Samoa China Digital Seismic Network (SCDSN) completed its final installations in June
2012. The SCDSN consists of 3 broadband seismic stations, 4 portable short period seismic
stations, one Data center and related data transmission equipments. This will significantly
enhance local monitoring capability for local earthquakes above magnitude 4 on the Richter
scale, located on Upolu and Savaii, and within a 200 km offshore radius of the islands. It was
the aim of the project that the deployment and utilisation of the seismic network to observe and
research local earthquake events associated with land-movements along major fault lines and
volcanism on both islands, as well as the potential for tsunami generation will enable strategic
adaptation and disaster planning associated with these hazards. Fostering regional seismic
monitoring collaborations with neighbouring South Pacific countries so as to improve the
efficiency of monitoring regional earthquake and tsunami events locally was also considered
when setting up the network.
Seismic Station Components
Each Seismic station includes the following equipments;
Table 1: Equipment for permanent broadband stations
No Item
1
Sensor
Seismometer
2
3
4
5
Accelerometer
Data Acquisition
Data Acquisition Server
Data Communication
Radio Link
Power Supply
Solar UPS Unit
Site Assembly
S pecification
Broadband 120sec ~40Hz, 3 component, selfnoise less than NLNM
3-component, ± 2g, DC-80Hz
3 channel, / 24bit AD/GPS/ 1,50,1 00,200sps/IP,
RS232 console, embed Linux
AC + Solar input, DC 12V, 48V output/150W,
12V*400Ah backup battery
Rack/Wire/Connector
Table 2: Equipments for short period stations
No Item
1
2
Specification
Sensor: Seismometer
SP 2 sec ~ 40Hz, 3-component
Digitizer: Data acquisition 3-channel,/24bit
AD/GPS/IP, RS232
server
console/embed Linux/2G flash memory
3
Data processor: Laptop PC
4
Power Supply: Solar UPS Solar DC 12V, 50W, 12V*60Ah backup
battery U nit
5
Site Assembly
Field instrument case/ wire/ connector/ tools
Figure 5: Installation layout of a BB stations.i.e. Afulilo station
Figure 6: Installation layout of a short period station. i.e. Togitogiga station
Figure 7: Installation layout of a Relay station. i.e. Mt.Fiamoe
Figure 8: Seismic Network distribution over Samoa (Source: Google Map, 2012)
Figure 9:
Figure A: Togitogiga short period
station
Figure B & C: Broadband stations at
Vaiaata and Afulilo,
Figure D: Relay station at Mt.Fiamoe.
Table 3: Seismic Station locations and types of seismometers
Coordinate
Seq.
Station
Type
Ins tallation date
13.82S
National Data Center
201 1-10
171.56 W
13.97 S
VBB+SM seismograph station
201 1-10
Togitogiga
171.72 W
14.02 S
Short Period station
201 1-11
4
Asau
172.65 W
13.52 S
VBB+SM seismograph station
2012-07
5
Vaiaata
172.24W
13.66 S
VBB+SM seismograph station
201 1-12
6
Lepiu
172.39 W
13.46 S
longitude
latitude
Apia
171.78W
2
Afulilo
3
1
Short Period station
2012-07
+Relay Station
7
MT- Fiamoe
171.80W
13.92S
Relay Station
201 1-10
8
Lufi-lufi
171.60W
13.88S
Relay Station
2012-06
The seismic data these stations record is transmitted to the National Data Center (NDC)
through a radiolink in real time. Radio links are often used for data transmission in a seismic
network. They offer seismic data transmission in real time, are continuous, independent, and
often robust to damaging earthquakes (ed. Bormann 2002). The NDC is located at the Apia
Observatory at the Mulinuu Peninsula. This center includes a data collection system, data
processing system, data storage management system, operations and maintenance system
and data sharing services system.
Figure 10: This shows the layout of the NDC where data analysis is conducted.
Figure 11: Network topology map of the NDC
Improved Detection Capabilities
The software used for the analysis of the seismic data is called JOPENS. Local staff of
geophysics have been undergoing continuous on the job analytical training by Chinese
experts on the use of this software as well as attending short term international intensive
training. With seismic monitoring, accurate and timely data depends on the density of the
network, the higher the number of stations in the network, the more accurate your data is. The
system is able to pick up and record seismic activities within the Tonga-Samoa region that is
not recorded by USGS/PTWC as well as active fault lines. We have been able to analyse
earthquakes with magnitudes less than 2.0 on the richter scale recorded by the local stations
within 5 minutes, a huge improvement from the 15 minutes that used to be the time it took to
get information from PTWC about an earthquake. The system is able to detect and record
seismic data seconds after the event, specifically local events within the Tonga-Samoa region
and this capability is crucial to Samoa’s early warning system, because every second counts.
Monitoring and detection of events have vastly improved with the systems ability to extract
data from other international stations or networks operated by countries such as Cook Islands,
Fiji, Vanuatu, Australia and many more whose station data are open to the seismic community
to use. This is heavily reliant on the internet and collaboration between the Pacific Island
countries is underway to look at the best communication options for sharing seismic data
amongst the Pacific Island countries. As a result of the network, Samoa now operates a 24
hour earthquake monitoring operation, a great improvement from 2009.
Figure 12: The waveform analysis on JOPENS for local and distant earthquake.
Figure 12: The waveform analysis on JOPENS for local and distant earthquake.
Figure 13: The earthquake epicenter and its parameters on JOPENS
Robust system
SCDSN in its formulation and design phase was setup to endure the envrironmental
conditions and hazards found in Samoa, with this in mind, the stations were set up to operate
independently from the power grid and runs on solar power but uses the power grid as the
backup. Similarly, the radio link has been setup so that there are multiple point to point
communication with multiple towers from a single station, however, an alternative mode of
data trasnmission from the stations to the NDC has yet to be finalised.
System Checks : Earthquake Catalogs
Since the establishment of our network, data has accumulated and we are slowly using the
data based on the capacity we adopt from trainings we attend in our daily work and for
research purposes. We have used the data to create a earthquake catalog for Samoa.
An earthquake catalog is constructed by merging catalogs developed by difference instituions
and running a completeness check to see if the data is healthy or not and this has never been
done before for Samoa. The catalogs used belonged to USGS, GEM, ISC and SCDSN. These
catalogs showed the same trend that in the earlier years the cluster of earthquakes is not very
distinct compared to recent years and this makes sence because the technology has improved
and able to detect tremors from the deeper parts of the interior of the earth. This information is
key in developing hazard resilience communities especially to earthquake and tsunamis. We
noted from comparison that the data our network recorded also shows some significant events
such as cyclone Evan because there was a gap in the data set right about the same time as
the cyclone. After merging the catalogs I was able to identify in the data that no explosions
was recorded within our region as depicted in the graph below.
Figure 14: This graph shows the data recorded by SCDSN with a wide distribution of
hypocenters. (Source:Seisan Software)
Figure 15: This graph shows the completeness check
of data and no explosions recorded. (Source: Seisan software)
This takes to show that data is very important as well as understanding it and having the
capability to interpret and read seismic data. Hence why our network is not just about analysis
but using and interpreting what the movement and tremors indicate.
Challenges to the New System
While the new system is considered relatively new and young, there are numerous challenges
that are cumbersome to the long term sustainability of the system. Despite it being a robust
system, there is no communication backup for the radio link that is used to transmit data.
Cyclone Evan in 2012 proved that the communications system can withstand cyclones but
given the test of time it might fail. The radio link is the backbone of the seismic system,
alternative options that are economically viable is crucial to its longevity and this is one area
that needs to be addressed immediately.
The software (JOPENS) used for analysis while it does the job also has its limitations,
discrepancies in analysed data has been detected and there is a need to compare the
performance of the software against other seismic analytical software’s.
Conclusion
The establishment of the new monitoring network has increased seismic analytical and
monitoring capacity for Samoa tremendously. From hosting a single auxillary station to
operating six stations, monitoring capability has boosted Samoa’s resilience to geohazards as
well as improved its Tsunami Early Warning System. Confidence in the system is growing over
the years as well as the analytical skills of the staff operating the system, the SCDSN system
has been tested many times with continuous simulations as well as real events and the
system has performed well but there is still room for improvement.
It is evident that our geological and meteorological observation and monitoring systems have
improved tremendously over the years. These systems could be integrated into a system to
form a multi-hazard monitoring system and enable impact forecasting for such hazards. This
improvement goes in line with theme of this conference and the vision and mission of MNRE
in utilizing principals of best practice and ensuring a sustainable development and
management of our natural resources and environment.
While it is good to have a system in place, it is equally important to look at moving forward,
asking the question of where to from here?
ACKNOWLEDGEMENT
This paper is the outcome of our experiences working at the Geosciences Section of the
Samoa Meteorological Services. We acknowledge the support and the hard work by every
individual and Organisations involved in establishing this network, we acknowledge the
support from the Chinese Earthquake Network Center, Professor Li Dahui, Dr Yang Cea and
team, the Ministry of Natural Resources Division, the late Taulealeausumai Laavasa Malua,
Mulipola Ausetalia Titimaea, Lameko Talia, Aliimalemanu Malaefatu Leavasa, Johnny Ah Kau,
Faigame Sale, Paseko Apisaloma, Jerryafa Akeripa, Katie Pogi, staff and management of the
Meteorology Division, Filomena Nelson (DMO), our families, friends and the numerous
individuals who contributed to the establishment of this network as well as editing this paper.
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