performance of broadband seismic network of the philippines

Melosantos, A. A. et al.

Survey Report:

Performance of Broadband Seismic Network of the PhilippinesArnaldo A. Melosantos, Karl Vincent C. Soriano, Ponzch Colleen M. Alcones,

Jose U. Pantig, Jun D. Bonita, Ishmael C. Narag,Hiroyuki Kumagai, and Hiroshi Inoue

Philippine Institute of Volcanology and Seismology (PHIVOLCS)PHIVOLCS Bldg., C.P. Garcia Avenue, University of the Philippines Campus, Diliman, Quezon City, the Philippines

E-mail: a [email protected] School of Environmental Studies, Nagoya University

Furo-cho, Chikusa-ku, Nagoya 464-8601, JapanNational Research Institute for Earth Science and Disaster Prevention (NIED)

3-1 Tenno-dai, Tsukuba-shi, Ibaraki 305-0006, Japan[Received August 10, 2014; accepted November 24, 2014]

The Philippine Institute of Volcanology and Seismol-ogy implements a program on seismic and tsunaminetwork development. It also plans to expand thePhilippine seismic network (PSN), commission newstations, rehabilitate and improve existing stations,and repair and maintain the PSN. The PSN consistsof 70 stations, 12 of which use broadband seismome-ters. Stations are strategically located to maximizethe use of data from stations. The broadband seismicnetwork is being developed to monitor earthquakesin and around the Philippines and to provide moreaccurate data for calculating earthquake parameters.Using data obtain from broadband records, the sys-temwill immediately calculate earthquake parametersuseful for making decisions that provide highly accu-rate, timely warnings and information. PSN perfor-mance is evaluated in this study to ensure this. We con-sider background noise by analyzing station locationsand conditions and their data contribution to SWIFTCMT solutions. We also use power spectral density(PSD) to compare station noise levels to global stan-dards and study data gaps and their causes. Based onthe above parameters and using a scale of poor-good-best, the broadband seismic network is currently per-forming well.

Keywords: broadband, Philippine seismic network,PHIVOLCS

1. Introduction

The Philippine Institute of Volcanology and Seismol-ogy (PHIVOLCS), a government agency, studies Philip-pines earthquakes and volcanoes and implements a pro-gram for developing seismic and tsunami networks, andis working to expand the Philippine seismic network(PSN). PHIVOLCS also commissions new seismic sta-tions, rehabilitates and improves existing seismic stations,and repairs and maintains the PSN. The PSN consists

of 70 seismic stations, 12 of which use broadband seis-mometers. A collaborative project Enhancement ofEarthquake and Volcano Monitoring and Effective Uti-lization of Disaster Mitigation Information in the Philip-pines being implemented by PHIVOLCS and the Na-tional Research Institute for Earth Science and DisasterPrevention (NIED) is funded by the Japan InternationalCooperation Agency (JICA) SATREPS. This projectcovers 10 of the 12 broadband seismic stations.

2. Seismic Network

The PSN consists of 70 seismic stations (Fig. 1), 12of which use the broadband seismometers. Ten of these12 stations are part of the JICA-SATREPS project (Fig. 2)and are being upgraded. Stations are strategically locatedto maximize the use of data gathered from these stations.

2.1. LocationsBroadband sensors placed in existing PSN stations as

follows:

(1) Basco, Batanes, northernmost part of the Philippines

(2) San Manuel, Pangasinan in Luzon mainland

(3) Lubang Island, Occidental Mindoro, Western Philip-pines

(4) El Nido, Palawan, Western Philippines

(5) Brookes Point, Palawan, Western Philippines

(6) Virac, Catanduanes, Eastern Philippines

(7) Jordan, Guimaras, Central Visayas

(8) Borongan, Eastern Samar, Eastern Philippines

(9) Mati, Davao Oriental in Southeastern, Philippines

(10) Pagadian, Southwest Mindanao

5 stations were operational by 2010, 3 in 2011, and 2in 2012. Table 1 lists broadband seismic stations, theirlocation (longitude, latitude) and station codes.

8 Journal of Disaster ResearchVol.10No.1, 2015

Performance of Broadband Seismic Network of the Philippines

Fig. 1. Philippine seismic network (PSN). Fig. 2. PHIVOLCS-JICA-JST-SATREPS broadband stations.

Table 1. PHIVOLCS-JICA-JST-SATREPS broadband stations.

Station name Station code Date of installation Latitude Longitude1. Virac, Catanduanes PVCP November, 2010 13.596 124.1542. Pagadian, Zamboanga del Sur PAGZ November, 2010 07.848 123.3823. Brookes Pt., Palawan BATP December, 2010 08.797 117.8014. Jordan, Guimaras GUIM December, 2010 10.626 122.5895. Looc, Occidental Mindoro LUBP December, 2010 13.734 120.2466. Mati, Davao Oriental MATI November, 2011 06.946 126.2577. Borongan, Eastern Samar BESP November, 2011 11.601 125.4388. El Nido, Palawan ENPP December, 2011 11.206 119.4259. Basco, Batanes BBPS June, 2012 20.441 121.964

10. San Manuel, Pangasinan SMPP September, 2012 16.150 120.680

2.2. SeismometersBroadband seismic stations use the Trillium 240 manu-

factured by Nanometrics of Canada [1], considered one ofthe highest performing seismic sensors. The Trillium 240has a response flat to velocity from 240 seconds to 35 Hzand noise below the new low noise model (NLNM) from100 seconds to 10 Hz [1]. Its advanced thermal design re-duces effects of significant temperature fluctuations, min-imizing requirements for external thermal insulation. Itslow power consumption of 650 mW [1] is an advantagefor remote installations using solar panel batteries. In ad-dition to the sensors cost effectiveness, it complementsthe existing electronics and power system.

2.3. Vault ConfigurationThe 10 broadband sensor vaults were constructed for

this purpose within the perimeters of existing PSN sta-

tions. The seismic vault has a 2 m2 outer housing 0.8 mhigh. The seismic pier is located centrally, 0.625 m fromall walls and decoupled from them to reduce wind noiseeffects. Fig. 3 shows an inner seismic vault 1.25 m highand 0.75 m in diameter and the seismic pier 0.2 m belowground level. It was constructed to minimize noise and tohit the bedrock. To be able to achieve this, we dig morethan 1.2 m deeper. If bedrock is not reached, we use aminimum of 4 galvanized iron pipes 1.5 inches in diame-ter and bury a maximum of 1.5 m deep. The area is thencovered with concrete and the sensor housed in a plasticdrum. After the broadband sensor was installed and testscompleted, space remaining inside the vault is filled with2 layers of 6-inch concrete hollow blocks at the 4 cornersof the outer housing and with fine sand to fill any remain-ing space. The fine sand also helps to avoid unwantedtemperature change.

Journal of Disaster ResearchVol.10No.1, 2015 9


Fig. 3. Seismic vault design.

2.4. Communication and Power Supply SystemSensor data is digitized using the 24-bit 3-channel

Nanometrics Trident digitizer, which has a sampling fre-quency of 50 samples per second [1]. Then, using aCygnus satellite modem transceiver [1], digitized datais transmitted to the PHIVOLCS Data Receiving Center(DRC). The system uses satellite technology to transmitseismic data to the DRC using the very small apertureterminal (VSAT) ku-band over a transmission frequencyrange of 14.014.5 GHz and a receiving frequency rangeof 10.9511.7 GHz [2]. This band uses less power thanthe C-band and an offset satellite dish antenna 1.8 metersin diameter at each broadband station with correspond-ing hardware peripherals satellite modem transceivers,low noise block (LNB) receivers, solidstate power block(SSPB) transmitter and feed horn assemblies. The satel-lite dish sits on a metal mast 1 to 1.5 m high and 4 inchesin diameter. The mast is mounted on a concrete pier. Thisband does not cause interference issues with microwavesignals.The power supply consists of 10 12V-65Ah batteries

charged by 8 80W solar panels with a solar charge regu-lator to prevent the overcharging of batteries. The systemuses GPS to ensure that timing is synchronized.

2.5. PHIVOLCS DRCThe PHIVOLCS DRC is located at the main

PHIVOLCS office in Quezon City, Metro Manila, thePhilippines. An offset Ku band satellite dish antenna3.8 meters in diameter is used by the PHIVOLCS DRC totransmit and receive data. Carina [1], a transceiver, man-ages data sending to avoid data traffic and congestion. Thetransceiver also remotely configures remote seismic sta-tions in the network. Data received by individual remotestations goes to a Naqs server (Nanometrics AcquisitionSoftware) [1] to display waveforms and store data. TheDRC also has data processing software. The system is

backed up by a mirror station in Davao City, Mindanao,the Philippines.

2.6. Data Processing and Management SystemPHIVOLCS DRC data processing software displays

waveforms on a screen [1]. Data are then processed byHydra [1] automatic earthquake location software or elseprocessed manually. Hydra calculates earthquake param-eters such as location, depth and magnitude. Furtherdata processing can be done using Atlas software [1].SWIFT earthquake source parameter determination basedon waveform inversion of Fourier transformed seismo-grams [3] software automatically calculates focal mech-anism solutions and is capable of manual recomputationusing data from the broadband seismic network. Thissoftware has already used broadband data to calculate fo-cal mechanism solutions of significant seismic events inthe Philippines.

3. Evaluation of Broadband Network Perfor-mance

3.1. Background NoiseTen broadband seismic stations are located strategically

to detect earthquakes in the Philippines. Location andinstrument selection consider background noise. We an-alyzed station locations and conditions and data contri-bution to SWIFT CMT solutions to identify its causesand effects on data. SWIFT calculated solutions for111 events with a magnitude range of 4.2 to 7.2 and depths5 to 550 km for 2013 [4]. The PHIVOLCS earthquake cat-alog located 243 events with the same magnitude range of4.2 to 7.2, showing that about 50% of the events locatedby the PSN have centroid moment tensor (CMT) solu-tions by SWIFT. Bonita et al. [5] showed that CMT so-lutions by SWIFT are mostly consistent with solutions bythe global CMT project (GCMT) [6, 7]. To further checkperformance in relation to background noise issues, weused power spectral density (PSD) considering data frombroadband stations with no recorded earthquake and nosignificant weather disturbance within a 24-hour period.The 1 day record represents the noise level of each stationregardless of season. The PSD of noise level is expectedto vary per season and its effect to earthquake monitor-ing. The variation of noise level with season may be in-vestigated further and not within the scope of this paper.The calculated PSD represents noise level of a quiet 1 dayrecord. Fig. 4 shows the calculated PSD of backgroundnoise records, i.e., no earthquake recorded and no data gapfor stations (thin line) compared to the PSD of the globalNLNM (dashed line) and the global new high noise model(NHNM) (bold line) [8]. Eight of the 9 stations show plotsbelow the NHNM and within or above the NLNM.The PVCP is located on private land used for breeding

game fowl. It is underlain by limestone [9] and 270 mfrom a feeder road 3.6 km from the sea and 500 m from



Fig. 4. Power Spectral Density (PSD) plot of the 10 broadband stations. Stations (thin line) comparing to the PSD ofglobal NLNM (dash line) and global NHNM (bold line).

a national road about 1 km from a river away from pop-ulated areas. PVCP PSD results show that it falls belowthe NHNM, except for periods exceeding 100 seconds tothe east and above the NLNM.

The PAGZ is located in an open area on top of a moun-tain of about 1 km from communication towers. ThePAGZ is underlain by pre-quaternary volcanics [9] andis located 130 m from a feeder road about 5 km from the



Fig. 4. Continued.

sea and 2.2 km from a national road away from populatedareas and 680 m asl. PAGZ PSD results show that it fallswithin the NHNM, except for periods exceeding 100 sec-onds to the east and north and the NLNM.The BATP is located inside a small private resort but

away from human activity. The BATP is underlain by al-luvium [9] about 2 km from a national road away frompopulated areas about 3 km from the sea. BATP PSD re-sults show that it falls below the NHNM and above theNLNM.The GUIM is located inside a science high school train-

ing facility. Activities inside the compound occur usuallyonly 1 or 2 times a year and human movement is very farfrom the seismic vault. The GUIM is underlain by allu-vium [9]. It is about 50 m from a dirt road and 200 mfrom a national road away from populated areas 3.4 kmfrom the sea. GUIM PSD results show that it falls withinthe NHNM and the NLNM.The LUBP is located on a small hill, underlain by al-

luvium [9] and is 340 m from a national road away frompopulated areas. A creek runs northeast and southwest

of a station about 150 m away and 740 m from the sea.LUBP PSD results show that it falls below the NHNMand above the NLNM.The MATI is located inside a government center of

very busy human activity because government offices arenearby. A Hall of Justice building is about 20 m away.The MATI is underlain by alluvium [9]. It is about 60 mfrom a secondary road and 90 m from a national road andabout 700 m from populated areas, so most human noiseis caused by daytime activities within government offices.It is about 2 km from the sea. MATI PSD results showthat it falls a bit below the NHNM and high for periodsexceeding 100 seconds east and north.The BESP is located inside a science high school where

the nearest school building is about 200 m from the sta-tion and is underlain by alluvium [9]. It is 150 m froma secondary road and 360 m from a national road 190 mfrom populated areas 400 km from the sea and 520m froma river. The PSD shows that the BESP is not recordingproperly due to a defective digitizer for seismic waves be-tween 1 to 20 seconds, so analysis of its noise level is not



Table 2. Start of operation, data availability per year, and date of satellite migration for each station.

Station code Start of operation Data availability for the year Date of satellite migration Remarks on data gaps2010 2011 2012 2013

PVCP November, 2010 55% 64% 88% 96% August, 2011 -Setting configuration-Replacement of defectiveTrident digitizer

PAGZ November, 2010 53% 95% 83% 97% August, 2011BATP December, 2010 51% 95% 82% 91% July, 2011GUIM December, 2010 93% 95% 96% July 2011LUBP December, 2010 58% 73% 80% August, 2011 -Satellite migration

-Delay in identifying the is-sue on satellite communi-cation interference

MATI November, 2011 99% 75% 96% August, 2011BESP November, 2011 99% 93% 99% September, 2011ENPP December, 2011 86% 92% 98% August, 2011BBPS June, 2012 97% 56% June, 2012 -Damaged by TyphoonSMPP September, 2012 99% 99% September, 2012

reliable using available data.The ENPP is located on a slope inside a state university

away from school buildings and is underlain by sedimen-tary deposits [9]. It is 110 m from a national road awayfrom populated areas 1 km from the sea. ENPP PSD re-sults show that it falls below the NHNM and above theNLNM.The BBPS is located in an open area along the slope

of a privately owned hill and is underlain by quaternaryvolcanic deposits [9]. It is about 100 m from a nationalroad and is 150 m from a diesel power plant supplyingpower to the island away from populated areas and 420 mfrom the sea. BBPS PSD results show that it falls belowthe NHNM and above the NLNM.The SMPP is inside a hydroelectric power plant. The

seismic vault is inside a 2.5 m2 10 m artificial tunnelabout 200 m high. The plant spillway is about 60 m fromthe power plant and the reservoir 50 m away from thetunnel. The SMPP is underlain by old sedimentary ma-rine deposits [9] and is 30 m from power plant roads usedduring operations and away from populated areas. SMPPPSD results show that it falls uniformly below the NHNMand above the NLNM. Fig. 4-SMPP shows that noise lev-els are uniformly distributed in all periods relative to theNLNM and NHNM, so the SMPP is ideal among stations.

3.2. Data Gap History of Station and PossibleSources

Since the broadband seismic network started partial op-eration in 2010 and full operation in 2012, we gathereddata from the 10 stations. Table 2 and Fig. 5 show an-nual station data availability. Data shows a gap during in-clement weather, especially during the rainy season, anddue to the satellite end of life (EOF) in December, 2010.The satellite source started migrating in July, 2011.In 2010, 3 stations commenced full operation. Data

availability is 50 to 55% for the 3 stations, gaps in this pe-

Fig. 5. Data availability.

riod are related to EOF of the satellite the PSN is leasingand bandwidth assigned to these stations has not yet beenadjusted.An additional 5 stations were installed in 2011. Signifi-

cant data gaps were apparent for the PVCP and LUBP andare related to satellite EOF issues. For the LUBP, anotherissue is the defective SSPB transmitter.In the last quarter of 2012, all 10 stations had been

fully installed. Data gaps for 6 were due to various rea-sons. The PVCP Trident digitizer became defective andwere replaced in May 2012. The LUBP Cygnus modemtransceiver became defective and were identified by thesatellite provider as the source of interference to othersatellite transponders.The 10 broadband stations were fully operational for

2013. Data availability charts of stations show, how-ever, that 3 fall below acceptable data availability, i.e., theLUBP, BATP and BBPS. The LUBP data gap remainedan issue related to communication for 2012. In March,2013, the defective Cygnusmodem transceiver was pulled



Fig. 5. Continued.

out and issues resolved in the first week of April, 2013.The BATPs signal became intermittent in July, 2013. TheBBPS power supply was adversely affected by the renova-tion of its building in February to April, 2013 but resumednormal operation in May, 2013.

4. Discussion

We analyzed station locations and conditions and datacontribution to SWIFT CMT solutions though locationand instrument selection that already considered the back-

ground noise issue. Aside from location, constructionprocedures for seismic vaults where seismometers wereplaced also took minimizing human and outside noiseinto consideration. SWIFT CMT solutions show thatdata gathered from broadband stations were used in so-lutions. We also used PSD to compare station noise levelsto global standards. PSD results show 8 of the 9 stationsplots below the NHNM and within or above the NLNM.Data gaps are attributed to issues such as communica-

tion due to satellite EOF, technical malfunctions of com-ponents and weather disturbances. These issues were ad-dressed through satellite migration and repair and main-



Fig. 5. Continued.

tenance of the system, except for weather disturbances.Gaps due to weather disturbance could be addressed bysetting up a mirror station, as has been done. Note, how-ever, that data analysis of the mirror station is not includedin this study.

5. Conclusions

We installed 10 broadband seismic stations as part ofthe Philippine seismic network to contribute to earthquakemonitoring in the Philippines. We selected station loca-

tions and instruments considering low background noise.We also used construction procedures for seismic vaultswhere seismometers were placed to minimize human andoutside noise. We analyzed station locations and condi-tions and data contributions to SWIFT CMT solutions.Stations were strategically located in the Philippines, butthey may be too few to increase detectability. PSD resultsshow 8 of the 9 stations plots below the NHNM and withinor above the NLNM or within global standards. Datagap issues were appropriately addressed through satellitemigration and repair and system maintenance, except forweather disturbances. PSD and data gap analysis helped



Fig. 5. Continued.

determine seismic station performance and could be use-ful for reference in the installation of seismic stations.Based on considered parameters used in this performanceevaluation and using a scale of poor-good-best, the broad-band seismic network of the Philippines is performingwell.Regional seismic network and source analysis is very

important in rapidly determining earthquake source in-formation. The current upgrade of PSN with broadbandseismic stations and the use of SWIFT help provide focalmechanisms and understanding of recent large damagingearthquakes [3]. Current PSN broadband stations providedata for regional source analysis using SWIFT, in which

SWIFT CMT solutions were found to be mostly consis-tent with the GCMT [5]. These thus indicate that the up-graded PSN is performing well and could be further im-proved by making a denser and more uniform broadbandseismic network.

AcknowledgementsWewould like to acknowledge the helpful support extended by theJapan International Cooperation Agency (JICA), the Japan Sci-ence and Technology Agency (JST), and SATREPS. We wouldalso like to acknowledge the support of PHIVOLCS and NIEDpartners who joined the team during installation of broadband sta-



tions. Some figures were generated using REDAS software. Seis-mic vault design was by Engr. Angelito Lanuza, licensed civilengineer.

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[7] G. Ekstrom, M. Nettles, and A. M. Dziewonski, The Global CMTProject 2004-2010: Centroid-Moment Tensors for 13,017 Earth-quakes, Phys. Earth Planet. Inter., Vol.200-201, pp. 1-9, 2012.

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Name:Arnaldo A. Melosantos

Affiliation:Supervising Science Research Specialist, Seis-mological Observation and Earthquake Predic-tion Division, Philippine Institute of Volcanol-ogy and Seismology

Address:PHIVOLCS Bldg., Carlos P. Garcia Ave., University of the PhilippinesDiliman Campus, Diliman, Quezon City, the PhilippinesBrief Career:1989 Joined the Philippine Institute of Volcanology and SeismologySelected Publications: Instrumentation Seismology

*Profiles of co-authors are omitted in this special issue.


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