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Seismic and Acoustic Signals Detected at Loihi Seamount by The Western Washington University Western CEDAR Geology Faculty Publications Geology 5-25-2001 Seismic and Acoustic Signals Detected at Loihi Seamount by the Hawaii Undersea Geo- Observatory Jacqueline Caplan-Auerbach Western Washington University, [email protected] F. Duennebier Follow this and additional works at: https://cedar.wwu.edu/geology_facpubs Part of the Geology Commons, and the Geophysics and Seismology Commons Recommended Citation Caplan-Auerbach, J. and F. Duennebier, Seismic and Acoustic Signals Detected at Loihi Seamount by the Hawaii Undersea Geo- Observatory, Geochem. Geophys. Geosyst., 2, paper #2000GC000113, May 25 2001 This Article is brought to you for free and open access by the Geology at Western CEDAR. It has been accepted for inclusion in Geology Faculty Publications by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. Article Geochemistry 3 Volume 2 Geophysics May 25, 2001 Geosystems Paper number 2000GC000113 G ISSN: 1525-2027 AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES Published by AGU and the Geochemical Society Seismic and acoustic signals detected at Lo^ihi Seamount by the Hawai^i Undersea Geo-Observatory J. Caplan-Auerbach Department of Geology and Geophysics, University of Hawai^i at Manoa, Honolulu, Hawaii 96822 Now at Alaska Volcano Observatory, University of Alaska Fairbanks, 903 Koyukuk Drive, P.O. Box 757320, Fairbanks, Alaska 99775-7320 [email protected]) F. Duennebier Department of Geology and Geophysics, University of Hawai^i at Manoa, Honolulu, Hawaii 96822 [email protected]) [1] Abstract: The Hawai^i Undersea Geo-Observatory 0HUGO) is an ocean bottom observatory located on the summit of Lo^ihi seamount, Hawai^i. An electro-optical cable connects the HUGO junction box to a shore station on the Big Island of Hawai^i, thereby enabling the first real-time monitoring of a submarine volcano. HUGO was active for 3 months in 1998, collecting nearly continuous, real-time data on a high-rate hydrophone. Signals detected during that time include local as well as teleseismic earthquakes, T phases from Pacific-wide earthquakes, landslides on the submarine flank of Kilauea, and eruption sounds from the current Kilauea eruption. The data do not indicate a Lo^ihi eruption during the time that HUGO was active. The variety and quality of signals detected by the HUGO hydrophone confirms that a real-time observatory can serve a valuable role in studies of oceanic acoustics, local and teleseismic earthquakes, and submarine eruption mechanics. Keywords: Lo^ihi seamount; Hawai^i; submarine observatory; hydroacoustic monitoring; marine instrumentation; earthquake location. Index terms: Marine geology and geophysics: instruments and techniques; ocean acoustics; volcano seismology; eruption monitoring. Received October 10, 2000; Revised February 26, 2001; Accepted April 3, 2001; Published May 25, 2001. Caplan-Auerbach, J., and F. Duennebier, 2001. Seismic and acoustic signals detected at Lo^ihi Seamount by the Hawai^i Undersea Geo-Observatory, Geochem. Geophys. Geosyst., vol. 2, Paper number 2000GC000113 [6301 words, 9 figures]. Published May 25, 2001. 1. Introduction lard et al., 1981; Francheteau et al., 1981]. The logistics of performing long-term monitoring in [2] Study of undersea volcanic systems began such an environment are challenging and can decades ago, on both mid-ocean ridges and be achieved in one of several ways: by a series intraplate volcanoes [e.g., Johnson, 1973; Bal- of visits to the volcano, through the use of Copyright 2001 by the American Geophysical Union Geochemistry Geophysics 3 caplan-auerbach and duennebier: seismic signals 2000GC000113 Geosystems G autonomous ocean bottom systems, by remote subject of this paper. HUGO was designed systems such as seismometers or hydrophone for long-term, real-time monitoring of Lo^ihi arrays, or by permanent observatories. submarine volcano and the surrounding ocean. Repeated submersible visits are costly and HUGO is composed of a junction box posi- provide a poorly sampled view of the volcano's tioned on Lo^ihi's summit at 1200-m water behavior. Autonomous data collection systems, depth, a 47-km electro-optical cable for data such as ocean bottom seismometers, provide a and power transmission, and a shore station continuous view of activity but are limited by on Hawai^i Island. Avariety of experiments power and storage capacity and must be rou- may be plugged into the system, and data are tinely replaced. Moreover, changes in the immediately sent to the shore station for behavior of the volcano are only determined processing. The system was designed to allow after the system is retrieved and the data installation and repair of experiments via processed, thus providing no information use- submersible or remote operated vehicle ful for rapid response. Delayed reception of 0ROV). Adescription of HUGO's technical data also means that any faults in the equipment details may be found in the work of Duen- cannot be discovered until retrieval. Distant nebier et al. [2001]. monitoring systems have been effective in detecting submarine eruptive activity [Fox et [5] Lo^ihi seamount, located 35 km south of al., 1995; Dziak and Fox, 1999; Fox et al., Hawai^iislandwithitssummit1000 m 2001], but only a few types of data, such as below the ocean surface 0Figure 1), has been seismic and acoustic signals, can be detected studied in detail by means of oceanographic remotely. surveys and autonomous data collection sys- tems. More than 50 submersible dives on the [3] An alternative to the methods described volcano have yielded a wealth of data on the above is the real-time submarine observatory, geology, chemistry, and biology of Lo^ihi capable of supplying continual power to experi- [e.g., Malahoff, 1987; Garcia et al., 1998; ments and transmitting data to a shore facility Hilton et al., 1998]. An autonomous ocean for analysis. Ocean observatories such as the bottom observatory 0OBO) deployed in 1991 New Millennium Observatory, deployed on contained a seismometer, pressure sensor, and Axial seamount in 1999, deliver data via an thermistor for monitoring of hydrothermal acoustic link to a surface buoy and then via vent temperatures. Data from the OBO show satellite to shore. Other observatories such as a number of features suggestive of an erup- LEO-15 0Long-Term Ecosystem Observatory) tion, including increased seismicity and in New Jersey, the Real-Time Deep Seafloor changes in both hydrothermal vent temper- Observatory off of Hatsushima, Japan, and the ature and summit elevation [Malahoff, 1993]. Hawaii-2 Observatory transmit data and power Unfortunately, the potential eruption was not to a shore station through undersea communi- recognized until the data were returned to cations cables. Plans are underway to monitor shore, too late to organize a thorough inves- the entire Juan de Fuca plate with the NEP- tigation of the event. In 1986, five ocean TUNE observatory, which will be connected by bottom seismometers were deployed on Lo^ihi cable to shore stations on the North American ihi in response to an earthquake swarm [Bryan west coast. and Cooper, 1995]. By the time the network was launched, however, the swarm had largely [4] The deep-ocean observatory HUGO, the diminished. An ocean bottom seismometer Hawai^i Undersea Geo-Observatory, is the was deployed during a 1996 earthquake Geochemistry Geophysics 3 caplan-auerbach and duennebier: seismic signals 2000GC000113 Geosystems G o o o o o o -156 30' -156 00' -155 30' -155 00' -154 30' -154 00' o o 20 30' 20 30' o o 20 00' 20 00' o o 19 30' 19 30' Waha`ula Kamokuna Honu`apo o o 19 00' 19 00' HUGO o o 18 30' 18 30' o o o o o o -156 30' -156 00' -155 30' -155 00' -154 30' -154 00' Figure 1. Location of the Hawai^i Undersea Geo-Observatory 0HUGO) junction box with respect to the island of Hawai^i. HUGO sits on the summit of Lo^ihi seamount, 35 km south of the Big Island of Hawai^i. The electro-optical cable follows the route shown between Lo^ihi and the shore station at Honu^apo. Black circles represent the locations of the seismic network operated by the Hawai^i Volcano Observatory. Stars at the Kilauea coast represent the WahauÁla and Kamokuna ocean entries, the sites where lava entered the ocean during the period when HUGO was active. swarm, but it also caught only the tail end of box. The HUGO system is described, as well as activity [Caplan-Auerbach and Duennebier, the chronology of its installation and repair. We 2001]. Thus, although a number of projects discuss the many kinds of signals detected by have successfully used autonomous data col- the HUGO hydrophone, of local, regional, and lection systems to study Lo^ihi, all have been Pacific-wide events and investigate the benefits compromised by delays in instrument deploy- of a real-time observatory on Lo^ihi. Many ment and data analysis. events were recorded only at HUGO and can- not be located or thoroughly characterized. The [6] In this paper we present the results of three purpose of this paper is to describe these events months of data collection from a high-rate as much as possible and to provide justification hydrophone connected to the HUGO junction for future use of similar systems. Geochemistry Geophysics 3 caplan-auerbach and duennebier: seismic signals 2000GC000113 Geosystems G 2. Geologic Setting Fingers Field 0Figure 2). Although a number of rocky outcrops surround the HUGO site, the [7] Lo^ihi seamount is the youngest volcano in seafloor beneath the junction box consists of the Hawaiian chain and is the only known volcaniclastic mud at least 1.5 m deep into member of that group still in the submarine which the junction box has settled to a depth phase of activity. Lo^ihi probably formed on the of 20 cm.
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