Study of a High Activity Eruption Sequence of Kadovar ... · Submarine earthquake Figure 3. The...
1
Study of a High Activity Eruption Sequence of Kadovar Volcano, Papua New Guinea, Using Data Recorded by the CTBT International Monitoring System Hiroyuki Matsumoto 1 , Mario Zampolli 2 , Georgios Haralabus 2 , Jerry Stanley 2 , James Robertson 2 and Nurcan Meral Özel 2 1 Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2 Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) The analysis of hydroacoustic signals originating from marine volcanic activity recorded by a remote hydroacoustic (HA) station, HA11 at Wake Island, of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System (IMS) is presented. The events studied pertain to an eruption series at Kadovar Island, Papua New Guinea during the period January to February 2018. Local visual observations determined that the Kadovar volcano began to erupt at the summit of the island, and then created new vent spots near the coast. The events included the collapse of a lava dome on 9 February 2018. Directions-of-arrivals (DOA) of the hydroacoustic signals detected at HA11 were evaluated using a cross- correlation technique. This allowed discrimination between hydroacoustic signals originating from the Kadovar volcanic activity and other numerous hydroacoustic signals generated by general seismic activity in the Pacific. Discrimination between volcanic activity and seismicity was achieved by examining the time-frequency characteristics of the hydroacoustic signals, i.e. associating short duration broadband bursts with volcanic eruptions, in line with criteria generally applied for such events. Episodes of high volcanic activity with as many as 80 detections per hour (calculation based on 30-s time-window with 25-s over-lap) were identified on two occasions, separated by a one-month period of relative quiet. Some of the hydroacoustic signals were characterized by broadband frequency content and high received levels (i.e. ca. 30 dB higher than the ocean background noise). It was found that corresponding non-hydroacoustic signals could not be identified by other regional IMS seismic stations, this providing an indication of the likely submarine origin of these events. ▋ IMS Hydroacoustic Network & Hydrophone Triplet The hydroacoustic network is part of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) and has 11 stations. Of the 11 hydroacoustic stations, five (denoted by green triangles) are T- phase stations which use seismometers to pick up water-borne signals from acoustic events coupled in the crust of coastal areas. The other six (orange triangles) are cabled stations that utilize underwater hydrophones. All the cabled stations have two triplets of underwater hydrophones suspended in the water column, in a horizontal triangular configuration with a separation of 2 km, except for HA01 at Cape Leeuwin, Australia which has only one triplet. The present study is concerned with the IMS hydroacoustic (HA) hydrophone stations, which have been installed since the early 2000’s. The hydrophone stations are based on islands and connected by electro/fiber-optic cables to the hydrophone triplets. The triplets are deployed up to 200 km from the island. All hydrophone sensors are located in the SOund Fixing And Ranging (SOFAR) channel axis at a depth of 600 m to 1200 m, suspended by subsurface floats. Hydrophones record the pressure change in the water caused by passing hydroacoustic waves, such as H-waves and T-waves. Figure 1. CTBT IMS hydroacoustic network. Figure 2. Overview of an IMS hydrophone triplet and events which generate underwater sound. Underwater hydrophone stations / T-phase stations HA03 – Juan Fernandez Island Chile HA10 – Ascension United Kingdom HA08 – BIOT/Chagos Archipelago United Kingdom HA04 – Crozet Islands France HA01 – Cape Leeuwin, WA Australia HA11 – Wake Island United States of America 1. The hydroacoustic detections at HA11 from the Kadovar volcanic eruptions for January and February 2018 were supported by flyover observations and documentation. 2. Estimation of the direction-of-arrival (DOA) of the signals recorded at HA11 by cross-correlation analysis made it possible to identify hydroacoustic arrivals from the volcanic activity at Kadovar. 3. Using the time-frequency characteristics of the arrivals, the present study made it possible to discriminate between volcanic eruptions and seismicity. Acknowledgements The IMS HA11 hydroacoustic station is operated as a part of the CTBT’s IMS verification regime. The authors thank P. Nielsen, T.Edwald, and R. Le Bras (IDC, CTBTO) for the scientific and technical discussions. This study is supported by the Grants-in-Aid for Scientific Research (KAKENHI: JP16KK0155) of the Japan Society for the Promotion of Science (JSPS). ▋ Kadovar Volcanic Island Flyover photo on 05 January 2018 The location of Kadovar Island volcano is denoted by a red star, and the IMS HA11 hydroacoustic station triplets at Wake Island are denoted by orange triangles in the left panels. HA11 comprises two triplets of hydrophones, referred to as H11N and H11S (see Figure 4). The distance between Kadovar and HA11 is about 3,500 km. Dark and bright red triangles locate above-surface and submarine volcanoes, respectively, as registered by the Smithsonian Institute. Radial marks are back-azimuths (BAZ) from the North triplet H11N. The central panel shows a local map off New Guinea Island. Two local flyover photos are present in the right panels; an eruption began at the summit of Kadovar Island on 05 January 2018, and then a new vent spot was created on 11 January 2018 . ▋ IMS HA11 Wake Island & Identification of Volcanic Eruptions The hydroacoustic signals associated with the Kadovar volcano eruption are identified at both the North and the South triplets between 09:44 UTC and 09:47 UTC, respectively (Figure 5). The Power Spectral Densities (PSDs) are calculated for these signals. Figure 6 compares PSDs between the ambient noise and the hydroacoustic signals of the Kadovar volcano eruptions. Amplitude is corrected by the Frequency-Amplitude-Phase (FAP) response of the hydrophones. The hydroacoustic signals associated with the volcanic eruptions are characterized by broad-band energy. ▋ Direction-Of-Arrivals (DOA) of Hydroacoustic Signals The back-azimuth of the signals detected by H11N, together with the corresponding spectrogram, are shown in Figure 7. Before the cross-correlation analysis, a digitial filter with pass-band 10 – 60 Hz is applied. Each of the plotted dots is calculated with a 30-s time window and a 25-s over-lap. The dashed line represents the true back-azimuth to Kadovar. The cross-correlation analysis suggests that the Kadovar volcano erupted very frequently from 00:20 UTC to 01:40 UTC. Long-duration signals with a frequency content below 30 Hz in the spectrogram can be associated with seismicity in the Pacific; the 23:23 UTC, 00:04 UTC and 00:42 UTC signals correspond to earthquakes off Kamchatka (M3.5), Papua New Guinea (M4.7) and a previously unknown signal from a north-north-western direction, respectively. ▋ Conclusions Each bin in Figure 8 shows counts of hourly detections of H11N hydroacoustic signals with a DOA consistent with sources at Kadovar. The red curve shows the cumulative detections of H11N hydroacoustic signals. A 30-s time- window with 25-s over-lap is used for cross- correlation analysis to associate the signals with volcanic activity over time. The time window overlap may lead to a slight over- estimation of the counts, similarly to what was found in previous work [H. Martsumoto et al., Scientific Reports 9, Art. No.: 19519 (2019)]. Arrivals between 5 and 10 January could not be identified because of a brief temporary outage of HA11, therefore the absence of arrivals during this period cannot be associated with a reduction of volcanic activity during those 5 days. With this caveat in mind, our results suggest that the Kadovar volcanic activity can be divided into two stages separated by a one- moth relatively quiet period; the first burst of activity was identified between 11 and 13 January 2018, and the second one was identified around 09 February 2018. These identifications correspond well with the available documentation and reports of flyover observations pertaining to the Kadovar volcano eruptive activity during this period. SOFAR channel H- or T-wave Land facilities Land-slide (Flank collapse) Hydrophone triplet Volcanic island IMS HA station Submarine earthquake Figure 3. The Asia-Pacific area and detailed map covered by the present study. Figure 5. An example of HA11 typical recordings associated with the Kadovar volcano eruptions on 11 January 2018 (10-min waveforms centered at 09:45:00 UTC). A band-pass filter with 10 – 60 Hz is applied. Figure 6. Comparison of Power Spectral Densities (PSDs) of ambient noise and a typical signal from a Kadovar volcano eruption. Figure 4. Locations of hydrophones on sea-mounts off HA11 Wake Island. Figure 7. Back-azimuth evaluated by the cross-correlation analysis of H11N and the corresponding spectrogram on 09 February 2018. Figure 8. Histograms of cross-correlation analysis for January and February 2018. Note that the dataset is not available for the entire period, because of a temporary outage between 05 and 10 January 2018. Disclaimer: The views expressed on this poster are those of the author and do not necessarily reflect the view of the CTBTO. Data Source: Bulletin Reports of the Smithsonian Institution The same packet from Kadovar Flyover photo on 11 January 2018 Report by Sharoi Romkentuo © Authors 2020, all rights reserved Disclaimer The views expressed in this poster are those of the authors and do not necessarily reflect the view of the CTBTO.
Transcript of Study of a High Activity Eruption Sequence of Kadovar ... · Submarine earthquake Figure 3. The...
Study of a High Activity Eruption Sequence of Kadovar Volcano, Papua New Guinea, Using Data Recorded by the CTBT International Monitoring System
Hiroyuki Matsumoto1, Mario Zampolli2, Georgios Haralabus2, Jerry Stanley2, James Robertson2 and Nurcan Meral Özel21Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO)
The analysis of hydroacoustic signals originating from marine volcanicactivity recorded by a remote hydroacoustic (HA) station, HA11 at WakeIsland, of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) InternationalMonitoring System (IMS) is presented. The events studied pertain to aneruption series at Kadovar Island, Papua New Guinea during the periodJanuary to February 2018. Local visual observations determined that theKadovar volcano began to erupt at the summit of the island, and thencreated new vent spots near the coast. The events included the collapse of alava dome on 9 February 2018. Directions-of-arrivals (DOA) of thehydroacoustic signals detected at HA11 were evaluated using a cross-correlation technique. This allowed discrimination between hydroacousticsignals originating from the Kadovar volcanic activity and other numeroushydroacoustic signals generated by general seismic activity in the Pacific.Discrimination between volcanic activity and seismicity was achieved byexamining the time-frequency characteristics of the hydroacoustic signals, i.e.associating short duration broadband bursts with volcanic eruptions, in linewith criteria generally applied for such events. Episodes of high volcanicactivity with as many as 80 detections per hour (calculation based on 30-stime-window with 25-s over-lap) were identified on two occasions,separated by a one-month period of relative quiet. Some of thehydroacoustic signals were characterized by broadband frequency contentand high received levels (i.e. ca. 30 dB higher than the ocean backgroundnoise). It was found that corresponding non-hydroacoustic signals could notbe identified by other regional IMS seismic stations, this providing anindication of the likely submarine origin of these events.
▋ IMS Hydroacoustic Network & Hydrophone Triplet
The hydroacoustic network is part of theInternational Monitoring System (IMS) of theComprehensive Nuclear-Test-Ban Treaty (CTBT)and has 11 stations. Of the 11 hydroacousticstations, five (denoted by green triangles) are T-phase stations which use seismometers to pickup water-borne signals from acoustic eventscoupled in the crust of coastal areas. The othersix (orange triangles) are cabled stations thatutilize underwater hydrophones. All the cabledstations have two triplets of underwaterhydrophones suspended in the water column, ina horizontal triangular configuration with aseparation of 2 km, except for HA01 at CapeLeeuwin, Australia which has only one triplet.
The present study is concerned with theIMS hydroacoustic (HA) hydrophonestations, which have been installed sincethe early 2000’s. The hydrophonestations are based on islands andconnected by electro/fiber-optic cablesto the hydrophone triplets. The tripletsare deployed up to 200 km from theisland. All hydrophone sensors arelocated in the SOund Fixing And Ranging(SOFAR) channel axis at a depth of 600 mto 1200 m, suspended by subsurfacefloats. Hydrophones record the pressurechange in the water caused by passinghydroacoustic waves, such as H-wavesand T-waves.
Figure 1. CTBT IMS hydroacoustic network.
Figure 2. Overview of an IMS hydrophone triplet and events which generateunderwater sound.
Underwater hydrophone stations / T-phase stations
HA03 – Juan Fernandez IslandChile
HA10 – AscensionUnited Kingdom
HA08 – BIOT/Chagos ArchipelagoUnited Kingdom
HA04 – Crozet IslandsFrance
HA01 – Cape Leeuwin, WAAustralia
HA11 – Wake IslandUnited States of America
1. The hydroacoustic detections at HA11 from the Kadovar volcanic eruptions for January and February 2018 weresupported by flyover observations and documentation.
2. Estimation of the direction-of-arrival (DOA) of the signals recorded at HA11 by cross-correlation analysis made itpossible to identify hydroacoustic arrivals from the volcanic activity at Kadovar.
3. Using the time-frequency characteristics of the arrivals, the present study made it possible to discriminate betweenvolcanic eruptions and seismicity.
AcknowledgementsThe IMS HA11 hydroacoustic station is operated as a part of the CTBT’s IMS verification regime. The authors thank P.Nielsen, T. Edwald, and R. Le Bras (IDC, CTBTO) for the scientific and technical discussions. This study is supported by theGrants-in-Aid for Scientific Research (KAKENHI: JP16KK0155) of the Japan Society for the Promotion of Science (JSPS).
▋ Kadovar Volcanic IslandFlyover photo on 05 January 2018
The location of Kadovar Island volcano is denoted by a red star, and the IMS HA11 hydroacoustic station triplets at Wake Island aredenoted by orange triangles in the left panels. HA11 comprises two triplets of hydrophones, referred to as H11N and H11S (see Figure4). The distance between Kadovar and HA11 is about 3,500 km. Dark and bright red triangles locate above-surface and submarinevolcanoes, respectively, as registered by the Smithsonian Institute. Radial marks are back-azimuths (BAZ) from the North triplet H11N.The central panel shows a local map off New Guinea Island. Two local flyover photos are present in the right panels; an eruptionbegan at the summit of Kadovar Island on 05 January 2018, and then a new vent spot was created on 11 January 2018 .
▋ IMS HA11 Wake Island & Identification of Volcanic Eruptions
The hydroacoustic signals associated with the Kadovar volcanoeruption are identified at both the North and the South tripletsbetween 09:44 UTC and 09:47 UTC, respectively (Figure 5). The PowerSpectral Densities (PSDs) are calculated for these signals. Figure 6compares PSDs between the ambient noise and the hydroacousticsignals of the Kadovar volcano eruptions. Amplitude is corrected by theFrequency-Amplitude-Phase (FAP) response of the hydrophones. Thehydroacoustic signals associated with the volcanic eruptions arecharacterized by broad-band energy.
▋ Direction-Of-Arrivals (DOA) of Hydroacoustic Signals
The back-azimuth of the signals detected by H11N, together with the corresponding spectrogram, are shown in Figure 7.Before the cross-correlation analysis, a digitial filter with pass-band 10 – 60 Hz is applied. Each of the plotted dots iscalculated with a 30-s time window and a 25-s over-lap. The dashed line represents the true back-azimuth to Kadovar.The cross-correlation analysis suggests that the Kadovar volcano erupted very frequently from 00:20 UTC to 01:40 UTC.Long-duration signals with a frequency content below 30 Hz in the spectrogram can be associated with seismicity in thePacific; the 23:23 UTC, 00:04 UTC and 00:42 UTC signals correspond to earthquakes off Kamchatka (M3.5), Papua NewGuinea (M4.7) and a previously unknown signal from a north-north-western direction, respectively.
▋ Conclusions
Each bin in Figure 8 shows counts of hourlydetections of H11N hydroacoustic signals witha DOA consistent with sources at Kadovar. Thered curve shows the cumulative detections ofH11N hydroacoustic signals. A 30-s time-window with 25-s over-lap is used for cross-correlation analysis to associate the signalswith volcanic activity over time. The timewindow overlap may lead to a slight over-estimation of the counts, similarly to what wasfound in previous work [H. Martsumoto et al.,Scientific Reports 9, Art. No.: 19519 (2019)].Arrivals between 5 and 10 January could not beidentified because of a brief temporary outageof HA11, therefore the absence of arrivalsduring this period cannot be associated with areduction of volcanic activity during those 5days. With this caveat in mind, our resultssuggest that the Kadovar volcanic activity canbe divided into two stages separated by a one-moth relatively quiet period; the first burst ofactivity was identified between 11 and 13January 2018, and the second one wasidentified around 09 February 2018. Theseidentifications correspond well with theavailable documentation and reports of flyoverobservations pertaining to the Kadovar volcanoeruptive activity during this period.
SOFAR channel
H- or T-wave
Land facilitiesLand-slide(Flank collapse)
Hydrophone triplet
Volcanic island IMS HA station
Submarine earthquake
Figure 3. The Asia-Pacific area and detailed map covered by the present study.
Figure 5. An example of HA11 typical recordings associated with the Kadovarvolcano eruptions on 11 January 2018 (10-min waveforms centered at09:45:00 UTC). A band-pass filter with 10 – 60 Hz is applied.
Figure 6. Comparison of Power Spectral Densities (PSDs) of ambientnoise and a typical signal from a Kadovar volcano eruption.
Figure 4. Locations of hydrophones onsea-mounts off HA11 Wake Island.
Figure 7. Back-azimuth evaluated by the cross-correlation analysis of H11N and the corresponding spectrogram on 09February 2018.
Figure 8. Histograms of cross-correlation analysis forJanuary and February 2018. Note that the datasetis not available for the entire period, because of atemporary outage between 05 and 10 January2018.
Disclaimer: The views expressed on this poster are those of the author and do not necessarily reflect the view of the CTBTO.
Data Source: Bulletin Reports of the Smithsonian Institution
The same packet from Kadovar
Flyover photo on 11 January 2018
Report by Sharoi Romkentuo
© Authors 2020, all rights reserved
DisclaimerThe views expressed in this poster are those of the authors and do not necessarily reflect the view of the CTBTO.
