EVALUATION OF CURRENT STATUS OF THE
UNIVERSITY SEISMIC NETWORK IN SRI LANKA
AND PROPOSAL OF ITS UPGRADE
Sanjeevani Nilmini Bandara THALDENA∗
MEE06019∗∗

Supervisor: Tatsuhiko HARA

ABSTRACT
In order to investigate the current status of the University Seismic Network in Sri Lanka, which was
funded by Japan International Cooperation Agency (JICA) and is operating since 2003, data
availability, detectability and P, S arrival times were checked. The results indicate that system is able
to detect events with magnitude greater than 6, within the epicentral distance up to 20 degrees. Due to
low S/N ratio, it is difficult to detect smaller events in regional scale and local events. There is a good
agreement between the observed P arrival time and the theoretical P arrival time but systematic
decrease in S-P time difference. Communication problem and poor site selection are the major
problems. An upgrade plan of the current network consisting of relocation of the sensors andestablishing real time data communication. It is desirable to combine data from the University Seismic
Network and data from the PALK broadband station for earthquake monitoring and tsunami alert for
Sri Lanka. Broadband moment magnitude, Mwp was calculated using data for PALK station to findthat it is possible to obtain relatively reliable magnitude estimates using data from single station.
Keywords: Seismic Network, Earthquake/Tsunami Monitoring, Sri Lanka

INTRODUCTIONAs Sri Lanka is placed well inside the Indo-Australian plate far away from an active platemargins, it is very unlikely to experience any substantial damage from a direct impact of earthquake.
The closest active plate margin is Sunda Trench and is located around 1200km away from the island.
However, secondary events such as tsunami can cause extensive damage as we already got similar
experience in the year 2004. In 2004 Indian Ocean Tsunami, the large causalities were caused becauseof no experience and incapability in the issuance of tsunami warning as well as lack of tsunami
awareness. In this context it is necessary to develop and strengthen the seismic/tsunami monitoring
system with earthquake locating and rapid magnitude determination in the earliest possible time tominimize the risk of earthquakes damages. In this paper, the utility the existing Local University
Seismic Network and GSN Station in seismic studies, rapid determinations of earthquakes andespecially in the tsunami warning are discussed and also this is the first attempt to analyze the datafrom University Seismic Network. The objectives of this study are: (1) Study the current status ofUniversity Seismic Network and preliminary analysis of data (2) Proposal for upgrading
Earthquake/Tsunami Monitoring System in Sri Lanka. Data used in this study is provided by
University Seismic Network which consists of four short period seismometers and the PALK, GSN
broad band station. Finally a plan which could be implemented for the network upgrading is discussed,
so that its capacity and reliability in Earthquake/Tsunami Monitoring can be enhanced.

∗∗∗

Geological Survey and Mines Bureau, Sri Lanka
International Institute of Seismology and Earthquake Engineering (IISEE), Japan

1

SEISMIC OBSERVATION IN SRI LANKA
The University of Peradeniya operates University Seismic Network which contains four seismologicalstations with short period sensors and Geological Survey and Mines Bureau together with Universityof California, San Diego operate PALK–GSN broadband station. The Government of Japan throughJapan International Corporation Agency (JICA) donated University Seismic Network to the
Department of Geology, University of Peradeniya for teaching and research purposes. It was operated
since May, 2003. Four seismometers which are able to receive seismic signals of regional and local
earthquakes are stationed at Matara (RHN), Mihintale(RJR), Olluvil(EST), and Peradeniya(PRD)
within university premises. The each station is equipped with Short period seismometer (GS-1), Forcebalance servo Accelerometer (Episensor), Data logger (K2) and relevant infrastructure facilities.
INVESTIGATION OF THE CURRENT STATUS OF UNIVERSITY SEISMIC NETWORKThe data availability and detectability of the events greater than magnitude 5.5 using the data available(transferred to central station) at Central Station at Peradeniya (PRD) within the 01/05/2005 and30/04/2006 was investigated. The original data obtained from the University Seismic Network is in“.evt” (Kinematrics K2) format and the data obtained were prepared to read in SEISAN. First theevents were selected using USGS/NEIC data base and the travel time was calculated using Taup_Time.
Then the availability of relevant events was checked in the triggered data base at Central Station withreference to each station. Finally among those records, seven events near the Andaman Region wereselected for further analysis. The theoretical travel time calculated using Taup toolkit and the timeobserved by University Network and the theoretical S-P time difference were compared
Availability of Data
Availability of the data from all the stations at central station, from May 05, 2005 to April 30, 2005 (asshown in the Table 1) was checked and the available data were categorized basically in to three
categories. Category A includes the records which are detected and can be used for phase picking andhypocenter determinations. It is seems that only S arrival was recorded in some cases and those cases
were categorized into category B. Category C represents the records which are very difficult to readeven related to large events. Availability of the data from all the stations at central station indicates
relatively higher number of records is available for station PRD and RJR.
Table 1. Data Availability at Central Station
Date
2005
2005
2005
2005
2005
2005
2005
2005
2005
2005
2005
2005
2005
2005
2005
2005
2006

6
7
7
7
7
7
7
7
8
8
8
8
9
9
10
10
2

26
13
23
23
24
29
30
30
2
4
9
13
10
13
11
15
3

Origin Time
8
23 3.87
029 29.81
7
34 56.77
22 53 35.08
15 42 6.21
20 33 40.03
11 3
49.12
15 13 20.12
8
39 51.70
926 52.81
5
26 17.53
7
36 52.77
16 57 47.27
14 32 57.82
3
37 56.85
15 51 8.13
447 36.36

Lat
1.77
10.35
35.50
5.11
7.92
2.86
-61.47
5.18
-4.00
-3.66
-20.94
20.13
4.86
8.07
10.89
25.31
36.16

Lon
125.82
92.00
139.98
94.80
92.19
93.56
154.2594.48
128.82140.18173.82145.80
95.04
91.91
92.30
123.35141.45

2

Mag
6.0
5.5
6.1
5.6
7.5
5.8
6.0
5.8
5.6
5.8
6.1
6.0
5.8
5.5
5.5
6.4
5.7

Depth
91
49
61
48
16
32
10
38
10
40
23
48
41
30
22
192
28

PRD
C
A
D
B
A
A
C
B
D
C
D
C

RJR
A
B
A
C

D
C
B
A

C
A
C

RHN

EST
D

2006
2006
2006
2006
2006

2
2
3
4
4

3
28
9
19
20

20
7
17
20
23

34
31
55
36
28

12.71
0.65
55.40
48.30
3.90

A
B

detected and readable
Only S arrival

11.90
28.12
0.79
2.65
60.87

92.41
56.87
-26.1293.24
167.01

6.1
6.2
6.0
6.2
6.1

30
18
10
30
10

C
D

triggered but difficult to read
not detected

A
D
D

D
B
D

Earthquake Detectability
First the earthquake detectability by these short period sensors was checked using the data of Station,
PRD and the Station RJR as those stations have relatively large number of records. The results asshown in the following graphs (Fig.1) indicate that this short period sensor can detect readable eventseven with magnitude greater than 6 and also the distance around 20 degrees.
Detection of events - Station RJR

Detection of events-Station PRD
8

8
7.5

7.5

only S arrival

7

deteced but difficult to read

Magnitude

Magnitudederected and readable

detected and readable

6.5
6
5.5

only S arrival

7

detected but difficult to read

6.5
6
5.5

5

5
0

20

40

60
Distance (deg)

80

100

120

0

20

40

60
Distance (deg)

80

100

120

Figure 1. Graphs showing the Detectability by (a) Station PRD (b) Station RJR
Arrival Times of P and S waves
Seven events, magnitude greater than 5.5 were selected among the available data and used for further
analysis. The P and S were picked to calculate S-P interval. The theoretical travel time for relative
events were calculated using the Taup-kit (based on IASP91 model). Finally the both theoretical andobserved results were compared to find the accuracy of the observations.
Comparison of S-P Time
160.0044:24.0

150.00S-P (sec), This StudyP arrival (observed)

Comparison of P- Arrival
47:16.8

41:31.2

38:38.4

35:45.6140.00130.00120.00110.0032:52.8
100.00100.00

30:00.0
30:00.0

32:52.8

35:45.6

38:38.4

41:31.2

44:24.0

110.00120.00130.00140.00150.00160.0047:16.8

S-P (sec) according to USGS data baseP arrival (theoritical)

Figure 2. (a) Comparison of P-arrival (observed) with P-arrival (theoretical)(b) Comparison of S-P time (observed) with S-P (theoretical)
Results in the Figure 2 show those theoretical and observed P-arrival times are almost identical but
there is a significant decrease in S-P time difference.

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PROPOSAL FOR UPGRADINGTSUNAMI/EARTHQUAKES MONITORING SYSTEM IN SRI LANKA
In this chapter, the current problems of the University Seismic Network and the proposals of its
upgrade are discussed in detailed.
Problems of current University Seismic Network
The result of the study on the current status of the University Seismic Network in Sri Lanka has shownthat this network can detect events with magnitude greater than 6, the epicentral distance up to 20
degrees. The ability to detect such large events in the Sumatra Andaman region is useful for Tsunami
Alert in Sri Lanka. Because Sri Lanka has a risk of tsunami which will originate from the Sunda trench
located around 1000-1700km away from the Island. However, there are two major problems that arehighly desirable to the solved to improve and enhance earthquake monitoring in Sri Lanka. One ofthese problems is the low S/N ratio. At present, it is difficult to detect local events as well as eventswith M<5.5 in the Sumatra – Andaman Region. The other problem is bad communication links
between the Central Station and four stations. Due to this problem the system did not function well.
Upgrade Plan for Earthquake/Tsunami Monitoring in Sri Lanka
Relocation - Because of the low S/N ratio, the system is unable to detect smaller events in regional
scale and local events. However Over the past few years, tremors have been reported within the
country (for example recent earth tremors occurred in Tissamaharama area, South-Eastern part of Sri
Lanka in July 2007) by the general public in frequent manner. Most of these tremors were very, local,
confined to particular region within the island and these events were not registered in any Global
Seismic Network. Local scientists were also unable to determine under the present conditions ofseismic monitoring. As most of those events are not registered in Global Network, the monitoring ofseismic activities by local seismic network is uttermost important. The sensors should be relocatedwith appropriate noise survey to enhance the data quality and get high quality data for early warningand research purpose. Relocation is one of the major important points otherwise this system can not be
used in hypocenter determination of local events.
Real Time Data Transferring - The observations indicate that there haven’t been any serious hardware
problems with the sensor and recording equipments. The lack of availability is mainly caused by bad
communication link. The modems are breakdown easily due to the interrupted power supply andthundering and it stop the data transfer between the data center and seismic stations. In the current
system, data is not transferred on real time basis. The data communication links within the system are
as follows. At each station, continuous data consisting of one minute data segments are kept for one
month. When it detects an arrival of seismic signal, that information is sent from station to the Data
Center every 20 minutes. Then the program at Data Center sends a batch file for retrieval of event
data to each station every 20 minutes. At each station, the continuous data files are copied from thedirectory where continuous data are kept to the directory where the event data files are kept (in thecurrent system, an actual event file is not created. Instead, series of continuous data segments which
are expected to contain seismic signals are kept). Then the data collection program running at theData Center retrieve event data every 40 minutes. After event data are collected at the Data Center, thefile conversion program converts “.evt” files to SEISAN files. This program also creates event files (Sfiles in SEISAN file system).
These three communication steps should be carried out properly between each station and thedata center for event triggering and registration. Due to the bad communication and often power
supply failure, these steps have not been properly completed. For continuous monitoring of large
earthquakes in regional distance range and small events in the island it is necessary to link all of thestations to the data center to collect data on a real time basis through a dedicated line instead of dial upphone connection. Since the current system is complicated and since one or some data transfer

4

procedure have not worked properly event files are not available. And also the data transfer takes longtime. It is too slow for tsunami alert. It is essential to data transfer on real time basis for tsunami
monitoring and alert. In addition to making the data transfer of the University Network on a real timebasis, it is necessary to receive broadband waveform data from PALK on a real time basis to establish
proper monitoring system.
Establishment of National Data Center - According to the National Disaster management System in
Sri Lanka, Geological Survey and Mines Bureau (GSMB) is responsible for monitoring of seismic
activities, especially the micro-seismic activity within the country and GSMB also advises the
Department of Meteorology on possible tsunami threats of seismic origin. The GSMB has now
established a National Data Centre for seismic information. Therefore, it is essential to transfer thenear real time data to the National Data Center at the Geological Survey and Mines Bureau. In future,
existing broadband station and another two proposed broadband stations which will be installed withthe assistance of the German Government as well as a University Seismic Network maintained by the
University of Peradeniya are to be gathered and analyzed at this Data Centre. To achieve this target,
personnel training are needed specially in hardware and network to face the problems with the
breakdown or maintenance of the equipments and also training on data processing. If this integration isrealized, it is possible to determine hypocenters and earthquake magnitudes (Mwp) for 24 hours a day.
Before it, still it is possible to determine epicentral distance using S-P. In 2004, Indian Ocean Tsunami
killed around 36 000 people because of lack of experience in tsunami issuance and also lack ofawareness. Therefore it is necessary to prepare to avoid such kind of disaster in future. In such a caseaccuracy as well as rapidness is important. Therefore in this study, Mwp using the data from PALK
station was determined as shown in another chapter to check the reliability of calculation of Mwp using
single station. The result of determination of Mwp even using single station is acceptable. This
integrated basic information is useful for making decision on tsunami warning. The data can beverified with the linkage of PTWC and JMA.
In this study, a good agreement between the observed P arrival time and the theoretical P
arrival time was observed but there is a systematic decrease in S-P time difference. It is important tocarry out further detailed study on this regard and also it may be interesting to try to determine the mb
using the currently available data.
DETERMINATION OF Mwp USING PALK BROADBAND DATA
I propose above real time data transfer from PALK station, and Mwp for some events were determined
to investigate the accuracy of magnitude estimates using single station within this system.
Mwp (This Study) Vs Mw (CMT Global)
9.5

Mw p (This Study)

9.0
8.5
8.0
7.5
7.0
6.5
6.0
6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

Mw (Global)

Figure 3. Events used for Mwp, Comparison of Mwp (This Study) and Mw (Global CMT)The procedure by Tsuboi et al. (1995, 1999) was followed. Tsuboi et al. (1995) introduced broadband
moment magnitude Mwp. Determination of the Moment Magnitude (Mwp) from the digital waveform by

5

PALK GSN station was done using the method described in Tsuboi et al. (1995, 1999) which uses thebroadband seismograms for calculating broadband moment magnitude Mwp. The P-wave moment
magnitude, Mwp is calculated from the vertical component of far-field P wave displacement. Eight
events were selected from the USGS/NEIC catalog from 2004 to 2007 within the 25 degrees from thestation and the hypocenter depth is less than 100km. The hypocenter parameters were taken from
USGS database. Distribution of the events and the location of the station are shown in Fig.4. The
results obtained by this study were compared with the moment magnitude determined by the Global
CMT solutions and the results are shown in Figure 3 up to magnitude 7.5. Results are within a lessuncertainty except two events (M>8)) which suggests that it is possible to obtain relatively reliableMwp by analyzing even single station. Result has shown that the MWp is reliable up to around 7.2 while
it is under estimate for large earthquakes. In this case December 26, 2004 Sumatra earthquake (Mw9.0)
and the March 28, 2005 Northern Sumatra earthquake (Mw8.6) are probably out of the range of theapplicability of Mwp calculation.
CONCLUSION
The investigation on data availability, detectability and P, S arrival times reviled that there is no major
hardware problem with sensors and recording instruments. Poor site selection, improper
communication links are the major drawbacks. The results show that many records of events are
missing at the Central Station due to the communication problem and the unstable power supply. The
system is able to detect events with magnitude greater than 6, within the epicentral distance up to 20
degrees. Due to low S/N ratio, it is difficult to detect smaller evens and local events. I found a good
agreement between the observed P arrival time and the theoretical P arrival time. It is possible toobtain rough guesses on the epicentral distance using S-P times although there is a systematic decreasein S-P time difference. Based on these results, I propose an upgrade plan of the current network
consisting of relocation of the sensors and establish real time data communication. As monitoring of
local events is an important and a primary issue, it is necessary to relocate the sensors and real time
data transferring is needed for quick decision making on Tsunami alert. It is desirable to combine datafrom the University Seismic Network and data from the PALK broadband station for earthquake
monitoring and tsunami alert for Sri Lanka. I calculated broadband moment magnitude to check thereliability of use of single station data for Mwp calculations and it is found that this procedure can beused to determine relatively reliable magnitude estimates.

ACKNOWLEDGEMENT
Thanks are also due to Mr. L.R.K Perera (Head, Department of Geology, University of Peradeniya, Sri
Lanka) for permitting me to use data of the University Seismic Network. Further I am extremely
thankful to Dr. Hiroshi Inoue (NIED) and Mr. Toru Kajiwara, Mr. Takamori Ito (Oyo Seismic
Instrumentation Cooperation) for their constructive comments regarding this work and Mr. Mahinda
Senevirathne (GSMB, Sri Lanka) for his numerous supports during this study.

REFERENCES
Kanamori, H., 1977, J. geophys. Res., 82, 2981-2987
Fernando M.J. et. al., 1986, Phy. Earth planet Inter., 44, 99-106
Tsuboi, S. et. al., 1995, Bull. Seis. Soc. Am., 83, 606-613
Tsuboi, S. et. al., 1999, Bull. Seis. Soc. Am., 89, 1345-1351
Wimalarathne, K. D., 1993, Daily News, Dec.23, 8

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