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Chapter 2 the Evolution of Seismic Monitoring Systems at the Hawaiian Volcano Observatory

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Chapter 2 the Evolution of Seismic Monitoring Systems at the Hawaiian Volcano Observatory Characteristics of Hawaiian Volcanoes Editors: Michael P. Poland, Taeko Jane Takahashi, and Claire M. Landowski U.S. Geological Survey Professional Paper 1801, 2014 Chapter 2 The Evolution of Seismic Monitoring Systems at the Hawaiian Volcano Observatory By Paul G. Okubo1, Jennifer S. Nakata1, and Robert Y. Koyanagi1 Abstract the Island of Hawai‘i. Over the past century, thousands of sci- entific reports and articles have been published in connection In the century since the Hawaiian Volcano Observatory with Hawaiian volcanism, and an extensive bibliography has (HVO) put its first seismographs into operation at the edge of accumulated, including numerous discussions of the history of Kīlauea Volcano’s summit caldera, seismic monitoring at HVO HVO and its seismic monitoring operations, as well as research (now administered by the U.S. Geological Survey [USGS]) has results. From among these references, we point to Klein and evolved considerably. The HVO seismic network extends across Koyanagi (1980), Apple (1987), Eaton (1996), and Klein and the entire Island of Hawai‘i and is complemented by stations Wright (2000) for details of the early growth of HVO’s seismic installed and operated by monitoring partners in both the USGS network. In particular, the work of Klein and Wright stands and the National Oceanic and Atmospheric Administration. The out because their compilation uses newspaper accounts and seismic data stream that is available to HVO for its monitoring other reports of the effects of historical earthquakes to extend of volcanic and seismic activity in Hawai‘i, therefore, is built Hawai‘i’s detailed seismic history to nearly a century before from hundreds of data channels from a diverse collection of instrumental monitoring began at HVO. Doing so required that instruments that can accurately record the ground motions they account for seismic monitoring capabilities throughout of earthquakes ranging in magnitude from <1 to >8. In this HVO’s history in order to better evaluate historical accounts chapter we describe the growth of HVO’s seismic monitoring when instrumental records were unavailable or limited. systems throughout its first hundred years of operation. Although We present here an updated discussion of the seismic other references provide specific details of the changes in monitoring systems at HVO. Rather than casting our discussion instrumentation and data handling over time, we recount here, in to include extensive details of instrumentation, our aim is to more general terms, the evolution of HVO’s seismic network. We speak to the evolution of HVO’s seismic network and monitor- focus not only on equipment but also on interpretative products ing practices in terms of the capabilities and data collection and results that were enabled by the new instrumentation and thus afforded by changes to the network. Readers who seek by improvements in HVO’s seismic monitoring, analytical, and greater detail regarding instrumentation can consult the publi- interpretative capabilities implemented during the past century. cations mentioned above, as well as the series of HVO weekly, As HVO enters its next hundred years of seismological studies, it monthly, and even annual reports and summaries (see compila- is well situated to further improve upon insights into seismic and tions by Fiske and others, 1987, and Bevens and others, 1988). volcanic processes by using contemporary seismological tools. Early Instrumental Monitoring, 1912–50 Introduction To begin systematic seismic monitoring of Kīlauea Vol- The U.S. Geological Survey (USGS) Hawaiian Volcano cano in 1912, HVO founder Thomas A. Jaggar, Jr., purchased Observatory (HVO) has been conducting routine volcano moni- two instruments from Fusakichi Omori of the University of toring and continuous measurement programs from the rim of Tokyo and installed them in HVO’s Whitney Vault (see Tilling Kīlauea Volcano’s summit caldera since 1912. HVO put its first and others, this volume, chap. 1). Omori had pioneered seis- seismographs into operation on July 31, 1912, which began mological research in Japan, including the study of seismicity more than 100 years of seismic monitoring at Kīlauea and on of both volcanic and nonvolcanic origins, and Jaggar’s interest was to establish similar observing and monitoring capabilities at 1U.S. Geological Survey. Kīlauea. One of the Omori instruments installed in 1912 was an 68 Characteristics of Hawaiian Volcanoes “ordinary” seismograph, meant to record relatively strong local record ground motion, the J.A. Bosch firm of Strasburg modi- earthquakes; the other was referred to as a “heavy” seismograph fied the original Omori design to add damping, and Jaggar that, because of its mass, was capable of registering relatively subsequently complemented his two Omori instruments with weak ground motions, such as those produced by teleseisms. Bosch-Omori seismographs (fig. 1). HVO continued to operate To set up the seismographs at HVO, Jaggar enlisted these Bosch-Omori instruments until 1963 (Apple, 1987). Harry Wood, who was working at the University of California, Seismology in the early 20th century was at an early Berkeley, at the time. Wood arrived in Hawai‘i in summer 1912 evolutionary stage, with much effort dedicated to collecting and, in addition to installing and maintaining the seismographs, more and better data by improving the designs of seismometers, documented the seismic activity recorded by them. Wood left timing mechanisms, and recording instruments. To promote its HVO in 1917 and, after World War I, was commissioned to volcano and seismic monitoring, HVO also undertook its own establish a seismic network in Southern California in coop- seismograph design and fabrication efforts to achieve greater eration with the California Institute of Technology (Caltech). instrument sensitivity and ease of installation and operation. Among Wood’s contributions at Caltech was his construction, The resulting instruments were deployed in Hawai‘i and later with astronomer John Anderson, of the Wood-Anderson torsion installed at stations in Alaska and California. seismometer (Anderson and Wood, 1925). Regional deployment HVO installed additional seismographs as they became of these seismometers led to Charles Richter’s publication of his available, at Hilo in 1919, Kona in 1922, and Hīlea in 1923. The magnitude scale for local earthquakes (Richter, 1935). distribution of seismic stations in 1923, reflecting the need to At Kīlauea, the heavy Omori seismograph routinely locate instruments at relatively accessible locations where hosts and clearly registered microseismic background noise that, agreed to serve as observers and record changers, is mapped in in Hawai‘i, is closely linked to oceanic swells. In addition, figure 2A. Along with the instruments installed on Kīlauea at the instrument recorded signals that generally correlated HVO, these additional stations expanded volcano and earth- with visible lava activity at Kīlauea’s summit and that were quake monitoring coverage on the island. HVO staff compiled subsequently called “volcanic vibrations” (Wood, 1913). The lists of event times, including tremor, local earthquakes, and November 25, 1914, eruption of Mauna Loa was preceded teleseisms, which were reported in HVO’s weekly and monthly by about 2 months of seismicity recorded on the two HVO bulletins (Bevens and others, 1988; Fiske and others, 1987). seismographs. Although instrumentally determined epicenters Sizes of local earthquakes, as determined from amplitudes were not available from the single station that was in operation measured on available instrumental records, were also provided at that time, estimated distances of the recorded earthquakes (Klein and Wright, 2000). suggested their origin to be beneath Mauna Loa (Wood, 1915). A principal—possibly the most basic—goal of seismic Like other contemporary instruments, the Omori seismo- monitoring was, and continues to be, the accurate cataloging graphs were large mechanical devices whose sensitivity to (or and reporting of earthquake time, location, and size. Time refer- magnification of) ground movement resulted from their overall ence at the early HVO seismographic stations was provided size (Wood, 1913). The two Omori instruments first brought to by means of Howard precision astronomical clocks that were Hawai‘i did not feature viscous damping. To more accurately wired to produce reference marks on the records by lifting the recording pens once per minute. Earthquake epicenters were determined graphically on the basis of estimates of the respec- tive distances between recording stations and earthquakes, as derived from seismic-wave traveltimes. Wood (1914) initially selected traveltime-versus-distance curves, compiled by Conrad Zeissig for earthquakes and seismic stations in Europe, to pro- vide these estimates for Hawai‘i. Bosch-Omori Ruy Finch, who assumed seismological tasks at HVO in seismographs 1919, resumed estimating the distances between earthquakes and seismographic stations, which had been abandoned since Wood’s departure from HVO in 1917. Finch also changed this procedure by using the time-distance tables, compiled and Omori published by Omori, which were tabulated over shorter dis- seismograph tance ranges and considered to be more suited for application in Hawai‘i, to determine earthquake locations (Finch, 1925). After working for several years to establish seismographic stations and volcano observatories on Mount Lassen in Cali- fornia and in the Aleutian Islands,
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